Fix ICEs on local aliases at AIX

[Jan Hubicka]

Hi,
enabling local aliases on AIX causes few ICEs. This is because localias 
function looks
for existing alias. C++ FE produces those for thunk code but doesn't make them 
correctly,
so we end up with missing DECL_CONTEXT that later confuses ipa-devirt.
This patch adds sanity checking of the alias (so we won't get fooled by user 
aliases)
and I will try to fix the C++ side too (ideally by switchign it to localalias 
machinery)

Bootstrapped/regtested rs6000-aix
comitted.

        * symtab.c: Include calls.h
        (symtab_nonoverwritable_alias_1): Check sanity of the local
        alias.
Index: symtab.c
===================================================================
--- symtab.c    (revision 212279)
+++ symtab.c    (working copy)
@@ -43,6 +43,7 @@
 #include "lto-streamer.h"
 #include "output.h"
 #include "ipa-utils.h"
+#include "calls.h"
 
 static const char *ipa_ref_use_name[] = {"read","write","addr","alias"};
 
@@ -1727,6 +1728,19 @@
 {
   if (decl_binds_to_current_def_p (node->decl))
     {
+      symtab_node *fn = symtab_alias_ultimate_target (node);
+
+      /* Ensure that the alias is well formed this may not be the case
+        of user defined aliases and currently it is not always the case
+        of C++ same body aliases (that is a bug).  */
+      if (TREE_TYPE (node->decl) != TREE_TYPE (fn->decl)
+         || DECL_CONTEXT (node->decl) != DECL_CONTEXT (fn->decl)
+         || (TREE_CODE (node->decl) == FUNCTION_DECL
+             && flags_from_decl_or_type (node->decl)
+                != flags_from_decl_or_type (fn->decl))
+         || DECL_ATTRIBUTES (node->decl) != DECL_ATTRIBUTES (fn->decl))
+       return false;
+
       *(symtab_node **)data = node;
       return true;
     }