PR inline-asm/52813 revisited

The original patch for this PR made it an error to list the stack
pointer in the clobber list of an inline asm.  However, the general
feeling seemed to be that going straight to a hard error was too harsh,
since there's quite a bit of existing code that has the clobber.

This patch implements the compromise discussed on IRC of making it
a -Wdeprecated warning instead.

2019-01-15  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR inline-asm/52813
	* doc/extend.texi: Document that listing the stack pointer in the
	clobber list of an asm is a deprecated feature.
	* common.opt (Wdeprecated): Moved from c-family/c.opt.
	* cfgexpand.c (asm_clobber_reg_is_valid): Issue a -Wdeprecated
	warning instead of an error for clobbers of the stack pointer.
	Add a note explaining why.

gcc/c-family/
	PR inline-asm/52813
	* c.opt (Wdeprecated): Move documentation and variable to common.opt.

gcc/d/
	PR inline-asm/52813
	* lang.opt (Wdeprecated): Reference common.opt instead of c.opt.

gcc/testsuite/
	PR inline-asm/52813
	* gcc.target/i386/pr52813.c (test1): Turn the diagnostic into a
	-Wdeprecated warning and expect a following note:.

From-SVN: r267941

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index c3b9f14de520dc215cd36643c6a91d35b0e83ef4..83d4fa4af0c61848fe8e33ca66c2593790cba650 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2019-01-15  Richard Sandiford  <richard.sandiford@arm.com>
+
+       PR inline-asm/52813
+       * doc/extend.texi: Document that listing the stack pointer in the
+       clobber list of an asm is a deprecated feature.
+       * common.opt (Wdeprecated): Moved from c-family/c.opt.
+       * cfgexpand.c (asm_clobber_reg_is_valid): Issue a -Wdeprecated
+       warning instead of an error for clobbers of the stack pointer.
+       Add a note explaining why.
+
 2019-01-15  Richard Biener  <rguenther@suse.de>
 
        PR debug/88046

diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index 10e5cc131e980b240a282a66a3a6e33657d61be9..03ea65b4bce40b43f6993f726fd00d8079abfa69 100644 (file)
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,8 @@
+2019-01-15  Richard Sandiford  <richard.sandiford@arm.com>
+
+       PR inline-asm/52813
+       * c.opt (Wdeprecated): Move documentation and variable to common.opt.
+
 2019-01-14  Jakub Jelinek  <jakub@redhat.com>
 
        * c-cppbuiltin.c (c_cpp_builtin): Define __cpp_guaranteed_copy_elision

diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 858beff53d6dd2bc39e6fd42048eaabbcfa16db4..88c72c51c210f99d86ecf765684832483836280e 100644 (file)
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -477,8 +477,8 @@ C++ ObjC++ Var(warn_delnonvdtor) Warning LangEnabledBy(C++ ObjC++,Wall || Weffc+
 Warn about deleting polymorphic objects with non-virtual destructors.
 
 Wdeprecated
-C C++ ObjC ObjC++ CPP(cpp_warn_deprecated) CppReason(CPP_W_DEPRECATED) Var(warn_deprecated) Init(1) Warning
-Warn if a deprecated compiler feature, class, method, or field is used.
+C C++ ObjC ObjC++ CPP(cpp_warn_deprecated) CppReason(CPP_W_DEPRECATED)
+; Documented in common.opt
 
 Wdeprecated-copy
 C++ ObjC++ Var(warn_deprecated_copy) Warning LangEnabledBy(C++ ObjC++, Wextra)

diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index 3b7a6e59c3bd9a908a62efeaebcf7371fb194dcf..2337c6312d01d525d14a73ae9463743176a1c28e 100644 (file)
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -2872,12 +2872,16 @@ asm_clobber_reg_is_valid (int regno, int nregs, const char *regname)
       error ("PIC register clobbered by %qs in %<asm%>", regname);
       is_valid = false;
     }
-  /* Clobbering the STACK POINTER register is an error.  */
-  if (overlaps_hard_reg_set_p (regset, Pmode, STACK_POINTER_REGNUM))
-    {
-      error ("Stack Pointer register clobbered by %qs in %<asm%>", regname);
-      is_valid = false;
-    }
+  /* Clobbering the stack pointer register is deprecated.  GCC expects
+     the value of the stack pointer after an asm statement to be the same
+     as it was before, so no asm can validly clobber the stack pointer in
+     the usual sense.  Adding the stack pointer to the clobber list has
+     traditionally had some undocumented and somewhat obscure side-effects.  */
+  if (overlaps_hard_reg_set_p (regset, Pmode, STACK_POINTER_REGNUM)
+      && warning (OPT_Wdeprecated, "listing the stack pointer register"
+                 " %qs in a clobber list is deprecated", regname))
+    inform (input_location, "the value of the stack pointer after an %<asm%>"
+           " statement must be the same as it was before the statement");
 
   return is_valid;
 }

diff --git a/gcc/common.opt b/gcc/common.opt
index 035f2ba7dec11da696ab602ed0ee78b1962951c7..9a5e9af06ca002e7c17bc65a6cda6ad0fc3d48d8 100644 (file)
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -579,6 +579,10 @@ Wattribute-warning
 Common Var(warn_attribute_warning) Init(1) Warning
 Warn about uses of __attribute__((warning)) declarations.
 
+Wdeprecated
+Common Var(warn_deprecated) Init(1) Warning
+Warn if a deprecated compiler feature, class, method, or field is used.
+
 Wdeprecated-declarations
 Common Var(warn_deprecated_decl) Init(1) Warning
 Warn about uses of __attribute__((deprecated)) declarations.

diff --git a/gcc/d/ChangeLog b/gcc/d/ChangeLog
index 6fa01f57897b7509ef57086e36d36d71ba21b1e7..974b098226819804583208799d91cc98fa69be4e 100644 (file)
--- a/gcc/d/ChangeLog
+++ b/gcc/d/ChangeLog
@@ -1,3 +1,8 @@
+2019-01-15  Richard Sandiford  <richard.sandiford@arm.com>
+
+       PR inline-asm/52813
+       * lang.opt (Wdeprecated): Reference common.opt instead of c.opt.
+
 2019-01-12  Iain Buclaw  <ibuclaw@gdcproject.org>
 
        * README.gcc: New file.

diff --git a/gcc/d/lang.opt b/gcc/d/lang.opt
index 52ddd77f2cad322dd05dc046d3b64d5af4d8c5ee..83d3d21a1a68b2da753ff572b7f894ea35ded615 100644 (file)
--- a/gcc/d/lang.opt
+++ b/gcc/d/lang.opt
@@ -124,7 +124,7 @@ Warn about casts that will produce a null result.
 
 Wdeprecated
 D
-; Documented in C
+; Documented in common.opt
 
 Werror
 D

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index c81092dfe0c25c2e0580f29bb1ca790e961f20e2..eb1cde492c8a618c9778d8f75455e8f7443f2340 100644 (file)
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -9441,6 +9441,15 @@ 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.
 
+Another restriction is that the clobber list should not contain the
+stack pointer register.  This is because the compiler requires the
+value of the stack pointer to be the same after an @code{asm}
+statement as it was on entry to the statement.  However, previous
+versions of GCC did not enforce this rule and allowed the stack
+pointer to appear in the list, with unclear semantics.  This behavior
+is deprecated and listing the stack pointer may become an error in
+future versions of GCC@.
+
 Here is a realistic example for the VAX showing the use of clobbered 
 registers: 
 

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 1b0689d5ea20a36842222579662dfe899b20e1ab..e4fbb15dfeffb7485cc1c4596d1b76203f6427a5 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2019-01-15  Richard Sandiford  <richard.sandiford@arm.com>
+
+       PR inline-asm/52813
+       * gcc.target/i386/pr52813.c (test1): Turn the diagnostic into a
+       -Wdeprecated warning and expect a following note:.
+
 2019-01-15  Richard Biener  <rguenther@suse.de>
 
        PR debug/88046

diff --git a/gcc/testsuite/gcc.target/i386/pr52813.c b/gcc/testsuite/gcc.target/i386/pr52813.c
index 154ebbfc4233dbcfb7987877a1e400e4b1c555f6..8772cfb0aee2f2b36d3db196c147c6099b78c135 100644 (file)
--- a/gcc/testsuite/gcc.target/i386/pr52813.c
+++ b/gcc/testsuite/gcc.target/i386/pr52813.c
@@ -5,5 +5,6 @@
 void
 test1 (void)
 {
-  asm volatile ("" : : : "%esp"); /* { dg-error "Stack Pointer register clobbered" } */
+  asm volatile ("" : : : "%esp"); /* { dg-warning "listing the stack pointer register '%esp' in a clobber list is deprecated" } */
+  /* { dg-message "note: the value of the stack pointer after an 'asm' statement must be the same as it was before the statement" "" { target *-*-* } .-1 } */
 }