[PATCH] x86: allow to suppress default clobbers added to asm()s

["Jan Beulich" <JBeulich at suse dot com>]

While it always seemed wrong to me that there's no way to avoid the
default "flags" and "fpsr" clobbers, the regression the fix for
PR/60663 introduced (see PR/63637) makes it even more desirable to have
such a mechanism: This way, at least asm()s with a single output and no
explicit clobbers can again be made subject to CSE.

gcc:
2014-10-31  Jan Beulich  <jbeulich@suse.com>

	* config/i386/i386.c (ix86_target_string): Add
	-mno-default-asm-clobbers.
	(ix86_valid_target_attribute_inner_p): Handle
	-m{,no-}default-asm-clobbers.
	(ix86_md_asm_clobbers): Handle "inverse" clobbers.
	* config/i386/i386.h (NOCC_REGNUM, NOFPSR_REGNUM): Define.
	(ADDITIONAL_REGISTER_NAMES): Add "cc", "!cc", "!flags", and
	"!fpsr".
	* config/i386/i386.opt: Add mdefault-asm-clobbers and
	mno-default-asm-clobbers.
	* varasm.c (decode_reg_name_and_count): Permit negative
	register numbers in ADDITIONAL_REGISTER_NAMES.

gcc/testsuite:
2014-10-31  Jan Beulich  <jbeulich@suse.com>

	* gcc.target/i386/20060218-1.c: Adjust expected error.
	* gcc.target/i386/invclbr[123].c: New.

--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -2664,6 +2664,7 @@ ix86_target_string (HOST_WIDE_INT isa, i
     { "-minline-stringops-dynamically",	MASK_INLINE_STRINGOPS_DYNAMICALLY },
     { "-mms-bitfields",			MASK_MS_BITFIELD_LAYOUT },
     { "-mno-align-stringops",		MASK_NO_ALIGN_STRINGOPS },
+    { "-mno-default-asm-clobbers",	MASK_NO_DEFAULT_ASM_CLOBBERS },
     { "-mno-fancy-math-387",		MASK_NO_FANCY_MATH_387 },
     { "-mno-push-args",			MASK_NO_PUSH_ARGS },
     { "-mno-red-zone",			MASK_NO_RED_ZONE },
@@ -4649,6 +4650,10 @@ ix86_valid_target_attribute_inner_p (tre
 		  OPT_mno_align_stringops,
 		  MASK_NO_ALIGN_STRINGOPS),
 
+    IX86_ATTR_NO ("default-asm-clobbers",
+		  OPT_mno_default_asm_clobbers,
+		  MASK_NO_DEFAULT_ASM_CLOBBERS),
+
     IX86_ATTR_YES ("recip",
 		   OPT_mrecip,
 		   MASK_RECIP),
@@ -44165,10 +44170,31 @@ ix86_c_mode_for_suffix (char suffix)
 static tree
 ix86_md_asm_clobbers (tree, tree, tree clobbers)
 {
-  clobbers = tree_cons (NULL_TREE, build_string (5, "flags"),
-			clobbers);
-  clobbers = tree_cons (NULL_TREE, build_string (4, "fpsr"),
-			clobbers);
+  tree clobber;
+  bool flags_used = false, fpsr_used = false;
+  bool nocc_used = false, nofpsr_used = false;
+
+  if (!TARGET_DEFAULT_ASM_CLOBBERS)
+    return clobbers;
+
+  for (clobber = clobbers; clobber; clobber = TREE_CHAIN (clobber))
+    switch (decode_reg_name (TREE_STRING_POINTER (TREE_VALUE (clobber))))
+      {
+      case FLAGS_REG:     flags_used  = true; break;
+      case FPSR_REG:      fpsr_used   = true; break;
+      case NOCC_REGNUM:   nocc_used   = true; break;
+      case NOFPSR_REGNUM: nofpsr_used = true; break;
+      }
+
+  if ((flags_used && nocc_used) || (fpsr_used && nofpsr_used))
+    error ("conflicting clobbers in %<asm%>");
+
+  if (!flags_used && !nocc_used)
+    clobbers = tree_cons (NULL_TREE, build_string (5, "flags"),
+			  clobbers);
+  if (!fpsr_used && !nofpsr_used)
+    clobbers = tree_cons (NULL_TREE, build_string (4, "fpsr"),
+			  clobbers);
   return clobbers;
 }
 
--- a/gcc/config/i386/i386.h
+++ b/gcc/config/i386/i386.h
@@ -1242,6 +1242,11 @@ extern const char *host_detect_local_cpu
      ? INVALID_REGNUM							\
      : REAL_PIC_OFFSET_TABLE_REGNUM)
 
+/* Fake register numbers to be used as "inverse" asm() clobber specifiers.
+   Any negative numbers below the range used by decode_reg_name () will do.  */
+#define NOCC_REGNUM   (-127)
+#define NOFPSR_REGNUM (-126)
+
 #define GOT_SYMBOL_NAME "_GLOBAL_OFFSET_TABLE_"
 
 /* This is overridden by <cygwin.h>.  */
@@ -2059,7 +2064,9 @@ do {							\
   { "zmm16", 53}, { "zmm17", 54}, { "zmm18", 55}, { "zmm19", 56},	\
   { "zmm20", 57}, { "zmm21", 58}, { "zmm22", 59}, { "zmm23", 60},	\
   { "zmm24", 61}, { "zmm25", 62}, { "zmm26", 63}, { "zmm27", 64},	\
-  { "zmm28", 65}, { "zmm29", 66}, { "zmm30", 67}, { "zmm31", 68} }
+  { "zmm28", 65}, { "zmm29", 66}, { "zmm30", 67}, { "zmm31", 68},	\
+  { "cc", FLAGS_REG }, { "!cc", NOCC_REGNUM },				\
+  { "!flags", NOCC_REGNUM }, { "!fpsr", NOFPSR_REGNUM } }
 
 /* Note we are omitting these since currently I don't know how
 to get gcc to use these, since they want the same but different
--- a/gcc/config/i386/i386.opt
+++ b/gcc/config/i386/i386.opt
@@ -287,6 +287,10 @@ Enum(pmode) String(long) Value(PMODE_DI)
 mcpu=
 Target RejectNegative Joined Undocumented Alias(mtune=) Warn(%<-mcpu=%> is deprecated; use %<-mtune=%> or %<-march=%> instead)
 
+mdefault-asm-clobbers
+Target RejectNegative Report InverseMask(NO_DEFAULT_ASM_CLOBBERS, DEFAULT_ASM_CLOBBERS) Undocumented Save
+Attach compatibility clobbers (flags and fpsr) to every asm().
+
 mfancy-math-387
 Target RejectNegative Report InverseMask(NO_FANCY_MATH_387, USE_FANCY_MATH_387) Save
 Generate sin, cos, sqrt for FPU
@@ -355,6 +359,10 @@ Use native (MS) bitfield layout
 mno-align-stringops
 Target RejectNegative Report Mask(NO_ALIGN_STRINGOPS) Undocumented Save
 
+mno-default-asm-clobbers
+Target RejectNegative Report Mask(NO_DEFAULT_ASM_CLOBBERS) Save
+Don't attach compatibility clobbers (flags and fpsr) to every asm().
+
 mno-fancy-math-387
 Target RejectNegative Report Mask(NO_FANCY_MATH_387) Undocumented Save
 
--- a/gcc/testsuite/gcc.target/i386/20060218-1.c
+++ b/gcc/testsuite/gcc.target/i386/20060218-1.c
@@ -3,6 +3,6 @@
 void
 foo (void)
 {
-  register int cc __asm ("cc"); /* { dg-error "invalid register name" } */
+  register int cc __asm ("cc"); /* { dg-error "register specified .* not general enough" } */
   __asm ("" : : "r" (cc) : "cc");
 }
--- a/gcc/testsuite/gcc.target/i386/invclbr1.c
+++ b/gcc/testsuite/gcc.target/i386/invclbr1.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+void test(void)
+{
+  asm ("" ::: "cc" );
+  asm ("" ::: "!cc" );
+  asm ("" ::: "flags" );
+  asm ("" ::: "!flags" );
+  asm ("" ::: "fpsr" );
+  asm ("" ::: "!fpsr" );
+
+  asm ("" ::: "cc", "!cc" );		/* { dg-error "conflicting clobbers" } */
+  asm ("" ::: "flags", "!cc" );		/* { dg-error "conflicting clobbers" } */
+  asm ("" ::: "cc", "!flags" );		/* { dg-error "conflicting clobbers" } */
+  asm ("" ::: "flags", "!flags" );	/* { dg-error "conflicting clobbers" } */
+  asm ("" ::: "fpsr", "!fpsr" );	/* { dg-error "conflicting clobbers" } */
+
+  asm ("" ::: "cc", "!fpsr" );
+  asm ("" ::: "flags", "!fpsr" );
+  asm ("" ::: "fpsr", "!flags" );
+  asm ("" ::: "fpsr", "!cc" );
+}
--- a/gcc/testsuite/gcc.target/i386/invclbr2.c
+++ b/gcc/testsuite/gcc.target/i386/invclbr2.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-rtl-expand" } */
+
+void test(void)
+{
+  asm ("" ::: "!cc", "!fpsr" );
+  asm ("" ::: "!fpsr", "!flags" );
+}
+
+/* { dg-final { scan-rtl-dump-not "clobber" "expand" } } */
+/* { dg-final { cleanup-rtl-dump "expand" } } */
--- a/gcc/testsuite/gcc.target/i386/invclbr3.c
+++ b/gcc/testsuite/gcc.target/i386/invclbr3.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-rtl-expand" } */
+
+void test(void)
+{
+  asm ("" ::: "!cc");
+  asm ("" ::: "!flags");
+  asm ("" ::: "!fpsr");
+}
+
+/* { dg-final { scan-rtl-dump-times "\\(clobber \\(reg\[^()\]* fpsr\\)\\)" 2 "expand" } } */
+/* { dg-final { scan-rtl-dump-times "\\(clobber \\(reg\[^()\]* flags\\)\\)" 1 "expand" } } */
+/* { dg-final { cleanup-rtl-dump "expand" } } */
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -936,7 +936,7 @@ decode_reg_name_and_count (const char *a
 	for (i = 0; i < (int) ARRAY_SIZE (table); i++)
 	  if (table[i].name[0]
 	      && ! strcmp (asmspec, table[i].name)
-	      && reg_names[table[i].number][0])
+	      && (table[i].number < 0 || reg_names[table[i].number][0]))
 	    return table[i].number;
       }
 #endif /* ADDITIONAL_REGISTER_NAMES */

Attachment: gcc-trunk-x86-no-default-asm-clobbers.patch
Description: Text document