Do not expand the call to memcmp at all when overflow is detected.

From-SVN: r263563

gcc/ChangeLog

+2018-08-15  Qing Zhao  <qing.zhao@oracle.com>
+
+	PR testsuite/86519
+	* builtins.c (expand_builtin_memcmp): Do not expand the call
+	when overflow is detected.
+
 2018-08-15  Martin Sebor  <msebor@redhat.com>
 
 	PR tree-optimization/71625

gcc/builtins.c

@@ -4481,11 +4481,16 @@ expand_builtin_memcmp (tree exp, rtx target, bool result_eq)
 				  /*objsize=*/NULL_TREE);
     }
 
+  /* If the specified length exceeds the size of either object, 
+     call the function.  */
+  if (!no_overflow)
+    return NULL_RTX;
+
   /* Due to the performance benefit, always inline the calls first
      when result_eq is false.  */
   rtx result = NULL_RTX;
 
-  if (!result_eq && fcode != BUILT_IN_BCMP && no_overflow)
+  if (!result_eq && fcode != BUILT_IN_BCMP)
     {
       result = inline_expand_builtin_string_cmp (exp, target);
       if (result)

gcc/testsuite/ChangeLog

+2018-08-15  Qing Zhao <qing.zhao@oracle.com>
+
+	PR testsuite/86519
+	* gcc.dg/strcmpopt_6.c: Scan the assembly file instead of
+	the .expand file.
+
 2018-08-15  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>
 
 	* gcc.dg/wmain.c: New test.

gcc/testsuite/gcc.dg/strcmpopt_6.c

 /* When the specified length exceeds one of the arguments of the call to memcmp, 
    the call to memcmp should NOT be inlined.  */
-/* { dg-do run } */
-/* { dg-options "-O2 -fdump-rtl-expand -Wno-stringop-overflow" } */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wno-stringop-overflow" } */
 
 typedef struct { char s[8]; int x; } S;
 
@@ -33,4 +33,4 @@ int main (void)
 
 }
 
-/* { dg-final { scan-rtl-dump-times "__builtin_memcmp" 6 "expand" } } */
+/* { dg-final { scan-assembler-times "memcmp" 2 } } */