[PATCH] Fix PR optimization/11637 (x86)

[Eric Christopher]

On Tue, 2003-09-16 at 02:56, Eric Botcazou wrote:
> > Can we not use SUBST to copy one over the other and then pull out just
> > the one to preserve the notes on the second and discard the first?
> 
> I'm not sure I understand. Here's the main message:
> http://gcc.gnu.org/ml/gcc-patches/2003-09/msg00872.html
> 

Thanks.

> The problem boils down to this: we have a REG_EQUAL note that corresponds to 
> a SET and we delete the SET without deleting the note. So either we don't 
> delete the SET or we delete the note.
> 
> The note updating machinery of the combiner basically ignores REG_EQUAL 
> notes, probably because the combine pass is not intended to modify the dest 
> of the SETs. Here we remove a SET so we could teach the machinery to remove 
> the note.

Removing the note would be the best solution IMO. This seems like too
useful of an optimization (and has been there since at least 1991) to be
turned off.

-eric

-- 
Eric Christopher <echristo@redhat.com>