re PR middle-end/33779 (folds unsigned multiplication == 0 to true)

2007-10-31  Richard Guenther  <rguenther@suse.de>

	PR middle-end/33779
	* fold-const.c (extract_muldiv_1): Make sure to not introduce
	new undefined integer overflow.
	(fold_binary): Avoid useless conversion.

	* gcc.c-torture/execute/pr33779-1.c: New testcase.
	* gcc.c-torture/execute/pr33779-2.c: Likewise.

From-SVN: r129796

gcc/ChangeLog

+2007-10-31  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/33779
+	* fold-const.c (extract_muldiv_1): Make sure to not introduce
+	new undefined integer overflow.
+	(fold_binary): Avoid useless conversion.
+
 2007-10-31  Richard Sandiford  <rsandifo@nildram.co.uk>
 
 	PR target/33948

gcc/fold-const.c

@@ -6060,7 +6060,12 @@ extract_muldiv_1 (tree t, tree c, enum tree_code code, tree wide_type,
 		 then we cannot pass through this conversion.  */
 	      || (code != MULT_EXPR
 		  && (TYPE_UNSIGNED (ctype)
-		      != TYPE_UNSIGNED (TREE_TYPE (op0))))))
+		      != TYPE_UNSIGNED (TREE_TYPE (op0))))
+	      /* ... or has undefined overflow while the converted to
+		 type has not, we cannot do the operation in the inner type
+		 as that would introduce undefined overflow.  */
+	      || (TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (op0))
+		  && !TYPE_OVERFLOW_UNDEFINED (type))))
 	break;
 
       /* Pass the constant down and see if we can make a simplification.  If
@@ -10266,9 +10271,7 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
 
 	  strict_overflow_p = false;
 	  if (TREE_CODE (arg1) == INTEGER_CST
-	      && 0 != (tem = extract_muldiv (op0,
-					     fold_convert (type, arg1),
-					     code, NULL_TREE,
+	      && 0 != (tem = extract_muldiv (op0, arg1, code, NULL_TREE,
 					     &strict_overflow_p)))
 	    {
 	      if (strict_overflow_p)

gcc/testsuite/ChangeLog

+2007-10-31  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/33779
+	* gcc.c-torture/execute/pr33779-1.c: New testcase.
+	* gcc.c-torture/execute/pr33779-2.c: Likewise.
+
 2007-10-31  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/33897

gcc/testsuite/gcc.c-torture/execute/pr33779-1.c

+int foo(int i)
+{
+  if (((unsigned)(i + 1)) * 4 == 0)
+    return 1;
+  return 0;
+}
+
+extern void abort(void);
+int main()
+{
+  if (foo(0x3fffffff) == 0)
+    abort ();
+  return 0;
+}

gcc/testsuite/gcc.c-torture/execute/pr33779-2.c

+int foo(int i)
+{
+  return ((int)((unsigned)(i + 1) * 4)) / 4;
+}
+
+extern void abort(void);
+int main()
+{
+  if (foo(0x3fffffff) != 0)
+    abort ();
+  return 0;
+}