re PR middle-end/78228 (fstrict-overflow breaks code without overflow?)

2016-11-07  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/78228
	* tree-ssa-phiopt.c (abs_replacement): Avoid introducing
	undefined behavior.

	* gcc.dg/tree-ssa/phi-opt-15.c: New testcase.

From-SVN: r241899

gcc/ChangeLog

+2016-11-07  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/78228
+	* tree-ssa-phiopt.c (abs_replacement): Avoid introducing
+	undefined behavior.
+
 2016-11-07  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	PR target/77822

gcc/testsuite/ChangeLog

+2016-11-07  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/78228
+	* gcc.dg/tree-ssa/phi-opt-15.c: New testcase.
+
 2016-11-07  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	PR target/77822

gcc/testsuite/gcc.dg/tree-ssa/phi-opt-15.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int
+foo (int i)
+{
+  if (i > 0)
+    i = -i;
+  return i;
+}
+
+/* { dg-final { scan-tree-dump-not "ABS" "optimized" } } */

gcc/tree-ssa-phiopt.c

@@ -1474,6 +1474,14 @@ abs_replacement (basic_block cond_bb, basic_block middle_bb,
   else
     negate = false;
 
+  /* If the code negates only iff positive then make sure to not
+     introduce undefined behavior when negating or computing the absolute.
+     ???  We could use range info if present to check for arg1 == INT_MIN.  */
+  if (negate
+      && (ANY_INTEGRAL_TYPE_P (TREE_TYPE (arg1))
+	  && ! TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg1))))
+    return false;
+
   result = duplicate_ssa_name (result, NULL);
 
   if (negate)