re PR middle-end/50199 (wrong code with -flto -fno-merge-constants)

	PR middle-end/50199
	* lto-lang.c (lto_post_options): Force flag_merge_constants = 1
	if it was 0.

	* gcc.dg/lto/pr50199_0.c: New test.

From-SVN: r244304

gcc/lto/ChangeLog

+2017-01-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/50199
+	* lto-lang.c (lto_post_options): Force flag_merge_constants = 1
+	if it was 0.
+
 2017-01-09  Jakub Jelinek  <jakub@redhat.com>
 
 	PR translation/79019

gcc/lto/lto-lang.c

@@ -857,6 +857,12 @@ lto_post_options (const char **pfilename ATTRIBUTE_UNUSED)
      support.  */
   flag_excess_precision_cmdline = EXCESS_PRECISION_FAST;
 
+  /* When partitioning, we can tear appart STRING_CSTs uses from the same
+     TU into multiple partitions.  Without constant merging the constants
+     might not be equal at runtime.  See PR50199.  */
+  if (!flag_merge_constants)
+    flag_merge_constants = 1;
+
   /* Initialize the compiler back end.  */
   return false;
 }

gcc/testsuite/ChangeLog

+2017-01-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/50199
+	* gcc.dg/lto/pr50199_0.c: New test.
+
 2017-01-10  Martin Sebor  <msebor@redhat.com>
 
 	PR testsuite/78960

gcc/testsuite/gcc.dg/lto/pr50199_0.c

+/* PR middle-end/50199 */
+/* { dg-lto-options {{-O2 -flto -fno-merge-constants --param=lto-min-partition=1}} } */
+
+__attribute__ ((noinline)) const char *
+foo (const char *x)
+{
+  return x;
+}
+
+int
+main ()
+{
+  const char *a = "ab";
+  if (a != foo (a))
+    __builtin_abort ();
+  return 0;
+}