[partial backport of gcc-4.8.1 r199179 <mikpe@it.uu.se>]

gcc/

2013-05-22  Richard Biener  <rguenther@suse.de>

	Backport from mainline
	2013-05-21  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/57303
	* tree-ssa-sink.c (statement_sink_location): Properly handle
	self-assignments.

gcc/testsuite/

2013-05-22  Richard Biener  <rguenther@suse.de>

	Backport from mainline
	2013-05-21  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/57303
	* gcc.dg/torture/pr57303.c: New testcase.

--- gcc-4.7.3/gcc/testsuite/gcc.dg/torture/pr57303.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.3/gcc/testsuite/gcc.dg/torture/pr57303.c	2013-06-16 14:15:07.954607303 +0200
@@ -0,0 +1,33 @@
+/* { dg-do run } */
+
+void abort (void);
+
+struct S0
+{
+  int f0;
+};
+struct S1
+{
+  struct S0 f0;
+};
+
+struct S1 x = { {0} };
+struct S1 y = { {1} };
+
+static void
+foo (struct S0 p)
+{
+  struct S0 *l = &y.f0;
+  *l = x.f0;
+  if (p.f0)
+    *l = *l;
+}
+
+int
+main ()
+{
+  foo(y.f0);
+  if (y.f0.f0 != 0)
+    abort ();
+  return 0;
+}
--- gcc-4.7.3/gcc/tree-ssa-sink.c.~1~	2011-10-26 15:26:50.000000000 +0200
+++ gcc-4.7.3/gcc/tree-ssa-sink.c	2013-06-16 14:15:07.954607303 +0200
@@ -412,7 +412,15 @@ statement_sink_location (gimple stmt, ba
 	      && gimple_vdef (use_stmt)
 	      && operand_equal_p (gimple_assign_lhs (stmt),
 				  gimple_assign_lhs (use_stmt), 0))
-	    continue;
+	    {
+	      /* If use_stmt is or might be a nop assignment then USE_STMT
+		 acts as a use as well as definition.  */
+	      if (stmt != use_stmt
+		  && ref_maybe_used_by_stmt_p (use_stmt,
+					       gimple_assign_lhs (stmt)))
+		return false;
+	      continue;
+	    }
 
 	  if (gimple_code (use_stmt) != GIMPLE_PHI)
 	    return false;