[PATCH] fwprop: Avoid volatile defines to be propagated

[HAO CHEN GUI]

Hi,
  This patch tries to fix a potential problem which is raised by the patch
for PR111267. The volatile asm operand tries to be propagated to a single
set insn with the patch for PR111267. It has potential risk as the behavior
is wrong. Currently set_src_cost comparison can reject such propagation.
But the propagation might be taken after replacing set_src_cost with insn
cost. Actually I found the problem in testing my patch which replacing
et_src_cost with insn cost for fwprop.

  Bootstrapped and tested on x86 and powerpc64-linux BE and LE with no
regressions. Is it OK for the trunk?

Thanks
Gui Haochen

ChangeLog
fwprop: Avoid volatile defines to be propagated

The patch for PR111267 (commit id 86de9b66480b710202a2898cf513db105d8c432f)
which introduces an exception for propagation on single set insn.  The
propagation which might not be profitable (checked by profitable_p) is still
allowed to be propagated to single set insn.  It has a potential problem
that a volatile asm operand will try to be propagated to a single set insn.
The volatile asm operand is originally banned in profitable_p.  This patch
fixes the problem by skipping volatile set source in define set finding.

gcc/
        * fwprop.cc (forward_propagate_into): Return false for volatile set
        source.

gcc/testsuite/
        * gcc.target/powerpc/fwprop-1.c: New.

patch.diff
diff --git a/gcc/fwprop.cc b/gcc/fwprop.cc
index 7872609b336..89dce88b43d 100644
--- a/gcc/fwprop.cc
+++ b/gcc/fwprop.cc
@@ -854,6 +854,8 @@ forward_propagate_into (use_info *use, bool reg_prop_only = 
false)

   rtx dest = SET_DEST (def_set);
   rtx src = SET_SRC (def_set);
+  if (volatile_insn_p (src))
+    return false;

   /* Allow propagations into a loop only for reg-to-reg copies, since
      replacing one register by another shouldn't increase the cost.
diff --git a/gcc/testsuite/gcc.target/powerpc/fwprop-1.c 
b/gcc/testsuite/gcc.target/powerpc/fwprop-1.c
new file mode 100644
index 00000000000..07b207f980c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/fwprop-1.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-rtl-fwprop1-details" } */
+/* { dg-final { scan-rtl-dump-not "propagating insn" "fwprop1" } } */
+
+/* Verify that volatile asm operands doesn't try to be propagated.  */
+long long foo ()
+{
+  long long res;
+  __asm__ __volatile__(
+    ""
+      : "=r" (res)
+      :
+      : "memory");
+  return res;
+}