GCC currently defaults to -fcommon. As discussed in the PR, this is an ancient
C feature which is not conforming with the latest C standards. On many targets
this means global variable accesses have a codesize and performance penalty.
This applies to C code only, C++ code is not affected by -fcommon. It is about
time to change the default.
gcc/
PR85678
* common.opt (fcommon): Change init to 1.
* invoke.texi (-fcommon): Update documentation.
testsuite/
* g++.dg/lto/odr-6_1.c: Add -fcommon.
* gcc.dg/alias-15.c: Likewise.
* gcc.dg/fdata-sections-1.c: Likewise.
* gcc.dg/ipa/pr77653.c: Likewise.
* gcc.dg/lto/20090729_0.c: Likewise.
* gcc.dg/lto/
20111207-1_0.c: Likewise.
* gcc.dg/lto/c-compatible-types-1_0.c: Likewise.
* gcc.dg/lto/pr55525_0.c: Likewise.
* gcc.dg/lto/pr88077_0.c: Use long to avoid alignment warning.
* gcc.dg/lto/pr88077_1.c: Add -fcommon.
* gcc.target/aarch64/sve/peel_ind_1.c: Allow ANCHOR0.
* gcc.target/aarch64/sve/peel_ind_2.c: Likewise.
* gcc.target/aarch64/sve/peel_ind_3.c: Likewise.
* gcc.target/i386/volatile-bitfields-2.c: Allow movl or movq.
From-SVN: r278509
+2019-11-20 Wilco Dijkstra <wdijkstr@arm.com>
+
+ PR85678
+ * common.opt (fcommon): Change init to 1.
+ * doc/invoke.texi (-fcommon): Update documentation.
+
2019-11-20 Jan Hubicka <jh@suse.cz>
* fibonacci_heap.h (fibonacci_heap<K,V>::consolidate): Turn auto_vec
Looks for opportunities to reduce stack adjustments and stack references.
fcommon
-Common Report Var(flag_no_common,0)
+Common Report Var(flag_no_common,0) Init(1)
Put uninitialized globals in the common section.
fcompare-debug
-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
-fasynchronous-unwind-tables @gol
-fno-gnu-unique @gol
--finhibit-size-directive -fno-common -fno-ident @gol
+-finhibit-size-directive -fcommon -fno-ident @gol
-fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol
-fno-jump-tables @gol
-frecord-gcc-switches @gol
code that is not binary compatible with code generated without that switch.
Use it to conform to a non-default application binary interface.
-@item -fno-common
-@opindex fno-common
+@item -fcommon
@opindex fcommon
+@opindex fno-common
@cindex tentative definitions
-In C code, this option controls the placement of global variables
-defined without an initializer, known as @dfn{tentative definitions}
-in the C standard. Tentative definitions are distinct from declarations
+In C code, this option controls the placement of global variables
+defined without an initializer, known as @dfn{tentative definitions}
+in the C standard. Tentative definitions are distinct from declarations
of a variable with the @code{extern} keyword, which do not allocate storage.
-Unix C compilers have traditionally allocated storage for
-uninitialized global variables in a common block. This allows the
-linker to resolve all tentative definitions of the same variable
+The default is @option{-fno-common}, which specifies that the compiler places
+uninitialized global variables in the BSS section of the object file.
+This inhibits the merging of tentative definitions by the linker so you get a
+multiple-definition error if the same variable is accidentally defined in more
+than one compilation unit.
+
+The @option{-fcommon} places uninitialized global variables in a common block.
+This allows the linker to resolve all tentative definitions of the same variable
in different compilation units to the same object, or to a non-tentative
-definition.
-This is the behavior specified by @option{-fcommon}, and is the default for
-GCC on most targets.
-On the other hand, this behavior is not required by ISO
-C, and on some targets may carry a speed or code size penalty on
-variable references.
-
-The @option{-fno-common} option specifies that the compiler should instead
-place uninitialized global variables in the BSS section of the object file.
-This inhibits the merging of tentative definitions by the linker so
-you get a multiple-definition error if the same
-variable is defined in more than one compilation unit.
-Compiling with @option{-fno-common} is useful on targets for which
-it provides better performance, or if you wish to verify that the
-program will work on other systems that always treat uninitialized
-variable definitions this way.
+definition. This behavior does not conform to ISO C, is inconsistent with C++,
+and on many targets implies a speed and code size penalty on global variable
+references. It is mainly useful to enable legacy code to link without errors.
@item -fno-ident
@opindex fno-ident
+2019-11-20 Wilco Dijkstra <wdijkstr@arm.com>
+
+ PR85678
+ * g++.dg/lto/odr-6_1.c: Add -fcommon.
+ * gcc.dg/alias-15.c: Likewise.
+ * gcc.dg/fdata-sections-1.c: Likewise.
+ * gcc.dg/ipa/pr77653.c: Likewise.
+ * gcc.dg/lto/20090729_0.c: Likewise.
+ * gcc.dg/lto/20111207-1_0.c: Likewise.
+ * gcc.dg/lto/c-compatible-types-1_0.c: Likewise.
+ * gcc.dg/lto/pr55525_0.c: Likewise.
+ * gcc.dg/lto/pr88077_0.c: Use long to avoid alignment warning.
+ * gcc.dg/lto/pr88077_1.c: Add -fcommon.
+ * gcc.target/aarch64/sve/peel_ind_1.c: Allow ANCHOR0.
+ * gcc.target/aarch64/sve/peel_ind_2.c: Likewise.
+ * gcc.target/aarch64/sve/peel_ind_3.c: Likewise.
+ * gcc.target/i386/volatile-bitfields-2.c: Allow movl or movq.
+
2019-11-20 Richard Biener <rguenther@suse.de>
* gcc.dg/vect/bb-slp-42.c: Adjust.
+/* { dg-options {-fcommon} } */
struct {} admbaserest_; // { dg-lto-message "type of " 2 }
/* { dg-do compile } */
-/* { dg-additional-options "-O2 -fdump-ipa-cgraph" } */
+/* { dg-additional-options "-O2 -fcommon -fdump-ipa-cgraph" } */
/* RTL-level CSE shouldn't introduce LCO (for the string) into varpool */
char *p;
/* Origin: Jonathan Larmour <jifl-bugzilla@jifvik.org> */
/* { dg-do compile { target *-*-linux* *-*-gnu* *-*-uclinux* } } */
-/* { dg-options "-fdata-sections" } */
+/* { dg-options "-fcommon -fdata-sections" } */
int x;
/* { dg-require-alias "" } */
-/* { dg-options "-O2 -fdump-ipa-icf-details" } */
+/* { dg-options "-O2 -fcommon -fdump-ipa-icf-details" } */
int a, b, c, d, e, h, i, j, k, l;
const int f;
-/* { dg-lto-options "-w" } */
+/* { dg-lto-options { {-fcommon -w} {-fcommon} } } */
double i;
int j;
/* { dg-lto-do run } */
-/* { dg-lto-options { { -flto } } } */
+/* { dg-lto-options { { -flto -fcommon } {-fcommon} {-fcommon} {-fcommon} } } */
/* { dg-require-linker-plugin "" } */
/* { dg-extra-ld-options "-fuse-linker-plugin" } */
/* { dg-lto-do run } */
-/* { dg-lto-options "-O3" } */
+/* { dg-lto-options { {-O3 -fcommon} {-fcommon} } } */
/* By C standard Each enumerated type shall be compatible with char, a signed
integer, type, or an unsigned integer type. The choice of type is
/* { dg-lto-do link } */
-/* { dg-lto-options { { -flto -w } } } */
+/* { dg-lto-options { { -fcommon -flto -w } } } */
char s[sizeof (char *)];
int main(void)
/* { dg-lto-do link } */
-int HeaderStr;
+long HeaderStr;
+/* { dg-options {-fcommon} } */
+
char HeaderStr[1];
int main()
}
/* We should operate on aligned vectors. */
-/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, x\n} } } */
+/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, (x|\.LANCHOR0)\n} } } */
/* We should use an induction that starts at -5, with only the last
7 elements of the first iteration being active. */
/* { dg-final { scan-assembler {\tindex\tz[0-9]+\.s, #-5, #5\n} } } */
}
/* We should operate on aligned vectors. */
-/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, x\n} } } */
+/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, (x|\.LANCHOR0)\n} } } */
/* We should unroll the loop three times. */
/* { dg-final { scan-assembler-times "\tst1w\t" 3 } } */
/* { dg-final { scan-assembler {\tptrue\t(p[0-9]+)\.s, vl7\n.*\teor\tp[0-7]\.b, (p[0-7])/z, (\1\.b, \2\.b|\2\.b, \1\.b)\n} } } */
}
/* We should operate on aligned vectors. */
-/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, x\n} } } */
+/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, (x|\.LANCHOR0)\n} } } */
/* { dg-final { scan-assembler {\tubfx\t} } } */
return bits.b;
}
-/* { dg-final { scan-assembler "movl.*bits" } } */
+/* { dg-final { scan-assembler "mov(q|l).*bits" } } */
projects / gcc.git / commitdiff