[backport from gcc-4.8/trunk r191694 <mikpe@it.uu.se>]

gcc/

2012-09-25  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/53663
	* tree-ssa-sccvn.c (vn_reference_lookup_3): Conditional
	native encode/interpret translation on VN_WALKREWRITE.

gcc/testsuite/

2012-09-25  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/53663
	* gcc.dg/torture/pr53663-1.c: New testcase.
	* gcc.dg/torture/pr53663-2.c: Likewise.
	* gcc.dg/torture/pr53663-3.c: Likewise.

--- gcc-4.7.2/gcc/testsuite/gcc.dg/torture/pr53663-1.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.2/gcc/testsuite/gcc.dg/torture/pr53663-1.c	2012-09-29 16:16:17.000000000 +0200
@@ -0,0 +1,30 @@
+/* { dg-do run } */
+
+extern void abort (void);
+
+union u
+{
+  int i;
+  _Bool b;
+};
+
+void f(union u * vp, union u v)
+{
+  *vp = v;
+}
+
+int main()
+{
+  union u v;
+  union u v1;
+  union u v2;
+
+  v.i = 10;
+  f(&v1, v);
+
+  v.b = 0;
+  f(&v2, v);
+  if (v2.b != 0)
+    abort ();
+  return 0;
+}
--- gcc-4.7.2/gcc/testsuite/gcc.dg/torture/pr53663-2.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.2/gcc/testsuite/gcc.dg/torture/pr53663-2.c	2012-09-29 16:16:17.000000000 +0200
@@ -0,0 +1,24 @@
+/* { dg-do run } */
+
+extern void abort (void);
+
+union u
+{
+  int i;
+  short f;
+} v;
+
+short foo (short *f)
+{
+  *f = 1;
+  v.i = 0;
+  v.f = 0;
+  return *f;
+}
+
+int main()
+{
+  if (foo (&v.f) != 0)
+    abort ();
+  return 0;
+}
--- gcc-4.7.2/gcc/testsuite/gcc.dg/torture/pr53663-3.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.2/gcc/testsuite/gcc.dg/torture/pr53663-3.c	2012-09-29 16:16:17.000000000 +0200
@@ -0,0 +1,24 @@
+/* { dg-do run } */
+
+extern void abort (void);
+
+union u
+{
+  int i;
+  float f;
+} v;
+
+float foo (float *f)
+{
+  *f = 1;
+  v.i = 0;
+  v.f = 0.;
+  return *f;
+}
+
+int main()
+{
+  if (foo (&v.f) != 0.)
+    abort ();
+  return 0;
+}
--- gcc-4.7.2/gcc/tree-ssa-sccvn.c.~1~	2012-08-21 15:34:19.000000000 +0200
+++ gcc-4.7.2/gcc/tree-ssa-sccvn.c	2012-09-29 16:16:17.000000000 +0200
@@ -1484,7 +1484,8 @@ vn_reference_lookup_3 (ao_ref *ref, tree
 
   /* 3) Assignment from a constant.  We can use folds native encode/interpret
      routines to extract the assigned bits.  */
-  else if (CHAR_BIT == 8 && BITS_PER_UNIT == 8
+  else if (vn_walk_kind == VN_WALKREWRITE
+	   && CHAR_BIT == 8 && BITS_PER_UNIT == 8
 	   && ref->size == maxsize
 	   && maxsize % BITS_PER_UNIT == 0
 	   && offset % BITS_PER_UNIT == 0