PR lto/53604 (incorrectly optmized out comdats)

[Jan Hubicka]

Hi,
this patch solves problem where comdat symbols are incorrectly optimized out 
even if used from
object file.  With V1 plugin API this will lead to unnecesary symbols kept in 
the object file.
I am not sure how important it is, since they are not that common. 

I will backport this to 4.7 if Mozilla will build well with V1 API.

Honza

Bootstrapped/regtested x86_64-linux, comitted.

    PR lto/53572
    * cgraph.h (varpool_can_remove_if_no_refs): Fix handling of
    used symbols.

--- trunk/gcc/cgraph.h  2012/06/26 10:13:11     188981
+++ trunk/gcc/cgraph.h  2012/06/26 10:15:18     188982
@@ -1126,7 +1126,8 @@
   if (DECL_EXTERNAL (node->symbol.decl))
     return true;
   return (!node->symbol.force_output && !node->symbol.used_from_other_partition
-         && (DECL_COMDAT (node->symbol.decl)
+         && ((DECL_COMDAT (node->symbol.decl)
+              && !symtab_used_from_object_file_p ((symtab_node) node))
              || !node->symbol.externally_visible
              || DECL_HAS_VALUE_EXPR_P (node->symbol.decl)));
 }