Extensions to the C Language Family
***********************************

GNU C provides several language features not found in ISO standard C. (The -pedantic option directs GCC to print a warning message if any of these features is used.)  To test for the availability of these features in conditional compilation, check for a predefined macro __GNUC__, which is always defined under GCC.

These extensions are available in C and Objective-C.  Most of them are also available in C++.  See Extensions to the C++ Language, for extensions that apply only to C++.

Some features that are in ISO C99 but not C90 or C++ are also, as extensions, accepted by GCC in C90 mode and in C++.

Statements and Declarations in Expressions
==========================================

A compound statement enclosed in parentheses may appear as an expression in GNU C.  This allows you to use loops, switches, and local variables within an expression.

Recall that a compound statement is a sequence of statements surrounded by braces; in this construct, parentheses go around the braces.  For example:

     ({ int y = foo (); int z;
        if (y > 0) z = y;
        else z = - y;
        z; })

is a valid (though slightly more complex than necessary) expression for the absolute value of foo ().

The last thing in the compound statement should be an expression followed by a semicolon; the value of this subexpression serves as the value of the entire construct.  (If you use some other kind of statement last within the braces, the construct has type void, and thus effectively no value.)

This feature is especially useful in making macro definitions ``safe'' (so that they evaluate each operand exactly once).  For example, the ``maximum'' function is commonly defined as a macro in standard C as follows:

     #define max(a,b) ((a) > (b) ? (a) : (b))

But this definition computes either A or B twice, with bad results if the operand has side effects.  In GNU C, if you know the type of the operands (here taken as int), you can define the macro safely as follows:

     #define maxint(a,b) \
       ({int _a = (a), _b = (b); _a > _b ? _a : _b; })

Embedded statements are not allowed in constant expressions, such as the value of an enumeration constant, the width of a bit-field, or the initial value of a static variable.

If you don't know the type of the operand, you can still do this, but you must use typeof or __auto_type (see Typeof).

In G++, the result value of a statement expression undergoes array and function pointer decay, and is returned by value to the enclosing expression.  For instance, if A is a class, then

             A a;

             ({a;}).Foo ()

constructs a temporary A object to hold the result of the statement expression, and that is used to invoke Foo. Therefore the this pointer observed by Foo is not the address of a.

In a statement expression, any temporaries created within a statement are destroyed at that statement's end.  This makes statement expressions inside macros slightly different from function calls.  In the latter case temporaries introduced during argument evaluation are destroyed at the end of the statement that includes the function call.  In the statement expression case they are destroyed during the statement expression.  For instance,

     #define macro(a)  ({__typeof__(a) b = (a); b + 3; })
     template<typename T> T function(T a) { T b = a; return b + 3; }

     void foo ()
     {
       macro (X ());
       function (X ());
     }

has different places where temporaries are destroyed.  For the macro case, the temporary X is destroyed just after the initialization of b.  In the function case that temporary is destroyed when the function returns.

These considerations mean that it is probably a bad idea to use statement expressions of this form in header files that are designed to work with C++.  (Note that some versions of the GNU C Library contained header files using statement expressions that lead to precisely this bug.)

Jumping into a statement expression with goto or using a switch statement outside the statement expression with a case or default label inside the statement expression is not permitted.  Jumping into a statement expression with a computed goto (see Labels as Values) has undefined behavior. Jumping out of a statement expression is permitted, but if the statement expression is part of a larger expression then it is unspecified which other subexpressions of that expression have been evaluated except where the language definition requires certain subexpressions to be evaluated before or after the statement expression.  In any case, as with a function call, the evaluation of a statement expression is not interleaved with the evaluation of other parts of the containing expression.  For example,

       foo (), (({ bar1 (); goto a; 0; }) + bar2 ()), baz();

calls foo and bar1 and does not call baz but may or may not call bar2.  If bar2 is called, it is called after foo and before bar1.

Locally Declared Labels
=======================

GCC allows you to declare local labels in any nested block scope.  A local label is just like an ordinary label, but you can only reference it (with a goto statement, or by taking its address) within the block in which it is declared.

A local label declaration looks like this:

     __label__ LABEL;

or

     __label__ LABEL1, LABEL2, /* ... */;

Local label declarations must come at the beginning of the block, before any ordinary declarations or statements.

The label declaration defines the label name, but does not define the label itself.  You must do this in the usual way, with LABEL:, within the statements of the statement expression.

The local label feature is useful for complex macros.  If a macro contains nested loops, a goto can be useful for breaking out of them.  However, an ordinary label whose scope is the whole function cannot be used: if the macro can be expanded several times in one function, the label is multiply defined in that function.  A local label avoids this problem.  For example:

     #define SEARCH(value, array, target)              \
     do {                                              \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { (value) = i; goto found; }              \
       (value) = -1;                                   \
      found:;                                          \
     } while (0)

This could also be written using a statement expression:

     #define SEARCH(array, target)                     \
     ({                                                \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { value = i; goto found; }                \
       value = -1;                                     \
      found:                                           \
       value;                                          \
     })

Local label declarations also make the labels they declare visible to nested functions, if there are any.  See Nested Functions, for details.

Labels as Values
================

You can get the address of a label defined in the current function (or a containing function) with the unary operator &&.  The value has type void *.  This value is a constant and can be used wherever a constant of that type is valid.  For example:

     void *ptr;
     /* ... */
     ptr = &&foo;

To use these values, you need to be able to jump to one.  This is done with the computed goto statement (The analogous feature in Fortran is called an assigned goto, but that name seems inappropriate in C, where one can do more than simply store label addresses in label variables.), goto *EXP;.  For example,

     goto *ptr;

Any expression of type void * is allowed.

One way of using these constants is in initializing a static array that serves as a jump table:

     static void *array[] = { &&foo, &&bar, &&hack };

Then you can select a label with indexing, like this:

     goto *array[i];

Note that this does not check whether the subscript is in bounds---array indexing in C never does that.

Such an array of label values serves a purpose much like that of the switch statement.  The switch statement is cleaner, so use that rather than an array unless the problem does not fit a switch statement very well.

Another use of label values is in an interpreter for threaded code. The labels within the interpreter function can be stored in the threaded code for super-fast dispatching.

You may not use this mechanism to jump to code in a different function. If you do that, totally unpredictable things happen.  The best way to avoid this is to store the label address only in automatic variables and never pass it as an argument.

An alternate way to write the above example is

     static const int array[] = { &&foo - &&foo, &&bar - &&foo,
                                  &&hack - &&foo };
     goto *(&&foo + array[i]);

This is more friendly to code living in shared libraries, as it reduces the number of dynamic relocations that are needed, and by consequence, allows the data to be read-only. This alternative with label differences is not supported for the AVR target, please use the first approach for AVR programs.

The &&foo expressions for the same label might have different values if the containing function is inlined or cloned.  If a program relies on them being always the same, __attribute__((__noinline__,__noclone__)) should be used to prevent inlining and cloning.  If &&foo is used in a static variable initializer, inlining and cloning is forbidden.

Nested Functions
================

A nested function is a function defined inside another function. Nested functions are supported as an extension in GNU C, but are not supported by GNU C++.

The nested function's name is local to the block where it is defined. For example, here we define a nested function named square, and call it twice:

     foo (double a, double b)
     {
       double square (double z) { return z * z; }

       return square (a) + square (b);
     }

The nested function can access all the variables of the containing function that are visible at the point of its definition.  This is called lexical scoping.  For example, here we show a nested function which uses an inherited variable named offset:

     bar (int *array, int offset, int size)
     {
       int access (int *array, int index)
         { return array[index + offset]; }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
     }

Nested function definitions are permitted within functions in the places where variable definitions are allowed; that is, in any block, mixed with the other declarations and statements in the block.

It is possible to call the nested function from outside the scope of its name by storing its address or passing the address to another function:

     hack (int *array, int size)
     {
       void store (int index, int value)
         { array[index] = value; }

       intermediate (store, size);
     }

Here, the function intermediate receives the address of store as an argument.  If intermediate calls store, the arguments given to store are used to store into array. But this technique works only so long as the containing function (hack, in this example) does not exit.

If you try to call the nested function through its address after the containing function exits, all hell breaks loose.  If you try to call it after a containing scope level exits, and if it refers to some of the variables that are no longer in scope, you may be lucky, but it's not wise to take the risk.  If, however, the nested function does not refer to anything that has gone out of scope, you should be safe.

GCC implements taking the address of a nested function using a technique called trampolines.  This technique was described in Lexical Closures for C++ (Thomas M. Breuel, USENIX C++ Conference Proceedings, October 17-21, 1988).

A nested function can jump to a label inherited from a containing function, provided the label is explicitly declared in the containing function (see Local Labels).  Such a jump returns instantly to the containing function, exiting the nested function that did the goto and any intermediate functions as well.  Here is an example:

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
       /* ... */
       return 0;

      /* Control comes here from access
         if it detects an error.  */
      failure:
       return -1;
     }

A nested function always has no linkage.  Declaring one with extern or static is erroneous.  If you need to declare the nested function before its definition, use auto (which is otherwise meaningless for function declarations).

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       auto int access (int *, int);
       /* ... */
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       /* ... */
     }

Constructing Function Calls
===========================

Using the built-in functions described below, you can record the arguments a function received, and call another function with the same arguments, without knowing the number or types of the arguments.

You can also record the return value of that function call, and later return that value, without knowing what data type the function tried to return (as long as your caller expects that data type).

However, these built-in functions may interact badly with some sophisticated features or other extensions of the language.  It is, therefore, not recommended to use them outside very simple functions acting as mere forwarders for their arguments.

 -- Built-in Function: void * __builtin_apply_args ()
     This built-in function returns a pointer to data describing how to perform a call with the same arguments as are passed to the current function.

     The function saves the arg pointer register, structure value address, and all registers that might be used to pass arguments to a function into a block of memory allocated on the stack.  Then it returns the address of that block.

 -- Built-in Function: void * __builtin_apply (void (*FUNCTION)(), void *ARGUMENTS, size_t SIZE)
     This built-in function invokes FUNCTION with a copy of the parameters described by ARGUMENTS and SIZE.

     The value of ARGUMENTS should be the value returned by __builtin_apply_args.  The argument SIZE specifies the size of the stack argument data, in bytes.

     This function returns a pointer to data describing how to return whatever value is returned by FUNCTION.  The data is saved in a block of memory allocated on the stack.

     It is not always simple to compute the proper value for SIZE.  The value is used by __builtin_apply to compute the amount of data that should be pushed on the stack and copied from the incoming argument area.

 -- Built-in Function: void __builtin_return (void *RESULT)
     This built-in function returns the value described by RESULT from the containing function.  You should specify, for RESULT, a value returned by __builtin_apply.

 -- Built-in Function: __builtin_va_arg_pack ()
     This built-in function represents all anonymous arguments of an inline function.  It can be used only in inline functions that are always inlined, never compiled as a separate function, such as those using __attribute__ ((__always_inline__)) or __attribute__ ((__gnu_inline__)) extern inline functions. It must be only passed as last argument to some other function with variable arguments.  This is useful for writing small wrapper inlines for variable argument functions, when using preprocessor macros is undesirable.  For example:

          extern int myprintf (FILE *f, const char *format, ...);
          extern inline __attribute__ ((__gnu_inline__)) int
          myprintf (FILE *f, const char *format, ...)
          {
            int r = fprintf (f, "myprintf: ");
            if (r < 0)
              return r;
            int s = fprintf (f, format, __builtin_va_arg_pack ());
            if (s < 0)
              return s;
            return r + s;
          }

 -- Built-in Function: size_t __builtin_va_arg_pack_len ()
     This built-in function returns the number of anonymous arguments of an inline function.  It can be used only in inline functions that are always inlined, never compiled as a separate function, such as those using __attribute__ ((__always_inline__)) or __attribute__ ((__gnu_inline__)) extern inline functions. For example following does link- or run-time checking of open arguments for optimized code:

          #ifdef __OPTIMIZE__
          extern inline __attribute__((__gnu_inline__)) int
          myopen (const char *path, int oflag, ...)
          {
            if (__builtin_va_arg_pack_len () > 1)
              warn_open_too_many_arguments ();

            if (__builtin_constant_p (oflag))
              {
                if ((oflag & O_CREAT) != 0 && __builtin_va_arg_pack_len () < 1)
                  {
                    warn_open_missing_mode ();
                    return __open_2 (path, oflag);
                  }
                return open (path, oflag, __builtin_va_arg_pack ());
              }

            if (__builtin_va_arg_pack_len () < 1)
              return __open_2 (path, oflag);

            return open (path, oflag, __builtin_va_arg_pack ());
          }
          #endif

Referring to a Type with typeof
===============================

Another way to refer to the type of an expression is with typeof. The syntax of using of this keyword looks like sizeof, but the construct acts semantically like a type name defined with typedef.

There are two ways of writing the argument to typeof: with an expression or with a type.  Here is an example with an expression:

     typeof (x[0](1))

This assumes that x is an array of pointers to functions; the type described is that of the values of the functions.

Here is an example with a typename as the argument:

     typeof (int *)

Here the type described is that of pointers to int.

If you are writing a header file that must work when included in ISO C programs, write __typeof__ instead of typeof. See Alternate Keywords.

A typeof construct can be used anywhere a typedef name can be used.  For example, you can use it in a declaration, in a cast, or inside of sizeof or typeof.

The operand of typeof is evaluated for its side effects if and only if it is an expression of variably modified type or the name of such a type.

typeof is often useful in conjunction with statement expressions (see Statement Exprs). Here is how the two together can be used to define a safe ``maximum'' macro which operates on any arithmetic type and evaluates each of its arguments exactly once:

     #define max(a,b) \
       ({ typeof (a) _a = (a); \
           typeof (b) _b = (b); \
         _a > _b ? _a : _b; })

The reason for using names that start with underscores for the local variables is to avoid conflicts with variable names that occur within the expressions that are substituted for a and b.  Eventually we hope to design a new form of declaration syntax that allows you to declare variables whose scopes start only after their initializers; this will be a more reliable way to prevent such conflicts.

Some more examples of the use of typeof:

  * This declares y with the type of what x points to.

          typeof (*x) y;

  * This declares y as an array of such values.

          typeof (*x) y[4];

  * This declares y as an array of pointers to characters:

          typeof (typeof (char *)[4]) y;

     It is equivalent to the following traditional C declaration:

          char *y[4];

     To see the meaning of the declaration using typeof, and why it might be a useful way to write, rewrite it with these macros:

          #define pointer(T)  typeof(T *)
          #define array(T, N) typeof(T [N])

     Now the declaration can be rewritten this way:

          array (pointer (char), 4) y;

     Thus, array (pointer (char), 4) is the type of arrays of 4 pointers to char.

In GNU C, but not GNU C++, you may also declare the type of a variable as __auto_type.  In that case, the declaration must declare only one variable, whose declarator must just be an identifier, the declaration must be initialized, and the type of the variable is determined by the initializer; the name of the variable is not in scope until after the initializer.  (In C++, you should use C++11 auto for this purpose.)  Using __auto_type, the ``maximum'' macro above could be written as:

     #define max(a,b) \
       ({ __auto_type _a = (a); \
           __auto_type _b = (b); \
         _a > _b ? _a : _b; })

Using __auto_type instead of typeof has two advantages:

  * Each argument to the macro appears only once in the expansion of the macro.  This prevents the size of the macro expansion growing exponentially when calls to such macros are nested inside arguments of such macros.

  * If the argument to the macro has variably modified type, it is evaluated only once when using __auto_type, but twice if typeof is used.

Conditionals with Omitted Operands
==================================

The middle operand in a conditional expression may be omitted.  Then if the first operand is nonzero, its value is the value of the conditional expression.

Therefore, the expression

     x ? : y

has the value of x if that is nonzero; otherwise, the value of y.

This example is perfectly equivalent to

     x ? x : y

In this simple case, the ability to omit the middle operand is not especially useful.  When it becomes useful is when the first operand does, or may (if it is a macro argument), contain a side effect.  Then repeating the operand in the middle would perform the side effect twice.  Omitting the middle operand uses the value already computed without the undesirable effects of recomputing it.

128-bit Integers
================

As an extension the integer scalar type __int128 is supported for targets which have an integer mode wide enough to hold 128 bits. Simply write __int128 for a signed 128-bit integer, or unsigned __int128 for an unsigned 128-bit integer.  There is no support in GCC for expressing an integer constant of type __int128 for targets with long long integer less than 128 bits wide.

Double-Word Integers
====================

ISO C99 supports data types for integers that are at least 64 bits wide, and as an extension GCC supports them in C90 mode and in C++. Simply write long long int for a signed integer, or unsigned long long int for an unsigned integer.  To make an integer constant of type long long int, add the suffix LL to the integer.  To make an integer constant of type unsigned long long int, add the suffix ULL to the integer.

You can use these types in arithmetic like any other integer types. Addition, subtraction, and bitwise boolean operations on these types are open-coded on all types of machines.  Multiplication is open-coded if the machine supports a fullword-to-doubleword widening multiply instruction.  Division and shifts are open-coded only on machines that provide special support.  The operations that are not open-coded use special library routines that come with GCC.

There may be pitfalls when you use long long types for function arguments without function prototypes.  If a function expects type int for its argument, and you pass a value of type long long int, confusion results because the caller and the subroutine disagree about the number of bytes for the argument. Likewise, if the function expects long long int and you pass int.  The best way to avoid such problems is to use prototypes.

Complex Numbers
===============

ISO C99 supports complex floating data types, and as an extension GCC supports them in C90 mode and in C++.  GCC also supports complex integer data types which are not part of ISO C99.  You can declare complex types using the keyword _Complex.  As an extension, the older GNU keyword __complex__ is also supported.

For example, _Complex double x; declares x as a variable whose real part and imaginary part are both of type double.  _Complex short int y; declares y to have real and imaginary parts of type short int; this is not likely to be useful, but it shows that the set of complex types is complete.

To write a constant with a complex data type, use the suffix i or j (either one; they are equivalent).  For example, 2.5fi has type _Complex float and 3i has type _Complex int.  Such a constant always has a pure imaginary value, but you can form any complex value you like by adding one to a real constant.  This is a GNU extension; if you have an ISO C99 conforming C library (such as the GNU C Library), and want to construct complex constants of floating type, you should include <complex.h> and use the macros I or _Complex_I instead.

To extract the real part of a complex-valued expression EXP, write __real__ EXP.  Likewise, use __imag__ to extract the imaginary part.  This is a GNU extension; for values of floating type, you should use the ISO C99 functions crealf, creal, creall, cimagf, cimag and cimagl, declared in <complex.h> and also provided as built-in functions by GCC.

The operator ~ performs complex conjugation when used on a value with a complex type.  This is a GNU extension; for values of floating type, you should use the ISO C99 functions conjf, conj and conjl, declared in <complex.h> and also provided as built-in functions by GCC.

GCC can allocate complex automatic variables in a noncontiguous fashion; it's even possible for the real part to be in a register while the imaginary part is on the stack (or vice versa).  Only the DWARF 2 debug info format can represent this, so use of DWARF 2 is recommended. If you are using the stabs debug info format, GCC describes a noncontiguous complex variable as if it were two separate variables of noncomplex type. If the variable's actual name is foo, the two fictitious variables are named foo$real and foo$imag.  You can examine and set these two fictitious variables with your debugger.

Additional Floating Types
=========================

As an extension, GNU C supports additional floating types, __float80 and __float128 to support 80-bit (XFmode) and 128-bit (TFmode) floating types. Support for additional types includes the arithmetic operators: add, subtract, multiply, divide; unary arithmetic operators; relational operators; equality operators; and conversions to and from integer and other floating types.  Use a suffix w or W in a literal constant of type __float80 and q or Q for _float128.  You can declare complex types using the corresponding internal complex type, XCmode for __float80 type and TCmode for __float128 type:

     typedef _Complex float __attribute__((mode(TC))) _Complex128;
     typedef _Complex float __attribute__((mode(XC))) _Complex80;

Not all targets support additional floating-point types.  __float80 and __float128 types are supported on x86 and IA-64 targets. The __float128 type is supported on hppa HP-UX targets.

Half-Precision Floating Point
=============================

On ARM targets, GCC supports half-precision (16-bit) floating point via the __fp16 type.  You must enable this type explicitly with the -mfp16-format command-line option in order to use it.

ARM supports two incompatible representations for half-precision floating-point values.  You must choose one of the representations and use it consistently in your program.

Specifying -mfp16-format=ieee selects the IEEE 754-2008 format. This format can represent normalized values in the range of 2^-14 to 65504. There are 11 bits of significand precision, approximately 3 decimal digits.

Specifying -mfp16-format=alternative selects the ARM alternative format.  This representation is similar to the IEEE format, but does not support infinities or NaNs.  Instead, the range of exponents is extended, so that this format can represent normalized values in the range of 2^-14 to 131008.

The __fp16 type is a storage format only.  For purposes of arithmetic and other operations, __fp16 values in C or C++ expressions are automatically promoted to float.  In addition, you cannot declare a function with a return value or parameters of type __fp16.

Note that conversions from double to __fp16 involve an intermediate conversion to float.  Because of rounding, this can sometimes produce a different result than a direct conversion.

ARM provides hardware support for conversions between __fp16 and float values as an extension to VFP and NEON (Advanced SIMD).  GCC generates code using these hardware instructions if you compile with options to select an FPU that provides them; for example, -mfpu=neon-fp16 -mfloat-abi=softfp, in addition to the -mfp16-format option to select a half-precision format.

Language-level support for the __fp16 data type is independent of whether GCC generates code using hardware floating-point instructions.  In cases where hardware support is not specified, GCC implements conversions between __fp16 and float values as library calls.

Decimal Floating Types
======================

As an extension, GNU C supports decimal floating types as defined in the N1312 draft of ISO/IEC WDTR24732.  Support for decimal floating types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change.  Not all targets support decimal floating types.

The decimal floating types are _Decimal32, _Decimal64, and _Decimal128.  They use a radix of ten, unlike the floating types float, double, and long double whose radix is not specified by the C standard but is usually two.

Support for decimal floating types includes the arithmetic operators add, subtract, multiply, divide; unary arithmetic operators; relational operators; equality operators; and conversions to and from integer and other floating types.  Use a suffix df or DF in a literal constant of type _Decimal32, dd or DD for _Decimal64, and dl or DL for _Decimal128.

GCC support of decimal float as specified by the draft technical report is incomplete:

  * When the value of a decimal floating type cannot be represented in the integer type to which it is being converted, the result is undefined rather than the result value specified by the draft technical report.

  * GCC does not provide the C library functionality associated with math.h, fenv.h, stdio.h, stdlib.h, and wchar.h, which must come from a separate C library implementation. Because of this the GNU C compiler does not define macro __STDC_DEC_FP__ to indicate that the implementation conforms to the technical report.

Types _Decimal32, _Decimal64, and _Decimal128 are supported by the DWARF 2 debug information format.

Hex Floats
==========

ISO C99 supports floating-point numbers written not only in the usual decimal notation, such as 1.55e1, but also numbers such as 0x1.fp3 written in hexadecimal format.  As a GNU extension, GCC supports this in C90 mode (except in some cases when strictly conforming) and in C++.  In that format the 0x hex introducer and the p or P exponent field are mandatory.  The exponent is a decimal number that indicates the power of 2 by which the significant part is multiplied.  Thus 0x1.f is 1 15/16, p3 multiplies it by 8, and the value of 0x1.fp3 is the same as 1.55e1.

Unlike for floating-point numbers in the decimal notation the exponent is always required in the hexadecimal notation.  Otherwise the compiler would not be able to resolve the ambiguity of, e.g., 0x1.f.  This could mean 1.0f or 1.9375 since f is also the extension for floating-point constants of type float.

Fixed-Point Types
=================

As an extension, GNU C supports fixed-point types as defined in the N1169 draft of ISO/IEC DTR 18037.  Support for fixed-point types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change.  Not all targets support fixed-point types.

The fixed-point types are short _Fract, _Fract, long _Fract, long long _Fract, unsigned short _Fract, unsigned _Fract, unsigned long _Fract, unsigned long long _Fract, _Sat short _Fract, _Sat _Fract, _Sat long _Fract, _Sat long long _Fract, _Sat unsigned short _Fract, _Sat unsigned _Fract, _Sat unsigned long _Fract, _Sat unsigned long long _Fract, short _Accum, _Accum, long _Accum, long long _Accum, unsigned short _Accum, unsigned _Accum, unsigned long _Accum, unsigned long long _Accum, _Sat short _Accum, _Sat _Accum, _Sat long _Accum, _Sat long long _Accum, _Sat unsigned short _Accum, _Sat unsigned _Accum, _Sat unsigned long _Accum, _Sat unsigned long long _Accum.

Fixed-point data values contain fractional and optional integral parts. The format of fixed-point data varies and depends on the target machine.

Support for fixed-point types includes:

  * prefix and postfix increment and decrement operators (++, --)

  * unary arithmetic operators (+, -, !)

  * binary arithmetic operators (+, -, *, /)

  * binary shift operators (<<, >>)

  * relational operators (<, <=, >=, >)

  * equality operators (==, !=)

  * assignment operators (+=, -=, *=, /=, <<=, >>=)

  * conversions to and from integer, floating-point, or fixed-point types

Use a suffix in a fixed-point literal constant:

  * hr or HR for short _Fract and _Sat short _Fract

  * r or R for _Fract and _Sat _Fract

  * lr or LR for long _Fract and _Sat long _Fract

  * llr or LLR for long long _Fract and _Sat long long _Fract

  * uhr or UHR for unsigned short _Fract and _Sat unsigned short _Fract

  * ur or UR for unsigned _Fract and _Sat unsigned _Fract

  * ulr or ULR for unsigned long _Fract and _Sat unsigned long _Fract

  * ullr or ULLR for unsigned long long _Fract and _Sat unsigned long long _Fract

  * hk or HK for short _Accum and _Sat short _Accum

  * k or K for _Accum and _Sat _Accum

  * lk or LK for long _Accum and _Sat long _Accum

  * llk or LLK for long long _Accum and _Sat long long _Accum

  * uhk or UHK for unsigned short _Accum and _Sat unsigned short _Accum

  * uk or UK for unsigned _Accum and _Sat unsigned _Accum

  * ulk or ULK for unsigned long _Accum and _Sat unsigned long _Accum

  * ullk or ULLK for unsigned long long _Accum and _Sat unsigned long long _Accum

GCC support of fixed-point types as specified by the draft technical report is incomplete:

  * Pragmas to control overflow and rounding behaviors are not implemented.

Fixed-point types are supported by the DWARF 2 debug information format.

Named Address Spaces
====================

As an extension, GNU C supports named address spaces as defined in the N1275 draft of ISO/IEC DTR 18037.  Support for named address spaces in GCC will evolve as the draft technical report changes.  Calling conventions for any target might also change.  At present, only the AVR, SPU, M32C, and RL78 targets support address spaces other than the generic address space.

Address space identifiers may be used exactly like any other C type qualifier (e.g., const or volatile).  See the N1275 document for more details.

AVR Named Address Spaces
------------------------

On the AVR target, there are several address spaces that can be used in order to put read-only data into the flash memory and access that data by means of the special instructions LPM or ELPM needed to read from flash.

Per default, any data including read-only data is located in RAM (the generic address space) so that non-generic address spaces are needed to locate read-only data in flash memory and to generate the right instructions to access this data without using (inline) assembler code.

__flash
     The __flash qualifier locates data in the .progmem.data section. Data is read using the LPM instruction. Pointers to this address space are 16 bits wide.

__flash1
__flash2
__flash3
__flash4
__flash5
     These are 16-bit address spaces locating data in section .progmemN.data where N refers to address space __flashN. The compiler sets the RAMPZ segment register appropriately before reading data by means of the ELPM instruction.

__memx
     This is a 24-bit address space that linearizes flash and RAM: If the high bit of the address is set, data is read from RAM using the lower two bytes as RAM address. If the high bit of the address is clear, data is read from flash with RAMPZ set according to the high byte of the address. See __builtin_avr_flash_segment.

     Objects in this address space are located in .progmemx.data.

Example

     char my_read (const __flash char ** p)
     {
         /* p is a pointer to RAM that points to a pointer to flash.
            The first indirection of p reads that flash pointer
            from RAM and the second indirection reads a char from this
            flash address.  */

         return **p;
     }

     /* Locate array[] in flash memory */
     const __flash int array[] = { 3, 5, 7, 11, 13, 17, 19 };

     int i = 1;

     int main (void)
     {
        /* Return 17 by reading from flash memory */
        return array[array[i]];
     }

For each named address space supported by avr-gcc there is an equally named but uppercase built-in macro defined. The purpose is to facilitate testing if respective address space support is available or not:

     #ifdef __FLASH
     const __flash int var = 1;

     int read_var (void)
     {
         return var;
     }
     #else
     #include <avr/pgmspace.h> /* From AVR-LibC */

     const int var PROGMEM = 1;

     int read_var (void)
     {
         return (int) pgm_read_word (&var);
     }
     #endif /* __FLASH */

Notice that attribute progmem locates data in flash but accesses to these data read from generic address space, i.e. from RAM, so that you need special accessors like pgm_read_byte from AVR-LibC (http://nongnu.org/avr-libc/user-manual/) together with attribute progmem.

Limitations and caveats

  * Reading across the 64 KiB section boundary of the __flash or __flashN address spaces shows undefined behavior. The only address space that supports reading across the 64 KiB flash segment boundaries is __memx.

  * If you use one of the __flashN address spaces you must arrange your linker script to locate the .progmemN.data sections according to your needs.

  * Any data or pointers to the non-generic address spaces must be qualified as const, i.e. as read-only data. This still applies if the data in one of these address spaces like software version number or calibration lookup table are intended to be changed after load time by, say, a boot loader. In this case the right qualification is const volatile so that the compiler must not optimize away known values or insert them as immediates into operands of instructions.

  * The following code initializes a variable pfoo located in static storage with a 24-bit address:

          extern const __memx char foo;
          const __memx void *pfoo = &foo;

     Such code requires at least binutils 2.23, see PR13503 (http://sourceware.org/PR13503).

M32C Named Address Spaces
-------------------------

On the M32C target, with the R8C and M16C CPU variants, variables qualified with __far are accessed using 32-bit addresses in order to access memory beyond the first 64 Ki bytes.  If __far is used with the M32CM or M32C CPU variants, it has no effect.

RL78 Named Address Spaces
-------------------------

On the RL78 target, variables qualified with __far are accessed with 32-bit pointers (20-bit addresses) rather than the default 16-bit addresses.  Non-far variables are assumed to appear in the topmost 64 KiB of the address space.

SPU Named Address Spaces
------------------------

On the SPU target variables may be declared as belonging to another address space by qualifying the type with the __ea address space identifier:

     extern int __ea i;

The compiler generates special code to access the variable i. It may use runtime library support, or generate special machine instructions to access that address space.

Arrays of Length Zero
=====================

Zero-length arrays are allowed in GNU C.  They are very useful as the last element of a structure that is really a header for a variable-length object:

     struct line {
       int length;
       char contents[0];
     };

     struct line *thisline = (struct line *)
       malloc (sizeof (struct line) + this_length);
     thisline->length = this_length;

In ISO C90, you would have to give contents a length of 1, which means either you waste space or complicate the argument to malloc.

In ISO C99, you would use a flexible array member, which is slightly different in syntax and semantics:

  * Flexible array members are written as contents[] without the 0.

  * Flexible array members have incomplete type, and so the sizeof operator may not be applied.  As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero.

  * Flexible array members may only appear as the last member of a struct that is otherwise non-empty.

  * A structure containing a flexible array member, or a union containing such a structure (possibly recursively), may not be a member of a structure or an element of an array.  (However, these uses are permitted by GCC as extensions.)

Non-empty initialization of zero-length arrays is treated like any case where there are more initializer elements than the array holds, in that a suitable warning about ``excess elements in array'' is given, and the excess elements (all of them, in this case) are ignored.

GCC allows static initialization of flexible array members. This is equivalent to defining a new structure containing the original structure followed by an array of sufficient size to contain the data. E.g. in the following, f1 is constructed as if it were declared like f2.

     struct f1 {
       int x; int y[];
     } f1 = { 1, { 2, 3, 4 } };

     struct f2 {
       struct f1 f1; int data[3];
     } f2 = { { 1 }, { 2, 3, 4 } };

The convenience of this extension is that f1 has the desired type, eliminating the need to consistently refer to f2.f1.

This has symmetry with normal static arrays, in that an array of unknown size is also written with [].

Of course, this extension only makes sense if the extra data comes at the end of a top-level object, as otherwise we would be overwriting data at subsequent offsets.  To avoid undue complication and confusion with initialization of deeply nested arrays, we simply disallow any non-empty initialization except when the structure is the top-level object.  For example:

     struct foo { int x; int y[]; };
     struct bar { struct foo z; };

     struct foo a = { 1, { 2, 3, 4 } };        // Valid.
     struct bar b = { { 1, { 2, 3, 4 } } };    // Invalid.
     struct bar c = { { 1, { } } };            // Valid.
     struct foo d[1] = { { 1, { 2, 3, 4 } } };  // Invalid.

Structures with No Members
==========================

GCC permits a C structure to have no members:

     struct empty {
     };

The structure has size zero.  In C++, empty structures are part of the language.  G++ treats empty structures as if they had a single member of type char.

Arrays of Variable Length
=========================

Variable-length automatic arrays are allowed in ISO C99, and as an extension GCC accepts them in C90 mode and in C++.  These arrays are declared like any other automatic arrays, but with a length that is not a constant expression.  The storage is allocated at the point of declaration and deallocated when the block scope containing the declaration exits.  For example:

     FILE *
     concat_fopen (char *s1, char *s2, char *mode)
     {
       char str[strlen (s1) + strlen (s2) + 1];
       strcpy (str, s1);
       strcat (str, s2);
       return fopen (str, mode);
     }

Jumping or breaking out of the scope of the array name deallocates the storage.  Jumping into the scope is not allowed; you get an error message for it.

As an extension, GCC accepts variable-length arrays as a member of a structure or a union.  For example:

     void
     foo (int n)
     {
       struct S { int x[n]; };
     }

You can use the function alloca to get an effect much like variable-length arrays.  The function alloca is available in many other C implementations (but not in all).  On the other hand, variable-length arrays are more elegant.

There are other differences between these two methods.  Space allocated with alloca exists until the containing function returns. The space for a variable-length array is deallocated as soon as the array name's scope ends.  (If you use both variable-length arrays and alloca in the same function, deallocation of a variable-length array also deallocates anything more recently allocated with alloca.)

You can also use variable-length arrays as arguments to functions:

     struct entry
     tester (int len, char data[len][len])
     {
       /* ... */
     }

The length of an array is computed once when the storage is allocated and is remembered for the scope of the array in case you access it with sizeof.

If you want to pass the array first and the length afterward, you can use a forward declaration in the parameter list---another GNU extension.

     struct entry
     tester (int len; char data[len][len], int len)
     {
       /* ... */
     }

The int len before the semicolon is a parameter forward declaration, and it serves the purpose of making the name len known when the declaration of data is parsed.

You can write any number of such parameter forward declarations in the parameter list.  They can be separated by commas or semicolons, but the last one must end with a semicolon, which is followed by the ``real'' parameter declarations.  Each forward declaration must match a ``real'' declaration in parameter name and data type.  ISO C99 does not support parameter forward declarations.

Macros with a Variable Number of Arguments.
===========================================

In the ISO C standard of 1999, a macro can be declared to accept a variable number of arguments much as a function can.  The syntax for defining the macro is similar to that of a function.  Here is an example:

     #define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)

Here ... is a variable argument.  In the invocation of such a macro, it represents the zero or more tokens until the closing parenthesis that ends the invocation, including any commas.  This set of tokens replaces the identifier __VA_ARGS__ in the macro body wherever it appears.  See the CPP manual for more information.

GCC has long supported variadic macros, and used a different syntax that allowed you to give a name to the variable arguments just like any other argument.  Here is an example:

     #define debug(format, args...) fprintf (stderr, format, args)

This is in all ways equivalent to the ISO C example above, but arguably more readable and descriptive.

GNU CPP has two further variadic macro extensions, and permits them to be used with either of the above forms of macro definition.

In standard C, you are not allowed to leave the variable argument out entirely; but you are allowed to pass an empty argument.  For example, this invocation is invalid in ISO C, because there is no comma after the string:

     debug ("A message")

GNU CPP permits you to completely omit the variable arguments in this way.  In the above examples, the compiler would complain, though since the expansion of the macro still has the extra comma after the format string.

To help solve this problem, CPP behaves specially for variable arguments used with the token paste operator, ##.  If instead you write

     #define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)

and if the variable arguments are omitted or empty, the ## operator causes the preprocessor to remove the comma before it.  If you do provide some variable arguments in your macro invocation, GNU CPP does not complain about the paste operation and instead places the variable arguments after the comma.  Just like any other pasted macro argument, these arguments are not macro expanded.

Slightly Looser Rules for Escaped Newlines
==========================================

The preprocessor treatment of escaped newlines is more relaxed than that specified by the C90 standard, which requires the newline to immediately follow a backslash. GCC's implementation allows whitespace in the form of spaces, horizontal and vertical tabs, and form feeds between the backslash and the subsequent newline.  The preprocessor issues a warning, but treats it as a valid escaped newline and combines the two lines to form a single logical line.  This works within comments and tokens, as well as between tokens.  Comments are not treated as whitespace for the purposes of this relaxation, since they have not yet been replaced with spaces.

Non-Lvalue Arrays May Have Subscripts
=====================================

In ISO C99, arrays that are not lvalues still decay to pointers, and may be subscripted, although they may not be modified or used after the next sequence point and the unary & operator may not be applied to them.  As an extension, GNU C allows such arrays to be subscripted in C90 mode, though otherwise they do not decay to pointers outside C99 mode.  For example, this is valid in GNU C though not valid in C90:

     struct foo {int a[4];};

     struct foo f();

     bar (int index)
     {
       return f().a[index];
     }

Arithmetic on void- and Function-Pointers
=========================================

In GNU C, addition and subtraction operations are supported on pointers to void and on pointers to functions.  This is done by treating the size of a void or of a function as 1.

A consequence of this is that sizeof is also allowed on void and on function types, and returns 1.

The option -Wpointer-arith requests a warning if these extensions are used.

Pointers to Arrays with Qualifiers Work as Expected
===================================================

In GNU C, pointers to arrays with qualifiers work similar to pointers to other qualified types. For example, a value of type int (*)[5] can be used to initialize a variable of type const int (*)[5]. These types are incompatible in ISO C because the const qualifier is formally attached to the element type of the array and not the array itself.

     extern void
     transpose (int N, int M, double out[M][N], const double in[N][M]);
     double x[3][2];
     double y[2][3];
     ...
     transpose(3, 2, y, x);

Non-Constant Initializers
=========================

As in standard C++ and ISO C99, the elements of an aggregate initializer for an automatic variable are not required to be constant expressions in GNU C. Here is an example of an initializer with run-time varying elements:

     foo (float f, float g)
     {
       float beat_freqs[2] = { f-g, f+g };
       /* ... */
     }

Compound Literals
=================

ISO C99 supports compound literals.  A compound literal looks like a cast containing an initializer.  Its value is an object of the type specified in the cast, containing the elements specified in the initializer; it is an lvalue.  As an extension, GCC supports compound literals in C90 mode and in C++, though the semantics are somewhat different in C++.

Usually, the specified type is a structure.  Assume that struct foo and structure are declared as shown:

     struct foo {int a; char b[2];} structure;

Here is an example of constructing a struct foo with a compound literal:

     structure = ((struct foo) {x + y, 'a', 0});

This is equivalent to writing the following:

     {
       struct foo temp = {x + y, 'a', 0};
       structure = temp;
     }

You can also construct an array, though this is dangerous in C++, as explained below.  If all the elements of the compound literal are (made up of) simple constant expressions, suitable for use in initializers of objects of static storage duration, then the compound literal can be coerced to a pointer to its first element and used in such an initializer, as shown here:

     char **foo = (char *[]) { "x", "y", "z" };

Compound literals for scalar types and union types are also allowed, but then the compound literal is equivalent to a cast.

As a GNU extension, GCC allows initialization of objects with static storage duration by compound literals (which is not possible in ISO C99, because the initializer is not a constant). It is handled as if the object is initialized only with the bracket enclosed list if the types of the compound literal and the object match. The initializer list of the compound literal must be constant. If the object being initialized has array type of unknown size, the size is determined by compound literal size.

     static struct foo x = (struct foo) {1, 'a', 'b'};
     static int y[] = (int []) {1, 2, 3};
     static int z[] = (int [3]) {1};

The above lines are equivalent to the following:

     static struct foo x = {1, 'a', 'b'};
     static int y[] = {1, 2, 3};
     static int z[] = {1, 0, 0};

In C, a compound literal designates an unnamed object with static or automatic storage duration.  In C++, a compound literal designates a temporary object, which only lives until the end of its full-expression.  As a result, well-defined C code that takes the address of a subobject of a compound literal can be undefined in C++, so the C++ compiler rejects the conversion of a temporary array to a pointer. For instance, if the array compound literal example above appeared inside a function, any subsequent use of foo in C++ has undefined behavior because the lifetime of the array ends after the declaration of foo.

As an optimization, the C++ compiler sometimes gives array compound literals longer lifetimes: when the array either appears outside a function or has const-qualified type.  If foo and its initializer had elements of char *const type rather than char *, or if foo were a global variable, the array would have static storage duration.  But it is probably safest just to avoid the use of array compound literals in code compiled as C++.

Designated Initializers
=======================

Standard C90 requires the elements of an initializer to appear in a fixed order, the same as the order of the elements in the array or structure being initialized.

In ISO C99 you can give the elements in any order, specifying the array indices or structure field names they apply to, and GNU C allows this as an extension in C90 mode as well.  This extension is not implemented in GNU C++.

To specify an array index, write [INDEX] = before the element value.  For example,

     int a[6] = { [4] = 29, [2] = 15 };

is equivalent to

     int a[6] = { 0, 0, 15, 0, 29, 0 };

The index values must be constant expressions, even if the array being initialized is automatic.

An alternative syntax for this that has been obsolete since GCC 2.5 but GCC still accepts is to write [INDEX] before the element value, with no =.

To initialize a range of elements to the same value, write [FIRST ... LAST] = VALUE.  This is a GNU extension.  For example,

     int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

If the value in it has side-effects, the side-effects happen only once, not for each initialized field by the range initializer.

Note that the length of the array is the highest value specified plus one.

In a structure initializer, specify the name of a field to initialize with .FIELDNAME = before the element value.  For example, given the following structure,

     struct point { int x, y; };

the following initialization

     struct point p = { .y = yvalue, .x = xvalue };

is equivalent to

     struct point p = { xvalue, yvalue };

Another syntax that has the same meaning, obsolete since GCC 2.5, is FIELDNAME:, as shown here:

     struct point p = { y: yvalue, x: xvalue };

Omitted field members are implicitly initialized the same as objects that have static storage duration.

The [INDEX] or .FIELDNAME is known as a designator.  You can also use a designator (or the obsolete colon syntax) when initializing a union, to specify which element of the union should be used.  For example,

     union foo { int i; double d; };

     union foo f = { .d = 4 };

converts 4 to a double to store it in the union using the second element.  By contrast, casting 4 to type union foo stores it into the union as the integer i, since it is an integer.  (see Cast to Union.)

You can combine this technique of naming elements with ordinary C initialization of successive elements.  Each initializer element that does not have a designator applies to the next consecutive element of the array or structure.  For example,

     int a[6] = { [1] = v1, v2, [4] = v4 };

is equivalent to

     int a[6] = { 0, v1, v2, 0, v4, 0 };

Labeling the elements of an array initializer is especially useful when the indices are characters or belong to an enum type. For example:

     int whitespace[256]
       = { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
           ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };

You can also write a series of .FIELDNAME and [INDEX] designators before an = to specify a nested subobject to initialize; the list is taken relative to the subobject corresponding to the closest surrounding brace pair.  For example, with the struct point declaration above:

     struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };

If the same field is initialized multiple times, it has the value from the last initialization.  If any such overridden initialization has side-effect, it is unspecified whether the side-effect happens or not. Currently, GCC discards them and issues a warning.

Case Ranges
===========

You can specify a range of consecutive values in a single case label, like this:

     case LOW ... HIGH:

This has the same effect as the proper number of individual case labels, one for each integer value from LOW to HIGH, inclusive.

This feature is especially useful for ranges of ASCII character codes:

     case 'A' ... 'Z':

Be careful: Write spaces around the ..., for otherwise it may be parsed wrong when you use it with integer values.  For example, write this:

     case 1 ... 5:

rather than this:

     case 1...5:

Cast to a Union Type
====================

A cast to union type is similar to other casts, except that the type specified is a union type.  You can specify the type either with union TAG or with a typedef name.  A cast to union is actually a constructor, not a cast, and hence does not yield an lvalue like normal casts.  (see Compound Literals.)

The types that may be cast to the union type are those of the members of the union.  Thus, given the following union and variables:

     union foo { int i; double d; };
     int x;
     double y;

both x and y can be cast to type union foo.

Using the cast as the right-hand side of an assignment to a variable of union type is equivalent to storing in a member of the union:

     union foo u;
     /* ... */
     u = (union foo) x  ==  u.i = x
     u = (union foo) y  ==  u.d = y

You can also use the union cast as a function argument:

     void hack (union foo);
     /* ... */
     hack ((union foo) x);

Mixed Declarations and Code
===========================

ISO C99 and ISO C++ allow declarations and code to be freely mixed within compound statements.  As an extension, GNU C also allows this in C90 mode.  For example, you could do:

     int i;
     /* ... */
     i++;
     int j = i + 2;

Each identifier is visible from where it is declared until the end of the enclosing block.

Declaring Attributes of Functions
=================================

In GNU C, you can use function attributes to declare certain things about functions called in your program which help the compiler optimize calls and check your code more carefully.  For example, you can use attributes to declare that a function never returns (noreturn), returns a value depending only on its arguments (pure), or has printf-style arguments (format).

You can also use attributes to control memory placement, code generation options or call/return conventions within the function being annotated.  Many of these attributes are target-specific.  For example, many targets support attributes for defining interrupt handler functions, which typically must follow special register usage and return conventions.

Function attributes are introduced by the __attribute__ keyword on a declaration, followed by an attribute specification inside double parentheses.  You can specify multiple attributes in a declaration by separating them by commas within the double parentheses or by immediately following an attribute declaration with another attribute declaration.  See Attribute Syntax, for the exact rules on attribute syntax and placement.

GCC also supports attributes on variable declarations (see Variable Attributes), labels (see Label Attributes), enumerators (see Enumerator Attributes), and types (see Type Attributes).

There is some overlap between the purposes of attributes and pragmas (see Pragmas Accepted by GCC).  It has been found convenient to use __attribute__ to achieve a natural attachment of attributes to their corresponding declarations, whereas #pragma is of use for compatibility with other compilers or constructs that do not naturally form part of the grammar.

In addition to the attributes documented here, GCC plugins may provide their own attributes.

Common Function Attributes
--------------------------

The following attributes are supported on most targets.

alias ("TARGET")
     The alias attribute causes the declaration to be emitted as an alias for another symbol, which must be specified.  For instance,

          void __f () { /* Do something. */; }
          void f () __attribute__ ((weak, alias ("__f")));

     defines f to be a weak alias for __f.  In C++, the mangled name for the target must be used.  It is an error if __f is not defined in the same translation unit.

     This attribute requires assembler and object file support, and may not be available on all targets.

aligned (ALIGNMENT)
     This attribute specifies a minimum alignment for the function, measured in bytes.

     You cannot use this attribute to decrease the alignment of a function, only to increase it.  However, when you explicitly specify a function alignment this overrides the effect of the -falign-functions (see Optimize Options) option for this function.

     Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker.  On many systems, the linker is only able to arrange for functions to be aligned up to a certain maximum alignment.  (For some linkers, the maximum supported alignment may be very very small.)  See your linker documentation for further information.

     The aligned attribute can also be used for variables and fields (see Variable Attributes.)

alloc_align
     The alloc_align attribute is used to tell the compiler that the function return value points to memory, where the returned pointer minimum alignment is given by one of the functions parameters.  GCC uses this information to improve pointer alignment analysis.

     The function parameter denoting the allocated alignment is specified by one integer argument, whose number is the argument of the attribute. Argument numbering starts at one.

     For instance,

          void* my_memalign(size_t, size_t) __attribute__((alloc_align(1)))

     declares that my_memalign returns memory with minimum alignment given by parameter 1.

alloc_size
     The alloc_size attribute is used to tell the compiler that the function return value points to memory, where the size is given by one or two of the functions parameters.  GCC uses this information to improve the correctness of __builtin_object_size.

     The function parameter(s) denoting the allocated size are specified by one or two integer arguments supplied to the attribute.  The allocated size is either the value of the single function argument specified or the product of the two function arguments specified.  Argument numbering starts at one.

     For instance,

          void* my_calloc(size_t, size_t) __attribute__((alloc_size(1,2)))
          void* my_realloc(void*, size_t) __attribute__((alloc_size(2)))

     declares that my_calloc returns memory of the size given by the product of parameter 1 and 2 and that my_realloc returns memory of the size given by parameter 2.

always_inline
     Generally, functions are not inlined unless optimization is specified. For functions declared inline, this attribute inlines the function independent of any restrictions that otherwise apply to inlining. Failure to inline such a function is diagnosed as an error. Note that if such a function is called indirectly the compiler may or may not inline it depending on optimization level and a failure to inline an indirect call may or may not be diagnosed.

artificial
     This attribute is useful for small inline wrappers that if possible should appear during debugging as a unit.  Depending on the debug info format it either means marking the function as artificial or using the caller location for all instructions within the inlined body.

assume_aligned
     The assume_aligned attribute is used to tell the compiler that the function return value points to memory, where the returned pointer minimum alignment is given by the first argument. If the attribute has two arguments, the second argument is misalignment offset.

     For instance

          void* my_alloc1(size_t) __attribute__((assume_aligned(16)))
          void* my_alloc2(size_t) __attribute__((assume_aligned(32, 8)))

     declares that my_alloc1 returns 16-byte aligned pointer and that my_alloc2 returns a pointer whose value modulo 32 is equal to 8.

bnd_instrument
     The bnd_instrument attribute on functions is used to inform the compiler that the function should be instrumented when compiled with the -fchkp-instrument-marked-only option.

bnd_legacy
     The bnd_legacy attribute on functions is used to inform the compiler that the function should not be instrumented when compiled with the -fcheck-pointer-bounds option.

cold
     The cold attribute on functions is used to inform the compiler that the function is unlikely to be executed.  The function is optimized for size rather than speed and on many targets it is placed into a special subsection of the text section so all cold functions appear close together, improving code locality of non-cold parts of program.  The paths leading to calls of cold functions within code are marked as unlikely by the branch prediction mechanism.  It is thus useful to mark functions used to handle unlikely conditions, such as perror, as cold to improve optimization of hot functions that do call marked functions in rare occasions.

     When profile feedback is available, via -fprofile-use, cold functions are automatically detected and this attribute is ignored.

const
     Many functions do not examine any values except their arguments, and have no effects except the return value.  Basically this is just slightly more strict class than the pure attribute below, since function is not allowed to read global memory.

     Note that a function that has pointer arguments and examines the data pointed to must not be declared const.  Likewise, a function that calls a non-const function usually must not be const.  It does not make sense for a const function to return void.

constructor
destructor
constructor (PRIORITY)
destructor (PRIORITY)
     The constructor attribute causes the function to be called automatically before execution enters main ().  Similarly, the destructor attribute causes the function to be called automatically after main () completes or exit () is called.  Functions with these attributes are useful for initializing data that is used implicitly during the execution of the program.

     You may provide an optional integer priority to control the order in which constructor and destructor functions are run.  A constructor with a smaller priority number runs before a constructor with a larger priority number; the opposite relationship holds for destructors.  So, if you have a constructor that allocates a resource and a destructor that deallocates the same resource, both functions typically have the same priority.  The priorities for constructor and destructor functions are the same as those specified for namespace-scope C++ objects (see C++ Attributes).

     These attributes are not currently implemented for Objective-C.

deprecated
deprecated (MSG)
     The deprecated attribute results in a warning if the function is used anywhere in the source file.  This is useful when identifying functions that are expected to be removed in a future version of a program.  The warning also includes the location of the declaration of the deprecated function, to enable users to easily find further information about why the function is deprecated, or what they should do instead.  Note that the warnings only occurs for uses:

          int old_fn () __attribute__ ((deprecated));
          int old_fn ();
          int (*fn_ptr)() = old_fn;

     results in a warning on line 3 but not line 2.  The optional MSG argument, which must be a string, is printed in the warning if present.

     The deprecated attribute can also be used for variables and types (see Variable Attributes, see Type Attributes.)

error ("MESSAGE")
warning ("MESSAGE")
     If the error or warning attribute is used on a function declaration and a call to such a function is not eliminated through dead code elimination or other optimizations, an error or warning (respectively) that includes MESSAGE is diagnosed. This is useful for compile-time checking, especially together with __builtin_constant_p and inline functions where checking the inline function arguments is not possible through extern char [(condition) ? 1 : -1]; tricks.

     While it is possible to leave the function undefined and thus invoke a link failure (to define the function with a message in .gnu.warning* section), when using these attributes the problem is diagnosed earlier and with exact location of the call even in presence of inline functions or when not emitting debugging information.

externally_visible
     This attribute, attached to a global variable or function, nullifies the effect of the -fwhole-program command-line option, so the object remains visible outside the current compilation unit.

     If -fwhole-program is used together with -flto and gold is used as the linker plugin, externally_visible attributes are automatically added to functions (not variable yet due to a current gold issue) that are accessed outside of LTO objects according to resolution file produced by gold. For other linkers that cannot generate resolution file, explicit externally_visible attributes are still necessary.

flatten
     Generally, inlining into a function is limited.  For a function marked with this attribute, every call inside this function is inlined, if possible. Whether the function itself is considered for inlining depends on its size and the current inlining parameters.

format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)
     The format attribute specifies that a function takes printf, scanf, strftime or strfmon style arguments that should be type-checked against a format string.  For example, the declaration:

          extern int
          my_printf (void *my_object, const char *my_format, ...)
                __attribute__ ((format (printf, 2, 3)));

     causes the compiler to check the arguments in calls to my_printf for consistency with the printf style format string argument my_format.

     The parameter ARCHETYPE determines how the format string is interpreted, and should be printf, scanf, strftime, gnu_printf, gnu_scanf, gnu_strftime or strfmon.  (You can also use __printf__, __scanf__, __strftime__ or __strfmon__.)  On MinGW targets, ms_printf, ms_scanf, and ms_strftime are also present. ARCHETYPE values such as printf refer to the formats accepted by the system's C runtime library, while values prefixed with gnu_ always refer to the formats accepted by the GNU C Library.  On Microsoft Windows targets, values prefixed with ms_ refer to the formats accepted by the msvcrt.dll library. The parameter STRING-INDEX specifies which argument is the format string argument (starting from 1), while FIRST-TO-CHECK is the number of the first argument to check against the format string.  For functions where the arguments are not available to be checked (such as vprintf), specify the third parameter as zero.  In this case the compiler only checks the format string for consistency.  For strftime formats, the third parameter is required to be zero. Since non-static C++ methods have an implicit this argument, the arguments of such methods should be counted from two, not one, when giving values for STRING-INDEX and FIRST-TO-CHECK.

     In the example above, the format string (my_format) is the second argument of the function my_print, and the arguments to check start with the third argument, so the correct parameters for the format attribute are 2 and 3.

     The format attribute allows you to identify your own functions that take format strings as arguments, so that GCC can check the calls to these functions for errors.  The compiler always (unless -ffreestanding or -fno-builtin is used) checks formats for the standard library functions printf, fprintf, sprintf, scanf, fscanf, sscanf, strftime, vprintf, vfprintf and vsprintf whenever such warnings are requested (using -Wformat), so there is no need to modify the header file stdio.h.  In C99 mode, the functions snprintf, vsnprintf, vscanf, vfscanf and vsscanf are also checked.  Except in strictly conforming C standard modes, the X/Open function strfmon is also checked as are printf_unlocked and fprintf_unlocked. See Options Controlling C Dialect.

     For Objective-C dialects, NSString (or __NSString__) is recognized in the same context.  Declarations including these format attributes are parsed for correct syntax, however the result of checking of such format strings is not yet defined, and is not carried out by this version of the compiler.

     The target may also provide additional types of format checks. See Format Checks Specific to Particular Target Machines.

format_arg (STRING-INDEX)
     The format_arg attribute specifies that a function takes a format string for a printf, scanf, strftime or strfmon style function and modifies it (for example, to translate it into another language), so the result can be passed to a printf, scanf, strftime or strfmon style function (with the remaining arguments to the format function the same as they would have been for the unmodified string).  For example, the declaration:

          extern char *
          my_dgettext (char *my_domain, const char *my_format)
                __attribute__ ((format_arg (2)));

     causes the compiler to check the arguments in calls to a printf, scanf, strftime or strfmon type function, whose format string argument is a call to the my_dgettext function, for consistency with the format string argument my_format.  If the format_arg attribute had not been specified, all the compiler could tell in such calls to format functions would be that the format string argument is not constant; this would generate a warning when -Wformat-nonliteral is used, but the calls could not be checked without the attribute.

     The parameter STRING-INDEX specifies which argument is the format string argument (starting from one).  Since non-static C++ methods have an implicit this argument, the arguments of such methods should be counted from two.

     The format_arg attribute allows you to identify your own functions that modify format strings, so that GCC can check the calls to printf, scanf, strftime or strfmon type function whose operands are a call to one of your own function. The compiler always treats gettext, dgettext, and dcgettext in this manner except when strict ISO C support is requested by -ansi or an appropriate -std option, or -ffreestanding or -fno-builtin is used.  See Options Controlling C Dialect.

     For Objective-C dialects, the format-arg attribute may refer to an NSString reference for compatibility with the format attribute above.

     The target may also allow additional types in format-arg attributes. See Format Checks Specific to Particular Target Machines.

gnu_inline
     This attribute should be used with a function that is also declared with the inline keyword.  It directs GCC to treat the function as if it were defined in gnu90 mode even when compiling in C99 or gnu99 mode.

     If the function is declared extern, then this definition of the function is used only for inlining.  In no case is the function compiled as a standalone function, not even if you take its address explicitly.  Such an address becomes an external reference, as if you had only declared the function, and had not defined it.  This has almost the effect of a macro.  The way to use this is to put a function definition in a header file with this attribute, and put another copy of the function, without extern, in a library file.  The definition in the header file causes most calls to the function to be inlined.  If any uses of the function remain, they refer to the single copy in the library.  Note that the two definitions of the functions need not be precisely the same, although if they do not have the same effect your program may behave oddly.

     In C, if the function is neither extern nor static, then the function is compiled as a standalone function, as well as being inlined where possible.

     This is how GCC traditionally handled functions declared inline.  Since ISO C99 specifies a different semantics for inline, this function attribute is provided as a transition measure and as a useful feature in its own right.  This attribute is available in GCC 4.1.3 and later.  It is available if either of the preprocessor macros __GNUC_GNU_INLINE__ or __GNUC_STDC_INLINE__ are defined.  See An Inline Function is As Fast As a Macro.

     In C++, this attribute does not depend on extern in any way, but it still requires the inline keyword to enable its special behavior.

hot
     The hot attribute on a function is used to inform the compiler that the function is a hot spot of the compiled program.  The function is optimized more aggressively and on many targets it is placed into a special subsection of the text section so all hot functions appear close together, improving locality.

     When profile feedback is available, via -fprofile-use, hot functions are automatically detected and this attribute is ignored.

ifunc ("RESOLVER")
     The ifunc attribute is used to mark a function as an indirect function using the STT_GNU_IFUNC symbol type extension to the ELF standard.  This allows the resolution of the symbol value to be determined dynamically at load time, and an optimized version of the routine can be selected for the particular processor or other system characteristics determined then.  To use this attribute, first define the implementation functions available, and a resolver function that returns a pointer to the selected implementation function.  The implementation functions' declarations must match the API of the function being implemented, the resolver's declaration is be a function returning pointer to void function returning void:

          void *my_memcpy (void *dst, const void *src, size_t len)
          {
            ...
          }

          static void (*resolve_memcpy (void)) (void)
          {
            return my_memcpy; // we'll just always select this routine
          }

     The exported header file declaring the function the user calls would contain:

          extern void *memcpy (void *, const void *, size_t);

     allowing the user to call this as a regular function, unaware of the implementation.  Finally, the indirect function needs to be defined in the same translation unit as the resolver function:

          void *memcpy (void *, const void *, size_t)
               __attribute__ ((ifunc ("resolve_memcpy")));

     Indirect functions cannot be weak.  Binutils version 2.20.1 or higher and GNU C Library version 2.11.1 are required to use this feature.

interrupt
interrupt_handler
     Many GCC back ends support attributes to indicate that a function is an interrupt handler, which tells the compiler to generate function entry and exit sequences that differ from those from regular functions.  The exact syntax and behavior are target-specific; refer to the following subsections for details.

leaf
     Calls to external functions with this attribute must return to the current compilation unit only by return or by exception handling.  In particular, leaf functions are not allowed to call callback function passed to it from the current compilation unit or directly call functions exported by the unit or longjmp into the unit.  Leaf function might still call functions from other compilation units and thus they are not necessarily leaf in the sense that they contain no function calls at all.

     The attribute is intended for library functions to improve dataflow analysis. The compiler takes the hint that any data not escaping the current compilation unit can not be used or modified by the leaf function.  For example, the sin function is a leaf function, but qsort is not.

     Note that leaf functions might invoke signals and signal handlers might be defined in the current compilation unit and use static variables.  The only compliant way to write such a signal handler is to declare such variables volatile.

     The attribute has no effect on functions defined within the current compilation unit.  This is to allow easy merging of multiple compilation units into one, for example, by using the link-time optimization.  For this reason the attribute is not allowed on types to annotate indirect calls.

malloc
     This tells the compiler that a function is malloc-like, i.e., that the pointer P returned by the function cannot alias any other pointer valid when the function returns, and moreover no pointers to valid objects occur in any storage addressed by P.

     Using this attribute can improve optimization.  Functions like malloc and calloc have this property because they return a pointer to uninitialized or zeroed-out storage.  However, functions like realloc do not have this property, as they can return a pointer to storage containing pointers.

no_icf
     This function attribute prevents a functions from being merged with another semantically equivalent function.

no_instrument_function
     If -finstrument-functions is given, profiling function calls are generated at entry and exit of most user-compiled functions. Functions with this attribute are not so instrumented.

no_reorder
     Do not reorder functions or variables marked no_reorder against each other or top level assembler statements the executable. The actual order in the program will depend on the linker command line. Static variables marked like this are also not removed. This has a similar effect as the -fno-toplevel-reorder option, but only applies to the marked symbols.

no_sanitize_address
no_address_safety_analysis
     The no_sanitize_address attribute on functions is used to inform the compiler that it should not instrument memory accesses in the function when compiling with the -fsanitize=address option. The no_address_safety_analysis is a deprecated alias of the no_sanitize_address attribute, new code should use no_sanitize_address.

no_sanitize_thread
     The no_sanitize_thread attribute on functions is used to inform the compiler that it should not instrument memory accesses in the function when compiling with the -fsanitize=thread option.

no_sanitize_undefined
     The no_sanitize_undefined attribute on functions is used to inform the compiler that it should not check for undefined behavior in the function when compiling with the -fsanitize=undefined option.

no_split_stack
     If -fsplit-stack is given, functions have a small prologue which decides whether to split the stack.  Functions with the no_split_stack attribute do not have that prologue, and thus may run with only a small amount of stack space available.

noclone
     This function attribute prevents a function from being considered for cloning---a mechanism that produces specialized copies of functions and which is (currently) performed by interprocedural constant propagation.

noinline
     This function attribute prevents a function from being considered for inlining. If the function does not have side-effects, there are optimizations other than inlining that cause function calls to be optimized away, although the function call is live.  To keep such calls from being optimized away, put

          asm ("");

     (see Extended Asm) in the called function, to serve as a special side-effect.

nonnull (ARG-INDEX, ...)
     The nonnull attribute specifies that some function parameters should be non-null pointers.  For instance, the declaration:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
                  __attribute__((nonnull (1, 2)));

     causes the compiler to check that, in calls to my_memcpy, arguments DEST and SRC are non-null.  If the compiler determines that a null pointer is passed in an argument slot marked as non-null, and the -Wnonnull option is enabled, a warning is issued.  The compiler may also choose to make optimizations based on the knowledge that certain function arguments will never be null.

     If no argument index list is given to the nonnull attribute, all pointer arguments are marked as non-null.  To illustrate, the following declaration is equivalent to the previous example:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
                  __attribute__((nonnull));

noreturn
     A few standard library functions, such as abort and exit, cannot return.  GCC knows this automatically.  Some programs define their own functions that never return.  You can declare them noreturn to tell the compiler this fact.  For example,

          void fatal () __attribute__ ((noreturn));

          void
          fatal (/* ... */)
          {
            /* ... */ /* Print error message. */ /* ... */
            exit (1);
          }

     The noreturn keyword tells the compiler to assume that fatal cannot return.  It can then optimize without regard to what would happen if fatal ever did return.  This makes slightly better code.  More importantly, it helps avoid spurious warnings of uninitialized variables.

     The noreturn keyword does not affect the exceptional path when that applies: a noreturn-marked function may still return to the caller by throwing an exception or calling longjmp.

     Do not assume that registers saved by the calling function are restored before calling the noreturn function.

     It does not make sense for a noreturn function to have a return type other than void.

nothrow
     The nothrow attribute is used to inform the compiler that a function cannot throw an exception.  For example, most functions in the standard C library can be guaranteed not to throw an exception with the notable exceptions of qsort and bsearch that take function pointer arguments.

noplt
     The noplt attribute is the counterpart to option -fno-plt and does not use PLT for calls to functions marked with this attribute in position independent code.

          /* Externally defined function foo.  */
          int foo () __attribute__ ((noplt));

          int
          main (/* ... */)
          {
            /* ... */
            foo ();
            /* ... */
          }

     The noplt attribute on function foo tells the compiler to assume that the function foo is externally defined and the call to foo must avoid the PLT in position independent code.

     Additionally, a few targets also convert calls to those functions that are marked to not use the PLT to use the GOT instead for non-position independent code.

optimize
     The optimize attribute is used to specify that a function is to be compiled with different optimization options than specified on the command line.  Arguments can either be numbers or strings.  Numbers are assumed to be an optimization level.  Strings that begin with O are assumed to be an optimization option, while other options are assumed to be used with a -f prefix.  You can also use the #pragma GCC optimize pragma to set the optimization options that affect more than one function. See Function Specific Option Pragmas, for details about the #pragma GCC optimize pragma.

     This can be used for instance to have frequently-executed functions compiled with more aggressive optimization options that produce faster and larger code, while other functions can be compiled with less aggressive options.

pure
     Many functions have no effects except the return value and their return value depends only on the parameters and/or global variables. Such a function can be subject to common subexpression elimination and loop optimization just as an arithmetic operator would be.  These functions should be declared with the attribute pure.  For example,

          int square (int) __attribute__ ((pure));

     says that the hypothetical function square is safe to call fewer times than the program says.

     Some of common examples of pure functions are strlen or memcmp. Interesting non-pure functions are functions with infinite loops or those depending on volatile memory or other system resource, that may change between two consecutive calls (such as feof in a multithreading environment).

returns_nonnull
     The returns_nonnull attribute specifies that the function return value should be a non-null pointer.  For instance, the declaration:

          extern void *
          mymalloc (size_t len) __attribute__((returns_nonnull));

     lets the compiler optimize callers based on the knowledge that the return value will never be null.

returns_twice
     The returns_twice attribute tells the compiler that a function may return more than one time.  The compiler ensures that all registers are dead before calling such a function and emits a warning about the variables that may be clobbered after the second return from the function.  Examples of such functions are setjmp and vfork. The longjmp-like counterpart of such function, if any, might need to be marked with the noreturn attribute.

section ("SECTION-NAME")
     Normally, the compiler places the code it generates in the text section. Sometimes, however, you need additional sections, or you need certain particular functions to appear in special sections.  The section attribute specifies that a function lives in a particular section. For example, the declaration:

          extern void foobar (void) __attribute__ ((section ("bar")));

     puts the function foobar in the bar section.

     Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.

sentinel
     This function attribute ensures that a parameter in a function call is an explicit NULL.  The attribute is only valid on variadic functions.  By default, the sentinel is located at position zero, the last parameter of the function call.  If an optional integer position argument P is supplied to the attribute, the sentinel must be located at position P counting backwards from the end of the argument list.

          __attribute__ ((sentinel))
          is equivalent to
          __attribute__ ((sentinel(0)))

     The attribute is automatically set with a position of 0 for the built-in functions execl and execlp.  The built-in function execle has the attribute set with a position of 1.

     A valid NULL in this context is defined as zero with any pointer type.  If your system defines the NULL macro with an integer type then you need to add an explicit cast.  GCC replaces stddef.h with a copy that redefines NULL appropriately.

     The warnings for missing or incorrect sentinels are enabled with -Wformat.

stack_protect
     This function attribute make a stack protection of the function if flags fstack-protector or fstack-protector-strong or fstack-protector-explicit are set.

target (OPTIONS)
     Multiple target back ends implement the target attribute to specify that a function is to be compiled with different target options than specified on the command line.  This can be used for instance to have functions compiled with a different ISA (instruction set architecture) than the default.  You can also use the #pragma GCC target pragma to set more than one function to be compiled with specific target options. See Function Specific Option Pragmas, for details about the #pragma GCC target pragma.

     For instance, on an x86, you could declare one function with the target("sse4.1,arch=core2") attribute and another with target("sse4a,arch=amdfam10").  This is equivalent to compiling the first function with -msse4.1 and -march=core2 options, and the second function with -msse4a and -march=amdfam10 options.  It is up to you to make sure that a function is only invoked on a machine that supports the particular ISA it is compiled for (for example by using cpuid on x86 to determine what feature bits and architecture family are used).

          int core2_func (void) __attribute__ ((__target__ ("arch=core2")));
          int sse3_func (void) __attribute__ ((__target__ ("sse3")));

     You can either use multiple strings separated by commas to specify multiple options, or separate the options with a comma (,) within a single string.

     The options supported are specific to each target; refer to x86 Function Attributes, PowerPC Function Attributes, ARM Function Attributes,and Nios II Function Attributes, for details.

unused
     This attribute, attached to a function, means that the function is meant to be possibly unused.  GCC does not produce a warning for this function.

used
     This attribute, attached to a function, means that code must be emitted for the function even if it appears that the function is not referenced. This is useful, for example, when the function is referenced only in inline assembly.

     When applied to a member function of a C++ class template, the attribute also means that the function is instantiated if the class itself is instantiated.

visibility ("VISIBILITY_TYPE")
     This attribute affects the linkage of the declaration to which it is attached. There are four supported VISIBILITY_TYPE values: default, hidden, protected or internal visibility.

          void __attribute__ ((visibility ("protected")))
          f () { /* Do something. */; }
          int i __attribute__ ((visibility ("hidden")));

     The possible values of VISIBILITY_TYPE correspond to the visibility settings in the ELF gABI.

     default
          Default visibility is the normal case for the object file format. This value is available for the visibility attribute to override other options that may change the assumed visibility of entities.

          On ELF, default visibility means that the declaration is visible to other modules and, in shared libraries, means that the declared entity may be overridden.

          On Darwin, default visibility means that the declaration is visible to other modules.

          Default visibility corresponds to ``external linkage'' in the language.

     hidden
          Hidden visibility indicates that the entity declared has a new form of linkage, which we call ``hidden linkage''.  Two declarations of an object with hidden linkage refer to the same object if they are in the same shared object.

     internal
          Internal visibility is like hidden visibility, but with additional processor specific semantics.  Unless otherwise specified by the psABI, GCC defines internal visibility to mean that a function is never called from another module.  Compare this with hidden functions which, while they cannot be referenced directly by other modules, can be referenced indirectly via function pointers.  By indicating that a function cannot be called from outside the module, GCC may for instance omit the load of a PIC register since it is known that the calling function loaded the correct value.

     protected
          Protected visibility is like default visibility except that it indicates that references within the defining module bind to the definition in that module.  That is, the declared entity cannot be overridden by another module.

     All visibilities are supported on many, but not all, ELF targets (supported when the assembler supports the .visibility pseudo-op).  Default visibility is supported everywhere.  Hidden visibility is supported on Darwin targets.

     The visibility attribute should be applied only to declarations that would otherwise have external linkage.  The attribute should be applied consistently, so that the same entity should not be declared with different settings of the attribute.

     In C++, the visibility attribute applies to types as well as functions and objects, because in C++ types have linkage.  A class must not have greater visibility than its non-static data member types and bases, and class members default to the visibility of their class.  Also, a declaration without explicit visibility is limited to the visibility of its type.

     In C++, you can mark member functions and static member variables of a class with the visibility attribute.  This is useful if you know a particular method or static member variable should only be used from one shared object; then you can mark it hidden while the rest of the class has default visibility.  Care must be taken to avoid breaking the One Definition Rule; for example, it is usually not useful to mark an inline method as hidden without marking the whole class as hidden.

     A C++ namespace declaration can also have the visibility attribute.

          namespace nspace1 __attribute__ ((visibility ("protected")))
          { /* Do something. */; }

     This attribute applies only to the particular namespace body, not to other definitions of the same namespace; it is equivalent to using #pragma GCC visibility before and after the namespace definition (see Visibility Pragmas).

     In C++, if a template argument has limited visibility, this restriction is implicitly propagated to the template instantiation. Otherwise, template instantiations and specializations default to the visibility of their template.

     If both the template and enclosing class have explicit visibility, the visibility from the template is used.

warn_unused_result
     The warn_unused_result attribute causes a warning to be emitted if a caller of the function with this attribute does not use its return value.  This is useful for functions where not checking the result is either a security problem or always a bug, such as realloc.

          int fn () __attribute__ ((warn_unused_result));
          int foo ()
          {
            if (fn () < 0) return -1;
            fn ();
            return 0;
          }

     results in warning on line 5.

weak
     The weak attribute causes the declaration to be emitted as a weak symbol rather than a global.  This is primarily useful in defining library functions that can be overridden in user code, though it can also be used with non-function declarations.  Weak symbols are supported for ELF targets, and also for a.out targets when using the GNU assembler and linker.

weakref
weakref ("TARGET")
     The weakref attribute marks a declaration as a weak reference. Without arguments, it should be accompanied by an alias attribute naming the target symbol.  Optionally, the TARGET may be given as an argument to weakref itself.  In either case, weakref implicitly marks the declaration as weak.  Without a TARGET, given as an argument to weakref or to alias, weakref is equivalent to weak.

          static int x() __attribute__ ((weakref ("y")));
          /* is equivalent to... */
          static int x() __attribute__ ((weak, weakref, alias ("y")));
          /* and to... */
          static int x() __attribute__ ((weakref));
          static int x() __attribute__ ((alias ("y")));

     A weak reference is an alias that does not by itself require a definition to be given for the target symbol.  If the target symbol is only referenced through weak references, then it becomes a weak undefined symbol.  If it is directly referenced, however, then such strong references prevail, and a definition is required for the symbol, not necessarily in the same translation unit.

     The effect is equivalent to moving all references to the alias to a separate translation unit, renaming the alias to the aliased symbol, declaring it as weak, compiling the two separate translation units and performing a reloadable link on them.

     At present, a declaration to which weakref is attached can only be static.

lower
upper
either
     On the MSP430 target these attributes can be used to specify whether the function or variable should be placed into low memory, high memory, or the placement should be left to the linker to decide.  The attributes are only significant if compiling for the MSP430X architecture.

     The attributes work in conjunction with a linker script that has been augmented to specify where to place sections with a .lower and a .upper prefix.  So for example as well as placing the .data section the script would also specify the placement of a .lower.data and a .upper.data section.  The intention being that lower sections are placed into a small but easier to access memory region and the upper sections are placed into a larger, but slower to access region.

     The either attribute is special.  It tells the linker to place the object into the corresponding lower section if there is room for it.  If there is insufficient room then the object is placed into the corresponding upper section instead.  Note - the placement algorithm is not very sophisticated.  It will not attempt to find an optimal packing of the lower sections.  It just makes one pass over the objects and does the best that it can.  Using the -ffunction-sections and -fdata-sections command line options can help the packing however, since they produce smaller, easier to pack regions.

AArch64 Function Attributes
---------------------------

The following target-specific function attributes are available for the AArch64 target.  For the most part, these options mirror the behavior of similar command-line options (see AArch64 Options), but on a per-function basis.

general-regs-only
     Indicates that no floating-point or Advanced SIMD registers should be used when generating code for this function.  If the function explicitly uses floating-point code, then the compiler gives an error.  This is the same behavior as that of the command-line option -mgeneral-regs-only.

fix-cortex-a53-835769
     Indicates that the workaround for the Cortex-A53 erratum 835769 should be applied to this function.  To explicitly disable the workaround for this function specify the negated form: no-fix-cortex-a53-835769. This corresponds to the behavior of the command line options -mfix-cortex-a53-835769 and -mno-fix-cortex-a53-835769.

cmodel=
     Indicates that code should be generated for a particular code model for this function.  The behavior and permissible arguments are the same as for the command line option -mcmodel=.

strict-align
     Indicates that the compiler should not assume that unaligned memory references are handled by the system.  The behavior is the same as for the command-line option -mstrict-align.

omit-leaf-frame-pointer
     Indicates that the frame pointer should be omitted for a leaf function call. To keep the frame pointer, the inverse attribute no-omit-leaf-frame-pointer can be specified.  These attributes have the same behavior as the command-line options -momit-leaf-frame-pointer and -mno-omit-leaf-frame-pointer.

tls-dialect=
     Specifies the TLS dialect to use for this function.  The behavior and permissible arguments are the same as for the command-line option -mtls-dialect=.

arch=
     Specifies the architecture version and architectural extensions to use for this function.  The behavior and permissible arguments are the same as for the -march= command-line option.

tune=
     Specifies the core for which to tune the performance of this function. The behavior and permissible arguments are the same as for the -mtune= command-line option.

cpu=
     Specifies the core for which to tune the performance of this function and also whose architectural features to use.  The behavior and valid arguments are the same as for the -mcpu= command-line option.

The above target attributes can be specified as follows:

     __attribute__((target("ATTR-STRING")))
     int
     f (int a)
     {
       return a + 5;
     }

where ATTR-STRING is one of the attribute strings specified above.

Additionally, the architectural extension string may be specified on its own.  This can be used to turn on and off particular architectural extensions without having to specify a particular architecture version or core.  Example:

     __attribute__((target("+crc+nocrypto")))
     int
     foo (int a)
     {
       return a + 5;
     }

In this example target("+crc+nocrypto") enables the crc extension and disables the crypto extension for the function foo without modifying an existing -march= or -mcpu option.

Multiple target function attributes can be specified by separating them with a comma.  For example:

     __attribute__((target("arch=armv8-a+crc+crypto,tune=cortex-a53")))
     int
     foo (int a)
     {
       return a + 5;
     }

is valid and compiles function foo for ARMv8-A with crc and crypto extensions and tunes it for cortex-a53.

Inlining rules
..............

Specifying target attributes on individual functions or performing link-time optimization across translation units compiled with different target options can affect function inlining rules:

In particular, a caller function can inline a callee function only if the architectural features available to the callee are a subset of the features available to the caller. For example: A function foo compiled with -march=armv8-a+crc, or tagged with the equivalent arch=armv8-a+crc attribute, can inline a function bar compiled with -march=armv8-a+nocrc because the all the architectural features that function bar requires are available to function foo.  Conversely, function bar cannot inline function foo.

Additionally inlining a function compiled with -mstrict-align into a function compiled without -mstrict-align is not allowed. However, inlining a function compiled without -mstrict-align into a function compiled with -mstrict-align is allowed.

Note that CPU tuning options and attributes such as the -mcpu=, -mtune= do not inhibit inlining unless the CPU specified by the -mcpu= option or the cpu= attribute conflicts with the architectural feature rules specified above.

ARC Function Attributes
-----------------------

These function attributes are supported by the ARC back end:

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

     On the ARC, you must specify the kind of interrupt to be handled in a parameter to the interrupt attribute like this:

          void f () __attribute__ ((interrupt ("ilink1")));

     Permissible values for this parameter are: ilink1 and ilink2.

long_call
medium_call
short_call
     These attributes specify how a particular function is called. These attributes override the -mlong-calls and -mmedium-calls (see ARC Options) command-line switches and #pragma long_calls settings.

     For ARC, a function marked with the long_call attribute is always called using register-indirect jump-and-link instructions, thereby enabling the called function to be placed anywhere within the 32-bit address space.  A function marked with the medium_call attribute will always be close enough to be called with an unconditional branch-and-link instruction, which has a 25-bit offset from the call site.  A function marked with the short_call attribute will always be close enough to be called with a conditional branch-and-link instruction, which has a 21-bit offset from the call site.

ARM Function Attributes
-----------------------

These function attributes are supported for ARM targets:

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

     You can specify the kind of interrupt to be handled by adding an optional parameter to the interrupt attribute like this:

          void f () __attribute__ ((interrupt ("IRQ")));

     Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF.

     On ARMv7-M the interrupt type is ignored, and the attribute means the function may be called with a word-aligned stack pointer.

isr
     Use this attribute on ARM to write Interrupt Service Routines. This is an alias to the interrupt attribute above.

long_call
short_call
     These attributes specify how a particular function is called. These attributes override the -mlong-calls (see ARM Options) command-line switch and #pragma long_calls settings.  For ARM, the long_call attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence.   The short_call attribute always places the offset to the function from the call site into the BL instruction directly.

naked
     This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (see Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.

pcs

     The pcs attribute can be used to control the calling convention used for a function on ARM.  The attribute takes an argument that specifies the calling convention to use.

     When compiling using the AAPCS ABI (or a variant of it) then valid values for the argument are "aapcs" and "aapcs-vfp".  In order to use a variant other than "aapcs" then the compiler must be permitted to use the appropriate co-processor registers (i.e., the VFP registers must be available in order to use "aapcs-vfp"). For example,

          /* Argument passed in r0, and result returned in r0+r1.  */
          double f2d (float) __attribute__((pcs("aapcs")));

     Variadic functions always use the "aapcs" calling convention and the compiler rejects attempts to specify an alternative.

target (OPTIONS)
     As discussed in Common Function Attributes, this attribute allows specification of target-specific compilation options.

     On ARM, the following options are allowed:

     thumb
          Force code generation in the Thumb (T16/T32) ISA, depending on the architecture level.

     arm
          Force code generation in the ARM (A32) ISA.

     Functions from different modes can be inlined in the caller's mode.

AVR Function Attributes
-----------------------

These function attributes are supported by the AVR back end:

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

     On the AVR, the hardware globally disables interrupts when an interrupt is executed.  The first instruction of an interrupt handler declared with this attribute is a SEI instruction to re-enable interrupts.  See also the signal function attribute that does not insert a SEI instruction.  If both signal and interrupt are specified for the same function, signal is silently ignored.

naked
     This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (see Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.

OS_main
OS_task
     On AVR, functions with the OS_main or OS_task attribute do not save/restore any call-saved register in their prologue/epilogue.

     The OS_main attribute can be used when there is guarantee that interrupts are disabled at the time when the function is entered.  This saves resources when the stack pointer has to be changed to set up a frame for local variables.

     The OS_task attribute can be used when there is no guarantee that interrupts are disabled at that time when the function is entered like for, e.g. task functions in a multi-threading operating system. In that case, changing the stack pointer register is guarded by save/clear/restore of the global interrupt enable flag.

     The differences to the naked function attribute are:

       * naked functions do not have a return instruction whereas OS_main and OS_task functions have a RET or RETI return instruction.

       * naked functions do not set up a frame for local variables or a frame pointer whereas OS_main and OS_task do this as needed.

signal
     Use this attribute on the AVR to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

     See also the interrupt function attribute.

     The AVR hardware globally disables interrupts when an interrupt is executed. Interrupt handler functions defined with the signal attribute do not re-enable interrupts.  It is save to enable interrupts in a signal handler.  This ``save'' only applies to the code generated by the compiler and not to the IRQ layout of the application which is responsibility of the application.

     If both signal and interrupt are specified for the same function, signal is silently ignored.

Blackfin Function Attributes
----------------------------

These function attributes are supported by the Blackfin back end:

exception_handler
     Use this attribute on the Blackfin to indicate that the specified function is an exception handler.  The compiler generates function entry and exit sequences suitable for use in an exception handler when this attribute is present.

interrupt_handler
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

kspisusp
     When used together with interrupt_handler, exception_handler or nmi_handler, code is generated to load the stack pointer from the USP register in the function prologue.

l1_text
     This attribute specifies a function to be placed into L1 Instruction SRAM. The function is put into a specific section named .l1.text. With -mfdpic, function calls with a such function as the callee or caller uses inlined PLT.

l2
     This attribute specifies a function to be placed into L2 SRAM. The function is put into a specific section named .l2.text. With -mfdpic, callers of such functions use an inlined PLT.

longcall
shortcall
     The longcall attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence.  The shortcall attribute indicates that the function is always close enough for the shorter calling sequence to be used.  These attributes override the -mlongcall switch.

nesting
     Use this attribute together with interrupt_handler, exception_handler or nmi_handler to indicate that the function entry code should enable nested interrupts or exceptions.

nmi_handler
     Use this attribute on the Blackfin to indicate that the specified function is an NMI handler.  The compiler generates function entry and exit sequences suitable for use in an NMI handler when this attribute is present.

saveall
     Use this attribute to indicate that all registers except the stack pointer should be saved in the prologue regardless of whether they are used or not.

CR16 Function Attributes
------------------------

These function attributes are supported by the CR16 back end:

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

Epiphany Function Attributes
----------------------------

These function attributes are supported by the Epiphany back end:

disinterrupt
     This attribute causes the compiler to emit instructions to disable interrupts for the duration of the given function.

forwarder_section
     This attribute modifies the behavior of an interrupt handler. The interrupt handler may be in external memory which cannot be reached by a branch instruction, so generate a local memory trampoline to transfer control.  The single parameter identifies the section where the trampoline is placed.

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.  It may also generate a special section with code to initialize the interrupt vector table.

     On Epiphany targets one or more optional parameters can be added like this:

          void __attribute__ ((interrupt ("dma0, dma1"))) universal_dma_handler ();

     Permissible values for these parameters are: reset, software_exception, page_miss, timer0, timer1, message, dma0, dma1, wand and swi. Multiple parameters indicate that multiple entries in the interrupt vector table should be initialized for this function, i.e. for each parameter NAME, a jump to the function is emitted in the section ivt_entry_NAME.  The parameter(s) may be omitted entirely, in which case no interrupt vector table entry is provided.

     Note that interrupts are enabled inside the function unless the disinterrupt attribute is also specified.

     The following examples are all valid uses of these attributes on Epiphany targets:

          void __attribute__ ((interrupt)) universal_handler ();
          void __attribute__ ((interrupt ("dma1"))) dma1_handler ();
          void __attribute__ ((interrupt ("dma0, dma1")))
            universal_dma_handler ();
          void __attribute__ ((interrupt ("timer0"), disinterrupt))
            fast_timer_handler ();
          void __attribute__ ((interrupt ("dma0, dma1"),
                               forwarder_section ("tramp")))
            external_dma_handler ();

long_call
short_call
     These attributes specify how a particular function is called. These attributes override the -mlong-calls (see Adapteva Epiphany Options) command-line switch and #pragma long_calls settings.

H8/300 Function Attributes
--------------------------

These function attributes are available for H8/300 targets:

function_vector
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified function should be called through the function vector. Calling a function through the function vector reduces code size; however, the function vector has a limited size (maximum 128 entries on the H8/300 and 64 entries on the H8/300H and H8S) and shares space with the interrupt vector.

interrupt_handler
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

saveall
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that all registers except the stack pointer should be saved in the prologue regardless of whether they are used or not.

IA-64 Function Attributes
-------------------------

These function attributes are supported on IA-64 targets:

syscall_linkage
     This attribute is used to modify the IA-64 calling convention by marking all input registers as live at all function exits.  This makes it possible to restart a system call after an interrupt without having to save/restore the input registers.  This also prevents kernel data from leaking into application code.

version_id
     This IA-64 HP-UX attribute, attached to a global variable or function, renames a symbol to contain a version string, thus allowing for function level versioning.  HP-UX system header files may use function level versioning for some system calls.

          extern int foo () __attribute__((version_id ("20040821")));

     Calls to foo are mapped to calls to foo{20040821}.

M32C Function Attributes
------------------------

These function attributes are supported by the M32C back end:

bank_switch
     When added to an interrupt handler with the M32C port, causes the prologue and epilogue to use bank switching to preserve the registers rather than saving them on the stack.

fast_interrupt
     Use this attribute on the M32C port to indicate that the specified function is a fast interrupt handler.  This is just like the interrupt attribute, except that freit is used to return instead of reit.

function_vector
     On M16C/M32C targets, the function_vector attribute declares a special page subroutine call function. Use of this attribute reduces the code size by 2 bytes for each call generated to the subroutine. The argument to the attribute is the vector number entry from the special page vector table which contains the 16 low-order bits of the subroutine's entry address. Each vector table has special page number (18 to 255) that is used in jsrs instructions. Jump addresses of the routines are generated by adding 0x0F0000 (in case of M16C targets) or 0xFF0000 (in case of M32C targets), to the 2-byte addresses set in the vector table. Therefore you need to ensure that all the special page vector routines should get mapped within the address range 0x0F0000 to 0x0FFFFF (for M16C) and 0xFF0000 to 0xFFFFFF (for M32C).

     In the following example 2 bytes are saved for each call to function foo.

          void foo (void) __attribute__((function_vector(0x18)));
          void foo (void)
          {
          }

          void bar (void)
          {
              foo();
          }

     If functions are defined in one file and are called in another file, then be sure to write this declaration in both files.

     This attribute is ignored for R8C target.

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

M32R/D Function Attributes
--------------------------

These function attributes are supported by the M32R/D back end:

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

model (MODEL-NAME)

     On the M32R/D, use this attribute to set the addressability of an object, and of the code generated for a function.  The identifier MODEL-NAME is one of small, medium, or large, representing each of the code models.

     Small model objects live in the lower 16MB of memory (so that their addresses can be loaded with the ld24 instruction), and are callable with the bl instruction.

     Medium model objects may live anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses), and are callable with the bl instruction.

     Large model objects may live anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses), and may not be reachable with the bl instruction (the compiler generates the much slower seth/add3/jl instruction sequence).

m68k Function Attributes
------------------------

These function attributes are supported by the m68k back end:

interrupt
interrupt_handler
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.  Either name may be used.

interrupt_thread
     Use this attribute on fido, a subarchitecture of the m68k, to indicate that the specified function is an interrupt handler that is designed to run as a thread.  The compiler omits generate prologue/epilogue sequences and replaces the return instruction with a sleep instruction.  This attribute is available only on fido.

MCORE Function Attributes
-------------------------

These function attributes are supported by the MCORE back end:

naked
     This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (see Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.

MeP Function Attributes
-----------------------

These function attributes are supported by the MeP back end:

disinterrupt
     On MeP targets, this attribute causes the compiler to emit instructions to disable interrupts for the duration of the given function.

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

near
     This attribute causes the compiler to assume the called function is close enough to use the normal calling convention, overriding the -mtf command-line option.

far
     On MeP targets this causes the compiler to use a calling convention that assumes the called function is too far away for the built-in addressing modes.

vliw
     The vliw attribute tells the compiler to emit instructions in VLIW mode instead of core mode.  Note that this attribute is not allowed unless a VLIW coprocessor has been configured and enabled through command-line options.

MicroBlaze Function Attributes
------------------------------

These function attributes are supported on MicroBlaze targets:

save_volatiles
     Use this attribute to indicate that the function is an interrupt handler.  All volatile registers (in addition to non-volatile registers) are saved in the function prologue.  If the function is a leaf function, only volatiles used by the function are saved.  A normal function return is generated instead of a return from interrupt.

break_handler
     Use this attribute to indicate that the specified function is a break handler.  The compiler generates function entry and exit sequences suitable for use in an break handler when this attribute is present. The return from break_handler is done through the rtbd instead of rtsd.

          void f () __attribute__ ((break_handler));

Microsoft Windows Function Attributes
-------------------------------------

The following attributes are available on Microsoft Windows and Symbian OS targets.

dllexport
     On Microsoft Windows targets and Symbian OS targets the dllexport attribute causes the compiler to provide a global pointer to a pointer in a DLL, so that it can be referenced with the dllimport attribute.  On Microsoft Windows targets, the pointer name is formed by combining _imp__ and the function or variable name.

     You can use __declspec(dllexport) as a synonym for __attribute__ ((dllexport)) for compatibility with other compilers.

     On systems that support the visibility attribute, this attribute also implies ``default'' visibility.  It is an error to explicitly specify any other visibility.

     GCC's default behavior is to emit all inline functions with the dllexport attribute.  Since this can cause object file-size bloat, you can use -fno-keep-inline-dllexport, which tells GCC to ignore the attribute for inlined functions unless the -fkeep-inline-functions flag is used instead.

     The attribute is ignored for undefined symbols.

     When applied to C++ classes, the attribute marks defined non-inlined member functions and static data members as exports.  Static consts initialized in-class are not marked unless they are also defined out-of-class.

     For Microsoft Windows targets there are alternative methods for including the symbol in the DLL's export table such as using a .def file with an EXPORTS section or, with GNU ld, using the --export-all linker flag.

dllimport
     On Microsoft Windows and Symbian OS targets, the dllimport attribute causes the compiler to reference a function or variable via a global pointer to a pointer that is set up by the DLL exporting the symbol.  The attribute implies extern.  On Microsoft Windows targets, the pointer name is formed by combining _imp__ and the function or variable name.

     You can use __declspec(dllimport) as a synonym for __attribute__ ((dllimport)) for compatibility with other compilers.

     On systems that support the visibility attribute, this attribute also implies ``default'' visibility.  It is an error to explicitly specify any other visibility.

     Currently, the attribute is ignored for inlined functions.  If the attribute is applied to a symbol definition, an error is reported. If a symbol previously declared dllimport is later defined, the attribute is ignored in subsequent references, and a warning is emitted. The attribute is also overridden by a subsequent declaration as dllexport.

     When applied to C++ classes, the attribute marks non-inlined member functions and static data members as imports.  However, the attribute is ignored for virtual methods to allow creation of vtables using thunks.

     On the SH Symbian OS target the dllimport attribute also has another affect---it can cause the vtable and run-time type information for a class to be exported.  This happens when the class has a dllimported constructor or a non-inline, non-pure virtual function and, for either of those two conditions, the class also has an inline constructor or destructor and has a key function that is defined in the current translation unit.

     For Microsoft Windows targets the use of the dllimport attribute on functions is not necessary, but provides a small performance benefit by eliminating a thunk in the DLL.  The use of the dllimport attribute on imported variables can be avoided by passing the --enable-auto-import switch to the GNU linker.  As with functions, using the attribute for a variable eliminates a thunk in the DLL.

     One drawback to using this attribute is that a pointer to a variable marked as dllimport cannot be used as a constant address. However, a pointer to a function with the dllimport attribute can be used as a constant initializer; in this case, the address of a stub function in the import lib is referenced.  On Microsoft Windows targets, the attribute can be disabled for functions by setting the -mnop-fun-dllimport flag.

MIPS Function Attributes
------------------------

These function attributes are supported by the MIPS back end:

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present. An optional argument is supported for the interrupt attribute which allows the interrupt mode to be described.  By default GCC assumes the external interrupt controller (EIC) mode is in use, this can be explicitly set using eic.  When interrupts are non-masked then the requested Interrupt Priority Level (IPL) is copied to the current IPL which has the effect of only enabling higher priority interrupts.  To use vectored interrupt mode use the argument vector=[sw0|sw1|hw0|hw1|hw2|hw3|hw4|hw5], this will change the behaviour of the non-masked interrupt support and GCC will arrange to mask all interrupts from sw0 up to and including the specified interrupt vector.

     You can use the following attributes to modify the behavior of an interrupt handler:

     use_shadow_register_set
          Assume that the handler uses a shadow register set, instead of the main general-purpose registers.  An optional argument intstack is supported to indicate that the shadow register set contains a valid stack pointer.

     keep_interrupts_masked
          Keep interrupts masked for the whole function.  Without this attribute, GCC tries to reenable interrupts for as much of the function as it can.

     use_debug_exception_return
          Return using the deret instruction.  Interrupt handlers that don't have this attribute return using eret instead.

     You can use any combination of these attributes, as shown below:

          void __attribute__ ((interrupt)) v0 ();
          void __attribute__ ((interrupt, use_shadow_register_set)) v1 ();
          void __attribute__ ((interrupt, keep_interrupts_masked)) v2 ();
          void __attribute__ ((interrupt, use_debug_exception_return)) v3 ();
          void __attribute__ ((interrupt, use_shadow_register_set,
                               keep_interrupts_masked)) v4 ();
          void __attribute__ ((interrupt, use_shadow_register_set,
                               use_debug_exception_return)) v5 ();
          void __attribute__ ((interrupt, keep_interrupts_masked,
                               use_debug_exception_return)) v6 ();
          void __attribute__ ((interrupt, use_shadow_register_set,
                               keep_interrupts_masked,
                               use_debug_exception_return)) v7 ();
          void __attribute__ ((interrupt("eic"))) v8 ();
          void __attribute__ ((interrupt("vector=hw3"))) v9 ();

long_call
near
far
     These attributes specify how a particular function is called on MIPS. The attributes override the -mlong-calls (see MIPS Options) command-line switch.  The long_call and far attributes are synonyms, and cause the compiler to always call the function by first loading its address into a register, and then using the contents of that register.  The near attribute has the opposite effect; it specifies that non-PIC calls should be made using the more efficient jal instruction.

mips16
nomips16

     On MIPS targets, you can use the mips16 and nomips16 function attributes to locally select or turn off MIPS16 code generation. A function with the mips16 attribute is emitted as MIPS16 code, while MIPS16 code generation is disabled for functions with the nomips16 attribute.  These attributes override the -mips16 and -mno-mips16 options on the command line (see MIPS Options).

     When compiling files containing mixed MIPS16 and non-MIPS16 code, the preprocessor symbol __mips16 reflects the setting on the command line, not that within individual functions.  Mixed MIPS16 and non-MIPS16 code may interact badly with some GCC extensions such as __builtin_apply (see Constructing Calls).

micromips, MIPS
nomicromips, MIPS

     On MIPS targets, you can use the micromips and nomicromips function attributes to locally select or turn off microMIPS code generation. A function with the micromips attribute is emitted as microMIPS code, while microMIPS code generation is disabled for functions with the nomicromips attribute.  These attributes override the -mmicromips and -mno-micromips options on the command line (see MIPS Options).

     When compiling files containing mixed microMIPS and non-microMIPS code, the preprocessor symbol __mips_micromips reflects the setting on the command line, not that within individual functions.  Mixed microMIPS and non-microMIPS code may interact badly with some GCC extensions such as __builtin_apply (see Constructing Calls).

nocompression
     On MIPS targets, you can use the nocompression function attribute to locally turn off MIPS16 and microMIPS code generation.  This attribute overrides the -mips16 and -mmicromips options on the command line (see MIPS Options).

MSP430 Function Attributes
--------------------------

These function attributes are supported by the MSP430 back end:

critical
     Critical functions disable interrupts upon entry and restore the previous interrupt state upon exit.  Critical functions cannot also have the naked or reentrant attributes.  They can have the interrupt attribute.

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

     You can provide an argument to the interrupt attribute which specifies a name or number.  If the argument is a number it indicates the slot in the interrupt vector table (0 - 31) to which this handler should be assigned.  If the argument is a name it is treated as a symbolic name for the vector slot.  These names should match up with appropriate entries in the linker script.  By default the names watchdog for vector 26, nmi for vector 30 and reset for vector 31 are recognized.

naked
     This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (see Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.

reentrant
     Reentrant functions disable interrupts upon entry and enable them upon exit.  Reentrant functions cannot also have the naked or critical attributes.  They can have the interrupt attribute.

wakeup
     This attribute only applies to interrupt functions.  It is silently ignored if applied to a non-interrupt function.  A wakeup interrupt function will rouse the processor from any low-power state that it might be in when the function exits.

NDS32 Function Attributes
-------------------------

These function attributes are supported by the NDS32 back end:

exception
     Use this attribute on the NDS32 target to indicate that the specified function is an exception handler.  The compiler will generate corresponding sections for use in an exception handler.

interrupt
     On NDS32 target, this attribute indicates that the specified function is an interrupt handler.  The compiler generates corresponding sections for use in an interrupt handler.  You can use the following attributes to modify the behavior:

     nested
          This interrupt service routine is interruptible.

     not_nested
          This interrupt service routine is not interruptible.

     nested_ready
          This interrupt service routine is interruptible after PSW.GIE (global interrupt enable) is set.  This allows interrupt service routine to finish some short critical code before enabling interrupts.

     save_all
          The system will help save all registers into stack before entering interrupt handler.

     partial_save
          The system will help save caller registers into stack before entering interrupt handler.

naked
     This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (see Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.

reset
     Use this attribute on the NDS32 target to indicate that the specified function is a reset handler.  The compiler will generate corresponding sections for use in a reset handler.  You can use the following attributes to provide extra exception handling:

     nmi
          Provide a user-defined function to handle NMI exception.

     warm
          Provide a user-defined function to handle warm reset exception.

Nios II Function Attributes
---------------------------

These function attributes are supported by the Nios II back end:

target (OPTIONS)
     As discussed in Common Function Attributes, this attribute allows specification of target-specific compilation options.

     When compiling for Nios II, the following options are allowed:

     custom-INSN=N
     no-custom-INSN
          Each custom-INSN=N attribute locally enables use of a custom instruction with encoding N when generating code that uses INSN.  Similarly, no-custom-INSN locally inhibits use of the custom instruction INSN. These target attributes correspond to the -mcustom-INSN=N and -mno-custom-INSN command-line options, and support the same set of INSN keywords. See Nios II Options, for more information.

     custom-fpu-cfg=NAME
          This attribute corresponds to the -mcustom-fpu-cfg=NAME command-line option, to select a predefined set of custom instructions named NAME. See Nios II Options, for more information.

PowerPC Function Attributes
---------------------------

These function attributes are supported by the PowerPC back end:

longcall
shortcall
     The longcall attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence.  The shortcall attribute indicates that the function is always close enough for the shorter calling sequence to be used.  These attributes override both the -mlongcall switch and the #pragma longcall setting.

     See RS/6000 and PowerPC Options, for more information on whether long calls are necessary.

target (OPTIONS)
     As discussed in Common Function Attributes, this attribute allows specification of target-specific compilation options.

     On the PowerPC, the following options are allowed:

     altivec
     no-altivec
          Generate code that uses (does not use) AltiVec instructions.  In 32-bit code, you cannot enable AltiVec instructions unless -mabi=altivec is used on the command line.

     cmpb
     no-cmpb
          Generate code that uses (does not use) the compare bytes instruction implemented on the POWER6 processor and other processors that support the PowerPC V2.05 architecture.

     dlmzb
     no-dlmzb
          Generate code that uses (does not use) the string-search dlmzb instruction on the IBM 405, 440, 464 and 476 processors.  This instruction is generated by default when targeting those processors.

     fprnd
     no-fprnd
          Generate code that uses (does not use) the FP round to integer instructions implemented on the POWER5+ processor and other processors that support the PowerPC V2.03 architecture.

     hard-dfp
     no-hard-dfp
          Generate code that uses (does not use) the decimal floating-point instructions implemented on some POWER processors.

     isel
     no-isel
          Generate code that uses (does not use) ISEL instruction.

     mfcrf
     no-mfcrf
          Generate code that uses (does not use) the move from condition register field instruction implemented on the POWER4 processor and other processors that support the PowerPC V2.01 architecture.

     mfpgpr
     no-mfpgpr
          Generate code that uses (does not use) the FP move to/from general purpose register instructions implemented on the POWER6X processor and other processors that support the extended PowerPC V2.05 architecture.

     mulhw
     no-mulhw
          Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. These instructions are generated by default when targeting those processors.

     multiple
     no-multiple
          Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions.

     update
     no-update
          Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location.

     popcntb
     no-popcntb
          Generate code that uses (does not use) the popcount and double-precision FP reciprocal estimate instruction implemented on the POWER5 processor and other processors that support the PowerPC V2.02 architecture.

     popcntd
     no-popcntd
          Generate code that uses (does not use) the popcount instruction implemented on the POWER7 processor and other processors that support the PowerPC V2.06 architecture.

     powerpc-gfxopt
     no-powerpc-gfxopt
          Generate code that uses (does not use) the optional PowerPC architecture instructions in the Graphics group, including floating-point select.

     powerpc-gpopt
     no-powerpc-gpopt
          Generate code that uses (does not use) the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root.

     recip-precision
     no-recip-precision
          Assume (do not assume) that the reciprocal estimate instructions provide higher-precision estimates than is mandated by the PowerPC ABI.

     string
     no-string
          Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves.

     vsx
     no-vsx
          Generate code that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of built-in functions that allow more direct access to the VSX instruction set.  In 32-bit code, you cannot enable VSX or AltiVec instructions unless -mabi=altivec is used on the command line.

     friz
     no-friz
          Generate (do not generate) the friz instruction when the -funsafe-math-optimizations option is used to optimize rounding a floating-point value to 64-bit integer and back to floating point.  The friz instruction does not return the same value if the floating-point number is too large to fit in an integer.

     avoid-indexed-addresses
     no-avoid-indexed-addresses
          Generate code that tries to avoid (not avoid) the use of indexed load or store instructions.

     paired
     no-paired
          Generate code that uses (does not use) the generation of PAIRED simd instructions.

     longcall
     no-longcall
          Generate code that assumes (does not assume) that all calls are far away so that a longer more expensive calling sequence is required.

     cpu=CPU
          Specify the architecture to generate code for when compiling the function.  If you select the target("cpu=power7") attribute when generating 32-bit code, VSX and AltiVec instructions are not generated unless you use the -mabi=altivec option on the command line.

     tune=TUNE
          Specify the architecture to tune for when compiling the function.  If you do not specify the target("tune=TUNE") attribute and you do specify the target("cpu=CPU") attribute, compilation tunes for the CPU architecture, and not the default tuning specified on the command line.

     On the PowerPC, the inliner does not inline a function that has different target options than the caller, unless the callee has a subset of the target options of the caller.

RL78 Function Attributes
------------------------

These function attributes are supported by the RL78 back end:

interrupt
brk_interrupt
     These attributes indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

     Use brk_interrupt instead of interrupt for handlers intended to be used with the BRK opcode (i.e. those that must end with RETB instead of RETI).

naked
     This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (see Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.

RX Function Attributes
----------------------

These function attributes are supported by the RX back end:

fast_interrupt
     Use this attribute on the RX port to indicate that the specified function is a fast interrupt handler.  This is just like the interrupt attribute, except that freit is used to return instead of reit.

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

     On RX targets, you may specify one or more vector numbers as arguments to the attribute, as well as naming an alternate table name. Parameters are handled sequentially, so one handler can be assigned to multiple entries in multiple tables.  One may also pass the magic string "$default" which causes the function to be used for any unfilled slots in the current table.

     This example shows a simple assignment of a function to one vector in the default table (note that preprocessor macros may be used for chip-specific symbolic vector names):

          void __attribute__ ((interrupt (5))) txd1_handler ();

     This example assigns a function to two slots in the default table (using preprocessor macros defined elsewhere) and makes it the default for the dct table:

          void __attribute__ ((interrupt (RXD1_VECT,RXD2_VECT,"dct","$default")))
          	txd1_handler ();

naked
     This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (see Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.

vector
     This RX attribute is similar to the interrupt attribute, including its parameters, but does not make the function an interrupt-handler type function (i.e. it retains the normal C function calling ABI).  See the interrupt attribute for a description of its arguments.

S/390 Function Attributes
-------------------------

These function attributes are supported on the S/390:

hotpatch (HALFWORDS-BEFORE-FUNCTION-LABEL,HALFWORDS-AFTER-FUNCTION-LABEL)

     On S/390 System z targets, you can use this function attribute to make GCC generate a ``hot-patching'' function prologue.  If the -mhotpatch= command-line option is used at the same time, the hotpatch attribute takes precedence.  The first of the two arguments specifies the number of halfwords to be added before the function label.  A second argument can be used to specify the number of halfwords to be added after the function label.  For both arguments the maximum allowed value is 1000000.

     If both arguments are zero, hotpatching is disabled.

SH Function Attributes
----------------------

These function attributes are supported on the SH family of processors:

function_vector
     On SH2A targets, this attribute declares a function to be called using the TBR relative addressing mode.  The argument to this attribute is the entry number of the same function in a vector table containing all the TBR relative addressable functions.  For correct operation the TBR must be setup accordingly to point to the start of the vector table before any functions with this attribute are invoked.  Usually a good place to do the initialization is the startup routine.  The TBR relative vector table can have at max 256 function entries.  The jumps to these functions are generated using a SH2A specific, non delayed branch instruction JSR/N @(disp8,TBR).  You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.

     In an application, for a function being called once, this attribute saves at least 8 bytes of code; and if other successive calls are being made to the same function, it saves 2 bytes of code per each of these calls.

interrupt_handler
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

nosave_low_regs
     Use this attribute on SH targets to indicate that an interrupt_handler function should not save and restore registers R0..R7.  This can be used on SH3* and SH4* targets that have a second R0..R7 register bank for non-reentrant interrupt handlers.

renesas
     On SH targets this attribute specifies that the function or struct follows the Renesas ABI.

resbank
     On the SH2A target, this attribute enables the high-speed register saving and restoration using a register bank for interrupt_handler routines.  Saving to the bank is performed automatically after the CPU accepts an interrupt that uses a register bank.

     The nineteen 32-bit registers comprising general register R0 to R14, control register GBR, and system registers MACH, MACL, and PR and the vector table address offset are saved into a register bank.  Register banks are stacked in first-in last-out (FILO) sequence.  Restoration from the bank is executed by issuing a RESBANK instruction.

sp_switch
     Use this attribute on the SH to indicate an interrupt_handler function should switch to an alternate stack.  It expects a string argument that names a global variable holding the address of the alternate stack.

          void *alt_stack;
          void f () __attribute__ ((interrupt_handler,
                                    sp_switch ("alt_stack")));

trap_exit
     Use this attribute on the SH for an interrupt_handler to return using trapa instead of rte.  This attribute expects an integer argument specifying the trap number to be used.

trapa_handler
     On SH targets this function attribute is similar to interrupt_handler but it does not save and restore all registers.

SPU Function Attributes
-----------------------

These function attributes are supported by the SPU back end:

naked
     This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (see Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.

Symbian OS Function Attributes
------------------------------

See Microsoft Windows Function Attributes, for discussion of the dllexport and dllimport attributes.

Visium Function Attributes
--------------------------

These function attributes are supported by the Visium back end:

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

x86 Function Attributes
-----------------------

These function attributes are supported by the x86 back end:

cdecl
     On the x86-32 targets, the cdecl attribute causes the compiler to assume that the calling function pops off the stack space used to pass arguments.  This is useful to override the effects of the -mrtd switch.

fastcall
     On x86-32 targets, the fastcall attribute causes the compiler to pass the first argument (if of integral type) in the register ECX and the second argument (if of integral type) in the register EDX.  Subsequent and other typed arguments are passed on the stack.  The called function pops the arguments off the stack.  If the number of arguments is variable all arguments are pushed on the stack.

thiscall
     On x86-32 targets, the thiscall attribute causes the compiler to pass the first argument (if of integral type) in the register ECX. Subsequent and other typed arguments are passed on the stack. The called function pops the arguments off the stack. If the number of arguments is variable all arguments are pushed on the stack. The thiscall attribute is intended for C++ non-static member functions. As a GCC extension, this calling convention can be used for C functions and for static member methods.

ms_abi
sysv_abi

     On 32-bit and 64-bit x86 targets, you can use an ABI attribute to indicate which calling convention should be used for a function.  The ms_abi attribute tells the compiler to use the Microsoft ABI, while the sysv_abi attribute tells the compiler to use the ABI used on GNU/Linux and other systems.  The default is to use the Microsoft ABI when targeting Windows.  On all other systems, the default is the x86/AMD ABI.

     Note, the ms_abi attribute for Microsoft Windows 64-bit targets currently requires the -maccumulate-outgoing-args option.

callee_pop_aggregate_return (NUMBER)

     On x86-32 targets, you can use this attribute to control how aggregates are returned in memory.  If the caller is responsible for popping the hidden pointer together with the rest of the arguments, specify NUMBER equal to zero.  If callee is responsible for popping the hidden pointer, specify NUMBER equal to one.

     The default x86-32 ABI assumes that the callee pops the stack for hidden pointer.  However, on x86-32 Microsoft Windows targets, the compiler assumes that the caller pops the stack for hidden pointer.

ms_hook_prologue

     On 32-bit and 64-bit x86 targets, you can use this function attribute to make GCC generate the ``hot-patching'' function prologue used in Win32 API functions in Microsoft Windows XP Service Pack 2 and newer.

regparm (NUMBER)
     On x86-32 targets, the regparm attribute causes the compiler to pass arguments number one to NUMBER if they are of integral type in registers EAX, EDX, and ECX instead of on the stack.  Functions that take a variable number of arguments continue to be passed all of their arguments on the stack.

     Beware that on some ELF systems this attribute is unsuitable for global functions in shared libraries with lazy binding (which is the default).  Lazy binding sends the first call via resolving code in the loader, which might assume EAX, EDX and ECX can be clobbered, as per the standard calling conventions.  Solaris 8 is affected by this. Systems with the GNU C Library version 2.1 or higher and FreeBSD are believed to be safe since the loaders there save EAX, EDX and ECX.  (Lazy binding can be disabled with the linker or the loader if desired, to avoid the problem.)

sseregparm
     On x86-32 targets with SSE support, the sseregparm attribute causes the compiler to pass up to 3 floating-point arguments in SSE registers instead of on the stack.  Functions that take a variable number of arguments continue to pass all of their floating-point arguments on the stack.

force_align_arg_pointer
     On x86 targets, the force_align_arg_pointer attribute may be applied to individual function definitions, generating an alternate prologue and epilogue that realigns the run-time stack if necessary. This supports mixing legacy codes that run with a 4-byte aligned stack with modern codes that keep a 16-byte stack for SSE compatibility.

stdcall
     On x86-32 targets, the stdcall attribute causes the compiler to assume that the called function pops off the stack space used to pass arguments, unless it takes a variable number of arguments.

target (OPTIONS)
     As discussed in Common Function Attributes, this attribute allows specification of target-specific compilation options.

     On the x86, the following options are allowed:

     abm
     no-abm
          Enable/disable the generation of the advanced bit instructions.

     aes
     no-aes
          Enable/disable the generation of the AES instructions.

     default
          See Function Multiversioning, where it is used to specify the default function version.

     mmx
     no-mmx
          Enable/disable the generation of the MMX instructions.

     pclmul
     no-pclmul
          Enable/disable the generation of the PCLMUL instructions.

     popcnt
     no-popcnt
          Enable/disable the generation of the POPCNT instruction.

     sse
     no-sse
          Enable/disable the generation of the SSE instructions.

     sse2
     no-sse2
          Enable/disable the generation of the SSE2 instructions.

     sse3
     no-sse3
          Enable/disable the generation of the SSE3 instructions.

     sse4
     no-sse4
          Enable/disable the generation of the SSE4 instructions (both SSE4.1 and SSE4.2).

     sse4.1
     no-sse4.1
          Enable/disable the generation of the sse4.1 instructions.

     sse4.2
     no-sse4.2
          Enable/disable the generation of the sse4.2 instructions.

     sse4a
     no-sse4a
          Enable/disable the generation of the SSE4A instructions.

     fma4
     no-fma4
          Enable/disable the generation of the FMA4 instructions.

     xop
     no-xop
          Enable/disable the generation of the XOP instructions.

     lwp
     no-lwp
          Enable/disable the generation of the LWP instructions.

     ssse3
     no-ssse3
          Enable/disable the generation of the SSSE3 instructions.

     cld
     no-cld
          Enable/disable the generation of the CLD before string moves.

     fancy-math-387
     no-fancy-math-387
          Enable/disable the generation of the sin, cos, and sqrt instructions on the 387 floating-point unit.

     fused-madd
     no-fused-madd
          Enable/disable the generation of the fused multiply/add instructions.

     ieee-fp
     no-ieee-fp
          Enable/disable the generation of floating point that depends on IEEE arithmetic.

     inline-all-stringops
     no-inline-all-stringops
          Enable/disable inlining of string operations.

     inline-stringops-dynamically
     no-inline-stringops-dynamically
          Enable/disable the generation of the inline code to do small string operations and calling the library routines for large operations.

     align-stringops
     no-align-stringops
          Do/do not align destination of inlined string operations.

     recip
     no-recip
          Enable/disable the generation of RCPSS, RCPPS, RSQRTSS and RSQRTPS instructions followed an additional Newton-Raphson step instead of doing a floating-point division.

     arch=ARCH
          Specify the architecture to generate code for in compiling the function.

     tune=TUNE
          Specify the architecture to tune for in compiling the function.

     fpmath=FPMATH
          Specify which floating-point unit to use.  You must specify the target("fpmath=sse,387") option as target("fpmath=sse+387") because the comma would separate different options.

     On the x86, the inliner does not inline a function that has different target options than the caller, unless the callee has a subset of the target options of the caller.  For example a function declared with target("sse3") can inline a function with target("sse2"), since -msse3 implies -msse2.

Xstormy16 Function Attributes
-----------------------------

These function attributes are supported by the Xstormy16 back end:

interrupt
     Use this attribute to indicate that the specified function is an interrupt handler.  The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

Specifying Attributes of Variables
==================================

The keyword __attribute__ allows you to specify special attributes of variables or structure fields.  This keyword is followed by an attribute specification inside double parentheses.  Some attributes are currently defined generically for variables. Other attributes are defined for variables on particular target systems.  Other attributes are available for functions (see Function Attributes), labels (see Label Attributes), enumerators (see Enumerator Attributes), and for types (see Type Attributes). Other front ends might define more attributes (see Extensions to the C++ Language).

See Attribute Syntax, for details of the exact syntax for using attributes.

Common Variable Attributes
--------------------------

The following attributes are supported on most targets.

aligned (ALIGNMENT)
     This attribute specifies a minimum alignment for the variable or structure field, measured in bytes.  For example, the declaration:

          int x __attribute__ ((aligned (16))) = 0;

     causes the compiler to allocate the global variable x on a 16-byte boundary.  On a 68040, this could be used in conjunction with an asm expression to access the move16 instruction which requires 16-byte aligned operands.

     You can also specify the alignment of structure fields.  For example, to create a double-word aligned int pair, you could write:

          struct foo { int x[2] __attribute__ ((aligned (8))); };

     This is an alternative to creating a union with a double member, which forces the union to be double-word aligned.

     As in the preceding examples, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given variable or structure field.  Alternatively, you can leave out the alignment factor and just ask the compiler to align a variable or field to the default alignment for the target architecture you are compiling for. The default alignment is sufficient for all scalar types, but may not be enough for all vector types on a target that supports vector operations. The default alignment is fixed for a particular target ABI.

     GCC also provides a target specific macro __BIGGEST_ALIGNMENT__, which is the largest alignment ever used for any data type on the target machine you are compiling for.  For example, you could write:

          short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__)));

     The compiler automatically sets the alignment for the declared variable or field to __BIGGEST_ALIGNMENT__.  Doing this can often make copy operations more efficient, because the compiler can use whatever instructions copy the biggest chunks of memory when performing copies to or from the variables or fields that you have aligned this way.  Note that the value of __BIGGEST_ALIGNMENT__ may change depending on command-line options.

     When used on a struct, or struct member, the aligned attribute can only increase the alignment; in order to decrease it, the packed attribute must be specified as well.  When used as part of a typedef, the aligned attribute can both increase and decrease alignment, and specifying the packed attribute generates a warning.

     Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker.  On many systems, the linker is only able to arrange for variables to be aligned up to a certain maximum alignment.  (For some linkers, the maximum supported alignment may be very very small.)  If your linker is only able to align variables up to a maximum of 8-byte alignment, then specifying aligned(16) in an __attribute__ still only provides you with 8-byte alignment.  See your linker documentation for further information.

     The aligned attribute can also be used for functions (see Common Function Attributes.)

cleanup (CLEANUP_FUNCTION)
     The cleanup attribute runs a function when the variable goes out of scope.  This attribute can only be applied to auto function scope variables; it may not be applied to parameters or variables with static storage duration.  The function must take one parameter, a pointer to a type compatible with the variable.  The return value of the function (if any) is ignored.

     If -fexceptions is enabled, then CLEANUP_FUNCTION is run during the stack unwinding that happens during the processing of the exception.  Note that the cleanup attribute does not allow the exception to be caught, only to perform an action. It is undefined what happens if CLEANUP_FUNCTION does not return normally.

common
nocommon
     The common attribute requests GCC to place a variable in ``common'' storage.  The nocommon attribute requests the opposite---to allocate space for it directly.

     These attributes override the default chosen by the -fno-common and -fcommon flags respectively.

deprecated
deprecated (MSG)
     The deprecated attribute results in a warning if the variable is used anywhere in the source file.  This is useful when identifying variables that are expected to be removed in a future version of a program.  The warning also includes the location of the declaration of the deprecated variable, to enable users to easily find further information about why the variable is deprecated, or what they should do instead.  Note that the warning only occurs for uses:

          extern int old_var __attribute__ ((deprecated));
          extern int old_var;
          int new_fn () { return old_var; }

     results in a warning on line 3 but not line 2.  The optional MSG argument, which must be a string, is printed in the warning if present.

     The deprecated attribute can also be used for functions and types (see Common Function Attributes, see Common Type Attributes).

mode (MODE)
     This attribute specifies the data type for the declaration---whichever type corresponds to the mode MODE.  This in effect lets you request an integer or floating-point type according to its width.

     You may also specify a mode of byte or __byte__ to indicate the mode corresponding to a one-byte integer, word or __word__ for the mode of a one-word integer, and pointer or __pointer__ for the mode used to represent pointers.

packed
     The packed attribute specifies that a variable or structure field should have the smallest possible alignment---one byte for a variable, and one bit for a field, unless you specify a larger value with the aligned attribute.

     Here is a structure in which the field x is packed, so that it immediately follows a:

          struct foo
          {
            char a;
            int x[2] __attribute__ ((packed));
          };

     Note: The 4.1, 4.2 and 4.3 series of GCC ignore the packed attribute on bit-fields of type char.  This has been fixed in GCC 4.4 but the change can lead to differences in the structure layout.  See the documentation of -Wpacked-bitfield-compat for more information.

section ("SECTION-NAME")
     Normally, the compiler places the objects it generates in sections like data and bss.  Sometimes, however, you need additional sections, or you need certain particular variables to appear in special sections, for example to map to special hardware.  The section attribute specifies that a variable (or function) lives in a particular section.  For example, this small program uses several specific section names:

          struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
          struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
          char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
          int init_data __attribute__ ((section ("INITDATA")));

          main()
          {
            /* Initialize stack pointer */
            init_sp (stack + sizeof (stack));

            /* Initialize initialized data */
            memcpy (&init_data, &data, &edata - &data);

            /* Turn on the serial ports */
            init_duart (&a);
            init_duart (&b);
          }

     Use the section attribute with global variables and not local variables, as shown in the example.

     You may use the section attribute with initialized or uninitialized global variables but the linker requires each object be defined once, with the exception that uninitialized variables tentatively go in the common (or bss) section and can be multiply ``defined''.  Using the section attribute changes what section the variable goes into and may cause the linker to issue an error if an uninitialized variable has multiple definitions.  You can force a variable to be initialized with the -fno-common flag or the nocommon attribute.

     Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.

tls_model ("TLS_MODEL")
     The tls_model attribute sets thread-local storage model (see Thread-Local) of a particular __thread variable, overriding -ftls-model= command-line switch on a per-variable basis. The TLS_MODEL argument should be one of global-dynamic, local-dynamic, initial-exec or local-exec.

     Not all targets support this attribute.

unused
     This attribute, attached to a variable, means that the variable is meant to be possibly unused.  GCC does not produce a warning for this variable.

used
     This attribute, attached to a variable with static storage, means that the variable must be emitted even if it appears that the variable is not referenced.

     When applied to a static data member of a C++ class template, the attribute also means that the member is instantiated if the class itself is instantiated.

vector_size (BYTES)
     This attribute specifies the vector size for the variable, measured in bytes.  For example, the declaration:

          int foo __attribute__ ((vector_size (16)));

     causes the compiler to set the mode for foo, to be 16 bytes, divided into int sized units.  Assuming a 32-bit int (a vector of 4 units of 4 bytes), the corresponding mode of foo is V4SI.

     This attribute is only applicable to integral and float scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct.

     Aggregates with this attribute are invalid, even if they are of the same size as a corresponding scalar.  For example, the declaration:

          struct S { int a; };
          struct S  __attribute__ ((vector_size (16))) foo;

     is invalid even if the size of the structure is the same as the size of the int.

weak
     The weak attribute is described in Common Function Attributes.

AVR Variable Attributes
-----------------------

progmem
     The progmem attribute is used on the AVR to place read-only data in the non-volatile program memory (flash). The progmem attribute accomplishes this by putting respective variables into a section whose name starts with .progmem.

     This attribute works similar to the section attribute but adds additional checking. Notice that just like the section attribute, progmem affects the location of the data but not how this data is accessed.

     In order to read data located with the progmem attribute (inline) assembler must be used.

          /* Use custom macros from AVR-LibC (http://nongnu.org/avr-libc/user-manual/) */
          #include <avr/pgmspace.h>

          /* Locate var in flash memory */
          const int var[2] PROGMEM = { 1, 2 };

          int read_var (int i)
          {
              /* Access var[] by accessor macro from avr/pgmspace.h */
              return (int) pgm_read_word (& var[i]);
          }

     AVR is a Harvard architecture processor and data and read-only data normally resides in the data memory (RAM).

     See also the AVR Named Address Spaces section for an alternate way to locate and access data in flash memory.

io
io (ADDR)
     Variables with the io attribute are used to address memory-mapped peripherals in the io address range. If an address is specified, the variable is assigned that address, and the value is interpreted as an address in the data address space. Example:

          volatile int porta __attribute__((io (0x22)));

     The address specified in the address in the data address range.

     Otherwise, the variable it is not assigned an address, but the compiler will still use in/out instructions where applicable, assuming some other module assigns an address in the io address range. Example:

          extern volatile int porta __attribute__((io));

io_low
io_low (ADDR)
     This is like the io attribute, but additionally it informs the compiler that the object lies in the lower half of the I/O area, allowing the use of cbi, sbi, sbic and sbis instructions.

address
address (ADDR)
     Variables with the address attribute are used to address memory-mapped peripherals that may lie outside the io address range.

          volatile int porta __attribute__((address (0x600)));

Blackfin Variable Attributes
----------------------------

Three attributes are currently defined for the Blackfin.

l1_data
l1_data_A
l1_data_B
     Use these attributes on the Blackfin to place the variable into L1 Data SRAM. Variables with l1_data attribute are put into the specific section named .l1.data. Those with l1_data_A attribute are put into the specific section named .l1.data.A. Those with l1_data_B attribute are put into the specific section named .l1.data.B.

l2
     Use this attribute on the Blackfin to place the variable into L2 SRAM. Variables with l2 attribute are put into the specific section named .l2.data.

H8/300 Variable Attributes
--------------------------

These variable attributes are available for H8/300 targets:

eightbit_data
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified variable should be placed into the eight-bit data section. The compiler generates more efficient code for certain operations on data in the eight-bit data area.  Note the eight-bit data area is limited to 256 bytes of data.

     You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.

tiny_data
     Use this attribute on the H8/300H and H8S to indicate that the specified variable should be placed into the tiny data section. The compiler generates more efficient code for loads and stores on data in the tiny data section.  Note the tiny data area is limited to slightly under 32KB of data.

IA-64 Variable Attributes
-------------------------

The IA-64 back end supports the following variable attribute:

model (MODEL-NAME)

     On IA-64, use this attribute to set the addressability of an object. At present, the only supported identifier for MODEL-NAME is small, indicating addressability via ``small'' (22-bit) addresses (so that their addresses can be loaded with the addl instruction).  Caveat: such addressing is by definition not position independent and hence this attribute must not be used for objects defined by shared libraries.

M32R/D Variable Attributes
--------------------------

One attribute is currently defined for the M32R/D.

model (MODEL-NAME)
     Use this attribute on the M32R/D to set the addressability of an object. The identifier MODEL-NAME is one of small, medium, or large, representing each of the code models.

     Small model objects live in the lower 16MB of memory (so that their addresses can be loaded with the ld24 instruction).

     Medium and large model objects may live anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses).

MeP Variable Attributes
-----------------------

The MeP target has a number of addressing modes and busses.  The near space spans the standard memory space's first 16 megabytes (24 bits).  The far space spans the entire 32-bit memory space. The based space is a 128-byte region in the memory space that is addressed relative to the $tp register.  The tiny space is a 65536-byte region relative to the $gp register.  In addition to these memory regions, the MeP target has a separate 16-bit control bus which is specified with cb attributes.

based
     Any variable with the based attribute is assigned to the .based section, and is accessed with relative to the $tp register.

tiny
     Likewise, the tiny attribute assigned variables to the .tiny section, relative to the $gp register.

near
     Variables with the near attribute are assumed to have addresses that fit in a 24-bit addressing mode.  This is the default for large variables (-mtiny=4 is the default) but this attribute can override -mtiny= for small variables, or override -ml.

far
     Variables with the far attribute are addressed using a full 32-bit address.  Since this covers the entire memory space, this allows modules to make no assumptions about where variables might be stored.

io
io (ADDR)
     Variables with the io attribute are used to address memory-mapped peripherals.  If an address is specified, the variable is assigned that address, else it is not assigned an address (it is assumed some other module assigns an address).  Example:

          int timer_count __attribute__((io(0x123)));

cb
cb (ADDR)
     Variables with the cb attribute are used to access the control bus, using special instructions.  addr indicates the control bus address.  Example:

          int cpu_clock __attribute__((cb(0x123)));

Microsoft Windows Variable Attributes
-------------------------------------

You can use these attributes on Microsoft Windows targets. x86 Variable Attributes for additional Windows compatibility attributes available on all x86 targets.

dllimport
dllexport
     The dllimport and dllexport attributes are described in Microsoft Windows Function Attributes.

selectany
     The selectany attribute causes an initialized global variable to have link-once semantics.  When multiple definitions of the variable are encountered by the linker, the first is selected and the remainder are discarded.  Following usage by the Microsoft compiler, the linker is told not to warn about size or content differences of the multiple definitions.

     Although the primary usage of this attribute is for POD types, the attribute can also be applied to global C++ objects that are initialized by a constructor.  In this case, the static initialization and destruction code for the object is emitted in each translation defining the object, but the calls to the constructor and destructor are protected by a link-once guard variable.

     The selectany attribute is only available on Microsoft Windows targets.  You can use __declspec (selectany) as a synonym for __attribute__ ((selectany)) for compatibility with other compilers.

shared
     On Microsoft Windows, in addition to putting variable definitions in a named section, the section can also be shared among all running copies of an executable or DLL.  For example, this small program defines shared data by putting it in a named section shared and marking the section shareable:

          int foo __attribute__((section ("shared"), shared)) = 0;

          int
          main()
          {
            /* Read and write foo.  All running
               copies see the same value.  */
            return 0;
          }

     You may only use the shared attribute along with section attribute with a fully-initialized global definition because of the way linkers work.  See section attribute for more information.

     The shared attribute is only available on Microsoft Windows.

PowerPC Variable Attributes
---------------------------

Three attributes currently are defined for PowerPC configurations: altivec, ms_struct and gcc_struct.

For full documentation of the struct attributes please see the documentation in x86 Variable Attributes.

For documentation of altivec attribute please see the documentation in PowerPC Type Attributes.

SPU Variable Attributes
-----------------------

The SPU supports the spu_vector attribute for variables.  For documentation of this attribute please see the documentation in SPU Type Attributes.

x86 Variable Attributes
-----------------------

Two attributes are currently defined for x86 configurations: ms_struct and gcc_struct.

ms_struct
gcc_struct

     If packed is used on a structure, or if bit-fields are used, it may be that the Microsoft ABI lays out the structure differently than the way GCC normally does.  Particularly when moving packed data between functions compiled with GCC and the native Microsoft compiler (either via function call or as data in a file), it may be necessary to access either format.

     Currently -m[no-]ms-bitfields is provided for the Microsoft Windows x86 compilers to match the native Microsoft compiler.

     The Microsoft structure layout algorithm is fairly simple with the exception of the bit-field packing. The padding and alignment of members of structures and whether a bit-field can straddle a storage-unit boundary are determine by these rules:

      1. Structure members are stored sequentially in the order in which they are declared: the first member has the lowest memory address and the last member the highest.

      2. Every data object has an alignment requirement.  The alignment requirement for all data except structures, unions, and arrays is either the size of the object or the current packing size (specified with either the aligned attribute or the pack pragma), whichever is less.  For structures, unions, and arrays, the alignment requirement is the largest alignment requirement of its members. Every object is allocated an offset so that:

               offset % alignment_requirement == 0

      3. Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation unit if the integral types are the same size and if the next bit-field fits into the current allocation unit without crossing the boundary imposed by the common alignment requirements of the bit-fields.

     MSVC interprets zero-length bit-fields in the following ways:

      1. If a zero-length bit-field is inserted between two bit-fields that are normally coalesced, the bit-fields are not coalesced.

          For example:

               struct
                {
                  unsigned long bf_1 : 12;
                  unsigned long : 0;
                  unsigned long bf_2 : 12;
                } t1;

          The size of t1 is 8 bytes with the zero-length bit-field.  If the zero-length bit-field were removed, t1's size would be 4 bytes.

      2. If a zero-length bit-field is inserted after a bit-field, foo, and the alignment of the zero-length bit-field is greater than the member that follows it, bar, bar is aligned as the type of the zero-length bit-field.

          For example:

               struct
                {
                  char foo : 4;
                  short : 0;
                  char bar;
                } t2;

               struct
                {
                  char foo : 4;
                  short : 0;
                  double bar;
                } t3;

          For t2, bar is placed at offset 2, rather than offset 1. Accordingly, the size of t2 is 4.  For t3, the zero-length bit-field does not affect the alignment of bar or, as a result, the size of the structure.

          Taking this into account, it is important to note the following:

           1. If a zero-length bit-field follows a normal bit-field, the type of the zero-length bit-field may affect the alignment of the structure as whole. For example, t2 has a size of 4 bytes, since the zero-length bit-field follows a normal bit-field, and is of type short.

           2. Even if a zero-length bit-field is not followed by a normal bit-field, it may still affect the alignment of the structure:

                    struct
                     {
                       char foo : 6;
                       long : 0;
                     } t4;

               Here, t4 takes up 4 bytes.

      3. Zero-length bit-fields following non-bit-field members are ignored:

               struct
                {
                  char foo;
                  long : 0;
                  char bar;
                } t5;

          Here, t5 takes up 2 bytes.

Xstormy16 Variable Attributes
-----------------------------

One attribute is currently defined for xstormy16 configurations: below100.

below100

     If a variable has the below100 attribute (BELOW100 is allowed also), GCC places the variable in the first 0x100 bytes of memory and use special opcodes to access it.  Such variables are placed in either the .bss_below100 section or the .data_below100 section.

Specifying Attributes of Types
==============================

The keyword __attribute__ allows you to specify special attributes of types.  Some type attributes apply only to struct and union types, while others can apply to any type defined via a typedef declaration.  Other attributes are defined for functions (see Function Attributes), labels (see Label Attributes), enumerators (see Enumerator Attributes), and for variables (see Variable Attributes).

The __attribute__ keyword is followed by an attribute specification inside double parentheses.

You may specify type attributes in an enum, struct or union type declaration or definition by placing them immediately after the struct, union or enum keyword.  A less preferred syntax is to place them just past the closing curly brace of the definition.

You can also include type attributes in a typedef declaration. See Attribute Syntax, for details of the exact syntax for using attributes.

Common Type Attributes
----------------------

The following type attributes are supported on most targets.

aligned (ALIGNMENT)
     This attribute specifies a minimum alignment (in bytes) for variables of the specified type.  For example, the declarations:

          struct S { short f[3]; } __attribute__ ((aligned (8)));
          typedef int more_aligned_int __attribute__ ((aligned (8)));

     force the compiler to ensure (as far as it can) that each variable whose type is struct S or more_aligned_int is allocated and aligned at least on a 8-byte boundary.  On a SPARC, having all variables of type struct S aligned to 8-byte boundaries allows the compiler to use the ldd and std (doubleword load and store) instructions when copying one variable of type struct S to another, thus improving run-time efficiency.

     Note that the alignment of any given struct or union type is required by the ISO C standard to be at least a perfect multiple of the lowest common multiple of the alignments of all of the members of the struct or union in question.  This means that you can effectively adjust the alignment of a struct or union type by attaching an aligned attribute to any one of the members of such a type, but the notation illustrated in the example above is a more obvious, intuitive, and readable way to request the compiler to adjust the alignment of an entire struct or union type.

     As in the preceding example, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given struct or union type.  Alternatively, you can leave out the alignment factor and just ask the compiler to align a type to the maximum useful alignment for the target machine you are compiling for.  For example, you could write:

          struct S { short f[3]; } __attribute__ ((aligned));

     Whenever you leave out the alignment factor in an aligned attribute specification, the compiler automatically sets the alignment for the type to the largest alignment that is ever used for any data type on the target machine you are compiling for.  Doing this can often make copy operations more efficient, because the compiler can use whatever instructions copy the biggest chunks of memory when performing copies to or from the variables that have types that you have aligned this way.

     In the example above, if the size of each short is 2 bytes, then the size of the entire struct S type is 6 bytes.  The smallest power of two that is greater than or equal to that is 8, so the compiler sets the alignment for the entire struct S type to 8 bytes.

     Note that although you can ask the compiler to select a time-efficient alignment for a given type and then declare only individual stand-alone objects of that type, the compiler's ability to select a time-efficient alignment is primarily useful only when you plan to create arrays of variables having the relevant (efficiently aligned) type.  If you declare or use arrays of variables of an efficiently-aligned type, then it is likely that your program also does pointer arithmetic (or subscripting, which amounts to the same thing) on pointers to the relevant type, and the code that the compiler generates for these pointer arithmetic operations is often more efficient for efficiently-aligned types than for other types.

     The aligned attribute can only increase the alignment; but you can decrease it by specifying packed as well.  See below.

     Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker.  On many systems, the linker is only able to arrange for variables to be aligned up to a certain maximum alignment.  (For some linkers, the maximum supported alignment may be very very small.)  If your linker is only able to align variables up to a maximum of 8-byte alignment, then specifying aligned(16) in an __attribute__ still only provides you with 8-byte alignment.  See your linker documentation for further information.

     Specifying this attribute for struct and union types is equivalent to specifying the packed attribute on each of the structure or union members.  Specifying the -fshort-enums flag on the line is equivalent to specifying the packed attribute on all enum definitions.

     In the following example struct my_packed_struct's members are packed closely together, but the internal layout of its s member is not packed---to do that, struct my_unpacked_struct needs to be packed too.

          struct my_unpacked_struct
           {
              char c;
              int i;
           };

          struct __attribute__ ((__packed__)) my_packed_struct
            {
               char c;
               int  i;
               struct my_unpacked_struct s;
            };

     You may only specify this attribute on the definition of an enum, struct or union, not on a typedef that does not also define the enumerated type, structure or union.

bnd_variable_size
     When applied to a structure field, this attribute tells Pointer Bounds Checker that the size of this field should not be computed using static type information.  It may be used to mark variably-sized static array fields placed at the end of a structure.

          struct S
          {
            int size;
            char data[1];
          }
          S *p = (S *)malloc (sizeof(S) + 100);
          p->data[10] = 0; //Bounds violation

     By using an attribute for the field we may avoid unwanted bound violation checks:

          struct S
          {
            int size;
            char data[1] __attribute__((bnd_variable_size));
          }
          S *p = (S *)malloc (sizeof(S) + 100);
          p->data[10] = 0; //OK

deprecated
deprecated (MSG)
     The deprecated attribute results in a warning if the type is used anywhere in the source file.  This is useful when identifying types that are expected to be removed in a future version of a program. If possible, the warning also includes the location of the declaration of the deprecated type, to enable users to easily find further information about why the type is deprecated, or what they should do instead.  Note that the warnings only occur for uses and then only if the type is being applied to an identifier that itself is not being declared as deprecated.

          typedef int T1 __attribute__ ((deprecated));
          T1 x;
          typedef T1 T2;
          T2 y;
          typedef T1 T3 __attribute__ ((deprecated));
          T3 z __attribute__ ((deprecated));

     results in a warning on line 2 and 3 but not lines 4, 5, or 6.  No warning is issued for line 4 because T2 is not explicitly deprecated.  Line 5 has no warning because T3 is explicitly deprecated.  Similarly for line 6.  The optional MSG argument, which must be a string, is printed in the warning if present.

     The deprecated attribute can also be used for functions and variables (see Function Attributes, see Variable Attributes.)

designated_init
     This attribute may only be applied to structure types.  It indicates that any initialization of an object of this type must use designated initializers rather than positional initializers.  The intent of this attribute is to allow the programmer to indicate that a structure's layout may change, and that therefore relying on positional initialization will result in future breakage.

     GCC emits warnings based on this attribute by default; use -Wno-designated-init to suppress them.

may_alias
     Accesses through pointers to types with this attribute are not subject to type-based alias analysis, but are instead assumed to be able to alias any other type of objects. In the context of section 6.5 paragraph 7 of the C99 standard, an lvalue expression dereferencing such a pointer is treated like having a character type. See -fstrict-aliasing for more information on aliasing issues. This extension exists to support some vector APIs, in which pointers to one vector type are permitted to alias pointers to a different vector type.

     Note that an object of a type with this attribute does not have any special semantics.

     Example of use:

          typedef short __attribute__((__may_alias__)) short_a;

          int
          main (void)
          {
            int a = 0x12345678;
            short_a *b = (short_a *) &a;

            b[1] = 0;

            if (a == 0x12345678)
              abort();

            exit(0);
          }

     If you replaced short_a with short in the variable declaration, the above program would abort when compiled with -fstrict-aliasing, which is on by default at -O2 or above.

packed
     This attribute, attached to struct or union type definition, specifies that each member (other than zero-width bit-fields) of the structure or union is placed to minimize the memory required.  When attached to an enum definition, it indicates that the smallest integral type should be used.

transparent_union

     This attribute, attached to a union type definition, indicates that any function parameter having that union type causes calls to that function to be treated in a special way.

     First, the argument corresponding to a transparent union type can be of any type in the union; no cast is required.  Also, if the union contains a pointer type, the corresponding argument can be a null pointer constant or a void pointer expression; and if the union contains a void pointer type, the corresponding argument can be any pointer expression. If the union member type is a pointer, qualifiers like const on the referenced type must be respected, just as with normal pointer conversions.

     Second, the argument is passed to the function using the calling conventions of the first member of the transparent union, not the calling conventions of the union itself.  All members of the union must have the same machine representation; this is necessary for this argument passing to work properly.

     Transparent unions are designed for library functions that have multiple interfaces for compatibility reasons.  For example, suppose the wait function must accept either a value of type int * to comply with POSIX, or a value of type union wait * to comply with the 4.1BSD interface.  If wait's parameter were void *, wait would accept both kinds of arguments, but it would also accept any other pointer type and this would make argument type checking less useful.  Instead, <sys/wait.h> might define the interface as follows:

          typedef union __attribute__ ((__transparent_union__))
            {
              int *__ip;
              union wait *__up;
            } wait_status_ptr_t;

          pid_t wait (wait_status_ptr_t);

     This interface allows either int * or union wait * arguments to be passed, using the int * calling convention. The program can call wait with arguments of either type:

          int w1 () { int w; return wait (&w); }
          int w2 () { union wait w; return wait (&w); }

     With this interface, wait's implementation might look like this:

          pid_t wait (wait_status_ptr_t p)
          {
            return waitpid (-1, p.__ip, 0);
          }

unused
     When attached to a type (including a union or a struct), this attribute means that variables of that type are meant to appear possibly unused.  GCC does not produce a warning for any variables of that type, even if the variable appears to do nothing.  This is often the case with lock or thread classes, which are usually defined and then not referenced, but contain constructors and destructors that have nontrivial bookkeeping functions.

visibility
     In C++, attribute visibility (see Function Attributes) can also be applied to class, struct, union and enum types.  Unlike other type attributes, the attribute must appear between the initial keyword and the name of the type; it cannot appear after the body of the type.

     Note that the type visibility is applied to vague linkage entities associated with the class (vtable, typeinfo node, etc.).  In particular, if a class is thrown as an exception in one shared object and caught in another, the class must have default visibility. Otherwise the two shared objects are unable to use the same typeinfo node and exception handling will break.

To specify multiple attributes, separate them by commas within the double parentheses: for example, __attribute__ ((aligned (16), packed)).

ARM Type Attributes
-------------------

On those ARM targets that support dllimport (such as Symbian OS), you can use the notshared attribute to indicate that the virtual table and other similar data for a class should not be exported from a DLL.  For example:

     class __declspec(notshared) C {
     public:
       __declspec(dllimport) C();
       virtual void f();
     }

     __declspec(dllexport)
     C::C() {}

In this code, C::C is exported from the current DLL, but the virtual table for C is not exported.  (You can use __attribute__ instead of __declspec if you prefer, but most Symbian OS code uses __declspec.)

MeP Type Attributes
-------------------

Many of the MeP variable attributes may be applied to types as well. Specifically, the based, tiny, near, and far attributes may be applied to either.  The io and cb attributes may not be applied to types.

PowerPC Type Attributes
-----------------------

Three attributes currently are defined for PowerPC configurations: altivec, ms_struct and gcc_struct.

For full documentation of the ms_struct and gcc_struct attributes please see the documentation in x86 Type Attributes.

The altivec attribute allows one to declare AltiVec vector data types supported by the AltiVec Programming Interface Manual.  The attribute requires an argument to specify one of three vector types: vector__, pixel__ (always followed by unsigned short), and bool__ (always followed by unsigned).

     __attribute__((altivec(vector__)))
     __attribute__((altivec(pixel__))) unsigned short
     __attribute__((altivec(bool__))) unsigned

These attributes mainly are intended to support the __vector, __pixel, and __bool AltiVec keywords.

SPU Type Attributes
-------------------

The SPU supports the spu_vector attribute for types.  This attribute allows one to declare vector data types supported by the Sony/Toshiba/IBM SPU Language Extensions Specification.  It is intended to support the __vector keyword.

x86 Type Attributes
-------------------

Two attributes are currently defined for x86 configurations: ms_struct and gcc_struct.

ms_struct
gcc_struct

     If packed is used on a structure, or if bit-fields are used it may be that the Microsoft ABI packs them differently than GCC normally packs them.  Particularly when moving packed data between functions compiled with GCC and the native Microsoft compiler (either via function call or as data in a file), it may be necessary to access either format.

     Currently -m[no-]ms-bitfields is provided for the Microsoft Windows x86 compilers to match the native Microsoft compiler.

Label Attributes
================

GCC allows attributes to be set on C labels.  See Attribute Syntax, for details of the exact syntax for using attributes.  Other attributes are available for functions (see Function Attributes), variables (see Variable Attributes), enumerators (see Enumerator Attributes), and for types (see Type Attributes).

This example uses the cold label attribute to indicate the ErrorHandling branch is unlikely to be taken and that the ErrorHandling label is unused:

        asm goto ("some asm" : : : : NoError);

     /* This branch (the fall-through from the asm) is less commonly used */
     ErrorHandling:
        __attribute__((cold, unused)); /* Semi-colon is required here */
        printf("error\n");
        return 0;

     NoError:
        printf("no error\n");
        return 1;

unused
     This feature is intended for program-generated code that may contain unused labels, but which is compiled with -Wall.  It is not normally appropriate to use in it human-written code, though it could be useful in cases where the code that jumps to the label is contained within an #ifdef conditional.

hot
     The hot attribute on a label is used to inform the compiler that the path following the label is more likely than paths that are not so annotated.  This attribute is used in cases where __builtin_expect cannot be used, for instance with computed goto or asm goto.

cold
     The cold attribute on labels is used to inform the compiler that the path following the label is unlikely to be executed.  This attribute is used in cases where __builtin_expect cannot be used, for instance with computed goto or asm goto.

Enumerator Attributes
=====================

GCC allows attributes to be set on enumerators.  See Attribute Syntax, for details of the exact syntax for using attributes.  Other attributes are available for functions (see Function Attributes), variables (see Variable Attributes), labels (see Label Attributes), and for types (see Type Attributes).

This example uses the deprecated enumerator attribute to indicate the oldval enumerator is deprecated:

     enum E {
       oldval __attribute__((deprecated)),
       newval
     };

     int
     fn (void)
     {
       return oldval;
     }

deprecated
     The deprecated attribute results in a warning if the enumerator is used anywhere in the source file.  This is useful when identifying enumerators that are expected to be removed in a future version of a program.  The warning also includes the location of the declaration of the deprecated enumerator, to enable users to easily find further information about why the enumerator is deprecated, or what they should do instead.  Note that the warnings only occurs for uses.

Attribute Syntax
================

This section describes the syntax with which __attribute__ may be used, and the constructs to which attribute specifiers bind, for the C language.  Some details may vary for C++ and Objective-C.  Because of infelicities in the grammar for attributes, some forms described here may not be successfully parsed in all cases.

There are some problems with the semantics of attributes in C++.  For example, there are no manglings for attributes, although they may affect code generation, so problems may arise when attributed types are used in conjunction with templates or overloading.  Similarly, typeid does not distinguish between types with different attributes.  Support for attributes in C++ may be restricted in future to attributes on declarations only, but not on nested declarators.

See Function Attributes, for details of the semantics of attributes applying to functions.  See Variable Attributes, for details of the semantics of attributes applying to variables.  See Type Attributes, for details of the semantics of attributes applying to structure, union and enumerated types. See Label Attributes, for details of the semantics of attributes applying to labels. See Enumerator Attributes, for details of the semantics of attributes applying to enumerators.

An attribute specifier is of the form __attribute__ ((ATTRIBUTE-LIST)).  An attribute list is a possibly empty comma-separated sequence of attributes, where each attribute is one of the following:

  * Empty.  Empty attributes are ignored.

  * An attribute name (which may be an identifier such as unused, or a reserved word such as const).

  * An attribute name followed by a parenthesized list of parameters for the attribute. These parameters take one of the following forms:

       * An identifier.  For example, mode attributes use this form.

       * An identifier followed by a comma and a non-empty comma-separated list of expressions.  For example, format attributes use this form.

       * A possibly empty comma-separated list of expressions.  For example, format_arg attributes use this form with the list being a single integer constant expression, and alias attributes use this form with the list being a single string constant.

An attribute specifier list is a sequence of one or more attribute specifiers, not separated by any other tokens.

You may optionally specify attribute names with __ preceding and following the name. This allows you to use them in header files without being concerned about a possible macro of the same name.  For example, you may use the attribute name __noreturn__ instead of noreturn.

Label Attributes
................

In GNU C, an attribute specifier list may appear after the colon following a label, other than a case or default label.  GNU C++ only permits attributes on labels if the attribute specifier is immediately followed by a semicolon (i.e., the label applies to an empty statement).  If the semicolon is missing, C++ label attributes are ambiguous, as it is permissible for a declaration, which could begin with an attribute list, to be labelled in C++.  Declarations cannot be labelled in C90 or C99, so the ambiguity does not arise there.

Enumerator Attributes
.....................

In GNU C, an attribute specifier list may appear as part of an enumerator. The attribute goes after the enumeration constant, before =, if present.  The optional attribute in the enumerator appertains to the enumeration constant.  It is not possible to place the attribute after the constant expression, if present.

Type Attributes
...............

An attribute specifier list may appear as part of a struct, union or enum specifier.  It may go either immediately after the struct, union or enum keyword, or after the closing brace.  The former syntax is preferred. Where attribute specifiers follow the closing brace, they are considered to relate to the structure, union or enumerated type defined, not to any enclosing declaration the type specifier appears in, and the type defined is not complete until after the attribute specifiers.

All other attributes
....................

Otherwise, an attribute specifier appears as part of a declaration, counting declarations of unnamed parameters and type names, and relates to that declaration (which may be nested in another declaration, for example in the case of a parameter declaration), or to a particular declarator within a declaration.  Where an attribute specifier is applied to a parameter declared as a function or an array, it should apply to the function or array rather than the pointer to which the parameter is implicitly converted, but this is not yet correctly implemented.

Any list of specifiers and qualifiers at the start of a declaration may contain attribute specifiers, whether or not such a list may in that context contain storage class specifiers.  (Some attributes, however, are essentially in the nature of storage class specifiers, and only make sense where storage class specifiers may be used; for example, section.)  There is one necessary limitation to this syntax: the first old-style parameter declaration in a function definition cannot begin with an attribute specifier, because such an attribute applies to the function instead by syntax described below (which, however, is not yet implemented in this case).  In some other cases, attribute specifiers are permitted by this grammar but not yet supported by the compiler.  All attribute specifiers in this place relate to the declaration as a whole.  In the obsolescent usage where a type of int is implied by the absence of type specifiers, such a list of specifiers and qualifiers may be an attribute specifier list with no other specifiers or qualifiers.

At present, the first parameter in a function prototype must have some type specifier that is not an attribute specifier; this resolves an ambiguity in the interpretation of void f(int (__attribute__((foo)) x)), but is subject to change.  At present, if the parentheses of a function declarator contain only attributes then those attributes are ignored, rather than yielding an error or warning or implying a single parameter of type int, but this is subject to change.

An attribute specifier list may appear immediately before a declarator (other than the first) in a comma-separated list of declarators in a declaration of more than one identifier using a single list of specifiers and qualifiers.  Such attribute specifiers apply only to the identifier before whose declarator they appear.  For example, in

     __attribute__((noreturn)) void d0 (void),
         __attribute__((format(printf, 1, 2))) d1 (const char *, ...),
          d2 (void);

the noreturn attribute applies to all the functions declared; the format attribute only applies to d1.

An attribute specifier list may appear immediately before the comma, = or semicolon terminating the declaration of an identifier other than a function definition.  Such attribute specifiers apply to the declared object or function.  Where an assembler name for an object or function is specified (see Asm Labels), the attribute must follow the asm specification.

An attribute specifier list may, in future, be permitted to appear after the declarator in a function definition (before any old-style parameter declarations or the function body).

Attribute specifiers may be mixed with type qualifiers appearing inside the [] of a parameter array declarator, in the C99 construct by which such qualifiers are applied to the pointer to which the array is implicitly converted.  Such attribute specifiers apply to the pointer, not to the array, but at present this is not implemented and they are ignored.

An attribute specifier list may appear at the start of a nested declarator.  At present, there are some limitations in this usage: the attributes correctly apply to the declarator, but for most individual attributes the semantics this implies are not implemented. When attribute specifiers follow the * of a pointer declarator, they may be mixed with any type qualifiers present. The following describes the formal semantics of this syntax.  It makes the most sense if you are familiar with the formal specification of declarators in the ISO C standard.

Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration T D1, where T contains declaration specifiers that specify a type TYPE (such as int) and D1 is a declarator that contains an identifier IDENT.  The type specified for IDENT for derived declarators whose type does not include an attribute specifier is as in the ISO C standard.

If D1 has the form ( ATTRIBUTE-SPECIFIER-LIST D ), and the declaration T D specifies the type ``DERIVED-DECLARATOR-TYPE-LIST TYPE'' for IDENT, then T D1 specifies the type ``DERIVED-DECLARATOR-TYPE-LIST ATTRIBUTE-SPECIFIER-LIST TYPE'' for IDENT.

If D1 has the form * TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST D, and the declaration T D specifies the type ``DERIVED-DECLARATOR-TYPE-LIST TYPE'' for IDENT, then T D1 specifies the type ``DERIVED-DECLARATOR-TYPE-LIST TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST pointer to TYPE'' for IDENT.

For example,

     void (__attribute__((noreturn)) ****f) (void);

specifies the type ``pointer to pointer to pointer to pointer to non-returning function returning void''.  As another example,

     char *__attribute__((aligned(8))) *f;

specifies the type ``pointer to 8-byte-aligned pointer to char''. Note again that this does not work with most attributes; for example, the usage of aligned and noreturn attributes given above is not yet supported.

For compatibility with existing code written for compiler versions that did not implement attributes on nested declarators, some laxity is allowed in the placing of attributes.  If an attribute that only applies to types is applied to a declaration, it is treated as applying to the type of that declaration.  If an attribute that only applies to declarations is applied to the type of a declaration, it is treated as applying to that declaration; and, for compatibility with code placing the attributes immediately before the identifier declared, such an attribute applied to a function return type is treated as applying to the function type, and such an attribute applied to an array element type is treated as applying to the array type.  If an attribute that only applies to function types is applied to a pointer-to-function type, it is treated as applying to the pointer target type; if such an attribute is applied to a function return type that is not a pointer-to-function type, it is treated as applying to the function type.

Prototypes and Old-Style Function Definitions
=============================================

GNU C extends ISO C to allow a function prototype to override a later old-style non-prototype definition.  Consider the following example:

     /* Use prototypes unless the compiler is old-fashioned.  */
     #ifdef __STDC__
     #define P(x) x
     #else
     #define P(x) ()
     #endif

     /* Prototype function declaration.  */
     int isroot P((uid_t));

     /* Old-style function definition.  */
     int
     isroot (x)   /* ??? lossage here ??? */
          uid_t x;
     {
       return x == 0;
     }

Suppose the type uid_t happens to be short.  ISO C does not allow this example, because subword arguments in old-style non-prototype definitions are promoted.  Therefore in this example the function definition's argument is really an int, which does not match the prototype argument type of short.

This restriction of ISO C makes it hard to write code that is portable to traditional C compilers, because the programmer does not know whether the uid_t type is short, int, or long.  Therefore, in cases like these GNU C allows a prototype to override a later old-style definition.  More precisely, in GNU C, a function prototype argument type overrides the argument type specified by a later old-style definition if the former type is the same as the latter type before promotion.  Thus in GNU C the above example is equivalent to the following:

     int isroot (uid_t);

     int
     isroot (uid_t x)
     {
       return x == 0;
     }

GNU C++ does not support old-style function definitions, so this extension is irrelevant.

C++ Style Comments
==================

In GNU C, you may use C++ style comments, which start with // and continue until the end of the line.  Many other C implementations allow such comments, and they are included in the 1999 C standard.  However, C++ style comments are not recognized if you specify an -std option specifying a version of ISO C before C99, or -ansi (equivalent to -std=c90).

Dollar Signs in Identifier Names
================================

In GNU C, you may normally use dollar signs in identifier names. This is because many traditional C implementations allow such identifiers. However, dollar signs in identifiers are not supported on a few target machines, typically because the target assembler does not allow them.

The Character ESC in Constants
==============================

You can use the sequence \e in a string or character constant to stand for the ASCII character ESC.

Inquiring on Alignment of Types or Variables
============================================

The keyword __alignof__ allows you to inquire about how an object is aligned, or the minimum alignment usually required by a type.  Its syntax is just like sizeof.

For example, if the target machine requires a double value to be aligned on an 8-byte boundary, then __alignof__ (double) is 8. This is true on many RISC machines.  On more traditional machine designs, __alignof__ (double) is 4 or even 2.

Some machines never actually require alignment; they allow reference to any data type even at an odd address.  For these machines, __alignof__ reports the smallest alignment that GCC gives the data type, usually as mandated by the target ABI.

If the operand of __alignof__ is an lvalue rather than a type, its value is the required alignment for its type, taking into account any minimum alignment specified with GCC's __attribute__ extension (see Variable Attributes).  For example, after this declaration:

     struct foo { int x; char y; } foo1;

the value of __alignof__ (foo1.y) is 1, even though its actual alignment is probably 2 or 4, the same as __alignof__ (int).

It is an error to ask for the alignment of an incomplete type.

An Inline Function is As Fast As a Macro
========================================

By declaring a function inline, you can direct GCC to make calls to that function faster.  One way GCC can achieve this is to integrate that function's code into the code for its callers.  This makes execution faster by eliminating the function-call overhead; in addition, if any of the actual argument values are constant, their known values may permit simplifications at compile time so that not all of the inline function's code needs to be included.  The effect on code size is less predictable; object code may be larger or smaller with function inlining, depending on the particular case.  You can also direct GCC to try to integrate all ``simple enough'' functions into their callers with the option -finline-functions.

GCC implements three different semantics of declaring a function inline.  One is available with -std=gnu89 or -fgnu89-inline or when gnu_inline attribute is present on all inline declarations, another when -std=c99, -std=c11, -std=gnu99 or -std=gnu11 (without -fgnu89-inline), and the third is used when compiling C++.

To declare a function inline, use the inline keyword in its declaration, like this:

     static inline int
     inc (int *a)
     {
       return (*a)++;
     }

If you are writing a header file to be included in ISO C90 programs, write __inline__ instead of inline.  See Alternate Keywords.

The three types of inlining behave similarly in two important cases: when the inline keyword is used on a static function, like the example above, and when a function is first declared without using the inline keyword and then is defined with inline, like this:

     extern int inc (int *a);
     inline int
     inc (int *a)
     {
       return (*a)++;
     }

In both of these common cases, the program behaves the same as if you had not used the inline keyword, except for its speed.

When a function is both inline and static, if all calls to the function are integrated into the caller, and the function's address is never used, then the function's own assembler code is never referenced. In this case, GCC does not actually output assembler code for the function, unless you specify the option -fkeep-inline-functions. Some calls cannot be integrated for various reasons (in particular, calls that precede the function's definition cannot be integrated, and neither can recursive calls within the definition).  If there is a nonintegrated call, then the function is compiled to assembler code as usual.  The function must also be compiled as usual if the program refers to its address, because that can't be inlined.

Note that certain usages in a function definition can make it unsuitable for inline substitution.  Among these usages are: variadic functions, use of alloca, use of variable-length data types (see Variable Length), use of computed goto (see Labels as Values), use of nonlocal goto, and nested functions (see Nested Functions).  Using -Winline warns when a function marked inline could not be substituted, and gives the reason for the failure.

As required by ISO C++, GCC considers member functions defined within the body of a class to be marked inline even if they are not explicitly declared with the inline keyword.  You can override this with -fno-default-inline; see Options Controlling C++ Dialect.

GCC does not inline any functions when not optimizing unless you specify the always_inline attribute for the function, like this:

     /* Prototype.  */
     inline void foo (const char) __attribute__((always_inline));

The remainder of this section is specific to GNU C90 inlining.

When an inline function is not static, then the compiler must assume that there may be calls from other source files; since a global symbol can be defined only once in any program, the function must not be defined in the other source files, so the calls therein cannot be integrated. Therefore, a non-static inline function is always compiled on its own in the usual fashion.

If you specify both inline and extern in the function definition, then the definition is used only for inlining.  In no case is the function compiled on its own, not even if you refer to its address explicitly.  Such an address becomes an external reference, as if you had only declared the function, and had not defined it.

This combination of inline and extern has almost the effect of a macro.  The way to use it is to put a function definition in a header file with these keywords, and put another copy of the definition (lacking inline and extern) in a library file. The definition in the header file causes most calls to the function to be inlined.  If any uses of the function remain, they refer to the single copy in the library.

When is a Volatile Object Accessed?
===================================

C has the concept of volatile objects.  These are normally accessed by pointers and used for accessing hardware or inter-thread communication.  The standard encourages compilers to refrain from optimizations concerning accesses to volatile objects, but leaves it implementation defined as to what constitutes a volatile access.  The minimum requirement is that at a sequence point all previous accesses to volatile objects have stabilized and no subsequent accesses have occurred.  Thus an implementation is free to reorder and combine volatile accesses that occur between sequence points, but cannot do so for accesses across a sequence point.  The use of volatile does not allow you to violate the restriction on updating objects multiple times between two sequence points.

Accesses to non-volatile objects are not ordered with respect to volatile accesses.  You cannot use a volatile object as a memory barrier to order a sequence of writes to non-volatile memory.  For instance:

     int *ptr = SOMETHING;
     volatile int vobj;
     *ptr = SOMETHING;
     vobj = 1;

Unless *PTR and VOBJ can be aliased, it is not guaranteed that the write to *PTR occurs by the time the update of VOBJ happens.  If you need this guarantee, you must use a stronger memory barrier such as:

     int *ptr = SOMETHING;
     volatile int vobj;
     *ptr = SOMETHING;
     asm volatile ("" : : : "memory");
     vobj = 1;

A scalar volatile object is read when it is accessed in a void context:

     volatile int *src = SOMEVALUE;
     *src;

Such expressions are rvalues, and GCC implements this as a read of the volatile object being pointed to.

Assignments are also expressions and have an rvalue.  However when assigning to a scalar volatile, the volatile object is not reread, regardless of whether the assignment expression's rvalue is used or not.  If the assignment's rvalue is used, the value is that assigned to the volatile object.  For instance, there is no read of VOBJ in all the following cases:

     int obj;
     volatile int vobj;
     vobj = SOMETHING;
     obj = vobj = SOMETHING;
     obj ? vobj = ONETHING : vobj = ANOTHERTHING;
     obj = (SOMETHING, vobj = ANOTHERTHING);

If you need to read the volatile object after an assignment has occurred, you must use a separate expression with an intervening sequence point.

As bit-fields are not individually addressable, volatile bit-fields may be implicitly read when written to, or when adjacent bit-fields are accessed.  Bit-field operations may be optimized such that adjacent bit-fields are only partially accessed, if they straddle a storage unit boundary.  For these reasons it is unwise to use volatile bit-fields to access hardware.

How to Use Inline Assembly Language in C Code
=============================================

The asm keyword allows you to embed assembler instructions within C code.  GCC provides two forms of inline asm statements.  A basic asm statement is one with no operands (see Basic Asm), while an extended asm statement (see Extended Asm) includes one or more operands. The extended form is preferred for mixing C and assembly language within a function, but to include assembly language at top level you must use basic asm.

You can also use the asm keyword to override the assembler name for a C symbol, or to place a C variable in a specific register.

Basic Asm --- Assembler Instructions Without Operands
-----------------------------------------------------

A basic asm statement has the following syntax:

     asm [ volatile ] ( ASSEMBLERINSTRUCTIONS )

The asm keyword is a GNU extension. When writing code that can be compiled with -ansi and the various -std options, use __asm__ instead of asm (see Alternate Keywords).

Qualifiers
..........

volatile
     The optional volatile qualifier has no effect. All basic asm blocks are implicitly volatile.

Parameters
..........

AssemblerInstructions
     This is a literal string that specifies the assembler code. The string can contain any instructions recognized by the assembler, including directives. GCC does not parse the assembler instructions themselves and does not know what they mean or even whether they are valid assembler input.

     You may place multiple assembler instructions together in a single asm string, separated by the characters normally used in assembly code for the system. A combination that works in most places is a newline to break the line, plus a tab character (written as \n\t). Some assemblers allow semicolons as a line separator. However, note that some assembler dialects use semicolons to start a comment.

Remarks
.......

Using extended asm typically produces smaller, safer, and more efficient code, and in most cases it is a better solution than basic asm.  However, there are two situations where only basic asm can be used:

  * Extended asm statements have to be inside a C function, so to write inline assembly language at file scope (``top-level''), outside of C functions, you must use basic asm. You can use this technique to emit assembler directives, define assembly language macros that can be invoked elsewhere in the file, or write entire functions in assembly language.

  * Functions declared with the naked attribute also require basic asm (see Function Attributes).

Safely accessing C data and calling functions from basic asm is more complex than it may appear. To access C data, it is better to use extended asm.

Do not expect a sequence of asm statements to remain perfectly consecutive after compilation. If certain instructions need to remain consecutive in the output, put them in a single multi-instruction asm statement. Note that GCC's optimizers can move asm statements relative to other code, including across jumps.

asm statements may not perform jumps into other asm statements. GCC does not know about these jumps, and therefore cannot take account of them when deciding how to optimize. Jumps from asm to C labels are only supported in extended asm.

Under certain circumstances, GCC may duplicate (or remove duplicates of) your assembly code when optimizing. This can lead to unexpected duplicate symbol errors during compilation if your assembly code defines symbols or labels.

Since GCC does not parse the ASSEMBLERINSTRUCTIONS, it has no visibility of any symbols it references. This may result in GCC discarding those symbols as unreferenced.

The compiler copies the assembler instructions in a basic asm verbatim to the assembly language output file, without processing dialects or any of the % operators that are available with extended asm. This results in minor differences between basic asm strings and extended asm templates. For example, to refer to registers you might use %eax in basic asm and %%eax in extended asm.

On targets such as x86 that support multiple assembler dialects, all basic asm blocks use the assembler dialect specified by the -masm command-line option (see x86 Options). Basic asm provides no mechanism to provide different assembler strings for different dialects.

Here is an example of basic asm for i386:

     /* Note that this code will not compile with -masm=intel */
     #define DebugBreak() asm("int $3")

Extended Asm - Assembler Instructions with C Expression Operands
----------------------------------------------------------------

With extended asm you can read and write C variables from assembler and perform jumps from assembler code to C labels. Extended asm syntax uses colons (:) to delimit the operand parameters after the assembler template:

     asm [volatile] ( ASSEMBLERTEMPLATE
                      : OUTPUTOPERANDS
                      [ : INPUTOPERANDS
                      [ : CLOBBERS ] ])

     asm [volatile] goto ( ASSEMBLERTEMPLATE
                           :
                           : INPUTOPERANDS
                           : CLOBBERS
                           : GOTOLABELS)

The asm keyword is a GNU extension. When writing code that can be compiled with -ansi and the various -std options, use __asm__ instead of asm (see Alternate Keywords).

Qualifiers
..........

volatile
     The typical use of extended asm statements is to manipulate input values to produce output values. However, your asm statements may also produce side effects. If so, you may need to use the volatile qualifier to disable certain optimizations. See Volatile.

goto
     This qualifier informs the compiler that the asm statement may perform a jump to one of the labels listed in the GOTOLABELS. See GotoLabels.

Parameters
..........

AssemblerTemplate
     This is a literal string that is the template for the assembler code. It is a combination of fixed text and tokens that refer to the input, output, and goto parameters. See AssemblerTemplate.

OutputOperands
     A comma-separated list of the C variables modified by the instructions in the ASSEMBLERTEMPLATE.  An empty list is permitted.  See OutputOperands.

InputOperands
     A comma-separated list of C expressions read by the instructions in the ASSEMBLERTEMPLATE.  An empty list is permitted.  See InputOperands.

Clobbers
     A comma-separated list of registers or other values changed by the ASSEMBLERTEMPLATE, beyond those listed as outputs. An empty list is permitted.  See Clobbers.

GotoLabels
     When you are using the goto form of asm, this section contains the list of all C labels to which the code in the ASSEMBLERTEMPLATE may jump. See GotoLabels.

     asm statements may not perform jumps into other asm statements, only to the listed GOTOLABELS. GCC's optimizers do not know about other jumps; therefore they cannot take account of them when deciding how to optimize.

The total number of input + output + goto operands is limited to 30.

Remarks
.......

The asm statement allows you to include assembly instructions directly within C code. This may help you to maximize performance in time-sensitive code or to access assembly instructions that are not readily available to C programs.

Note that extended asm statements must be inside a function. Only basic asm may be outside functions (see Basic Asm). Functions declared with the naked attribute also require basic asm (see Function Attributes).

While the uses of asm are many and varied, it may help to think of an asm statement as a series of low-level instructions that convert input parameters to output parameters. So a simple (if not particularly useful) example for i386 using asm might look like this:

     int src = 1;
     int dst;

     asm ("mov %1, %0\n\t"
         "add $1, %0"
         : "=r" (dst)
         : "r" (src));

     printf("%d\n", dst);

This code copies src to dst and add 1 to dst.

Volatile
........

GCC's optimizers sometimes discard asm statements if they determine there is no need for the output variables. Also, the optimizers may move code out of loops if they believe that the code will always return the same result (i.e. none of its input values change between calls). Using the volatile qualifier disables these optimizations. asm statements that have no output operands, including asm goto statements, are implicitly volatile.

This i386 code demonstrates a case that does not use (or require) the volatile qualifier. If it is performing assertion checking, this code uses asm to perform the validation. Otherwise, dwRes is unreferenced by any code. As a result, the optimizers can discard the asm statement, which in turn removes the need for the entire DoCheck routine. By omitting the volatile qualifier when it isn't needed you allow the optimizers to produce the most efficient code possible.

     void DoCheck(uint32_t dwSomeValue)
     {
        uint32_t dwRes;

        // Assumes dwSomeValue is not zero.
        asm ("bsfl %1,%0"
          : "=r" (dwRes)
          : "r" (dwSomeValue)
          : "cc");

        assert(dwRes > 3);
     }

The next example shows a case where the optimizers can recognize that the input (dwSomeValue) never changes during the execution of the function and can therefore move the asm outside the loop to produce more efficient code. Again, using volatile disables this type of optimization.

     void do_print(uint32_t dwSomeValue)
     {
        uint32_t dwRes;

        for (uint32_t x=0; x < 5; x++)
        {
           // Assumes dwSomeValue is not zero.
           asm ("bsfl %1,%0"
             : "=r" (dwRes)
             : "r" (dwSomeValue)
             : "cc");

           printf("%u: %u %u\n", x, dwSomeValue, dwRes);
        }
     }

The following example demonstrates a case where you need to use the volatile qualifier. It uses the x86 rdtsc instruction, which reads the computer's time-stamp counter. Without the volatile qualifier, the optimizers might assume that the asm block will always return the same value and therefore optimize away the second call.

     uint64_t msr;

     asm volatile ( "rdtsc\n\t"    // Returns the time in EDX:EAX.
             "shl $32, %%rdx\n\t"  // Shift the upper bits left.
             "or %%rdx, %0"        // 'Or' in the lower bits.
             : "=a" (msr)
             :
             : "rdx");

     printf("msr: %llx\n", msr);

     // Do other work...

     // Reprint the timestamp
     asm volatile ( "rdtsc\n\t"    // Returns the time in EDX:EAX.
             "shl $32, %%rdx\n\t"  // Shift the upper bits left.
             "or %%rdx, %0"        // 'Or' in the lower bits.
             : "=a" (msr)
             :
             : "rdx");

     printf("msr: %llx\n", msr);

GCC's optimizers do not treat this code like the non-volatile code in the earlier examples. They do not move it out of loops or omit it on the assumption that the result from a previous call is still valid.

Note that the compiler can move even volatile asm instructions relative to other code, including across jump instructions. For example, on many targets there is a system register that controls the rounding mode of floating-point operations. Setting it with a volatile asm, as in the following PowerPC example, does not work reliably.

     asm volatile("mtfsf 255, %0" : : "f" (fpenv));
     sum = x + y;

The compiler may move the addition back before the volatile asm. To make it work as expected, add an artificial dependency to the asm by referencing a variable in the subsequent code, for example:

     asm volatile ("mtfsf 255,%1" : "=X" (sum) : "f" (fpenv));
     sum = x + y;

Under certain circumstances, GCC may duplicate (or remove duplicates of) your assembly code when optimizing. This can lead to unexpected duplicate symbol errors during compilation if your asm code defines symbols or labels. Using %= (see AssemblerTemplate) may help resolve this problem.

Assembler Template
..................

An assembler template is a literal string containing assembler instructions. The compiler replaces tokens in the template that refer to inputs, outputs, and goto labels, and then outputs the resulting string to the assembler. The string can contain any instructions recognized by the assembler, including directives. GCC does not parse the assembler instructions themselves and does not know what they mean or even whether they are valid assembler input. However, it does count the statements (see Size of an asm).

You may place multiple assembler instructions together in a single asm string, separated by the characters normally used in assembly code for the system. A combination that works in most places is a newline to break the line, plus a tab character to move to the instruction field (written as \n\t). Some assemblers allow semicolons as a line separator. However, note that some assembler dialects use semicolons to start a comment.

Do not expect a sequence of asm statements to remain perfectly consecutive after compilation, even when you are using the volatile qualifier. If certain instructions need to remain consecutive in the output, put them in a single multi-instruction asm statement.

Accessing data from C programs without using input/output operands (such as by using global symbols directly from the assembler template) may not work as expected. Similarly, calling functions directly from an assembler template requires a detailed understanding of the target assembler and ABI.

Since GCC does not parse the assembler template, it has no visibility of any symbols it references. This may result in GCC discarding those symbols as unreferenced unless they are also listed as input, output, or goto operands.

Special format strings
......................

In addition to the tokens described by the input, output, and goto operands, these tokens have special meanings in the assembler template:

%%
     Outputs a single % into the assembler code.

%=
     Outputs a number that is unique to each instance of the asm statement in the entire compilation. This option is useful when creating local labels and referring to them multiple times in a single template that generates multiple assembler instructions.

%{
%|
%}
     Outputs {, |, and } characters (respectively) into the assembler code.  When unescaped, these characters have special meaning to indicate multiple assembler dialects, as described below.

Multiple assembler dialects in asm templates
............................................

On targets such as x86, GCC supports multiple assembler dialects. The -masm option controls which dialect GCC uses as its default for inline assembler. The target-specific documentation for the -masm option contains the list of supported dialects, as well as the default dialect if the option is not specified. This information may be important to understand, since assembler code that works correctly when compiled using one dialect will likely fail if compiled using another. See x86 Options.

If your code needs to support multiple assembler dialects (for example, if you are writing public headers that need to support a variety of compilation options), use constructs of this form:

     { dialect0 | dialect1 | dialect2... }

This construct outputs dialect0 when using dialect #0 to compile the code, dialect1 for dialect #1, etc. If there are fewer alternatives within the braces than the number of dialects the compiler supports, the construct outputs nothing.

For example, if an x86 compiler supports two dialects (att, intel), an assembler template such as this:

     "bt{l %[Offset],%[Base] | %[Base],%[Offset]}; jc %l2"

is equivalent to one of

     "btl %[Offset],%[Base] ; jc %l2"   /* att dialect */
     "bt %[Base],%[Offset]; jc %l2"     /* intel dialect */

Using that same compiler, this code:

     "xchg{l}\t{%%}ebx, %1"

corresponds to either

     "xchgl\t%%ebx, %1"                 /* att dialect */
     "xchg\tebx, %1"                    /* intel dialect */

There is no support for nesting dialect alternatives.

Output Operands
...............

An asm statement has zero or more output operands indicating the names of C variables modified by the assembler code.

In this i386 example, old (referred to in the template string as %0) and *Base (as %1) are outputs and Offset (%2) is an input:

     bool old;

     __asm__ ("btsl %2,%1\n\t" // Turn on zero-based bit #Offset in Base.
              "sbb %0,%0"      // Use the CF to calculate old.
        : "=r" (old), "+rm" (*Base)
        : "Ir" (Offset)
        : "cc");

     return old;

Operands are separated by commas.  Each operand has this format:

     [ [ASMSYMBOLICNAME] ] CONSTRAINT (CVARIABLENAME)

asmSymbolicName
     Specifies a symbolic name for the operand. Reference the name in the assembler template by enclosing it in square brackets (i.e. %[Value]). The scope of the name is the asm statement that contains the definition. Any valid C variable name is acceptable, including names already defined in the surrounding code. No two operands within the same asm statement can use the same symbolic name.

     When not using an ASMSYMBOLICNAME, use the (zero-based) position of the operand in the list of operands in the assembler template. For example if there are three output operands, use %0 in the template to refer to the first, %1 for the second, and %2 for the third.

constraint
     A string constant specifying constraints on the placement of the operand; see Constraints, for details.

     Output constraints must begin with either = (a variable overwriting an existing value) or + (when reading and writing). When using =, do not assume the location contains the existing value on entry to the asm, except when the operand is tied to an input; see Input Operands.

     After the prefix, there must be one or more additional constraints (see Constraints) that describe where the value resides. Common constraints include r for register and m for memory. When you list more than one possible location (for example, "=rm"), the compiler chooses the most efficient one based on the current context. If you list as many alternates as the asm statement allows, you permit the optimizers to produce the best possible code. If you must use a specific register, but your Machine Constraints do not provide sufficient control to select the specific register you want, local register variables may provide a solution (see Local Reg Vars).

cvariablename
     Specifies a C lvalue expression to hold the output, typically a variable name. The enclosing parentheses are a required part of the syntax.

When the compiler selects the registers to use to represent the output operands, it does not use any of the clobbered registers (see Clobbers).

Output operand expressions must be lvalues. The compiler cannot check whether the operands have data types that are reasonable for the instruction being executed. For output expressions that are not directly addressable (for example a bit-field), the constraint must allow a register. In that case, GCC uses the register as the output of the asm, and then stores that register into the output.

Operands using the + constraint modifier count as two operands (that is, both as input and output) towards the total maximum of 30 operands per asm statement.

Use the & constraint modifier (see Modifiers) on all output operands that must not overlap an input.  Otherwise, GCC may allocate the output operand in the same register as an unrelated input operand, on the assumption that the assembler code consumes its inputs before producing outputs. This assumption may be false if the assembler code actually consists of more than one instruction.

The same problem can occur if one output parameter (A) allows a register constraint and another output parameter (B) allows a memory constraint. The code generated by GCC to access the memory address in B can contain registers which might be shared by A, and GCC considers those registers to be inputs to the asm. As above, GCC assumes that such input registers are consumed before any outputs are written. This assumption may result in incorrect behavior if the asm writes to A before using B. Combining the & modifier with the register constraint on A ensures that modifying A does not affect the address referenced by B. Otherwise, the location of B is undefined if A is modified before using B.

asm supports operand modifiers on operands (for example %k2 instead of simply %2). Typically these qualifiers are hardware dependent. The list of supported modifiers for x86 is found at x86 Operand modifiers.

If the C code that follows the asm makes no use of any of the output operands, use volatile for the asm statement to prevent the optimizers from discarding the asm statement as unneeded (see Volatile).

This code makes no use of the optional ASMSYMBOLICNAME. Therefore it references the first output operand as %0 (were there a second, it would be %1, etc). The number of the first input operand is one greater than that of the last output operand. In this i386 example, that makes Mask referenced as %1:

     uint32_t Mask = 1234;
     uint32_t Index;

       asm ("bsfl %1, %0"
          : "=r" (Index)
          : "r" (Mask)
          : "cc");

That code overwrites the variable Index (=), placing the value in a register (r). Using the generic r constraint instead of a constraint for a specific register allows the compiler to pick the register to use, which can result in more efficient code. This may not be possible if an assembler instruction requires a specific register.

The following i386 example uses the ASMSYMBOLICNAME syntax. It produces the same result as the code above, but some may consider it more readable or more maintainable since reordering index numbers is not necessary when adding or removing operands. The names aIndex and aMask are only used in this example to emphasize which names get used where. It is acceptable to reuse the names Index and Mask.

     uint32_t Mask = 1234;
     uint32_t Index;

       asm ("bsfl %[aMask], %[aIndex]"
          : [aIndex] "=r" (Index)
          : [aMask] "r" (Mask)
          : "cc");

Here are some more examples of output operands.

     uint32_t c = 1;
     uint32_t d;
     uint32_t *e = &c;

     asm ("mov %[e], %[d]"
        : [d] "=rm" (d)
        : [e] "rm" (*e));

Here, d may either be in a register or in memory. Since the compiler might already have the current value of the uint32_t location pointed to by e in a register, you can enable it to choose the best location for d by specifying both constraints.

Flag Output Operands
--------------------

Some targets have a special register that holds the ``flags'' for the result of an operation or comparison.  Normally, the contents of that register are either unmodifed by the asm, or the asm is considered to clobber the contents.

On some targets, a special form of output operand exists by which conditions in the flags register may be outputs of the asm.  The set of conditions supported are target specific, but the general rule is that the output variable must be a scalar integer, and the value will be boolean. When supported, the target will define the preprocessor symbol __GCC_ASM_FLAG_OUTPUTS__.

Because of the special nature of the flag output operands, the constraint may not include alternatives.

Most often, the target has only one flags register, and thus is an implied operand of many instructions.  In this case, the operand should not be referenced within the assembler template via %0 etc, as there's no corresponding text in the assembly language.

x86 family
     The flag output constraints for the x86 family are of the form =@ccCOND where COND is one of the standard conditions defined in the ISA manual for jCC or setCC.

     a
          ``above'' or unsigned greater than

     ae
          ``above or equal'' or unsigned greater than or equal

     b
          ``below'' or unsigned less than

     be
          ``below or equal'' or unsigned less than or equal

     c
          carry flag set

     e
     z
          ``equal'' or zero flag set

     g
          signed greater than

     ge
          signed greater than or equal

     l
          signed less than

     le
          signed less than or equal

     o
          overflow flag set

     p
          parity flag set

     s
          sign flag set

     na
     nae
     nb
     nbe
     nc
     ne
     ng
     nge
     nl
     nle
     no
     np
     ns
     nz
          ``not'' FLAG, or inverted versions of those above

Input Operands
..............

Input operands make values from C variables and expressions available to the assembly code.

Operands are separated by commas.  Each operand has this format:

     [ [ASMSYMBOLICNAME] ] CONSTRAINT (CEXPRESSION)

asmSymbolicName
     Specifies a symbolic name for the operand. Reference the name in the assembler template by enclosing it in square brackets (i.e. %[Value]). The scope of the name is the asm statement that contains the definition. Any valid C variable name is acceptable, including names already defined in the surrounding code. No two operands within the same asm statement can use the same symbolic name.

     When not using an ASMSYMBOLICNAME, use the (zero-based) position of the operand in the list of operands in the assembler template. For example if there are two output operands and three inputs, use %2 in the template to refer to the first input operand, %3 for the second, and %4 for the third.

constraint
     A string constant specifying constraints on the placement of the operand; see Constraints, for details.

     Input constraint strings may not begin with either = or +. When you list more than one possible location (for example, "irm"), the compiler chooses the most efficient one based on the current context. If you must use a specific register, but your Machine Constraints do not provide sufficient control to select the specific register you want, local register variables may provide a solution (see Local Reg Vars).

     Input constraints can also be digits (for example, "0"). This indicates that the specified input must be in the same place as the output constraint at the (zero-based) index in the output constraint list. When using ASMSYMBOLICNAME syntax for the output operands, you may use these names (enclosed in brackets []) instead of digits.

cexpression
     This is the C variable or expression being passed to the asm statement as input.  The enclosing parentheses are a required part of the syntax.

When the compiler selects the registers to use to represent the input operands, it does not use any of the clobbered registers (see Clobbers).

If there are no output operands but there are input operands, place two consecutive colons where the output operands would go:

     __asm__ ("some instructions"
        : /* No outputs. */
        : "r" (Offset / 8));

Warning: Do not modify the contents of input-only operands (except for inputs tied to outputs). The compiler assumes that on exit from the asm statement these operands contain the same values as they had before executing the statement. It is not possible to use clobbers to inform the compiler that the values in these inputs are changing. One common work-around is to tie the changing input variable to an output variable that never gets used. Note, however, that if the code that follows the asm statement makes no use of any of the output operands, the GCC optimizers may discard the asm statement as unneeded (see Volatile).

asm supports operand modifiers on operands (for example %k2 instead of simply %2). Typically these qualifiers are hardware dependent. The list of supported modifiers for x86 is found at x86 Operand modifiers.

In this example using the fictitious combine instruction, the constraint "0" for input operand 1 says that it must occupy the same location as output operand 0. Only input operands may use numbers in constraints, and they must each refer to an output operand. Only a number (or the symbolic assembler name) in the constraint can guarantee that one operand is in the same place as another. The mere fact that foo is the value of both operands is not enough to guarantee that they are in the same place in the generated assembler code.

     asm ("combine %2, %0"
        : "=r" (foo)
        : "0" (foo), "g" (bar));

Here is an example using symbolic names.

     asm ("cmoveq %1, %2, %[result]"
        : [result] "=r"(result)
        : "r" (test), "r" (new), "[result]" (old));

Clobbers
........

While the compiler is aware of changes to entries listed in the output operands, the inline asm code may modify more than just the outputs. For example, calculations may require additional registers, or the processor may overwrite a register as a side effect of a particular assembler instruction. In order to inform the compiler of these changes, list them in the clobber list. Clobber list items are either register names or the special clobbers (listed below). Each clobber list item is a string constant enclosed in double quotes and separated by commas.

Clobber descriptions may not in any way overlap with an input or output operand. For example, you may not have an operand describing a register class with one member when listing that register in the clobber list. Variables declared to live in specific registers (see Explicit Reg Vars) and used as asm input or output operands must have no part mentioned in the clobber description. In particular, there is no way to specify that input operands get modified without also specifying them as output operands.

When the compiler selects which registers to use to represent input and output operands, it does not use any of the clobbered registers. As a result, clobbered registers are available for any use in the assembler code.

Here is a realistic example for the VAX showing the use of clobbered registers:

     asm volatile ("movc3 %0, %1, %2"
                        : /* No outputs. */
                        : "g" (from), "g" (to), "g" (count)
                        : "r0", "r1", "r2", "r3", "r4", "r5");

Also, there are two special clobber arguments:

"cc"
     The "cc" clobber indicates that the assembler code modifies the flags register. On some machines, GCC represents the condition codes as a specific hardware register; "cc" serves to name this register. On other machines, condition code handling is different, and specifying "cc" has no effect. But it is valid no matter what the target.

"memory"
     The "memory" clobber tells the compiler that the assembly code performs memory reads or writes to items other than those listed in the input and output operands (for example, accessing the memory pointed to by one of the input parameters). To ensure memory contains correct values, GCC may need to flush specific register values to memory before executing the asm. Further, the compiler does not assume that any values read from memory before an asm remain unchanged after that asm; it reloads them as needed. Using the "memory" clobber effectively forms a read/write memory barrier for the compiler.

     Note that this clobber does not prevent the processor from doing speculative reads past the asm statement. To prevent that, you need processor-specific fence instructions.

     Flushing registers to memory has performance implications and may be an issue for time-sensitive code.  You can use a trick to avoid this if the size of the memory being accessed is known at compile time. For example, if accessing ten bytes of a string, use a memory input like:

     {"m"( ({ struct { char x[10]; } *p = (void *)ptr ; *p; }) )}.

Goto Labels
...........

asm goto allows assembly code to jump to one or more C labels.  The GOTOLABELS section in an asm goto statement contains a comma-separated list of all C labels to which the assembler code may jump. GCC assumes that asm execution falls through to the next statement (if this is not the case, consider using the __builtin_unreachable intrinsic after the asm statement). Optimization of asm goto may be improved by using the hot and cold label attributes (see Label Attributes).

An asm goto statement cannot have outputs. This is due to an internal restriction of the compiler: control transfer instructions cannot have outputs. If the assembler code does modify anything, use the "memory" clobber to force the optimizers to flush all register values to memory and reload them if necessary after the asm statement.

Also note that an asm goto statement is always implicitly considered volatile.

To reference a label in the assembler template, prefix it with %l (lowercase L) followed by its (zero-based) position in GOTOLABELS plus the number of input operands.  For example, if the asm has three inputs and references two labels, refer to the first label as %l3 and the second as %l4).

Alternately, you can reference labels using the actual C label name enclosed in brackets.  For example, to reference a label named carry, you can use %l[carry].  The label must still be listed in the GOTOLABELS section when using this approach.

Here is an example of asm goto for i386:

     asm goto (
         "btl %1, %0\n\t"
         "jc %l2"
         : /* No outputs. */
         : "r" (p1), "r" (p2)
         : "cc"
         : carry);

     return 0;

     carry:
     return 1;

The following example shows an asm goto that uses a memory clobber.

     int frob(int x)
     {
       int y;
       asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
                 : /* No outputs. */
                 : "r"(x), "r"(&y)
                 : "r5", "memory"
                 : error);
       return y;
     error:
       return -1;
     }

x86 Operand Modifiers
.....................

References to input, output, and goto operands in the assembler template of extended asm statements can use modifiers to affect the way the operands are formatted in the code output to the assembler. For example, the following code uses the h and b modifiers for x86:

     uint16_t  num;
     asm volatile ("xchg %h0, %b0" : "+a" (num) );

These modifiers generate this assembler code:

     xchg %ah, %al

The rest of this discussion uses the following code for illustrative purposes.

     int main()
     {
        int iInt = 1;

     top:

        asm volatile goto ("some assembler instructions here"
        : /* No outputs. */
        : "q" (iInt), "X" (sizeof(unsigned char) + 1)
        : /* No clobbers. */
        : top);
     }

With no modifiers, this is what the output from the operands would be for the att and intel dialects of assembler:

Operand   masm=att   masm=intel
%0
%eax
eax
%1
$2
2
%2
$.L2
OFFSET FLAT:.L2

The table below shows the list of supported modifiers and their effects.

Modifier   Description   Operand   masm=att   masm=intel
z
Print the opcode suffix for the size of the current integer operand (one of b/w/l/q).
%z0
l

b
Print the QImode name of the register.
%b0
%al
al
h
Print the QImode name for a ``high'' register.
%h0
%ah
ah
w
Print the HImode name of the register.
%w0
%ax
ax
k
Print the SImode name of the register.
%k0
%eax
eax
q
Print the DImode name of the register.
%q0
%rax
rax
l
Print the label name with no punctuation.
%l2
.L2
.L2
c
Require a constant operand and print the constant expression with no punctuation.
%c1
2
2

x86 Floating-Point asm Operands
...............................

On x86 targets, there are several rules on the usage of stack-like registers in the operands of an asm.  These rules apply only to the operands that are stack-like registers:

 1. Given a set of input registers that die in an asm, it is necessary to know which are implicitly popped by the asm, and which must be explicitly popped by GCC.

     An input register that is implicitly popped by the asm must be explicitly clobbered, unless it is constrained to match an output operand.

 2. For any input register that is implicitly popped by an asm, it is necessary to know how to adjust the stack to compensate for the pop. If any non-popped input is closer to the top of the reg-stack than the implicitly popped register, it would not be possible to know what the stack looked like---it's not clear how the rest of the stack ``slides up''.

     All implicitly popped input registers must be closer to the top of the reg-stack than any input that is not implicitly popped.

     It is possible that if an input dies in an asm, the compiler might use the input register for an output reload.  Consider this example:

          asm ("foo" : "=t" (a) : "f" (b));

     This code says that input b is not popped by the asm, and that the asm pushes a result onto the reg-stack, i.e., the stack is one deeper after the asm than it was before.  But, it is possible that reload may think that it can use the same register for both the input and the output.

     To prevent this from happening, if any input operand uses the f constraint, all output register constraints must use the & early-clobber modifier.

     The example above is correctly written as:

          asm ("foo" : "=&t" (a) : "f" (b));

 3. Some operands need to be in particular places on the stack.  All output operands fall in this category---GCC has no other way to know which registers the outputs appear in unless you indicate this in the constraints.

     Output operands must specifically indicate which register an output appears in after an asm.  =f is not allowed: the operand constraints must select a class with a single register.

 4. Output operands may not be ``inserted'' between existing stack registers. Since no 387 opcode uses a read/write operand, all output operands are dead before the asm, and are pushed by the asm. It makes no sense to push anywhere but the top of the reg-stack.

     Output operands must start at the top of the reg-stack: output operands may not ``skip'' a register.

 5. Some asm statements may need extra stack space for internal calculations.  This can be guaranteed by clobbering stack registers unrelated to the inputs and outputs.

This asm takes one input, which is internally popped, and produces two outputs.

     asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));

This asm takes two inputs, which are popped by the fyl2xp1 opcode, and replaces them with one output.  The st(1) clobber is necessary for the compiler to know that fyl2xp1 pops both inputs.

     asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");

     [file md.texi not included]

Controlling Names Used in Assembler Code
----------------------------------------

You can specify the name to be used in the assembler code for a C function or variable by writing the asm (or __asm__) keyword after the declarator. It is up to you to make sure that the assembler names you choose do not conflict with any other assembler symbols, or reference registers.

Assembler names for data:
.........................

This sample shows how to specify the assembler name for data:

     int foo asm ("myfoo") = 2;

This specifies that the name to be used for the variable foo in the assembler code should be myfoo rather than the usual _foo.

On systems where an underscore is normally prepended to the name of a C variable, this feature allows you to define names for the linker that do not start with an underscore.

GCC does not support using this feature with a non-static local variable since such variables do not have assembler names.  If you are trying to put the variable in a particular register, see Explicit Reg Vars.

Assembler names for functions:
..............................

To specify the assembler name for functions, write a declaration for the function before its definition and put asm there, like this:

     int func (int x, int y) asm ("MYFUNC");

     int func (int x, int y)
     {
        /* ... */

This specifies that the name to be used for the function func in the assembler code should be MYFUNC.

Variables in Specified Registers
--------------------------------

GNU C allows you to put a few global variables into specified hardware registers.  You can also specify the register in which an ordinary register variable should be allocated.

  * Global register variables reserve registers throughout the program. This may be useful in programs such as programming language interpreters that have a couple of global variables that are accessed very often.

  * Local register variables in specific registers do not reserve the registers, except at the point where they are used as input or output operands in an asm statement and the asm statement itself is not deleted.  The compiler's data flow analysis is capable of determining where the specified registers contain live values, and where they are available for other uses.  Stores into local register variables may be deleted when they appear to be dead according to dataflow analysis.  References to local register variables may be deleted or moved or simplified.

     These local variables are sometimes convenient for use with the extended asm feature (see Extended Asm), if you want to write one output of the assembler instruction directly into a particular register. (This works provided the register you specify fits the constraints specified for that operand in the asm.)

Defining Global Register Variables
..................................

You can define a global register variable in GNU C like this:

     register int *foo asm ("a5");

Here a5 is the name of the register that should be used.  Choose a register that is normally saved and restored by function calls on your machine, so that library routines will not clobber it.

Naturally the register name is CPU-dependent, so you need to conditionalize your program according to CPU type.  The register a5 is a good choice on a 68000 for a variable of pointer type.  On machines with register windows, be sure to choose a ``global'' register that is not affected magically by the function call mechanism.

In addition, different operating systems on the same CPU may differ in how they name the registers; then you need additional conditionals.  For example, some 68000 operating systems call this register %a5.

Eventually there may be a way of asking the compiler to choose a register automatically, but first we need to figure out how it should choose and how to enable you to guide the choice.  No solution is evident.

Defining a global register variable in a certain register reserves that register entirely for this use, at least within the current compilation. The register is not allocated for any other purpose in the functions in the current compilation, and is not saved and restored by these functions.  Stores into this register are never deleted even if they appear to be dead, but references may be deleted or moved or simplified.

It is not safe to access the global register variables from signal handlers, or from more than one thread of control, because the system library routines may temporarily use the register for other things (unless you recompile them specially for the task at hand).

It is not safe for one function that uses a global register variable to call another such function foo by way of a third function lose that is compiled without knowledge of this variable (i.e. in a different source file in which the variable isn't declared).  This is because lose might save the register and put some other value there. For example, you can't expect a global register variable to be available in the comparison-function that you pass to qsort, since qsort might have put something else in that register.  (If you are prepared to recompile qsort with the same global register variable, you can solve this problem.)

If you want to recompile qsort or other source files that do not actually use your global register variable, so that they do not use that register for any other purpose, then it suffices to specify the compiler option -ffixed-REG.  You need not actually add a global register declaration to their source code.

A function that can alter the value of a global register variable cannot safely be called from a function compiled without this variable, because it could clobber the value the caller expects to find there on return. Therefore, the function that is the entry point into the part of the program that uses the global register variable must explicitly save and restore the value that belongs to its caller.

On most machines, longjmp restores to each global register variable the value it had at the time of the setjmp.  On some machines, however, longjmp does not change the value of global register variables.  To be portable, the function that called setjmp should make other arrangements to save the values of the global register variables, and to restore them in a longjmp.  This way, the same thing happens regardless of what longjmp does.

All global register variable declarations must precede all function definitions.  If such a declaration could appear after function definitions, the declaration would be too late to prevent the register from being used for other purposes in the preceding functions.

Global register variables may not have initial values, because an executable file has no means to supply initial contents for a register.

On the SPARC, there are reports that g3 ... g7 are suitable registers, but certain library functions, such as getwd, as well as the subroutines for division and remainder, modify g3 and g4.  g1 and g2 are local temporaries.

On the 68000, a2 ... a5 should be suitable, as should d2 ... d7. Of course, it does not do to use more than a few of those.

Specifying Registers for Local Variables
........................................

You can define a local register variable with a specified register like this:

     register int *foo asm ("a5");

Here a5 is the name of the register that should be used.  Note that this is the same syntax used for defining global register variables, but for a local variable it appears within a function.

Naturally the register name is CPU-dependent, but this is not a problem, since specific registers are most often useful with explicit assembler instructions (see Extended Asm).  Both of these things generally require that you conditionalize your program according to CPU type.

In addition, operating systems on one type of CPU may differ in how they name the registers; then you need additional conditionals.  For example, some 68000 operating systems call this register %a5.

Defining such a register variable does not reserve the register; it remains available for other uses in places where flow control determines the variable's value is not live.

This option does not guarantee that GCC generates code that has this variable in the register you specify at all times.  You may not code an explicit reference to this register in the assembler instruction template part of an asm statement and assume it always refers to this variable. However, using the variable as an input or output operand to the asm guarantees that the specified register is used for that operand. See Extended Asm, for more information.

Stores into local register variables may be deleted when they appear to be dead according to dataflow analysis.  References to local register variables may be deleted or moved or simplified.

As with global register variables, it is recommended that you choose a register that is normally saved and restored by function calls on your machine, so that library routines will not clobber it.

Sometimes when writing inline asm code, you need to make an operand be a specific register, but there's no matching constraint letter for that register. To force the operand into that register, create a local variable and specify the register in the variable's declaration. Then use the local variable for the asm operand and specify any constraint letter that matches the register:

     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = ...;
     register int *result asm ("r0");
     asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

Warning: In the above example, be aware that a register (for example r0) can be call-clobbered by subsequent code, including function calls and library calls for arithmetic operators on other variables (for example the initialization of p2). In this case, use temporary variables for expressions between the register assignments:

     int t1 = ...;
     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = t1;
     register int *result asm ("r0");
     asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

Size of an asm
--------------

Some targets require that GCC track the size of each instruction used in order to generate correct code.  Because the final length of the code produced by an asm statement is only known by the assembler, GCC must make an estimate as to how big it will be.  It does this by counting the number of instructions in the pattern of the asm and multiplying that by the length of the longest instruction supported by that processor.  (When working out the number of instructions, it assumes that any occurrence of a newline or of whatever statement separator character is supported by the assembler -- typically ; --- indicates the end of an instruction.)

Normally, GCC's estimate is adequate to ensure that correct code is generated, but it is possible to confuse the compiler if you use pseudo instructions or assembler macros that expand into multiple real instructions, or if you use assembler directives that expand to more space in the object file than is needed for a single instruction. If this happens then the assembler may produce a diagnostic saying that a label is unreachable.

Alternate Keywords
==================

-ansi and the various -std options disable certain keywords.  This causes trouble when you want to use GNU C extensions, or a general-purpose header file that should be usable by all programs, including ISO C programs.  The keywords asm, typeof and inline are not available in programs compiled with -ansi or -std (although inline can be used in a program compiled with -std=c99 or -std=c11).  The ISO C99 keyword restrict is only available when -std=gnu99 (which will eventually be the default) or -std=c99 (or the equivalent -std=iso9899:1999), or an option for a later standard version, is used.

The way to solve these problems is to put __ at the beginning and end of each problematical keyword.  For example, use __asm__ instead of asm, and __inline__ instead of inline.

Other C compilers won't accept these alternative keywords; if you want to compile with another compiler, you can define the alternate keywords as macros to replace them with the customary keywords.  It looks like this:

     #ifndef __GNUC__
     #define __asm__ asm
     #endif

-pedantic and other options cause warnings for many GNU C extensions. You can prevent such warnings within one expression by writing __extension__ before the expression.  __extension__ has no effect aside from this.

Incomplete enum Types
=====================

You can define an enum tag without specifying its possible values. This results in an incomplete type, much like what you get if you write struct foo without describing the elements.  A later declaration that does specify the possible values completes the type.

You can't allocate variables or storage using the type while it is incomplete.  However, you can work with pointers to that type.

This extension may not be very useful, but it makes the handling of enum more consistent with the way struct and union are handled.

This extension is not supported by GNU C++.

Function Names as Strings
=========================

GCC provides three magic variables that hold the name of the current function, as a string.  The first of these is __func__, which is part of the C99 standard:

The identifier __func__ is implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration

     static const char __func__[] = "function-name";

appeared, where function-name is the name of the lexically-enclosing function.  This name is the unadorned name of the function.

__FUNCTION__ is another name for __func__, provided for backward compatibility with old versions of GCC.

In C, __PRETTY_FUNCTION__ is yet another name for __func__.  However, in C++, __PRETTY_FUNCTION__ contains the type signature of the function as well as its bare name.  For example, this program:

     extern "C" {
     extern int printf (char *, ...);
     }

     class a {
      public:
       void sub (int i)
         {
           printf ("__FUNCTION__ = %s\n", __FUNCTION__);
           printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
         }
     };

     int
     main (void)
     {
       a ax;
       ax.sub (0);
       return 0;
     }

gives this output:

     __FUNCTION__ = sub
     __PRETTY_FUNCTION__ = void a::sub(int)

These identifiers are variables, not preprocessor macros, and may not be used to initialize char arrays or be concatenated with other string literals.

Getting the Return or Frame Address of a Function
=================================================

These functions may be used to get information about the callers of a function.

 -- Built-in Function: void * __builtin_return_address (unsigned int LEVEL)
     This function returns the return address of the current function, or of one of its callers.  The LEVEL argument is number of frames to scan up the call stack.  A value of 0 yields the return address of the current function, a value of 1 yields the return address of the caller of the current function, and so forth.  When inlining the expected behavior is that the function returns the address of the function that is returned to.  To work around this behavior use the noinline function attribute.

     The LEVEL argument must be a constant integer.

     On some machines it may be impossible to determine the return address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function returns 0 or a random value.  In addition, __builtin_frame_address may be used to determine if the top of the stack has been reached.

     Additional post-processing of the returned value may be needed, see __builtin_extract_return_addr.

     Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program.  As a result, calls that are considered unsafe are diagnosed when the -Wframe-address option is in effect.  Such calls should only be made in debugging situations.

 -- Built-in Function: void * __builtin_extract_return_addr (void *ADDR)
     The address as returned by __builtin_return_address may have to be fed through this function to get the actual encoded address.  For example, on the 31-bit S/390 platform the highest bit has to be masked out, or on SPARC platforms an offset has to be added for the true next instruction to be executed.

     If no fixup is needed, this function simply passes through ADDR.

 -- Built-in Function: void * __builtin_frob_return_address (void *ADDR)
     This function does the reverse of __builtin_extract_return_addr.

 -- Built-in Function: void * __builtin_frame_address (unsigned int LEVEL)
     This function is similar to __builtin_return_address, but it returns the address of the function frame rather than the return address of the function.  Calling __builtin_frame_address with a value of 0 yields the frame address of the current function, a value of 1 yields the frame address of the caller of the current function, and so forth.

     The frame is the area on the stack that holds local variables and saved registers.  The frame address is normally the address of the first word pushed on to the stack by the function.  However, the exact definition depends upon the processor and the calling convention.  If the processor has a dedicated frame pointer register, and the function has a frame, then __builtin_frame_address returns the value of the frame pointer register.

     On some machines it may be impossible to determine the frame address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function returns 0 if the first frame pointer is properly initialized by the startup code.

     Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program.  As a result, calls that are considered unsafe are diagnosed when the -Wframe-address option is in effect.  Such calls should only be made in debugging situations.

Using Vector Instructions through Built-in Functions
====================================================

On some targets, the instruction set contains SIMD vector instructions which operate on multiple values contained in one large register at the same time. For example, on the x86 the MMX, 3DNow! and SSE extensions can be used this way.

The first step in using these extensions is to provide the necessary data types.  This should be done using an appropriate typedef:

     typedef int v4si __attribute__ ((vector_size (16)));

The int type specifies the base type, while the attribute specifies the vector size for the variable, measured in bytes.  For example, the declaration above causes the compiler to set the mode for the v4si type to be 16 bytes wide and divided into int sized units.  For a 32-bit int this means a vector of 4 units of 4 bytes, and the corresponding mode of foo is V4SI.

The vector_size attribute is only applicable to integral and float scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct. Only sizes that are a power of two are currently allowed.

All the basic integer types can be used as base types, both as signed and as unsigned: char, short, int, long, long long.  In addition, float and double can be used to build floating-point vector types.

Specifying a combination that is not valid for the current architecture causes GCC to synthesize the instructions using a narrower mode. For example, if you specify a variable of type V4SI and your architecture does not allow for this specific SIMD type, GCC produces code that uses 4 SIs.

The types defined in this manner can be used with a subset of normal C operations.  Currently, GCC allows using the following operators on these types: +, -, *, /, unary minus, ^, |, &, ~, %.

The operations behave like C++ valarrays.  Addition is defined as the addition of the corresponding elements of the operands.  For example, in the code below, each of the 4 elements in A is added to the corresponding 4 elements in B and the resulting vector is stored in C.

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a, b, c;

     c = a + b;

Subtraction, multiplication, division, and the logical operations operate in a similar manner.  Likewise, the result of using the unary minus or complement operators on a vector type is a vector whose elements are the negative or complemented values of the corresponding elements in the operand.

It is possible to use shifting operators <<, >> on integer-type vectors. The operation is defined as following: {a0, a1, ..., an} >> {b0, b1, ..., bn} == {a0 >> b0, a1 >> b1, ..., an >> bn}. Vector operands must have the same number of elements.

For convenience, it is allowed to use a binary vector operation where one operand is a scalar. In that case the compiler transforms the scalar operand into a vector where each element is the scalar from the operation. The transformation happens only if the scalar could be safely converted to the vector-element type. Consider the following code.

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a, b, c;
     long l;

     a = b + 1;    /* a = b + {1,1,1,1}; */
     a = 2 * b;    /* a = {2,2,2,2} * b; */

     a = l + a;    /* Error, cannot convert long to int. */

Vectors can be subscripted as if the vector were an array with the same number of elements and base type.  Out of bound accesses invoke undefined behavior at run time.  Warnings for out of bound accesses for vector subscription can be enabled with -Warray-bounds.

Vector comparison is supported with standard comparison operators: ==, !=, <, <=, >, >=. Comparison operands can be vector expressions of integer-type or real-type. Comparison between integer-type vectors and real-type vectors are not supported.  The result of the comparison is a vector of the same width and number of elements as the comparison operands with a signed integral element type.

Vectors are compared element-wise producing 0 when comparison is false and -1 (constant of the appropriate type where all bits are set) otherwise. Consider the following example.

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a = {1,2,3,4};
     v4si b = {3,2,1,4};
     v4si c;

     c = a >  b;     /* The result would be {0, 0,-1, 0}  */
     c = a == b;     /* The result would be {0,-1, 0,-1}  */

In C++, the ternary operator ?: is available. a?b:c, where b and c are vectors of the same type and a is an integer vector with the same number of elements of the same size as b and c, computes all three arguments and creates a vector {a[0]?b[0]:c[0], a[1]?b[1]:c[1], ...}.  Note that unlike in OpenCL, a is thus interpreted as a != 0 and not a < 0. As in the case of binary operations, this syntax is also accepted when one of b or c is a scalar that is then transformed into a vector. If both b and c are scalars and the type of true?b:c has the same size as the element type of a, then b and c are converted to a vector type whose elements have this type and with the same number of elements as a.

In C++, the logic operators !, &&, || are available for vectors. !v is equivalent to v == 0, a && b is equivalent to a!=0 & b!=0 and a || b is equivalent to a!=0 | b!=0. For mixed operations between a scalar s and a vector v, s && v is equivalent to s?v!=0:0 (the evaluation is short-circuit) and v && s is equivalent to v!=0 & (s?-1:0).

Vector shuffling is available using functions __builtin_shuffle (vec, mask) and __builtin_shuffle (vec0, vec1, mask). Both functions construct a permutation of elements from one or two vectors and return a vector of the same type as the input vector(s). The MASK is an integral vector with the same width (W) and element count (N) as the output vector.

The elements of the input vectors are numbered in memory ordering of VEC0 beginning at 0 and VEC1 beginning at N.  The elements of MASK are considered modulo N in the single-operand case and modulo 2*N in the two-operand case.

Consider the following example,

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a = {1,2,3,4};
     v4si b = {5,6,7,8};
     v4si mask1 = {0,1,1,3};
     v4si mask2 = {0,4,2,5};
     v4si res;

     res = __builtin_shuffle (a, mask1);       /* res is {1,2,2,4}  */
     res = __builtin_shuffle (a, b, mask2);    /* res is {1,5,3,6}  */

Note that __builtin_shuffle is intentionally semantically compatible with the OpenCL shuffle and shuffle2 functions.

You can declare variables and use them in function calls and returns, as well as in assignments and some casts.  You can specify a vector type as a return type for a function.  Vector types can also be used as function arguments.  It is possible to cast from one vector type to another, provided they are of the same size (in fact, you can also cast vectors to and from other datatypes of the same size).

You cannot operate between vectors of different lengths or different signedness without a cast.

Support for offsetof
====================

GCC implements for both C and C++ a syntactic extension to implement the offsetof macro.

     primary:
             "__builtin_offsetof" "(" typename "," offsetof_member_designator ")"

     offsetof_member_designator:
               identifier
             | offsetof_member_designator "." identifier
             | offsetof_member_designator "[" expr "]"

This extension is sufficient such that

     #define offsetof(TYPE, MEMBER)  __builtin_offsetof (TYPE, MEMBER)

is a suitable definition of the offsetof macro.  In C++, TYPE may be dependent.  In either case, MEMBER may consist of a single identifier, or a sequence of member accesses and array references.

Legacy __sync Built-in Functions for Atomic Memory Access
=========================================================

The following built-in functions are intended to be compatible with those described in the Intel Itanium Processor-specific Application Binary Interface, section 7.4.  As such, they depart from normal GCC practice by not using the __builtin_ prefix and also by being overloaded so that they work on multiple types.

The definition given in the Intel documentation allows only for the use of the types int, long, long long or their unsigned counterparts.  GCC allows any integral scalar or pointer type that is 1, 2, 4 or 8 bytes in length.

These functions are implemented in terms of the __atomic builtins (see __atomic Builtins).  They should not be used for new code which should use the __atomic builtins instead.

Not all operations are supported by all target processors.  If a particular operation cannot be implemented on the target processor, a warning is generated and a call to an external function is generated.  The external function carries the same name as the built-in version, with an additional suffix _N where N is the size of the data type.

In most cases, these built-in functions are considered a full barrier. That is, no memory operand is moved across the operation, either forward or backward.  Further, instructions are issued as necessary to prevent the processor from speculating loads across the operation and from queuing stores after the operation.

All of the routines are described in the Intel documentation to take ``an optional list of variables protected by the memory barrier''.  It's not clear what is meant by that; it could mean that only the listed variables are protected, or it could mean a list of additional variables to be protected.  The list is ignored by GCC which treats it as empty.  GCC interprets an empty list as meaning that all globally accessible variables should be protected.

TYPE __sync_fetch_and_add (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_sub (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_or (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_and (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_xor (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_nand (TYPE *ptr, TYPE value, ...)
     These built-in functions perform the operation suggested by the name, and returns the value that had previously been in memory.  That is,

          { tmp = *ptr; *ptr OP= value; return tmp; }
          { tmp = *ptr; *ptr = ~(tmp & value); return tmp; }   // nand

     Note: GCC 4.4 and later implement __sync_fetch_and_nand as *ptr = ~(tmp & value) instead of *ptr = ~tmp & value.

TYPE __sync_add_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_sub_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_or_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_and_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_xor_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_nand_and_fetch (TYPE *ptr, TYPE value, ...)
     These built-in functions perform the operation suggested by the name, and return the new value.  That is,

          { *ptr OP= value; return *ptr; }
          { *ptr = ~(*ptr & value); return *ptr; }   // nand

     Note: GCC 4.4 and later implement __sync_nand_and_fetch as *ptr = ~(*ptr & value) instead of *ptr = ~*ptr & value.

bool __sync_bool_compare_and_swap (TYPE *ptr, TYPE oldval, TYPE newval, ...)
TYPE __sync_val_compare_and_swap (TYPE *ptr, TYPE oldval, TYPE newval, ...)
     These built-in functions perform an atomic compare and swap. That is, if the current value of *PTR is OLDVAL, then write NEWVAL into *PTR.

     The ``bool'' version returns true if the comparison is successful and NEWVAL is written.  The ``val'' version returns the contents of *PTR before the operation.

__sync_synchronize (...)
     This built-in function issues a full memory barrier.

TYPE __sync_lock_test_and_set (TYPE *ptr, TYPE value, ...)
     This built-in function, as described by Intel, is not a traditional test-and-set operation, but rather an atomic exchange operation.  It writes VALUE into *PTR, and returns the previous contents of *PTR.

     Many targets have only minimal support for such locks, and do not support a full exchange operation.  In this case, a target may support reduced functionality here by which the only valid value to store is the immediate constant 1.  The exact value actually stored in *PTR is implementation defined.

     This built-in function is not a full barrier, but rather an acquire barrier. This means that references after the operation cannot move to (or be speculated to) before the operation, but previous memory stores may not be globally visible yet, and previous memory loads may not yet be satisfied.

void __sync_lock_release (TYPE *ptr, ...)
     This built-in function releases the lock acquired by __sync_lock_test_and_set. Normally this means writing the constant 0 to *PTR.

     This built-in function is not a full barrier, but rather a release barrier. This means that all previous memory stores are globally visible, and all previous memory loads have been satisfied, but following memory reads are not prevented from being speculated to before the barrier.

Built-in Functions for Memory Model Aware Atomic Operations
===========================================================

The following built-in functions approximately match the requirements for the C++11 memory model.  They are all identified by being prefixed with __atomic and most are overloaded so that they work with multiple types.

These functions are intended to replace the legacy __sync builtins.  The main difference is that the memory order that is requested is a parameter to the functions.  New code should always use the __atomic builtins rather than the __sync builtins.

Note that the __atomic builtins assume that programs will conform to the C++11 memory model.  In particular, they assume that programs are free of data races.  See the C++11 standard for detailed requirements.

The __atomic builtins can be used with any integral scalar or pointer type that is 1, 2, 4, or 8 bytes in length.  16-byte integral types are also allowed if __int128 (see __int128) is supported by the architecture.

The four non-arithmetic functions (load, store, exchange, and compare_exchange) all have a generic version as well.  This generic version works on any data type.  It uses the lock-free built-in function if the specific data type size makes that possible; otherwise, an external call is left to be resolved at run time.  This external call is the same format with the addition of a size_t parameter inserted as the first parameter indicating the size of the object being pointed to. All objects must be the same size.

There are 6 different memory orders that can be specified.  These map to the C++11 memory orders with the same names, see the C++11 standard or the GCC wiki on atomic synchronization (http://gcc.gnu.org/wiki/Atomic/GCCMM/AtomicSync) for detailed definitions.  Individual targets may also support additional memory orders for use on specific architectures.  Refer to the target documentation for details of these.

An atomic operation can both constrain code motion and be mapped to hardware instructions for synchronization between threads (e.g., a fence).  To which extent this happens is controlled by the memory orders, which are listed here in approximately ascending order of strength.  The description of each memory order is only meant to roughly illustrate the effects and is not a specification; see the C++11 memory model for precise semantics.

__ATOMIC_RELAXED
     Implies no inter-thread ordering constraints.

__ATOMIC_CONSUME
     This is currently implemented using the stronger __ATOMIC_ACQUIRE memory order because of a deficiency in C++11's semantics for memory_order_consume.

__ATOMIC_ACQUIRE
     Creates an inter-thread happens-before constraint from the release (or stronger) semantic store to this acquire load.  Can prevent hoisting of code to before the operation.

__ATOMIC_RELEASE
     Creates an inter-thread happens-before constraint to acquire (or stronger) semantic loads that read from this release store.  Can prevent sinking of code to after the operation.

__ATOMIC_ACQ_REL
     Combines the effects of both __ATOMIC_ACQUIRE and __ATOMIC_RELEASE.

__ATOMIC_SEQ_CST
     Enforces total ordering with all other __ATOMIC_SEQ_CST operations.

Note that in the C++11 memory model, fences (e.g., __atomic_thread_fence) take effect in combination with other atomic operations on specific memory locations (e.g., atomic loads); operations on specific memory locations do not necessarily affect other operations in the same way.

Target architectures are encouraged to provide their own patterns for each of the atomic built-in functions.  If no target is provided, the original non-memory model set of __sync atomic built-in functions are used, along with any required synchronization fences surrounding it in order to achieve the proper behavior.  Execution in this case is subject to the same restrictions as those built-in functions.

If there is no pattern or mechanism to provide a lock-free instruction sequence, a call is made to an external routine with the same parameters to be resolved at run time.

When implementing patterns for these built-in functions, the memory order parameter can be ignored as long as the pattern implements the most restrictive __ATOMIC_SEQ_CST memory order.  Any of the other memory orders execute correctly with this memory order but they may not execute as efficiently as they could with a more appropriate implementation of the relaxed requirements.

Note that the C++11 standard allows for the memory order parameter to be determined at run time rather than at compile time.  These built-in functions map any run-time value to __ATOMIC_SEQ_CST rather than invoke a runtime library call or inline a switch statement.  This is standard compliant, safe, and the simplest approach for now.

The memory order parameter is a signed int, but only the lower 16 bits are reserved for the memory order.  The remainder of the signed int is reserved for target use and should be 0.  Use of the predefined atomic values ensures proper usage.

 -- Built-in Function: TYPE __atomic_load_n (TYPE *ptr, int memorder)
     This built-in function implements an atomic load operation.  It returns the contents of *PTR.

     The valid memory order variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, __ATOMIC_ACQUIRE, and __ATOMIC_CONSUME.

 -- Built-in Function: void __atomic_load (TYPE *ptr, TYPE *ret, int memorder)
     This is the generic version of an atomic load.  It returns the contents of *PTR in *RET.

 -- Built-in Function: void __atomic_store_n (TYPE *ptr, TYPE val, int memorder)
     This built-in function implements an atomic store operation.  It writes VAL into *PTR.

     The valid memory order variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, and __ATOMIC_RELEASE.

 -- Built-in Function: void __atomic_store (TYPE *ptr, TYPE *val, int memorder)
     This is the generic version of an atomic store.  It stores the value of *VAL into *PTR.

 -- Built-in Function: TYPE __atomic_exchange_n (TYPE *ptr, TYPE val, int memorder)
     This built-in function implements an atomic exchange operation.  It writes VAL into *PTR, and returns the previous contents of *PTR.

     The valid memory order variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, __ATOMIC_ACQUIRE, __ATOMIC_RELEASE, and __ATOMIC_ACQ_REL.

 -- Built-in Function: void __atomic_exchange (TYPE *ptr, TYPE *val, TYPE *ret, int memorder)
     This is the generic version of an atomic exchange.  It stores the contents of *VAL into *PTR. The original value of *PTR is copied into *RET.

 -- Built-in Function: bool __atomic_compare_exchange_n (TYPE *ptr, TYPE *expected, TYPE desired, bool weak, int success_memorder, int failure_memorder)
     This built-in function implements an atomic compare and exchange operation. This compares the contents of *PTR with the contents of *EXPECTED. If equal, the operation is a read-modify-write operation that writes DESIRED into *PTR.  If they are not equal, the operation is a read and the current contents of *PTR is written into *EXPECTED.  WEAK is true for weak compare_exchange, and false for the strong variation.  Many targets only offer the strong variation and ignore the parameter.  When in doubt, use the strong variation.

     True is returned if DESIRED is written into *PTR and the operation is considered to conform to the memory order specified by SUCCESS_MEMORDER.  There are no restrictions on what memory order can be used here.

     False is returned otherwise, and the operation is considered to conform to FAILURE_MEMORDER. This memory order cannot be __ATOMIC_RELEASE nor __ATOMIC_ACQ_REL.  It also cannot be a stronger order than that specified by SUCCESS_MEMORDER.

 -- Built-in Function: bool __atomic_compare_exchange (TYPE *ptr, TYPE *expected, TYPE *desired, bool weak, int success_memorder, int failure_memorder)
     This built-in function implements the generic version of __atomic_compare_exchange.  The function is virtually identical to __atomic_compare_exchange_n, except the desired value is also a pointer.

 -- Built-in Function: TYPE __atomic_add_fetch (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_sub_fetch (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_and_fetch (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_xor_fetch (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_or_fetch (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_nand_fetch (TYPE *ptr, TYPE val, int memorder)
     These built-in functions perform the operation suggested by the name, and return the result of the operation. That is,

          { *ptr OP= val; return *ptr; }

     All memory orders are valid.

 -- Built-in Function: TYPE __atomic_fetch_add (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_fetch_sub (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_fetch_and (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_fetch_xor (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_fetch_or (TYPE *ptr, TYPE val, int memorder)
 -- Built-in Function: TYPE __atomic_fetch_nand (TYPE *ptr, TYPE val, int memorder)
     These built-in functions perform the operation suggested by the name, and return the value that had previously been in *PTR.  That is,

          { tmp = *ptr; *ptr OP= val; return tmp; }

     All memory orders are valid.

 -- Built-in Function: bool __atomic_test_and_set (void *ptr, int memorder)

     This built-in function performs an atomic test-and-set operation on the byte at *PTR.  The byte is set to some implementation defined nonzero ``set'' value and the return value is true if and only if the previous contents were ``set''. It should be only used for operands of type bool or char. For other types only part of the value may be set.

     All memory orders are valid.

 -- Built-in Function: void __atomic_clear (bool *ptr, int memorder)

     This built-in function performs an atomic clear operation on *PTR.  After the operation, *PTR contains 0. It should be only used for operands of type bool or char and in conjunction with __atomic_test_and_set. For other types it may only clear partially. If the type is not bool prefer using __atomic_store.

     The valid memory order variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, and __ATOMIC_RELEASE.

 -- Built-in Function: void __atomic_thread_fence (int memorder)

     This built-in function acts as a synchronization fence between threads based on the specified memory order.

     All memory orders are valid.

 -- Built-in Function: void __atomic_signal_fence (int memorder)

     This built-in function acts as a synchronization fence between a thread and signal handlers based in the same thread.

     All memory orders are valid.

 -- Built-in Function: bool __atomic_always_lock_free (size_t size, void *ptr)

     This built-in function returns true if objects of SIZE bytes always generate lock-free atomic instructions for the target architecture. SIZE must resolve to a compile-time constant and the result also resolves to a compile-time constant.

     PTR is an optional pointer to the object that may be used to determine alignment.  A value of 0 indicates typical alignment should be used.  The compiler may also ignore this parameter.

          if (_atomic_always_lock_free (sizeof (long long), 0))

 -- Built-in Function: bool __atomic_is_lock_free (size_t size, void *ptr)

     This built-in function returns true if objects of SIZE bytes always generate lock-free atomic instructions for the target architecture.  If the built-in function is not known to be lock-free, a call is made to a runtime routine named __atomic_is_lock_free.

     PTR is an optional pointer to the object that may be used to determine alignment.  A value of 0 indicates typical alignment should be used.  The compiler may also ignore this parameter.

Built-in Functions to Perform Arithmetic with Overflow Checking
===============================================================

The following built-in functions allow performing simple arithmetic operations together with checking whether the operations overflowed.

 -- Built-in Function: bool __builtin_add_overflow (TYPE1 a, TYPE2 b, TYPE3 *res)
 -- Built-in Function: bool __builtin_sadd_overflow (int a, int b, int *res)
 -- Built-in Function: bool __builtin_saddl_overflow (long int a, long int b, long int *res)
 -- Built-in Function: bool __builtin_saddll_overflow (long long int a, long long int b, long int *res)
 -- Built-in Function: bool __builtin_uadd_overflow (unsigned int a, unsigned int b, unsigned int *res)
 -- Built-in Function: bool __builtin_uaddl_overflow (unsigned long int a, unsigned long int b, unsigned long int *res)
 -- Built-in Function: bool __builtin_uaddll_overflow (unsigned long long int a, unsigned long long int b, unsigned long int *res)

     These built-in functions promote the first two operands into infinite precision signed type and perform addition on those promoted operands.  The result is then cast to the type the third pointer argument points to and stored there. If the stored result is equal to the infinite precision result, the built-in functions return false, otherwise they return true.  As the addition is performed in infinite signed precision, these built-in functions have fully defined behavior for all argument values.

     The first built-in function allows arbitrary integral types for operands and the result type must be pointer to some integer type, the rest of the built-in functions have explicit integer types.

     The compiler will attempt to use hardware instructions to implement these built-in functions where possible, like conditional jump on overflow after addition, conditional jump on carry etc.

 -- Built-in Function: bool __builtin_sub_overflow (TYPE1 a, TYPE2 b, TYPE3 *res)
 -- Built-in Function: bool __builtin_ssub_overflow (int a, int b, int *res)
 -- Built-in Function: bool __builtin_ssubl_overflow (long int a, long int b, long int *res)
 -- Built-in Function: bool __builtin_ssubll_overflow (long long int a, long long int b, long int *res)
 -- Built-in Function: bool __builtin_usub_overflow (unsigned int a, unsigned int b, unsigned int *res)
 -- Built-in Function: bool __builtin_usubl_overflow (unsigned long int a, unsigned long int b, unsigned long int *res)
 -- Built-in Function: bool __builtin_usubll_overflow (unsigned long long int a, unsigned long long int b, unsigned long int *res)

     These built-in functions are similar to the add overflow checking built-in functions above, except they perform subtraction, subtract the second argument from the first one, instead of addition.

 -- Built-in Function: bool __builtin_mul_overflow (TYPE1 a, TYPE2 b, TYPE3 *res)
 -- Built-in Function: bool __builtin_smul_overflow (int a, int b, int *res)
 -- Built-in Function: bool __builtin_smull_overflow (long int a, long int b, long int *res)
 -- Built-in Function: bool __builtin_smulll_overflow (long long int a, long long int b, long int *res)
 -- Built-in Function: bool __builtin_umul_overflow (unsigned int a, unsigned int b, unsigned int *res)
 -- Built-in Function: bool __builtin_umull_overflow (unsigned long int a, unsigned long int b, unsigned long int *res)
 -- Built-in Function: bool __builtin_umulll_overflow (unsigned long long int a, unsigned long long int b, unsigned long int *res)

     These built-in functions are similar to the add overflow checking built-in functions above, except they perform multiplication, instead of addition.

x86-Specific Memory Model Extensions for Transactional Memory
=============================================================

The x86 architecture supports additional memory ordering flags to mark lock critical sections for hardware lock elision. These must be specified in addition to an existing memory order to atomic intrinsics.

__ATOMIC_HLE_ACQUIRE
     Start lock elision on a lock variable. Memory order must be __ATOMIC_ACQUIRE or stronger.

__ATOMIC_HLE_RELEASE
     End lock elision on a lock variable. Memory order must be __ATOMIC_RELEASE or stronger.

When a lock acquire fails, it is required for good performance to abort the transaction quickly. This can be done with a _mm_pause.

     #include <immintrin.h> // For _mm_pause

     int lockvar;

     /* Acquire lock with lock elision */
     while (__atomic_exchange_n(&lockvar, 1, __ATOMIC_ACQUIRE|__ATOMIC_HLE_ACQUIRE))
         _mm_pause(); /* Abort failed transaction */
     ...
     /* Free lock with lock elision */
     __atomic_store_n(&lockvar, 0, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE);

Object Size Checking Built-in Functions
=======================================

GCC implements a limited buffer overflow protection mechanism that can prevent some buffer overflow attacks.

 -- Built-in Function: size_t __builtin_object_size (void * PTR, int TYPE)
     is a built-in construct that returns a constant number of bytes from PTR to the end of the object PTR pointer points to (if known at compile time).  __builtin_object_size never evaluates its arguments for side-effects.  If there are any side-effects in them, it returns (size_t) -1 for TYPE 0 or 1 and (size_t) 0 for TYPE 2 or 3.  If there are multiple objects PTR can point to and all of them are known at compile time, the returned number is the maximum of remaining byte counts in those objects if TYPE & 2 is 0 and minimum if nonzero.  If it is not possible to determine which objects PTR points to at compile time, __builtin_object_size should return (size_t) -1 for TYPE 0 or 1 and (size_t) 0 for TYPE 2 or 3.

     TYPE is an integer constant from 0 to 3.  If the least significant bit is clear, objects are whole variables, if it is set, a closest surrounding subobject is considered the object a pointer points to. The second bit determines if maximum or minimum of remaining bytes is computed.

          struct V { char buf1[10]; int b; char buf2[10]; } var;
          char *p = &var.buf1[1], *q = &var.b;

          /* Here the object p points to is var.  */
          assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
          /* The subobject p points to is var.buf1.  */
          assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
          /* The object q points to is var.  */
          assert (__builtin_object_size (q, 0)
                  == (char *) (&var + 1) - (char *) &var.b);
          /* The subobject q points to is var.b.  */
          assert (__builtin_object_size (q, 1) == sizeof (var.b));

There are built-in functions added for many common string operation functions, e.g., for memcpy __builtin___memcpy_chk built-in is provided.  This built-in has an additional last argument, which is the number of bytes remaining in object the DEST argument points to or (size_t) -1 if the size is not known.

The built-in functions are optimized into the normal string functions like memcpy if the last argument is (size_t) -1 or if it is known at compile time that the destination object will not be overflown.  If the compiler can determine at compile time the object will be always overflown, it issues a warning.

The intended use can be e.g.

     #undef memcpy
     #define bos0(dest) __builtin_object_size (dest, 0)
     #define memcpy(dest, src, n) \
       __builtin___memcpy_chk (dest, src, n, bos0 (dest))

     char *volatile p;
     char buf[10];
     /* It is unknown what object p points to, so this is optimized
        into plain memcpy - no checking is possible.  */
     memcpy (p, "abcde", n);
     /* Destination is known and length too.  It is known at compile
        time there will be no overflow.  */
     memcpy (&buf[5], "abcde", 5);
     /* Destination is known, but the length is not known at compile time.
        This will result in __memcpy_chk call that can check for overflow
        at run time.  */
     memcpy (&buf[5], "abcde", n);
     /* Destination is known and it is known at compile time there will
        be overflow.  There will be a warning and __memcpy_chk call that
        will abort the program at run time.  */
     memcpy (&buf[6], "abcde", 5);

Such built-in functions are provided for memcpy, mempcpy, memmove, memset, strcpy, stpcpy, strncpy, strcat and strncat.

There are also checking built-in functions for formatted output functions.

     int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
     int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                                   const char *fmt, ...);
     int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
                                   va_list ap);
     int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                                    const char *fmt, va_list ap);

The added FLAG argument is passed unchanged to __sprintf_chk etc. functions and can contain implementation specific flags on what additional security measures the checking function might take, such as handling %n differently.

The OS argument is the object size S points to, like in the other built-in functions.  There is a small difference in the behavior though, if OS is (size_t) -1, the built-in functions are optimized into the non-checking functions only if FLAG is 0, otherwise the checking function is called with OS argument set to (size_t) -1.

In addition to this, there are checking built-in functions __builtin___printf_chk, __builtin___vprintf_chk, __builtin___fprintf_chk and __builtin___vfprintf_chk. These have just one additional argument, FLAG, right before format string FMT.  If the compiler is able to optimize them to fputc etc. functions, it does, otherwise the checking function is called and the FLAG argument passed to it.

Pointer Bounds Checker Built-in Functions
=========================================

GCC provides a set of built-in functions to control Pointer Bounds Checker instrumentation.  Note that all Pointer Bounds Checker builtins can be used even if you compile with Pointer Bounds Checker off (-fno-check-pointer-bounds). The behavior may differ in such case as documented below.

 -- Built-in Function: void * __builtin___bnd_set_ptr_bounds (const void *Q, size_t SIZE)

     This built-in function returns a new pointer with the value of Q, and associate it with the bounds [Q, Q+SIZE-1].  With Pointer Bounds Checker off, the built-in function just returns the first argument.

          extern void *__wrap_malloc (size_t n)
          {
            void *p = (void *)__real_malloc (n);
            if (!p) return __builtin___bnd_null_ptr_bounds (p);
            return __builtin___bnd_set_ptr_bounds (p, n);
          }

 -- Built-in Function: void * __builtin___bnd_narrow_ptr_bounds (const void *P, const void *Q, size_t SIZE)

     This built-in function returns a new pointer with the value of P and associates it with the narrowed bounds formed by the intersection of bounds associated with Q and the bounds [P, P + SIZE - 1]. With Pointer Bounds Checker off, the built-in function just returns the first argument.

          void init_objects (object *objs, size_t size)
          {
            size_t i;
            /* Initialize objects one-by-one passing pointers with bounds of
               an object, not the full array of objects.  */
            for (i = 0; i < size; i++)
              init_object (__builtin___bnd_narrow_ptr_bounds (objs + i, objs,
                                                              sizeof(object)));
          }

 -- Built-in Function: void * __builtin___bnd_copy_ptr_bounds (const void *Q, const void *R)

     This built-in function returns a new pointer with the value of Q, and associates it with the bounds already associated with pointer R. With Pointer Bounds Checker off, the built-in function just returns the first argument.

          /* Here is a way to get pointer to object's field but
             still with the full object's bounds.  */
          int *field_ptr = __builtin___bnd_copy_ptr_bounds (&objptr->int_field,
                                                            objptr);

 -- Built-in Function: void * __builtin___bnd_init_ptr_bounds (const void *Q)

     This built-in function returns a new pointer with the value of Q, and associates it with INIT (allowing full memory access) bounds. With Pointer Bounds Checker off, the built-in function just returns the first argument.

 -- Built-in Function: void * __builtin___bnd_null_ptr_bounds (const void *Q)

     This built-in function returns a new pointer with the value of Q, and associates it with NULL (allowing no memory access) bounds. With Pointer Bounds Checker off, the built-in function just returns the first argument.

 -- Built-in Function: void __builtin___bnd_store_ptr_bounds (const void **PTR_ADDR, const void *PTR_VAL)

     This built-in function stores the bounds associated with pointer PTR_VAL and location PTR_ADDR into Bounds Table.  This can be useful to propagate bounds from legacy code without touching the associated pointer's memory when pointers are copied as integers.  With Pointer Bounds Checker off, the built-in function call is ignored.

 -- Built-in Function: void __builtin___bnd_chk_ptr_lbounds (const void *Q)

     This built-in function checks if the pointer Q is within the lower bound of its associated bounds.  With Pointer Bounds Checker off, the built-in function call is ignored.

          extern void *__wrap_memset (void *dst, int c, size_t len)
          {
            if (len > 0)
              {
                __builtin___bnd_chk_ptr_lbounds (dst);
                __builtin___bnd_chk_ptr_ubounds ((char *)dst + len - 1);
                __real_memset (dst, c, len);
              }
            return dst;
          }

 -- Built-in Function: void __builtin___bnd_chk_ptr_ubounds (const void *Q)

     This built-in function checks if the pointer Q is within the upper bound of its associated bounds.  With Pointer Bounds Checker off, the built-in function call is ignored.

 -- Built-in Function: void __builtin___bnd_chk_ptr_bounds (const void *Q, size_t SIZE)

     This built-in function checks if [Q, Q + SIZE - 1] is within the lower and upper bounds associated with Q.  With Pointer Bounds Checker off, the built-in function call is ignored.

          extern void *__wrap_memcpy (void *dst, const void *src, size_t n)
          {
            if (n > 0)
              {
                __bnd_chk_ptr_bounds (dst, n);
                __bnd_chk_ptr_bounds (src, n);
                __real_memcpy (dst, src, n);
              }
            return dst;
          }

 -- Built-in Function: const void * __builtin___bnd_get_ptr_lbound (const void *Q)

     This built-in function returns the lower bound associated with the pointer Q, as a pointer value. This is useful for debugging using printf. With Pointer Bounds Checker off, the built-in function returns 0.

          void *lb = __builtin___bnd_get_ptr_lbound (q);
          void *ub = __builtin___bnd_get_ptr_ubound (q);
          printf ("q = %p  lb(q) = %p  ub(q) = %p", q, lb, ub);

 -- Built-in Function: const void * __builtin___bnd_get_ptr_ubound (const void *Q)

     This built-in function returns the upper bound (which is a pointer) associated with the pointer Q.  With Pointer Bounds Checker off, the built-in function returns -1.

Cilk Plus C/C++ Language Extension Built-in Functions
=====================================================

GCC provides support for the following built-in reduction functions if Cilk Plus is enabled. Cilk Plus can be enabled using the -fcilkplus flag.

  * __sec_implicit_index

  * __sec_reduce

  * __sec_reduce_add

  * __sec_reduce_all_nonzero

  * __sec_reduce_all_zero

  * __sec_reduce_any_nonzero

  * __sec_reduce_any_zero

  * __sec_reduce_max

  * __sec_reduce_min

  * __sec_reduce_max_ind

  * __sec_reduce_min_ind

  * __sec_reduce_mul

  * __sec_reduce_mutating

Further details and examples about these built-in functions are described in the Cilk Plus language manual which can be found at http://www.cilkplus.org.

Other Built-in Functions Provided by GCC
========================================

GCC provides a large number of built-in functions other than the ones mentioned above.  Some of these are for internal use in the processing of exceptions or variable-length argument lists and are not documented here because they may change from time to time; we do not recommend general use of these functions.

The remaining functions are provided for optimization purposes.

With the exception of built-ins that have library equivalents such as the standard C library functions discussed below, or that expand to library calls, GCC built-in functions are always expanded inline and thus do not have corresponding entry points and their address cannot be obtained.  Attempting to use them in an expression other than a function call results in a compile-time error.

GCC includes built-in versions of many of the functions in the standard C library.  These functions come in two forms: one whose names start with the __builtin_ prefix, and the other without.  Both forms have the same type (including prototype), the same address (when their address is taken), and the same meaning as the C library functions even if you specify the -fno-builtin option see C Dialect Options).  Many of these functions are only optimized in certain cases; if they are not optimized in a particular case, a call to the library function is emitted.

Outside strict ISO C mode (-ansi, -std=c90, -std=c99 or -std=c11), the functions _exit, alloca, bcmp, bzero, dcgettext, dgettext, dremf, dreml, drem, exp10f, exp10l, exp10, ffsll, ffsl, ffs, fprintf_unlocked, fputs_unlocked, gammaf, gammal, gamma, gammaf_r, gammal_r, gamma_r, gettext, index, isascii, j0f, j0l, j0, j1f, j1l, j1, jnf, jnl, jn, lgammaf_r, lgammal_r, lgamma_r, mempcpy, pow10f, pow10l, pow10, printf_unlocked, rindex, scalbf, scalbl, scalb, signbit, signbitf, signbitl, signbitd32, signbitd64, signbitd128, significandf, significandl, significand, sincosf, sincosl, sincos, stpcpy, stpncpy, strcasecmp, strdup, strfmon, strncasecmp, strndup, toascii, y0f, y0l, y0, y1f, y1l, y1, ynf, ynl and yn may be handled as built-in functions. All these functions have corresponding versions prefixed with __builtin_, which may be used even in strict C90 mode.

The ISO C99 functions _Exit, acoshf, acoshl, acosh, asinhf, asinhl, asinh, atanhf, atanhl, atanh, cabsf, cabsl, cabs, cacosf, cacoshf, cacoshl, cacosh, cacosl, cacos, cargf, cargl, carg, casinf, casinhf, casinhl, casinh, casinl, casin, catanf, catanhf, catanhl, catanh, catanl, catan, cbrtf, cbrtl, cbrt, ccosf, ccoshf, ccoshl, ccosh, ccosl, ccos, cexpf, cexpl, cexp, cimagf, cimagl, cimag, clogf, clogl, clog, conjf, conjl, conj, copysignf, copysignl, copysign, cpowf, cpowl, cpow, cprojf, cprojl, cproj, crealf, creall, creal, csinf, csinhf, csinhl, csinh, csinl, csin, csqrtf, csqrtl, csqrt, ctanf, ctanhf, ctanhl, ctanh, ctanl, ctan, erfcf, erfcl, erfc, erff, erfl, erf, exp2f, exp2l, exp2, expm1f, expm1l, expm1, fdimf, fdiml, fdim, fmaf, fmal, fmaxf, fmaxl, fmax, fma, fminf, fminl, fmin, hypotf, hypotl, hypot, ilogbf, ilogbl, ilogb, imaxabs, isblank, iswblank, lgammaf, lgammal, lgamma, llabs, llrintf, llrintl, llrint, llroundf, llroundl, llround, log1pf, log1pl, log1p, log2f, log2l, log2, logbf, logbl, logb, lrintf, lrintl, lrint, lroundf, lroundl, lround, nearbyintf, nearbyintl, nearbyint, nextafterf, nextafterl, nextafter, nexttowardf, nexttowardl, nexttoward, remainderf, remainderl, remainder, remquof, remquol, remquo, rintf, rintl, rint, roundf, roundl, round, scalblnf, scalblnl, scalbln, scalbnf, scalbnl, scalbn, snprintf, tgammaf, tgammal, tgamma, truncf, truncl, trunc, vfscanf, vscanf, vsnprintf and vsscanf are handled as built-in functions except in strict ISO C90 mode (-ansi or -std=c90).

There are also built-in versions of the ISO C99 functions acosf, acosl, asinf, asinl, atan2f, atan2l, atanf, atanl, ceilf, ceill, cosf, coshf, coshl, cosl, expf, expl, fabsf, fabsl, floorf, floorl, fmodf, fmodl, frexpf, frexpl, ldexpf, ldexpl, log10f, log10l, logf, logl, modfl, modf, powf, powl, sinf, sinhf, sinhl, sinl, sqrtf, sqrtl, tanf, tanhf, tanhl and tanl that are recognized in any mode since ISO C90 reserves these names for the purpose to which ISO C99 puts them.  All these functions have corresponding versions prefixed with __builtin_.

The ISO C94 functions iswalnum, iswalpha, iswcntrl, iswdigit, iswgraph, iswlower, iswprint, iswpunct, iswspace, iswupper, iswxdigit, towlower and towupper are handled as built-in functions except in strict ISO C90 mode (-ansi or -std=c90).

The ISO C90 functions abort, abs, acos, asin, atan2, atan, calloc, ceil, cosh, cos, exit, exp, fabs, floor, fmod, fprintf, fputs, frexp, fscanf, isalnum, isalpha, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit, tolower, toupper, labs, ldexp, log10, log, malloc, memchr, memcmp, memcpy, memset, modf, pow, printf, putchar, puts, scanf, sinh, sin, snprintf, sprintf, sqrt, sscanf, strcat, strchr, strcmp, strcpy, strcspn, strlen, strncat, strncmp, strncpy, strpbrk, strrchr, strspn, strstr, tanh, tan, vfprintf, vprintf and vsprintf are all recognized as built-in functions unless -fno-builtin is specified (or -fno-builtin-FUNCTION is specified for an individual function).  All of these functions have corresponding versions prefixed with __builtin_.

GCC provides built-in versions of the ISO C99 floating-point comparison macros that avoid raising exceptions for unordered operands.  They have the same names as the standard macros ( isgreater, isgreaterequal, isless, islessequal, islessgreater, and isunordered) , with __builtin_ prefixed.  We intend for a library implementor to be able to simply #define each standard macro to its built-in equivalent. In the same fashion, GCC provides fpclassify, isfinite, isinf_sign, isnormal and signbit built-ins used with __builtin_ prefixed.  The isinf and isnan built-in functions appear both with and without the __builtin_ prefix.

 -- Built-in Function: int __builtin_types_compatible_p (TYPE1, TYPE2)

     You can use the built-in function __builtin_types_compatible_p to determine whether two types are the same.

     This built-in function returns 1 if the unqualified versions of the types TYPE1 and TYPE2 (which are types, not expressions) are compatible, 0 otherwise.  The result of this built-in function can be used in integer constant expressions.

     This built-in function ignores top level qualifiers (e.g., const, volatile).  For example, int is equivalent to const int.

     The type int[] and int[5] are compatible.  On the other hand, int and char * are not compatible, even if the size of their types, on the particular architecture are the same.  Also, the amount of pointer indirection is taken into account when determining similarity.  Consequently, short * is not similar to short **.  Furthermore, two types that are typedefed are considered compatible if their underlying types are compatible.

     An enum type is not considered to be compatible with another enum type even if both are compatible with the same integer type; this is what the C standard specifies. For example, enum {foo, bar} is not similar to enum {hot, dog}.

     You typically use this function in code whose execution varies depending on the arguments' types.  For example:

          #define foo(x)                                                  \
            ({                                                           \
              typeof (x) tmp = (x);                                       \
              if (__builtin_types_compatible_p (typeof (x), long double)) \
                tmp = foo_long_double (tmp);                              \
              else if (__builtin_types_compatible_p (typeof (x), double)) \
                tmp = foo_double (tmp);                                   \
              else if (__builtin_types_compatible_p (typeof (x), float))  \
                tmp = foo_float (tmp);                                    \
              else                                                        \
                abort ();                                                 \
              tmp;                                                        \
            })

     Note: This construct is only available for C.

 -- Built-in Function: TYPE __builtin_call_with_static_chain (CALL_EXP, POINTER_EXP)

     The CALL_EXP expression must be a function call, and the POINTER_EXP expression must be a pointer.  The POINTER_EXP is passed to the function call in the target's static chain location. The result of builtin is the result of the function call.

     Note: This builtin is only available for C. This builtin can be used to call Go closures from C.

 -- Built-in Function: TYPE __builtin_choose_expr (CONST_EXP, EXP1, EXP2)

     You can use the built-in function __builtin_choose_expr to evaluate code depending on the value of a constant expression.  This built-in function returns EXP1 if CONST_EXP, which is an integer constant expression, is nonzero.  Otherwise it returns EXP2.

     This built-in function is analogous to the ? : operator in C, except that the expression returned has its type unaltered by promotion rules.  Also, the built-in function does not evaluate the expression that is not chosen.  For example, if CONST_EXP evaluates to true, EXP2 is not evaluated even if it has side-effects.

     This built-in function can return an lvalue if the chosen argument is an lvalue.

     If EXP1 is returned, the return type is the same as EXP1's type.  Similarly, if EXP2 is returned, its return type is the same as EXP2.

     Example:

          #define foo(x)                                                    \
            __builtin_choose_expr (                                         \
              __builtin_types_compatible_p (typeof (x), double),            \
              foo_double (x),                                               \
              __builtin_choose_expr (                                       \
                __builtin_types_compatible_p (typeof (x), float),           \
                foo_float (x),                                              \
                /* The void expression results in a compile-time error  \
                   when assigning the result to something.  */          \
                (void)0))

     Note: This construct is only available for C.  Furthermore, the unused expression (EXP1 or EXP2 depending on the value of CONST_EXP) may still generate syntax errors.  This may change in future revisions.

 -- Built-in Function: TYPE __builtin_complex (REAL, IMAG)

     The built-in function __builtin_complex is provided for use in implementing the ISO C11 macros CMPLXF, CMPLX and CMPLXL.  REAL and IMAG must have the same type, a real binary floating-point type, and the result has the corresponding complex type with real and imaginary parts REAL and IMAG. Unlike REAL + I * IMAG, this works even when infinities, NaNs and negative zeros are involved.

 -- Built-in Function: int __builtin_constant_p (EXP)
     You can use the built-in function __builtin_constant_p to determine if a value is known to be constant at compile time and hence that GCC can perform constant-folding on expressions involving that value.  The argument of the function is the value to test.  The function returns the integer 1 if the argument is known to be a compile-time constant and 0 if it is not known to be a compile-time constant.  A return of 0 does not indicate that the value is not a constant, but merely that GCC cannot prove it is a constant with the specified value of the -O option.

     You typically use this function in an embedded application where memory is a critical resource.  If you have some complex calculation, you may want it to be folded if it involves constants, but need to call a function if it does not.  For example:

          #define Scale_Value(X)      \
            (__builtin_constant_p (X) \
            ? ((X) * SCALE + OFFSET) : Scale (X))

     You may use this built-in function in either a macro or an inline function.  However, if you use it in an inlined function and pass an argument of the function as the argument to the built-in, GCC never returns 1 when you call the inline function with a string constant or compound literal (see Compound Literals) and does not return 1 when you pass a constant numeric value to the inline function unless you specify the -O option.

     You may also use __builtin_constant_p in initializers for static data.  For instance, you can write

          static const int table[] = {
             __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
             /* ... */
          };

     This is an acceptable initializer even if EXPRESSION is not a constant expression, including the case where __builtin_constant_p returns 1 because EXPRESSION can be folded to a constant but EXPRESSION contains operands that are not otherwise permitted in a static initializer (for example, 0 && foo ()).  GCC must be more conservative about evaluating the built-in in this case, because it has no opportunity to perform optimization.

 -- Built-in Function: long __builtin_expect (long EXP, long C)
     You may use __builtin_expect to provide the compiler with branch prediction information.  In general, you should prefer to use actual profile feedback for this (-fprofile-arcs), as programmers are notoriously bad at predicting how their programs actually perform.  However, there are applications in which this data is hard to collect.

     The return value is the value of EXP, which should be an integral expression.  The semantics of the built-in are that it is expected that EXP == C.  For example:

          if (__builtin_expect (x, 0))
            foo ();

     indicates that we do not expect to call foo, since we expect x to be zero.  Since you are limited to integral expressions for EXP, you should use constructions such as

          if (__builtin_expect (ptr != NULL, 1))
            foo (*ptr);

     when testing pointer or floating-point values.

 -- Built-in Function: void __builtin_trap (void)
     This function causes the program to exit abnormally.  GCC implements this function by using a target-dependent mechanism (such as intentionally executing an illegal instruction) or by calling abort.  The mechanism used may vary from release to release so you should not rely on any particular implementation.

 -- Built-in Function: void __builtin_unreachable (void)
     If control flow reaches the point of the __builtin_unreachable, the program is undefined.  It is useful in situations where the compiler cannot deduce the unreachability of the code.

     One such case is immediately following an asm statement that either never terminates, or one that transfers control elsewhere and never returns.  In this example, without the __builtin_unreachable, GCC issues a warning that control reaches the end of a non-void function.  It also generates code to return after the asm.

          int f (int c, int v)
          {
            if (c)
              {
                return v;
              }
            else
              {
                asm("jmp error_handler");
                __builtin_unreachable ();
              }
          }

     Because the asm statement unconditionally transfers control out of the function, control never reaches the end of the function body.  The __builtin_unreachable is in fact unreachable and communicates this fact to the compiler.

     Another use for __builtin_unreachable is following a call a function that never returns but that is not declared __attribute__((noreturn)), as in this example:

          void function_that_never_returns (void);

          int g (int c)
          {
            if (c)
              {
                return 1;
              }
            else
              {
                function_that_never_returns ();
                __builtin_unreachable ();
              }
          }

 -- Built-in Function: void *__builtin_assume_aligned (const void *EXP, size_t ALIGN, ...)
     This function returns its first argument, and allows the compiler to assume that the returned pointer is at least ALIGN bytes aligned.  This built-in can have either two or three arguments, if it has three, the third argument should have integer type, and if it is nonzero means misalignment offset.  For example:

          void *x = __builtin_assume_aligned (arg, 16);

     means that the compiler can assume x, set to arg, is at least 16-byte aligned, while:

          void *x = __builtin_assume_aligned (arg, 32, 8);

     means that the compiler can assume for x, set to arg, that (char *) x - 8 is 32-byte aligned.

 -- Built-in Function: int __builtin_LINE ()
     This function is the equivalent to the preprocessor __LINE__ macro and returns the line number of the invocation of the built-in. In a C++ default argument for a function F, it gets the line number of the call to F.

 -- Built-in Function: const char * __builtin_FUNCTION ()
     This function is the equivalent to the preprocessor __FUNCTION__ macro and returns the function name the invocation of the built-in is in.

 -- Built-in Function: const char * __builtin_FILE ()
     This function is the equivalent to the preprocessor __FILE__ macro and returns the file name the invocation of the built-in is in. In a C++ default argument for a function F, it gets the file name of the call to F.

 -- Built-in Function: void __builtin___clear_cache (char *BEGIN, char *END)
     This function is used to flush the processor's instruction cache for the region of memory between BEGIN inclusive and END exclusive.  Some targets require that the instruction cache be flushed, after modifying memory containing code, in order to obtain deterministic behavior.

     If the target does not require instruction cache flushes, __builtin___clear_cache has no effect.  Otherwise either instructions are emitted in-line to clear the instruction cache or a call to the __clear_cache function in libgcc is made.

 -- Built-in Function: void __builtin_prefetch (const void *ADDR, ...)
     This function is used to minimize cache-miss latency by moving data into a cache before it is accessed. You can insert calls to __builtin_prefetch into code for which you know addresses of data in memory that is likely to be accessed soon. If the target supports them, data prefetch instructions are generated. If the prefetch is done early enough before the access then the data will be in the cache by the time it is accessed.

     The value of ADDR is the address of the memory to prefetch. There are two optional arguments, RW and LOCALITY. The value of RW is a compile-time constant one or zero; one means that the prefetch is preparing for a write to the memory address and zero, the default, means that the prefetch is preparing for a read. The value LOCALITY must be a compile-time constant integer between zero and three.  A value of zero means that the data has no temporal locality, so it need not be left in the cache after the access.  A value of three means that the data has a high degree of temporal locality and should be left in all levels of cache possible.  Values of one and two mean, respectively, a low or moderate degree of temporal locality.  The default is three.

          for (i = 0; i < n; i++)
            {
              a[i] = a[i] + b[i];
              __builtin_prefetch (&a[i+j], 1, 1);
              __builtin_prefetch (&b[i+j], 0, 1);
              /* ... */
            }

     Data prefetch does not generate faults if ADDR is invalid, but the address expression itself must be valid.  For example, a prefetch of p->next does not fault if p->next is not a valid address, but evaluation faults if p is not a valid address.

     If the target does not support data prefetch, the address expression is evaluated if it includes side effects but no other code is generated and GCC does not issue a warning.

 -- Built-in Function: double __builtin_huge_val (void)
     Returns a positive infinity, if supported by the floating-point format, else DBL_MAX.  This function is suitable for implementing the ISO C macro HUGE_VAL.

 -- Built-in Function: float __builtin_huge_valf (void)
     Similar to __builtin_huge_val, except the return type is float.

 -- Built-in Function: long double __builtin_huge_vall (void)
     Similar to __builtin_huge_val, except the return type is long double.

 -- Built-in Function: int __builtin_fpclassify (int, int, int, int, int, ...)
     This built-in implements the C99 fpclassify functionality.  The first five int arguments should be the target library's notion of the possible FP classes and are used for return values.  They must be constant values and they must appear in this order: FP_NAN, FP_INFINITE, FP_NORMAL, FP_SUBNORMAL and FP_ZERO.  The ellipsis is for exactly one floating-point value to classify.  GCC treats the last argument as type-generic, which means it does not do default promotion from float to double.

 -- Built-in Function: double __builtin_inf (void)
     Similar to __builtin_huge_val, except a warning is generated if the target floating-point format does not support infinities.

 -- Built-in Function: _Decimal32 __builtin_infd32 (void)
     Similar to __builtin_inf, except the return type is _Decimal32.

 -- Built-in Function: _Decimal64 __builtin_infd64 (void)
     Similar to __builtin_inf, except the return type is _Decimal64.

 -- Built-in Function: _Decimal128 __builtin_infd128 (void)
     Similar to __builtin_inf, except the return type is _Decimal128.

 -- Built-in Function: float __builtin_inff (void)
     Similar to __builtin_inf, except the return type is float. This function is suitable for implementing the ISO C99 macro INFINITY.

 -- Built-in Function: long double __builtin_infl (void)
     Similar to __builtin_inf, except the return type is long double.

 -- Built-in Function: int __builtin_isinf_sign (...)
     Similar to isinf, except the return value is -1 for an argument of -Inf and 1 for an argument of +Inf. Note while the parameter list is an ellipsis, this function only accepts exactly one floating-point argument.  GCC treats this parameter as type-generic, which means it does not do default promotion from float to double.

 -- Built-in Function: double __builtin_nan (const char *str)
     This is an implementation of the ISO C99 function nan.

     Since ISO C99 defines this function in terms of strtod, which we do not implement, a description of the parsing is in order.  The string is parsed as by strtol; that is, the base is recognized by leading 0 or 0x prefixes.  The number parsed is placed in the significand such that the least significant bit of the number is at the least significant bit of the significand.  The number is truncated to fit the significand field provided.  The significand is forced to be a quiet NaN.

     This function, if given a string literal all of which would have been consumed by strtol, is evaluated early enough that it is considered a compile-time constant.

 -- Built-in Function: _Decimal32 __builtin_nand32 (const char *str)
     Similar to __builtin_nan, except the return type is _Decimal32.

 -- Built-in Function: _Decimal64 __builtin_nand64 (const char *str)
     Similar to __builtin_nan, except the return type is _Decimal64.

 -- Built-in Function: _Decimal128 __builtin_nand128 (const char *str)
     Similar to __builtin_nan, except the return type is _Decimal128.

 -- Built-in Function: float __builtin_nanf (const char *str)
     Similar to __builtin_nan, except the return type is float.

 -- Built-in Function: long double __builtin_nanl (const char *str)
     Similar to __builtin_nan, except the return type is long double.

 -- Built-in Function: double __builtin_nans (const char *str)
     Similar to __builtin_nan, except the significand is forced to be a signaling NaN.  The nans function is proposed by WG14 N965.

 -- Built-in Function: float __builtin_nansf (const char *str)
     Similar to __builtin_nans, except the return type is float.

 -- Built-in Function: long double __builtin_nansl (const char *str)
     Similar to __builtin_nans, except the return type is long double.

 -- Built-in Function: int __builtin_ffs (int x)
     Returns one plus the index of the least significant 1-bit of X, or if X is zero, returns zero.

 -- Built-in Function: int __builtin_clz (unsigned int x)
     Returns the number of leading 0-bits in X, starting at the most significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_ctz (unsigned int x)
     Returns the number of trailing 0-bits in X, starting at the least significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_clrsb (int x)
     Returns the number of leading redundant sign bits in X, i.e. the number of bits following the most significant bit that are identical to it.  There are no special cases for 0 or other values.

 -- Built-in Function: int __builtin_popcount (unsigned int x)
     Returns the number of 1-bits in X.

 -- Built-in Function: int __builtin_parity (unsigned int x)
     Returns the parity of X, i.e. the number of 1-bits in X modulo 2.

 -- Built-in Function: int __builtin_ffsl (long)
     Similar to __builtin_ffs, except the argument type is long.

 -- Built-in Function: int __builtin_clzl (unsigned long)
     Similar to __builtin_clz, except the argument type is unsigned long.

 -- Built-in Function: int __builtin_ctzl (unsigned long)
     Similar to __builtin_ctz, except the argument type is unsigned long.

 -- Built-in Function: int __builtin_clrsbl (long)
     Similar to __builtin_clrsb, except the argument type is long.

 -- Built-in Function: int __builtin_popcountl (unsigned long)
     Similar to __builtin_popcount, except the argument type is unsigned long.

 -- Built-in Function: int __builtin_parityl (unsigned long)
     Similar to __builtin_parity, except the argument type is unsigned long.

 -- Built-in Function: int __builtin_ffsll (long long)
     Similar to __builtin_ffs, except the argument type is long long.

 -- Built-in Function: int __builtin_clzll (unsigned long long)
     Similar to __builtin_clz, except the argument type is unsigned long long.

 -- Built-in Function: int __builtin_ctzll (unsigned long long)
     Similar to __builtin_ctz, except the argument type is unsigned long long.

 -- Built-in Function: int __builtin_clrsbll (long long)
     Similar to __builtin_clrsb, except the argument type is long long.

 -- Built-in Function: int __builtin_popcountll (unsigned long long)
     Similar to __builtin_popcount, except the argument type is unsigned long long.

 -- Built-in Function: int __builtin_parityll (unsigned long long)
     Similar to __builtin_parity, except the argument type is unsigned long long.

 -- Built-in Function: double __builtin_powi (double, int)
     Returns the first argument raised to the power of the second.  Unlike the pow function no guarantees about precision and rounding are made.

 -- Built-in Function: float __builtin_powif (float, int)
     Similar to __builtin_powi, except the argument and return types are float.

 -- Built-in Function: long double __builtin_powil (long double, int)
     Similar to __builtin_powi, except the argument and return types are long double.

 -- Built-in Function: uint16_t __builtin_bswap16 (uint16_t x)
     Returns X with the order of the bytes reversed; for example, 0xaabb becomes 0xbbaa.  Byte here always means exactly 8 bits.

 -- Built-in Function: uint32_t __builtin_bswap32 (uint32_t x)
     Similar to __builtin_bswap16, except the argument and return types are 32 bit.

 -- Built-in Function: uint64_t __builtin_bswap64 (uint64_t x)
     Similar to __builtin_bswap32, except the argument and return types are 64 bit.

Built-in Functions Specific to Particular Target Machines
=========================================================

On some target machines, GCC supports many built-in functions specific to those machines.  Generally these generate calls to specific machine instructions, but allow the compiler to schedule those calls.

AArch64 Built-in Functions
--------------------------

These built-in functions are available for the AArch64 family of processors.

     unsigned int __builtin_aarch64_get_fpcr ()
     void __builtin_aarch64_set_fpcr (unsigned int)
     unsigned int __builtin_aarch64_get_fpsr ()
     void __builtin_aarch64_set_fpsr (unsigned int)

Alpha Built-in Functions
------------------------

These built-in functions are available for the Alpha family of processors, depending on the command-line switches used.

The following built-in functions are always available.  They all generate the machine instruction that is part of the name.

     long __builtin_alpha_implver (void)
     long __builtin_alpha_rpcc (void)
     long __builtin_alpha_amask (long)
     long __builtin_alpha_cmpbge (long, long)
     long __builtin_alpha_extbl (long, long)
     long __builtin_alpha_extwl (long, long)
     long __builtin_alpha_extll (long, long)
     long __builtin_alpha_extql (long, long)
     long __builtin_alpha_extwh (long, long)
     long __builtin_alpha_extlh (long, long)
     long __builtin_alpha_extqh (long, long)
     long __builtin_alpha_insbl (long, long)
     long __builtin_alpha_inswl (long, long)
     long __builtin_alpha_insll (long, long)
     long __builtin_alpha_insql (long, long)
     long __builtin_alpha_inswh (long, long)
     long __builtin_alpha_inslh (long, long)
     long __builtin_alpha_insqh (long, long)
     long __builtin_alpha_mskbl (long, long)
     long __builtin_alpha_mskwl (long, long)
     long __builtin_alpha_mskll (long, long)
     long __builtin_alpha_mskql (long, long)
     long __builtin_alpha_mskwh (long, long)
     long __builtin_alpha_msklh (long, long)
     long __builtin_alpha_mskqh (long, long)
     long __builtin_alpha_umulh (long, long)
     long __builtin_alpha_zap (long, long)
     long __builtin_alpha_zapnot (long, long)

The following built-in functions are always with -mmax or -mcpu=CPU where CPU is pca56 or later.  They all generate the machine instruction that is part of the name.

     long __builtin_alpha_pklb (long)
     long __builtin_alpha_pkwb (long)
     long __builtin_alpha_unpkbl (long)
     long __builtin_alpha_unpkbw (long)
     long __builtin_alpha_minub8 (long, long)
     long __builtin_alpha_minsb8 (long, long)
     long __builtin_alpha_minuw4 (long, long)
     long __builtin_alpha_minsw4 (long, long)
     long __builtin_alpha_maxub8 (long, long)
     long __builtin_alpha_maxsb8 (long, long)
     long __builtin_alpha_maxuw4 (long, long)
     long __builtin_alpha_maxsw4 (long, long)
     long __builtin_alpha_perr (long, long)

The following built-in functions are always with -mcix or -mcpu=CPU where CPU is ev67 or later.  They all generate the machine instruction that is part of the name.

     long __builtin_alpha_cttz (long)
     long __builtin_alpha_ctlz (long)
     long __builtin_alpha_ctpop (long)

The following built-in functions are available on systems that use the OSF/1 PALcode.  Normally they invoke the rduniq and wruniq PAL calls, but when invoked with -mtls-kernel, they invoke rdval and wrval.

     void *__builtin_thread_pointer (void)
     void __builtin_set_thread_pointer (void *)

Altera Nios II Built-in Functions
---------------------------------

These built-in functions are available for the Altera Nios II family of processors.

The following built-in functions are always available.  They all generate the machine instruction that is part of the name.

     int __builtin_ldbio (volatile const void *)
     int __builtin_ldbuio (volatile const void *)
     int __builtin_ldhio (volatile const void *)
     int __builtin_ldhuio (volatile const void *)
     int __builtin_ldwio (volatile const void *)
     void __builtin_stbio (volatile void *, int)
     void __builtin_sthio (volatile void *, int)
     void __builtin_stwio (volatile void *, int)
     void __builtin_sync (void)
     int __builtin_rdctl (int)
     int __builtin_rdprs (int, int)
     void __builtin_wrctl (int, int)
     void __builtin_flushd (volatile void *)
     void __builtin_flushda (volatile void *)
     int __builtin_wrpie (int);
     void __builtin_eni (int);
     int __builtin_ldex (volatile const void *)
     int __builtin_stex (volatile void *, int)
     int __builtin_ldsex (volatile const void *)
     int __builtin_stsex (volatile void *, int)

The following built-in functions are always available.  They all generate a Nios II Custom Instruction. The name of the function represents the types that the function takes and returns. The letter before the n is the return type or void if absent. The n represents the first parameter to all the custom instructions, the custom instruction number. The two letters after the n represent the up to two parameters to the function.

The letters represent the following data types:

<no letter>
     void for return type and no parameter for parameter types.

i
     int for return type and parameter type

f
     float for return type and parameter type

p
     void * for return type and parameter type

And the function names are:

     void __builtin_custom_n (void)
     void __builtin_custom_ni (int)
     void __builtin_custom_nf (float)
     void __builtin_custom_np (void *)
     void __builtin_custom_nii (int, int)
     void __builtin_custom_nif (int, float)
     void __builtin_custom_nip (int, void *)
     void __builtin_custom_nfi (float, int)
     void __builtin_custom_nff (float, float)
     void __builtin_custom_nfp (float, void *)
     void __builtin_custom_npi (void *, int)
     void __builtin_custom_npf (void *, float)
     void __builtin_custom_npp (void *, void *)
     int __builtin_custom_in (void)
     int __builtin_custom_ini (int)
     int __builtin_custom_inf (float)
     int __builtin_custom_inp (void *)
     int __builtin_custom_inii (int, int)
     int __builtin_custom_inif (int, float)
     int __builtin_custom_inip (int, void *)
     int __builtin_custom_infi (float, int)
     int __builtin_custom_inff (float, float)
     int __builtin_custom_infp (float, void *)
     int __builtin_custom_inpi (void *, int)
     int __builtin_custom_inpf (void *, float)
     int __builtin_custom_inpp (void *, void *)
     float __builtin_custom_fn (void)
     float __builtin_custom_fni (int)
     float __builtin_custom_fnf (float)
     float __builtin_custom_fnp (void *)
     float __builtin_custom_fnii (int, int)
     float __builtin_custom_fnif (int, float)
     float __builtin_custom_fnip (int, void *)
     float __builtin_custom_fnfi (float, int)
     float __builtin_custom_fnff (float, float)
     float __builtin_custom_fnfp (float, void *)
     float __builtin_custom_fnpi (void *, int)
     float __builtin_custom_fnpf (void *, float)
     float __builtin_custom_fnpp (void *, void *)
     void * __builtin_custom_pn (void)
     void * __builtin_custom_pni (int)
     void * __builtin_custom_pnf (float)
     void * __builtin_custom_pnp (void *)
     void * __builtin_custom_pnii (int, int)
     void * __builtin_custom_pnif (int, float)
     void * __builtin_custom_pnip (int, void *)
     void * __builtin_custom_pnfi (float, int)
     void * __builtin_custom_pnff (float, float)
     void * __builtin_custom_pnfp (float, void *)
     void * __builtin_custom_pnpi (void *, int)
     void * __builtin_custom_pnpf (void *, float)
     void * __builtin_custom_pnpp (void *, void *)

ARC Built-in Functions
----------------------

The following built-in functions are provided for ARC targets.  The built-ins generate the corresponding assembly instructions.  In the examples given below, the generated code often requires an operand or result to be in a register.  Where necessary further code will be generated to ensure this is true, but for brevity this is not described in each case.

Note: Using a built-in to generate an instruction not supported by a target may cause problems. At present the compiler is not guaranteed to detect such misuse, and as a result an internal compiler error may be generated.

 -- Built-in Function: int __builtin_arc_aligned (void *VAL, int ALIGNVAL)
     Return 1 if VAL is known to have the byte alignment given by ALIGNVAL, otherwise return 0. Note that this is different from

          __alignof__(*(char *)VAL) >= alignval

     because __alignof__ sees only the type of the dereference, whereas __builtin_arc_align uses alignment information from the pointer as well as from the pointed-to type. The information available will depend on optimization level.

 -- Built-in Function: void __builtin_arc_brk (void)
     Generates

          brk

 -- Built-in Function: unsigned int __builtin_arc_core_read (unsigned int REGNO)
     The operand is the number of a register to be read.  Generates:

          mov  DEST, rREGNO

     where the value in DEST will be the result returned from the built-in.

 -- Built-in Function: void __builtin_arc_core_write (unsigned int REGNO, unsigned int VAL)
     The first operand is the number of a register to be written, the second operand is a compile time constant to write into that register.  Generates:

          mov  rREGNO, VAL

 -- Built-in Function: int __builtin_arc_divaw (int A, int B)
     Only available if either -mcpu=ARC700 or -meA is set. Generates:

          divaw  DEST, A, B

     where the value in DEST will be the result returned from the built-in.

 -- Built-in Function: void __builtin_arc_flag (unsigned int A)
     Generates

          flag  A

 -- Built-in Function: unsigned int __builtin_arc_lr (unsigned int AUXR)
     The operand, AUXV, is the address of an auxiliary register and must be a compile time constant.  Generates:

          lr  DEST, [AUXR]

     Where the value in DEST will be the result returned from the built-in.

 -- Built-in Function: void __builtin_arc_mul64 (int A, int B)
     Only available with -mmul64.  Generates:

          mul64  A, B

 -- Built-in Function: void __builtin_arc_mulu64 (unsigned int A, unsigned int B)
     Only available with -mmul64.  Generates:

          mulu64  A, B

 -- Built-in Function: void __builtin_arc_nop (void)
     Generates:

          nop

 -- Built-in Function: int __builtin_arc_norm (int SRC)
     Only valid if the norm instruction is available through the -mnorm option or by default with -mcpu=ARC700. Generates:

          norm  DEST, SRC

     Where the value in DEST will be the result returned from the built-in.

 -- Built-in Function: short int __builtin_arc_normw (short int SRC)
     Only valid if the normw instruction is available through the -mnorm option or by default with -mcpu=ARC700. Generates:

          normw  DEST, SRC

     Where the value in DEST will be the result returned from the built-in.

 -- Built-in Function: void __builtin_arc_rtie (void)
     Generates:

          rtie

 -- Built-in Function: void __builtin_arc_sleep (int A
     Generates:

          sleep  A

 -- Built-in Function: void __builtin_arc_sr (unsigned int AUXR, unsigned int VAL)
     The first argument, AUXV, is the address of an auxiliary register, the second argument, VAL, is a compile time constant to be written to the register.  Generates:

          sr  AUXR, [VAL]

 -- Built-in Function: int __builtin_arc_swap (int SRC)
     Only valid with -mswap.  Generates:

          swap  DEST, SRC

     Where the value in DEST will be the result returned from the built-in.

 -- Built-in Function: void __builtin_arc_swi (void)
     Generates:

          swi

 -- Built-in Function: void __builtin_arc_sync (void)
     Only available with -mcpu=ARC700.  Generates:

          sync

 -- Built-in Function: void __builtin_arc_trap_s (unsigned int C)
     Only available with -mcpu=ARC700.  Generates:

          trap_s  C

 -- Built-in Function: void __builtin_arc_unimp_s (void)
     Only available with -mcpu=ARC700.  Generates:

          unimp_s

The instructions generated by the following builtins are not considered as candidates for scheduling.  They are not moved around by the compiler during scheduling, and thus can be expected to appear where they are put in the C code:

     __builtin_arc_brk()
     __builtin_arc_core_read()
     __builtin_arc_core_write()
     __builtin_arc_flag()
     __builtin_arc_lr()
     __builtin_arc_sleep()
     __builtin_arc_sr()
     __builtin_arc_swi()

ARC SIMD Built-in Functions
---------------------------

SIMD builtins provided by the compiler can be used to generate the vector instructions.  This section describes the available builtins and their usage in programs.  With the -msimd option, the compiler provides 128-bit vector types, which can be specified using the vector_size attribute.  The header file arc-simd.h can be included to use the following predefined types:

     typedef int __v4si   __attribute__((vector_size(16)));
     typedef short __v8hi __attribute__((vector_size(16)));

These types can be used to define 128-bit variables.  The built-in functions listed in the following section can be used on these variables to generate the vector operations.

For all builtins, __builtin_arc_SOMEINSN, the header file arc-simd.h also provides equivalent macros called _SOMEINSN that can be used for programming ease and improved readability.  The following macros for DMA control are also provided:

     #define _setup_dma_in_channel_reg _vdiwr
     #define _setup_dma_out_channel_reg _vdowr

The following is a complete list of all the SIMD built-ins provided for ARC, grouped by calling signature.

The following take two __v8hi arguments and return a __v8hi result:

     __v8hi __builtin_arc_vaddaw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vaddw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vand (__v8hi, __v8hi)
     __v8hi __builtin_arc_vandaw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vavb (__v8hi, __v8hi)
     __v8hi __builtin_arc_vavrb (__v8hi, __v8hi)
     __v8hi __builtin_arc_vbic (__v8hi, __v8hi)
     __v8hi __builtin_arc_vbicaw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vdifaw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vdifw (__v8hi, __v8hi)
     __v8hi __builtin_arc_veqw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vh264f (__v8hi, __v8hi)
     __v8hi __builtin_arc_vh264ft (__v8hi, __v8hi)
     __v8hi __builtin_arc_vh264fw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vlew (__v8hi, __v8hi)
     __v8hi __builtin_arc_vltw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmaxaw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmaxw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vminaw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vminw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr1aw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr1w (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr2aw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr2w (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr3aw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr3w (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr4aw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr4w (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr5aw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr5w (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr6aw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr6w (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr7aw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmr7w (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmrb (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmulaw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmulfaw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmulfw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vmulw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vnew (__v8hi, __v8hi)
     __v8hi __builtin_arc_vor (__v8hi, __v8hi)
     __v8hi __builtin_arc_vsubaw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vsubw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vsummw (__v8hi, __v8hi)
     __v8hi __builtin_arc_vvc1f (__v8hi, __v8hi)
     __v8hi __builtin_arc_vvc1ft (__v8hi, __v8hi)
     __v8hi __builtin_arc_vxor (__v8hi, __v8hi)
     __v8hi __builtin_arc_vxoraw (__v8hi, __v8hi)

The following take one __v8hi and one int argument and return a __v8hi result:

     __v8hi __builtin_arc_vbaddw (__v8hi, int)
     __v8hi __builtin_arc_vbmaxw (__v8hi, int)
     __v8hi __builtin_arc_vbminw (__v8hi, int)
     __v8hi __builtin_arc_vbmulaw (__v8hi, int)
     __v8hi __builtin_arc_vbmulfw (__v8hi, int)
     __v8hi __builtin_arc_vbmulw (__v8hi, int)
     __v8hi __builtin_arc_vbrsubw (__v8hi, int)
     __v8hi __builtin_arc_vbsubw (__v8hi, int)

The following take one __v8hi argument and one int argument which must be a 3-bit compile time constant indicating a register number I0-I7.  They return a __v8hi result.

     __v8hi __builtin_arc_vasrw (__v8hi, const int)
     __v8hi __builtin_arc_vsr8 (__v8hi, const int)
     __v8hi __builtin_arc_vsr8aw (__v8hi, const int)

The following take one __v8hi argument and one int argument which must be a 6-bit compile time constant.  They return a __v8hi result.

     __v8hi __builtin_arc_vasrpwbi (__v8hi, const int)
     __v8hi __builtin_arc_vasrrpwbi (__v8hi, const int)
     __v8hi __builtin_arc_vasrrwi (__v8hi, const int)
     __v8hi __builtin_arc_vasrsrwi (__v8hi, const int)
     __v8hi __builtin_arc_vasrwi (__v8hi, const int)
     __v8hi __builtin_arc_vsr8awi (__v8hi, const int)
     __v8hi __builtin_arc_vsr8i (__v8hi, const int)

The following take one __v8hi argument and one int argument which must be a 8-bit compile time constant.  They return a __v8hi result.

     __v8hi __builtin_arc_vd6tapf (__v8hi, const int)
     __v8hi __builtin_arc_vmvaw (__v8hi, const int)
     __v8hi __builtin_arc_vmvw (__v8hi, const int)
     __v8hi __builtin_arc_vmvzw (__v8hi, const int)

The following take two int arguments, the second of which which must be a 8-bit compile time constant.  They return a __v8hi result:

     __v8hi __builtin_arc_vmovaw (int, const int)
     __v8hi __builtin_arc_vmovw (int, const int)
     __v8hi __builtin_arc_vmovzw (int, const int)

The following take a single __v8hi argument and return a __v8hi result:

     __v8hi __builtin_arc_vabsaw (__v8hi)
     __v8hi __builtin_arc_vabsw (__v8hi)
     __v8hi __builtin_arc_vaddsuw (__v8hi)
     __v8hi __builtin_arc_vexch1 (__v8hi)
     __v8hi __builtin_arc_vexch2 (__v8hi)
     __v8hi __builtin_arc_vexch4 (__v8hi)
     __v8hi __builtin_arc_vsignw (__v8hi)
     __v8hi __builtin_arc_vupbaw (__v8hi)
     __v8hi __builtin_arc_vupbw (__v8hi)
     __v8hi __builtin_arc_vupsbaw (__v8hi)
     __v8hi __builtin_arc_vupsbw (__v8hi)

The following take two int arguments and return no result:

     void __builtin_arc_vdirun (int, int)
     void __builtin_arc_vdorun (int, int)

The following take two int arguments and return no result.  The first argument must a 3-bit compile time constant indicating one of the DR0-DR7 DMA setup channels:

     void __builtin_arc_vdiwr (const int, int)
     void __builtin_arc_vdowr (const int, int)

The following take an int argument and return no result:

     void __builtin_arc_vendrec (int)
     void __builtin_arc_vrec (int)
     void __builtin_arc_vrecrun (int)
     void __builtin_arc_vrun (int)

The following take a __v8hi argument and two int arguments and return a __v8hi result.  The second argument must be a 3-bit compile time constants, indicating one the registers I0-I7, and the third argument must be an 8-bit compile time constant.

Note: Although the equivalent hardware instructions do not take an SIMD register as an operand, these builtins overwrite the relevant bits of the __v8hi register provided as the first argument with the value loaded from the [Ib, u8] location in the SDM.

     __v8hi __builtin_arc_vld32 (__v8hi, const int, const int)
     __v8hi __builtin_arc_vld32wh (__v8hi, const int, const int)
     __v8hi __builtin_arc_vld32wl (__v8hi, const int, const int)
     __v8hi __builtin_arc_vld64 (__v8hi, const int, const int)

The following take two int arguments and return a __v8hi result.  The first argument must be a 3-bit compile time constants, indicating one the registers I0-I7, and the second argument must be an 8-bit compile time constant.

     __v8hi __builtin_arc_vld128 (const int, const int)
     __v8hi __builtin_arc_vld64w (const int, const int)

The following take a __v8hi argument and two int arguments and return no result.  The second argument must be a 3-bit compile time constants, indicating one the registers I0-I7, and the third argument must be an 8-bit compile time constant.

     void __builtin_arc_vst128 (__v8hi, const int, const int)
     void __builtin_arc_vst64 (__v8hi, const int, const int)

The following take a __v8hi argument and three int arguments and return no result.  The second argument must be a 3-bit compile-time constant, identifying the 16-bit sub-register to be stored, the third argument must be a 3-bit compile time constants, indicating one the registers I0-I7, and the fourth argument must be an 8-bit compile time constant.

     void __builtin_arc_vst16_n (__v8hi, const int, const int, const int)
     void __builtin_arc_vst32_n (__v8hi, const int, const int, const int)

ARM iWMMXt Built-in Functions
-----------------------------

These built-in functions are available for the ARM family of processors when the -mcpu=iwmmxt switch is used:

     typedef int v2si __attribute__ ((vector_size (8)));
     typedef short v4hi __attribute__ ((vector_size (8)));
     typedef char v8qi __attribute__ ((vector_size (8)));

     int __builtin_arm_getwcgr0 (void)
     void __builtin_arm_setwcgr0 (int)
     int __builtin_arm_getwcgr1 (void)
     void __builtin_arm_setwcgr1 (int)
     int __builtin_arm_getwcgr2 (void)
     void __builtin_arm_setwcgr2 (int)
     int __builtin_arm_getwcgr3 (void)
     void __builtin_arm_setwcgr3 (int)
     int __builtin_arm_textrmsb (v8qi, int)
     int __builtin_arm_textrmsh (v4hi, int)
     int __builtin_arm_textrmsw (v2si, int)
     int __builtin_arm_textrmub (v8qi, int)
     int __builtin_arm_textrmuh (v4hi, int)
     int __builtin_arm_textrmuw (v2si, int)
     v8qi __builtin_arm_tinsrb (v8qi, int, int)
     v4hi __builtin_arm_tinsrh (v4hi, int, int)
     v2si __builtin_arm_tinsrw (v2si, int, int)
     long long __builtin_arm_tmia (long long, int, int)
     long long __builtin_arm_tmiabb (long long, int, int)
     long long __builtin_arm_tmiabt (long long, int, int)
     long long __builtin_arm_tmiaph (long long, int, int)
     long long __builtin_arm_tmiatb (long long, int, int)
     long long __builtin_arm_tmiatt (long long, int, int)
     int __builtin_arm_tmovmskb (v8qi)
     int __builtin_arm_tmovmskh (v4hi)
     int __builtin_arm_tmovmskw (v2si)
     long long __builtin_arm_waccb (v8qi)
     long long __builtin_arm_wacch (v4hi)
     long long __builtin_arm_waccw (v2si)
     v8qi __builtin_arm_waddb (v8qi, v8qi)
     v8qi __builtin_arm_waddbss (v8qi, v8qi)
     v8qi __builtin_arm_waddbus (v8qi, v8qi)
     v4hi __builtin_arm_waddh (v4hi, v4hi)
     v4hi __builtin_arm_waddhss (v4hi, v4hi)
     v4hi __builtin_arm_waddhus (v4hi, v4hi)
     v2si __builtin_arm_waddw (v2si, v2si)
     v2si __builtin_arm_waddwss (v2si, v2si)
     v2si __builtin_arm_waddwus (v2si, v2si)
     v8qi __builtin_arm_walign (v8qi, v8qi, int)
     long long __builtin_arm_wand(long long, long long)
     long long __builtin_arm_wandn (long long, long long)
     v8qi __builtin_arm_wavg2b (v8qi, v8qi)
     v8qi __builtin_arm_wavg2br (v8qi, v8qi)
     v4hi __builtin_arm_wavg2h (v4hi, v4hi)
     v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
     v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
     v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
     v2si __builtin_arm_wcmpeqw (v2si, v2si)
     v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
     v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)
     v2si __builtin_arm_wcmpgtsw (v2si, v2si)
     v8qi __builtin_arm_wcmpgtub (v8qi, v8qi)
     v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi)
     v2si __builtin_arm_wcmpgtuw (v2si, v2si)
     long long __builtin_arm_wmacs (long long, v4hi, v4hi)
     long long __builtin_arm_wmacsz (v4hi, v4hi)
     long long __builtin_arm_wmacu (long long, v4hi, v4hi)
     long long __builtin_arm_wmacuz (v4hi, v4hi)
     v4hi __builtin_arm_wmadds (v4hi, v4hi)
     v4hi __builtin_arm_wmaddu (v4hi, v4hi)
     v8qi __builtin_arm_wmaxsb (v8qi, v8qi)
     v4hi __builtin_arm_wmaxsh (v4hi, v4hi)
     v2si __builtin_arm_wmaxsw (v2si, v2si)
     v8qi __builtin_arm_wmaxub (v8qi, v8qi)
     v4hi __builtin_arm_wmaxuh (v4hi, v4hi)
     v2si __builtin_arm_wmaxuw (v2si, v2si)
     v8qi __builtin_arm_wminsb (v8qi, v8qi)
     v4hi __builtin_arm_wminsh (v4hi, v4hi)
     v2si __builtin_arm_wminsw (v2si, v2si)
     v8qi __builtin_arm_wminub (v8qi, v8qi)
     v4hi __builtin_arm_wminuh (v4hi, v4hi)
     v2si __builtin_arm_wminuw (v2si, v2si)
     v4hi __builtin_arm_wmulsm (v4hi, v4hi)
     v4hi __builtin_arm_wmulul (v4hi, v4hi)
     v4hi __builtin_arm_wmulum (v4hi, v4hi)
     long long __builtin_arm_wor (long long, long long)
     v2si __builtin_arm_wpackdss (long long, long long)
     v2si __builtin_arm_wpackdus (long long, long long)
     v8qi __builtin_arm_wpackhss (v4hi, v4hi)
     v8qi __builtin_arm_wpackhus (v4hi, v4hi)
     v4hi __builtin_arm_wpackwss (v2si, v2si)
     v4hi __builtin_arm_wpackwus (v2si, v2si)
     long long __builtin_arm_wrord (long long, long long)
     long long __builtin_arm_wrordi (long long, int)
     v4hi __builtin_arm_wrorh (v4hi, long long)
     v4hi __builtin_arm_wrorhi (v4hi, int)
     v2si __builtin_arm_wrorw (v2si, long long)
     v2si __builtin_arm_wrorwi (v2si, int)
     v2si __builtin_arm_wsadb (v2si, v8qi, v8qi)
     v2si __builtin_arm_wsadbz (v8qi, v8qi)
     v2si __builtin_arm_wsadh (v2si, v4hi, v4hi)
     v2si __builtin_arm_wsadhz (v4hi, v4hi)
     v4hi __builtin_arm_wshufh (v4hi, int)
     long long __builtin_arm_wslld (long long, long long)
     long long __builtin_arm_wslldi (long long, int)
     v4hi __builtin_arm_wsllh (v4hi, long long)
     v4hi __builtin_arm_wsllhi (v4hi, int)
     v2si __builtin_arm_wsllw (v2si, long long)
     v2si __builtin_arm_wsllwi (v2si, int)
     long long __builtin_arm_wsrad (long long, long long)
     long long __builtin_arm_wsradi (long long, int)
     v4hi __builtin_arm_wsrah (v4hi, long long)
     v4hi __builtin_arm_wsrahi (v4hi, int)
     v2si __builtin_arm_wsraw (v2si, long long)
     v2si __builtin_arm_wsrawi (v2si, int)
     long long __builtin_arm_wsrld (long long, long long)
     long long __builtin_arm_wsrldi (long long, int)
     v4hi __builtin_arm_wsrlh (v4hi, long long)
     v4hi __builtin_arm_wsrlhi (v4hi, int)
     v2si __builtin_arm_wsrlw (v2si, long long)
     v2si __builtin_arm_wsrlwi (v2si, int)
     v8qi __builtin_arm_wsubb (v8qi, v8qi)
     v8qi __builtin_arm_wsubbss (v8qi, v8qi)
     v8qi __builtin_arm_wsubbus (v8qi, v8qi)
     v4hi __builtin_arm_wsubh (v4hi, v4hi)
     v4hi __builtin_arm_wsubhss (v4hi, v4hi)
     v4hi __builtin_arm_wsubhus (v4hi, v4hi)
     v2si __builtin_arm_wsubw (v2si, v2si)
     v2si __builtin_arm_wsubwss (v2si, v2si)
     v2si __builtin_arm_wsubwus (v2si, v2si)
     v4hi __builtin_arm_wunpckehsb (v8qi)
     v2si __builtin_arm_wunpckehsh (v4hi)
     long long __builtin_arm_wunpckehsw (v2si)
     v4hi __builtin_arm_wunpckehub (v8qi)
     v2si __builtin_arm_wunpckehuh (v4hi)
     long long __builtin_arm_wunpckehuw (v2si)
     v4hi __builtin_arm_wunpckelsb (v8qi)
     v2si __builtin_arm_wunpckelsh (v4hi)
     long long __builtin_arm_wunpckelsw (v2si)
     v4hi __builtin_arm_wunpckelub (v8qi)
     v2si __builtin_arm_wunpckeluh (v4hi)
     long long __builtin_arm_wunpckeluw (v2si)
     v8qi __builtin_arm_wunpckihb (v8qi, v8qi)
     v4hi __builtin_arm_wunpckihh (v4hi, v4hi)
     v2si __builtin_arm_wunpckihw (v2si, v2si)
     v8qi __builtin_arm_wunpckilb (v8qi, v8qi)
     v4hi __builtin_arm_wunpckilh (v4hi, v4hi)
     v2si __builtin_arm_wunpckilw (v2si, v2si)
     long long __builtin_arm_wxor (long long, long long)
     long long __builtin_arm_wzero ()

ARM C Language Extensions (ACLE)
--------------------------------

GCC implements extensions for C as described in the ARM C Language Extensions (ACLE) specification, which can be found at http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf.

As a part of ACLE, GCC implements extensions for Advanced SIMD as described in the ARM C Language Extensions Specification.  The complete list of Advanced SIMD intrinsics can be found at http://infocenter.arm.com/help/topic/com.arm.doc.ihi0073a/IHI0073A_arm_neon_intrinsics_ref.pdf. The built-in intrinsics for the Advanced SIMD extension are available when NEON is enabled.

Currently, ARM and AArch64 back ends do not support ACLE 2.0 fully.  Both back ends support CRC32 intrinsics from arm_acle.h.  The ARM back end's 16-bit floating-point Advanced SIMD intrinsics currently comply to ACLE v1.1. AArch64's back end does not have support for 16-bit floating point Advanced SIMD intrinsics yet.

See ARM Options and AArch64 Options for more information on the availability of extensions.

ARM Floating Point Status and Control Intrinsics
------------------------------------------------

These built-in functions are available for the ARM family of processors with floating-point unit.

     unsigned int __builtin_arm_get_fpscr ()
     void __builtin_arm_set_fpscr (unsigned int)

AVR Built-in Functions
----------------------

For each built-in function for AVR, there is an equally named, uppercase built-in macro defined. That way users can easily query if or if not a specific built-in is implemented or not. For example, if __builtin_avr_nop is available the macro __BUILTIN_AVR_NOP is defined to 1 and undefined otherwise.

The following built-in functions map to the respective machine instruction, i.e. nop, sei, cli, sleep, wdr, swap, fmul, fmuls resp. fmulsu. The three fmul* built-ins are implemented as library call if no hardware multiplier is available.

     void __builtin_avr_nop (void)
     void __builtin_avr_sei (void)
     void __builtin_avr_cli (void)
     void __builtin_avr_sleep (void)
     void __builtin_avr_wdr (void)
     unsigned char __builtin_avr_swap (unsigned char)
     unsigned int __builtin_avr_fmul (unsigned char, unsigned char)
     int __builtin_avr_fmuls (char, char)
     int __builtin_avr_fmulsu (char, unsigned char)

In order to delay execution for a specific number of cycles, GCC implements

     void __builtin_avr_delay_cycles (unsigned long ticks)

ticks is the number of ticks to delay execution. Note that this built-in does not take into account the effect of interrupts that might increase delay time. ticks must be a compile-time integer constant; delays with a variable number of cycles are not supported.

     char __builtin_avr_flash_segment (const __memx void*)

This built-in takes a byte address to the 24-bit address space __memx and returns the number of the flash segment (the 64 KiB chunk) where the address points to.  Counting starts at 0. If the address does not point to flash memory, return -1.

     unsigned char __builtin_avr_insert_bits (unsigned long map, unsigned char bits, unsigned char val)

Insert bits from BITS into VAL and return the resulting value. The nibbles of MAP determine how the insertion is performed: Let X be the N-th nibble of MAP

 1. If X is 0xf, then the N-th bit of VAL is returned unaltered.

 2. If X is in the range 0...7, then the N-th result bit is set to the X-th bit of BITS

 3. If X is in the range 8...0xe, then the N-th result bit is undefined.

One typical use case for this built-in is adjusting input and output values to non-contiguous port layouts. Some examples:

     // same as val, bits is unused
     __builtin_avr_insert_bits (0xffffffff, bits, val)

     // same as bits, val is unused
     __builtin_avr_insert_bits (0x76543210, bits, val)

     // same as rotating bits by 4
     __builtin_avr_insert_bits (0x32107654, bits, 0)

     // high nibble of result is the high nibble of val
     // low nibble of result is the low nibble of bits
     __builtin_avr_insert_bits (0xffff3210, bits, val)

     // reverse the bit order of bits
     __builtin_avr_insert_bits (0x01234567, bits, 0)

Blackfin Built-in Functions
---------------------------

Currently, there are two Blackfin-specific built-in functions.  These are used for generating CSYNC and SSYNC machine insns without using inline assembly; by using these built-in functions the compiler can automatically add workarounds for hardware errata involving these instructions.  These functions are named as follows:

     void __builtin_bfin_csync (void)
     void __builtin_bfin_ssync (void)

FR-V Built-in Functions
-----------------------

GCC provides many FR-V-specific built-in functions.  In general, these functions are intended to be compatible with those described by FR-V Family, Softune C/C++ Compiler Manual (V6), Fujitsu Semiconductor.  The two exceptions are __MDUNPACKH and __MBTOHE, the GCC forms of which pass 128-bit values by pointer rather than by value.

Most of the functions are named after specific FR-V instructions. Such functions are said to be ``directly mapped'' and are summarized here in tabular form.

Argument Types
..............

The arguments to the built-in functions can be divided into three groups: register numbers, compile-time constants and run-time values.  In order to make this classification clear at a glance, the arguments and return values are given the following pseudo types:

Pseudo type   Real C type   Constant?   Description
uh   unsigned short   No   an unsigned halfword
uw1   unsigned int   No   an unsigned word
sw1   int   No   a signed word
uw2   unsigned long long   No
an unsigned doubleword
sw2   long long   No   a signed doubleword
const   int   Yes   an integer constant
acc   int   Yes   an ACC register number
iacc   int   Yes   an IACC register number

These pseudo types are not defined by GCC, they are simply a notational convenience used in this manual.

Arguments of type uh, uw1, sw1, uw2 and sw2 are evaluated at run time.  They correspond to register operands in the underlying FR-V instructions.

const arguments represent immediate operands in the underlying FR-V instructions.  They must be compile-time constants.

acc arguments are evaluated at compile time and specify the number of an accumulator register.  For example, an acc argument of 2 selects the ACC2 register.

iacc arguments are similar to acc arguments but specify the number of an IACC register.  See Other Built-in Functions for more details.

Directly-Mapped Integer Functions
.................................

The functions listed below map directly to FR-V I-type instructions.

Function prototype   Example usage   Assembly output
sw1 __ADDSS (sw1, sw1)
C = __ADDSS (A, B)
ADDSS A,B,C
sw1 __SCAN (sw1, sw1)
C = __SCAN (A, B)
SCAN A,B,C
sw1 __SCUTSS (sw1)
B = __SCUTSS (A)
SCUTSS A,B
sw1 __SLASS (sw1, sw1)
C = __SLASS (A, B)
SLASS A,B,C
void __SMASS (sw1, sw1)
__SMASS (A, B)
SMASS A,B
void __SMSSS (sw1, sw1)
__SMSSS (A, B)
SMSSS A,B
void __SMU (sw1, sw1)
__SMU (A, B)
SMU A,B
sw2 __SMUL (sw1, sw1)
C = __SMUL (A, B)
SMUL A,B,C
sw1 __SUBSS (sw1, sw1)
C = __SUBSS (A, B)
SUBSS A,B,C
uw2 __UMUL (uw1, uw1)
C = __UMUL (A, B)
UMUL A,B,C

Directly-Mapped Media Functions
...............................

The functions listed below map directly to FR-V M-type instructions.

Function prototype   Example usage   Assembly output
uw1 __MABSHS (sw1)
B = __MABSHS (A)
MABSHS A,B
void __MADDACCS (acc, acc)
__MADDACCS (B, A)
MADDACCS A,B
sw1 __MADDHSS (sw1, sw1)
C = __MADDHSS (A, B)
MADDHSS A,B,C
uw1 __MADDHUS (uw1, uw1)
C = __MADDHUS (A, B)
MADDHUS A,B,C
uw1 __MAND (uw1, uw1)
C = __MAND (A, B)
MAND A,B,C
void __MASACCS (acc, acc)
__MASACCS (B, A)
MASACCS A,B
uw1 __MAVEH (uw1, uw1)
C = __MAVEH (A, B)
MAVEH A,B,C
uw2 __MBTOH (uw1)
B = __MBTOH (A)
MBTOH A,B
void __MBTOHE (uw1 *, uw1)
__MBTOHE (&B, A)
MBTOHE A,B
void __MCLRACC (acc)
__MCLRACC (A)
MCLRACC A
void __MCLRACCA (void)
__MCLRACCA ()
MCLRACCA
uw1 __Mcop1 (uw1, uw1)
C = __Mcop1 (A, B)
Mcop1 A,B,C
uw1 __Mcop2 (uw1, uw1)
C = __Mcop2 (A, B)
Mcop2 A,B,C
uw1 __MCPLHI (uw2, const)
C = __MCPLHI (A, B)
MCPLHI A,#B,C
uw1 __MCPLI (uw2, const)
C = __MCPLI (A, B)
MCPLI A,#B,C
void __MCPXIS (acc, sw1, sw1)
__MCPXIS (C, A, B)
MCPXIS A,B,C
void __MCPXIU (acc, uw1, uw1)
__MCPXIU (C, A, B)
MCPXIU A,B,C
void __MCPXRS (acc, sw1, sw1)
__MCPXRS (C, A, B)
MCPXRS A,B,C
void __MCPXRU (acc, uw1, uw1)
__MCPXRU (C, A, B)
MCPXRU A,B,C
uw1 __MCUT (acc, uw1)
C = __MCUT (A, B)
MCUT A,B,C
uw1 __MCUTSS (acc, sw1)
C = __MCUTSS (A, B)
MCUTSS A,B,C
void __MDADDACCS (acc, acc)
__MDADDACCS (B, A)
MDADDACCS A,B
void __MDASACCS (acc, acc)
__MDASACCS (B, A)
MDASACCS A,B
uw2 __MDCUTSSI (acc, const)
C = __MDCUTSSI (A, B)
MDCUTSSI A,#B,C
uw2 __MDPACKH (uw2, uw2)
C = __MDPACKH (A, B)
MDPACKH A,B,C
uw2 __MDROTLI (uw2, const)
C = __MDROTLI (A, B)
MDROTLI A,#B,C
void __MDSUBACCS (acc, acc)
__MDSUBACCS (B, A)
MDSUBACCS A,B
void __MDUNPACKH (uw1 *, uw2)
__MDUNPACKH (&B, A)
MDUNPACKH A,B
uw2 __MEXPDHD (uw1, const)
C = __MEXPDHD (A, B)
MEXPDHD A,#B,C
uw1 __MEXPDHW (uw1, const)
C = __MEXPDHW (A, B)
MEXPDHW A,#B,C
uw1 __MHDSETH (uw1, const)
C = __MHDSETH (A, B)
MHDSETH A,#B,C
sw1 __MHDSETS (const)
B = __MHDSETS (A)
MHDSETS #A,B
uw1 __MHSETHIH (uw1, const)
B = __MHSETHIH (B, A)
MHSETHIH #A,B
sw1 __MHSETHIS (sw1, const)
B = __MHSETHIS (B, A)
MHSETHIS #A,B
uw1 __MHSETLOH (uw1, const)
B = __MHSETLOH (B, A)
MHSETLOH #A,B
sw1 __MHSETLOS (sw1, const)
B = __MHSETLOS (B, A)
MHSETLOS #A,B
uw1 __MHTOB (uw2)
B = __MHTOB (A)
MHTOB A,B
void __MMACHS (acc, sw1, sw1)
__MMACHS (C, A, B)
MMACHS A,B,C
void __MMACHU (acc, uw1, uw1)
__MMACHU (C, A, B)
MMACHU A,B,C
void __MMRDHS (acc, sw1, sw1)
__MMRDHS (C, A, B)
MMRDHS A,B,C
void __MMRDHU (acc, uw1, uw1)
__MMRDHU (C, A, B)
MMRDHU A,B,C
void __MMULHS (acc, sw1, sw1)
__MMULHS (C, A, B)
MMULHS A,B,C
void __MMULHU (acc, uw1, uw1)
__MMULHU (C, A, B)
MMULHU A,B,C
void __MMULXHS (acc, sw1, sw1)
__MMULXHS (C, A, B)
MMULXHS A,B,C
void __MMULXHU (acc, uw1, uw1)
__MMULXHU (C, A, B)
MMULXHU A,B,C
uw1 __MNOT (uw1)
B = __MNOT (A)
MNOT A,B
uw1 __MOR (uw1, uw1)
C = __MOR (A, B)
MOR A,B,C
uw1 __MPACKH (uh, uh)
C = __MPACKH (A, B)
MPACKH A,B,C
sw2 __MQADDHSS (sw2, sw2)
C = __MQADDHSS (A, B)
MQADDHSS A,B,C
uw2 __MQADDHUS (uw2, uw2)
C = __MQADDHUS (A, B)
MQADDHUS A,B,C
void __MQCPXIS (acc, sw2, sw2)
__MQCPXIS (C, A, B)
MQCPXIS A,B,C
void __MQCPXIU (acc, uw2, uw2)
__MQCPXIU (C, A, B)
MQCPXIU A,B,C
void __MQCPXRS (acc, sw2, sw2)
__MQCPXRS (C, A, B)
MQCPXRS A,B,C
void __MQCPXRU (acc, uw2, uw2)
__MQCPXRU (C, A, B)
MQCPXRU A,B,C
sw2 __MQLCLRHS (sw2, sw2)
C = __MQLCLRHS (A, B)
MQLCLRHS A,B,C
sw2 __MQLMTHS (sw2, sw2)
C = __MQLMTHS (A, B)
MQLMTHS A,B,C
void __MQMACHS (acc, sw2, sw2)
__MQMACHS (C, A, B)
MQMACHS A,B,C
void __MQMACHU (acc, uw2, uw2)
__MQMACHU (C, A, B)
MQMACHU A,B,C
void __MQMACXHS (acc, sw2, sw2)
__MQMACXHS (C, A, B)
MQMACXHS A,B,C
void __MQMULHS (acc, sw2, sw2)
__MQMULHS (C, A, B)
MQMULHS A,B,C
void __MQMULHU (acc, uw2, uw2)
__MQMULHU (C, A, B)
MQMULHU A,B,C
void __MQMULXHS (acc, sw2, sw2)
__MQMULXHS (C, A, B)
MQMULXHS A,B,C
void __MQMULXHU (acc, uw2, uw2)
__MQMULXHU (C, A, B)
MQMULXHU A,B,C
sw2 __MQSATHS (sw2, sw2)
C = __MQSATHS (A, B)
MQSATHS A,B,C
uw2 __MQSLLHI (uw2, int)
C = __MQSLLHI (A, B)
MQSLLHI A,B,C
sw2 __MQSRAHI (sw2, int)
C = __MQSRAHI (A, B)
MQSRAHI A,B,C
sw2 __MQSUBHSS (sw2, sw2)
C = __MQSUBHSS (A, B)
MQSUBHSS A,B,C
uw2 __MQSUBHUS (uw2, uw2)
C = __MQSUBHUS (A, B)
MQSUBHUS A,B,C
void __MQXMACHS (acc, sw2, sw2)
__MQXMACHS (C, A, B)
MQXMACHS A,B,C
void __MQXMACXHS (acc, sw2, sw2)
__MQXMACXHS (C, A, B)
MQXMACXHS A,B,C
uw1 __MRDACC (acc)
B = __MRDACC (A)
MRDACC A,B
uw1 __MRDACCG (acc)
B = __MRDACCG (A)
MRDACCG A,B
uw1 __MROTLI (uw1, const)
C = __MROTLI (A, B)
MROTLI A,#B,C
uw1 __MROTRI (uw1, const)
C = __MROTRI (A, B)
MROTRI A,#B,C
sw1 __MSATHS (sw1, sw1)
C = __MSATHS (A, B)
MSATHS A,B,C
uw1 __MSATHU (uw1, uw1)
C = __MSATHU (A, B)
MSATHU A,B,C
uw1 __MSLLHI (uw1, const)
C = __MSLLHI (A, B)
MSLLHI A,#B,C
sw1 __MSRAHI (sw1, const)
C = __MSRAHI (A, B)
MSRAHI A,#B,C
uw1 __MSRLHI (uw1, const)
C = __MSRLHI (A, B)
MSRLHI A,#B,C
void __MSUBACCS (acc, acc)
__MSUBACCS (B, A)
MSUBACCS A,B
sw1 __MSUBHSS (sw1, sw1)
C = __MSUBHSS (A, B)
MSUBHSS A,B,C
uw1 __MSUBHUS (uw1, uw1)
C = __MSUBHUS (A, B)
MSUBHUS A,B,C
void __MTRAP (void)
__MTRAP ()
MTRAP
uw2 __MUNPACKH (uw1)
B = __MUNPACKH (A)
MUNPACKH A,B
uw1 __MWCUT (uw2, uw1)
C = __MWCUT (A, B)
MWCUT A,B,C
void __MWTACC (acc, uw1)
__MWTACC (B, A)
MWTACC A,B
void __MWTACCG (acc, uw1)
__MWTACCG (B, A)
MWTACCG A,B
uw1 __MXOR (uw1, uw1)
C = __MXOR (A, B)
MXOR A,B,C

Raw Read/Write Functions
........................

This sections describes built-in functions related to read and write instructions to access memory.  These functions generate membar instructions to flush the I/O load and stores where appropriate, as described in Fujitsu's manual described above.

unsigned char __builtin_read8 (void *DATA)

unsigned short __builtin_read16 (void *DATA)

unsigned long __builtin_read32 (void *DATA)

unsigned long long __builtin_read64 (void *DATA)

void __builtin_write8 (void *DATA, unsigned char DATUM)

void __builtin_write16 (void *DATA, unsigned short DATUM)

void __builtin_write32 (void *DATA, unsigned long DATUM)

void __builtin_write64 (void *DATA, unsigned long long DATUM)

Other Built-in Functions
........................

This section describes built-in functions that are not named after a specific FR-V instruction.

sw2 __IACCreadll (iacc REG)
     Return the full 64-bit value of IACC0.  The REG argument is reserved for future expansion and must be 0.

sw1 __IACCreadl (iacc REG)
     Return the value of IACC0H if REG is 0 and IACC0L if REG is 1. Other values of REG are rejected as invalid.

void __IACCsetll (iacc REG, sw2 X)
     Set the full 64-bit value of IACC0 to X.  The REG argument is reserved for future expansion and must be 0.

void __IACCsetl (iacc REG, sw1 X)
     Set IACC0H to X if REG is 0 and IACC0L to X if REG is 1.  Other values of REG are rejected as invalid.

void __data_prefetch0 (const void *X)
     Use the dcpl instruction to load the contents of address X into the data cache.

void __data_prefetch (const void *X)
     Use the nldub instruction to load the contents of address X into the data cache.  The instruction is issued in slot I1.

MIPS DSP Built-in Functions
---------------------------

The MIPS DSP Application-Specific Extension (ASE) includes new instructions that are designed to improve the performance of DSP and media applications.  It provides instructions that operate on packed 8-bit/16-bit integer data, Q7, Q15 and Q31 fractional data.

GCC supports MIPS DSP operations using both the generic vector extensions (see Vector Extensions) and a collection of MIPS-specific built-in functions.  Both kinds of support are enabled by the -mdsp command-line option.

Revision 2 of the ASE was introduced in the second half of 2006. This revision adds extra instructions to the original ASE, but is otherwise backwards-compatible with it.  You can select revision 2 using the command-line option -mdspr2; this option implies -mdsp.

The SCOUNT and POS bits of the DSP control register are global.  The WRDSP, EXTPDP, EXTPDPV and MTHLIP instructions modify the SCOUNT and POS bits.  During optimization, the compiler does not delete these instructions and it does not delete calls to functions containing these instructions.

At present, GCC only provides support for operations on 32-bit vectors.  The vector type associated with 8-bit integer data is usually called v4i8, the vector type associated with Q7 is usually called v4q7, the vector type associated with 16-bit integer data is usually called v2i16, and the vector type associated with Q15 is usually called v2q15.  They can be defined in C as follows:

     typedef signed char v4i8 __attribute__ ((vector_size(4)));
     typedef signed char v4q7 __attribute__ ((vector_size(4)));
     typedef short v2i16 __attribute__ ((vector_size(4)));
     typedef short v2q15 __attribute__ ((vector_size(4)));

v4i8, v4q7, v2i16 and v2q15 values are initialized in the same way as aggregates.  For example:

     v4i8 a = {1, 2, 3, 4};
     v4i8 b;
     b = (v4i8) {5, 6, 7, 8};

     v2q15 c = {0x0fcb, 0x3a75};
     v2q15 d;
     d = (v2q15) {0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15};

Note: The CPU's endianness determines the order in which values are packed.  On little-endian targets, the first value is the least significant and the last value is the most significant.  The opposite order applies to big-endian targets.  For example, the code above sets the lowest byte of a to 1 on little-endian targets and 4 on big-endian targets.

Note: Q7, Q15 and Q31 values must be initialized with their integer representation.  As shown in this example, the integer representation of a Q7 value can be obtained by multiplying the fractional value by 0x1.0p7.  The equivalent for Q15 values is to multiply by 0x1.0p15.  The equivalent for Q31 values is to multiply by 0x1.0p31.

The table below lists the v4i8 and v2q15 operations for which hardware support exists.  a and b are v4i8 values, and c and d are v2q15 values.

C code   MIPS instruction
a + b   addu.qb
c + d   addq.ph
a - b   subu.qb
c - d   subq.ph

The table below lists the v2i16 operation for which hardware support exists for the DSP ASE REV 2.  e and f are v2i16 values.

C code   MIPS instruction
e * f   mul.ph

It is easier to describe the DSP built-in functions if we first define the following types:

     typedef int q31;
     typedef int i32;
     typedef unsigned int ui32;
     typedef long long a64;

q31 and i32 are actually the same as int, but we use q31 to indicate a Q31 fractional value and i32 to indicate a 32-bit integer value.  Similarly, a64 is the same as long long, but we use a64 to indicate values that are placed in one of the four DSP accumulators ($ac0, $ac1, $ac2 or $ac3).

Also, some built-in functions prefer or require immediate numbers as parameters, because the corresponding DSP instructions accept both immediate numbers and register operands, or accept immediate numbers only.  The immediate parameters are listed as follows.

     imm0_3: 0 to 3.
     imm0_7: 0 to 7.
     imm0_15: 0 to 15.
     imm0_31: 0 to 31.
     imm0_63: 0 to 63.
     imm0_255: 0 to 255.
     imm_n32_31: -32 to 31.
     imm_n512_511: -512 to 511.

The following built-in functions map directly to a particular MIPS DSP instruction.  Please refer to the architecture specification for details on what each instruction does.

     v2q15 __builtin_mips_addq_ph (v2q15, v2q15)
     v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15)
     q31 __builtin_mips_addq_s_w (q31, q31)
     v4i8 __builtin_mips_addu_qb (v4i8, v4i8)
     v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8)
     v2q15 __builtin_mips_subq_ph (v2q15, v2q15)
     v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15)
     q31 __builtin_mips_subq_s_w (q31, q31)
     v4i8 __builtin_mips_subu_qb (v4i8, v4i8)
     v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8)
     i32 __builtin_mips_addsc (i32, i32)
     i32 __builtin_mips_addwc (i32, i32)
     i32 __builtin_mips_modsub (i32, i32)
     i32 __builtin_mips_raddu_w_qb (v4i8)
     v2q15 __builtin_mips_absq_s_ph (v2q15)
     q31 __builtin_mips_absq_s_w (q31)
     v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15)
     v2q15 __builtin_mips_precrq_ph_w (q31, q31)
     v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31)
     v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15)
     q31 __builtin_mips_preceq_w_phl (v2q15)
     q31 __builtin_mips_preceq_w_phr (v2q15)
     v2q15 __builtin_mips_precequ_ph_qbl (v4i8)
     v2q15 __builtin_mips_precequ_ph_qbr (v4i8)
     v2q15 __builtin_mips_precequ_ph_qbla (v4i8)
     v2q15 __builtin_mips_precequ_ph_qbra (v4i8)
     v2q15 __builtin_mips_preceu_ph_qbl (v4i8)
     v2q15 __builtin_mips_preceu_ph_qbr (v4i8)
     v2q15 __builtin_mips_preceu_ph_qbla (v4i8)
     v2q15 __builtin_mips_preceu_ph_qbra (v4i8)
     v4i8 __builtin_mips_shll_qb (v4i8, imm0_7)
     v4i8 __builtin_mips_shll_qb (v4i8, i32)
     v2q15 __builtin_mips_shll_ph (v2q15, imm0_15)
     v2q15 __builtin_mips_shll_ph (v2q15, i32)
     v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15)
     v2q15 __builtin_mips_shll_s_ph (v2q15, i32)
     q31 __builtin_mips_shll_s_w (q31, imm0_31)
     q31 __builtin_mips_shll_s_w (q31, i32)
     v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7)
     v4i8 __builtin_mips_shrl_qb (v4i8, i32)
     v2q15 __builtin_mips_shra_ph (v2q15, imm0_15)
     v2q15 __builtin_mips_shra_ph (v2q15, i32)
     v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15)
     v2q15 __builtin_mips_shra_r_ph (v2q15, i32)
     q31 __builtin_mips_shra_r_w (q31, imm0_31)
     q31 __builtin_mips_shra_r_w (q31, i32)
     v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15)
     v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15)
     v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15)
     q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15)
     q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15)
     a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8)
     a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8)
     a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8)
     a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8)
     a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15)
     a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31)
     a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15)
     a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31)
     a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15)
     a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15)
     a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15)
     a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15)
     a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15)
     i32 __builtin_mips_bitrev (i32)
     i32 __builtin_mips_insv (i32, i32)
     v4i8 __builtin_mips_repl_qb (imm0_255)
     v4i8 __builtin_mips_repl_qb (i32)
     v2q15 __builtin_mips_repl_ph (imm_n512_511)
     v2q15 __builtin_mips_repl_ph (i32)
     void __builtin_mips_cmpu_eq_qb (v4i8, v4i8)
     void __builtin_mips_cmpu_lt_qb (v4i8, v4i8)
     void __builtin_mips_cmpu_le_qb (v4i8, v4i8)
     i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8)
     i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8)
     i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8)
     void __builtin_mips_cmp_eq_ph (v2q15, v2q15)
     void __builtin_mips_cmp_lt_ph (v2q15, v2q15)
     void __builtin_mips_cmp_le_ph (v2q15, v2q15)
     v4i8 __builtin_mips_pick_qb (v4i8, v4i8)
     v2q15 __builtin_mips_pick_ph (v2q15, v2q15)
     v2q15 __builtin_mips_packrl_ph (v2q15, v2q15)
     i32 __builtin_mips_extr_w (a64, imm0_31)
     i32 __builtin_mips_extr_w (a64, i32)
     i32 __builtin_mips_extr_r_w (a64, imm0_31)
     i32 __builtin_mips_extr_s_h (a64, i32)
     i32 __builtin_mips_extr_rs_w (a64, imm0_31)
     i32 __builtin_mips_extr_rs_w (a64, i32)
     i32 __builtin_mips_extr_s_h (a64, imm0_31)
     i32 __builtin_mips_extr_r_w (a64, i32)
     i32 __builtin_mips_extp (a64, imm0_31)
     i32 __builtin_mips_extp (a64, i32)
     i32 __builtin_mips_extpdp (a64, imm0_31)
     i32 __builtin_mips_extpdp (a64, i32)
     a64 __builtin_mips_shilo (a64, imm_n32_31)
     a64 __builtin_mips_shilo (a64, i32)
     a64 __builtin_mips_mthlip (a64, i32)
     void __builtin_mips_wrdsp (i32, imm0_63)
     i32 __builtin_mips_rddsp (imm0_63)
     i32 __builtin_mips_lbux (void *, i32)
     i32 __builtin_mips_lhx (void *, i32)
     i32 __builtin_mips_lwx (void *, i32)
     a64 __builtin_mips_ldx (void *, i32) [MIPS64 only]
     i32 __builtin_mips_bposge32 (void)
     a64 __builtin_mips_madd (a64, i32, i32);
     a64 __builtin_mips_maddu (a64, ui32, ui32);
     a64 __builtin_mips_msub (a64, i32, i32);
     a64 __builtin_mips_msubu (a64, ui32, ui32);
     a64 __builtin_mips_mult (i32, i32);
     a64 __builtin_mips_multu (ui32, ui32);

The following built-in functions map directly to a particular MIPS DSP REV 2 instruction.  Please refer to the architecture specification for details on what each instruction does.

     v4q7 __builtin_mips_absq_s_qb (v4q7);
     v2i16 __builtin_mips_addu_ph (v2i16, v2i16);
     v2i16 __builtin_mips_addu_s_ph (v2i16, v2i16);
     v4i8 __builtin_mips_adduh_qb (v4i8, v4i8);
     v4i8 __builtin_mips_adduh_r_qb (v4i8, v4i8);
     i32 __builtin_mips_append (i32, i32, imm0_31);
     i32 __builtin_mips_balign (i32, i32, imm0_3);
     i32 __builtin_mips_cmpgdu_eq_qb (v4i8, v4i8);
     i32 __builtin_mips_cmpgdu_lt_qb (v4i8, v4i8);
     i32 __builtin_mips_cmpgdu_le_qb (v4i8, v4i8);
     a64 __builtin_mips_dpa_w_ph (a64, v2i16, v2i16);
     a64 __builtin_mips_dps_w_ph (a64, v2i16, v2i16);
     v2i16 __builtin_mips_mul_ph (v2i16, v2i16);
     v2i16 __builtin_mips_mul_s_ph (v2i16, v2i16);
     q31 __builtin_mips_mulq_rs_w (q31, q31);
     v2q15 __builtin_mips_mulq_s_ph (v2q15, v2q15);
     q31 __builtin_mips_mulq_s_w (q31, q31);
     a64 __builtin_mips_mulsa_w_ph (a64, v2i16, v2i16);
     v4i8 __builtin_mips_precr_qb_ph (v2i16, v2i16);
     v2i16 __builtin_mips_precr_sra_ph_w (i32, i32, imm0_31);
     v2i16 __builtin_mips_precr_sra_r_ph_w (i32, i32, imm0_31);
     i32 __builtin_mips_prepend (i32, i32, imm0_31);
     v4i8 __builtin_mips_shra_qb (v4i8, imm0_7);
     v4i8 __builtin_mips_shra_r_qb (v4i8, imm0_7);
     v4i8 __builtin_mips_shra_qb (v4i8, i32);
     v4i8 __builtin_mips_shra_r_qb (v4i8, i32);
     v2i16 __builtin_mips_shrl_ph (v2i16, imm0_15);
     v2i16 __builtin_mips_shrl_ph (v2i16, i32);
     v2i16 __builtin_mips_subu_ph (v2i16, v2i16);
     v2i16 __builtin_mips_subu_s_ph (v2i16, v2i16);
     v4i8 __builtin_mips_subuh_qb (v4i8, v4i8);
     v4i8 __builtin_mips_subuh_r_qb (v4i8, v4i8);
     v2q15 __builtin_mips_addqh_ph (v2q15, v2q15);
     v2q15 __builtin_mips_addqh_r_ph (v2q15, v2q15);
     q31 __builtin_mips_addqh_w (q31, q31);
     q31 __builtin_mips_addqh_r_w (q31, q31);
     v2q15 __builtin_mips_subqh_ph (v2q15, v2q15);
     v2q15 __builtin_mips_subqh_r_ph (v2q15, v2q15);
     q31 __builtin_mips_subqh_w (q31, q31);
     q31 __builtin_mips_subqh_r_w (q31, q31);
     a64 __builtin_mips_dpax_w_ph (a64, v2i16, v2i16);
     a64 __builtin_mips_dpsx_w_ph (a64, v2i16, v2i16);
     a64 __builtin_mips_dpaqx_s_w_ph (a64, v2q15, v2q15);
     a64 __builtin_mips_dpaqx_sa_w_ph (a64, v2q15, v2q15);
     a64 __builtin_mips_dpsqx_s_w_ph (a64, v2q15, v2q15);
     a64 __builtin_mips_dpsqx_sa_w_ph (a64, v2q15, v2q15);

MIPS Paired-Single Support
--------------------------

The MIPS64 architecture includes a number of instructions that operate on pairs of single-precision floating-point values. Each pair is packed into a 64-bit floating-point register, with one element being designated the ``upper half'' and the other being designated the ``lower half''.

GCC supports paired-single operations using both the generic vector extensions (see Vector Extensions) and a collection of MIPS-specific built-in functions.  Both kinds of support are enabled by the -mpaired-single command-line option.

The vector type associated with paired-single values is usually called v2sf.  It can be defined in C as follows:

     typedef float v2sf __attribute__ ((vector_size (8)));

v2sf values are initialized in the same way as aggregates. For example:

     v2sf a = {1.5, 9.1};
     v2sf b;
     float e, f;
     b = (v2sf) {e, f};

Note: The CPU's endianness determines which value is stored in the upper half of a register and which value is stored in the lower half. On little-endian targets, the first value is the lower one and the second value is the upper one.  The opposite order applies to big-endian targets. For example, the code above sets the lower half of a to 1.5 on little-endian targets and 9.1 on big-endian targets.

MIPS Loongson Built-in Functions
--------------------------------

GCC provides intrinsics to access the SIMD instructions provided by the ST Microelectronics Loongson-2E and -2F processors.  These intrinsics, available after inclusion of the loongson.h header file, operate on the following 64-bit vector types:

  * uint8x8_t, a vector of eight unsigned 8-bit integers;

  * uint16x4_t, a vector of four unsigned 16-bit integers;

  * uint32x2_t, a vector of two unsigned 32-bit integers;

  * int8x8_t, a vector of eight signed 8-bit integers;

  * int16x4_t, a vector of four signed 16-bit integers;

  * int32x2_t, a vector of two signed 32-bit integers.

The intrinsics provided are listed below; each is named after the machine instruction to which it corresponds, with suffixes added as appropriate to distinguish intrinsics that expand to the same machine instruction yet have different argument types.  Refer to the architecture documentation for a description of the functionality of each instruction.

     int16x4_t packsswh (int32x2_t s, int32x2_t t);
     int8x8_t packsshb (int16x4_t s, int16x4_t t);
     uint8x8_t packushb (uint16x4_t s, uint16x4_t t);
     uint32x2_t paddw_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t paddh_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t paddb_u (uint8x8_t s, uint8x8_t t);
     int32x2_t paddw_s (int32x2_t s, int32x2_t t);
     int16x4_t paddh_s (int16x4_t s, int16x4_t t);
     int8x8_t paddb_s (int8x8_t s, int8x8_t t);
     uint64_t paddd_u (uint64_t s, uint64_t t);
     int64_t paddd_s (int64_t s, int64_t t);
     int16x4_t paddsh (int16x4_t s, int16x4_t t);
     int8x8_t paddsb (int8x8_t s, int8x8_t t);
     uint16x4_t paddush (uint16x4_t s, uint16x4_t t);
     uint8x8_t paddusb (uint8x8_t s, uint8x8_t t);
     uint64_t pandn_ud (uint64_t s, uint64_t t);
     uint32x2_t pandn_uw (uint32x2_t s, uint32x2_t t);
     uint16x4_t pandn_uh (uint16x4_t s, uint16x4_t t);
     uint8x8_t pandn_ub (uint8x8_t s, uint8x8_t t);
     int64_t pandn_sd (int64_t s, int64_t t);
     int32x2_t pandn_sw (int32x2_t s, int32x2_t t);
     int16x4_t pandn_sh (int16x4_t s, int16x4_t t);
     int8x8_t pandn_sb (int8x8_t s, int8x8_t t);
     uint16x4_t pavgh (uint16x4_t s, uint16x4_t t);
     uint8x8_t pavgb (uint8x8_t s, uint8x8_t t);
     uint32x2_t pcmpeqw_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t pcmpeqh_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t pcmpeqb_u (uint8x8_t s, uint8x8_t t);
     int32x2_t pcmpeqw_s (int32x2_t s, int32x2_t t);
     int16x4_t pcmpeqh_s (int16x4_t s, int16x4_t t);
     int8x8_t pcmpeqb_s (int8x8_t s, int8x8_t t);
     uint32x2_t pcmpgtw_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t pcmpgth_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t pcmpgtb_u (uint8x8_t s, uint8x8_t t);
     int32x2_t pcmpgtw_s (int32x2_t s, int32x2_t t);
     int16x4_t pcmpgth_s (int16x4_t s, int16x4_t t);
     int8x8_t pcmpgtb_s (int8x8_t s, int8x8_t t);
     uint16x4_t pextrh_u (uint16x4_t s, int field);
     int16x4_t pextrh_s (int16x4_t s, int field);
     uint16x4_t pinsrh_0_u (uint16x4_t s, uint16x4_t t);
     uint16x4_t pinsrh_1_u (uint16x4_t s, uint16x4_t t);
     uint16x4_t pinsrh_2_u (uint16x4_t s, uint16x4_t t);
     uint16x4_t pinsrh_3_u (uint16x4_t s, uint16x4_t t);
     int16x4_t pinsrh_0_s (int16x4_t s, int16x4_t t);
     int16x4_t pinsrh_1_s (int16x4_t s, int16x4_t t);
     int16x4_t pinsrh_2_s (int16x4_t s, int16x4_t t);
     int16x4_t pinsrh_3_s (int16x4_t s, int16x4_t t);
     int32x2_t pmaddhw (int16x4_t s, int16x4_t t);
     int16x4_t pmaxsh (int16x4_t s, int16x4_t t);
     uint8x8_t pmaxub (uint8x8_t s, uint8x8_t t);
     int16x4_t pminsh (int16x4_t s, int16x4_t t);
     uint8x8_t pminub (uint8x8_t s, uint8x8_t t);
     uint8x8_t pmovmskb_u (uint8x8_t s);
     int8x8_t pmovmskb_s (int8x8_t s);
     uint16x4_t pmulhuh (uint16x4_t s, uint16x4_t t);
     int16x4_t pmulhh (int16x4_t s, int16x4_t t);
     int16x4_t pmullh (int16x4_t s, int16x4_t t);
     int64_t pmuluw (uint32x2_t s, uint32x2_t t);
     uint8x8_t pasubub (uint8x8_t s, uint8x8_t t);
     uint16x4_t biadd (uint8x8_t s);
     uint16x4_t psadbh (uint8x8_t s, uint8x8_t t);
     uint16x4_t pshufh_u (uint16x4_t dest, uint16x4_t s, uint8_t order);
     int16x4_t pshufh_s (int16x4_t dest, int16x4_t s, uint8_t order);
     uint16x4_t psllh_u (uint16x4_t s, uint8_t amount);
     int16x4_t psllh_s (int16x4_t s, uint8_t amount);
     uint32x2_t psllw_u (uint32x2_t s, uint8_t amount);
     int32x2_t psllw_s (int32x2_t s, uint8_t amount);
     uint16x4_t psrlh_u (uint16x4_t s, uint8_t amount);
     int16x4_t psrlh_s (int16x4_t s, uint8_t amount);
     uint32x2_t psrlw_u (uint32x2_t s, uint8_t amount);
     int32x2_t psrlw_s (int32x2_t s, uint8_t amount);
     uint16x4_t psrah_u (uint16x4_t s, uint8_t amount);
     int16x4_t psrah_s (int16x4_t s, uint8_t amount);
     uint32x2_t psraw_u (uint32x2_t s, uint8_t amount);
     int32x2_t psraw_s (int32x2_t s, uint8_t amount);
     uint32x2_t psubw_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t psubh_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t psubb_u (uint8x8_t s, uint8x8_t t);
     int32x2_t psubw_s (int32x2_t s, int32x2_t t);
     int16x4_t psubh_s (int16x4_t s, int16x4_t t);
     int8x8_t psubb_s (int8x8_t s, int8x8_t t);
     uint64_t psubd_u (uint64_t s, uint64_t t);
     int64_t psubd_s (int64_t s, int64_t t);
     int16x4_t psubsh (int16x4_t s, int16x4_t t);
     int8x8_t psubsb (int8x8_t s, int8x8_t t);
     uint16x4_t psubush (uint16x4_t s, uint16x4_t t);
     uint8x8_t psubusb (uint8x8_t s, uint8x8_t t);
     uint32x2_t punpckhwd_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t punpckhhw_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t punpckhbh_u (uint8x8_t s, uint8x8_t t);
     int32x2_t punpckhwd_s (int32x2_t s, int32x2_t t);
     int16x4_t punpckhhw_s (int16x4_t s, int16x4_t t);
     int8x8_t punpckhbh_s (int8x8_t s, int8x8_t t);
     uint32x2_t punpcklwd_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t punpcklhw_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t punpcklbh_u (uint8x8_t s, uint8x8_t t);
     int32x2_t punpcklwd_s (int32x2_t s, int32x2_t t);
     int16x4_t punpcklhw_s (int16x4_t s, int16x4_t t);
     int8x8_t punpcklbh_s (int8x8_t s, int8x8_t t);

Paired-Single Arithmetic
........................

The table below lists the v2sf operations for which hardware support exists.  a, b and c are v2sf values and x is an integral value.

C code   MIPS instruction
a + b   add.ps
a - b   sub.ps
-a   neg.ps
a * b   mul.ps
a * b + c   madd.ps
a * b - c   msub.ps
-(a * b + c)   nmadd.ps
-(a * b - c)   nmsub.ps
x ? a : b   movn.ps/movz.ps

Note that the multiply-accumulate instructions can be disabled using the command-line option -mno-fused-madd.

Paired-Single Built-in Functions
................................

The following paired-single functions map directly to a particular MIPS instruction.  Please refer to the architecture specification for details on what each instruction does.

v2sf __builtin_mips_pll_ps (v2sf, v2sf)
     Pair lower lower (pll.ps).

v2sf __builtin_mips_pul_ps (v2sf, v2sf)
     Pair upper lower (pul.ps).

v2sf __builtin_mips_plu_ps (v2sf, v2sf)
     Pair lower upper (plu.ps).

v2sf __builtin_mips_puu_ps (v2sf, v2sf)
     Pair upper upper (puu.ps).

v2sf __builtin_mips_cvt_ps_s (float, float)
     Convert pair to paired single (cvt.ps.s).

float __builtin_mips_cvt_s_pl (v2sf)
     Convert pair lower to single (cvt.s.pl).

float __builtin_mips_cvt_s_pu (v2sf)
     Convert pair upper to single (cvt.s.pu).

v2sf __builtin_mips_abs_ps (v2sf)
     Absolute value (abs.ps).

v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int)
     Align variable (alnv.ps).

     Note: The value of the third parameter must be 0 or 4 modulo 8, otherwise the result is unpredictable.  Please read the instruction description for details.

The following multi-instruction functions are also available. In each case, COND can be any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq, ngl, lt, nge, le or ngt.

v2sf __builtin_mips_movt_c_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)
v2sf __builtin_mips_movf_c_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)
     Conditional move based on floating-point comparison (c.COND.ps, movt.ps/movf.ps).

     The movt functions return the value X computed by:

          c.COND.ps CC,A,B
          mov.ps X,C
          movt.ps X,D,CC

     The movf functions are similar but use movf.ps instead of movt.ps.

int __builtin_mips_upper_c_COND_ps (v2sf A, v2sf B)
int __builtin_mips_lower_c_COND_ps (v2sf A, v2sf B)
     Comparison of two paired-single values (c.COND.ps, bc1t/bc1f).

     These functions compare A and B using c.COND.ps and return either the upper or lower half of the result.  For example:

          v2sf a, b;
          if (__builtin_mips_upper_c_eq_ps (a, b))
            upper_halves_are_equal ();
          else
            upper_halves_are_unequal ();

          if (__builtin_mips_lower_c_eq_ps (a, b))
            lower_halves_are_equal ();
          else
            lower_halves_are_unequal ();

MIPS-3D Built-in Functions
..........................

The MIPS-3D Application-Specific Extension (ASE) includes additional paired-single instructions that are designed to improve the performance of 3D graphics operations.  Support for these instructions is controlled by the -mips3d command-line option.

The functions listed below map directly to a particular MIPS-3D instruction.  Please refer to the architecture specification for more details on what each instruction does.

v2sf __builtin_mips_addr_ps (v2sf, v2sf)
     Reduction add (addr.ps).

v2sf __builtin_mips_mulr_ps (v2sf, v2sf)
     Reduction multiply (mulr.ps).

v2sf __builtin_mips_cvt_pw_ps (v2sf)
     Convert paired single to paired word (cvt.pw.ps).

v2sf __builtin_mips_cvt_ps_pw (v2sf)
     Convert paired word to paired single (cvt.ps.pw).

float __builtin_mips_recip1_s (float)
double __builtin_mips_recip1_d (double)
v2sf __builtin_mips_recip1_ps (v2sf)
     Reduced-precision reciprocal (sequence step 1) (recip1.FMT).

float __builtin_mips_recip2_s (float, float)
double __builtin_mips_recip2_d (double, double)
v2sf __builtin_mips_recip2_ps (v2sf, v2sf)
     Reduced-precision reciprocal (sequence step 2) (recip2.FMT).

float __builtin_mips_rsqrt1_s (float)
double __builtin_mips_rsqrt1_d (double)
v2sf __builtin_mips_rsqrt1_ps (v2sf)
     Reduced-precision reciprocal square root (sequence step 1) (rsqrt1.FMT).

float __builtin_mips_rsqrt2_s (float, float)
double __builtin_mips_rsqrt2_d (double, double)
v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf)
     Reduced-precision reciprocal square root (sequence step 2) (rsqrt2.FMT).

The following multi-instruction functions are also available. In each case, COND can be any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq, ngl, lt, nge, le or ngt.

int __builtin_mips_cabs_COND_s (float A, float B)
int __builtin_mips_cabs_COND_d (double A, double B)
     Absolute comparison of two scalar values (cabs.COND.FMT, bc1t/bc1f).

     These functions compare A and B using cabs.COND.s or cabs.COND.d and return the result as a boolean value. For example:

          float a, b;
          if (__builtin_mips_cabs_eq_s (a, b))
            true ();
          else
            false ();

int __builtin_mips_upper_cabs_COND_ps (v2sf A, v2sf B)
int __builtin_mips_lower_cabs_COND_ps (v2sf A, v2sf B)
     Absolute comparison of two paired-single values (cabs.COND.ps, bc1t/bc1f).

     These functions compare A and B using cabs.COND.ps and return either the upper or lower half of the result.  For example:

          v2sf a, b;
          if (__builtin_mips_upper_cabs_eq_ps (a, b))
            upper_halves_are_equal ();
          else
            upper_halves_are_unequal ();

          if (__builtin_mips_lower_cabs_eq_ps (a, b))
            lower_halves_are_equal ();
          else
            lower_halves_are_unequal ();

v2sf __builtin_mips_movt_cabs_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)
v2sf __builtin_mips_movf_cabs_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)
     Conditional move based on absolute comparison (cabs.COND.ps, movt.ps/movf.ps).

     The movt functions return the value X computed by:

          cabs.COND.ps CC,A,B
          mov.ps X,C
          movt.ps X,D,CC

     The movf functions are similar but use movf.ps instead of movt.ps.

int __builtin_mips_any_c_COND_ps (v2sf A, v2sf B)
int __builtin_mips_all_c_COND_ps (v2sf A, v2sf B)
int __builtin_mips_any_cabs_COND_ps (v2sf A, v2sf B)
int __builtin_mips_all_cabs_COND_ps (v2sf A, v2sf B)
     Comparison of two paired-single values (c.COND.ps/cabs.COND.ps, bc1any2t/bc1any2f).

     These functions compare A and B using c.COND.ps or cabs.COND.ps.  The any forms return true if either result is true and the all forms return true if both results are true. For example:

          v2sf a, b;
          if (__builtin_mips_any_c_eq_ps (a, b))
            one_is_true ();
          else
            both_are_false ();

          if (__builtin_mips_all_c_eq_ps (a, b))
            both_are_true ();
          else
            one_is_false ();

int __builtin_mips_any_c_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)
int __builtin_mips_all_c_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)
int __builtin_mips_any_cabs_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)
int __builtin_mips_all_cabs_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)
     Comparison of four paired-single values (c.COND.ps/cabs.COND.ps, bc1any4t/bc1any4f).

     These functions use c.COND.ps or cabs.COND.ps to compare A with B and to compare C with D. The any forms return true if any of the four results are true and the all forms return true if all four results are true. For example:

          v2sf a, b, c, d;
          if (__builtin_mips_any_c_eq_4s (a, b, c, d))
            some_are_true ();
          else
            all_are_false ();

          if (__builtin_mips_all_c_eq_4s (a, b, c, d))
            all_are_true ();
          else
            some_are_false ();

Other MIPS Built-in Functions
-----------------------------

GCC provides other MIPS-specific built-in functions:

void __builtin_mips_cache (int OP, const volatile void *ADDR)
     Insert a cache instruction with operands OP and ADDR. GCC defines the preprocessor macro ___GCC_HAVE_BUILTIN_MIPS_CACHE when this function is available.

unsigned int __builtin_mips_get_fcsr (void)
void __builtin_mips_set_fcsr (unsigned int VALUE)
     Get and set the contents of the floating-point control and status register (FPU control register 31).  These functions are only available in hard-float code but can be called in both MIPS16 and non-MIPS16 contexts.

     __builtin_mips_set_fcsr can be used to change any bit of the register except the condition codes, which GCC assumes are preserved.

MSP430 Built-in Functions
-------------------------

GCC provides a couple of special builtin functions to aid in the writing of interrupt handlers in C.

__bic_SR_register_on_exit (int MASK)
     This clears the indicated bits in the saved copy of the status register currently residing on the stack.  This only works inside interrupt handlers and the changes to the status register will only take affect once the handler returns.

__bis_SR_register_on_exit (int MASK)
     This sets the indicated bits in the saved copy of the status register currently residing on the stack.  This only works inside interrupt handlers and the changes to the status register will only take affect once the handler returns.

__delay_cycles (long long CYCLES)
     This inserts an instruction sequence that takes exactly CYCLES cycles (between 0 and about 17E9) to complete.  The inserted sequence may use jumps, loops, or no-ops, and does not interfere with any other instructions.  Note that CYCLES must be a compile-time constant integer - that is, you must pass a number, not a variable that may be optimized to a constant later.  The number of cycles delayed by this builtin is exact.

NDS32 Built-in Functions
------------------------

These built-in functions are available for the NDS32 target:

 -- Built-in Function: void __builtin_nds32_isync (int *ADDR)
     Insert an ISYNC instruction into the instruction stream where ADDR is an instruction address for serialization.

 -- Built-in Function: void __builtin_nds32_isb (void)
     Insert an ISB instruction into the instruction stream.

 -- Built-in Function: int __builtin_nds32_mfsr (int SR)
     Return the content of a system register which is mapped by SR.

 -- Built-in Function: int __builtin_nds32_mfusr (int USR)
     Return the content of a user space register which is mapped by USR.

 -- Built-in Function: void __builtin_nds32_mtsr (int VALUE, int SR)
     Move the VALUE to a system register which is mapped by SR.

 -- Built-in Function: void __builtin_nds32_mtusr (int VALUE, int USR)
     Move the VALUE to a user space register which is mapped by USR.

 -- Built-in Function: void __builtin_nds32_setgie_en (void)
     Enable global interrupt.

 -- Built-in Function: void __builtin_nds32_setgie_dis (void)
     Disable global interrupt.

picoChip Built-in Functions
---------------------------

GCC provides an interface to selected machine instructions from the picoChip instruction set.

int __builtin_sbc (int VALUE)
     Sign bit count.  Return the number of consecutive bits in VALUE that have the same value as the sign bit.  The result is the number of leading sign bits minus one, giving the number of redundant sign bits in VALUE.

int __builtin_byteswap (int VALUE)
     Byte swap.  Return the result of swapping the upper and lower bytes of VALUE.

int __builtin_brev (int VALUE)
     Bit reversal.  Return the result of reversing the bits in VALUE.  Bit 15 is swapped with bit 0, bit 14 is swapped with bit 1, and so on.

int __builtin_adds (int X, int Y)
     Saturating addition.  Return the result of adding X and Y, storing the value 32767 if the result overflows.

int __builtin_subs (int X, int Y)
     Saturating subtraction.  Return the result of subtracting Y from X, storing the value -32768 if the result overflows.

void __builtin_halt (void)
     Halt.  The processor stops execution.  This built-in is useful for implementing assertions.

PowerPC Built-in Functions
--------------------------

These built-in functions are available for the PowerPC family of processors:

     float __builtin_recipdivf (float, float);
     float __builtin_rsqrtf (float);
     double __builtin_recipdiv (double, double);
     double __builtin_rsqrt (double);
     uint64_t __builtin_ppc_get_timebase ();
     unsigned long __builtin_ppc_mftb ();
     double __builtin_unpack_longdouble (long double, int);
     long double __builtin_pack_longdouble (double, double);

The vec_rsqrt, __builtin_rsqrt, and __builtin_rsqrtf functions generate multiple instructions to implement the reciprocal sqrt functionality using reciprocal sqrt estimate instructions.

The __builtin_recipdiv, and __builtin_recipdivf functions generate multiple instructions to implement division using the reciprocal estimate instructions.

The __builtin_ppc_get_timebase and __builtin_ppc_mftb functions generate instructions to read the Time Base Register.  The __builtin_ppc_get_timebase function may generate multiple instructions and always returns the 64 bits of the Time Base Register. The __builtin_ppc_mftb function always generates one instruction and returns the Time Base Register value as an unsigned long, throwing away the most significant word on 32-bit environments.

The following built-in functions are available for the PowerPC family of processors, starting with ISA 2.06 or later (-mcpu=power7 or -mpopcntd):

     long __builtin_bpermd (long, long);
     int __builtin_divwe (int, int);
     int __builtin_divweo (int, int);
     unsigned int __builtin_divweu (unsigned int, unsigned int);
     unsigned int __builtin_divweuo (unsigned int, unsigned int);
     long __builtin_divde (long, long);
     long __builtin_divdeo (long, long);
     unsigned long __builtin_divdeu (unsigned long, unsigned long);
     unsigned long __builtin_divdeuo (unsigned long, unsigned long);
     unsigned int cdtbcd (unsigned int);
     unsigned int cbcdtd (unsigned int);
     unsigned int addg6s (unsigned int, unsigned int);

The __builtin_divde, __builtin_divdeo, __builtin_divdeu, __builtin_divdeou functions require a 64-bit environment support ISA 2.06 or later.

The following built-in functions are available for the PowerPC family of processors when hardware decimal floating point (-mhard-dfp) is available:

     _Decimal64 __builtin_dxex (_Decimal64);
     _Decimal128 __builtin_dxexq (_Decimal128);
     _Decimal64 __builtin_ddedpd (int, _Decimal64);
     _Decimal128 __builtin_ddedpdq (int, _Decimal128);
     _Decimal64 __builtin_denbcd (int, _Decimal64);
     _Decimal128 __builtin_denbcdq (int, _Decimal128);
     _Decimal64 __builtin_diex (_Decimal64, _Decimal64);
     _Decimal128 _builtin_diexq (_Decimal128, _Decimal128);
     _Decimal64 __builtin_dscli (_Decimal64, int);
     _Decimal128 __builtin_dscliq (_Decimal128, int);
     _Decimal64 __builtin_dscri (_Decimal64, int);
     _Decimal128 __builtin_dscriq (_Decimal128, int);
     unsigned long long __builtin_unpack_dec128 (_Decimal128, int);
     _Decimal128 __builtin_pack_dec128 (unsigned long long, unsigned long long);

The following built-in functions are available for the PowerPC family of processors when the Vector Scalar (vsx) instruction set is available:

     unsigned long long __builtin_unpack_vector_int128 (vector __int128_t, int);
     vector __int128_t __builtin_pack_vector_int128 (unsigned long long,
                                                     unsigned long long);

PowerPC AltiVec Built-in Functions
----------------------------------

GCC provides an interface for the PowerPC family of processors to access the AltiVec operations described in Motorola's AltiVec Programming Interface Manual.  The interface is made available by including <altivec.h> and using -maltivec and -mabi=altivec.  The interface supports the following vector types.

     vector unsigned char
     vector signed char
     vector bool char

     vector unsigned short
     vector signed short
     vector bool short
     vector pixel

     vector unsigned int
     vector signed int
     vector bool int
     vector float

If -mvsx is used the following additional vector types are implemented.

     vector unsigned long
     vector signed long
     vector double

The long types are only implemented for 64-bit code generation, and the long type is only used in the floating point/integer conversion instructions.

GCC's implementation of the high-level language interface available from C and C++ code differs from Motorola's documentation in several ways.

  * A vector constant is a list of constant expressions within curly braces.

  * A vector initializer requires no cast if the vector constant is of the same type as the variable it is initializing.

  * If signed or unsigned is omitted, the signedness of the vector type is the default signedness of the base type.  The default varies depending on the operating system, so a portable program should always specify the signedness.

  * Compiling with -maltivec adds keywords __vector, vector, __pixel, pixel, __bool and bool.  When compiling ISO C, the context-sensitive substitution of the keywords vector, pixel and bool is disabled.  To use them, you must include <altivec.h> instead.

  * GCC allows using a typedef name as the type specifier for a vector type.

  * For C, overloaded functions are implemented with macros so the following does not work:

            vec_add ((vector signed int){1, 2, 3, 4}, foo);

     Since vec_add is a macro, the vector constant in the example is treated as four separate arguments.  Wrap the entire argument in parentheses for this to work.

Note: Only the <altivec.h> interface is supported. Internally, GCC uses built-in functions to achieve the functionality in the aforementioned header file, but they are not supported and are subject to change without notice.

The following interfaces are supported for the generic and specific AltiVec operations and the AltiVec predicates.  In cases where there is a direct mapping between generic and specific operations, only the generic names are shown here, although the specific operations can also be used.

Arguments that are documented as const int require literal integral values within the range required for that operation.

     vector signed char vec_abs (vector signed char);
     vector signed short vec_abs (vector signed short);
     vector signed int vec_abs (vector signed int);
     vector float vec_abs (vector float);

     vector signed char vec_abss (vector signed char);
     vector signed short vec_abss (vector signed short);
     vector signed int vec_abss (vector signed int);

     vector signed char vec_add (vector bool char, vector signed char);
     vector signed char vec_add (vector signed char, vector bool char);
     vector signed char vec_add (vector signed char, vector signed char);
     vector unsigned char vec_add (vector bool char, vector unsigned char);
     vector unsigned char vec_add (vector unsigned char, vector bool char);
     vector unsigned char vec_add (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_add (vector bool short, vector signed short);
     vector signed short vec_add (vector signed short, vector bool short);
     vector signed short vec_add (vector signed short, vector signed short);
     vector unsigned short vec_add (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_add (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_add (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_add (vector bool int, vector signed int);
     vector signed int vec_add (vector signed int, vector bool int);
     vector signed int vec_add (vector signed int, vector signed int);
     vector unsigned int vec_add (vector bool int, vector unsigned int);
     vector unsigned int vec_add (vector unsigned int, vector bool int);
     vector unsigned int vec_add (vector unsigned int, vector unsigned int);
     vector float vec_add (vector float, vector float);

     vector float vec_vaddfp (vector float, vector float);

     vector signed int vec_vadduwm (vector bool int, vector signed int);
     vector signed int vec_vadduwm (vector signed int, vector bool int);
     vector signed int vec_vadduwm (vector signed int, vector signed int);
     vector unsigned int vec_vadduwm (vector bool int, vector unsigned int);
     vector unsigned int vec_vadduwm (vector unsigned int, vector bool int);
     vector unsigned int vec_vadduwm (vector unsigned int,
                                      vector unsigned int);

     vector signed short vec_vadduhm (vector bool short,
                                      vector signed short);
     vector signed short vec_vadduhm (vector signed short,
                                      vector bool short);
     vector signed short vec_vadduhm (vector signed short,
                                      vector signed short);
     vector unsigned short vec_vadduhm (vector bool short,
                                        vector unsigned short);
     vector unsigned short vec_vadduhm (vector unsigned short,
                                        vector bool short);
     vector unsigned short vec_vadduhm (vector unsigned short,
                                        vector unsigned short);

     vector signed char vec_vaddubm (vector bool char, vector signed char);
     vector signed char vec_vaddubm (vector signed char, vector bool char);
     vector signed char vec_vaddubm (vector signed char, vector signed char);
     vector unsigned char vec_vaddubm (vector bool char,
                                       vector unsigned char);
     vector unsigned char vec_vaddubm (vector unsigned char,
                                       vector bool char);
     vector unsigned char vec_vaddubm (vector unsigned char,
                                       vector unsigned char);

     vector unsigned int vec_addc (vector unsigned int, vector unsigned int);

     vector unsigned char vec_adds (vector bool char, vector unsigned char);
     vector unsigned char vec_adds (vector unsigned char, vector bool char);
     vector unsigned char vec_adds (vector unsigned char,
                                    vector unsigned char);
     vector signed char vec_adds (vector bool char, vector signed char);
     vector signed char vec_adds (vector signed char, vector bool char);
     vector signed char vec_adds (vector signed char, vector signed char);
     vector unsigned short vec_adds (vector bool short,
                                     vector unsigned short);
     vector unsigned short vec_adds (vector unsigned short,
                                     vector bool short);
     vector unsigned short vec_adds (vector unsigned short,
                                     vector unsigned short);
     vector signed short vec_adds (vector bool short, vector signed short);
     vector signed short vec_adds (vector signed short, vector bool short);
     vector signed short vec_adds (vector signed short, vector signed short);
     vector unsigned int vec_adds (vector bool int, vector unsigned int);
     vector unsigned int vec_adds (vector unsigned int, vector bool int);
     vector unsigned int vec_adds (vector unsigned int, vector unsigned int);
     vector signed int vec_adds (vector bool int, vector signed int);
     vector signed int vec_adds (vector signed int, vector bool int);
     vector signed int vec_adds (vector signed int, vector signed int);

     vector signed int vec_vaddsws (vector bool int, vector signed int);
     vector signed int vec_vaddsws (vector signed int, vector bool int);
     vector signed int vec_vaddsws (vector signed int, vector signed int);

     vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
     vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
     vector unsigned int vec_vadduws (vector unsigned int,
                                      vector unsigned int);

     vector signed short vec_vaddshs (vector bool short,
                                      vector signed short);
     vector signed short vec_vaddshs (vector signed short,
                                      vector bool short);
     vector signed short vec_vaddshs (vector signed short,
                                      vector signed short);

     vector unsigned short vec_vadduhs (vector bool short,
                                        vector unsigned short);
     vector unsigned short vec_vadduhs (vector unsigned short,
                                        vector bool short);
     vector unsigned short vec_vadduhs (vector unsigned short,
                                        vector unsigned short);

     vector signed char vec_vaddsbs (vector bool char, vector signed char);
     vector signed char vec_vaddsbs (vector signed char, vector bool char);
     vector signed char vec_vaddsbs (vector signed char, vector signed char);

     vector unsigned char vec_vaddubs (vector bool char,
                                       vector unsigned char);
     vector unsigned char vec_vaddubs (vector unsigned char,
                                       vector bool char);
     vector unsigned char vec_vaddubs (vector unsigned char,
                                       vector unsigned char);

     vector float vec_and (vector float, vector float);
     vector float vec_and (vector float, vector bool int);
     vector float vec_and (vector bool int, vector float);
     vector bool int vec_and (vector bool int, vector bool int);
     vector signed int vec_and (vector bool int, vector signed int);
     vector signed int vec_and (vector signed int, vector bool int);
     vector signed int vec_and (vector signed int, vector signed int);
     vector unsigned int vec_and (vector bool int, vector unsigned int);
     vector unsigned int vec_and (vector unsigned int, vector bool int);
     vector unsigned int vec_and (vector unsigned int, vector unsigned int);
     vector bool short vec_and (vector bool short, vector bool short);
     vector signed short vec_and (vector bool short, vector signed short);
     vector signed short vec_and (vector signed short, vector bool short);
     vector signed short vec_and (vector signed short, vector signed short);
     vector unsigned short vec_and (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_and (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_and (vector unsigned short,
                                    vector unsigned short);
     vector signed char vec_and (vector bool char, vector signed char);
     vector bool char vec_and (vector bool char, vector bool char);
     vector signed char vec_and (vector signed char, vector bool char);
     vector signed char vec_and (vector signed char, vector signed char);
     vector unsigned char vec_and (vector bool char, vector unsigned char);
     vector unsigned char vec_and (vector unsigned char, vector bool char);
     vector unsigned char vec_and (vector unsigned char,
                                   vector unsigned char);

     vector float vec_andc (vector float, vector float);
     vector float vec_andc (vector float, vector bool int);
     vector float vec_andc (vector bool int, vector float);
     vector bool int vec_andc (vector bool int, vector bool int);
     vector signed int vec_andc (vector bool int, vector signed int);
     vector signed int vec_andc (vector signed int, vector bool int);
     vector signed int vec_andc (vector signed int, vector signed int);
     vector unsigned int vec_andc (vector bool int, vector unsigned int);
     vector unsigned int vec_andc (vector unsigned int, vector bool int);
     vector unsigned int vec_andc (vector unsigned int, vector unsigned int);
     vector bool short vec_andc (vector bool short, vector bool short);
     vector signed short vec_andc (vector bool short, vector signed short);
     vector signed short vec_andc (vector signed short, vector bool short);
     vector signed short vec_andc (vector signed short, vector signed short);
     vector unsigned short vec_andc (vector bool short,
                                     vector unsigned short);
     vector unsigned short vec_andc (vector unsigned short,
                                     vector bool short);
     vector unsigned short vec_andc (vector unsigned short,
                                     vector unsigned short);
     vector signed char vec_andc (vector bool char, vector signed char);
     vector bool char vec_andc (vector bool char, vector bool char);
     vector signed char vec_andc (vector signed char, vector bool char);
     vector signed char vec_andc (vector signed char, vector signed char);
     vector unsigned char vec_andc (vector bool char, vector unsigned char);
     vector unsigned char vec_andc (vector unsigned char, vector bool char);
     vector unsigned char vec_andc (vector unsigned char,
                                    vector unsigned char);

     vector unsigned char vec_avg (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_avg (vector signed char, vector signed char);
     vector unsigned short vec_avg (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_avg (vector signed short, vector signed short);
     vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
     vector signed int vec_avg (vector signed int, vector signed int);

     vector signed int vec_vavgsw (vector signed int, vector signed int);

     vector unsigned int vec_vavguw (vector unsigned int,
                                     vector unsigned int);

     vector signed short vec_vavgsh (vector signed short,
                                     vector signed short);

     vector unsigned short vec_vavguh (vector unsigned short,
                                       vector unsigned short);

     vector signed char vec_vavgsb (vector signed char, vector signed char);

     vector unsigned char vec_vavgub (vector unsigned char,
                                      vector unsigned char);

     vector float vec_copysign (vector float);

     vector float vec_ceil (vector float);

     vector signed int vec_cmpb (vector float, vector float);

     vector bool char vec_cmpeq (vector signed char, vector signed char);
     vector bool char vec_cmpeq (vector unsigned char, vector unsigned char);
     vector bool short vec_cmpeq (vector signed short, vector signed short);
     vector bool short vec_cmpeq (vector unsigned short,
                                  vector unsigned short);
     vector bool int vec_cmpeq (vector signed int, vector signed int);
     vector bool int vec_cmpeq (vector unsigned int, vector unsigned int);
     vector bool int vec_cmpeq (vector float, vector float);

     vector bool int vec_vcmpeqfp (vector float, vector float);

     vector bool int vec_vcmpequw (vector signed int, vector signed int);
     vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);

     vector bool short vec_vcmpequh (vector signed short,
                                     vector signed short);
     vector bool short vec_vcmpequh (vector unsigned short,
                                     vector unsigned short);

     vector bool char vec_vcmpequb (vector signed char, vector signed char);
     vector bool char vec_vcmpequb (vector unsigned char,
                                    vector unsigned char);

     vector bool int vec_cmpge (vector float, vector float);

     vector bool char vec_cmpgt (vector unsigned char, vector unsigned char);
     vector bool char vec_cmpgt (vector signed char, vector signed char);
     vector bool short vec_cmpgt (vector unsigned short,
                                  vector unsigned short);
     vector bool short vec_cmpgt (vector signed short, vector signed short);
     vector bool int vec_cmpgt (vector unsigned int, vector unsigned int);
     vector bool int vec_cmpgt (vector signed int, vector signed int);
     vector bool int vec_cmpgt (vector float, vector float);

     vector bool int vec_vcmpgtfp (vector float, vector float);

     vector bool int vec_vcmpgtsw (vector signed int, vector signed int);

     vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);

     vector bool short vec_vcmpgtsh (vector signed short,
                                     vector signed short);

     vector bool short vec_vcmpgtuh (vector unsigned short,
                                     vector unsigned short);

     vector bool char vec_vcmpgtsb (vector signed char, vector signed char);

     vector bool char vec_vcmpgtub (vector unsigned char,
                                    vector unsigned char);

     vector bool int vec_cmple (vector float, vector float);

     vector bool char vec_cmplt (vector unsigned char, vector unsigned char);
     vector bool char vec_cmplt (vector signed char, vector signed char);
     vector bool short vec_cmplt (vector unsigned short,
                                  vector unsigned short);
     vector bool short vec_cmplt (vector signed short, vector signed short);
     vector bool int vec_cmplt (vector unsigned int, vector unsigned int);
     vector bool int vec_cmplt (vector signed int, vector signed int);
     vector bool int vec_cmplt (vector float, vector float);

     vector float vec_cpsgn (vector float, vector float);

     vector float vec_ctf (vector unsigned int, const int);
     vector float vec_ctf (vector signed int, const int);
     vector double vec_ctf (vector unsigned long, const int);
     vector double vec_ctf (vector signed long, const int);

     vector float vec_vcfsx (vector signed int, const int);

     vector float vec_vcfux (vector unsigned int, const int);

     vector signed int vec_cts (vector float, const int);
     vector signed long vec_cts (vector double, const int);

     vector unsigned int vec_ctu (vector float, const int);
     vector unsigned long vec_ctu (vector double, const int);

     void vec_dss (const int);

     void vec_dssall (void);

     void vec_dst (const vector unsigned char *, int, const int);
     void vec_dst (const vector signed char *, int, const int);
     void vec_dst (const vector bool char *, int, const int);
     void vec_dst (const vector unsigned short *, int, const int);
     void vec_dst (const vector signed short *, int, const int);
     void vec_dst (const vector bool short *, int, const int);
     void vec_dst (const vector pixel *, int, const int);
     void vec_dst (const vector unsigned int *, int, const int);
     void vec_dst (const vector signed int *, int, const int);
     void vec_dst (const vector bool int *, int, const int);
     void vec_dst (const vector float *, int, const int);
     void vec_dst (const unsigned char *, int, const int);
     void vec_dst (const signed char *, int, const int);
     void vec_dst (const unsigned short *, int, const int);
     void vec_dst (const short *, int, const int);
     void vec_dst (const unsigned int *, int, const int);
     void vec_dst (const int *, int, const int);
     void vec_dst (const unsigned long *, int, const int);
     void vec_dst (const long *, int, const int);
     void vec_dst (const float *, int, const int);

     void vec_dstst (const vector unsigned char *, int, const int);
     void vec_dstst (const vector signed char *, int, const int);
     void vec_dstst (const vector bool char *, int, const int);
     void vec_dstst (const vector unsigned short *, int, const int);
     void vec_dstst (const vector signed short *, int, const int);
     void vec_dstst (const vector bool short *, int, const int);
     void vec_dstst (const vector pixel *, int, const int);
     void vec_dstst (const vector unsigned int *, int, const int);
     void vec_dstst (const vector signed int *, int, const int);
     void vec_dstst (const vector bool int *, int, const int);
     void vec_dstst (const vector float *, int, const int);
     void vec_dstst (const unsigned char *, int, const int);
     void vec_dstst (const signed char *, int, const int);
     void vec_dstst (const unsigned short *, int, const int);
     void vec_dstst (const short *, int, const int);
     void vec_dstst (const unsigned int *, int, const int);
     void vec_dstst (const int *, int, const int);
     void vec_dstst (const unsigned long *, int, const int);
     void vec_dstst (const long *, int, const int);
     void vec_dstst (const float *, int, const int);

     void vec_dststt (const vector unsigned char *, int, const int);
     void vec_dststt (const vector signed char *, int, const int);
     void vec_dststt (const vector bool char *, int, const int);
     void vec_dststt (const vector unsigned short *, int, const int);
     void vec_dststt (const vector signed short *, int, const int);
     void vec_dststt (const vector bool short *, int, const int);
     void vec_dststt (const vector pixel *, int, const int);
     void vec_dststt (const vector unsigned int *, int, const int);
     void vec_dststt (const vector signed int *, int, const int);
     void vec_dststt (const vector bool int *, int, const int);
     void vec_dststt (const vector float *, int, const int);
     void vec_dststt (const unsigned char *, int, const int);
     void vec_dststt (const signed char *, int, const int);
     void vec_dststt (const unsigned short *, int, const int);
     void vec_dststt (const short *, int, const int);
     void vec_dststt (const unsigned int *, int, const int);
     void vec_dststt (const int *, int, const int);
     void vec_dststt (const unsigned long *, int, const int);
     void vec_dststt (const long *, int, const int);
     void vec_dststt (const float *, int, const int);

     void vec_dstt (const vector unsigned char *, int, const int);
     void vec_dstt (const vector signed char *, int, const int);
     void vec_dstt (const vector bool char *, int, const int);
     void vec_dstt (const vector unsigned short *, int, const int);
     void vec_dstt (const vector signed short *, int, const int);
     void vec_dstt (const vector bool short *, int, const int);
     void vec_dstt (const vector pixel *, int, const int);
     void vec_dstt (const vector unsigned int *, int, const int);
     void vec_dstt (const vector signed int *, int, const int);
     void vec_dstt (const vector bool int *, int, const int);
     void vec_dstt (const vector float *, int, const int);
     void vec_dstt (const unsigned char *, int, const int);
     void vec_dstt (const signed char *, int, const int);
     void vec_dstt (const unsigned short *, int, const int);
     void vec_dstt (const short *, int, const int);
     void vec_dstt (const unsigned int *, int, const int);
     void vec_dstt (const int *, int, const int);
     void vec_dstt (const unsigned long *, int, const int);
     void vec_dstt (const long *, int, const int);
     void vec_dstt (const float *, int, const int);

     vector float vec_expte (vector float);

     vector float vec_floor (vector float);

     vector float vec_ld (int, const vector float *);
     vector float vec_ld (int, const float *);
     vector bool int vec_ld (int, const vector bool int *);
     vector signed int vec_ld (int, const vector signed int *);
     vector signed int vec_ld (int, const int *);
     vector signed int vec_ld (int, const long *);
     vector unsigned int vec_ld (int, const vector unsigned int *);
     vector unsigned int vec_ld (int, const unsigned int *);
     vector unsigned int vec_ld (int, const unsigned long *);
     vector bool short vec_ld (int, const vector bool short *);
     vector pixel vec_ld (int, const vector pixel *);
     vector signed short vec_ld (int, const vector signed short *);
     vector signed short vec_ld (int, const short *);
     vector unsigned short vec_ld (int, const vector unsigned short *);
     vector unsigned short vec_ld (int, const unsigned short *);
     vector bool char vec_ld (int, const vector bool char *);
     vector signed char vec_ld (int, const vector signed char *);
     vector signed char vec_ld (int, const signed char *);
     vector unsigned char vec_ld (int, const vector unsigned char *);
     vector unsigned char vec_ld (int, const unsigned char *);

     vector signed char vec_lde (int, const signed char *);
     vector unsigned char vec_lde (int, const unsigned char *);
     vector signed short vec_lde (int, const short *);
     vector unsigned short vec_lde (int, const unsigned short *);
     vector float vec_lde (int, const float *);
     vector signed int vec_lde (int, const int *);
     vector unsigned int vec_lde (int, const unsigned int *);
     vector signed int vec_lde (int, const long *);
     vector unsigned int vec_lde (int, const unsigned long *);

     vector float vec_lvewx (int, float *);
     vector signed int vec_lvewx (int, int *);
     vector unsigned int vec_lvewx (int, unsigned int *);
     vector signed int vec_lvewx (int, long *);
     vector unsigned int vec_lvewx (int, unsigned long *);

     vector signed short vec_lvehx (int, short *);
     vector unsigned short vec_lvehx (int, unsigned short *);

     vector signed char vec_lvebx (int, char *);
     vector unsigned char vec_lvebx (int, unsigned char *);

     vector float vec_ldl (int, const vector float *);
     vector float vec_ldl (int, const float *);
     vector bool int vec_ldl (int, const vector bool int *);
     vector signed int vec_ldl (int, const vector signed int *);
     vector signed int vec_ldl (int, const int *);
     vector signed int vec_ldl (int, const long *);
     vector unsigned int vec_ldl (int, const vector unsigned int *);
     vector unsigned int vec_ldl (int, const unsigned int *);
     vector unsigned int vec_ldl (int, const unsigned long *);
     vector bool short vec_ldl (int, const vector bool short *);
     vector pixel vec_ldl (int, const vector pixel *);
     vector signed short vec_ldl (int, const vector signed short *);
     vector signed short vec_ldl (int, const short *);
     vector unsigned short vec_ldl (int, const vector unsigned short *);
     vector unsigned short vec_ldl (int, const unsigned short *);
     vector bool char vec_ldl (int, const vector bool char *);
     vector signed char vec_ldl (int, const vector signed char *);
     vector signed char vec_ldl (int, const signed char *);
     vector unsigned char vec_ldl (int, const vector unsigned char *);
     vector unsigned char vec_ldl (int, const unsigned char *);

     vector float vec_loge (vector float);

     vector unsigned char vec_lvsl (int, const volatile unsigned char *);
     vector unsigned char vec_lvsl (int, const volatile signed char *);
     vector unsigned char vec_lvsl (int, const volatile unsigned short *);
     vector unsigned char vec_lvsl (int, const volatile short *);
     vector unsigned char vec_lvsl (int, const volatile unsigned int *);
     vector unsigned char vec_lvsl (int, const volatile int *);
     vector unsigned char vec_lvsl (int, const volatile unsigned long *);
     vector unsigned char vec_lvsl (int, const volatile long *);
     vector unsigned char vec_lvsl (int, const volatile float *);

     vector unsigned char vec_lvsr (int, const volatile unsigned char *);
     vector unsigned char vec_lvsr (int, const volatile signed char *);
     vector unsigned char vec_lvsr (int, const volatile unsigned short *);
     vector unsigned char vec_lvsr (int, const volatile short *);
     vector unsigned char vec_lvsr (int, const volatile unsigned int *);
     vector unsigned char vec_lvsr (int, const volatile int *);
     vector unsigned char vec_lvsr (int, const volatile unsigned long *);
     vector unsigned char vec_lvsr (int, const volatile long *);
     vector unsigned char vec_lvsr (int, const volatile float *);

     vector float vec_madd (vector float, vector float, vector float);

     vector signed short vec_madds (vector signed short,
                                    vector signed short,
                                    vector signed short);

     vector unsigned char vec_max (vector bool char, vector unsigned char);
     vector unsigned char vec_max (vector unsigned char, vector bool char);
     vector unsigned char vec_max (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_max (vector bool char, vector signed char);
     vector signed char vec_max (vector signed char, vector bool char);
     vector signed char vec_max (vector signed char, vector signed char);
     vector unsigned short vec_max (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_max (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_max (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_max (vector bool short, vector signed short);
     vector signed short vec_max (vector signed short, vector bool short);
     vector signed short vec_max (vector signed short, vector signed short);
     vector unsigned int vec_max (vector bool int, vector unsigned int);
     vector unsigned int vec_max (vector unsigned int, vector bool int);
     vector unsigned int vec_max (vector unsigned int, vector unsigned int);
     vector signed int vec_max (vector bool int, vector signed int);
     vector signed int vec_max (vector signed int, vector bool int);
     vector signed int vec_max (vector signed int, vector signed int);
     vector float vec_max (vector float, vector float);

     vector float vec_vmaxfp (vector float, vector float);

     vector signed int vec_vmaxsw (vector bool int, vector signed int);
     vector signed int vec_vmaxsw (vector signed int, vector bool int);
     vector signed int vec_vmaxsw (vector signed int, vector signed int);

     vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
     vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
     vector unsigned int vec_vmaxuw (vector unsigned int,
                                     vector unsigned int);

     vector signed short vec_vmaxsh (vector bool short, vector signed short);
     vector signed short vec_vmaxsh (vector signed short, vector bool short);
     vector signed short vec_vmaxsh (vector signed short,
                                     vector signed short);

     vector unsigned short vec_vmaxuh (vector bool short,
                                       vector unsigned short);
     vector unsigned short vec_vmaxuh (vector unsigned short,
                                       vector bool short);
     vector unsigned short vec_vmaxuh (vector unsigned short,
                                       vector unsigned short);

     vector signed char vec_vmaxsb (vector bool char, vector signed char);
     vector signed char vec_vmaxsb (vector signed char, vector bool char);
     vector signed char vec_vmaxsb (vector signed char, vector signed char);

     vector unsigned char vec_vmaxub (vector bool char,
                                      vector unsigned char);
     vector unsigned char vec_vmaxub (vector unsigned char,
                                      vector bool char);
     vector unsigned char vec_vmaxub (vector unsigned char,
                                      vector unsigned char);

     vector bool char vec_mergeh (vector bool char, vector bool char);
     vector signed char vec_mergeh (vector signed char, vector signed char);
     vector unsigned char vec_mergeh (vector unsigned char,
                                      vector unsigned char);
     vector bool short vec_mergeh (vector bool short, vector bool short);
     vector pixel vec_mergeh (vector pixel, vector pixel);
     vector signed short vec_mergeh (vector signed short,
                                     vector signed short);
     vector unsigned short vec_mergeh (vector unsigned short,
                                       vector unsigned short);
     vector float vec_mergeh (vector float, vector float);
     vector bool int vec_mergeh (vector bool int, vector bool int);
     vector signed int vec_mergeh (vector signed int, vector signed int);
     vector unsigned int vec_mergeh (vector unsigned int,
                                     vector unsigned int);

     vector float vec_vmrghw (vector float, vector float);
     vector bool int vec_vmrghw (vector bool int, vector bool int);
     vector signed int vec_vmrghw (vector signed int, vector signed int);
     vector unsigned int vec_vmrghw (vector unsigned int,
                                     vector unsigned int);

     vector bool short vec_vmrghh (vector bool short, vector bool short);
     vector signed short vec_vmrghh (vector signed short,
                                     vector signed short);
     vector unsigned short vec_vmrghh (vector unsigned short,
                                       vector unsigned short);
     vector pixel vec_vmrghh (vector pixel, vector pixel);

     vector bool char vec_vmrghb (vector bool char, vector bool char);
     vector signed char vec_vmrghb (vector signed char, vector signed char);
     vector unsigned char vec_vmrghb (vector unsigned char,
                                      vector unsigned char);

     vector bool char vec_mergel (vector bool char, vector bool char);
     vector signed char vec_mergel (vector signed char, vector signed char);
     vector unsigned char vec_mergel (vector unsigned char,
                                      vector unsigned char);
     vector bool short vec_mergel (vector bool short, vector bool short);
     vector pixel vec_mergel (vector pixel, vector pixel);
     vector signed short vec_mergel (vector signed short,
                                     vector signed short);
     vector unsigned short vec_mergel (vector unsigned short,
                                       vector unsigned short);
     vector float vec_mergel (vector float, vector float);
     vector bool int vec_mergel (vector bool int, vector bool int);
     vector signed int vec_mergel (vector signed int, vector signed int);
     vector unsigned int vec_mergel (vector unsigned int,
                                     vector unsigned int);

     vector float vec_vmrglw (vector float, vector float);
     vector signed int vec_vmrglw (vector signed int, vector signed int);
     vector unsigned int vec_vmrglw (vector unsigned int,
                                     vector unsigned int);
     vector bool int vec_vmrglw (vector bool int, vector bool int);

     vector bool short vec_vmrglh (vector bool short, vector bool short);
     vector signed short vec_vmrglh (vector signed short,
                                     vector signed short);
     vector unsigned short vec_vmrglh (vector unsigned short,
                                       vector unsigned short);
     vector pixel vec_vmrglh (vector pixel, vector pixel);

     vector bool char vec_vmrglb (vector bool char, vector bool char);
     vector signed char vec_vmrglb (vector signed char, vector signed char);
     vector unsigned char vec_vmrglb (vector unsigned char,
                                      vector unsigned char);

     vector unsigned short vec_mfvscr (void);

     vector unsigned char vec_min (vector bool char, vector unsigned char);
     vector unsigned char vec_min (vector unsigned char, vector bool char);
     vector unsigned char vec_min (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_min (vector bool char, vector signed char);
     vector signed char vec_min (vector signed char, vector bool char);
     vector signed char vec_min (vector signed char, vector signed char);
     vector unsigned short vec_min (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_min (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_min (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_min (vector bool short, vector signed short);
     vector signed short vec_min (vector signed short, vector bool short);
     vector signed short vec_min (vector signed short, vector signed short);
     vector unsigned int vec_min (vector bool int, vector unsigned int);
     vector unsigned int vec_min (vector unsigned int, vector bool int);
     vector unsigned int vec_min (vector unsigned int, vector unsigned int);
     vector signed int vec_min (vector bool int, vector signed int);
     vector signed int vec_min (vector signed int, vector bool int);
     vector signed int vec_min (vector signed int, vector signed int);
     vector float vec_min (vector float, vector float);

     vector float vec_vminfp (vector float, vector float);

     vector signed int vec_vminsw (vector bool int, vector signed int);
     vector signed int vec_vminsw (vector signed int, vector bool int);
     vector signed int vec_vminsw (vector signed int, vector signed int);

     vector unsigned int vec_vminuw (vector bool int, vector unsigned int);
     vector unsigned int vec_vminuw (vector unsigned int, vector bool int);
     vector unsigned int vec_vminuw (vector unsigned int,
                                     vector unsigned int);

     vector signed short vec_vminsh (vector bool short, vector signed short);
     vector signed short vec_vminsh (vector signed short, vector bool short);
     vector signed short vec_vminsh (vector signed short,
                                     vector signed short);

     vector unsigned short vec_vminuh (vector bool short,
                                       vector unsigned short);
     vector unsigned short vec_vminuh (vector unsigned short,
                                       vector bool short);
     vector unsigned short vec_vminuh (vector unsigned short,
                                       vector unsigned short);

     vector signed char vec_vminsb (vector bool char, vector signed char);
     vector signed char vec_vminsb (vector signed char, vector bool char);
     vector signed char vec_vminsb (vector signed char, vector signed char);

     vector unsigned char vec_vminub (vector bool char,
                                      vector unsigned char);
     vector unsigned char vec_vminub (vector unsigned char,
                                      vector bool char);
     vector unsigned char vec_vminub (vector unsigned char,
                                      vector unsigned char);

     vector signed short vec_mladd (vector signed short,
                                    vector signed short,
                                    vector signed short);
     vector signed short vec_mladd (vector signed short,
                                    vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_mladd (vector unsigned short,
                                    vector signed short,
                                    vector signed short);
     vector unsigned short vec_mladd (vector unsigned short,
                                      vector unsigned short,
                                      vector unsigned short);

     vector signed short vec_mradds (vector signed short,
                                     vector signed short,
                                     vector signed short);

     vector unsigned int vec_msum (vector unsigned char,
                                   vector unsigned char,
                                   vector unsigned int);
     vector signed int vec_msum (vector signed char,
                                 vector unsigned char,
                                 vector signed int);
     vector unsigned int vec_msum (vector unsigned short,
                                   vector unsigned short,
                                   vector unsigned int);
     vector signed int vec_msum (vector signed short,
                                 vector signed short,
                                 vector signed int);

     vector signed int vec_vmsumshm (vector signed short,
                                     vector signed short,
                                     vector signed int);

     vector unsigned int vec_vmsumuhm (vector unsigned short,
                                       vector unsigned short,
                                       vector unsigned int);

     vector signed int vec_vmsummbm (vector signed char,
                                     vector unsigned char,
                                     vector signed int);

     vector unsigned int vec_vmsumubm (vector unsigned char,
                                       vector unsigned char,
                                       vector unsigned int);

     vector unsigned int vec_msums (vector unsigned short,
                                    vector unsigned short,
                                    vector unsigned int);
     vector signed int vec_msums (vector signed short,
                                  vector signed short,
                                  vector signed int);

     vector signed int vec_vmsumshs (vector signed short,
                                     vector signed short,
                                     vector signed int);

     vector unsigned int vec_vmsumuhs (vector unsigned short,
                                       vector unsigned short,
                                       vector unsigned int);

     void vec_mtvscr (vector signed int);
     void vec_mtvscr (vector unsigned int);
     void vec_mtvscr (vector bool int);
     void vec_mtvscr (vector signed short);
     void vec_mtvscr (vector unsigned short);
     void vec_mtvscr (vector bool short);
     void vec_mtvscr (vector pixel);
     void vec_mtvscr (vector signed char);
     void vec_mtvscr (vector unsigned char);
     void vec_mtvscr (vector bool char);

     vector unsigned short vec_mule (vector unsigned char,
                                     vector unsigned char);
     vector signed short vec_mule (vector signed char,
                                   vector signed char);
     vector unsigned int vec_mule (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_mule (vector signed short, vector signed short);

     vector signed int vec_vmulesh (vector signed short,
                                    vector signed short);

     vector unsigned int vec_vmuleuh (vector unsigned short,
                                      vector unsigned short);

     vector signed short vec_vmulesb (vector signed char,
                                      vector signed char);

     vector unsigned short vec_vmuleub (vector unsigned char,
                                       vector unsigned char);

     vector unsigned short vec_mulo (vector unsigned char,
                                     vector unsigned char);
     vector signed short vec_mulo (vector signed char, vector signed char);
     vector unsigned int vec_mulo (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_mulo (vector signed short, vector signed short);

     vector signed int vec_vmulosh (vector signed short,
                                    vector signed short);

     vector unsigned int vec_vmulouh (vector unsigned short,
                                      vector unsigned short);

     vector signed short vec_vmulosb (vector signed char,
                                      vector signed char);

     vector unsigned short vec_vmuloub (vector unsigned char,
                                        vector unsigned char);

     vector float vec_nmsub (vector float, vector float, vector float);

     vector float vec_nor (vector float, vector float);
     vector signed int vec_nor (vector signed int, vector signed int);
     vector unsigned int vec_nor (vector unsigned int, vector unsigned int);
     vector bool int vec_nor (vector bool int, vector bool int);
     vector signed short vec_nor (vector signed short, vector signed short);
     vector unsigned short vec_nor (vector unsigned short,
                                    vector unsigned short);
     vector bool short vec_nor (vector bool short, vector bool short);
     vector signed char vec_nor (vector signed char, vector signed char);
     vector unsigned char vec_nor (vector unsigned char,
                                   vector unsigned char);
     vector bool char vec_nor (vector bool char, vector bool char);

     vector float vec_or (vector float, vector float);
     vector float vec_or (vector float, vector bool int);
     vector float vec_or (vector bool int, vector float);
     vector bool int vec_or (vector bool int, vector bool int);
     vector signed int vec_or (vector bool int, vector signed int);
     vector signed int vec_or (vector signed int, vector bool int);
     vector signed int vec_or (vector signed int, vector signed int);
     vector unsigned int vec_or (vector bool int, vector unsigned int);
     vector unsigned int vec_or (vector unsigned int, vector bool int);
     vector unsigned int vec_or (vector unsigned int, vector unsigned int);
     vector bool short vec_or (vector bool short, vector bool short);
     vector signed short vec_or (vector bool short, vector signed short);
     vector signed short vec_or (vector signed short, vector bool short);
     vector signed short vec_or (vector signed short, vector signed short);
     vector unsigned short vec_or (vector bool short, vector unsigned short);
     vector unsigned short vec_or (vector unsigned short, vector bool short);
     vector unsigned short vec_or (vector unsigned short,
                                   vector unsigned short);
     vector signed char vec_or (vector bool char, vector signed char);
     vector bool char vec_or (vector bool char, vector bool char);
     vector signed char vec_or (vector signed char, vector bool char);
     vector signed char vec_or (vector signed char, vector signed char);
     vector unsigned char vec_or (vector bool char, vector unsigned char);
     vector unsigned char vec_or (vector unsigned char, vector bool char);
     vector unsigned char vec_or (vector unsigned char,
                                  vector unsigned char);

     vector signed char vec_pack (vector signed short, vector signed short);
     vector unsigned char vec_pack (vector unsigned short,
                                    vector unsigned short);
     vector bool char vec_pack (vector bool short, vector bool short);
     vector signed short vec_pack (vector signed int, vector signed int);
     vector unsigned short vec_pack (vector unsigned int,
                                     vector unsigned int);
     vector bool short vec_pack (vector bool int, vector bool int);

     vector bool short vec_vpkuwum (vector bool int, vector bool int);
     vector signed short vec_vpkuwum (vector signed int, vector signed int);
     vector unsigned short vec_vpkuwum (vector unsigned int,
                                        vector unsigned int);

     vector bool char vec_vpkuhum (vector bool short, vector bool short);
     vector signed char vec_vpkuhum (vector signed short,
                                     vector signed short);
     vector unsigned char vec_vpkuhum (vector unsigned short,
                                       vector unsigned short);

     vector pixel vec_packpx (vector unsigned int, vector unsigned int);

     vector unsigned char vec_packs (vector unsigned short,
                                     vector unsigned short);
     vector signed char vec_packs (vector signed short, vector signed short);
     vector unsigned short vec_packs (vector unsigned int,
                                      vector unsigned int);
     vector signed short vec_packs (vector signed int, vector signed int);

     vector signed short vec_vpkswss (vector signed int, vector signed int);

     vector unsigned short vec_vpkuwus (vector unsigned int,
                                        vector unsigned int);

     vector signed char vec_vpkshss (vector signed short,
                                     vector signed short);

     vector unsigned char vec_vpkuhus (vector unsigned short,
                                       vector unsigned short);

     vector unsigned char vec_packsu (vector unsigned short,
                                      vector unsigned short);
     vector unsigned char vec_packsu (vector signed short,
                                      vector signed short);
     vector unsigned short vec_packsu (vector unsigned int,
                                       vector unsigned int);
     vector unsigned short vec_packsu (vector signed int, vector signed int);

     vector unsigned short vec_vpkswus (vector signed int,
                                        vector signed int);

     vector unsigned char vec_vpkshus (vector signed short,
                                       vector signed short);

     vector float vec_perm (vector float,
                            vector float,
                            vector unsigned char);
     vector signed int vec_perm (vector signed int,
                                 vector signed int,
                                 vector unsigned char);
     vector unsigned int vec_perm (vector unsigned int,
                                   vector unsigned int,
                                   vector unsigned char);
     vector bool int vec_perm (vector bool int,
                               vector bool int,
                               vector unsigned char);
     vector signed short vec_perm (vector signed short,
                                   vector signed short,
                                   vector unsigned char);
     vector unsigned short vec_perm (vector unsigned short,
                                     vector unsigned short,
                                     vector unsigned char);
     vector bool short vec_perm (vector bool short,
                                 vector bool short,
                                 vector unsigned char);
     vector pixel vec_perm (vector pixel,
                            vector pixel,
                            vector unsigned char);
     vector signed char vec_perm (vector signed char,
                                  vector signed char,
                                  vector unsigned char);
     vector unsigned char vec_perm (vector unsigned char,
                                    vector unsigned char,
                                    vector unsigned char);
     vector bool char vec_perm (vector bool char,
                                vector bool char,
                                vector unsigned char);

     vector float vec_re (vector float);

     vector signed char vec_rl (vector signed char,
                                vector unsigned char);
     vector unsigned char vec_rl (vector unsigned char,
                                  vector unsigned char);
     vector signed short vec_rl (vector signed short, vector unsigned short);
     vector unsigned short vec_rl (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_rl (vector signed int, vector unsigned int);
     vector unsigned int vec_rl (vector unsigned int, vector unsigned int);

     vector signed int vec_vrlw (vector signed int, vector unsigned int);
     vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int);

     vector signed short vec_vrlh (vector signed short,
                                   vector unsigned short);
     vector unsigned short vec_vrlh (vector unsigned short,
                                     vector unsigned short);

     vector signed char vec_vrlb (vector signed char, vector unsigned char);
     vector unsigned char vec_vrlb (vector unsigned char,
                                    vector unsigned char);

     vector float vec_round (vector float);

     vector float vec_recip (vector float, vector float);

     vector float vec_rsqrt (vector float);

     vector float vec_rsqrte (vector float);

     vector float vec_sel (vector float, vector float, vector bool int);
     vector float vec_sel (vector float, vector float, vector unsigned int);
     vector signed int vec_sel (vector signed int,
                                vector signed int,
                                vector bool int);
     vector signed int vec_sel (vector signed int,
                                vector signed int,
                                vector unsigned int);
     vector unsigned int vec_sel (vector unsigned int,
                                  vector unsigned int,
                                  vector bool int);
     vector unsigned int vec_sel (vector unsigned int,
                                  vector unsigned int,
                                  vector unsigned int);
     vector bool int vec_sel (vector bool int,
                              vector bool int,
                              vector bool int);
     vector bool int vec_sel (vector bool int,
                              vector bool int,
                              vector unsigned int);
     vector signed short vec_sel (vector signed short,
                                  vector signed short,
                                  vector bool short);
     vector signed short vec_sel (vector signed short,
                                  vector signed short,
                                  vector unsigned short);
     vector unsigned short vec_sel (vector unsigned short,
                                    vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_sel (vector unsigned short,
                                    vector unsigned short,
                                    vector unsigned short);
     vector bool short vec_sel (vector bool short,
                                vector bool short,
                                vector bool short);
     vector bool short vec_sel (vector bool short,
                                vector bool short,
                                vector unsigned short);
     vector signed char vec_sel (vector signed char,
                                 vector signed char,
                                 vector bool char);
     vector signed char vec_sel (vector signed char,
                                 vector signed char,
                                 vector unsigned char);
     vector unsigned char vec_sel (vector unsigned char,
                                   vector unsigned char,
                                   vector bool char);
     vector unsigned char vec_sel (vector unsigned char,
                                   vector unsigned char,
                                   vector unsigned char);
     vector bool char vec_sel (vector bool char,
                               vector bool char,
                               vector bool char);
     vector bool char vec_sel (vector bool char,
                               vector bool char,
                               vector unsigned char);

     vector signed char vec_sl (vector signed char,
                                vector unsigned char);
     vector unsigned char vec_sl (vector unsigned char,
                                  vector unsigned char);
     vector signed short vec_sl (vector signed short, vector unsigned short);
     vector unsigned short vec_sl (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_sl (vector signed int, vector unsigned int);
     vector unsigned int vec_sl (vector unsigned int, vector unsigned int);

     vector signed int vec_vslw (vector signed int, vector unsigned int);
     vector unsigned int vec_vslw (vector unsigned int, vector unsigned int);

     vector signed short vec_vslh (vector signed short,
                                   vector unsigned short);
     vector unsigned short vec_vslh (vector unsigned short,
                                     vector unsigned short);

     vector signed char vec_vslb (vector signed char, vector unsigned char);
     vector unsigned char vec_vslb (vector unsigned char,
                                    vector unsigned char);

     vector float vec_sld (vector float, vector float, const int);
     vector signed int vec_sld (vector signed int,
                                vector signed int,
                                const int);
     vector unsigned int vec_sld (vector unsigned int,
                                  vector unsigned int,
                                  const int);
     vector bool int vec_sld (vector bool int,
                              vector bool int,
                              const int);
     vector signed short vec_sld (vector signed short,
                                  vector signed short,
                                  const int);
     vector unsigned short vec_sld (vector unsigned short,
                                    vector unsigned short,
                                    const int);
     vector bool short vec_sld (vector bool short,
                                vector bool short,
                                const int);
     vector pixel vec_sld (vector pixel,
                           vector pixel,
                           const int);
     vector signed char vec_sld (vector signed char,
                                 vector signed char,
                                 const int);
     vector unsigned char vec_sld (vector unsigned char,
                                   vector unsigned char,
                                   const int);
     vector bool char vec_sld (vector bool char,
                               vector bool char,
                               const int);

     vector signed int vec_sll (vector signed int,
                                vector unsigned int);
     vector signed int vec_sll (vector signed int,
                                vector unsigned short);
     vector signed int vec_sll (vector signed int,
                                vector unsigned char);
     vector unsigned int vec_sll (vector unsigned int,
                                  vector unsigned int);
     vector unsigned int vec_sll (vector unsigned int,
                                  vector unsigned short);
     vector unsigned int vec_sll (vector unsigned int,
                                  vector unsigned char);
     vector bool int vec_sll (vector bool int,
                              vector unsigned int);
     vector bool int vec_sll (vector bool int,
                              vector unsigned short);
     vector bool int vec_sll (vector bool int,
                              vector unsigned char);
     vector signed short vec_sll (vector signed short,
                                  vector unsigned int);
     vector signed short vec_sll (vector signed short,
                                  vector unsigned short);
     vector signed short vec_sll (vector signed short,
                                  vector unsigned char);
     vector unsigned short vec_sll (vector unsigned short,
                                    vector unsigned int);
     vector unsigned short vec_sll (vector unsigned short,
                                    vector unsigned short);
     vector unsigned short vec_sll (vector unsigned short,
                                    vector unsigned char);
     vector bool short vec_sll (vector bool short, vector unsigned int);
     vector bool short vec_sll (vector bool short, vector unsigned short);
     vector bool short vec_sll (vector bool short, vector unsigned char);
     vector pixel vec_sll (vector pixel, vector unsigned int);
     vector pixel vec_sll (vector pixel, vector unsigned short);
     vector pixel vec_sll (vector pixel, vector unsigned char);
     vector signed char vec_sll (vector signed char, vector unsigned int);
     vector signed char vec_sll (vector signed char, vector unsigned short);
     vector signed char vec_sll (vector signed char, vector unsigned char);
     vector unsigned char vec_sll (vector unsigned char,
                                   vector unsigned int);
     vector unsigned char vec_sll (vector unsigned char,
                                   vector unsigned short);
     vector unsigned char vec_sll (vector unsigned char,
                                   vector unsigned char);
     vector bool char vec_sll (vector bool char, vector unsigned int);
     vector bool char vec_sll (vector bool char, vector unsigned short);
     vector bool char vec_sll (vector bool char, vector unsigned char);

     vector float vec_slo (vector float, vector signed char);
     vector float vec_slo (vector float, vector unsigned char);
     vector signed int vec_slo (vector signed int, vector signed char);
     vector signed int vec_slo (vector signed int, vector unsigned char);
     vector unsigned int vec_slo (vector unsigned int, vector signed char);
     vector unsigned int vec_slo (vector unsigned int, vector unsigned char);
     vector signed short vec_slo (vector signed short, vector signed char);
     vector signed short vec_slo (vector signed short, vector unsigned char);
     vector unsigned short vec_slo (vector unsigned short,
                                    vector signed char);
     vector unsigned short vec_slo (vector unsigned short,
                                    vector unsigned char);
     vector pixel vec_slo (vector pixel, vector signed char);
     vector pixel vec_slo (vector pixel, vector unsigned char);
     vector signed char vec_slo (vector signed char, vector signed char);
     vector signed char vec_slo (vector signed char, vector unsigned char);
     vector unsigned char vec_slo (vector unsigned char, vector signed char);
     vector unsigned char vec_slo (vector unsigned char,
                                   vector unsigned char);

     vector signed char vec_splat (vector signed char, const int);
     vector unsigned char vec_splat (vector unsigned char, const int);
     vector bool char vec_splat (vector bool char, const int);
     vector signed short vec_splat (vector signed short, const int);
     vector unsigned short vec_splat (vector unsigned short, const int);
     vector bool short vec_splat (vector bool short, const int);
     vector pixel vec_splat (vector pixel, const int);
     vector float vec_splat (vector float, const int);
     vector signed int vec_splat (vector signed int, const int);
     vector unsigned int vec_splat (vector unsigned int, const int);
     vector bool int vec_splat (vector bool int, const int);
     vector signed long vec_splat (vector signed long, const int);
     vector unsigned long vec_splat (vector unsigned long, const int);

     vector signed char vec_splats (signed char);
     vector unsigned char vec_splats (unsigned char);
     vector signed short vec_splats (signed short);
     vector unsigned short vec_splats (unsigned short);
     vector signed int vec_splats (signed int);
     vector unsigned int vec_splats (unsigned int);
     vector float vec_splats (float);

     vector float vec_vspltw (vector float, const int);
     vector signed int vec_vspltw (vector signed int, const int);
     vector unsigned int vec_vspltw (vector unsigned int, const int);
     vector bool int vec_vspltw (vector bool int, const int);

     vector bool short vec_vsplth (vector bool short, const int);
     vector signed short vec_vsplth (vector signed short, const int);
     vector unsigned short vec_vsplth (vector unsigned short, const int);
     vector pixel vec_vsplth (vector pixel, const int);

     vector signed char vec_vspltb (vector signed char, const int);
     vector unsigned char vec_vspltb (vector unsigned char, const int);
     vector bool char vec_vspltb (vector bool char, const int);

     vector signed char vec_splat_s8 (const int);

     vector signed short vec_splat_s16 (const int);

     vector signed int vec_splat_s32 (const int);

     vector unsigned char vec_splat_u8 (const int);

     vector unsigned short vec_splat_u16 (const int);

     vector unsigned int vec_splat_u32 (const int);

     vector signed char vec_sr (vector signed char, vector unsigned char);
     vector unsigned char vec_sr (vector unsigned char,
                                  vector unsigned char);
     vector signed short vec_sr (vector signed short,
                                 vector unsigned short);
     vector unsigned short vec_sr (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_sr (vector signed int, vector unsigned int);
     vector unsigned int vec_sr (vector unsigned int, vector unsigned int);

     vector signed int vec_vsrw (vector signed int, vector unsigned int);
     vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int);

     vector signed short vec_vsrh (vector signed short,
                                   vector unsigned short);
     vector unsigned short vec_vsrh (vector unsigned short,
                                     vector unsigned short);

     vector signed char vec_vsrb (vector signed char, vector unsigned char);
     vector unsigned char vec_vsrb (vector unsigned char,
                                    vector unsigned char);

     vector signed char vec_sra (vector signed char, vector unsigned char);
     vector unsigned char vec_sra (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_sra (vector signed short,
                                  vector unsigned short);
     vector unsigned short vec_sra (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_sra (vector signed int, vector unsigned int);
     vector unsigned int vec_sra (vector unsigned int, vector unsigned int);

     vector signed int vec_vsraw (vector signed int, vector unsigned int);
     vector unsigned int vec_vsraw (vector unsigned int,
                                    vector unsigned int);

     vector signed short vec_vsrah (vector signed short,
                                    vector unsigned short);
     vector unsigned short vec_vsrah (vector unsigned short,
                                      vector unsigned short);

     vector signed char vec_vsrab (vector signed char, vector unsigned char);
     vector unsigned char vec_vsrab (vector unsigned char,
                                     vector unsigned char);

     vector signed int vec_srl (vector signed int, vector unsigned int);
     vector signed int vec_srl (vector signed int, vector unsigned short);
     vector signed int vec_srl (vector signed int, vector unsigned char);
     vector unsigned int vec_srl (vector unsigned int, vector unsigned int);
     vector unsigned int vec_srl (vector unsigned int,
                                  vector unsigned short);
     vector unsigned int vec_srl (vector unsigned int, vector unsigned char);
     vector bool int vec_srl (vector bool int, vector unsigned int);
     vector bool int vec_srl (vector bool int, vector unsigned short);
     vector bool int vec_srl (vector bool int, vector unsigned char);
     vector signed short vec_srl (vector signed short, vector unsigned int);
     vector signed short vec_srl (vector signed short,
                                  vector unsigned short);
     vector signed short vec_srl (vector signed short, vector unsigned char);
     vector unsigned short vec_srl (vector unsigned short,
                                    vector unsigned int);
     vector unsigned short vec_srl (vector unsigned short,
                                    vector unsigned short);
     vector unsigned short vec_srl (vector unsigned short,
                                    vector unsigned char);
     vector bool short vec_srl (vector bool short, vector unsigned int);
     vector bool short vec_srl (vector bool short, vector unsigned short);
     vector bool short vec_srl (vector bool short, vector unsigned char);
     vector pixel vec_srl (vector pixel, vector unsigned int);
     vector pixel vec_srl (vector pixel, vector unsigned short);
     vector pixel vec_srl (vector pixel, vector unsigned char);
     vector signed char vec_srl (vector signed char, vector unsigned int);
     vector signed char vec_srl (vector signed char, vector unsigned short);
     vector signed char vec_srl (vector signed char, vector unsigned char);
     vector unsigned char vec_srl (vector unsigned char,
                                   vector unsigned int);
     vector unsigned char vec_srl (vector unsigned char,
                                   vector unsigned short);
     vector unsigned char vec_srl (vector unsigned char,
                                   vector unsigned char);
     vector bool char vec_srl (vector bool char, vector unsigned int);
     vector bool char vec_srl (vector bool char, vector unsigned short);
     vector bool char vec_srl (vector bool char, vector unsigned char);

     vector float vec_sro (vector float, vector signed char);
     vector float vec_sro (vector float, vector unsigned char);
     vector signed int vec_sro (vector signed int, vector signed char);
     vector signed int vec_sro (vector signed int, vector unsigned char);
     vector unsigned int vec_sro (vector unsigned int, vector signed char);
     vector unsigned int vec_sro (vector unsigned int, vector unsigned char);
     vector signed short vec_sro (vector signed short, vector signed char);
     vector signed short vec_sro (vector signed short, vector unsigned char);
     vector unsigned short vec_sro (vector unsigned short,
                                    vector signed char);
     vector unsigned short vec_sro (vector unsigned short,
                                    vector unsigned char);
     vector pixel vec_sro (vector pixel, vector signed char);
     vector pixel vec_sro (vector pixel, vector unsigned char);
     vector signed char vec_sro (vector signed char, vector signed char);
     vector signed char vec_sro (vector signed char, vector unsigned char);
     vector unsigned char vec_sro (vector unsigned char, vector signed char);
     vector unsigned char vec_sro (vector unsigned char,
                                   vector unsigned char);

     void vec_st (vector float, int, vector float *);
     void vec_st (vector float, int, float *);
     void vec_st (vector signed int, int, vector signed int *);
     void vec_st (vector signed int, int, int *);
     void vec_st (vector unsigned int, int, vector unsigned int *);
     void vec_st (vector unsigned int, int, unsigned int *);
     void vec_st (vector bool int, int, vector bool int *);
     void vec_st (vector bool int, int, unsigned int *);
     void vec_st (vector bool int, int, int *);
     void vec_st (vector signed short, int, vector signed short *);
     void vec_st (vector signed short, int, short *);
     void vec_st (vector unsigned short, int, vector unsigned short *);
     void vec_st (vector unsigned short, int, unsigned short *);
     void vec_st (vector bool short, int, vector bool short *);
     void vec_st (vector bool short, int, unsigned short *);
     void vec_st (vector pixel, int, vector pixel *);
     void vec_st (vector pixel, int, unsigned short *);
     void vec_st (vector pixel, int, short *);
     void vec_st (vector bool short, int, short *);
     void vec_st (vector signed char, int, vector signed char *);
     void vec_st (vector signed char, int, signed char *);
     void vec_st (vector unsigned char, int, vector unsigned char *);
     void vec_st (vector unsigned char, int, unsigned char *);
     void vec_st (vector bool char, int, vector bool char *);
     void vec_st (vector bool char, int, unsigned char *);
     void vec_st (vector bool char, int, signed char *);

     void vec_ste (vector signed char, int, signed char *);
     void vec_ste (vector unsigned char, int, unsigned char *);
     void vec_ste (vector bool char, int, signed char *);
     void vec_ste (vector bool char, int, unsigned char *);
     void vec_ste (vector signed short, int, short *);
     void vec_ste (vector unsigned short, int, unsigned short *);
     void vec_ste (vector bool short, int, short *);
     void vec_ste (vector bool short, int, unsigned short *);
     void vec_ste (vector pixel, int, short *);
     void vec_ste (vector pixel, int, unsigned short *);
     void vec_ste (vector float, int, float *);
     void vec_ste (vector signed int, int, int *);
     void vec_ste (vector unsigned int, int, unsigned int *);
     void vec_ste (vector bool int, int, int *);
     void vec_ste (vector bool int, int, unsigned int *);

     void vec_stvewx (vector float, int, float *);
     void vec_stvewx (vector signed int, int, int *);
     void vec_stvewx (vector unsigned int, int, unsigned int *);
     void vec_stvewx (vector bool int, int, int *);
     void vec_stvewx (vector bool int, int, unsigned int *);

     void vec_stvehx (vector signed short, int, short *);
     void vec_stvehx (vector unsigned short, int, unsigned short *);
     void vec_stvehx (vector bool short, int, short *);
     void vec_stvehx (vector bool short, int, unsigned short *);
     void vec_stvehx (vector pixel, int, short *);
     void vec_stvehx (vector pixel, int, unsigned short *);

     void vec_stvebx (vector signed char, int, signed char *);
     void vec_stvebx (vector unsigned char, int, unsigned char *);
     void vec_stvebx (vector bool char, int, signed char *);
     void vec_stvebx (vector bool char, int, unsigned char *);

     void vec_stl (vector float, int, vector float *);
     void vec_stl (vector float, int, float *);
     void vec_stl (vector signed int, int, vector signed int *);
     void vec_stl (vector signed int, int, int *);
     void vec_stl (vector unsigned int, int, vector unsigned int *);
     void vec_stl (vector unsigned int, int, unsigned int *);
     void vec_stl (vector bool int, int, vector bool int *);
     void vec_stl (vector bool int, int, unsigned int *);
     void vec_stl (vector bool int, int, int *);
     void vec_stl (vector signed short, int, vector signed short *);
     void vec_stl (vector signed short, int, short *);
     void vec_stl (vector unsigned short, int, vector unsigned short *);
     void vec_stl (vector unsigned short, int, unsigned short *);
     void vec_stl (vector bool short, int, vector bool short *);
     void vec_stl (vector bool short, int, unsigned short *);
     void vec_stl (vector bool short, int, short *);
     void vec_stl (vector pixel, int, vector pixel *);
     void vec_stl (vector pixel, int, unsigned short *);
     void vec_stl (vector pixel, int, short *);
     void vec_stl (vector signed char, int, vector signed char *);
     void vec_stl (vector signed char, int, signed char *);
     void vec_stl (vector unsigned char, int, vector unsigned char *);
     void vec_stl (vector unsigned char, int, unsigned char *);
     void vec_stl (vector bool char, int, vector bool char *);
     void vec_stl (vector bool char, int, unsigned char *);
     void vec_stl (vector bool char, int, signed char *);

     vector signed char vec_sub (vector bool char, vector signed char);
     vector signed char vec_sub (vector signed char, vector bool char);
     vector signed char vec_sub (vector signed char, vector signed char);
     vector unsigned char vec_sub (vector bool char, vector unsigned char);
     vector unsigned char vec_sub (vector unsigned char, vector bool char);
     vector unsigned char vec_sub (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_sub (vector bool short, vector signed short);
     vector signed short vec_sub (vector signed short, vector bool short);
     vector signed short vec_sub (vector signed short, vector signed short);
     vector unsigned short vec_sub (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_sub (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_sub (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_sub (vector bool int, vector signed int);
     vector signed int vec_sub (vector signed int, vector bool int);
     vector signed int vec_sub (vector signed int, vector signed int);
     vector unsigned int vec_sub (vector bool int, vector unsigned int);
     vector unsigned int vec_sub (vector unsigned int, vector bool int);
     vector unsigned int vec_sub (vector unsigned int, vector unsigned int);
     vector float vec_sub (vector float, vector float);

     vector float vec_vsubfp (vector float, vector float);

     vector signed int vec_vsubuwm (vector bool int, vector signed int);
     vector signed int vec_vsubuwm (vector signed int, vector bool int);
     vector signed int vec_vsubuwm (vector signed int, vector signed int);
     vector unsigned int vec_vsubuwm (vector bool int, vector unsigned int);
     vector unsigned int vec_vsubuwm (vector unsigned int, vector bool int);
     vector unsigned int vec_vsubuwm (vector unsigned int,
                                      vector unsigned int);

     vector signed short vec_vsubuhm (vector bool short,
                                      vector signed short);
     vector signed short vec_vsubuhm (vector signed short,
                                      vector bool short);
     vector signed short vec_vsubuhm (vector signed short,
                                      vector signed short);
     vector unsigned short vec_vsubuhm (vector bool short,
                                        vector unsigned short);
     vector unsigned short vec_vsubuhm (vector unsigned short,
                                        vector bool short);
     vector unsigned short vec_vsubuhm (vector unsigned short,
                                        vector unsigned short);

     vector signed char vec_vsububm (vector bool char, vector signed char);
     vector signed char vec_vsububm (vector signed char, vector bool char);
     vector signed char vec_vsububm (vector signed char, vector signed char);
     vector unsigned char vec_vsububm (vector bool char,
                                       vector unsigned char);
     vector unsigned char vec_vsububm (vector unsigned char,
                                       vector bool char);
     vector unsigned char vec_vsububm (vector unsigned char,
                                       vector unsigned char);

     vector unsigned int vec_subc (vector unsigned int, vector unsigned int);

     vector unsigned char vec_subs (vector bool char, vector unsigned char);
     vector unsigned char vec_subs (vector unsigned char, vector bool char);
     vector unsigned char vec_subs (vector unsigned char,
                                    vector unsigned char);
     vector signed char vec_subs (vector bool char, vector signed char);
     vector signed char vec_subs (vector signed char, vector bool char);
     vector signed char vec_subs (vector signed char, vector signed char);
     vector unsigned short vec_subs (vector bool short,
                                     vector unsigned short);
     vector unsigned short vec_subs (vector unsigned short,
                                     vector bool short);
     vector unsigned short vec_subs (vector unsigned short,
                                     vector unsigned short);
     vector signed short vec_subs (vector bool short, vector signed short);
     vector signed short vec_subs (vector signed short, vector bool short);
     vector signed short vec_subs (vector signed short, vector signed short);
     vector unsigned int vec_subs (vector bool int, vector unsigned int);
     vector unsigned int vec_subs (vector unsigned int, vector bool int);
     vector unsigned int vec_subs (vector unsigned int, vector unsigned int);
     vector signed int vec_subs (vector bool int, vector signed int);
     vector signed int vec_subs (vector signed int, vector bool int);
     vector signed int vec_subs (vector signed int, vector signed int);

     vector signed int vec_vsubsws (vector bool int, vector signed int);
     vector signed int vec_vsubsws (vector signed int, vector bool int);
     vector signed int vec_vsubsws (vector signed int, vector signed int);

     vector unsigned int vec_vsubuws (vector bool int, vector unsigned int);
     vector unsigned int vec_vsubuws (vector unsigned int, vector bool int);
     vector unsigned int vec_vsubuws (vector unsigned int,
                                      vector unsigned int);

     vector signed short vec_vsubshs (vector bool short,
                                      vector signed short);
     vector signed short vec_vsubshs (vector signed short,
                                      vector bool short);
     vector signed short vec_vsubshs (vector signed short,
                                      vector signed short);

     vector unsigned short vec_vsubuhs (vector bool short,
                                        vector unsigned short);
     vector unsigned short vec_vsubuhs (vector unsigned short,
                                        vector bool short);
     vector unsigned short vec_vsubuhs (vector unsigned short,
                                        vector unsigned short);

     vector signed char vec_vsubsbs (vector bool char, vector signed char);
     vector signed char vec_vsubsbs (vector signed char, vector bool char);
     vector signed char vec_vsubsbs (vector signed char, vector signed char);

     vector unsigned char vec_vsububs (vector bool char,
                                       vector unsigned char);
     vector unsigned char vec_vsububs (vector unsigned char,
                                       vector bool char);
     vector unsigned char vec_vsububs (vector unsigned char,
                                       vector unsigned char);

     vector unsigned int vec_sum4s (vector unsigned char,
                                    vector unsigned int);
     vector signed int vec_sum4s (vector signed char, vector signed int);
     vector signed int vec_sum4s (vector signed short, vector signed int);

     vector signed int vec_vsum4shs (vector signed short, vector signed int);

     vector signed int vec_vsum4sbs (vector signed char, vector signed int);

     vector unsigned int vec_vsum4ubs (vector unsigned char,
                                       vector unsigned int);

     vector signed int vec_sum2s (vector signed int, vector signed int);

     vector signed int vec_sums (vector signed int, vector signed int);

     vector float vec_trunc (vector float);

     vector signed short vec_unpackh (vector signed char);
     vector bool short vec_unpackh (vector bool char);
     vector signed int vec_unpackh (vector signed short);
     vector bool int vec_unpackh (vector bool short);
     vector unsigned int vec_unpackh (vector pixel);

     vector bool int vec_vupkhsh (vector bool short);
     vector signed int vec_vupkhsh (vector signed short);

     vector unsigned int vec_vupkhpx (vector pixel);

     vector bool short vec_vupkhsb (vector bool char);
     vector signed short vec_vupkhsb (vector signed char);

     vector signed short vec_unpackl (vector signed char);
     vector bool short vec_unpackl (vector bool char);
     vector unsigned int vec_unpackl (vector pixel);
     vector signed int vec_unpackl (vector signed short);
     vector bool int vec_unpackl (vector bool short);

     vector unsigned int vec_vupklpx (vector pixel);

     vector bool int vec_vupklsh (vector bool short);
     vector signed int vec_vupklsh (vector signed short);

     vector bool short vec_vupklsb (vector bool char);
     vector signed short vec_vupklsb (vector signed char);

     vector float vec_xor (vector float, vector float);
     vector float vec_xor (vector float, vector bool int);
     vector float vec_xor (vector bool int, vector float);
     vector bool int vec_xor (vector bool int, vector bool int);
     vector signed int vec_xor (vector bool int, vector signed int);
     vector signed int vec_xor (vector signed int, vector bool int);
     vector signed int vec_xor (vector signed int, vector signed int);
     vector unsigned int vec_xor (vector bool int, vector unsigned int);
     vector unsigned int vec_xor (vector unsigned int, vector bool int);
     vector unsigned int vec_xor (vector unsigned int, vector unsigned int);
     vector bool short vec_xor (vector bool short, vector bool short);
     vector signed short vec_xor (vector bool short, vector signed short);
     vector signed short vec_xor (vector signed short, vector bool short);
     vector signed short vec_xor (vector signed short, vector signed short);
     vector unsigned short vec_xor (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_xor (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_xor (vector unsigned short,
                                    vector unsigned short);
     vector signed char vec_xor (vector bool char, vector signed char);
     vector bool char vec_xor (vector bool char, vector bool char);
     vector signed char vec_xor (vector signed char, vector bool char);
     vector signed char vec_xor (vector signed char, vector signed char);
     vector unsigned char vec_xor (vector bool char, vector unsigned char);
     vector unsigned char vec_xor (vector unsigned char, vector bool char);
     vector unsigned char vec_xor (vector unsigned char,
                                   vector unsigned char);

     int vec_all_eq (vector signed char, vector bool char);
     int vec_all_eq (vector signed char, vector signed char);
     int vec_all_eq (vector unsigned char, vector bool char);
     int vec_all_eq (vector unsigned char, vector unsigned char);
     int vec_all_eq (vector bool char, vector bool char);
     int vec_all_eq (vector bool char, vector unsigned char);
     int vec_all_eq (vector bool char, vector signed char);
     int vec_all_eq (vector signed short, vector bool short);
     int vec_all_eq (vector signed short, vector signed short);
     int vec_all_eq (vector unsigned short, vector bool short);
     int vec_all_eq (vector unsigned short, vector unsigned short);
     int vec_all_eq (vector bool short, vector bool short);
     int vec_all_eq (vector bool short, vector unsigned short);
     int vec_all_eq (vector bool short, vector signed short);
     int vec_all_eq (vector pixel, vector pixel);
     int vec_all_eq (vector signed int, vector bool int);
     int vec_all_eq (vector signed int, vector signed int);
     int vec_all_eq (vector unsigned int, vector bool int);
     int vec_all_eq (vector unsigned int, vector unsigned int);
     int vec_all_eq (vector bool int, vector bool int);
     int vec_all_eq (vector bool int, vector unsigned int);
     int vec_all_eq (vector bool int, vector signed int);
     int vec_all_eq (vector float, vector float);

     int vec_all_ge (vector bool char, vector unsigned char);
     int vec_all_ge (vector unsigned char, vector bool char);
     int vec_all_ge (vector unsigned char, vector unsigned char);
     int vec_all_ge (vector bool char, vector signed char);
     int vec_all_ge (vector signed char, vector bool char);
     int vec_all_ge (vector signed char, vector signed char);
     int vec_all_ge (vector bool short, vector unsigned short);
     int vec_all_ge (vector unsigned short, vector bool short);
     int vec_all_ge (vector unsigned short, vector unsigned short);
     int vec_all_ge (vector signed short, vector signed short);
     int vec_all_ge (vector bool short, vector signed short);
     int vec_all_ge (vector signed short, vector bool short);
     int vec_all_ge (vector bool int, vector unsigned int);
     int vec_all_ge (vector unsigned int, vector bool int);
     int vec_all_ge (vector unsigned int, vector unsigned int);
     int vec_all_ge (vector bool int, vector signed int);
     int vec_all_ge (vector signed int, vector bool int);
     int vec_all_ge (vector signed int, vector signed int);
     int vec_all_ge (vector float, vector float);

     int vec_all_gt (vector bool char, vector unsigned char);
     int vec_all_gt (vector unsigned char, vector bool char);
     int vec_all_gt (vector unsigned char, vector unsigned char);
     int vec_all_gt (vector bool char, vector signed char);
     int vec_all_gt (vector signed char, vector bool char);
     int vec_all_gt (vector signed char, vector signed char);
     int vec_all_gt (vector bool short, vector unsigned short);
     int vec_all_gt (vector unsigned short, vector bool short);
     int vec_all_gt (vector unsigned short, vector unsigned short);
     int vec_all_gt (vector bool short, vector signed short);
     int vec_all_gt (vector signed short, vector bool short);
     int vec_all_gt (vector signed short, vector signed short);
     int vec_all_gt (vector bool int, vector unsigned int);
     int vec_all_gt (vector unsigned int, vector bool int);
     int vec_all_gt (vector unsigned int, vector unsigned int);
     int vec_all_gt (vector bool int, vector signed int);
     int vec_all_gt (vector signed int, vector bool int);
     int vec_all_gt (vector signed int, vector signed int);
     int vec_all_gt (vector float, vector float);

     int vec_all_in (vector float, vector float);

     int vec_all_le (vector bool char, vector unsigned char);
     int vec_all_le (vector unsigned char, vector bool char);
     int vec_all_le (vector unsigned char, vector unsigned char);
     int vec_all_le (vector bool char, vector signed char);
     int vec_all_le (vector signed char, vector bool char);
     int vec_all_le (vector signed char, vector signed char);
     int vec_all_le (vector bool short, vector unsigned short);
     int vec_all_le (vector unsigned short, vector bool short);
     int vec_all_le (vector unsigned short, vector unsigned short);
     int vec_all_le (vector bool short, vector signed short);
     int vec_all_le (vector signed short, vector bool short);
     int vec_all_le (vector signed short, vector signed short);
     int vec_all_le (vector bool int, vector unsigned int);
     int vec_all_le (vector unsigned int, vector bool int);
     int vec_all_le (vector unsigned int, vector unsigned int);
     int vec_all_le (vector bool int, vector signed int);
     int vec_all_le (vector signed int, vector bool int);
     int vec_all_le (vector signed int, vector signed int);
     int vec_all_le (vector float, vector float);

     int vec_all_lt (vector bool char, vector unsigned char);
     int vec_all_lt (vector unsigned char, vector bool char);
     int vec_all_lt (vector unsigned char, vector unsigned char);
     int vec_all_lt (vector bool char, vector signed char);
     int vec_all_lt (vector signed char, vector bool char);
     int vec_all_lt (vector signed char, vector signed char);
     int vec_all_lt (vector bool short, vector unsigned short);
     int vec_all_lt (vector unsigned short, vector bool short);
     int vec_all_lt (vector unsigned short, vector unsigned short);
     int vec_all_lt (vector bool short, vector signed short);
     int vec_all_lt (vector signed short, vector bool short);
     int vec_all_lt (vector signed short, vector signed short);
     int vec_all_lt (vector bool int, vector unsigned int);
     int vec_all_lt (vector unsigned int, vector bool int);
     int vec_all_lt (vector unsigned int, vector unsigned int);
     int vec_all_lt (vector bool int, vector signed int);
     int vec_all_lt (vector signed int, vector bool int);
     int vec_all_lt (vector signed int, vector signed int);
     int vec_all_lt (vector float, vector float);

     int vec_all_nan (vector float);

     int vec_all_ne (vector signed char, vector bool char);
     int vec_all_ne (vector signed char, vector signed char);
     int vec_all_ne (vector unsigned char, vector bool char);
     int vec_all_ne (vector unsigned char, vector unsigned char);
     int vec_all_ne (vector bool char, vector bool char);
     int vec_all_ne (vector bool char, vector unsigned char);
     int vec_all_ne (vector bool char, vector signed char);
     int vec_all_ne (vector signed short, vector bool short);
     int vec_all_ne (vector signed short, vector signed short);
     int vec_all_ne (vector unsigned short, vector bool short);
     int vec_all_ne (vector unsigned short, vector unsigned short);
     int vec_all_ne (vector bool short, vector bool short);
     int vec_all_ne (vector bool short, vector unsigned short);
     int vec_all_ne (vector bool short, vector signed short);
     int vec_all_ne (vector pixel, vector pixel);
     int vec_all_ne (vector signed int, vector bool int);
     int vec_all_ne (vector signed int, vector signed int);
     int vec_all_ne (vector unsigned int, vector bool int);
     int vec_all_ne (vector unsigned int, vector unsigned int);
     int vec_all_ne (vector bool int, vector bool int);
     int vec_all_ne (vector bool int, vector unsigned int);
     int vec_all_ne (vector bool int, vector signed int);
     int vec_all_ne (vector float, vector float);

     int vec_all_nge (vector float, vector float);

     int vec_all_ngt (vector float, vector float);

     int vec_all_nle (vector float, vector float);

     int vec_all_nlt (vector float, vector float);

     int vec_all_numeric (vector float);

     int vec_any_eq (vector signed char, vector bool char);
     int vec_any_eq (vector signed char, vector signed char);
     int vec_any_eq (vector unsigned char, vector bool char);
     int vec_any_eq (vector unsigned char, vector unsigned char);
     int vec_any_eq (vector bool char, vector bool char);
     int vec_any_eq (vector bool char, vector unsigned char);
     int vec_any_eq (vector bool char, vector signed char);
     int vec_any_eq (vector signed short, vector bool short);
     int vec_any_eq (vector signed short, vector signed short);
     int vec_any_eq (vector unsigned short, vector bool short);
     int vec_any_eq (vector unsigned short, vector unsigned short);
     int vec_any_eq (vector bool short, vector bool short);
     int vec_any_eq (vector bool short, vector unsigned short);
     int vec_any_eq (vector bool short, vector signed short);
     int vec_any_eq (vector pixel, vector pixel);
     int vec_any_eq (vector signed int, vector bool int);
     int vec_any_eq (vector signed int, vector signed int);
     int vec_any_eq (vector unsigned int, vector bool int);
     int vec_any_eq (vector unsigned int, vector unsigned int);
     int vec_any_eq (vector bool int, vector bool int);
     int vec_any_eq (vector bool int, vector unsigned int);
     int vec_any_eq (vector bool int, vector signed int);
     int vec_any_eq (vector float, vector float);

     int vec_any_ge (vector signed char, vector bool char);
     int vec_any_ge (vector unsigned char, vector bool char);
     int vec_any_ge (vector unsigned char, vector unsigned char);
     int vec_any_ge (vector signed char, vector signed char);
     int vec_any_ge (vector bool char, vector unsigned char);
     int vec_any_ge (vector bool char, vector signed char);
     int vec_any_ge (vector unsigned short, vector bool short);
     int vec_any_ge (vector unsigned short, vector unsigned short);
     int vec_any_ge (vector signed short, vector signed short);
     int vec_any_ge (vector signed short, vector bool short);
     int vec_any_ge (vector bool short, vector unsigned short);
     int vec_any_ge (vector bool short, vector signed short);
     int vec_any_ge (vector signed int, vector bool int);
     int vec_any_ge (vector unsigned int, vector bool int);
     int vec_any_ge (vector unsigned int, vector unsigned int);
     int vec_any_ge (vector signed int, vector signed int);
     int vec_any_ge (vector bool int, vector unsigned int);
     int vec_any_ge (vector bool int, vector signed int);
     int vec_any_ge (vector float, vector float);

     int vec_any_gt (vector bool char, vector unsigned char);
     int vec_any_gt (vector unsigned char, vector bool char);
     int vec_any_gt (vector unsigned char, vector unsigned char);
     int vec_any_gt (vector bool char, vector signed char);
     int vec_any_gt (vector signed char, vector bool char);
     int vec_any_gt (vector signed char, vector signed char);
     int vec_any_gt (vector bool short, vector unsigned short);
     int vec_any_gt (vector unsigned short, vector bool short);
     int vec_any_gt (vector unsigned short, vector unsigned short);
     int vec_any_gt (vector bool short, vector signed short);
     int vec_any_gt (vector signed short, vector bool short);
     int vec_any_gt (vector signed short, vector signed short);
     int vec_any_gt (vector bool int, vector unsigned int);
     int vec_any_gt (vector unsigned int, vector bool int);
     int vec_any_gt (vector unsigned int, vector unsigned int);
     int vec_any_gt (vector bool int, vector signed int);
     int vec_any_gt (vector signed int, vector bool int);
     int vec_any_gt (vector signed int, vector signed int);
     int vec_any_gt (vector float, vector float);

     int vec_any_le (vector bool char, vector unsigned char);
     int vec_any_le (vector unsigned char, vector bool char);
     int vec_any_le (vector unsigned char, vector unsigned char);
     int vec_any_le (vector bool char, vector signed char);
     int vec_any_le (vector signed char, vector bool char);
     int vec_any_le (vector signed char, vector signed char);
     int vec_any_le (vector bool short, vector unsigned short);
     int vec_any_le (vector unsigned short, vector bool short);
     int vec_any_le (vector unsigned short, vector unsigned short);
     int vec_any_le (vector bool short, vector signed short);
     int vec_any_le (vector signed short, vector bool short);
     int vec_any_le (vector signed short, vector signed short);
     int vec_any_le (vector bool int, vector unsigned int);
     int vec_any_le (vector unsigned int, vector bool int);
     int vec_any_le (vector unsigned int, vector unsigned int);
     int vec_any_le (vector bool int, vector signed int);
     int vec_any_le (vector signed int, vector bool int);
     int vec_any_le (vector signed int, vector signed int);
     int vec_any_le (vector float, vector float);

     int vec_any_lt (vector bool char, vector unsigned char);
     int vec_any_lt (vector unsigned char, vector bool char);
     int vec_any_lt (vector unsigned char, vector unsigned char);
     int vec_any_lt (vector bool char, vector signed char);
     int vec_any_lt (vector signed char, vector bool char);
     int vec_any_lt (vector signed char, vector signed char);
     int vec_any_lt (vector bool short, vector unsigned short);
     int vec_any_lt (vector unsigned short, vector bool short);
     int vec_any_lt (vector unsigned short, vector unsigned short);
     int vec_any_lt (vector bool short, vector signed short);
     int vec_any_lt (vector signed short, vector bool short);
     int vec_any_lt (vector signed short, vector signed short);
     int vec_any_lt (vector bool int, vector unsigned int);
     int vec_any_lt (vector unsigned int, vector bool int);
     int vec_any_lt (vector unsigned int, vector unsigned int);
     int vec_any_lt (vector bool int, vector signed int);
     int vec_any_lt (vector signed int, vector bool int);
     int vec_any_lt (vector signed int, vector signed int);
     int vec_any_lt (vector float, vector float);

     int vec_any_nan (vector float);

     int vec_any_ne (vector signed char, vector bool char);
     int vec_any_ne (vector signed char, vector signed char);
     int vec_any_ne (vector unsigned char, vector bool char);
     int vec_any_ne (vector unsigned char, vector unsigned char);
     int vec_any_ne (vector bool char, vector bool char);
     int vec_any_ne (vector bool char, vector unsigned char);
     int vec_any_ne (vector bool char, vector signed char);
     int vec_any_ne (vector signed short, vector bool short);
     int vec_any_ne (vector signed short, vector signed short);
     int vec_any_ne (vector unsigned short, vector bool short);
     int vec_any_ne (vector unsigned short, vector unsigned short);
     int vec_any_ne (vector bool short, vector bool short);
     int vec_any_ne (vector bool short, vector unsigned short);
     int vec_any_ne (vector bool short, vector signed short);
     int vec_any_ne (vector pixel, vector pixel);
     int vec_any_ne (vector signed int, vector bool int);
     int vec_any_ne (vector signed int, vector signed int);
     int vec_any_ne (vector unsigned int, vector bool int);
     int vec_any_ne (vector unsigned int, vector unsigned int);
     int vec_any_ne (vector bool int, vector bool int);
     int vec_any_ne (vector bool int, vector unsigned int);
     int vec_any_ne (vector bool int, vector signed int);
     int vec_any_ne (vector float, vector float);

     int vec_any_nge (vector float, vector float);

     int vec_any_ngt (vector float, vector float);

     int vec_any_nle (vector float, vector float);

     int vec_any_nlt (vector float, vector float);

     int vec_any_numeric (vector float);

     int vec_any_out (vector float, vector float);

If the vector/scalar (VSX) instruction set is available, the following additional functions are available:

     vector double vec_abs (vector double);
     vector double vec_add (vector double, vector double);
     vector double vec_and (vector double, vector double);
     vector double vec_and (vector double, vector bool long);
     vector double vec_and (vector bool long, vector double);
     vector long vec_and (vector long, vector long);
     vector long vec_and (vector long, vector bool long);
     vector long vec_and (vector bool long, vector long);
     vector unsigned long vec_and (vector unsigned long, vector unsigned long);
     vector unsigned long vec_and (vector unsigned long, vector bool long);
     vector unsigned long vec_and (vector bool long, vector unsigned long);
     vector double vec_andc (vector double, vector double);
     vector double vec_andc (vector double, vector bool long);
     vector double vec_andc (vector bool long, vector double);
     vector long vec_andc (vector long, vector long);
     vector long vec_andc (vector long, vector bool long);
     vector long vec_andc (vector bool long, vector long);
     vector unsigned long vec_andc (vector unsigned long, vector unsigned long);
     vector unsigned long vec_andc (vector unsigned long, vector bool long);
     vector unsigned long vec_andc (vector bool long, vector unsigned long);
     vector double vec_ceil (vector double);
     vector bool long vec_cmpeq (vector double, vector double);
     vector bool long vec_cmpge (vector double, vector double);
     vector bool long vec_cmpgt (vector double, vector double);
     vector bool long vec_cmple (vector double, vector double);
     vector bool long vec_cmplt (vector double, vector double);
     vector double vec_cpsgn (vector double, vector double);
     vector float vec_div (vector float, vector float);
     vector double vec_div (vector double, vector double);
     vector long vec_div (vector long, vector long);
     vector unsigned long vec_div (vector unsigned long, vector unsigned long);
     vector double vec_floor (vector double);
     vector double vec_ld (int, const vector double *);
     vector double vec_ld (int, const double *);
     vector double vec_ldl (int, const vector double *);
     vector double vec_ldl (int, const double *);
     vector unsigned char vec_lvsl (int, const volatile double *);
     vector unsigned char vec_lvsr (int, const volatile double *);
     vector double vec_madd (vector double, vector double, vector double);
     vector double vec_max (vector double, vector double);
     vector signed long vec_mergeh (vector signed long, vector signed long);
     vector signed long vec_mergeh (vector signed long, vector bool long);
     vector signed long vec_mergeh (vector bool long, vector signed long);
     vector unsigned long vec_mergeh (vector unsigned long, vector unsigned long);
     vector unsigned long vec_mergeh (vector unsigned long, vector bool long);
     vector unsigned long vec_mergeh (vector bool long, vector unsigned long);
     vector signed long vec_mergel (vector signed long, vector signed long);
     vector signed long vec_mergel (vector signed long, vector bool long);
     vector signed long vec_mergel (vector bool long, vector signed long);
     vector unsigned long vec_mergel (vector unsigned long, vector unsigned long);
     vector unsigned long vec_mergel (vector unsigned long, vector bool long);
     vector unsigned long vec_mergel (vector bool long, vector unsigned long);
     vector double vec_min (vector double, vector double);
     vector float vec_msub (vector float, vector float, vector float);
     vector double vec_msub (vector double, vector double, vector double);
     vector float vec_mul (vector float, vector float);
     vector double vec_mul (vector double, vector double);
     vector long vec_mul (vector long, vector long);
     vector unsigned long vec_mul (vector unsigned long, vector unsigned long);
     vector float vec_nearbyint (vector float);
     vector double vec_nearbyint (vector double);
     vector float vec_nmadd (vector float, vector float, vector float);
     vector double vec_nmadd (vector double, vector double, vector double);
     vector double vec_nmsub (vector double, vector double, vector double);
     vector double vec_nor (vector double, vector double);
     vector long vec_nor (vector long, vector long);
     vector long vec_nor (vector long, vector bool long);
     vector long vec_nor (vector bool long, vector long);
     vector unsigned long vec_nor (vector unsigned long, vector unsigned long);
     vector unsigned long vec_nor (vector unsigned long, vector bool long);
     vector unsigned long vec_nor (vector bool long, vector unsigned long);
     vector double vec_or (vector double, vector double);
     vector double vec_or (vector double, vector bool long);
     vector double vec_or (vector bool long, vector double);
     vector long vec_or (vector long, vector long);
     vector long vec_or (vector long, vector bool long);
     vector long vec_or (vector bool long, vector long);
     vector unsigned long vec_or (vector unsigned long, vector unsigned long);
     vector unsigned long vec_or (vector unsigned long, vector bool long);
     vector unsigned long vec_or (vector bool long, vector unsigned long);
     vector double vec_perm (vector double, vector double, vector unsigned char);
     vector long vec_perm (vector long, vector long, vector unsigned char);
     vector unsigned long vec_perm (vector unsigned long, vector unsigned long,
                                    vector unsigned char);
     vector double vec_rint (vector double);
     vector double vec_recip (vector double, vector double);
     vector double vec_rsqrt (vector double);
     vector double vec_rsqrte (vector double);
     vector double vec_sel (vector double, vector double, vector bool long);
     vector double vec_sel (vector double, vector double, vector unsigned long);
     vector long vec_sel (vector long, vector long, vector long);
     vector long vec_sel (vector long, vector long, vector unsigned long);
     vector long vec_sel (vector long, vector long, vector bool long);
     vector unsigned long vec_sel (vector unsigned long, vector unsigned long,
                                   vector long);
     vector unsigned long vec_sel (vector unsigned long, vector unsigned long,
                                   vector unsigned long);
     vector unsigned long vec_sel (vector unsigned long, vector unsigned long,
                                   vector bool long);
     vector double vec_splats (double);
     vector signed long vec_splats (signed long);
     vector unsigned long vec_splats (unsigned long);
     vector float vec_sqrt (vector float);
     vector double vec_sqrt (vector double);
     void vec_st (vector double, int, vector double *);
     void vec_st (vector double, int, double *);
     vector double vec_sub (vector double, vector double);
     vector double vec_trunc (vector double);
     vector double vec_xor (vector double, vector double);
     vector double vec_xor (vector double, vector bool long);
     vector double vec_xor (vector bool long, vector double);
     vector long vec_xor (vector long, vector long);
     vector long vec_xor (vector long, vector bool long);
     vector long vec_xor (vector bool long, vector long);
     vector unsigned long vec_xor (vector unsigned long, vector unsigned long);
     vector unsigned long vec_xor (vector unsigned long, vector bool long);
     vector unsigned long vec_xor (vector bool long, vector unsigned long);
     int vec_all_eq (vector double, vector double);
     int vec_all_ge (vector double, vector double);
     int vec_all_gt (vector double, vector double);
     int vec_all_le (vector double, vector double);
     int vec_all_lt (vector double, vector double);
     int vec_all_nan (vector double);
     int vec_all_ne (vector double, vector double);
     int vec_all_nge (vector double, vector double);
     int vec_all_ngt (vector double, vector double);
     int vec_all_nle (vector double, vector double);
     int vec_all_nlt (vector double, vector double);
     int vec_all_numeric (vector double);
     int vec_any_eq (vector double, vector double);
     int vec_any_ge (vector double, vector double);
     int vec_any_gt (vector double, vector double);
     int vec_any_le (vector double, vector double);
     int vec_any_lt (vector double, vector double);
     int vec_any_nan (vector double);
     int vec_any_ne (vector double, vector double);
     int vec_any_nge (vector double, vector double);
     int vec_any_ngt (vector double, vector double);
     int vec_any_nle (vector double, vector double);
     int vec_any_nlt (vector double, vector double);
     int vec_any_numeric (vector double);

     vector double vec_vsx_ld (int, const vector double *);
     vector double vec_vsx_ld (int, const double *);
     vector float vec_vsx_ld (int, const vector float *);
     vector float vec_vsx_ld (int, const float *);
     vector bool int vec_vsx_ld (int, const vector bool int *);
     vector signed int vec_vsx_ld (int, const vector signed int *);
     vector signed int vec_vsx_ld (int, const int *);
     vector signed int vec_vsx_ld (int, const long *);
     vector unsigned int vec_vsx_ld (int, const vector unsigned int *);
     vector unsigned int vec_vsx_ld (int, const unsigned int *);
     vector unsigned int vec_vsx_ld (int, const unsigned long *);
     vector bool short vec_vsx_ld (int, const vector bool short *);
     vector pixel vec_vsx_ld (int, const vector pixel *);
     vector signed short vec_vsx_ld (int, const vector signed short *);
     vector signed short vec_vsx_ld (int, const short *);
     vector unsigned short vec_vsx_ld (int, const vector unsigned short *);
     vector unsigned short vec_vsx_ld (int, const unsigned short *);
     vector bool char vec_vsx_ld (int, const vector bool char *);
     vector signed char vec_vsx_ld (int, const vector signed char *);
     vector signed char vec_vsx_ld (int, const signed char *);
     vector unsigned char vec_vsx_ld (int, const vector unsigned char *);
     vector unsigned char vec_vsx_ld (int, const unsigned char *);

     void vec_vsx_st (vector double, int, vector double *);
     void vec_vsx_st (vector double, int, double *);
     void vec_vsx_st (vector float, int, vector float *);
     void vec_vsx_st (vector float, int, float *);
     void vec_vsx_st (vector signed int, int, vector signed int *);
     void vec_vsx_st (vector signed int, int, int *);
     void vec_vsx_st (vector unsigned int, int, vector unsigned int *);
     void vec_vsx_st (vector unsigned int, int, unsigned int *);
     void vec_vsx_st (vector bool int, int, vector bool int *);
     void vec_vsx_st (vector bool int, int, unsigned int *);
     void vec_vsx_st (vector bool int, int, int *);
     void vec_vsx_st (vector signed short, int, vector signed short *);
     void vec_vsx_st (vector signed short, int, short *);
     void vec_vsx_st (vector unsigned short, int, vector unsigned short *);
     void vec_vsx_st (vector unsigned short, int, unsigned short *);
     void vec_vsx_st (vector bool short, int, vector bool short *);
     void vec_vsx_st (vector bool short, int, unsigned short *);
     void vec_vsx_st (vector pixel, int, vector pixel *);
     void vec_vsx_st (vector pixel, int, unsigned short *);
     void vec_vsx_st (vector pixel, int, short *);
     void vec_vsx_st (vector bool short, int, short *);
     void vec_vsx_st (vector signed char, int, vector signed char *);
     void vec_vsx_st (vector signed char, int, signed char *);
     void vec_vsx_st (vector unsigned char, int, vector unsigned char *);
     void vec_vsx_st (vector unsigned char, int, unsigned char *);
     void vec_vsx_st (vector bool char, int, vector bool char *);
     void vec_vsx_st (vector bool char, int, unsigned char *);
     void vec_vsx_st (vector bool char, int, signed char *);

     vector double vec_xxpermdi (vector double, vector double, int);
     vector float vec_xxpermdi (vector float, vector float, int);
     vector long long vec_xxpermdi (vector long long, vector long long, int);
     vector unsigned long long vec_xxpermdi (vector unsigned long long,
                                             vector unsigned long long, int);
     vector int vec_xxpermdi (vector int, vector int, int);
     vector unsigned int vec_xxpermdi (vector unsigned int,
                                       vector unsigned int, int);
     vector short vec_xxpermdi (vector short, vector short, int);
     vector unsigned short vec_xxpermdi (vector unsigned short,
                                         vector unsigned short, int);
     vector signed char vec_xxpermdi (vector signed char, vector signed char, int);
     vector unsigned char vec_xxpermdi (vector unsigned char,
                                        vector unsigned char, int);

     vector double vec_xxsldi (vector double, vector double, int);
     vector float vec_xxsldi (vector float, vector float, int);
     vector long long vec_xxsldi (vector long long, vector long long, int);
     vector unsigned long long vec_xxsldi (vector unsigned long long,
                                           vector unsigned long long, int);
     vector int vec_xxsldi (vector int, vector int, int);
     vector unsigned int vec_xxsldi (vector unsigned int, vector unsigned int, int);
     vector short vec_xxsldi (vector short, vector short, int);
     vector unsigned short vec_xxsldi (vector unsigned short,
                                       vector unsigned short, int);
     vector signed char vec_xxsldi (vector signed char, vector signed char, int);
     vector unsigned char vec_xxsldi (vector unsigned char,
                                      vector unsigned char, int);

Note that the vec_ld and vec_st built-in functions always generate the AltiVec LVX and STVX instructions even if the VSX instruction set is available.  The vec_vsx_ld and vec_vsx_st built-in functions always generate the VSX LXVD2X, LXVW4X, STXVD2X, and STXVW4X instructions.

If the ISA 2.07 additions to the vector/scalar (power8-vector) instruction set is available, the following additional functions are available for both 32-bit and 64-bit targets.  For 64-bit targets, you can use VECTOR LONG instead of VECTOR LONG LONG, VECTOR BOOL LONG instead of VECTOR BOOL LONG LONG, and VECTOR UNSIGNED LONG instead of VECTOR UNSIGNED LONG LONG.

     vector long long vec_abs (vector long long);

     vector long long vec_add (vector long long, vector long long);
     vector unsigned long long vec_add (vector unsigned long long,
                                        vector unsigned long long);

     int vec_all_eq (vector long long, vector long long);
     int vec_all_eq (vector unsigned long long, vector unsigned long long);
     int vec_all_ge (vector long long, vector long long);
     int vec_all_ge (vector unsigned long long, vector unsigned long long);
     int vec_all_gt (vector long long, vector long long);
     int vec_all_gt (vector unsigned long long, vector unsigned long long);
     int vec_all_le (vector long long, vector long long);
     int vec_all_le (vector unsigned long long, vector unsigned long long);
     int vec_all_lt (vector long long, vector long long);
     int vec_all_lt (vector unsigned long long, vector unsigned long long);
     int vec_all_ne (vector long long, vector long long);
     int vec_all_ne (vector unsigned long long, vector unsigned long long);

     int vec_any_eq (vector long long, vector long long);
     int vec_any_eq (vector unsigned long long, vector unsigned long long);
     int vec_any_ge (vector long long, vector long long);
     int vec_any_ge (vector unsigned long long, vector unsigned long long);
     int vec_any_gt (vector long long, vector long long);
     int vec_any_gt (vector unsigned long long, vector unsigned long long);
     int vec_any_le (vector long long, vector long long);
     int vec_any_le (vector unsigned long long, vector unsigned long long);
     int vec_any_lt (vector long long, vector long long);
     int vec_any_lt (vector unsigned long long, vector unsigned long long);
     int vec_any_ne (vector long long, vector long long);
     int vec_any_ne (vector unsigned long long, vector unsigned long long);

     vector long long vec_eqv (vector long long, vector long long);
     vector long long vec_eqv (vector bool long long, vector long long);
     vector long long vec_eqv (vector long long, vector bool long long);
     vector unsigned long long vec_eqv (vector unsigned long long,
                                        vector unsigned long long);
     vector unsigned long long vec_eqv (vector bool long long,
                                        vector unsigned long long);
     vector unsigned long long vec_eqv (vector unsigned long long,
                                        vector bool long long);
     vector int vec_eqv (vector int, vector int);
     vector int vec_eqv (vector bool int, vector int);
     vector int vec_eqv (vector int, vector bool int);
     vector unsigned int vec_eqv (vector unsigned int, vector unsigned int);
     vector unsigned int vec_eqv (vector bool unsigned int,
                                  vector unsigned int);
     vector unsigned int vec_eqv (vector unsigned int,
                                  vector bool unsigned int);
     vector short vec_eqv (vector short, vector short);
     vector short vec_eqv (vector bool short, vector short);
     vector short vec_eqv (vector short, vector bool short);
     vector unsigned short vec_eqv (vector unsigned short, vector unsigned short);
     vector unsigned short vec_eqv (vector bool unsigned short,
                                    vector unsigned short);
     vector unsigned short vec_eqv (vector unsigned short,
                                    vector bool unsigned short);
     vector signed char vec_eqv (vector signed char, vector signed char);
     vector signed char vec_eqv (vector bool signed char, vector signed char);
     vector signed char vec_eqv (vector signed char, vector bool signed char);
     vector unsigned char vec_eqv (vector unsigned char, vector unsigned char);
     vector unsigned char vec_eqv (vector bool unsigned char, vector unsigned char);
     vector unsigned char vec_eqv (vector unsigned char, vector bool unsigned char);

     vector long long vec_max (vector long long, vector long long);
     vector unsigned long long vec_max (vector unsigned long long,
                                        vector unsigned long long);

     vector signed int vec_mergee (vector signed int, vector signed int);
     vector unsigned int vec_mergee (vector unsigned int, vector unsigned int);
     vector bool int vec_mergee (vector bool int, vector bool int);

     vector signed int vec_mergeo (vector signed int, vector signed int);
     vector unsigned int vec_mergeo (vector unsigned int, vector unsigned int);
     vector bool int vec_mergeo (vector bool int, vector bool int);

     vector long long vec_min (vector long long, vector long long);
     vector unsigned long long vec_min (vector unsigned long long,
                                        vector unsigned long long);

     vector long long vec_nand (vector long long, vector long long);
     vector long long vec_nand (vector bool long long, vector long long);
     vector long long vec_nand (vector long long, vector bool long long);
     vector unsigned long long vec_nand (vector unsigned long long,
                                         vector unsigned long long);
     vector unsigned long long vec_nand (vector bool long long,
                                        vector unsigned long long);
     vector unsigned long long vec_nand (vector unsigned long long,
                                         vector bool long long);
     vector int vec_nand (vector int, vector int);
     vector int vec_nand (vector bool int, vector int);
     vector int vec_nand (vector int, vector bool int);
     vector unsigned int vec_nand (vector unsigned int, vector unsigned int);
     vector unsigned int vec_nand (vector bool unsigned int,
                                   vector unsigned int);
     vector unsigned int vec_nand (vector unsigned int,
                                   vector bool unsigned int);
     vector short vec_nand (vector short, vector short);
     vector short vec_nand (vector bool short, vector short);
     vector short vec_nand (vector short, vector bool short);
     vector unsigned short vec_nand (vector unsigned short, vector unsigned short);
     vector unsigned short vec_nand (vector bool unsigned short,
                                     vector unsigned short);
     vector unsigned short vec_nand (vector unsigned short,
                                     vector bool unsigned short);
     vector signed char vec_nand (vector signed char, vector signed char);
     vector signed char vec_nand (vector bool signed char, vector signed char);
     vector signed char vec_nand (vector signed char, vector bool signed char);
     vector unsigned char vec_nand (vector unsigned char, vector unsigned char);
     vector unsigned char vec_nand (vector bool unsigned char, vector unsigned char);
     vector unsigned char vec_nand (vector unsigned char, vector bool unsigned char);

     vector long long vec_orc (vector long long, vector long long);
     vector long long vec_orc (vector bool long long, vector long long);
     vector long long vec_orc (vector long long, vector bool long long);
     vector unsigned long long vec_orc (vector unsigned long long,
                                        vector unsigned long long);
     vector unsigned long long vec_orc (vector bool long long,
                                        vector unsigned long long);
     vector unsigned long long vec_orc (vector unsigned long long,
                                        vector bool long long);
     vector int vec_orc (vector int, vector int);
     vector int vec_orc (vector bool int, vector int);
     vector int vec_orc (vector int, vector bool int);
     vector unsigned int vec_orc (vector unsigned int, vector unsigned int);
     vector unsigned int vec_orc (vector bool unsigned int,
                                  vector unsigned int);
     vector unsigned int vec_orc (vector unsigned int,
                                  vector bool unsigned int);
     vector short vec_orc (vector short, vector short);
     vector short vec_orc (vector bool short, vector short);
     vector short vec_orc (vector short, vector bool short);
     vector unsigned short vec_orc (vector unsigned short, vector unsigned short);
     vector unsigned short vec_orc (vector bool unsigned short,
                                    vector unsigned short);
     vector unsigned short vec_orc (vector unsigned short,
                                    vector bool unsigned short);
     vector signed char vec_orc (vector signed char, vector signed char);
     vector signed char vec_orc (vector bool signed char, vector signed char);
     vector signed char vec_orc (vector signed char, vector bool signed char);
     vector unsigned char vec_orc (vector unsigned char, vector unsigned char);
     vector unsigned char vec_orc (vector bool unsigned char, vector unsigned char);
     vector unsigned char vec_orc (vector unsigned char, vector bool unsigned char);

     vector int vec_pack (vector long long, vector long long);
     vector unsigned int vec_pack (vector unsigned long long,
                                   vector unsigned long long);
     vector bool int vec_pack (vector bool long long, vector bool long long);

     vector int vec_packs (vector long long, vector long long);
     vector unsigned int vec_packs (vector unsigned long long,
                                    vector unsigned long long);

     vector unsigned int vec_packsu (vector long long, vector long long);
     vector unsigned int vec_packsu (vector unsigned long long,
                                     vector unsigned long long);

     vector long long vec_rl (vector long long,
                              vector unsigned long long);
     vector long long vec_rl (vector unsigned long long,
                              vector unsigned long long);

     vector long long vec_sl (vector long long, vector unsigned long long);
     vector long long vec_sl (vector unsigned long long,
                              vector unsigned long long);

     vector long long vec_sr (vector long long, vector unsigned long long);
     vector unsigned long long char vec_sr (vector unsigned long long,
                                            vector unsigned long long);

     vector long long vec_sra (vector long long, vector unsigned long long);
     vector unsigned long long vec_sra (vector unsigned long long,
                                        vector unsigned long long);

     vector long long vec_sub (vector long long, vector long long);
     vector unsigned long long vec_sub (vector unsigned long long,
                                        vector unsigned long long);

     vector long long vec_unpackh (vector int);
     vector unsigned long long vec_unpackh (vector unsigned int);

     vector long long vec_unpackl (vector int);
     vector unsigned long long vec_unpackl (vector unsigned int);

     vector long long vec_vaddudm (vector long long, vector long long);
     vector long long vec_vaddudm (vector bool long long, vector long long);
     vector long long vec_vaddudm (vector long long, vector bool long long);
     vector unsigned long long vec_vaddudm (vector unsigned long long,
                                            vector unsigned long long);
     vector unsigned long long vec_vaddudm (vector bool unsigned long long,
                                            vector unsigned long long);
     vector unsigned long long vec_vaddudm (vector unsigned long long,
                                            vector bool unsigned long long);

     vector long long vec_vbpermq (vector signed char, vector signed char);
     vector long long vec_vbpermq (vector unsigned char, vector unsigned char);

     vector long long vec_cntlz (vector long long);
     vector unsigned long long vec_cntlz (vector unsigned long long);
     vector int vec_cntlz (vector int);
     vector unsigned int vec_cntlz (vector int);
     vector short vec_cntlz (vector short);
     vector unsigned short vec_cntlz (vector unsigned short);
     vector signed char vec_cntlz (vector signed char);
     vector unsigned char vec_cntlz (vector unsigned char);

     vector long long vec_vclz (vector long long);
     vector unsigned long long vec_vclz (vector unsigned long long);
     vector int vec_vclz (vector int);
     vector unsigned int vec_vclz (vector int);
     vector short vec_vclz (vector short);
     vector unsigned short vec_vclz (vector unsigned short);
     vector signed char vec_vclz (vector signed char);
     vector unsigned char vec_vclz (vector unsigned char);

     vector signed char vec_vclzb (vector signed char);
     vector unsigned char vec_vclzb (vector unsigned char);

     vector long long vec_vclzd (vector long long);
     vector unsigned long long vec_vclzd (vector unsigned long long);

     vector short vec_vclzh (vector short);
     vector unsigned short vec_vclzh (vector unsigned short);

     vector int vec_vclzw (vector int);
     vector unsigned int vec_vclzw (vector int);

     vector signed char vec_vgbbd (vector signed char);
     vector unsigned char vec_vgbbd (vector unsigned char);

     vector long long vec_vmaxsd (vector long long, vector long long);

     vector unsigned long long vec_vmaxud (vector unsigned long long,
                                           unsigned vector long long);

     vector long long vec_vminsd (vector long long, vector long long);

     vector unsigned long long vec_vminud (vector long long,
                                           vector long long);

     vector int vec_vpksdss (vector long long, vector long long);
     vector unsigned int vec_vpksdss (vector long long, vector long long);

     vector unsigned int vec_vpkudus (vector unsigned long long,
                                      vector unsigned long long);

     vector int vec_vpkudum (vector long long, vector long long);
     vector unsigned int vec_vpkudum (vector unsigned long long,
                                      vector unsigned long long);
     vector bool int vec_vpkudum (vector bool long long, vector bool long long);

     vector long long vec_vpopcnt (vector long long);
     vector unsigned long long vec_vpopcnt (vector unsigned long long);
     vector int vec_vpopcnt (vector int);
     vector unsigned int vec_vpopcnt (vector int);
     vector short vec_vpopcnt (vector short);
     vector unsigned short vec_vpopcnt (vector unsigned short);
     vector signed char vec_vpopcnt (vector signed char);
     vector unsigned char vec_vpopcnt (vector unsigned char);

     vector signed char vec_vpopcntb (vector signed char);
     vector unsigned char vec_vpopcntb (vector unsigned char);

     vector long long vec_vpopcntd (vector long long);
     vector unsigned long long vec_vpopcntd (vector unsigned long long);

     vector short vec_vpopcnth (vector short);
     vector unsigned short vec_vpopcnth (vector unsigned short);

     vector int vec_vpopcntw (vector int);
     vector unsigned int vec_vpopcntw (vector int);

     vector long long vec_vrld (vector long long, vector unsigned long long);
     vector unsigned long long vec_vrld (vector unsigned long long,
                                         vector unsigned long long);

     vector long long vec_vsld (vector long long, vector unsigned long long);
     vector long long vec_vsld (vector unsigned long long,
                                vector unsigned long long);

     vector long long vec_vsrad (vector long long, vector unsigned long long);
     vector unsigned long long vec_vsrad (vector unsigned long long,
                                          vector unsigned long long);

     vector long long vec_vsrd (vector long long, vector unsigned long long);
     vector unsigned long long char vec_vsrd (vector unsigned long long,
                                              vector unsigned long long);

     vector long long vec_vsubudm (vector long long, vector long long);
     vector long long vec_vsubudm (vector bool long long, vector long long);
     vector long long vec_vsubudm (vector long long, vector bool long long);
     vector unsigned long long vec_vsubudm (vector unsigned long long,
                                            vector unsigned long long);
     vector unsigned long long vec_vsubudm (vector bool long long,
                                            vector unsigned long long);
     vector unsigned long long vec_vsubudm (vector unsigned long long,
                                            vector bool long long);

     vector long long vec_vupkhsw (vector int);
     vector unsigned long long vec_vupkhsw (vector unsigned int);

     vector long long vec_vupklsw (vector int);
     vector unsigned long long vec_vupklsw (vector int);

If the ISA 2.07 additions to the vector/scalar (power8-vector) instruction set is available, the following additional functions are available for 64-bit targets.  New vector types (VECTOR __INT128_T and VECTOR __UINT128_T) are available to hold the __INT128_T and __UINT128_T types to use these builtins.

The normal vector extract, and set operations work on VECTOR __INT128_T and VECTOR __UINT128_T types, but the index value must be 0.

     vector __int128_t vec_vaddcuq (vector __int128_t, vector __int128_t);
     vector __uint128_t vec_vaddcuq (vector __uint128_t, vector __uint128_t);

     vector __int128_t vec_vadduqm (vector __int128_t, vector __int128_t);
     vector __uint128_t vec_vadduqm (vector __uint128_t, vector __uint128_t);

     vector __int128_t vec_vaddecuq (vector __int128_t, vector __int128_t,
                                     vector __int128_t);
     vector __uint128_t vec_vaddecuq (vector __uint128_t, vector __uint128_t,
                                      vector __uint128_t);

     vector __int128_t vec_vaddeuqm (vector __int128_t, vector __int128_t,
                                     vector __int128_t);
     vector __uint128_t vec_vaddeuqm (vector __uint128_t, vector __uint128_t,
                                      vector __uint128_t);

     vector __int128_t vec_vsubecuq (vector __int128_t, vector __int128_t,
                                     vector __int128_t);
     vector __uint128_t vec_vsubecuq (vector __uint128_t, vector __uint128_t,
                                      vector __uint128_t);

     vector __int128_t vec_vsubeuqm (vector __int128_t, vector __int128_t,
                                     vector __int128_t);
     vector __uint128_t vec_vsubeuqm (vector __uint128_t, vector __uint128_t,
                                      vector __uint128_t);

     vector __int128_t vec_vsubcuq (vector __int128_t, vector __int128_t);
     vector __uint128_t vec_vsubcuq (vector __uint128_t, vector __uint128_t);

     __int128_t vec_vsubuqm (__int128_t, __int128_t);
     __uint128_t vec_vsubuqm (__uint128_t, __uint128_t);

     vector __int128_t __builtin_bcdadd (vector __int128_t, vector__int128_t);
     int __builtin_bcdadd_lt (vector __int128_t, vector__int128_t);
     int __builtin_bcdadd_eq (vector __int128_t, vector__int128_t);
     int __builtin_bcdadd_gt (vector __int128_t, vector__int128_t);
     int __builtin_bcdadd_ov (vector __int128_t, vector__int128_t);
     vector __int128_t bcdsub (vector __int128_t, vector__int128_t);
     int __builtin_bcdsub_lt (vector __int128_t, vector__int128_t);
     int __builtin_bcdsub_eq (vector __int128_t, vector__int128_t);
     int __builtin_bcdsub_gt (vector __int128_t, vector__int128_t);
     int __builtin_bcdsub_ov (vector __int128_t, vector__int128_t);

If the cryptographic instructions are enabled (-mcrypto or -mcpu=power8), the following builtins are enabled.

     vector unsigned long long __builtin_crypto_vsbox (vector unsigned long long);

     vector unsigned long long __builtin_crypto_vcipher (vector unsigned long long,
                                                         vector unsigned long long);

     vector unsigned long long __builtin_crypto_vcipherlast
                                          (vector unsigned long long,
                                           vector unsigned long long);

     vector unsigned long long __builtin_crypto_vncipher (vector unsigned long long,
                                                          vector unsigned long long);

     vector unsigned long long __builtin_crypto_vncipherlast
                                          (vector unsigned long long,
                                           vector unsigned long long);

     vector unsigned char __builtin_crypto_vpermxor (vector unsigned char,
                                                     vector unsigned char,
                                                     vector unsigned char);

     vector unsigned short __builtin_crypto_vpermxor (vector unsigned short,
                                                      vector unsigned short,
                                                      vector unsigned short);

     vector unsigned int __builtin_crypto_vpermxor (vector unsigned int,
                                                    vector unsigned int,
                                                    vector unsigned int);

     vector unsigned long long __builtin_crypto_vpermxor (vector unsigned long long,
                                                          vector unsigned long long,
                                                          vector unsigned long long);

     vector unsigned char __builtin_crypto_vpmsumb (vector unsigned char,
                                                    vector unsigned char);

     vector unsigned short __builtin_crypto_vpmsumb (vector unsigned short,
                                                     vector unsigned short);

     vector unsigned int __builtin_crypto_vpmsumb (vector unsigned int,
                                                   vector unsigned int);

     vector unsigned long long __builtin_crypto_vpmsumb (vector unsigned long long,
                                                         vector unsigned long long);

     vector unsigned long long __builtin_crypto_vshasigmad
                                    (vector unsigned long long, int, int);

     vector unsigned int __builtin_crypto_vshasigmaw (vector unsigned int,
                                                      int, int);

The second argument to the __BUILTIN_CRYPTO_VSHASIGMAD and __BUILTIN_CRYPTO_VSHASIGMAW builtin functions must be a constant integer that is 0 or 1.  The third argument to these builtin functions must be a constant integer in the range of 0 to 15.

PowerPC Hardware Transactional Memory Built-in Functions
--------------------------------------------------------

GCC provides two interfaces for accessing the Hardware Transactional Memory (HTM) instructions available on some of the PowerPC family of processors (eg, POWER8).  The two interfaces come in a low level interface, consisting of built-in functions specific to PowerPC and a higher level interface consisting of inline functions that are common between PowerPC and S/390.

PowerPC HTM Low Level Built-in Functions
........................................

The following low level built-in functions are available with -mhtm or -mcpu=CPU where CPU is `power8' or later. They all generate the machine instruction that is part of the name.

The HTM builtins (with the exception of __builtin_tbegin) return the full 4-bit condition register value set by their associated hardware instruction.  The header file htmintrin.h defines some macros that can be used to decipher the return value.  The __builtin_tbegin builtin returns a simple true or false value depending on whether a transaction was successfully started or not.  The arguments of the builtins match exactly the type and order of the associated hardware instruction's operands, except for the __builtin_tcheck builtin, which does not take any input arguments. Refer to the ISA manual for a description of each instruction's operands.

     unsigned int __builtin_tbegin (unsigned int)
     unsigned int __builtin_tend (unsigned int)

     unsigned int __builtin_tabort (unsigned int)
     unsigned int __builtin_tabortdc (unsigned int, unsigned int, unsigned int)
     unsigned int __builtin_tabortdci (unsigned int, unsigned int, int)
     unsigned int __builtin_tabortwc (unsigned int, unsigned int, unsigned int)
     unsigned int __builtin_tabortwci (unsigned int, unsigned int, int)

     unsigned int __builtin_tcheck (void)
     unsigned int __builtin_treclaim (unsigned int)
     unsigned int __builtin_trechkpt (void)
     unsigned int __builtin_tsr (unsigned int)

In addition to the above HTM built-ins, we have added built-ins for some common extended mnemonics of the HTM instructions:

     unsigned int __builtin_tendall (void)
     unsigned int __builtin_tresume (void)
     unsigned int __builtin_tsuspend (void)

The following set of built-in functions are available to gain access to the HTM specific special purpose registers.

     unsigned long __builtin_get_texasr (void)
     unsigned long __builtin_get_texasru (void)
     unsigned long __builtin_get_tfhar (void)
     unsigned long __builtin_get_tfiar (void)

     void __builtin_set_texasr (unsigned long);
     void __builtin_set_texasru (unsigned long);
     void __builtin_set_tfhar (unsigned long);
     void __builtin_set_tfiar (unsigned long);

Example usage of these low level built-in functions may look like:

     #include <htmintrin.h>

     int num_retries = 10;

     while (1)
       {
         if (__builtin_tbegin (0))
           {
             /* Transaction State Initiated.  */
             if (is_locked (lock))
               __builtin_tabort (0);
             ... transaction code...
             __builtin_tend (0);
             break;
           }
         else
           {
             /* Transaction State Failed.  Use locks if the transaction
                failure is "persistent" or we've tried too many times.  */
             if (num_retries-- <= 0
                 || _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
               {
                 acquire_lock (lock);
                 ... non transactional fallback path...
                 release_lock (lock);
                 break;
               }
           }
       }

One final built-in function has been added that returns the value of the 2-bit Transaction State field of the Machine Status Register (MSR) as stored in CR0.

     unsigned long __builtin_ttest (void)

This built-in can be used to determine the current transaction state using the following code example:

     #include <htmintrin.h>

     unsigned char tx_state = _HTM_STATE (__builtin_ttest ());

     if (tx_state == _HTM_TRANSACTIONAL)
       {
         /* Code to use in transactional state.  */
       }
     else if (tx_state == _HTM_NONTRANSACTIONAL)
       {
         /* Code to use in non-transactional state.  */
       }
     else if (tx_state == _HTM_SUSPENDED)
       {
         /* Code to use in transaction suspended state.  */
       }

PowerPC HTM High Level Inline Functions
.......................................

The following high level HTM interface is made available by including <htmxlintrin.h> and using -mhtm or -mcpu=CPU where CPU is `power8' or later.  This interface is common between PowerPC and S/390, allowing users to write one HTM source implementation that can be compiled and executed on either system.

     long __TM_simple_begin (void)
     long __TM_begin (void* const TM_buff)
     long __TM_end (void)
     void __TM_abort (void)
     void __TM_named_abort (unsigned char const code)
     void __TM_resume (void)
     void __TM_suspend (void)

     long __TM_is_user_abort (void* const TM_buff)
     long __TM_is_named_user_abort (void* const TM_buff, unsigned char *code)
     long __TM_is_illegal (void* const TM_buff)
     long __TM_is_footprint_exceeded (void* const TM_buff)
     long __TM_nesting_depth (void* const TM_buff)
     long __TM_is_nested_too_deep(void* const TM_buff)
     long __TM_is_conflict(void* const TM_buff)
     long __TM_is_failure_persistent(void* const TM_buff)
     long __TM_failure_address(void* const TM_buff)
     long long __TM_failure_code(void* const TM_buff)

Using these common set of HTM inline functions, we can create a more portable version of the HTM example in the previous section that will work on either PowerPC or S/390:

     #include <htmxlintrin.h>

     int num_retries = 10;
     TM_buff_type TM_buff;

     while (1)
       {
         if (__TM_begin (TM_buff) == _HTM_TBEGIN_STARTED)
           {
             /* Transaction State Initiated.  */
             if (is_locked (lock))
               __TM_abort ();
             ... transaction code...
             __TM_end ();
             break;
           }
         else
           {
             /* Transaction State Failed.  Use locks if the transaction
                failure is "persistent" or we've tried too many times.  */
             if (num_retries-- <= 0
                 || __TM_is_failure_persistent (TM_buff))
               {
                 acquire_lock (lock);
                 ... non transactional fallback path...
                 release_lock (lock);
                 break;
               }
           }
       }

RX Built-in Functions
---------------------

GCC supports some of the RX instructions which cannot be expressed in the C programming language via the use of built-in functions.  The following functions are supported:

 -- Built-in Function: void __builtin_rx_brk (void)
     Generates the brk machine instruction.

 -- Built-in Function: void __builtin_rx_clrpsw (int)
     Generates the clrpsw machine instruction to clear the specified bit in the processor status word.

 -- Built-in Function: void __builtin_rx_int (int)
     Generates the int machine instruction to generate an interrupt with the specified value.

 -- Built-in Function: void __builtin_rx_machi (int, int)
     Generates the machi machine instruction to add the result of multiplying the top 16 bits of the two arguments into the accumulator.

 -- Built-in Function: void __builtin_rx_maclo (int, int)
     Generates the maclo machine instruction to add the result of multiplying the bottom 16 bits of the two arguments into the accumulator.

 -- Built-in Function: void __builtin_rx_mulhi (int, int)
     Generates the mulhi machine instruction to place the result of multiplying the top 16 bits of the two arguments into the accumulator.

 -- Built-in Function: void __builtin_rx_mullo (int, int)
     Generates the mullo machine instruction to place the result of multiplying the bottom 16 bits of the two arguments into the accumulator.

 -- Built-in Function: int __builtin_rx_mvfachi (void)
     Generates the mvfachi machine instruction to read the top 32 bits of the accumulator.

 -- Built-in Function: int __builtin_rx_mvfacmi (void)
     Generates the mvfacmi machine instruction to read the middle 32 bits of the accumulator.

 -- Built-in Function: int __builtin_rx_mvfc (int)
     Generates the mvfc machine instruction which reads the control register specified in its argument and returns its value.

 -- Built-in Function: void __builtin_rx_mvtachi (int)
     Generates the mvtachi machine instruction to set the top 32 bits of the accumulator.

 -- Built-in Function: void __builtin_rx_mvtaclo (int)
     Generates the mvtaclo machine instruction to set the bottom 32 bits of the accumulator.

 -- Built-in Function: void __builtin_rx_mvtc (int reg, int val)
     Generates the mvtc machine instruction which sets control register number reg to val.

 -- Built-in Function: void __builtin_rx_mvtipl (int)
     Generates the mvtipl machine instruction set the interrupt priority level.

 -- Built-in Function: void __builtin_rx_racw (int)
     Generates the racw machine instruction to round the accumulator according to the specified mode.

 -- Built-in Function: int __builtin_rx_revw (int)
     Generates the revw machine instruction which swaps the bytes in the argument so that bits 0--7 now occupy bits 8--15 and vice versa, and also bits 16--23 occupy bits 24--31 and vice versa.

 -- Built-in Function: void __builtin_rx_rmpa (void)
     Generates the rmpa machine instruction which initiates a repeated multiply and accumulate sequence.

 -- Built-in Function: void __builtin_rx_round (float)
     Generates the round machine instruction which returns the floating-point argument rounded according to the current rounding mode set in the floating-point status word register.

 -- Built-in Function: int __builtin_rx_sat (int)
     Generates the sat machine instruction which returns the saturated value of the argument.

 -- Built-in Function: void __builtin_rx_setpsw (int)
     Generates the setpsw machine instruction to set the specified bit in the processor status word.

 -- Built-in Function: void __builtin_rx_wait (void)
     Generates the wait machine instruction.

S/390 System z Built-in Functions
---------------------------------

 -- Built-in Function: int __builtin_tbegin (void*)
     Generates the tbegin machine instruction starting a non-constraint hardware transaction.  If the parameter is non-NULL the memory area is used to store the transaction diagnostic buffer and will be passed as first operand to tbegin.  This buffer can be defined using the struct __htm_tdb C struct defined in htmintrin.h and must reside on a double-word boundary.  The second tbegin operand is set to 0xff0c. This enables save/restore of all GPRs and disables aborts for FPR and AR manipulations inside the transaction body.  The condition code set by the tbegin instruction is returned as integer value.  The tbegin instruction by definition overwrites the content of all FPRs.  The compiler will generate code which saves and restores the FPRs.  For soft-float code it is recommended to used the *_nofloat variant.  In order to prevent a TDB from being written it is required to pass an constant zero value as parameter.  Passing the zero value through a variable is not sufficient.  Although modifications of access registers inside the transaction will not trigger an transaction abort it is not supported to actually modify them.  Access registers do not get saved when entering a transaction. They will have undefined state when reaching the abort code.

Macros for the possible return codes of tbegin are defined in the htmintrin.h header file:

_HTM_TBEGIN_STARTED
     tbegin has been executed as part of normal processing.  The transaction body is supposed to be executed.

_HTM_TBEGIN_INDETERMINATE
     The transaction was aborted due to an indeterminate condition which might be persistent.

_HTM_TBEGIN_TRANSIENT
     The transaction aborted due to a transient failure.  The transaction should be re-executed in that case.

_HTM_TBEGIN_PERSISTENT
     The transaction aborted due to a persistent failure.  Re-execution under same circumstances will not be productive.

 -- Macro: _HTM_FIRST_USER_ABORT_CODE
     The _HTM_FIRST_USER_ABORT_CODE defined in htmintrin.h specifies the first abort code which can be used for __builtin_tabort.  Values below this threshold are reserved for machine use.

 -- Data type: struct __htm_tdb
     The struct __htm_tdb defined in htmintrin.h describes the structure of the transaction diagnostic block as specified in the Principles of Operation manual chapter 5-91.

 -- Built-in Function: int __builtin_tbegin_nofloat (void*)
     Same as __builtin_tbegin but without FPR saves and restores. Using this variant in code making use of FPRs will leave the FPRs in undefined state when entering the transaction abort handler code.

 -- Built-in Function: int __builtin_tbegin_retry (void*, int)
     In addition to __builtin_tbegin a loop for transient failures is generated.  If tbegin returns a condition code of 2 the transaction will be retried as often as specified in the second argument.  The perform processor assist instruction is used to tell the CPU about the number of fails so far.

 -- Built-in Function: int __builtin_tbegin_retry_nofloat (void*, int)
     Same as __builtin_tbegin_retry but without FPR saves and restores.  Using this variant in code making use of FPRs will leave the FPRs in undefined state when entering the transaction abort handler code.

 -- Built-in Function: void __builtin_tbeginc (void)
     Generates the tbeginc machine instruction starting a constraint hardware transaction.  The second operand is set to 0xff08.

 -- Built-in Function: int __builtin_tend (void)
     Generates the tend machine instruction finishing a transaction and making the changes visible to other threads.  The condition code generated by tend is returned as integer value.

 -- Built-in Function: void __builtin_tabort (int)
     Generates the tabort machine instruction with the specified abort code.  Abort codes from 0 through 255 are reserved and will result in an error message.

 -- Built-in Function: void __builtin_tx_assist (int)
     Generates the ppa rX,rY,1 machine instruction.  Where the integer parameter is loaded into rX and a value of zero is loaded into rY.  The integer parameter specifies the number of times the transaction repeatedly aborted.

 -- Built-in Function: int __builtin_tx_nesting_depth (void)
     Generates the etnd machine instruction.  The current nesting depth is returned as integer value.  For a nesting depth of 0 the code is not executed as part of an transaction.

 -- Built-in Function: void __builtin_non_tx_store (uint64_t *, uint64_t)

     Generates the ntstg machine instruction.  The second argument is written to the first arguments location.  The store operation will not be rolled-back in case of an transaction abort.

SH Built-in Functions
---------------------

The following built-in functions are supported on the SH1, SH2, SH3 and SH4 families of processors:

 -- Built-in Function: void __builtin_set_thread_pointer (void *PTR)
     Sets the GBR register to the specified value PTR.  This is usually used by system code that manages threads and execution contexts.  The compiler normally does not generate code that modifies the contents of GBR and thus the value is preserved across function calls.  Changing the GBR value in user code must be done with caution, since the compiler might use GBR in order to access thread local variables.

 -- Built-in Function: void * __builtin_thread_pointer (void)
     Returns the value that is currently set in the GBR register. Memory loads and stores that use the thread pointer as a base address are turned into GBR based displacement loads and stores, if possible. For example:

          struct my_tcb
          {
             int a, b, c, d, e;
          };

          int get_tcb_value (void)
          {
            // Generate mov.l @(8,gbr),r0 instruction
            return ((my_tcb*)__builtin_thread_pointer ())->c;
          }

 -- Built-in Function: unsigned int __builtin_sh_get_fpscr (void)
     Returns the value that is currently set in the FPSCR register.

 -- Built-in Function: void __builtin_sh_set_fpscr (unsigned int VAL)
     Sets the FPSCR register to the specified value VAL, while preserving the current values of the FR, SZ and PR bits.

SPARC VIS Built-in Functions
----------------------------

GCC supports SIMD operations on the SPARC using both the generic vector extensions (see Vector Extensions) as well as built-in functions for the SPARC Visual Instruction Set (VIS).  When you use the -mvis switch, the VIS extension is exposed as the following built-in functions:

     typedef int v1si __attribute__ ((vector_size (4)));
     typedef int v2si __attribute__ ((vector_size (8)));
     typedef short v4hi __attribute__ ((vector_size (8)));
     typedef short v2hi __attribute__ ((vector_size (4)));
     typedef unsigned char v8qi __attribute__ ((vector_size (8)));
     typedef unsigned char v4qi __attribute__ ((vector_size (4)));

     void __builtin_vis_write_gsr (int64_t);
     int64_t __builtin_vis_read_gsr (void);

     void * __builtin_vis_alignaddr (void *, long);
     void * __builtin_vis_alignaddrl (void *, long);
     int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
     v2si __builtin_vis_faligndatav2si (v2si, v2si);
     v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
     v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);

     v4hi __builtin_vis_fexpand (v4qi);

     v4hi __builtin_vis_fmul8x16 (v4qi, v4hi);
     v4hi __builtin_vis_fmul8x16au (v4qi, v2hi);
     v4hi __builtin_vis_fmul8x16al (v4qi, v2hi);
     v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi);
     v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi);
     v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi);
     v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi);

     v4qi __builtin_vis_fpack16 (v4hi);
     v8qi __builtin_vis_fpack32 (v2si, v8qi);
     v2hi __builtin_vis_fpackfix (v2si);
     v8qi __builtin_vis_fpmerge (v4qi, v4qi);

     int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);

     long __builtin_vis_edge8 (void *, void *);
     long __builtin_vis_edge8l (void *, void *);
     long __builtin_vis_edge16 (void *, void *);
     long __builtin_vis_edge16l (void *, void *);
     long __builtin_vis_edge32 (void *, void *);
     long __builtin_vis_edge32l (void *, void *);

     long __builtin_vis_fcmple16 (v4hi, v4hi);
     long __builtin_vis_fcmple32 (v2si, v2si);
     long __builtin_vis_fcmpne16 (v4hi, v4hi);
     long __builtin_vis_fcmpne32 (v2si, v2si);
     long __builtin_vis_fcmpgt16 (v4hi, v4hi);
     long __builtin_vis_fcmpgt32 (v2si, v2si);
     long __builtin_vis_fcmpeq16 (v4hi, v4hi);
     long __builtin_vis_fcmpeq32 (v2si, v2si);

     v4hi __builtin_vis_fpadd16 (v4hi, v4hi);
     v2hi __builtin_vis_fpadd16s (v2hi, v2hi);
     v2si __builtin_vis_fpadd32 (v2si, v2si);
     v1si __builtin_vis_fpadd32s (v1si, v1si);
     v4hi __builtin_vis_fpsub16 (v4hi, v4hi);
     v2hi __builtin_vis_fpsub16s (v2hi, v2hi);
     v2si __builtin_vis_fpsub32 (v2si, v2si);
     v1si __builtin_vis_fpsub32s (v1si, v1si);

     long __builtin_vis_array8 (long, long);
     long __builtin_vis_array16 (long, long);
     long __builtin_vis_array32 (long, long);

When you use the -mvis2 switch, the VIS version 2.0 built-in functions also become available:

     long __builtin_vis_bmask (long, long);
     int64_t __builtin_vis_bshuffledi (int64_t, int64_t);
     v2si __builtin_vis_bshufflev2si (v2si, v2si);
     v4hi __builtin_vis_bshufflev2si (v4hi, v4hi);
     v8qi __builtin_vis_bshufflev2si (v8qi, v8qi);

     long __builtin_vis_edge8n (void *, void *);
     long __builtin_vis_edge8ln (void *, void *);
     long __builtin_vis_edge16n (void *, void *);
     long __builtin_vis_edge16ln (void *, void *);
     long __builtin_vis_edge32n (void *, void *);
     long __builtin_vis_edge32ln (void *, void *);

When you use the -mvis3 switch, the VIS version 3.0 built-in functions also become available:

     void __builtin_vis_cmask8 (long);
     void __builtin_vis_cmask16 (long);
     void __builtin_vis_cmask32 (long);

     v4hi __builtin_vis_fchksm16 (v4hi, v4hi);

     v4hi __builtin_vis_fsll16 (v4hi, v4hi);
     v4hi __builtin_vis_fslas16 (v4hi, v4hi);
     v4hi __builtin_vis_fsrl16 (v4hi, v4hi);
     v4hi __builtin_vis_fsra16 (v4hi, v4hi);
     v2si __builtin_vis_fsll16 (v2si, v2si);
     v2si __builtin_vis_fslas16 (v2si, v2si);
     v2si __builtin_vis_fsrl16 (v2si, v2si);
     v2si __builtin_vis_fsra16 (v2si, v2si);

     long __builtin_vis_pdistn (v8qi, v8qi);

     v4hi __builtin_vis_fmean16 (v4hi, v4hi);

     int64_t __builtin_vis_fpadd64 (int64_t, int64_t);
     int64_t __builtin_vis_fpsub64 (int64_t, int64_t);

     v4hi __builtin_vis_fpadds16 (v4hi, v4hi);
     v2hi __builtin_vis_fpadds16s (v2hi, v2hi);
     v4hi __builtin_vis_fpsubs16 (v4hi, v4hi);
     v2hi __builtin_vis_fpsubs16s (v2hi, v2hi);
     v2si __builtin_vis_fpadds32 (v2si, v2si);
     v1si __builtin_vis_fpadds32s (v1si, v1si);
     v2si __builtin_vis_fpsubs32 (v2si, v2si);
     v1si __builtin_vis_fpsubs32s (v1si, v1si);

     long __builtin_vis_fucmple8 (v8qi, v8qi);
     long __builtin_vis_fucmpne8 (v8qi, v8qi);
     long __builtin_vis_fucmpgt8 (v8qi, v8qi);
     long __builtin_vis_fucmpeq8 (v8qi, v8qi);

     float __builtin_vis_fhadds (float, float);
     double __builtin_vis_fhaddd (double, double);
     float __builtin_vis_fhsubs (float, float);
     double __builtin_vis_fhsubd (double, double);
     float __builtin_vis_fnhadds (float, float);
     double __builtin_vis_fnhaddd (double, double);

     int64_t __builtin_vis_umulxhi (int64_t, int64_t);
     int64_t __builtin_vis_xmulx (int64_t, int64_t);
     int64_t __builtin_vis_xmulxhi (int64_t, int64_t);

SPU Built-in Functions
----------------------

GCC provides extensions for the SPU processor as described in the Sony/Toshiba/IBM SPU Language Extensions Specification, which can be found at http://cell.scei.co.jp/ or http://www.ibm.com/developerworks/power/cell/.  GCC's implementation differs in several ways.

  * The optional extension of specifying vector constants in parentheses is not supported.

  * A vector initializer requires no cast if the vector constant is of the same type as the variable it is initializing.

  * If signed or unsigned is omitted, the signedness of the vector type is the default signedness of the base type.  The default varies depending on the operating system, so a portable program should always specify the signedness.

  * By default, the keyword __vector is added. The macro vector is defined in <spu_intrinsics.h> and can be undefined.

  * GCC allows using a typedef name as the type specifier for a vector type.

  * For C, overloaded functions are implemented with macros so the following does not work:

            spu_add ((vector signed int){1, 2, 3, 4}, foo);

     Since spu_add is a macro, the vector constant in the example is treated as four separate arguments.  Wrap the entire argument in parentheses for this to work.

  * The extended version of __builtin_expect is not supported.

Note: Only the interface described in the aforementioned specification is supported. Internally, GCC uses built-in functions to implement the required functionality, but these are not supported and are subject to change without notice.

TI C6X Built-in Functions
-------------------------

GCC provides intrinsics to access certain instructions of the TI C6X processors.  These intrinsics, listed below, are available after inclusion of the c6x_intrinsics.h header file.  They map directly to C6X instructions.

     int _sadd (int, int)
     int _ssub (int, int)
     int _sadd2 (int, int)
     int _ssub2 (int, int)
     long long _mpy2 (int, int)
     long long _smpy2 (int, int)
     int _add4 (int, int)
     int _sub4 (int, int)
     int _saddu4 (int, int)

     int _smpy (int, int)
     int _smpyh (int, int)
     int _smpyhl (int, int)
     int _smpylh (int, int)

     int _sshl (int, int)
     int _subc (int, int)

     int _avg2 (int, int)
     int _avgu4 (int, int)

     int _clrr (int, int)
     int _extr (int, int)
     int _extru (int, int)
     int _abs (int)
     int _abs2 (int)

TILE-Gx Built-in Functions
--------------------------

GCC provides intrinsics to access every instruction of the TILE-Gx processor.  The intrinsics are of the form:

     unsigned long long __insn_OP (...)

Where OP is the name of the instruction.  Refer to the ISA manual for the complete list of instructions.

GCC also provides intrinsics to directly access the network registers. The intrinsics are:

     unsigned long long __tile_idn0_receive (void)
     unsigned long long __tile_idn1_receive (void)
     unsigned long long __tile_udn0_receive (void)
     unsigned long long __tile_udn1_receive (void)
     unsigned long long __tile_udn2_receive (void)
     unsigned long long __tile_udn3_receive (void)
     void __tile_idn_send (unsigned long long)
     void __tile_udn_send (unsigned long long)

The intrinsic void __tile_network_barrier (void) is used to guarantee that no network operations before it are reordered with those after it.

TILEPro Built-in Functions
--------------------------

GCC provides intrinsics to access every instruction of the TILEPro processor.  The intrinsics are of the form:

     unsigned __insn_OP (...)

where OP is the name of the instruction.  Refer to the ISA manual for the complete list of instructions.

GCC also provides intrinsics to directly access the network registers. The intrinsics are:

     unsigned __tile_idn0_receive (void)
     unsigned __tile_idn1_receive (void)
     unsigned __tile_sn_receive (void)
     unsigned __tile_udn0_receive (void)
     unsigned __tile_udn1_receive (void)
     unsigned __tile_udn2_receive (void)
     unsigned __tile_udn3_receive (void)
     void __tile_idn_send (unsigned)
     void __tile_sn_send (unsigned)
     void __tile_udn_send (unsigned)

The intrinsic void __tile_network_barrier (void) is used to guarantee that no network operations before it are reordered with those after it.

x86 Built-in Functions
----------------------

These built-in functions are available for the x86-32 and x86-64 family of computers, depending on the command-line switches used.

If you specify command-line switches such as -msse, the compiler could use the extended instruction sets even if the built-ins are not used explicitly in the program.  For this reason, applications that perform run-time CPU detection must compile separate files for each supported architecture, using the appropriate flags.  In particular, the file containing the CPU detection code should be compiled without these options.

The following machine modes are available for use with MMX built-in functions (see Vector Extensions): V2SI for a vector of two 32-bit integers, V4HI for a vector of four 16-bit integers, and V8QI for a vector of eight 8-bit integers.  Some of the built-in functions operate on MMX registers as a whole 64-bit entity, these use V1DI as their mode.

If 3DNow! extensions are enabled, V2SF is used as a mode for a vector of two 32-bit floating-point values.

If SSE extensions are enabled, V4SF is used for a vector of four 32-bit floating-point values.  Some instructions use a vector of four 32-bit integers, these use V4SI.  Finally, some instructions operate on an entire vector register, interpreting it as a 128-bit integer, these use mode TI.

In 64-bit mode, the x86-64 family of processors uses additional built-in functions for efficient use of TF (__float128) 128-bit floating point and TC 128-bit complex floating-point values.

The following floating-point built-in functions are available in 64-bit mode.  All of them implement the function that is part of the name.

     __float128 __builtin_fabsq (__float128)
     __float128 __builtin_copysignq (__float128, __float128)

The following built-in function is always available.

void __builtin_ia32_pause (void)
     Generates the pause machine instruction with a compiler memory barrier.

The following floating-point built-in functions are made available in the 64-bit mode.

__float128 __builtin_infq (void)
     Similar to __builtin_inf, except the return type is __float128.

__float128 __builtin_huge_valq (void)
     Similar to __builtin_huge_val, except the return type is __float128.

The following built-in functions are always available and can be used to check the target platform type.

 -- Built-in Function: void __builtin_cpu_init (void)
     This function runs the CPU detection code to check the type of CPU and the features supported.  This built-in function needs to be invoked along with the built-in functions to check CPU type and features, __builtin_cpu_is and __builtin_cpu_supports, only when used in a function that is executed before any constructors are called.  The CPU detection code is automatically executed in a very high priority constructor.

     For example, this function has to be used in ifunc resolvers that check for CPU type using the built-in functions __builtin_cpu_is and __builtin_cpu_supports, or in constructors on targets that don't support constructor priority.

          static void (*resolve_memcpy (void)) (void)
          {
            // ifunc resolvers fire before constructors, explicitly call the init
            // function.
            __builtin_cpu_init ();
            if (__builtin_cpu_supports ("ssse3"))
              return ssse3_memcpy; // super fast memcpy with ssse3 instructions.
            else
              return default_memcpy;
          }

          void *memcpy (void *, const void *, size_t)
               __attribute__ ((ifunc ("resolve_memcpy")));

 -- Built-in Function: int __builtin_cpu_is (const char *CPUNAME)
     This function returns a positive integer if the run-time CPU is of type CPUNAME and returns 0 otherwise. The following CPU names can be detected:

     intel
          Intel CPU.

     atom
          Intel Atom CPU.

     core2
          Intel Core 2 CPU.

     corei7
          Intel Core i7 CPU.

     nehalem
          Intel Core i7 Nehalem CPU.

     westmere
          Intel Core i7 Westmere CPU.

     sandybridge
          Intel Core i7 Sandy Bridge CPU.

     amd
          AMD CPU.

     amdfam10h
          AMD Family 10h CPU.

     barcelona
          AMD Family 10h Barcelona CPU.

     shanghai
          AMD Family 10h Shanghai CPU.

     istanbul
          AMD Family 10h Istanbul CPU.

     btver1
          AMD Family 14h CPU.

     amdfam15h
          AMD Family 15h CPU.

     bdver1
          AMD Family 15h Bulldozer version 1.

     bdver2
          AMD Family 15h Bulldozer version 2.

     bdver3
          AMD Family 15h Bulldozer version 3.

     bdver4
          AMD Family 15h Bulldozer version 4.

     btver2
          AMD Family 16h CPU.

     Here is an example:

          if (__builtin_cpu_is ("corei7"))
            {
               do_corei7 (); // Core i7 specific implementation.
            }
          else
            {
               do_generic (); // Generic implementation.
            }

 -- Built-in Function: int __builtin_cpu_supports (const char *FEATURE)
     This function returns a positive integer if the run-time CPU supports FEATURE and returns 0 otherwise. The following features can be detected:

     cmov
          CMOV instruction.

     mmx
          MMX instructions.

     popcnt
          POPCNT instruction.

     sse
          SSE instructions.

     sse2
          SSE2 instructions.

     sse3
          SSE3 instructions.

     ssse3
          SSSE3 instructions.

     sse4.1
          SSE4.1 instructions.

     sse4.2
          SSE4.2 instructions.

     avx
          AVX instructions.

     avx2
          AVX2 instructions.

     avx512f
          AVX512F instructions.

     Here is an example:

          if (__builtin_cpu_supports ("popcnt"))
            {
               asm("popcnt %1,%0" : "=r"(count) : "rm"(n) : "cc");
            }
          else
            {
               count = generic_countbits (n); //generic implementation.
            }

The following built-in functions are made available by -mmmx. All of them generate the machine instruction that is part of the name.

     v8qi __builtin_ia32_paddb (v8qi, v8qi)
     v4hi __builtin_ia32_paddw (v4hi, v4hi)
     v2si __builtin_ia32_paddd (v2si, v2si)
     v8qi __builtin_ia32_psubb (v8qi, v8qi)
     v4hi __builtin_ia32_psubw (v4hi, v4hi)
     v2si __builtin_ia32_psubd (v2si, v2si)
     v8qi __builtin_ia32_paddsb (v8qi, v8qi)
     v4hi __builtin_ia32_paddsw (v4hi, v4hi)
     v8qi __builtin_ia32_psubsb (v8qi, v8qi)
     v4hi __builtin_ia32_psubsw (v4hi, v4hi)
     v8qi __builtin_ia32_paddusb (v8qi, v8qi)
     v4hi __builtin_ia32_paddusw (v4hi, v4hi)
     v8qi __builtin_ia32_psubusb (v8qi, v8qi)
     v4hi __builtin_ia32_psubusw (v4hi, v4hi)
     v4hi __builtin_ia32_pmullw (v4hi, v4hi)
     v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
     di __builtin_ia32_pand (di, di)
     di __builtin_ia32_pandn (di,di)
     di __builtin_ia32_por (di, di)
     di __builtin_ia32_pxor (di, di)
     v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
     v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
     v2si __builtin_ia32_pcmpeqd (v2si, v2si)
     v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
     v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
     v2si __builtin_ia32_pcmpgtd (v2si, v2si)
     v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
     v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
     v2si __builtin_ia32_punpckhdq (v2si, v2si)
     v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
     v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
     v2si __builtin_ia32_punpckldq (v2si, v2si)
     v8qi __builtin_ia32_packsswb (v4hi, v4hi)
     v4hi __builtin_ia32_packssdw (v2si, v2si)
     v8qi __builtin_ia32_packuswb (v4hi, v4hi)

     v4hi __builtin_ia32_psllw (v4hi, v4hi)
     v2si __builtin_ia32_pslld (v2si, v2si)
     v1di __builtin_ia32_psllq (v1di, v1di)
     v4hi __builtin_ia32_psrlw (v4hi, v4hi)
     v2si __builtin_ia32_psrld (v2si, v2si)
     v1di __builtin_ia32_psrlq (v1di, v1di)
     v4hi __builtin_ia32_psraw (v4hi, v4hi)
     v2si __builtin_ia32_psrad (v2si, v2si)
     v4hi __builtin_ia32_psllwi (v4hi, int)
     v2si __builtin_ia32_pslldi (v2si, int)
     v1di __builtin_ia32_psllqi (v1di, int)
     v4hi __builtin_ia32_psrlwi (v4hi, int)
     v2si __builtin_ia32_psrldi (v2si, int)
     v1di __builtin_ia32_psrlqi (v1di, int)
     v4hi __builtin_ia32_psrawi (v4hi, int)
     v2si __builtin_ia32_psradi (v2si, int)

The following built-in functions are made available either with -msse, or with a combination of -m3dnow and -march=athlon.  All of them generate the machine instruction that is part of the name.

     v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
     v8qi __builtin_ia32_pavgb (v8qi, v8qi)
     v4hi __builtin_ia32_pavgw (v4hi, v4hi)
     v1di __builtin_ia32_psadbw (v8qi, v8qi)
     v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
     v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
     v8qi __builtin_ia32_pminub (v8qi, v8qi)
     v4hi __builtin_ia32_pminsw (v4hi, v4hi)
     int __builtin_ia32_pmovmskb (v8qi)
     void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
     void __builtin_ia32_movntq (di *, di)
     void __builtin_ia32_sfence (void)

The following built-in functions are available when -msse is used. All of them generate the machine instruction that is part of the name.

     int __builtin_ia32_comieq (v4sf, v4sf)
     int __builtin_ia32_comineq (v4sf, v4sf)
     int __builtin_ia32_comilt (v4sf, v4sf)
     int __builtin_ia32_comile (v4sf, v4sf)
     int __builtin_ia32_comigt (v4sf, v4sf)
     int __builtin_ia32_comige (v4sf, v4sf)
     int __builtin_ia32_ucomieq (v4sf, v4sf)
     int __builtin_ia32_ucomineq (v4sf, v4sf)
     int __builtin_ia32_ucomilt (v4sf, v4sf)
     int __builtin_ia32_ucomile (v4sf, v4sf)
     int __builtin_ia32_ucomigt (v4sf, v4sf)
     int __builtin_ia32_ucomige (v4sf, v4sf)
     v4sf __builtin_ia32_addps (v4sf, v4sf)
     v4sf __builtin_ia32_subps (v4sf, v4sf)
     v4sf __builtin_ia32_mulps (v4sf, v4sf)
     v4sf __builtin_ia32_divps (v4sf, v4sf)
     v4sf __builtin_ia32_addss (v4sf, v4sf)
     v4sf __builtin_ia32_subss (v4sf, v4sf)
     v4sf __builtin_ia32_mulss (v4sf, v4sf)
     v4sf __builtin_ia32_divss (v4sf, v4sf)
     v4sf __builtin_ia32_cmpeqps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpltps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpleps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpgtps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpgeps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpunordps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpneqps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpnltps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpnleps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpngtps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpngeps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpordps (v4sf, v4sf)
     v4sf __builtin_ia32_cmpeqss (v4sf, v4sf)
     v4sf __builtin_ia32_cmpltss (v4sf, v4sf)
     v4sf __builtin_ia32_cmpless (v4sf, v4sf)
     v4sf __builtin_ia32_cmpunordss (v4sf, v4sf)
     v4sf __builtin_ia32_cmpneqss (v4sf, v4sf)
     v4sf __builtin_ia32_cmpnltss (v4sf, v4sf)
     v4sf __builtin_ia32_cmpnless (v4sf, v4sf)
     v4sf __builtin_ia32_cmpordss (v4sf, v4sf)
     v4sf __builtin_ia32_maxps (v4sf, v4sf)
     v4sf __builtin_ia32_maxss (v4sf, v4sf)
     v4sf __builtin_ia32_minps (v4sf, v4sf)
     v4sf __builtin_ia32_minss (v4sf, v4sf)
     v4sf __builtin_ia32_andps (v4sf, v4sf)
     v4sf __builtin_ia32_andnps (v4sf, v4sf)
     v4sf __builtin_ia32_orps (v4sf, v4sf)
     v4sf __builtin_ia32_xorps (v4sf, v4sf)
     v4sf __builtin_ia32_movss (v4sf, v4sf)
     v4sf __builtin_ia32_movhlps (v4sf, v4sf)
     v4sf __builtin_ia32_movlhps (v4sf, v4sf)
     v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
     v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
     v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
     v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
     v2si __builtin_ia32_cvtps2pi (v4sf)
     int __builtin_ia32_cvtss2si (v4sf)
     v2si __builtin_ia32_cvttps2pi (v4sf)
     int __builtin_ia32_cvttss2si (v4sf)
     v4sf __builtin_ia32_rcpps (v4sf)
     v4sf __builtin_ia32_rsqrtps (v4sf)
     v4sf __builtin_ia32_sqrtps (v4sf)
     v4sf __builtin_ia32_rcpss (v4sf)
     v4sf __builtin_ia32_rsqrtss (v4sf)
     v4sf __builtin_ia32_sqrtss (v4sf)
     v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
     void __builtin_ia32_movntps (float *, v4sf)
     int __builtin_ia32_movmskps (v4sf)

The following built-in functions are available when -msse is used.

v4sf __builtin_ia32_loadups (float *)
     Generates the movups machine instruction as a load from memory.

void __builtin_ia32_storeups (float *, v4sf)
     Generates the movups machine instruction as a store to memory.

v4sf __builtin_ia32_loadss (float *)
     Generates the movss machine instruction as a load from memory.

v4sf __builtin_ia32_loadhps (v4sf, const v2sf *)
     Generates the movhps machine instruction as a load from memory.

v4sf __builtin_ia32_loadlps (v4sf, const v2sf *)
     Generates the movlps machine instruction as a load from memory

void __builtin_ia32_storehps (v2sf *, v4sf)
     Generates the movhps machine instruction as a store to memory.

void __builtin_ia32_storelps (v2sf *, v4sf)
     Generates the movlps machine instruction as a store to memory.

The following built-in functions are available when -msse2 is used. All of them generate the machine instruction that is part of the name.

     int __builtin_ia32_comisdeq (v2df, v2df)
     int __builtin_ia32_comisdlt (v2df, v2df)
     int __builtin_ia32_comisdle (v2df, v2df)
     int __builtin_ia32_comisdgt (v2df, v2df)
     int __builtin_ia32_comisdge (v2df, v2df)
     int __builtin_ia32_comisdneq (v2df, v2df)
     int __builtin_ia32_ucomisdeq (v2df, v2df)
     int __builtin_ia32_ucomisdlt (v2df, v2df)
     int __builtin_ia32_ucomisdle (v2df, v2df)
     int __builtin_ia32_ucomisdgt (v2df, v2df)
     int __builtin_ia32_ucomisdge (v2df, v2df)
     int __builtin_ia32_ucomisdneq (v2df, v2df)
     v2df __builtin_ia32_cmpeqpd (v2df, v2df)
     v2df __builtin_ia32_cmpltpd (v2df, v2df)
     v2df __builtin_ia32_cmplepd (v2df, v2df)
     v2df __builtin_ia32_cmpgtpd (v2df, v2df)
     v2df __builtin_ia32_cmpgepd (v2df, v2df)
     v2df __builtin_ia32_cmpunordpd (v2df, v2df)
     v2df __builtin_ia32_cmpneqpd (v2df, v2df)
     v2df __builtin_ia32_cmpnltpd (v2df, v2df)
     v2df __builtin_ia32_cmpnlepd (v2df, v2df)
     v2df __builtin_ia32_cmpngtpd (v2df, v2df)
     v2df __builtin_ia32_cmpngepd (v2df, v2df)
     v2df __builtin_ia32_cmpordpd (v2df, v2df)
     v2df __builtin_ia32_cmpeqsd (v2df, v2df)
     v2df __builtin_ia32_cmpltsd (v2df, v2df)
     v2df __builtin_ia32_cmplesd (v2df, v2df)
     v2df __builtin_ia32_cmpunordsd (v2df, v2df)
     v2df __builtin_ia32_cmpneqsd (v2df, v2df)
     v2df __builtin_ia32_cmpnltsd (v2df, v2df)
     v2df __builtin_ia32_cmpnlesd (v2df, v2df)
     v2df __builtin_ia32_cmpordsd (v2df, v2df)
     v2di __builtin_ia32_paddq (v2di, v2di)
     v2di __builtin_ia32_psubq (v2di, v2di)
     v2df __builtin_ia32_addpd (v2df, v2df)
     v2df __builtin_ia32_subpd (v2df, v2df)
     v2df __builtin_ia32_mulpd (v2df, v2df)
     v2df __builtin_ia32_divpd (v2df, v2df)
     v2df __builtin_ia32_addsd (v2df, v2df)
     v2df __builtin_ia32_subsd (v2df, v2df)
     v2df __builtin_ia32_mulsd (v2df, v2df)
     v2df __builtin_ia32_divsd (v2df, v2df)
     v2df __builtin_ia32_minpd (v2df, v2df)
     v2df __builtin_ia32_maxpd (v2df, v2df)
     v2df __builtin_ia32_minsd (v2df, v2df)
     v2df __builtin_ia32_maxsd (v2df, v2df)
     v2df __builtin_ia32_andpd (v2df, v2df)
     v2df __builtin_ia32_andnpd (v2df, v2df)
     v2df __builtin_ia32_orpd (v2df, v2df)
     v2df __builtin_ia32_xorpd (v2df, v2df)
     v2df __builtin_ia32_movsd (v2df, v2df)
     v2df __builtin_ia32_unpckhpd (v2df, v2df)
     v2df __builtin_ia32_unpcklpd (v2df, v2df)
     v16qi __builtin_ia32_paddb128 (v16qi, v16qi)
     v8hi __builtin_ia32_paddw128 (v8hi, v8hi)
     v4si __builtin_ia32_paddd128 (v4si, v4si)
     v2di __builtin_ia32_paddq128 (v2di, v2di)
     v16qi __builtin_ia32_psubb128 (v16qi, v16qi)
     v8hi __builtin_ia32_psubw128 (v8hi, v8hi)
     v4si __builtin_ia32_psubd128 (v4si, v4si)
     v2di __builtin_ia32_psubq128 (v2di, v2di)
     v8hi __builtin_ia32_pmullw128 (v8hi, v8hi)
     v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi)
     v2di __builtin_ia32_pand128 (v2di, v2di)
     v2di __builtin_ia32_pandn128 (v2di, v2di)
     v2di __builtin_ia32_por128 (v2di, v2di)
     v2di __builtin_ia32_pxor128 (v2di, v2di)
     v16qi __builtin_ia32_pavgb128 (v16qi, v16qi)
     v8hi __builtin_ia32_pavgw128 (v8hi, v8hi)
     v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi)
     v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi)
     v4si __builtin_ia32_pcmpeqd128 (v4si, v4si)
     v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi)
     v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi)
     v4si __builtin_ia32_pcmpgtd128 (v4si, v4si)
     v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi)
     v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi)
     v16qi __builtin_ia32_pminub128 (v16qi, v16qi)
     v8hi __builtin_ia32_pminsw128 (v8hi, v8hi)
     v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi)
     v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi)
     v4si __builtin_ia32_punpckhdq128 (v4si, v4si)
     v2di __builtin_ia32_punpckhqdq128 (v2di, v2di)
     v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi)
     v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi)
     v4si __builtin_ia32_punpckldq128 (v4si, v4si)
     v2di __builtin_ia32_punpcklqdq128 (v2di, v2di)
     v16qi __builtin_ia32_packsswb128 (v8hi, v8hi)
     v8hi __builtin_ia32_packssdw128 (v4si, v4si)
     v16qi __builtin_ia32_packuswb128 (v8hi, v8hi)
     v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi)
     void __builtin_ia32_maskmovdqu (v16qi, v16qi)
     v2df __builtin_ia32_loadupd (double *)
     void __builtin_ia32_storeupd (double *, v2df)
     v2df __builtin_ia32_loadhpd (v2df, double const *)
     v2df __builtin_ia32_loadlpd (v2df, double const *)
     int __builtin_ia32_movmskpd (v2df)
     int __builtin_ia32_pmovmskb128 (v16qi)
     void __builtin_ia32_movnti (int *, int)
     void __builtin_ia32_movnti64 (long long int *, long long int)
     void __builtin_ia32_movntpd (double *, v2df)
     void __builtin_ia32_movntdq (v2df *, v2df)
     v4si __builtin_ia32_pshufd (v4si, int)
     v8hi __builtin_ia32_pshuflw (v8hi, int)
     v8hi __builtin_ia32_pshufhw (v8hi, int)
     v2di __builtin_ia32_psadbw128 (v16qi, v16qi)
     v2df __builtin_ia32_sqrtpd (v2df)
     v2df __builtin_ia32_sqrtsd (v2df)
     v2df __builtin_ia32_shufpd (v2df, v2df, int)
     v2df __builtin_ia32_cvtdq2pd (v4si)
     v4sf __builtin_ia32_cvtdq2ps (v4si)
     v4si __builtin_ia32_cvtpd2dq (v2df)
     v2si __builtin_ia32_cvtpd2pi (v2df)
     v4sf __builtin_ia32_cvtpd2ps (v2df)
     v4si __builtin_ia32_cvttpd2dq (v2df)
     v2si __builtin_ia32_cvttpd2pi (v2df)
     v2df __builtin_ia32_cvtpi2pd (v2si)
     int __builtin_ia32_cvtsd2si (v2df)
     int __builtin_ia32_cvttsd2si (v2df)
     long long __builtin_ia32_cvtsd2si64 (v2df)
     long long __builtin_ia32_cvttsd2si64 (v2df)
     v4si __builtin_ia32_cvtps2dq (v4sf)
     v2df __builtin_ia32_cvtps2pd (v4sf)
     v4si __builtin_ia32_cvttps2dq (v4sf)
     v2df __builtin_ia32_cvtsi2sd (v2df, int)
     v2df __builtin_ia32_cvtsi642sd (v2df, long long)
     v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df)
     v2df __builtin_ia32_cvtss2sd (v2df, v4sf)
     void __builtin_ia32_clflush (const void *)
     void __builtin_ia32_lfence (void)
     void __builtin_ia32_mfence (void)
     v16qi __builtin_ia32_loaddqu (const char *)
     void __builtin_ia32_storedqu (char *, v16qi)
     v1di __builtin_ia32_pmuludq (v2si, v2si)
     v2di __builtin_ia32_pmuludq128 (v4si, v4si)
     v8hi __builtin_ia32_psllw128 (v8hi, v8hi)
     v4si __builtin_ia32_pslld128 (v4si, v4si)
     v2di __builtin_ia32_psllq128 (v2di, v2di)
     v8hi __builtin_ia32_psrlw128 (v8hi, v8hi)
     v4si __builtin_ia32_psrld128 (v4si, v4si)
     v2di __builtin_ia32_psrlq128 (v2di, v2di)
     v8hi __builtin_ia32_psraw128 (v8hi, v8hi)
     v4si __builtin_ia32_psrad128 (v4si, v4si)
     v2di __builtin_ia32_pslldqi128 (v2di, int)
     v8hi __builtin_ia32_psllwi128 (v8hi, int)
     v4si __builtin_ia32_pslldi128 (v4si, int)
     v2di __builtin_ia32_psllqi128 (v2di, int)
     v2di __builtin_ia32_psrldqi128 (v2di, int)
     v8hi __builtin_ia32_psrlwi128 (v8hi, int)
     v4si __builtin_ia32_psrldi128 (v4si, int)
     v2di __builtin_ia32_psrlqi128 (v2di, int)
     v8hi __builtin_ia32_psrawi128 (v8hi, int)
     v4si __builtin_ia32_psradi128 (v4si, int)
     v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi)
     v2di __builtin_ia32_movq128 (v2di)

The following built-in functions are available when -msse3 is used. All of them generate the machine instruction that is part of the name.

     v2df __builtin_ia32_addsubpd (v2df, v2df)
     v4sf __builtin_ia32_addsubps (v4sf, v4sf)
     v2df __builtin_ia32_haddpd (v2df, v2df)
     v4sf __builtin_ia32_haddps (v4sf, v4sf)
     v2df __builtin_ia32_hsubpd (v2df, v2df)
     v4sf __builtin_ia32_hsubps (v4sf, v4sf)
     v16qi __builtin_ia32_lddqu (char const *)
     void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
     v4sf __builtin_ia32_movshdup (v4sf)
     v4sf __builtin_ia32_movsldup (v4sf)
     void __builtin_ia32_mwait (unsigned int, unsigned int)

The following built-in functions are available when -mssse3 is used. All of them generate the machine instruction that is part of the name.

     v2si __builtin_ia32_phaddd (v2si, v2si)
     v4hi __builtin_ia32_phaddw (v4hi, v4hi)
     v4hi __builtin_ia32_phaddsw (v4hi, v4hi)
     v2si __builtin_ia32_phsubd (v2si, v2si)
     v4hi __builtin_ia32_phsubw (v4hi, v4hi)
     v4hi __builtin_ia32_phsubsw (v4hi, v4hi)
     v4hi __builtin_ia32_pmaddubsw (v8qi, v8qi)
     v4hi __builtin_ia32_pmulhrsw (v4hi, v4hi)
     v8qi __builtin_ia32_pshufb (v8qi, v8qi)
     v8qi __builtin_ia32_psignb (v8qi, v8qi)
     v2si __builtin_ia32_psignd (v2si, v2si)
     v4hi __builtin_ia32_psignw (v4hi, v4hi)
     v1di __builtin_ia32_palignr (v1di, v1di, int)
     v8qi __builtin_ia32_pabsb (v8qi)
     v2si __builtin_ia32_pabsd (v2si)
     v4hi __builtin_ia32_pabsw (v4hi)

The following built-in functions are available when -mssse3 is used. All of them generate the machine instruction that is part of the name.

     v4si __builtin_ia32_phaddd128 (v4si, v4si)
     v8hi __builtin_ia32_phaddw128 (v8hi, v8hi)
     v8hi __builtin_ia32_phaddsw128 (v8hi, v8hi)
     v4si __builtin_ia32_phsubd128 (v4si, v4si)
     v8hi __builtin_ia32_phsubw128 (v8hi, v8hi)
     v8hi __builtin_ia32_phsubsw128 (v8hi, v8hi)
     v8hi __builtin_ia32_pmaddubsw128 (v16qi, v16qi)
     v8hi __builtin_ia32_pmulhrsw128 (v8hi, v8hi)
     v16qi __builtin_ia32_pshufb128 (v16qi, v16qi)
     v16qi __builtin_ia32_psignb128 (v16qi, v16qi)
     v4si __builtin_ia32_psignd128 (v4si, v4si)
     v8hi __builtin_ia32_psignw128 (v8hi, v8hi)
     v2di __builtin_ia32_palignr128 (v2di, v2di, int)
     v16qi __builtin_ia32_pabsb128 (v16qi)
     v4si __builtin_ia32_pabsd128 (v4si)
     v8hi __builtin_ia32_pabsw128 (v8hi)

The following built-in functions are available when -msse4.1 is used.  All of them generate the machine instruction that is part of the name.

     v2df __builtin_ia32_blendpd (v2df, v2df, const int)
     v4sf __builtin_ia32_blendps (v4sf, v4sf, const int)
     v2df __builtin_ia32_blendvpd (v2df, v2df, v2df)
     v4sf __builtin_ia32_blendvps (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_dppd (v2df, v2df, const int)
     v4sf __builtin_ia32_dpps (v4sf, v4sf, const int)
     v4sf __builtin_ia32_insertps128 (v4sf, v4sf, const int)
     v2di __builtin_ia32_movntdqa (v2di *);
     v16qi __builtin_ia32_mpsadbw128 (v16qi, v16qi, const int)
     v8hi __builtin_ia32_packusdw128 (v4si, v4si)
     v16qi __builtin_ia32_pblendvb128 (v16qi, v16qi, v16qi)
     v8hi __builtin_ia32_pblendw128 (v8hi, v8hi, const int)
     v2di __builtin_ia32_pcmpeqq (v2di, v2di)
     v8hi __builtin_ia32_phminposuw128 (v8hi)
     v16qi __builtin_ia32_pmaxsb128 (v16qi, v16qi)
     v4si __builtin_ia32_pmaxsd128 (v4si, v4si)
     v4si __builtin_ia32_pmaxud128 (v4si, v4si)
     v8hi __builtin_ia32_pmaxuw128 (v8hi, v8hi)
     v16qi __builtin_ia32_pminsb128 (v16qi, v16qi)
     v4si __builtin_ia32_pminsd128 (v4si, v4si)
     v4si __builtin_ia32_pminud128 (v4si, v4si)
     v8hi __builtin_ia32_pminuw128 (v8hi, v8hi)
     v4si __builtin_ia32_pmovsxbd128 (v16qi)
     v2di __builtin_ia32_pmovsxbq128 (v16qi)
     v8hi __builtin_ia32_pmovsxbw128 (v16qi)
     v2di __builtin_ia32_pmovsxdq128 (v4si)
     v4si __builtin_ia32_pmovsxwd128 (v8hi)
     v2di __builtin_ia32_pmovsxwq128 (v8hi)
     v4si __builtin_ia32_pmovzxbd128 (v16qi)
     v2di __builtin_ia32_pmovzxbq128 (v16qi)
     v8hi __builtin_ia32_pmovzxbw128 (v16qi)
     v2di __builtin_ia32_pmovzxdq128 (v4si)
     v4si __builtin_ia32_pmovzxwd128 (v8hi)
     v2di __builtin_ia32_pmovzxwq128 (v8hi)
     v2di __builtin_ia32_pmuldq128 (v4si, v4si)
     v4si __builtin_ia32_pmulld128 (v4si, v4si)
     int __builtin_ia32_ptestc128 (v2di, v2di)
     int __builtin_ia32_ptestnzc128 (v2di, v2di)
     int __builtin_ia32_ptestz128 (v2di, v2di)
     v2df __builtin_ia32_roundpd (v2df, const int)
     v4sf __builtin_ia32_roundps (v4sf, const int)
     v2df __builtin_ia32_roundsd (v2df, v2df, const int)
     v4sf __builtin_ia32_roundss (v4sf, v4sf, const int)

The following built-in functions are available when -msse4.1 is used.

v4sf __builtin_ia32_vec_set_v4sf (v4sf, float, const int)
     Generates the insertps machine instruction.

int __builtin_ia32_vec_ext_v16qi (v16qi, const int)
     Generates the pextrb machine instruction.

v16qi __builtin_ia32_vec_set_v16qi (v16qi, int, const int)
     Generates the pinsrb machine instruction.

v4si __builtin_ia32_vec_set_v4si (v4si, int, const int)
     Generates the pinsrd machine instruction.

v2di __builtin_ia32_vec_set_v2di (v2di, long long, const int)
     Generates the pinsrq machine instruction in 64bit mode.

The following built-in functions are changed to generate new SSE4.1 instructions when -msse4.1 is used.

float __builtin_ia32_vec_ext_v4sf (v4sf, const int)
     Generates the extractps machine instruction.

int __builtin_ia32_vec_ext_v4si (v4si, const int)
     Generates the pextrd machine instruction.

long long __builtin_ia32_vec_ext_v2di (v2di, const int)
     Generates the pextrq machine instruction in 64bit mode.

The following built-in functions are available when -msse4.2 is used.  All of them generate the machine instruction that is part of the name.

     v16qi __builtin_ia32_pcmpestrm128 (v16qi, int, v16qi, int, const int)
     int __builtin_ia32_pcmpestri128 (v16qi, int, v16qi, int, const int)
     int __builtin_ia32_pcmpestria128 (v16qi, int, v16qi, int, const int)
     int __builtin_ia32_pcmpestric128 (v16qi, int, v16qi, int, const int)
     int __builtin_ia32_pcmpestrio128 (v16qi, int, v16qi, int, const int)
     int __builtin_ia32_pcmpestris128 (v16qi, int, v16qi, int, const int)
     int __builtin_ia32_pcmpestriz128 (v16qi, int, v16qi, int, const int)
     v16qi __builtin_ia32_pcmpistrm128 (v16qi, v16qi, const int)
     int __builtin_ia32_pcmpistri128 (v16qi, v16qi, const int)
     int __builtin_ia32_pcmpistria128 (v16qi, v16qi, const int)
     int __builtin_ia32_pcmpistric128 (v16qi, v16qi, const int)
     int __builtin_ia32_pcmpistrio128 (v16qi, v16qi, const int)
     int __builtin_ia32_pcmpistris128 (v16qi, v16qi, const int)
     int __builtin_ia32_pcmpistriz128 (v16qi, v16qi, const int)
     v2di __builtin_ia32_pcmpgtq (v2di, v2di)

The following built-in functions are available when -msse4.2 is used.

unsigned int __builtin_ia32_crc32qi (unsigned int, unsigned char)
     Generates the crc32b machine instruction.

unsigned int __builtin_ia32_crc32hi (unsigned int, unsigned short)
     Generates the crc32w machine instruction.

unsigned int __builtin_ia32_crc32si (unsigned int, unsigned int)
     Generates the crc32l machine instruction.

unsigned long long __builtin_ia32_crc32di (unsigned long long, unsigned long long)
     Generates the crc32q machine instruction.

The following built-in functions are changed to generate new SSE4.2 instructions when -msse4.2 is used.

int __builtin_popcount (unsigned int)
     Generates the popcntl machine instruction.

int __builtin_popcountl (unsigned long)
     Generates the popcntl or popcntq machine instruction, depending on the size of unsigned long.

int __builtin_popcountll (unsigned long long)
     Generates the popcntq machine instruction.

The following built-in functions are available when -mavx is used. All of them generate the machine instruction that is part of the name.

     v4df __builtin_ia32_addpd256 (v4df,v4df)
     v8sf __builtin_ia32_addps256 (v8sf,v8sf)
     v4df __builtin_ia32_addsubpd256 (v4df,v4df)
     v8sf __builtin_ia32_addsubps256 (v8sf,v8sf)
     v4df __builtin_ia32_andnpd256 (v4df,v4df)
     v8sf __builtin_ia32_andnps256 (v8sf,v8sf)
     v4df __builtin_ia32_andpd256 (v4df,v4df)
     v8sf __builtin_ia32_andps256 (v8sf,v8sf)
     v4df __builtin_ia32_blendpd256 (v4df,v4df,int)
     v8sf __builtin_ia32_blendps256 (v8sf,v8sf,int)
     v4df __builtin_ia32_blendvpd256 (v4df,v4df,v4df)
     v8sf __builtin_ia32_blendvps256 (v8sf,v8sf,v8sf)
     v2df __builtin_ia32_cmppd (v2df,v2df,int)
     v4df __builtin_ia32_cmppd256 (v4df,v4df,int)
     v4sf __builtin_ia32_cmpps (v4sf,v4sf,int)
     v8sf __builtin_ia32_cmpps256 (v8sf,v8sf,int)
     v2df __builtin_ia32_cmpsd (v2df,v2df,int)
     v4sf __builtin_ia32_cmpss (v4sf,v4sf,int)
     v4df __builtin_ia32_cvtdq2pd256 (v4si)
     v8sf __builtin_ia32_cvtdq2ps256 (v8si)
     v4si __builtin_ia32_cvtpd2dq256 (v4df)
     v4sf __builtin_ia32_cvtpd2ps256 (v4df)
     v8si __builtin_ia32_cvtps2dq256 (v8sf)
     v4df __builtin_ia32_cvtps2pd256 (v4sf)
     v4si __builtin_ia32_cvttpd2dq256 (v4df)
     v8si __builtin_ia32_cvttps2dq256 (v8sf)
     v4df __builtin_ia32_divpd256 (v4df,v4df)
     v8sf __builtin_ia32_divps256 (v8sf,v8sf)
     v8sf __builtin_ia32_dpps256 (v8sf,v8sf,int)
     v4df __builtin_ia32_haddpd256 (v4df,v4df)
     v8sf __builtin_ia32_haddps256 (v8sf,v8sf)
     v4df __builtin_ia32_hsubpd256 (v4df,v4df)
     v8sf __builtin_ia32_hsubps256 (v8sf,v8sf)
     v32qi __builtin_ia32_lddqu256 (pcchar)
     v32qi __builtin_ia32_loaddqu256 (pcchar)
     v4df __builtin_ia32_loadupd256 (pcdouble)
     v8sf __builtin_ia32_loadups256 (pcfloat)
     v2df __builtin_ia32_maskloadpd (pcv2df,v2df)
     v4df __builtin_ia32_maskloadpd256 (pcv4df,v4df)
     v4sf __builtin_ia32_maskloadps (pcv4sf,v4sf)
     v8sf __builtin_ia32_maskloadps256 (pcv8sf,v8sf)
     void __builtin_ia32_maskstorepd (pv2df,v2df,v2df)
     void __builtin_ia32_maskstorepd256 (pv4df,v4df,v4df)
     void __builtin_ia32_maskstoreps (pv4sf,v4sf,v4sf)
     void __builtin_ia32_maskstoreps256 (pv8sf,v8sf,v8sf)
     v4df __builtin_ia32_maxpd256 (v4df,v4df)
     v8sf __builtin_ia32_maxps256 (v8sf,v8sf)
     v4df __builtin_ia32_minpd256 (v4df,v4df)
     v8sf __builtin_ia32_minps256 (v8sf,v8sf)
     v4df __builtin_ia32_movddup256 (v4df)
     int __builtin_ia32_movmskpd256 (v4df)
     int __builtin_ia32_movmskps256 (v8sf)
     v8sf __builtin_ia32_movshdup256 (v8sf)
     v8sf __builtin_ia32_movsldup256 (v8sf)
     v4df __builtin_ia32_mulpd256 (v4df,v4df)
     v8sf __builtin_ia32_mulps256 (v8sf,v8sf)
     v4df __builtin_ia32_orpd256 (v4df,v4df)
     v8sf __builtin_ia32_orps256 (v8sf,v8sf)
     v2df __builtin_ia32_pd_pd256 (v4df)
     v4df __builtin_ia32_pd256_pd (v2df)
     v4sf __builtin_ia32_ps_ps256 (v8sf)
     v8sf __builtin_ia32_ps256_ps (v4sf)
     int __builtin_ia32_ptestc256 (v4di,v4di,ptest)
     int __builtin_ia32_ptestnzc256 (v4di,v4di,ptest)
     int __builtin_ia32_ptestz256 (v4di,v4di,ptest)
     v8sf __builtin_ia32_rcpps256 (v8sf)
     v4df __builtin_ia32_roundpd256 (v4df,int)
     v8sf __builtin_ia32_roundps256 (v8sf,int)
     v8sf __builtin_ia32_rsqrtps_nr256 (v8sf)
     v8sf __builtin_ia32_rsqrtps256 (v8sf)
     v4df __builtin_ia32_shufpd256 (v4df,v4df,int)
     v8sf __builtin_ia32_shufps256 (v8sf,v8sf,int)
     v4si __builtin_ia32_si_si256 (v8si)
     v8si __builtin_ia32_si256_si (v4si)
     v4df __builtin_ia32_sqrtpd256 (v4df)
     v8sf __builtin_ia32_sqrtps_nr256 (v8sf)
     v8sf __builtin_ia32_sqrtps256 (v8sf)
     void __builtin_ia32_storedqu256 (pchar,v32qi)
     void __builtin_ia32_storeupd256 (pdouble,v4df)
     void __builtin_ia32_storeups256 (pfloat,v8sf)
     v4df __builtin_ia32_subpd256 (v4df,v4df)
     v8sf __builtin_ia32_subps256 (v8sf,v8sf)
     v4df __builtin_ia32_unpckhpd256 (v4df,v4df)
     v8sf __builtin_ia32_unpckhps256 (v8sf,v8sf)
     v4df __builtin_ia32_unpcklpd256 (v4df,v4df)
     v8sf __builtin_ia32_unpcklps256 (v8sf,v8sf)
     v4df __builtin_ia32_vbroadcastf128_pd256 (pcv2df)
     v8sf __builtin_ia32_vbroadcastf128_ps256 (pcv4sf)
     v4df __builtin_ia32_vbroadcastsd256 (pcdouble)
     v4sf __builtin_ia32_vbroadcastss (pcfloat)
     v8sf __builtin_ia32_vbroadcastss256 (pcfloat)
     v2df __builtin_ia32_vextractf128_pd256 (v4df,int)
     v4sf __builtin_ia32_vextractf128_ps256 (v8sf,int)
     v4si __builtin_ia32_vextractf128_si256 (v8si,int)
     v4df __builtin_ia32_vinsertf128_pd256 (v4df,v2df,int)
     v8sf __builtin_ia32_vinsertf128_ps256 (v8sf,v4sf,int)
     v8si __builtin_ia32_vinsertf128_si256 (v8si,v4si,int)
     v4df __builtin_ia32_vperm2f128_pd256 (v4df,v4df,int)
     v8sf __builtin_ia32_vperm2f128_ps256 (v8sf,v8sf,int)
     v8si __builtin_ia32_vperm2f128_si256 (v8si,v8si,int)
     v2df __builtin_ia32_vpermil2pd (v2df,v2df,v2di,int)
     v4df __builtin_ia32_vpermil2pd256 (v4df,v4df,v4di,int)
     v4sf __builtin_ia32_vpermil2ps (v4sf,v4sf,v4si,int)
     v8sf __builtin_ia32_vpermil2ps256 (v8sf,v8sf,v8si,int)
     v2df __builtin_ia32_vpermilpd (v2df,int)
     v4df __builtin_ia32_vpermilpd256 (v4df,int)
     v4sf __builtin_ia32_vpermilps (v4sf,int)
     v8sf __builtin_ia32_vpermilps256 (v8sf,int)
     v2df __builtin_ia32_vpermilvarpd (v2df,v2di)
     v4df __builtin_ia32_vpermilvarpd256 (v4df,v4di)
     v4sf __builtin_ia32_vpermilvarps (v4sf,v4si)
     v8sf __builtin_ia32_vpermilvarps256 (v8sf,v8si)
     int __builtin_ia32_vtestcpd (v2df,v2df,ptest)
     int __builtin_ia32_vtestcpd256 (v4df,v4df,ptest)
     int __builtin_ia32_vtestcps (v4sf,v4sf,ptest)
     int __builtin_ia32_vtestcps256 (v8sf,v8sf,ptest)
     int __builtin_ia32_vtestnzcpd (v2df,v2df,ptest)
     int __builtin_ia32_vtestnzcpd256 (v4df,v4df,ptest)
     int __builtin_ia32_vtestnzcps (v4sf,v4sf,ptest)
     int __builtin_ia32_vtestnzcps256 (v8sf,v8sf,ptest)
     int __builtin_ia32_vtestzpd (v2df,v2df,ptest)
     int __builtin_ia32_vtestzpd256 (v4df,v4df,ptest)
     int __builtin_ia32_vtestzps (v4sf,v4sf,ptest)
     int __builtin_ia32_vtestzps256 (v8sf,v8sf,ptest)
     void __builtin_ia32_vzeroall (void)
     void __builtin_ia32_vzeroupper (void)
     v4df __builtin_ia32_xorpd256 (v4df,v4df)
     v8sf __builtin_ia32_xorps256 (v8sf,v8sf)

The following built-in functions are available when -mavx2 is used. All of them generate the machine instruction that is part of the name.

     v32qi __builtin_ia32_mpsadbw256 (v32qi,v32qi,int)
     v32qi __builtin_ia32_pabsb256 (v32qi)
     v16hi __builtin_ia32_pabsw256 (v16hi)
     v8si __builtin_ia32_pabsd256 (v8si)
     v16hi __builtin_ia32_packssdw256 (v8si,v8si)
     v32qi __builtin_ia32_packsswb256 (v16hi,v16hi)
     v16hi __builtin_ia32_packusdw256 (v8si,v8si)
     v32qi __builtin_ia32_packuswb256 (v16hi,v16hi)
     v32qi __builtin_ia32_paddb256 (v32qi,v32qi)
     v16hi __builtin_ia32_paddw256 (v16hi,v16hi)
     v8si __builtin_ia32_paddd256 (v8si,v8si)
     v4di __builtin_ia32_paddq256 (v4di,v4di)
     v32qi __builtin_ia32_paddsb256 (v32qi,v32qi)
     v16hi __builtin_ia32_paddsw256 (v16hi,v16hi)
     v32qi __builtin_ia32_paddusb256 (v32qi,v32qi)
     v16hi __builtin_ia32_paddusw256 (v16hi,v16hi)
     v4di __builtin_ia32_palignr256 (v4di,v4di,int)
     v4di __builtin_ia32_andsi256 (v4di,v4di)
     v4di __builtin_ia32_andnotsi256 (v4di,v4di)
     v32qi __builtin_ia32_pavgb256 (v32qi,v32qi)
     v16hi __builtin_ia32_pavgw256 (v16hi,v16hi)
     v32qi __builtin_ia32_pblendvb256 (v32qi,v32qi,v32qi)
     v16hi __builtin_ia32_pblendw256 (v16hi,v16hi,int)
     v32qi __builtin_ia32_pcmpeqb256 (v32qi,v32qi)
     v16hi __builtin_ia32_pcmpeqw256 (v16hi,v16hi)
     v8si __builtin_ia32_pcmpeqd256 (c8si,v8si)
     v4di __builtin_ia32_pcmpeqq256 (v4di,v4di)
     v32qi __builtin_ia32_pcmpgtb256 (v32qi,v32qi)
     v16hi __builtin_ia32_pcmpgtw256 (16hi,v16hi)
     v8si __builtin_ia32_pcmpgtd256 (v8si,v8si)
     v4di __builtin_ia32_pcmpgtq256 (v4di,v4di)
     v16hi __builtin_ia32_phaddw256 (v16hi,v16hi)
     v8si __builtin_ia32_phaddd256 (v8si,v8si)
     v16hi __builtin_ia32_phaddsw256 (v16hi,v16hi)
     v16hi __builtin_ia32_phsubw256 (v16hi,v16hi)
     v8si __builtin_ia32_phsubd256 (v8si,v8si)
     v16hi __builtin_ia32_phsubsw256 (v16hi,v16hi)
     v32qi __builtin_ia32_pmaddubsw256 (v32qi,v32qi)
     v16hi __builtin_ia32_pmaddwd256 (v16hi,v16hi)
     v32qi __builtin_ia32_pmaxsb256 (v32qi,v32qi)
     v16hi __builtin_ia32_pmaxsw256 (v16hi,v16hi)
     v8si __builtin_ia32_pmaxsd256 (v8si,v8si)
     v32qi __builtin_ia32_pmaxub256 (v32qi,v32qi)
     v16hi __builtin_ia32_pmaxuw256 (v16hi,v16hi)
     v8si __builtin_ia32_pmaxud256 (v8si,v8si)
     v32qi __builtin_ia32_pminsb256 (v32qi,v32qi)
     v16hi __builtin_ia32_pminsw256 (v16hi,v16hi)
     v8si __builtin_ia32_pminsd256 (v8si,v8si)
     v32qi __builtin_ia32_pminub256 (v32qi,v32qi)
     v16hi __builtin_ia32_pminuw256 (v16hi,v16hi)
     v8si __builtin_ia32_pminud256 (v8si,v8si)
     int __builtin_ia32_pmovmskb256 (v32qi)
     v16hi __builtin_ia32_pmovsxbw256 (v16qi)
     v8si __builtin_ia32_pmovsxbd256 (v16qi)
     v4di __builtin_ia32_pmovsxbq256 (v16qi)
     v8si __builtin_ia32_pmovsxwd256 (v8hi)
     v4di __builtin_ia32_pmovsxwq256 (v8hi)
     v4di __builtin_ia32_pmovsxdq256 (v4si)
     v16hi __builtin_ia32_pmovzxbw256 (v16qi)
     v8si __builtin_ia32_pmovzxbd256 (v16qi)
     v4di __builtin_ia32_pmovzxbq256 (v16qi)
     v8si __builtin_ia32_pmovzxwd256 (v8hi)
     v4di __builtin_ia32_pmovzxwq256 (v8hi)
     v4di __builtin_ia32_pmovzxdq256 (v4si)
     v4di __builtin_ia32_pmuldq256 (v8si,v8si)
     v16hi __builtin_ia32_pmulhrsw256 (v16hi, v16hi)
     v16hi __builtin_ia32_pmulhuw256 (v16hi,v16hi)
     v16hi __builtin_ia32_pmulhw256 (v16hi,v16hi)
     v16hi __builtin_ia32_pmullw256 (v16hi,v16hi)
     v8si __builtin_ia32_pmulld256 (v8si,v8si)
     v4di __builtin_ia32_pmuludq256 (v8si,v8si)
     v4di __builtin_ia32_por256 (v4di,v4di)
     v16hi __builtin_ia32_psadbw256 (v32qi,v32qi)
     v32qi __builtin_ia32_pshufb256 (v32qi,v32qi)
     v8si __builtin_ia32_pshufd256 (v8si,int)
     v16hi __builtin_ia32_pshufhw256 (v16hi,int)
     v16hi __builtin_ia32_pshuflw256 (v16hi,int)
     v32qi __builtin_ia32_psignb256 (v32qi,v32qi)
     v16hi __builtin_ia32_psignw256 (v16hi,v16hi)
     v8si __builtin_ia32_psignd256 (v8si,v8si)
     v4di __builtin_ia32_pslldqi256 (v4di,int)
     v16hi __builtin_ia32_psllwi256 (16hi,int)
     v16hi __builtin_ia32_psllw256(v16hi,v8hi)
     v8si __builtin_ia32_pslldi256 (v8si,int)
     v8si __builtin_ia32_pslld256(v8si,v4si)
     v4di __builtin_ia32_psllqi256 (v4di,int)
     v4di __builtin_ia32_psllq256(v4di,v2di)
     v16hi __builtin_ia32_psrawi256 (v16hi,int)
     v16hi __builtin_ia32_psraw256 (v16hi,v8hi)
     v8si __builtin_ia32_psradi256 (v8si,int)
     v8si __builtin_ia32_psrad256 (v8si,v4si)
     v4di __builtin_ia32_psrldqi256 (v4di, int)
     v16hi __builtin_ia32_psrlwi256 (v16hi,int)
     v16hi __builtin_ia32_psrlw256 (v16hi,v8hi)
     v8si __builtin_ia32_psrldi256 (v8si,int)
     v8si __builtin_ia32_psrld256 (v8si,v4si)
     v4di __builtin_ia32_psrlqi256 (v4di,int)
     v4di __builtin_ia32_psrlq256(v4di,v2di)
     v32qi __builtin_ia32_psubb256 (v32qi,v32qi)
     v32hi __builtin_ia32_psubw256 (v16hi,v16hi)
     v8si __builtin_ia32_psubd256 (v8si,v8si)
     v4di __builtin_ia32_psubq256 (v4di,v4di)
     v32qi __builtin_ia32_psubsb256 (v32qi,v32qi)
     v16hi __builtin_ia32_psubsw256 (v16hi,v16hi)
     v32qi __builtin_ia32_psubusb256 (v32qi,v32qi)
     v16hi __builtin_ia32_psubusw256 (v16hi,v16hi)
     v32qi __builtin_ia32_punpckhbw256 (v32qi,v32qi)
     v16hi __builtin_ia32_punpckhwd256 (v16hi,v16hi)
     v8si __builtin_ia32_punpckhdq256 (v8si,v8si)
     v4di __builtin_ia32_punpckhqdq256 (v4di,v4di)
     v32qi __builtin_ia32_punpcklbw256 (v32qi,v32qi)
     v16hi __builtin_ia32_punpcklwd256 (v16hi,v16hi)
     v8si __builtin_ia32_punpckldq256 (v8si,v8si)
     v4di __builtin_ia32_punpcklqdq256 (v4di,v4di)
     v4di __builtin_ia32_pxor256 (v4di,v4di)
     v4di __builtin_ia32_movntdqa256 (pv4di)
     v4sf __builtin_ia32_vbroadcastss_ps (v4sf)
     v8sf __builtin_ia32_vbroadcastss_ps256 (v4sf)
     v4df __builtin_ia32_vbroadcastsd_pd256 (v2df)
     v4di __builtin_ia32_vbroadcastsi256 (v2di)
     v4si __builtin_ia32_pblendd128 (v4si,v4si)
     v8si __builtin_ia32_pblendd256 (v8si,v8si)
     v32qi __builtin_ia32_pbroadcastb256 (v16qi)
     v16hi __builtin_ia32_pbroadcastw256 (v8hi)
     v8si __builtin_ia32_pbroadcastd256 (v4si)
     v4di __builtin_ia32_pbroadcastq256 (v2di)
     v16qi __builtin_ia32_pbroadcastb128 (v16qi)
     v8hi __builtin_ia32_pbroadcastw128 (v8hi)
     v4si __builtin_ia32_pbroadcastd128 (v4si)
     v2di __builtin_ia32_pbroadcastq128 (v2di)
     v8si __builtin_ia32_permvarsi256 (v8si,v8si)
     v4df __builtin_ia32_permdf256 (v4df,int)
     v8sf __builtin_ia32_permvarsf256 (v8sf,v8sf)
     v4di __builtin_ia32_permdi256 (v4di,int)
     v4di __builtin_ia32_permti256 (v4di,v4di,int)
     v4di __builtin_ia32_extract128i256 (v4di,int)
     v4di __builtin_ia32_insert128i256 (v4di,v2di,int)
     v8si __builtin_ia32_maskloadd256 (pcv8si,v8si)
     v4di __builtin_ia32_maskloadq256 (pcv4di,v4di)
     v4si __builtin_ia32_maskloadd (pcv4si,v4si)
     v2di __builtin_ia32_maskloadq (pcv2di,v2di)
     void __builtin_ia32_maskstored256 (pv8si,v8si,v8si)
     void __builtin_ia32_maskstoreq256 (pv4di,v4di,v4di)
     void __builtin_ia32_maskstored (pv4si,v4si,v4si)
     void __builtin_ia32_maskstoreq (pv2di,v2di,v2di)
     v8si __builtin_ia32_psllv8si (v8si,v8si)
     v4si __builtin_ia32_psllv4si (v4si,v4si)
     v4di __builtin_ia32_psllv4di (v4di,v4di)
     v2di __builtin_ia32_psllv2di (v2di,v2di)
     v8si __builtin_ia32_psrav8si (v8si,v8si)
     v4si __builtin_ia32_psrav4si (v4si,v4si)
     v8si __builtin_ia32_psrlv8si (v8si,v8si)
     v4si __builtin_ia32_psrlv4si (v4si,v4si)
     v4di __builtin_ia32_psrlv4di (v4di,v4di)
     v2di __builtin_ia32_psrlv2di (v2di,v2di)
     v2df __builtin_ia32_gathersiv2df (v2df, pcdouble,v4si,v2df,int)
     v4df __builtin_ia32_gathersiv4df (v4df, pcdouble,v4si,v4df,int)
     v2df __builtin_ia32_gatherdiv2df (v2df, pcdouble,v2di,v2df,int)
     v4df __builtin_ia32_gatherdiv4df (v4df, pcdouble,v4di,v4df,int)
     v4sf __builtin_ia32_gathersiv4sf (v4sf, pcfloat,v4si,v4sf,int)
     v8sf __builtin_ia32_gathersiv8sf (v8sf, pcfloat,v8si,v8sf,int)
     v4sf __builtin_ia32_gatherdiv4sf (v4sf, pcfloat,v2di,v4sf,int)
     v4sf __builtin_ia32_gatherdiv4sf256 (v4sf, pcfloat,v4di,v4sf,int)
     v2di __builtin_ia32_gathersiv2di (v2di, pcint64,v4si,v2di,int)
     v4di __builtin_ia32_gathersiv4di (v4di, pcint64,v4si,v4di,int)
     v2di __builtin_ia32_gatherdiv2di (v2di, pcint64,v2di,v2di,int)
     v4di __builtin_ia32_gatherdiv4di (v4di, pcint64,v4di,v4di,int)
     v4si __builtin_ia32_gathersiv4si (v4si, pcint,v4si,v4si,int)
     v8si __builtin_ia32_gathersiv8si (v8si, pcint,v8si,v8si,int)
     v4si __builtin_ia32_gatherdiv4si (v4si, pcint,v2di,v4si,int)
     v4si __builtin_ia32_gatherdiv4si256 (v4si, pcint,v4di,v4si,int)

The following built-in functions are available when -maes is used.  All of them generate the machine instruction that is part of the name.

     v2di __builtin_ia32_aesenc128 (v2di, v2di)
     v2di __builtin_ia32_aesenclast128 (v2di, v2di)
     v2di __builtin_ia32_aesdec128 (v2di, v2di)
     v2di __builtin_ia32_aesdeclast128 (v2di, v2di)
     v2di __builtin_ia32_aeskeygenassist128 (v2di, const int)
     v2di __builtin_ia32_aesimc128 (v2di)

The following built-in function is available when -mpclmul is used.

v2di __builtin_ia32_pclmulqdq128 (v2di, v2di, const int)
     Generates the pclmulqdq machine instruction.

The following built-in function is available when -mfsgsbase is used.  All of them generate the machine instruction that is part of the name.

     unsigned int __builtin_ia32_rdfsbase32 (void)
     unsigned long long __builtin_ia32_rdfsbase64 (void)
     unsigned int __builtin_ia32_rdgsbase32 (void)
     unsigned long long __builtin_ia32_rdgsbase64 (void)
     void _writefsbase_u32 (unsigned int)
     void _writefsbase_u64 (unsigned long long)
     void _writegsbase_u32 (unsigned int)
     void _writegsbase_u64 (unsigned long long)

The following built-in function is available when -mrdrnd is used.  All of them generate the machine instruction that is part of the name.

     unsigned int __builtin_ia32_rdrand16_step (unsigned short *)
     unsigned int __builtin_ia32_rdrand32_step (unsigned int *)
     unsigned int __builtin_ia32_rdrand64_step (unsigned long long *)

The following built-in functions are available when -msse4a is used. All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_movntsd (double *, v2df)
     void __builtin_ia32_movntss (float *, v4sf)
     v2di __builtin_ia32_extrq  (v2di, v16qi)
     v2di __builtin_ia32_extrqi (v2di, const unsigned int, const unsigned int)
     v2di __builtin_ia32_insertq (v2di, v2di)
     v2di __builtin_ia32_insertqi (v2di, v2di, const unsigned int, const unsigned int)

The following built-in functions are available when -mxop is used.

     v2df __builtin_ia32_vfrczpd (v2df)
     v4sf __builtin_ia32_vfrczps (v4sf)
     v2df __builtin_ia32_vfrczsd (v2df)
     v4sf __builtin_ia32_vfrczss (v4sf)
     v4df __builtin_ia32_vfrczpd256 (v4df)
     v8sf __builtin_ia32_vfrczps256 (v8sf)
     v2di __builtin_ia32_vpcmov (v2di, v2di, v2di)
     v2di __builtin_ia32_vpcmov_v2di (v2di, v2di, v2di)
     v4si __builtin_ia32_vpcmov_v4si (v4si, v4si, v4si)
     v8hi __builtin_ia32_vpcmov_v8hi (v8hi, v8hi, v8hi)
     v16qi __builtin_ia32_vpcmov_v16qi (v16qi, v16qi, v16qi)
     v2df __builtin_ia32_vpcmov_v2df (v2df, v2df, v2df)
     v4sf __builtin_ia32_vpcmov_v4sf (v4sf, v4sf, v4sf)
     v4di __builtin_ia32_vpcmov_v4di256 (v4di, v4di, v4di)
     v8si __builtin_ia32_vpcmov_v8si256 (v8si, v8si, v8si)
     v16hi __builtin_ia32_vpcmov_v16hi256 (v16hi, v16hi, v16hi)
     v32qi __builtin_ia32_vpcmov_v32qi256 (v32qi, v32qi, v32qi)
     v4df __builtin_ia32_vpcmov_v4df256 (v4df, v4df, v4df)
     v8sf __builtin_ia32_vpcmov_v8sf256 (v8sf, v8sf, v8sf)
     v16qi __builtin_ia32_vpcomeqb (v16qi, v16qi)
     v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
     v4si __builtin_ia32_vpcomeqd (v4si, v4si)
     v2di __builtin_ia32_vpcomeqq (v2di, v2di)
     v16qi __builtin_ia32_vpcomequb (v16qi, v16qi)
     v4si __builtin_ia32_vpcomequd (v4si, v4si)
     v2di __builtin_ia32_vpcomequq (v2di, v2di)
     v8hi __builtin_ia32_vpcomequw (v8hi, v8hi)
     v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
     v16qi __builtin_ia32_vpcomfalseb (v16qi, v16qi)
     v4si __builtin_ia32_vpcomfalsed (v4si, v4si)
     v2di __builtin_ia32_vpcomfalseq (v2di, v2di)
     v16qi __builtin_ia32_vpcomfalseub (v16qi, v16qi)
     v4si __builtin_ia32_vpcomfalseud (v4si, v4si)
     v2di __builtin_ia32_vpcomfalseuq (v2di, v2di)
     v8hi __builtin_ia32_vpcomfalseuw (v8hi, v8hi)
     v8hi __builtin_ia32_vpcomfalsew (v8hi, v8hi)
     v16qi __builtin_ia32_vpcomgeb (v16qi, v16qi)
     v4si __builtin_ia32_vpcomged (v4si, v4si)
     v2di __builtin_ia32_vpcomgeq (v2di, v2di)
     v16qi __builtin_ia32_vpcomgeub (v16qi, v16qi)
     v4si __builtin_ia32_vpcomgeud (v4si, v4si)
     v2di __builtin_ia32_vpcomgeuq (v2di, v2di)
     v8hi __builtin_ia32_vpcomgeuw (v8hi, v8hi)
     v8hi __builtin_ia32_vpcomgew (v8hi, v8hi)
     v16qi __builtin_ia32_vpcomgtb (v16qi, v16qi)
     v4si __builtin_ia32_vpcomgtd (v4si, v4si)
     v2di __builtin_ia32_vpcomgtq (v2di, v2di)
     v16qi __builtin_ia32_vpcomgtub (v16qi, v16qi)
     v4si __builtin_ia32_vpcomgtud (v4si, v4si)
     v2di __builtin_ia32_vpcomgtuq (v2di, v2di)
     v8hi __builtin_ia32_vpcomgtuw (v8hi, v8hi)
     v8hi __builtin_ia32_vpcomgtw (v8hi, v8hi)
     v16qi __builtin_ia32_vpcomleb (v16qi, v16qi)
     v4si __builtin_ia32_vpcomled (v4si, v4si)
     v2di __builtin_ia32_vpcomleq (v2di, v2di)
     v16qi __builtin_ia32_vpcomleub (v16qi, v16qi)
     v4si __builtin_ia32_vpcomleud (v4si, v4si)
     v2di __builtin_ia32_vpcomleuq (v2di, v2di)
     v8hi __builtin_ia32_vpcomleuw (v8hi, v8hi)
     v8hi __builtin_ia32_vpcomlew (v8hi, v8hi)
     v16qi __builtin_ia32_vpcomltb (v16qi, v16qi)
     v4si __builtin_ia32_vpcomltd (v4si, v4si)
     v2di __builtin_ia32_vpcomltq (v2di, v2di)
     v16qi __builtin_ia32_vpcomltub (v16qi, v16qi)
     v4si __builtin_ia32_vpcomltud (v4si, v4si)
     v2di __builtin_ia32_vpcomltuq (v2di, v2di)
     v8hi __builtin_ia32_vpcomltuw (v8hi, v8hi)
     v8hi __builtin_ia32_vpcomltw (v8hi, v8hi)
     v16qi __builtin_ia32_vpcomneb (v16qi, v16qi)
     v4si __builtin_ia32_vpcomned (v4si, v4si)
     v2di __builtin_ia32_vpcomneq (v2di, v2di)
     v16qi __builtin_ia32_vpcomneub (v16qi, v16qi)
     v4si __builtin_ia32_vpcomneud (v4si, v4si)
     v2di __builtin_ia32_vpcomneuq (v2di, v2di)
     v8hi __builtin_ia32_vpcomneuw (v8hi, v8hi)
     v8hi __builtin_ia32_vpcomnew (v8hi, v8hi)
     v16qi __builtin_ia32_vpcomtrueb (v16qi, v16qi)
     v4si __builtin_ia32_vpcomtrued (v4si, v4si)
     v2di __builtin_ia32_vpcomtrueq (v2di, v2di)
     v16qi __builtin_ia32_vpcomtrueub (v16qi, v16qi)
     v4si __builtin_ia32_vpcomtrueud (v4si, v4si)
     v2di __builtin_ia32_vpcomtrueuq (v2di, v2di)
     v8hi __builtin_ia32_vpcomtrueuw (v8hi, v8hi)
     v8hi __builtin_ia32_vpcomtruew (v8hi, v8hi)
     v4si __builtin_ia32_vphaddbd (v16qi)
     v2di __builtin_ia32_vphaddbq (v16qi)
     v8hi __builtin_ia32_vphaddbw (v16qi)
     v2di __builtin_ia32_vphadddq (v4si)
     v4si __builtin_ia32_vphaddubd (v16qi)
     v2di __builtin_ia32_vphaddubq (v16qi)
     v8hi __builtin_ia32_vphaddubw (v16qi)
     v2di __builtin_ia32_vphaddudq (v4si)
     v4si __builtin_ia32_vphadduwd (v8hi)
     v2di __builtin_ia32_vphadduwq (v8hi)
     v4si __builtin_ia32_vphaddwd (v8hi)
     v2di __builtin_ia32_vphaddwq (v8hi)
     v8hi __builtin_ia32_vphsubbw (v16qi)
     v2di __builtin_ia32_vphsubdq (v4si)
     v4si __builtin_ia32_vphsubwd (v8hi)
     v4si __builtin_ia32_vpmacsdd (v4si, v4si, v4si)
     v2di __builtin_ia32_vpmacsdqh (v4si, v4si, v2di)
     v2di __builtin_ia32_vpmacsdql (v4si, v4si, v2di)
     v4si __builtin_ia32_vpmacssdd (v4si, v4si, v4si)
     v2di __builtin_ia32_vpmacssdqh (v4si, v4si, v2di)
     v2di __builtin_ia32_vpmacssdql (v4si, v4si, v2di)
     v4si __builtin_ia32_vpmacsswd (v8hi, v8hi, v4si)
     v8hi __builtin_ia32_vpmacssww (v8hi, v8hi, v8hi)
     v4si __builtin_ia32_vpmacswd (v8hi, v8hi, v4si)
     v8hi __builtin_ia32_vpmacsww (v8hi, v8hi, v8hi)
     v4si __builtin_ia32_vpmadcsswd (v8hi, v8hi, v4si)
     v4si __builtin_ia32_vpmadcswd (v8hi, v8hi, v4si)
     v16qi __builtin_ia32_vpperm (v16qi, v16qi, v16qi)
     v16qi __builtin_ia32_vprotb (v16qi, v16qi)
     v4si __builtin_ia32_vprotd (v4si, v4si)
     v2di __builtin_ia32_vprotq (v2di, v2di)
     v8hi __builtin_ia32_vprotw (v8hi, v8hi)
     v16qi __builtin_ia32_vpshab (v16qi, v16qi)
     v4si __builtin_ia32_vpshad (v4si, v4si)
     v2di __builtin_ia32_vpshaq (v2di, v2di)
     v8hi __builtin_ia32_vpshaw (v8hi, v8hi)
     v16qi __builtin_ia32_vpshlb (v16qi, v16qi)
     v4si __builtin_ia32_vpshld (v4si, v4si)
     v2di __builtin_ia32_vpshlq (v2di, v2di)
     v8hi __builtin_ia32_vpshlw (v8hi, v8hi)

The following built-in functions are available when -mfma4 is used. All of them generate the machine instruction that is part of the name.

     v2df __builtin_ia32_vfmaddpd (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfmaddps (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_vfmaddsd (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfmaddss (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_vfmsubpd (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfmsubps (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_vfmsubsd (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfmsubss (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_vfnmaddpd (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfnmaddps (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_vfnmaddsd (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfnmaddss (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_vfnmsubpd (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfnmsubps (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_vfnmsubsd (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfnmsubss (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_vfmaddsubpd  (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfmaddsubps  (v4sf, v4sf, v4sf)
     v2df __builtin_ia32_vfmsubaddpd  (v2df, v2df, v2df)
     v4sf __builtin_ia32_vfmsubaddps  (v4sf, v4sf, v4sf)
     v4df __builtin_ia32_vfmaddpd256 (v4df, v4df, v4df)
     v8sf __builtin_ia32_vfmaddps256 (v8sf, v8sf, v8sf)
     v4df __builtin_ia32_vfmsubpd256 (v4df, v4df, v4df)
     v8sf __builtin_ia32_vfmsubps256 (v8sf, v8sf, v8sf)
     v4df __builtin_ia32_vfnmaddpd256 (v4df, v4df, v4df)
     v8sf __builtin_ia32_vfnmaddps256 (v8sf, v8sf, v8sf)
     v4df __builtin_ia32_vfnmsubpd256 (v4df, v4df, v4df)
     v8sf __builtin_ia32_vfnmsubps256 (v8sf, v8sf, v8sf)
     v4df __builtin_ia32_vfmaddsubpd256 (v4df, v4df, v4df)
     v8sf __builtin_ia32_vfmaddsubps256 (v8sf, v8sf, v8sf)
     v4df __builtin_ia32_vfmsubaddpd256 (v4df, v4df, v4df)
     v8sf __builtin_ia32_vfmsubaddps256 (v8sf, v8sf, v8sf)

The following built-in functions are available when -mlwp is used.

     void __builtin_ia32_llwpcb16 (void *);
     void __builtin_ia32_llwpcb32 (void *);
     void __builtin_ia32_llwpcb64 (void *);
     void * __builtin_ia32_llwpcb16 (void);
     void * __builtin_ia32_llwpcb32 (void);
     void * __builtin_ia32_llwpcb64 (void);
     void __builtin_ia32_lwpval16 (unsigned short, unsigned int, unsigned short)
     void __builtin_ia32_lwpval32 (unsigned int, unsigned int, unsigned int)
     void __builtin_ia32_lwpval64 (unsigned __int64, unsigned int, unsigned int)
     unsigned char __builtin_ia32_lwpins16 (unsigned short, unsigned int, unsigned short)
     unsigned char __builtin_ia32_lwpins32 (unsigned int, unsigned int, unsigned int)
     unsigned char __builtin_ia32_lwpins64 (unsigned __int64, unsigned int, unsigned int)

The following built-in functions are available when -mbmi is used. All of them generate the machine instruction that is part of the name.

     unsigned int __builtin_ia32_bextr_u32(unsigned int, unsigned int);
     unsigned long long __builtin_ia32_bextr_u64 (unsigned long long, unsigned long long);

The following built-in functions are available when -mbmi2 is used. All of them generate the machine instruction that is part of the name.

     unsigned int _bzhi_u32 (unsigned int, unsigned int)
     unsigned int _pdep_u32 (unsigned int, unsigned int)
     unsigned int _pext_u32 (unsigned int, unsigned int)
     unsigned long long _bzhi_u64 (unsigned long long, unsigned long long)
     unsigned long long _pdep_u64 (unsigned long long, unsigned long long)
     unsigned long long _pext_u64 (unsigned long long, unsigned long long)

The following built-in functions are available when -mlzcnt is used. All of them generate the machine instruction that is part of the name.

     unsigned short __builtin_ia32_lzcnt_16(unsigned short);
     unsigned int __builtin_ia32_lzcnt_u32(unsigned int);
     unsigned long long __builtin_ia32_lzcnt_u64 (unsigned long long);

The following built-in functions are available when -mfxsr is used. All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_fxsave (void *)
     void __builtin_ia32_fxrstor (void *)
     void __builtin_ia32_fxsave64 (void *)
     void __builtin_ia32_fxrstor64 (void *)

The following built-in functions are available when -mxsave is used. All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_xsave (void *, long long)
     void __builtin_ia32_xrstor (void *, long long)
     void __builtin_ia32_xsave64 (void *, long long)
     void __builtin_ia32_xrstor64 (void *, long long)

The following built-in functions are available when -mxsaveopt is used. All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_xsaveopt (void *, long long)
     void __builtin_ia32_xsaveopt64 (void *, long long)

The following built-in functions are available when -mtbm is used. Both of them generate the immediate form of the bextr machine instruction.

     unsigned int __builtin_ia32_bextri_u32 (unsigned int, const unsigned int);
     unsigned long long __builtin_ia32_bextri_u64 (unsigned long long, const unsigned long long);

The following built-in functions are available when -m3dnow is used. All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_femms (void)
     v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
     v2si __builtin_ia32_pf2id (v2sf)
     v2sf __builtin_ia32_pfacc (v2sf, v2sf)
     v2sf __builtin_ia32_pfadd (v2sf, v2sf)
     v2si __builtin_ia32_pfcmpeq (v2sf, v2sf)
     v2si __builtin_ia32_pfcmpge (v2sf, v2sf)
     v2si __builtin_ia32_pfcmpgt (v2sf, v2sf)
     v2sf __builtin_ia32_pfmax (v2sf, v2sf)
     v2sf __builtin_ia32_pfmin (v2sf, v2sf)
     v2sf __builtin_ia32_pfmul (v2sf, v2sf)
     v2sf __builtin_ia32_pfrcp (v2sf)
     v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf)
     v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf)
     v2sf __builtin_ia32_pfrsqrt (v2sf)
     v2sf __builtin_ia32_pfsub (v2sf, v2sf)
     v2sf __builtin_ia32_pfsubr (v2sf, v2sf)
     v2sf __builtin_ia32_pi2fd (v2si)
     v4hi __builtin_ia32_pmulhrw (v4hi, v4hi)

The following built-in functions are available when both -m3dnow and -march=athlon are used.  All of them generate the machine instruction that is part of the name.

     v2si __builtin_ia32_pf2iw (v2sf)
     v2sf __builtin_ia32_pfnacc (v2sf, v2sf)
     v2sf __builtin_ia32_pfpnacc (v2sf, v2sf)
     v2sf __builtin_ia32_pi2fw (v2si)
     v2sf __builtin_ia32_pswapdsf (v2sf)
     v2si __builtin_ia32_pswapdsi (v2si)

The following built-in functions are available when -mrtm is used They are used for restricted transactional memory. These are the internal low level functions. Normally the functions in x86 transactional memory intrinsics should be used instead.

     int __builtin_ia32_xbegin ()
     void __builtin_ia32_xend ()
     void __builtin_ia32_xabort (status)
     int __builtin_ia32_xtest ()

The following built-in functions are available when -mmwaitx is used. All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_monitorx (void *, unsigned int, unsigned int)
     void __builtin_ia32_mwaitx (unsigned int, unsigned int, unsigned int)

x86 Transactional Memory Intrinsics
-----------------------------------

These hardware transactional memory intrinsics for x86 allow you to use memory transactions with RTM (Restricted Transactional Memory). This support is enabled with the -mrtm option. For using HLE (Hardware Lock Elision) see x86 specific memory model extensions for transactional memory instead.

A memory transaction commits all changes to memory in an atomic way, as visible to other threads. If the transaction fails it is rolled back and all side effects discarded.

Generally there is no guarantee that a memory transaction ever succeeds and suitable fallback code always needs to be supplied.

 -- RTM Function: unsigned _xbegin ()
     Start a RTM (Restricted Transactional Memory) transaction. Returns _XBEGIN_STARTED when the transaction started successfully (note this is not 0, so the constant has to be explicitly tested).

     If the transaction aborts, all side-effects are undone and an abort code encoded as a bit mask is returned. The following macros are defined:

     _XABORT_EXPLICIT
          Transaction was explicitly aborted with _xabort.  The parameter passed to _xabort is available with _XABORT_CODE(status).

     _XABORT_RETRY
          Transaction retry is possible.

     _XABORT_CONFLICT
          Transaction abort due to a memory conflict with another thread.

     _XABORT_CAPACITY
          Transaction abort due to the transaction using too much memory.

     _XABORT_DEBUG
          Transaction abort due to a debug trap.

     _XABORT_NESTED
          Transaction abort in an inner nested transaction.

     There is no guarantee any transaction ever succeeds, so there always needs to be a valid fallback path.

 -- RTM Function: void _xend ()
     Commit the current transaction. When no transaction is active this faults. All memory side-effects of the transaction become visible to other threads in an atomic manner.

 -- RTM Function: int _xtest ()
     Return a nonzero value if a transaction is currently active, otherwise 0.

 -- RTM Function: void _xabort (status)
     Abort the current transaction. When no transaction is active this is a no-op. The STATUS is an 8-bit constant; its value is encoded in the return value from _xbegin.

Here is an example showing handling for _XABORT_RETRY and a fallback path for other failures:

     #include <immintrin.h>

     int n_tries, max_tries;
     unsigned status = _XABORT_EXPLICIT;
     ...

     for (n_tries = 0; n_tries < max_tries; n_tries++)
       {
         status = _xbegin ();
         if (status == _XBEGIN_STARTED || !(status & _XABORT_RETRY))
           break;
       }
     if (status == _XBEGIN_STARTED)
       {
         ... transaction code...
         _xend ();
       }
     else
       {
         ... non-transactional fallback path...
       }

Note that, in most cases, the transactional and non-transactional code must synchronize together to ensure consistency.

Format Checks Specific to Particular Target Machines
====================================================

For some target machines, GCC supports additional options to the format attribute (see Declaring Attributes of Functions).

Solaris Format Checks
---------------------

Solaris targets support the cmn_err (or __cmn_err__) format check.  cmn_err accepts a subset of the standard printf conversions, and the two-argument %b conversion for displaying bit-fields.  See the Solaris man page for cmn_err for more information.

Darwin Format Checks
--------------------

Darwin targets support the CFString (or __CFString__) in the format attribute context.  Declarations made with such attribution are parsed for correct syntax and format argument types.  However, parsing of the format string itself is currently undefined and is not carried out by this version of the compiler.

Additionally, CFStringRefs (defined by the CoreFoundation headers) may also be used as format arguments.  Note that the relevant headers are only likely to be available on Darwin (OSX) installations.  On such installations, the XCode and system documentation provide descriptions of CFString, CFStringRefs and associated functions.

Pragmas Accepted by GCC
=======================

GCC supports several types of pragmas, primarily in order to compile code originally written for other compilers.  Note that in general we do not recommend the use of pragmas; see Function Attributes, for further explanation.

AArch64 Pragmas
---------------

The pragmas defined by the AArch64 target correspond to the AArch64 target function attributes.  They can be specified as below:

     #pragma GCC target("string")

where STRING can be any string accepted as an AArch64 target attribute.  See AArch64 Function Attributes, for more details on the permissible values of string.

ARM Pragmas
-----------

The ARM target defines pragmas for controlling the default addition of long_call and short_call attributes to functions. See Function Attributes, for information about the effects of these attributes.

long_calls
     Set all subsequent functions to have the long_call attribute.

no_long_calls
     Set all subsequent functions to have the short_call attribute.

long_calls_off
     Do not affect the long_call or short_call attributes of subsequent functions.

M32C Pragmas
------------

GCC memregs NUMBER
     Overrides the command-line option -memregs= for the current file.  Use with care!  This pragma must be before any function in the file, and mixing different memregs values in different objects may make them incompatible.  This pragma is useful when a performance-critical function uses a memreg for temporary values, as it may allow you to reduce the number of memregs used.

ADDRESS NAME ADDRESS
     For any declared symbols matching NAME, this does three things to that symbol: it forces the symbol to be located at the given address (a number), it forces the symbol to be volatile, and it changes the symbol's scope to be static.  This pragma exists for compatibility with other compilers, but note that the common 1234H numeric syntax is not supported (use 0x1234 instead).  Example:

          #pragma ADDRESS port3 0x103
          char port3;

MeP Pragmas
-----------

custom io_volatile (on|off)
     Overrides the command-line option -mio-volatile for the current file.  Note that for compatibility with future GCC releases, this option should only be used once before any io variables in each file.

GCC coprocessor available REGISTERS
     Specifies which coprocessor registers are available to the register allocator.  REGISTERS may be a single register, register range separated by ellipses, or comma-separated list of those.  Example:

          #pragma GCC coprocessor available $c0...$c10, $c28

GCC coprocessor call_saved REGISTERS
     Specifies which coprocessor registers are to be saved and restored by any function using them.  REGISTERS may be a single register, register range separated by ellipses, or comma-separated list of those.  Example:

          #pragma GCC coprocessor call_saved $c4...$c6, $c31

GCC coprocessor subclass '(A|B|C|D)' = REGISTERS
     Creates and defines a register class.  These register classes can be used by inline asm constructs.  REGISTERS may be a single register, register range separated by ellipses, or comma-separated list of those.  Example:

          #pragma GCC coprocessor subclass 'B' = $c2, $c4, $c6

          asm ("cpfoo %0" : "=B" (x));

GCC disinterrupt NAME , NAME ...
     For the named functions, the compiler adds code to disable interrupts for the duration of those functions.  If any functions so named are not encountered in the source, a warning is emitted that the pragma is not used.  Examples:

          #pragma disinterrupt foo
          #pragma disinterrupt bar, grill
          int foo () { ... }

GCC call NAME , NAME ...
     For the named functions, the compiler always uses a register-indirect call model when calling the named functions.  Examples:

          extern int foo ();
          #pragma call foo

RS/6000 and PowerPC Pragmas
---------------------------

The RS/6000 and PowerPC targets define one pragma for controlling whether or not the longcall attribute is added to function declarations by default.  This pragma overrides the -mlongcall option, but not the longcall and shortcall attributes. See RS/6000 and PowerPC Options, for more information about when long calls are and are not necessary.

longcall (1)
     Apply the longcall attribute to all subsequent function declarations.

longcall (0)
     Do not apply the longcall attribute to subsequent function declarations.

Darwin Pragmas
--------------

The following pragmas are available for all architectures running the Darwin operating system.  These are useful for compatibility with other Mac OS compilers.

mark TOKENS...
     This pragma is accepted, but has no effect.

options align=ALIGNMENT
     This pragma sets the alignment of fields in structures.  The values of ALIGNMENT may be mac68k, to emulate m68k alignment, or power, to emulate PowerPC alignment.  Uses of this pragma nest properly; to restore the previous setting, use reset for the ALIGNMENT.

segment TOKENS...
     This pragma is accepted, but has no effect.

unused (VAR [, VAR]...)
     This pragma declares variables to be possibly unused.  GCC does not produce warnings for the listed variables.  The effect is similar to that of the unused attribute, except that this pragma may appear anywhere within the variables' scopes.

Solaris Pragmas
---------------

The Solaris target supports #pragma redefine_extname (see Symbol-Renaming Pragmas).  It also supports additional #pragma directives for compatibility with the system compiler.

align ALIGNMENT (VARIABLE [, VARIABLE]...)

     Increase the minimum alignment of each VARIABLE to ALIGNMENT. This is the same as GCC's aligned attribute see Variable Attributes).  Macro expansion occurs on the arguments to this pragma when compiling C and Objective-C.  It does not currently occur when compiling C++, but this is a bug which may be fixed in a future release.

fini (FUNCTION [, FUNCTION]...)

     This pragma causes each listed FUNCTION to be called after main, or during shared module unloading, by adding a call to the .fini section.

init (FUNCTION [, FUNCTION]...)

     This pragma causes each listed FUNCTION to be called during initialization (before main) or during shared module loading, by adding a call to the .init section.

Symbol-Renaming Pragmas
-----------------------

GCC supports a #pragma directive that changes the name used in assembly for a given declaration. While this pragma is supported on all platforms, it is intended primarily to provide compatibility with the Solaris system headers. This effect can also be achieved using the asm labels extension (see Asm Labels).

redefine_extname OLDNAME NEWNAME

     This pragma gives the C function OLDNAME the assembly symbol NEWNAME.  The preprocessor macro __PRAGMA_REDEFINE_EXTNAME is defined if this pragma is available (currently on all platforms).

This pragma and the asm labels extension interact in a complicated manner.  Here are some corner cases you may want to be aware of:

 1. This pragma silently applies only to declarations with external linkage.  Asm labels do not have this restriction.

 2. In C++, this pragma silently applies only to declarations with ``C'' linkage.  Again, asm labels do not have this restriction.

 3. If either of the ways of changing the assembly name of a declaration are applied to a declaration whose assembly name has already been determined (either by a previous use of one of these features, or because the compiler needed the assembly name in order to generate code), and the new name is different, a warning issues and the name does not change.

 4. The OLDNAME used by #pragma redefine_extname is always the C-language name.

Structure-Packing Pragmas
-------------------------

For compatibility with Microsoft Windows compilers, GCC supports a set of #pragma directives that change the maximum alignment of members of structures (other than zero-width bit-fields), unions, and classes subsequently defined. The N value below always is required to be a small power of two and specifies the new alignment in bytes.

 1. #pragma pack(N) simply sets the new alignment.

 2. #pragma pack() sets the alignment to the one that was in effect when compilation started (see also command-line option -fpack-struct[=N] see Code Gen Options).

 3. #pragma pack(push[,N]) pushes the current alignment setting on an internal stack and then optionally sets the new alignment.

 4. #pragma pack(pop) restores the alignment setting to the one saved at the top of the internal stack (and removes that stack entry). Note that #pragma pack([N]) does not influence this internal stack; thus it is possible to have #pragma pack(push) followed by multiple #pragma pack(N) instances and finalized by a single #pragma pack(pop).

Some targets, e.g. x86 and PowerPC, support the ms_struct #pragma which lays out a structure as the documented __attribute__ ((ms_struct)).

 1. #pragma ms_struct on turns on the layout for structures declared.

 2. #pragma ms_struct off turns off the layout for structures declared.

 3. #pragma ms_struct reset goes back to the default layout.

Weak Pragmas
------------

For compatibility with SVR4, GCC supports a set of #pragma directives for declaring symbols to be weak, and defining weak aliases.

#pragma weak SYMBOL
     This pragma declares SYMBOL to be weak, as if the declaration had the attribute of the same name.  The pragma may appear before or after the declaration of SYMBOL.  It is not an error for SYMBOL to never be defined at all.

#pragma weak SYMBOL1 = SYMBOL2
     This pragma declares SYMBOL1 to be a weak alias of SYMBOL2. It is an error if SYMBOL2 is not defined in the current translation unit.

Diagnostic Pragmas
------------------

GCC allows the user to selectively enable or disable certain types of diagnostics, and change the kind of the diagnostic.  For example, a project's policy might require that all sources compile with -Werror but certain files might have exceptions allowing specific types of warnings.  Or, a project might selectively enable diagnostics and treat them as errors depending on which preprocessor macros are defined.

#pragma GCC diagnostic KIND OPTION

     Modifies the disposition of a diagnostic.  Note that not all diagnostics are modifiable; at the moment only warnings (normally controlled by -W...) can be controlled, and not all of them. Use -fdiagnostics-show-option to determine which diagnostics are controllable and which option controls them.

     KIND is error to treat this diagnostic as an error, warning to treat it like a warning (even if -Werror is in effect), or ignored if the diagnostic is to be ignored. OPTION is a double quoted string that matches the command-line option.

          #pragma GCC diagnostic warning "-Wformat"
          #pragma GCC diagnostic error "-Wformat"
          #pragma GCC diagnostic ignored "-Wformat"

     Note that these pragmas override any command-line options.  GCC keeps track of the location of each pragma, and issues diagnostics according to the state as of that point in the source file.  Thus, pragmas occurring after a line do not affect diagnostics caused by that line.

#pragma GCC diagnostic push
#pragma GCC diagnostic pop

     Causes GCC to remember the state of the diagnostics as of each push, and restore to that point at each pop.  If a pop has no matching push, the command-line options are restored.

          #pragma GCC diagnostic error "-Wuninitialized"
            foo(a);                       /* error is given for this one */
          #pragma GCC diagnostic push
          #pragma GCC diagnostic ignored "-Wuninitialized"
            foo(b);                       /* no diagnostic for this one */
          #pragma GCC diagnostic pop
            foo(c);                       /* error is given for this one */
          #pragma GCC diagnostic pop
            foo(d);                       /* depends on command-line options */

GCC also offers a simple mechanism for printing messages during compilation.

#pragma message STRING

     Prints STRING as a compiler message on compilation.  The message is informational only, and is neither a compilation warning nor an error.

          #pragma message "Compiling " __FILE__ "..."

     STRING may be parenthesized, and is printed with location information.  For example,

          #define DO_PRAGMA(x) _Pragma (#x)
          #define TODO(x) DO_PRAGMA(message ("TODO - " #x))

          TODO(Remember to fix this)

     prints /tmp/file.c:4: note: #pragma message: TODO - Remember to fix this.

Visibility Pragmas
------------------

#pragma GCC visibility push(VISIBILITY)
#pragma GCC visibility pop

     This pragma allows the user to set the visibility for multiple declarations without having to give each a visibility attribute (see Function Attributes).

     In C++, #pragma GCC visibility affects only namespace-scope declarations.  Class members and template specializations are not affected; if you want to override the visibility for a particular member or instantiation, you must use an attribute.

Push/Pop Macro Pragmas
----------------------

For compatibility with Microsoft Windows compilers, GCC supports #pragma push_macro("MACRO_NAME") and #pragma pop_macro("MACRO_NAME").

#pragma push_macro("MACRO_NAME")
     This pragma saves the value of the macro named as MACRO_NAME to the top of the stack for this macro.

#pragma pop_macro("MACRO_NAME")
     This pragma sets the value of the macro named as MACRO_NAME to the value on top of the stack for this macro. If the stack for MACRO_NAME is empty, the value of the macro remains unchanged.

For example:

     #define X  1
     #pragma push_macro("X")
     #undef X
     #define X -1
     #pragma pop_macro("X")
     int x [X];

In this example, the definition of X as 1 is saved by #pragma push_macro and restored by #pragma pop_macro.

Function Specific Option Pragmas
--------------------------------

#pragma GCC target ("STRING"...)

     This pragma allows you to set target specific options for functions defined later in the source file.  One or more strings can be specified.  Each function that is defined after this point is as if attribute((target("STRING"))) was specified for that function.  The parenthesis around the options is optional. See Function Attributes, for more information about the target attribute and the attribute syntax.

     The #pragma GCC target pragma is presently implemented for x86, PowerPC, and Nios II targets only.

#pragma GCC optimize ("STRING"...)

     This pragma allows you to set global optimization options for functions defined later in the source file.  One or more strings can be specified.  Each function that is defined after this point is as if attribute((optimize("STRING"))) was specified for that function.  The parenthesis around the options is optional. See Function Attributes, for more information about the optimize attribute and the attribute syntax.

#pragma GCC push_options
#pragma GCC pop_options

     These pragmas maintain a stack of the current target and optimization options.  It is intended for include files where you temporarily want to switch to using a different #pragma GCC target or #pragma GCC optimize and then to pop back to the previous options.

#pragma GCC reset_options

     This pragma clears the current #pragma GCC target and #pragma GCC optimize to use the default switches as specified on the command line.

Loop-Specific Pragmas
---------------------

#pragma GCC ivdep

With this pragma, the programmer asserts that there are no loop-carried dependencies which would prevent consecutive iterations of the following loop from executing concurrently with SIMD (single instruction multiple data) instructions.

For example, the compiler can only unconditionally vectorize the following loop with the pragma:

     void foo (int n, int *a, int *b, int *c)
     {
       int i, j;
     #pragma GCC ivdep
       for (i = 0; i < n; ++i)
         a[i] = b[i] + c[i];
     }

In this example, using the restrict qualifier had the same effect. In the following example, that would not be possible. Assume k < -m or k >= m. Only with the pragma, the compiler knows that it can unconditionally vectorize the following loop:

     void ignore_vec_dep (int *a, int k, int c, int m)
     {
     #pragma GCC ivdep
       for (int i = 0; i < m; i++)
         a[i] = a[i + k] * c;
     }

Unnamed Structure and Union Fields
==================================

As permitted by ISO C11 and for compatibility with other compilers, GCC allows you to define a structure or union that contains, as fields, structures and unions without names.  For example:

     struct {
       int a;
       union {
         int b;
         float c;
       };
       int d;
     } foo;

In this example, you are able to access members of the unnamed union with code like foo.b.  Note that only unnamed structs and unions are allowed, you may not have, for example, an unnamed int.

You must never create such structures that cause ambiguous field definitions. For example, in this structure:

     struct {
       int a;
       struct {
         int a;
       };
     } foo;

it is ambiguous which a is being referred to with foo.a. The compiler gives errors for such constructs.

Unless -fms-extensions is used, the unnamed field must be a structure or union definition without a tag (for example, struct { int a; };).  If -fms-extensions is used, the field may also be a definition with a tag such as struct foo { int a; };, a reference to a previously defined structure or union such as struct foo;, or a reference to a typedef name for a previously defined structure or union type.

The option -fplan9-extensions enables -fms-extensions as well as two other extensions.  First, a pointer to a structure is automatically converted to a pointer to an anonymous field for assignments and function calls.  For example:

     struct s1 { int a; };
     struct s2 { struct s1; };
     extern void f1 (struct s1 *);
     void f2 (struct s2 *p) { f1 (p); }

In the call to f1 inside f2, the pointer p is converted into a pointer to the anonymous field.

Second, when the type of an anonymous field is a typedef for a struct or union, code may refer to the field using the name of the typedef.

     typedef struct { int a; } s1;
     struct s2 { s1; };
     s1 f1 (struct s2 *p) { return p->s1; }

These usages are only permitted when they are not ambiguous.

Thread-Local Storage
====================

Thread-local storage (TLS) is a mechanism by which variables are allocated such that there is one instance of the variable per extant thread.  The runtime model GCC uses to implement this originates in the IA-64 processor-specific ABI, but has since been migrated to other processors as well.  It requires significant support from the linker (ld), dynamic linker (ld.so), and system libraries (libc.so and libpthread.so), so it is not available everywhere.

At the user level, the extension is visible with a new storage class keyword: __thread.  For example:

     __thread int i;
     extern __thread struct state s;
     static __thread char *p;

The __thread specifier may be used alone, with the extern or static specifiers, but with no other storage class specifier. When used with extern or static, __thread must appear immediately after the other storage class specifier.

The __thread specifier may be applied to any global, file-scoped static, function-scoped static, or static data member of a class.  It may not be applied to block-scoped automatic or non-static data member.

When the address-of operator is applied to a thread-local variable, it is evaluated at run time and returns the address of the current thread's instance of that variable.  An address so obtained may be used by any thread.  When a thread terminates, any pointers to thread-local variables in that thread become invalid.

No static initialization may refer to the address of a thread-local variable.

In C++, if an initializer is present for a thread-local variable, it must be a CONSTANT-EXPRESSION, as defined in 5.19.2 of the ANSI/ISO C++ standard.

See ELF Handling For Thread-Local Storage (http://www.akkadia.org/drepper/tls.pdf) for a detailed explanation of the four thread-local storage addressing models, and how the runtime is expected to function.

ISO/IEC 9899:1999 Edits for Thread-Local Storage
------------------------------------------------

The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that document the exact semantics of the language extension.

  * 5.1.2  Execution environments

     Add new text after paragraph 1

          Within either execution environment, a thread is a flow of control within a program.  It is implementation defined whether or not there may be more than one thread associated with a program. It is implementation defined how threads beyond the first are created, the name and type of the function called at thread startup, and how threads may be terminated.  However, objects with thread storage duration shall be initialized before thread startup.

  * 6.2.4  Storage durations of objects

     Add new text before paragraph 3

          An object whose identifier is declared with the storage-class specifier __thread has thread storage duration. Its lifetime is the entire execution of the thread, and its stored value is initialized only once, prior to thread startup.

  * 6.4.1  Keywords

     Add __thread.

  * 6.7.1  Storage-class specifiers

     Add __thread to the list of storage class specifiers in paragraph 1.

     Change paragraph 2 to

          With the exception of __thread, at most one storage-class specifier may be given [...].  The __thread specifier may be used alone, or immediately following extern or static.

     Add new text after paragraph 6

          The declaration of an identifier for a variable that has block scope that specifies __thread shall also specify either extern or static.

          The __thread specifier shall be used only with variables.

ISO/IEC 14882:1998 Edits for Thread-Local Storage
-------------------------------------------------

The following are a set of changes to ISO/IEC 14882:1998 (aka C++98) that document the exact semantics of the language extension.

  * [intro.execution]

     New text after paragraph 4

          A thread is a flow of control within the abstract machine. It is implementation defined whether or not there may be more than one thread.

     New text after paragraph 7

          It is unspecified whether additional action must be taken to ensure when and whether side effects are visible to other threads.

  * [lex.key]

     Add __thread.

  * [basic.start.main]

     Add after paragraph 5

          The thread that begins execution at the main function is called the main thread.  It is implementation defined how functions beginning threads other than the main thread are designated or typed. A function so designated, as well as the main function, is called a thread startup function.  It is implementation defined what happens if a thread startup function returns.  It is implementation defined what happens to other threads when any thread calls exit.

  * [basic.start.init]

     Add after paragraph 4

          The storage for an object of thread storage duration shall be statically initialized before the first statement of the thread startup function.  An object of thread storage duration shall not require dynamic initialization.

  * [basic.start.term]

     Add after paragraph 3

          The type of an object with thread storage duration shall not have a non-trivial destructor, nor shall it be an array type whose elements (directly or indirectly) have non-trivial destructors.

  * [basic.stc]

     Add ``thread storage duration'' to the list in paragraph 1.

     Change paragraph 2

          Thread, static, and automatic storage durations are associated with objects introduced by declarations [...].

     Add __thread to the list of specifiers in paragraph 3.

  * [basic.stc.thread]

     New section before [basic.stc.static]

          The keyword __thread applied to a non-local object gives the object thread storage duration.

          A local variable or class data member declared both static and __thread gives the variable or member thread storage duration.

  * [basic.stc.static]

     Change paragraph 1

          All objects that have neither thread storage duration, dynamic storage duration nor are local [...].

  * [dcl.stc]

     Add __thread to the list in paragraph 1.

     Change paragraph 1

          With the exception of __thread, at most one STORAGE-CLASS-SPECIFIER shall appear in a given DECL-SPECIFIER-SEQ.  The __thread specifier may be used alone, or immediately following the extern or static specifiers.  [...]

     Add after paragraph 5

          The __thread specifier can be applied only to the names of objects and to anonymous unions.

  * [class.mem]

     Add after paragraph 6

          Non-static members shall not be __thread.

Binary Constants using the 0b Prefix
====================================

Integer constants can be written as binary constants, consisting of a sequence of 0 and 1 digits, prefixed by 0b or 0B.  This is particularly useful in environments that operate a lot on the bit level (like microcontrollers).

The following statements are identical:

     i =       42;
     i =     0x2a;
     i =      052;
     i = 0b101010;

The type of these constants follows the same rules as for octal or hexadecimal integer constants, so suffixes like L or UL can be applied.

Extensions to the C++ Language
******************************

The GNU compiler provides these extensions to the C++ language (and you can also use most of the C language extensions in your C++ programs).  If you want to write code that checks whether these features are available, you can test for the GNU compiler the same way as for C programs: check for a predefined macro __GNUC__.  You can also use __GNUG__ to test specifically for GNU C++ (see Predefined Macros (The GNU C Preprocessor)).

When is a Volatile C++ Object Accessed?
=======================================

The C++ standard differs from the C standard in its treatment of volatile objects.  It fails to specify what constitutes a volatile access, except to say that C++ should behave in a similar manner to C with respect to volatiles, where possible.  However, the different lvalueness of expressions between C and C++ complicate the behavior. G++ behaves the same as GCC for volatile access, see Volatiles, for a description of GCC's behavior.

The C and C++ language specifications differ when an object is accessed in a void context:

     volatile int *src = SOMEVALUE;
     *src;

The C++ standard specifies that such expressions do not undergo lvalue to rvalue conversion, and that the type of the dereferenced object may be incomplete.  The C++ standard does not specify explicitly that it is lvalue to rvalue conversion that is responsible for causing an access.  There is reason to believe that it is, because otherwise certain simple expressions become undefined.  However, because it would surprise most programmers, G++ treats dereferencing a pointer to volatile object of complete type as GCC would do for an equivalent type in C.  When the object has incomplete type, G++ issues a warning; if you wish to force an error, you must force a conversion to rvalue with, for instance, a static cast.

When using a reference to volatile, G++ does not treat equivalent expressions as accesses to volatiles, but instead issues a warning that no volatile is accessed.  The rationale for this is that otherwise it becomes difficult to determine where volatile access occur, and not possible to ignore the return value from functions returning volatile references.  Again, if you wish to force a read, cast the reference to an rvalue.

G++ implements the same behavior as GCC does when assigning to a volatile object---there is no reread of the assigned-to object, the assigned rvalue is reused.  Note that in C++ assignment expressions are lvalues, and if used as an lvalue, the volatile object is referred to.  For instance, VREF refers to VOBJ, as expected, in the following example:

     volatile int vobj;
     volatile int &vref = vobj = SOMETHING;

Restricting Pointer Aliasing
============================

As with the C front end, G++ understands the C99 feature of restricted pointers, specified with the __restrict__, or __restrict type qualifier.  Because you cannot compile C++ by specifying the -std=c99 language flag, restrict is not a keyword in C++.

In addition to allowing restricted pointers, you can specify restricted references, which indicate that the reference is not aliased in the local context.

     void fn (int *__restrict__ rptr, int &__restrict__ rref)
     {
       /* ... */
     }

In the body of fn, RPTR points to an unaliased integer and RREF refers to a (different) unaliased integer.

You may also specify whether a member function's THIS pointer is unaliased by using __restrict__ as a member function qualifier.

     void T::fn () __restrict__
     {
       /* ... */
     }

Within the body of T::fn, THIS has the effective definition T *__restrict__ const this.  Notice that the interpretation of a __restrict__ member function qualifier is different to that of const or volatile qualifier, in that it is applied to the pointer rather than the object.  This is consistent with other compilers that implement restricted pointers.

As with all outermost parameter qualifiers, __restrict__ is ignored in function definition matching.  This means you only need to specify __restrict__ in a function definition, rather than in a function prototype as well.

Vague Linkage
=============

There are several constructs in C++ that require space in the object file but are not clearly tied to a single translation unit.  We say that these constructs have ``vague linkage''.  Typically such constructs are emitted wherever they are needed, though sometimes we can be more clever.

Inline Functions
     Inline functions are typically defined in a header file which can be included in many different compilations.  Hopefully they can usually be inlined, but sometimes an out-of-line copy is necessary, if the address of the function is taken or if inlining fails.  In general, we emit an out-of-line copy in all translation units where one is needed.  As an exception, we only emit inline virtual functions with the vtable, since it always requires a copy.

     Local static variables and string constants used in an inline function are also considered to have vague linkage, since they must be shared between all inlined and out-of-line instances of the function.

VTables
     C++ virtual functions are implemented in most compilers using a lookup table, known as a vtable.  The vtable contains pointers to the virtual functions provided by a class, and each object of the class contains a pointer to its vtable (or vtables, in some multiple-inheritance situations).  If the class declares any non-inline, non-pure virtual functions, the first one is chosen as the ``key method'' for the class, and the vtable is only emitted in the translation unit where the key method is defined.

     Note: If the chosen key method is later defined as inline, the vtable is still emitted in every translation unit that defines it. Make sure that any inline virtuals are declared inline in the class body, even if they are not defined there.

type_info objects
     C++ requires information about types to be written out in order to implement dynamic_cast, typeid and exception handling. For polymorphic classes (classes with virtual functions), the type_info object is written out along with the vtable so that dynamic_cast can determine the dynamic type of a class object at run time.  For all other types, we write out the type_info object when it is used: when applying typeid to an expression, throwing an object, or referring to a type in a catch clause or exception specification.

Template Instantiations
     Most everything in this section also applies to template instantiations, but there are other options as well. See Where's the Template?.

When used with GNU ld version 2.8 or later on an ELF system such as GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of these constructs will be discarded at link time.  This is known as COMDAT support.

On targets that don't support COMDAT, but do support weak symbols, GCC uses them.  This way one copy overrides all the others, but the unused copies still take up space in the executable.

For targets that do not support either COMDAT or weak symbols, most entities with vague linkage are emitted as local symbols to avoid duplicate definition errors from the linker.  This does not happen for local statics in inlines, however, as having multiple copies almost certainly breaks things.

See Declarations and Definitions in One Header, for another way to control placement of these constructs.

C++ Interface and Implementation Pragmas
========================================

#pragma interface and #pragma implementation provide the user with a way of explicitly directing the compiler to emit entities with vague linkage (and debugging information) in a particular translation unit.

Note: These #pragmas have been superceded as of GCC 2.7.2 by COMDAT support and the ``key method'' heuristic mentioned in Vague Linkage.  Using them can actually cause your program to grow due to unnecessary out-of-line copies of inline functions.

#pragma interface
#pragma interface "SUBDIR/OBJECTS.h"
     Use this directive in header files that define object classes, to save space in most of the object files that use those classes.  Normally, local copies of certain information (backup copies of inline member functions, debugging information, and the internal tables that implement virtual functions) must be kept in each object file that includes class definitions.  You can use this pragma to avoid such duplication.  When a header file containing #pragma interface is included in a compilation, this auxiliary information is not generated (unless the main input source file itself uses #pragma implementation). Instead, the object files contain references to be resolved at link time.

     The second form of this directive is useful for the case where you have multiple headers with the same name in different directories.  If you use this form, you must specify the same string to #pragma implementation.

#pragma implementation
#pragma implementation "OBJECTS.h"
     Use this pragma in a main input file, when you want full output from included header files to be generated (and made globally visible).  The included header file, in turn, should use #pragma interface. Backup copies of inline member functions, debugging information, and the internal tables used to implement virtual functions are all generated in implementation files.

     If you use #pragma implementation with no argument, it applies to an include file with the same basename (A file's basename is the name stripped of all leading path information and of trailing suffixes, such as .h or .C or .cc.) as your source file.  For example, in allclass.cc, giving just #pragma implementation by itself is equivalent to #pragma implementation "allclass.h".

     Use the string argument if you want a single implementation file to include code from multiple header files.  (You must also use #include to include the header file; #pragma implementation only specifies how to use the file---it doesn't actually include it.)

     There is no way to split up the contents of a single header file into multiple implementation files.

#pragma implementation and #pragma interface also have an effect on function inlining.

If you define a class in a header file marked with #pragma interface, the effect on an inline function defined in that class is similar to an explicit extern declaration---the compiler emits no code at all to define an independent version of the function.  Its definition is used only for inlining with its callers.

Conversely, when you include the same header file in a main source file that declares it as #pragma implementation, the compiler emits code for the function itself; this defines a version of the function that can be found via pointers (or by callers compiled without inlining).  If all calls to the function can be inlined, you can avoid emitting the function by compiling with -fno-implement-inlines. If any calls are not inlined, you will get linker errors.

Where's the Template?
=====================

C++ templates are the first language feature to require more intelligence from the environment than one usually finds on a UNIX system.  Somehow the compiler and linker have to make sure that each template instance occurs exactly once in the executable if it is needed, and not at all otherwise.  There are two basic approaches to this problem, which are referred to as the Borland model and the Cfront model.

Borland model
     Borland C++ solved the template instantiation problem by adding the code equivalent of common blocks to their linker; the compiler emits template instances in each translation unit that uses them, and the linker collapses them together.  The advantage of this model is that the linker only has to consider the object files themselves; there is no external complexity to worry about.  This disadvantage is that compilation time is increased because the template code is being compiled repeatedly. Code written for this model tends to include definitions of all templates in the header file, since they must be seen to be instantiated.

Cfront model
     The AT&T C++ translator, Cfront, solved the template instantiation problem by creating the notion of a template repository, an automatically maintained place where template instances are stored.  A more modern version of the repository works as follows: As individual object files are built, the compiler places any template definitions and instantiations encountered in the repository.  At link time, the link wrapper adds in the objects in the repository and compiles any needed instances that were not previously emitted.  The advantages of this model are more optimal compilation speed and the ability to use the system linker; to implement the Borland model a compiler vendor also needs to replace the linker.  The disadvantages are vastly increased complexity, and thus potential for error; for some code this can be just as transparent, but in practice it can been very difficult to build multiple programs in one directory and one program in multiple directories.  Code written for this model tends to separate definitions of non-inline member templates into a separate file, which should be compiled separately.

When used with GNU ld version 2.8 or later on an ELF system such as GNU/Linux or Solaris 2, or on Microsoft Windows, G++ supports the Borland model.  On other systems, G++ implements neither automatic model.

You have the following options for dealing with template instantiations:

 1. Compile your template-using code with -frepo.  The compiler generates files with the extension .rpo listing all of the template instantiations used in the corresponding object files that could be instantiated there; the link wrapper, collect2, then updates the .rpo files to tell the compiler where to place those instantiations and rebuild any affected object files.  The link-time overhead is negligible after the first pass, as the compiler continues to place the instantiations in the same files.

     This is your best option for application code written for the Borland model, as it just works.  Code written for the Cfront model needs to be modified so that the template definitions are available at one or more points of instantiation; usually this is as simple as adding #include <tmethods.cc> to the end of each template header.

     For library code, if you want the library to provide all of the template instantiations it needs, just try to link all of its object files together; the link will fail, but cause the instantiations to be generated as a side effect.  Be warned, however, that this may cause conflicts if multiple libraries try to provide the same instantiations. For greater control, use explicit instantiation as described in the next option.

 2. Compile your code with -fno-implicit-templates to disable the implicit generation of template instances, and explicitly instantiate all the ones you use.  This approach requires more knowledge of exactly which instances you need than do the others, but it's less mysterious and allows greater control.  You can scatter the explicit instantiations throughout your program, perhaps putting them in the translation units where the instances are used or the translation units that define the templates themselves; you can put all of the explicit instantiations you need into one big file; or you can create small files like

          #include "Foo.h"
          #include "Foo.cc"

          template class Foo<int>;
          template ostream& operator <<
                          (ostream&, const Foo<int>&);

     for each of the instances you need, and create a template instantiation library from those.

     If you are using Cfront-model code, you can probably get away with not using -fno-implicit-templates when compiling files that don't #include the member template definitions.

     If you use one big file to do the instantiations, you may want to compile it without -fno-implicit-templates so you get all of the instances required by your explicit instantiations (but not by any other files) without having to specify them as well.

     The ISO C++ 2011 standard allows forward declaration of explicit instantiations (with extern). G++ supports explicit instantiation declarations in C++98 mode and has extended the template instantiation syntax to support instantiation of the compiler support data for a template class (i.e. the vtable) without instantiating any of its members (with inline), and instantiation of only the static data members of a template class, without the support data or member functions (with static):

          extern template int max (int, int);
          inline template class Foo<int>;
          static template class Foo<int>;

 3. Do nothing.  Pretend G++ does implement automatic instantiation management.  Code written for the Borland model works fine, but each translation unit contains instances of each of the templates it uses.  In a large program, this can lead to an unacceptable amount of code duplication.

Extracting the Function Pointer from a Bound Pointer to Member Function
=======================================================================

In C++, pointer to member functions (PMFs) are implemented using a wide pointer of sorts to handle all the possible call mechanisms; the PMF needs to store information about how to adjust the this pointer, and if the function pointed to is virtual, where to find the vtable, and where in the vtable to look for the member function.  If you are using PMFs in an inner loop, you should really reconsider that decision.  If that is not an option, you can extract the pointer to the function that would be called for a given object/PMF pair and call it directly inside the inner loop, to save a bit of time.

Note that you still pay the penalty for the call through a function pointer; on most modern architectures, such a call defeats the branch prediction features of the CPU.  This is also true of normal virtual function calls.

The syntax for this extension is

     extern A a;
     extern int (A::*fp)();
     typedef int (*fptr)(A *);

     fptr p = (fptr)(a.*fp);

For PMF constants (i.e. expressions of the form &Klasse::Member), no object is needed to obtain the address of the function.  They can be converted to function pointers directly:

     fptr p1 = (fptr)(&A::foo);

You must specify -Wno-pmf-conversions to use this extension.

C++-Specific Variable, Function, and Type Attributes
====================================================

Some attributes only make sense for C++ programs.

abi_tag ("TAG", ...)
     The abi_tag attribute can be applied to a function, variable, or class declaration.  It modifies the mangled name of the entity to incorporate the tag name, in order to distinguish the function or class from an earlier version with a different ABI; perhaps the class has changed size, or the function has a different return type that is not encoded in the mangled name.

     The attribute can also be applied to an inline namespace, but does not affect the mangled name of the namespace; in this case it is only used for -Wabi-tag warnings and automatic tagging of functions and variables.  Tagging inline namespaces is generally preferable to tagging individual declarations, but the latter is sometimes necessary, such as when only certain members of a class need to be tagged.

     The argument can be a list of strings of arbitrary length.  The strings are sorted on output, so the order of the list is unimportant.

     A redeclaration of an entity must not add new ABI tags, since doing so would change the mangled name.

     The ABI tags apply to a name, so all instantiations and specializations of a template have the same tags.  The attribute will be ignored if applied to an explicit specialization or instantiation.

     The -Wabi-tag flag enables a warning about a class which does not have all the ABI tags used by its subobjects and virtual functions; for users with code that needs to coexist with an earlier ABI, using this option can help to find all affected types that need to be tagged.

     When a type involving an ABI tag is used as the type of a variable or return type of a function where that tag is not already present in the signature of the function, the tag is automatically applied to the variable or function.  -Wabi-tag also warns about this situation; this warning can be avoided by explicitly tagging the variable or function or moving it into a tagged inline namespace.

init_priority (PRIORITY)

     In Standard C++, objects defined at namespace scope are guaranteed to be initialized in an order in strict accordance with that of their definitions in a given translation unit.  No guarantee is made for initializations across translation units.  However, GNU C++ allows users to control the order of initialization of objects defined at namespace scope with the init_priority attribute by specifying a relative PRIORITY, a constant integral expression currently bounded between 101 and 65535 inclusive.  Lower numbers indicate a higher priority.

     In the following example, A would normally be created before B, but the init_priority attribute reverses that order:

          Some_Class  A  __attribute__ ((init_priority (2000)));
          Some_Class  B  __attribute__ ((init_priority (543)));

     Note that the particular values of PRIORITY do not matter; only their relative ordering.

java_interface

     This type attribute informs C++ that the class is a Java interface.  It may only be applied to classes declared within an extern "Java" block. Calls to methods declared in this interface are dispatched using GCJ's interface table mechanism, instead of regular virtual table dispatch.

warn_unused

     For C++ types with non-trivial constructors and/or destructors it is impossible for the compiler to determine whether a variable of this type is truly unused if it is not referenced. This type attribute informs the compiler that variables of this type should be warned about if they appear to be unused, just like variables of fundamental types.

     This attribute is appropriate for types which just represent a value, such as std::string; it is not appropriate for types which control a resource, such as std::mutex.

     This attribute is also accepted in C, but it is unnecessary because C does not have constructors or destructors.

See also Namespace Association.

Function Multiversioning
========================

With the GNU C++ front end, for x86 targets, you may specify multiple versions of a function, where each function is specialized for a specific target feature.  At runtime, the appropriate version of the function is automatically executed depending on the characteristics of the execution platform.  Here is an example.

     __attribute__ ((target ("default")))
     int foo ()
     {
       // The default version of foo.
       return 0;
     }

     __attribute__ ((target ("sse4.2")))
     int foo ()
     {
       // foo version for SSE4.2
       return 1;
     }

     __attribute__ ((target ("arch=atom")))
     int foo ()
     {
       // foo version for the Intel ATOM processor
       return 2;
     }

     __attribute__ ((target ("arch=amdfam10")))
     int foo ()
     {
       // foo version for the AMD Family 0x10 processors.
       return 3;
     }

     int main ()
     {
       int (*p)() = &foo;
       assert ((*p) () == foo ());
       return 0;
     }

In the above example, four versions of function foo are created. The first version of foo with the target attribute "default" is the default version.  This version gets executed when no other target specific version qualifies for execution on a particular platform. A new version of foo is created by using the same function signature but with a different target string.  Function foo is called or a pointer to it is taken just like a regular function.  GCC takes care of doing the dispatching to call the right version at runtime.  Refer to the GCC wiki on Function Multiversioning (http://gcc.gnu.org/wiki/FunctionMultiVersioning) for more details.

Namespace Association
=====================

Caution: The semantics of this extension are equivalent to C++ 2011 inline namespaces.  Users should use inline namespaces instead as this extension will be removed in future versions of G++.

A using-directive with __attribute ((strong)) is stronger than a normal using-directive in two ways:

  * Templates from the used namespace can be specialized and explicitly instantiated as though they were members of the using namespace.

  * The using namespace is considered an associated namespace of all templates in the used namespace for purposes of argument-dependent name lookup.

The used namespace must be nested within the using namespace so that normal unqualified lookup works properly.

This is useful for composing a namespace transparently from implementation namespaces.  For example:

     namespace std {
       namespace debug {
         template <class T> struct A { };
       }
       using namespace debug __attribute ((__strong__));
       template <> struct A<int> { };   // OK to specialize

       template <class T> void f (A<T>);
     }

     int main()
     {
       f (std::A<float>());             // lookup finds std::f
       f (std::A<int>());
     }

Type Traits
===========

The C++ front end implements syntactic extensions that allow compile-time determination of various characteristics of a type (or of a pair of types).

__has_nothrow_assign (type)
     If type is const qualified or is a reference type then the trait is false.  Otherwise if __has_trivial_assign (type) is true then the trait is true, else if type is a cv class or union type with copy assignment operators that are known not to throw an exception then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__has_nothrow_copy (type)
     If __has_trivial_copy (type) is true then the trait is true, else if type is a cv class or union type with copy constructors that are known not to throw an exception then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__has_nothrow_constructor (type)
     If __has_trivial_constructor (type) is true then the trait is true, else if type is a cv class or union type (or array thereof) with a default constructor that is known not to throw an exception then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__has_trivial_assign (type)
     If type is const qualified or is a reference type then the trait is false.  Otherwise if __is_pod (type) is true then the trait is true, else if type is a cv class or union type with a trivial copy assignment ([class.copy]) then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__has_trivial_copy (type)
     If __is_pod (type) is true or type is a reference type then the trait is true, else if type is a cv class or union type with a trivial copy constructor ([class.copy]) then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__has_trivial_constructor (type)
     If __is_pod (type) is true then the trait is true, else if type is a cv class or union type (or array thereof) with a trivial default constructor ([class.ctor]) then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__has_trivial_destructor (type)
     If __is_pod (type) is true or type is a reference type then the trait is true, else if type is a cv class or union type (or array thereof) with a trivial destructor ([class.dtor]) then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__has_virtual_destructor (type)
     If type is a class type with a virtual destructor ([class.dtor]) then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__is_abstract (type)
     If type is an abstract class ([class.abstract]) then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__is_base_of (base_type, derived_type)
     If base_type is a base class of derived_type ([class.derived]) then the trait is true, otherwise it is false. Top-level cv qualifications of base_type and derived_type are ignored.  For the purposes of this trait, a class type is considered is own base.  Requires: if __is_class (base_type) and __is_class (derived_type) are true and base_type and derived_type are not the same type (disregarding cv-qualifiers), derived_type shall be a complete type.  Diagnostic is produced if this requirement is not met.

__is_class (type)
     If type is a cv class type, and not a union type ([basic.compound]) the trait is true, else it is false.

__is_empty (type)
     If __is_class (type) is false then the trait is false. Otherwise type is considered empty if and only if: type has no non-static data members, or all non-static data members, if any, are bit-fields of length 0, and type has no virtual members, and type has no virtual base classes, and type has no base classes base_type for which __is_empty (base_type) is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__is_enum (type)
     If type is a cv enumeration type ([basic.compound]) the trait is true, else it is false.

__is_literal_type (type)
     If type is a literal type ([basic.types]) the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__is_pod (type)
     If type is a cv POD type ([basic.types]) then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__is_polymorphic (type)
     If type is a polymorphic class ([class.virtual]) then the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__is_standard_layout (type)
     If type is a standard-layout type ([basic.types]) the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__is_trivial (type)
     If type is a trivial type ([basic.types]) the trait is true, else it is false.  Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.

__is_union (type)
     If type is a cv union type ([basic.compound]) the trait is true, else it is false.

__underlying_type (type)
     The underlying type of type.  Requires: type shall be an enumeration type ([dcl.enum]).

C++ Concepts
============

C++ concepts provide much-improved support for generic programming. In particular, they allow the specification of constraints on template arguments. The constraints are used to extend the usual overloading and partial specialization capabilities of the language, allowing generic data structures and algorithms to be ``refined'' based on their properties rather than their type names.

The following keywords are reserved for concepts.

assumes
     States an expression as an assumption, and if possible, verifies that the assumption is valid. For example, assume(n > 0).

axiom
     Introduces an axiom definition. Axioms introduce requirements on values.

forall
     Introduces a universally quantified object in an axiom. For example, forall (int n) n + 0 == n).

concept
     Introduces a concept definition. Concepts are sets of syntactic and semantic requirements on types and their values.

requires
     Introduces constraints on template arguments or requirements for a member function of a class template.

The front end also exposes a number of internal mechanism that can be used to simplify the writing of type traits. Note that some of these traits are likely to be removed in the future.

__is_same (type1, type2)
     A binary type trait: true whenever the type arguments are the same.

Java Exceptions
===============

The Java language uses a slightly different exception handling model from C++.  Normally, GNU C++ automatically detects when you are writing C++ code that uses Java exceptions, and handle them appropriately.  However, if C++ code only needs to execute destructors when Java exceptions are thrown through it, GCC guesses incorrectly. Sample problematic code is:

       struct S { ~S(); };
       extern void bar();    // is written in Java, and may throw exceptions
       void foo()
       {
         S s;
         bar();
       }

The usual effect of an incorrect guess is a link failure, complaining of a missing routine called __gxx_personality_v0.

You can inform the compiler that Java exceptions are to be used in a translation unit, irrespective of what it might think, by writing #pragma GCC java_exceptions at the head of the file.  This #pragma must appear before any functions that throw or catch exceptions, or run destructors when exceptions are thrown through them.

You cannot mix Java and C++ exceptions in the same translation unit.  It is believed to be safe to throw a C++ exception from one file through another file compiled for the Java exception model, or vice versa, but there may be bugs in this area.

Deprecated Features
===================

In the past, the GNU C++ compiler was extended to experiment with new features, at a time when the C++ language was still evolving.  Now that the C++ standard is complete, some of those features are superseded by superior alternatives.  Using the old features might cause a warning in some cases that the feature will be dropped in the future.  In other cases, the feature might be gone already.

While the list below is not exhaustive, it documents some of the options that are now deprecated:

-fexternal-templates
-falt-external-templates
     These are two of the many ways for G++ to implement template instantiation.  See Template Instantiation.  The C++ standard clearly defines how template definitions have to be organized across implementation units.  G++ has an implicit instantiation mechanism that should work just fine for standard-conforming code.

-fstrict-prototype
-fno-strict-prototype
     Previously it was possible to use an empty prototype parameter list to indicate an unspecified number of parameters (like C), rather than no parameters, as C++ demands.  This feature has been removed, except where it is required for backwards compatibility.   See Backwards Compatibility.

G++ allows a virtual function returning void * to be overridden by one returning a different pointer type.  This extension to the covariant return type rules is now deprecated and will be removed from a future version.

The G++ minimum and maximum operators (<? and >?) and their compound forms (<?=) and >?=) have been deprecated and are now removed from G++.  Code using these operators should be modified to use std::min and std::max instead.

The named return value extension has been deprecated, and is now removed from G++.

The use of initializer lists with new expressions has been deprecated, and is now removed from G++.

Floating and complex non-type template parameters have been deprecated, and are now removed from G++.

The implicit typename extension has been deprecated and is now removed from G++.

The use of default arguments in function pointers, function typedefs and other places where they are not permitted by the standard is deprecated and will be removed from a future version of G++.

G++ allows floating-point literals to appear in integral constant expressions, e.g.  enum E { e = int(2.2 * 3.7) } This extension is deprecated and will be removed from a future version.

G++ allows static data members of const floating-point type to be declared with an initializer in a class definition. The standard only allows initializers for static members of const integral types and const enumeration types so this extension has been deprecated and will be removed from a future version.

Backwards Compatibility
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Now that there is a definitive ISO standard C++, G++ has a specification to adhere to.  The C++ language evolved over time, and features that used to be acceptable in previous drafts of the standard, such as the ARM [Annotated C++ Reference Manual], are no longer accepted.  In order to allow compilation of C++ written to such drafts, G++ contains some backwards compatibilities.  All such backwards compatibility features are liable to disappear in future versions of G++. They should be considered deprecated.   See Deprecated Features.

For scope
     If a variable is declared at for scope, it used to remain in scope until the end of the scope that contained the for statement (rather than just within the for scope).  G++ retains this, but issues a warning, if such a variable is accessed outside the for scope.

Implicit C language
     Old C system header files did not contain an extern "C" {...} scope to set the language.  On such systems, all header files are implicitly scoped inside a C language scope.  Also, an empty prototype () is treated as an unspecified number of arguments, rather than no arguments, as C++ demands.