[PATCH, dataflow]: Fix PR55845, 454.calculix miscompares on x86 AVX due to movement of vzeroupper

[Uros Bizjak <ubizjak@gmail.com>]

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Hello!

Attached patch fixes runtime comparison failure of 454.calculix due to
wrong movement of vzeroupper in jump2 pass. It turns out, that
can_move_insns_accross function does not special-case
unspec_volatiles, so vzeroupper is allowed to pass various 256bit avx
instructions.

The patch rejects moves of unspec_volatile insns in can_move_insn_accross.

2012-01-06  Uros Bizjak  <ubizjak@gmail.com>

	PR rtl-optimization/55845
	* df-problems.c (can_move_insns_across): Stop scanning at
	unspec_volatile source instruction.

2012-01-06  Uros Bizjak  <ubizjak@gmail.com>
	    Vladimir Yakovlev  <vladimir.b.yakovlev@intel.com>

	PR rtl-optimization/55845
	* gcc.target/i386/pr55845.c: New test.

Bootstrapped and regression tested on x86_64-pc-linux-gnu {,-m32} AVX target.

OK for mainline and 4.7 branch?

Uros.

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Index: df-problems.c
===================================================================
--- df-problems.c	(revision 194945)
+++ df-problems.c	(working copy)
@@ -3916,6 +3916,10 @@ can_move_insns_across (rtx from, rtx to, rtx acros
 	break;
       if (NONDEBUG_INSN_P (insn))
 	{
+	  /* Do not move unspec_volatile insns.  */
+	  if (GET_CODE (PATTERN (insn)) == UNSPEC_VOLATILE)
+	    break;
+
 	  if (may_trap_or_fault_p (PATTERN (insn))
 	      && (trapping_insns_in_across || other_branch_live != NULL))
 	    break;
Index: testsuite/gcc.target/i386/pr55845.c
===================================================================
--- testsuite/gcc.target/i386/pr55845.c	(revision 0)
+++ testsuite/gcc.target/i386/pr55845.c	(working copy)
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target avx } */
+/* { dg-options "-O3 -ffast-math -fschedule-insns -mavx -mvzeroupper" } */
+
+#include "avx-check.h"
+
+#define N 100
+
+double
+__attribute__((noinline))
+foo (int size, double y[], double x[])
+{
+  double sum = 0.0;
+  int i;
+  for (i = 0, sum = 0.; i < size; i++)
+    sum += y[i] * x[i];
+  return (sum);
+}
+
+static void
+__attribute__ ((noinline))
+avx_test ()
+{
+  double x[N];
+  double y[N];
+  double s;
+  int i;
+
+  for (i = 0; i < N; i++)
+    {
+      x[i] = i;
+      y[i] = i;
+    }
+
+  s = foo (N, y, x);
+
+  if (s != 328350.0)
+    abort ();
+}