re PR middle-end/69845 (Expression getting incorrectly optimized after being rewritten by compiler)

2016-03-24  Richard Henderson  <rth@redhat.com>

	PR middle-end/69845
	* fold-const.c (extract_muldiv_1): Correct test for multiplication
	overflow.

	PR middle-end/69845
	* gcc.dg/tree-ssa/pr69845-1.c: New test.
	* gcc.dg/tree-ssa/pr69845-2.c: New test.

From-SVN: r234462

gcc/ChangeLog

+2016-03-24  Richard Henderson  <rth@redhat.com>
+
+        PR middle-end/69845
+	* fold-const.c (extract_muldiv_1): Correct test for multiplication
+	overflow.
+
 2016-03-24  Uros Bizjak  <ubizjak@gmail.com>
 
 	* config/i386/i386.md (*anddi3_doubleword): Generate AND insn

gcc/fold-const.c

@@ -6116,11 +6116,9 @@ extract_muldiv_1 (tree t, tree c, enum tree_code code, tree wide_type,
 	{
 	  tree tem = const_binop (code, fold_convert (ctype, t),
 				  fold_convert (ctype, c));
-	  /* If the multiplication overflowed to INT_MIN then we lost sign
-	     information on it and a subsequent multiplication might
-	     spuriously overflow.  See PR68142.  */
-	  if (TREE_OVERFLOW (tem)
-	      && wi::eq_p (tem, wi::min_value (TYPE_PRECISION (ctype), SIGNED)))
+	  /* If the multiplication overflowed, we lost information on it.
+	     See PR68142 and PR69845.  */
+	  if (TREE_OVERFLOW (tem))
 	    return NULL_TREE;
 	  return tem;
 	}

gcc/testsuite/ChangeLog

+2016-03-24  Richard Henderson  <rth@redhat.com>
+
+	PR middle-end/69845
+	* gcc.dg/tree-ssa/pr69845-1.c: New test.
+	* gcc.dg/tree-ssa/pr69845-2.c: New test.
+
 2016-03-24  Tom de Vries  <tom@codesourcery.com>
 
 	* gfortran.dg/goacc/host_data-tree.f95: Add missing initialization.

gcc/testsuite/gcc.dg/tree-ssa/pr69845-1.c

+/* { dg-do compile } */
+/* { dg-require-effective-target int32 } */
+/* { dg-options "-O -fdump-tree-gimple -fdump-tree-optimized" } */
+
+int
+main ()
+{
+  struct S { char s; } v;
+  v.s = 47;
+  int a = (int) v.s;
+  int b = (27005061 + (a + 680455));
+  int c = ((1207142401 * (((8 * b) + 9483541) - 230968044)) + 469069442);
+  if (c != 1676211843)
+    __builtin_abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "b \\\* 8" 1 "gimple" } } */
+/* { dg-final { scan-tree-dump-not "abort" "optimized" } } */

gcc/testsuite/gcc.dg/tree-ssa/pr69845-2.c

+/* { dg-do compile } */
+/* { dg-require-effective-target int32 } */
+/* { dg-options "-O -fdump-tree-gimple -fdump-tree-optimized" } */
+
+int
+main ()
+{
+  struct S { char s; } v;
+  v.s = 47;
+  unsigned int a = (unsigned int) v.s;
+  unsigned int b = (27005061 + (a + 680455));
+  unsigned int c
+    = ((1207142401u * (((8u * b) + 9483541u) - 230968044u)) + 469069442u);
+  if (c != 1676211843u)
+    __builtin_abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "b \\\* 1067204616" 1 "gimple" } } */
+/* { dg-final { scan-tree-dump-not "abort" "optimized" } } */