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Re: [C++ PATCH] Fix PR c++/6037


On Fri, Mar 22, 2002 at 10:33:27AM -0800, Mark Mitchell wrote:
> >        enumtype = make_node (ENUMERAL_TYPE);
> >        pushtag (name, enumtype, 0);
> > +      if (current_class_type)
> > +	{
> > +	  /* pushtag might have pushed the tag into some other binding
> > +	     level.  */
> > +	  while (b && (b->tags == NULL || TREE_VALUE (b->tags) != enumtype))
> > +	    b = b->level_chain;
> > +	  if (b == NULL)
> > +	    abort ();
> > +	  TREE_ADDRESSABLE (b->tags) = 1;
> > +	}
> >      }
> 
> I don't understand this change.  What binding level did the enum get
> put in to?

current_binding_level at this point had tag_transparent 1 (because of
some cleanup), so pushtag put it one level up.

>  Why not just call lookup_tag again after calling pushtag,
> rather than manipulating binding levels directly?

lookup_tag returns TREE_VALUE (b->tags), so setting
TREE_ADDRESSABLE (lookup_tag ()) is not the same as
TREE_ADDRESSABLE (b->tags).

> > -  if (current_class_type)
> > -    TREE_ADDRESSABLE (b->tags) = 1;
> > -
> 
> What is the point of the TREE_ADDRESSABLE bits?  I know they were
> alread there, but I don't remember them.

It has been there for eons:

Wed Jan  6 17:43:23 1993  Brendan Kehoe  (brendan@lisa.cygnus.com)

        * cp-decl.c (current_local_enum): New variable.
        (start_enum): Set TREE_ADDRESSABLE on the tag here, and clear
        current_local_enum.
        (build_enumerator): Build the field decl here, rather than in
        grok_enum_decls; set its TREE_CHAIN to the current_local_enum.
        (grok_enum_decls): Chain down, setting the type.

My bet would be it has something with obstacks, but I could be wrong.
Certainly gcc-2.4.5 doesn't reveal why it is used.

>  Should we really be using
> some other macro that has a clearer name?

Definitely, if somebody tells me what it means (if anything).
I certainly cannot find anything about TREE_ADDRESSABLE on TREE_LIST
nodes.

	Jakub


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