This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Possible CSE quirk involving SUBREG on the i386
- To: law at cygnus dot com
- Subject: Re: Possible CSE quirk involving SUBREG on the i386
- From: john at feith dot com (John Wehle)
- Date: Fri, 10 Jul 1998 18:23:23 -0400
- cc: rth at cygnus dot com, egcs at cygnus dot com
> Based on the comments in combine.c, I think at one time MODES_TIEABLE_P
> did have to be symmetric because of the reload issue. I'm starting to
> think we can relax this now.
>
> The last issue is register allocation -- I get the impression from reading
> the code in cse, combine & regclass that this change may make register
> allocation worse in some cases. So we need to have some guess about the
> benefit vs the cost.
Yep, I got the same impression though sometimes it's hard to guess without
trying it.
> I propose we table this until after egcs-1.1. Or better yet, instead of
> tabling it, we just install your patch in the mainline sources after egcs-1.1
> branches.
Okay, I'll see about throwing together a patch.
> That gives us plenty of time to study what actually happens instead of
> doing something rather risky at this stage.
Sounds reasonable to me.
-- John
-------------------------------------------------------------------------
| Feith Systems | Voice: 1-215-646-8000 | Email: john@feith.com |
| John Wehle | Fax: 1-215-540-5495 | |
-------------------------------------------------------------------------