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Re: How to clean up i386 machine description?
- To: Joern Rennecke <amylaar at cygnus dot co dot uk>
- Subject: Re: How to clean up i386 machine description?
- From: Jeffrey A Law <law at cygnus dot com>
- Date: Wed, 18 Nov 1998 12:21:45 -0700
- cc: rth at cygnus dot com, hubicka at horac dot ta dot jcu dot cz, howell at cs dot stanford dot edu, pcg at goof dot com, egcs at cygnus dot com
- Reply-To: law at cygnus dot com
In message <199811122030.UAA18085@phal.cygnus.co.uk>you write:
> > Special patterns for inc/dec is ok, but which_alternative cannot
> > handle implementation specific instruction selection.
>
> special patterns for inc/dec are actually a problem; they should not be
> enabled before reload.
Can you state precisely why? There are ports that have special patterns
to increment registers that don't have to worry about reload problems.
> If you need to order instruction alternatives differently for different
> CPUs or use different constraint modifiers so that the alternative
> selection is changed, currently the only way is to have different
> patterns for the different CPUs.
> I'm afraid this doesn't sound like much of a cleanup...
I disagree. We want to move the x86 port away from depending on reload to
clean things up.
Jeff