2014-07-01  Jakub Jelinek  <jakub@redhat.com>

	* tree-ssa.c (useless_type_conversion_p_1): If
	lang_hooks.types_compatible_p returns true, but the aggregate
	types have different integer sizes, return false.

--- gcc/tree-ssa.c.jj	2014-04-24 21:34:05.000000000 +0200
+++ gcc/tree-ssa.c	2014-07-01 18:25:34.544656536 +0200
@@ -1520,7 +1520,19 @@ useless_type_conversion_p_1 (tree outer_
 	 have TYPE_STRUCTURAL_EQUALITY_P set.  */
 
       /* ???  This should eventually just return false.  */
-      return lang_hooks.types_compatible_p (inner_type, outer_type);
+      if (!lang_hooks.types_compatible_p (inner_type, outer_type))
+	return false;
+      /* The C FE langhook sometimes returns true even for aggregates
+	 with different size.  Make sure those aren't counted as
+	 useless.  */
+      if (TYPE_SIZE_UNIT (inner_type)
+	  && TYPE_SIZE_UNIT (outer_type)
+	  && TREE_CODE (TYPE_SIZE_UNIT (inner_type)) == INTEGER_CST
+	  && TREE_CODE (TYPE_SIZE_UNIT (outer_type)) == INTEGER_CST
+	  && !tree_int_cst_equal (TYPE_SIZE_UNIT (inner_type),
+				  TYPE_SIZE_UNIT (outer_type)))
+	return false;
+      return true;
     }
   /* Also for functions and possibly other types with
      TYPE_STRUCTURAL_EQUALITY_P set.  */
--- gcc/testsuite/gcc.c-torture/execute/20140701-1.c.jj	2014-03-19 15:57:57.735114622 +0100
+++ gcc/testsuite/gcc.c-torture/execute/20140701-1.c	2014-07-01 18:23:55.996149630 +0200
@@ -0,0 +1,30 @@
+struct S
+{
+  int a[20];
+  int b;
+};
+
+void
+foo (struct S *p)
+{
+  if (p->b != 0xff)
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  struct T
+  {
+    int a[20];
+    int b;
+    int c[10];
+  };
+  struct T d;
+  struct S e;
+  __builtin_memset (&d, 0, sizeof (d));
+  d.b = 0xff;
+  __builtin_memcpy (&e, &d, sizeof (e));
+  foo (&e);
+  return 0;
+}