PR tree-optimization/78162: Reject negative offsets in store merging early

	PR tree-optimization/78162
	* gimple-ssa-store-merging.c (execute): Mark stores with bitpos < 0
	as invalid.

	* gcc.c-torture/compile/pr78162.c: New test.

From-SVN: r241778

gcc/ChangeLog

 2016-11-02  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
+	PR tree-optimization/78162
+	* gimple-ssa-store-merging.c (execute): Mark stores with bitpos < 0
+	as invalid.
+
+2016-11-02  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
 	* config/aarch64/aarch64.c (aarch64_register_saved_on_entry): Add
 	function comment.
 	(aarch64_next_callee_save): Likewise.

gcc/gimple-ssa-store-merging.c

@@ -1361,7 +1361,7 @@ pass_store_merging::execute (function *fun)
 				       &unsignedp, &reversep, &volatilep);
 	      /* As a future enhancement we could handle stores with the same
 		 base and offset.  */
-	      bool invalid = offset || reversep
+	      bool invalid = offset || reversep || bitpos < 0
 			     || ((bitsize > MAX_BITSIZE_MODE_ANY_INT)
 				  && (TREE_CODE (rhs) != INTEGER_CST))
 			     || !rhs_valid_for_store_merging_p (rhs)

gcc/testsuite/ChangeLog

+2016-11-02  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
+	PR tree-optimization/78162
+	* gcc.c-torture/compile/pr78162.c: New test.
+
 2016-11-02  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/78035

gcc/testsuite/gcc.c-torture/compile/pr78162.c

+/* PR tree-optimization/78162.
+   Handle negative offsets in store merging gracefully.  */
+
+int a, b[1][2];
+
+void fn1()
+{
+  for (a = 0; a < 2; a++)
+    b[-1][a] = 0;
+}