Re: ipa-visibility TLC 2/n

[Jan Hubicka <hubicka at ucw dot cz>]

> On Sun, May 25, 2014 at 6:54 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
> > Hi,
> > this patch adds code to rerite references in vtable initializers to local aliases
> > when doing so is a win.
> >
> > Bootstrapped/regtested x86_64-linux, comitted.
> 
> This is the most likely patch to have caused build failures on
> arm-linux-gnueabihf
>          ^
> /work/trunk-nightlies/builds/build-210913/armv7l-unknown-linux-gnueabihf/libstdc++-v3/include/backward/strstream:143:9:
> note: _std::ostrstream::_ZTVSt10ostrstream_ was declared here
> /work/trunk-nightlies/builds/build-210913/armv7l-unknown-linux-gnueabihf/libstdc++-v3/include/backward/strstream:160:9:
> error: std::strstream::_ZTVSt9strstream.localalias.2 causes a section
> type conflict with std::strstream::_ZTVSt9strstream
>    class strstream : public basic_iostream<char>
>          ^
> /work/trunk-nightlies/builds/build-210913/armv7l-unknown-linux-gnueabihf/libstdc++-v3/include/backward/strstream:160:9:
> note: _std::strstream::_ZTVSt9strstream_ was declared here

I suppose it is because wrong readonly flag on the alias created. Does the following patch help?

Index: symtab.c
===================================================================
--- symtab.c	(revision 210914)
+++ symtab.c	(working copy)
@@ -1163,7 +1163,10 @@
 				 (new_decl, node->decl);
     }
   else
-    new_node = varpool_create_variable_alias (new_decl, node->decl);
+    {
+      DECL_READONLY (new_decl) = DECL_READONLY (node->decl);
+      new_node = varpool_create_variable_alias (new_decl, node->decl);
+    }
   symtab_resolve_alias (new_node, node);  
   gcc_assert (decl_binds_to_current_def_p (new_decl));
   return new_node;
> 
> 
> regards
> Ramana
> 
> 
> >
> > Honza
> >
> >         * ipa-visibility.c (can_replace_by_local_alias_in_vtable): New function.
> >         (update_vtable_references): New function.
> >         (function_and_variable_visibility): Rewrite also vtable initializers.
> >         * varpool.c (cgraph_variable_initializer_availability): Remove assert.
> > Index: varpool.c
> > ===================================================================
> > --- varpool.c   (revision 210908)
> > +++ varpool.c   (working copy)
> > @@ -355,7 +355,6 @@ varpool_add_new_variable (tree decl)
> >  enum availability
> >  cgraph_variable_initializer_availability (varpool_node *node)
> >  {
> > -  gcc_assert (cgraph_function_flags_ready);
> >    if (!node->definition)
> >      return AVAIL_NOT_AVAILABLE;
> >    if (!TREE_PUBLIC (node->decl))
> > Index: ipa-visibility.c
> > ===================================================================
> > --- ipa-visibility.c    (revision 210908)
> > +++ ipa-visibility.c    (working copy)
> > @@ -343,6 +343,36 @@ can_replace_by_local_alias (symtab_node
> >           && !symtab_can_be_discarded (node));
> >  }
> >
> > +/* Return true if we can replace refernece to NODE by local alias
> > +   within a virtual table.  Generally we can replace function pointers
> > +   and virtual table pointers.  */
> > +
> > +bool
> > +can_replace_by_local_alias_in_vtable (symtab_node *node)
> > +{
> > +  if (is_a <varpool_node *> (node)
> > +      && !DECL_VIRTUAL_P (node->decl))
> > +    return false;
> > +  return can_replace_by_local_alias (node);
> > +}
> > +
> > +/* walk_tree callback that rewrites initializer references.   */
> > +
> > +static tree
> > +update_vtable_references (tree *tp, int *walk_subtrees, void *data ATTRIBUTE_UNUSED)
> > +{
> > +  if (TREE_CODE (*tp) == VAR_DECL
> > +      || TREE_CODE (*tp) == FUNCTION_DECL)
> > +    {
> > +      if (can_replace_by_local_alias_in_vtable (symtab_get_node (*tp)))
> > +       *tp = symtab_nonoverwritable_alias (symtab_get_node (*tp))->decl;
> > +      *walk_subtrees = 0;
> > +    }
> > +  else if (IS_TYPE_OR_DECL_P (*tp))
> > +    *walk_subtrees = 0;
> > +  return NULL;
> > +}
> > +
> >  /* In LTO we can remove COMDAT groups and weak symbols.
> >     Either turn them into normal symbols or external symbol depending on
> >     resolution info.  */
> > @@ -625,6 +655,34 @@ function_and_variable_visibility (bool w
> >           vnode->resolution = LDPR_PREVAILING_DEF_IRONLY;
> >         }
> >        update_visibility_by_resolution_info (vnode);
> > +
> > +      /* Update virutal tables to point to local aliases where possible.  */
> > +      if (DECL_VIRTUAL_P (vnode->decl)
> > +         && !DECL_EXTERNAL (vnode->decl))
> > +       {
> > +         int i;
> > +         struct ipa_ref *ref;
> > +         bool found = false;
> > +
> > +         /* See if there is something to update.  */
> > +         for (i = 0; ipa_ref_list_referring_iterate (&vnode->ref_list,
> > +                                                     i, ref); i++)
> > +           if (ref->use == IPA_REF_ADDR
> > +               && can_replace_by_local_alias_in_vtable (ref->referred))
> > +             {
> > +               found = true;
> > +               break;
> > +             }
> > +         if (found)
> > +           {
> > +             struct pointer_set_t *visited_nodes = pointer_set_create ();
> > +             walk_tree (&DECL_INITIAL (vnode->decl),
> > +                        update_vtable_references, NULL, visited_nodes);
> > +             pointer_set_destroy (visited_nodes);
> > +             ipa_remove_all_references (&vnode->ref_list);
> > +             record_references_in_initializer (vnode->decl, false);
> > +           }
> > +       }
> >      }
> >
> >    if (dump_file)