re PR tree-optimization/63445 (request: make -Wstrict-overflow avoid a class of false positives)

2014-10-09  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/63445
	* tree-vrp.c (simplify_cond_using_ranges): Only warn about
	overflow for non-equality compares.

	* gcc.dg/Wstrict-overflow-26.c: New testcase.

From-SVN: r216028

gcc/ChangeLog

+2014-10-09  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/63445
+	* tree-vrp.c (simplify_cond_using_ranges): Only warn about
+	overflow for non-equality compares.
+
 2014-10-09  Uros Bizjak  <ubizjak@gmail.com>
 
 	PR rtl-optimization/57003

gcc/testsuite/ChangeLog

+2014-10-09  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/63445
+	* gcc.dg/Wstrict-overflow-26.c: New testcase.
+
 2014-10-08  Pat Haugen  <pthaugen@us.ibm.com>
 
 	* gcc.dg/vmx/3c-01a.c: Add default options from vmx.exp.

gcc/testsuite/gcc.dg/Wstrict-overflow-26.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -Wstrict-overflow" } */
+
+int
+f (int i, int j)
+{
+  unsigned int c = 0;                                                          
+  if (i < j)
+    {
+      unsigned int n = j - i;
+      unsigned int i;
+      for (i = 0; i < n; i++) /* { dg-bogus "signed overflow" } */
+	c++;
+    }
+  return c;
+}

gcc/tree-vrp.c

@@ -9189,8 +9189,9 @@ simplify_cond_using_ranges (gimple stmt)
 	      /* If the range overflowed and the user has asked for warnings
 		 when strict overflow semantics were used to optimize code,
 		 issue an appropriate warning.  */
-	      if ((is_negative_overflow_infinity (vr->min)
-		   || is_positive_overflow_infinity (vr->max))
+	      if (cond_code != EQ_EXPR && cond_code != NE_EXPR
+		  && (is_negative_overflow_infinity (vr->min)
+		      || is_positive_overflow_infinity (vr->max))
 		  && issue_strict_overflow_warning (WARN_STRICT_OVERFLOW_CONDITIONAL))
 		{
 		  location_t location;