ipa-icf.c (sem_item_optimizer::merge): Don't pick 'main' as the source function.

	gcc/
	* ipa-icf.c (sem_item_optimizer::merge): Don't pick 'main' as the
	source function.

	gcc/testsuite/
	* gcc.dg/ipa/ipa-icf-merge-1.c: New.

From-SVN: r231787

gcc/ChangeLog

+2015-12-17  Nathan Sidwell  <nathan@acm.org>
+
+	* ipa-icf.c (sem_item_optimizer::merge): Don't pick 'main' as the
+	source function.
+
 2015-12-17  Sebastian Pop  <s.pop@samsung.com>
 
 	* Makefile.in: Replace ISL with isl.

gcc/ipa-icf.c

@@ -3398,14 +3398,20 @@ sem_item_optimizer::merge_classes (unsigned int prev_class_count)
 	if (c->members.length () == 1)
 	  continue;
 
-	gcc_assert (c->members.length ());
-
 	sem_item *source = c->members[0];
 
-	for (unsigned int j = 1; j < c->members.length (); j++)
+	if (MAIN_NAME_P (DECL_NAME (source->decl)))
+	  /* If merge via wrappers, picking main as the target can be
+	     problematic.  */
+	  source = c->members[1];
+
+	for (unsigned int j = 0; j < c->members.length (); j++)
 	  {
 	    sem_item *alias = c->members[j];
 
+	    if (alias == source)
+	      continue;
+
 	    if (dump_file)
 	      {
 		fprintf (dump_file, "Semantic equality hit:%s->%s\n",

gcc/testsuite/ChangeLog

+2015-12-17  Nathan Sidwell  <nathan@acm.org>
+
+	* gcc.dg/ipa/ipa-icf-merge-1.c: New.
+	
 2015-12-17  David Malcolm  <dmalcolm@redhat.com>
 
 	* gcc.dg/diagnostic-range-bad-return.c: New test case.

gcc/testsuite/gcc.dg/ipa/ipa-icf-merge-1.c

+/* { dg-do compile } */
+/* { dg-additional-options "-O2 -fdump-ipa-icf" } */
+
+/* Picking 'main' as a candiate target for equivalent functios is not a
+   good idea.  */
+
+int baz (int);
+
+int foo ()
+{
+  return baz (baz (0));
+}
+
+
+int main ()
+{
+  return baz (baz (0));
+}
+
+/* Notice the two functions are the same.  */
+/* { dg-final { scan-ipa-dump "Semantic equality hit:foo->main" "icf" } } */
+
+/* Make sure we don't tail call main.  */
+/* { dg-final { scan-ipa-dump-not "= main \\(\\);" "icf" } } */
+
+/* Make sure we tail call foo.  */
+/* { dg-final { scan-ipa-dump "= foo \\(\\);" "icf" } } */