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Re: [PATCH] Allow fpmath differences in inlining when callee doesn't use FP math


On Thu, 24 Aug 2017, Uros Bizjak wrote:

> On Thu, Aug 24, 2017 at 1:10 PM, Richard Biener <rguenther@suse.de> wrote:
> >
> > This adjusts the x86 backend to allow -mfpmath differences when
> > deciding whether to allow inlining.  -mfpmath doesn't really
> > matter for functions not containing FP operations.
> >
> > It appears that the can_inline_p target hook is called from the
> > C++ FE for multi-versioning, thus the ! ipa_fn_summaries check.
> >
> > Bootstrapped and tested on x86_64-unknown-linux-gnu, ok for trunk?
> >
> > Incidentically this fixes the bootstrap issue I have when enabling
> > free-lang-data without LTO.
> >
> > It doesn't fully solve the fpmath difference issue we have with
> > intrinsics but is an optimization.
> >
> > Thanks,
> > Richard.
> >
> > 2017-08-24  Richard Biener  <rguenther@suse.de>
> >
> >         * config/i386/i386.c: Include symbol-summary.h, ipa-prop.h
> >         and ipa-fnsummary.h.
> >         (ix86_can_inline_p): When ix86_fpmath flags do not match
> >         check whether the callee uses FP math at all.
> 
> LGTM for branches, but for trunk, I'd still like to remove fpmath

Hmm, it should be indeed safe but fp_expression is only available
on the GCC 7 branch.  Might be the only change that doesn't have
the chance to reject code that we previously accepted...

> processing from outside ix86_option_override_internal. As mentioned in
> the comment in i_o_o_i, blindly switching fpmath for TARGET_SSE can
> violate ABI for some environments.

Yeah.  The following has also passed bootstrap & regtest on 
x86_64-unknown-linux-gnu.

Ok for trunk?

Thanks,
Richard.

2017-08-23  Richard Biener  <rguenther@suse.de>

        PR target/81921
        * targhooks.c (default_target_can_inline_p): Properly
        use target_option_default_node when no DECL_FUNCTION_SPECIFIC_TARGET
        is present and always compare.
        * config/i386/i386.c (ix86_valid_target_attribute_tree): Do not
	imply -mfpmath=sse from TARGET_SSE_P.
        (ix86_can_inline_p): Properly use target_option_default_node when
        no DECL_FUNCTION_SPECIFIC_TARGET is present and always compare.

	* gcc.target/i386/pr81921.c: New testcase.

Index: gcc/config/i386/i386.c
===================================================================
--- gcc/config/i386/i386.c	(revision 251270)
+++ gcc/config/i386/i386.c	(working copy)
@@ -7398,16 +7398,6 @@ ix86_valid_target_attribute_tree (tree a
       /* If fpmath= is not set, and we now have sse2 on 32-bit, use it.  */
       if (enum_opts_set.x_ix86_fpmath)
 	opts_set->x_ix86_fpmath = (enum fpmath_unit) 1;
-      else if (!TARGET_64BIT_P (opts->x_ix86_isa_flags)
-	       && TARGET_SSE_P (opts->x_ix86_isa_flags))
-	{
-	  if (TARGET_80387_P (opts->x_target_flags))
-	    opts->x_ix86_fpmath = (enum fpmath_unit) (FPMATH_SSE
-						      | FPMATH_387);
-	  else
-	    opts->x_ix86_fpmath = (enum fpmath_unit) FPMATH_SSE;
-	  opts_set->x_ix86_fpmath = (enum fpmath_unit) 1;
-	}
 
       /* Do any overrides, such as arch=xxx, or tune=xxx support.  */
       bool r = ix86_option_override_internal (false, opts, opts_set);
@@ -7502,53 +7492,47 @@ ix86_valid_target_attribute_p (tree fnde
 static bool
 ix86_can_inline_p (tree caller, tree callee)
 {
-  bool ret = false;
   tree caller_tree = DECL_FUNCTION_SPECIFIC_TARGET (caller);
   tree callee_tree = DECL_FUNCTION_SPECIFIC_TARGET (callee);
-
-  /* If callee has no option attributes, then it is ok to inline.  */
   if (!callee_tree)
-    ret = true;
+    callee_tree = target_option_default_node;
+  if (!caller_tree)
+    caller_tree = target_option_default_node;
+  if (callee_tree == caller_tree)
+    return true;
+
+  struct cl_target_option *caller_opts = TREE_TARGET_OPTION (caller_tree);
+  struct cl_target_option *callee_opts = TREE_TARGET_OPTION (callee_tree);
+  bool ret = false;
 
-  /* If caller has no option attributes, but callee does then it is not ok to
-     inline.  */
-  else if (!caller_tree)
+  /* Callee's isa options should be a subset of the caller's, i.e. a SSE4
+     function can inline a SSE2 function but a SSE2 function can't inline
+     a SSE4 function.  */
+  if (((caller_opts->x_ix86_isa_flags & callee_opts->x_ix86_isa_flags)
+       != callee_opts->x_ix86_isa_flags)
+      || ((caller_opts->x_ix86_isa_flags2 & callee_opts->x_ix86_isa_flags2)
+	  != callee_opts->x_ix86_isa_flags2))
     ret = false;
 
-  else
-    {
-      struct cl_target_option *caller_opts = TREE_TARGET_OPTION (caller_tree);
-      struct cl_target_option *callee_opts = TREE_TARGET_OPTION (callee_tree);
+  /* See if we have the same non-isa options.  */
+  else if (caller_opts->x_target_flags != callee_opts->x_target_flags)
+    ret = false;
 
-      /* Callee's isa options should be a subset of the caller's, i.e. a SSE4
-	 function can inline a SSE2 function but a SSE2 function can't inline
-	 a SSE4 function.  */
-      if (((caller_opts->x_ix86_isa_flags & callee_opts->x_ix86_isa_flags)
-	   != callee_opts->x_ix86_isa_flags)
-	  || ((caller_opts->x_ix86_isa_flags2 & callee_opts->x_ix86_isa_flags2)
-	      != callee_opts->x_ix86_isa_flags2))
-	ret = false;
-
-      /* See if we have the same non-isa options.  */
-      else if (caller_opts->x_target_flags != callee_opts->x_target_flags)
-	ret = false;
-
-      /* See if arch, tune, etc. are the same.  */
-      else if (caller_opts->arch != callee_opts->arch)
-	ret = false;
-
-      else if (caller_opts->tune != callee_opts->tune)
-	ret = false;
+  /* See if arch, tune, etc. are the same.  */
+  else if (caller_opts->arch != callee_opts->arch)
+    ret = false;
 
-      else if (caller_opts->x_ix86_fpmath != callee_opts->x_ix86_fpmath)
-	ret = false;
+  else if (caller_opts->tune != callee_opts->tune)
+    ret = false;
 
-      else if (caller_opts->branch_cost != callee_opts->branch_cost)
-	ret = false;
+  else if (caller_opts->x_ix86_fpmath != callee_opts->x_ix86_fpmath)
+    ret = false;
 
-      else
-	ret = true;
-    }
+  else if (caller_opts->branch_cost != callee_opts->branch_cost)
+    ret = false;
+
+  else
+    ret = true;
 
   return ret;
 }
Index: gcc/targhooks.c
===================================================================
--- gcc/targhooks.c	(revision 251270)
+++ gcc/targhooks.c	(working copy)
@@ -1442,27 +1442,18 @@ default_target_option_pragma_parse (tree
 bool
 default_target_can_inline_p (tree caller, tree callee)
 {
-  bool ret = false;
   tree callee_opts = DECL_FUNCTION_SPECIFIC_TARGET (callee);
   tree caller_opts = DECL_FUNCTION_SPECIFIC_TARGET (caller);
-
-  /* If callee has no option attributes, then it is ok to inline */
-  if (!callee_opts)
-    ret = true;
-
-  /* If caller has no option attributes, but callee does then it is not ok to
-     inline */
-  else if (!caller_opts)
-    ret = false;
+  if (! callee_opts)
+    callee_opts = target_option_default_node;
+  if (! caller_opts)
+    caller_opts = target_option_default_node;
 
   /* If both caller and callee have attributes, assume that if the
      pointer is different, the two functions have different target
      options since build_target_option_node uses a hash table for the
      options.  */
-  else
-    ret = (callee_opts == caller_opts);
-
-  return ret;
+  return callee_opts == caller_opts;
 }
 
 /* If the machine does not have a case insn that compares the bounds,
Index: gcc/testsuite/gcc.target/i386/pr81921.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr81921.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr81921.c	(working copy)
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target lto } */
+/* { dg-options "-flto -march=x86-64" } */
+
+extern __inline int  __attribute__((__gnu_inline__, __always_inline__, __artificial__, target("sse2")))
+_mm_loadu_si128 (int const *__P)
+{
+    return *__P;
+}
+
+void __attribute__((target("ssse3"))) foo (void *p)
+{
+  volatile int x = _mm_loadu_si128 (p);
+}


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