Re: [PATCH] Fix PR optimization/11637 (x86)

[Eric Botcazou <ebotcazou at libertysurf dot fr>]

> 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

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.

-- 
Eric Botcazou