[backport from gcc-4.7/trunk <mikpe@it.uu.se>]

gcc/

2011-05-23  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/49115
	* tree-ssa-alias.c (stmt_kills_ref_p_1): If the assignment
	is not necessarily carried out, do not claim it kills the ref.
	* tree-ssa-dce.c (mark_aliased_reaching_defs_necessary_1): Likewise.

gcc/testsuite/

2011-05-23  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/49115
	* g++.dg/torture/pr49115.C: New testcase.

--- gcc-4.6.0/gcc/testsuite/g++.dg/torture/pr49115.C.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.6.0/gcc/testsuite/g++.dg/torture/pr49115.C	2011-05-23 21:50:58.000000000 +0200
@@ -0,0 +1,25 @@
+// { dg-do run }
+
+extern "C" void abort (void);
+struct MyException {};
+struct Data {
+    int nr;
+    Data() : nr(66) {}
+};
+Data __attribute__((noinline,noclone)) getData(int i)
+{
+  if (i) throw MyException();
+  Data data;
+  data.nr = i;
+  return data;
+}
+int main(int, char **)
+{
+  Data data;
+  try {
+      data = getData(1);
+  } catch (MyException& e) {
+      if (data.nr != 66)
+	abort ();
+  }
+}
--- gcc-4.6.0/gcc/tree-ssa-alias.c.~1~	2011-03-03 13:10:40.000000000 +0100
+++ gcc-4.6.0/gcc/tree-ssa-alias.c	2011-05-23 21:50:58.000000000 +0200
@@ -1607,7 +1607,14 @@ static bool
 stmt_kills_ref_p_1 (gimple stmt, ao_ref *ref)
 {
   if (gimple_has_lhs (stmt)
-      && TREE_CODE (gimple_get_lhs (stmt)) != SSA_NAME)
+      && TREE_CODE (gimple_get_lhs (stmt)) != SSA_NAME
+      /* The assignment is not necessarily carried out if it can throw
+	 and we can catch it in the current function where we could inspect
+	 the previous value.
+	 ???  We only need to care about the RHS throwing.  For aggregate
+	 assignments or similar calls and non-call exceptions the LHS
+	 might throw as well.  */
+      && !stmt_can_throw_internal (stmt))
     {
       tree base, lhs = gimple_get_lhs (stmt);
       HOST_WIDE_INT size, offset, max_size;
--- gcc-4.6.0/gcc/tree-ssa-dce.c.~1~	2010-11-17 11:43:21.000000000 +0100
+++ gcc-4.6.0/gcc/tree-ssa-dce.c	2011-05-23 21:50:58.000000000 +0200
@@ -529,7 +529,14 @@ mark_aliased_reaching_defs_necessary_1 (
 
   /* If the stmt lhs kills ref, then we can stop walking.  */
   if (gimple_has_lhs (def_stmt)
-      && TREE_CODE (gimple_get_lhs (def_stmt)) != SSA_NAME)
+      && TREE_CODE (gimple_get_lhs (def_stmt)) != SSA_NAME
+      /* The assignment is not necessarily carried out if it can throw
+         and we can catch it in the current function where we could inspect
+	 the previous value.
+         ???  We only need to care about the RHS throwing.  For aggregate
+	 assignments or similar calls and non-call exceptions the LHS
+	 might throw as well.  */
+      && !stmt_can_throw_internal (def_stmt))
     {
       tree base, lhs = gimple_get_lhs (def_stmt);
       HOST_WIDE_INT size, offset, max_size;