Fix ice on comdat groups with -check-pointer-bounds

[Jan Hubicka <hubicka@ucw.cz>]

Hi,
this patch fixes bug in symtab_node::verify_symtab_nodes pointed out by Ilya.
The loop checking that there all comdats are linked by same_comdat_group was
completely bogus.  In addition it checked also external symbols that are
currently not kept in groups.  This bug was in mainline for months but
apparently bounds checking is first code producing interesting comdat groups to
trigger it.

Ilya, can you please mind comitting the testcase? I am not quite sure where
bounds checking should go offhand.

Also concerning linking the comdat groups, currently all non-DECL_EXTERNAL symbols
are linked and all !DECL_EXTERNAL symbols are non-linked.  Bounds checking should
follow this scheme.  It may be cleaner to keep links for DECL_EXTERNAL, but lets
deffer that for next stage1.

Bootstrapped/regtested x86_64-linux. Committed.

Honza

Index: ChangeLog
===================================================================
--- ChangeLog	(revision 221735)
+++ ChangeLog	(working copy)
@@ -1,5 +1,11 @@
 2015-03-27  Jan Hubicka  <hubicka@ucw.cz>
 
+	PR target/65531
+	* symtab.c (symtab_node::verify_symtab_nodes): Fix verification of
+	comdat groups.
+
+2015-03-27  Jan Hubicka  <hubicka@ucw.cz>
+
 	PR ipa/65600
 	* cgraph.c (cgraph_update_edges_for_call_stmt_node): Fix the case
 	of optimized out indirect call.
Index: symtab.c
===================================================================
--- symtab.c	(revision 221734)
+++ symtab.c	(working copy)
@@ -1130,15 +1130,20 @@ symtab_node::verify_symtab_nodes (void)
 						  &existed);
 	  if (!existed)
 	    *entry = node;
-	  else
-	    for (s = (*entry)->same_comdat_group; s != NULL && s != node; s = s->same_comdat_group)
+	  else if (!DECL_EXTERNAL (node->decl))
+	    {
+	      for (s = (*entry)->same_comdat_group; s != NULL && s != node;
+		   s = s->same_comdat_group)
+		;
 	      if (!s || s == *entry)
 		{
-		  error ("Two symbols with same comdat_group are not linked by the same_comdat_group list.");
+		  error ("Two symbols with same comdat_group are not linked by "
+			 "the same_comdat_group list.");
 		  (*entry)->debug ();
 		  node->debug ();
 		  internal_error ("symtab_node::verify failed");
 		}
+	    }
 	}
     }
 }