Re: varpool alias reorg

[Michael Matz <matz@suse.de>]

Hi,

On Mon, 27 Jun 2011, Jan Hubicka wrote:

> > I still like to stream unmodified builtins as builtins, as that is 
> > similar to pre-loading the streamer caches with things like 
> > void_type_node or sizetype.
> 
> Doing so will need us to solve the other one decl rules probly. I didn't 
> really got what the preloading is useful for after all?

One important thing that really affects correctness which preloading does 
is to guarantee pointer equality for things like void_type_node or 
error_mark_node, which are used sometimes.  If we weren't doing preloading 
we would have to forcibly merge all these trees over different units, and 
what's worse, also fill out the global tree arrays with that merged 
variant.  And for that we'd need to note somehow which array slot a 
certain tree is coming from (and deal with the fact that different 
language frontends fill this array differently, sometimes with 
pointer-eqal tree nodes, sometimes only with semantically equal tree 
nodes, sometimes not at all).

Or we could fix all places where we use pointer equality with some of the 
global trees, which I wouldn't like, even for abstract considerations.  
There's really no point in having different but equal void_type nodes, or 
error_mark nodes.

preloading really is the easiest way to solve all this.  It's just 
important that all .o files have the same idea about "tree at slot 
so-and-so" (e.g. meaning "error_mark_node"), which I fixed some weeks ago.

And with early-debug-info we don't even then have the issue of e.g. the 
base integer types not being named like the frontend emitted them.


Ciao,
Michael.