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Re: How to clean up i386 machine description?
- To: law at cygnus dot com
- Subject: Re: How to clean up i386 machine description?
- From: Jan Hubicka <hubicka at horac dot ta dot jcu dot cz>
- Date: Wed, 4 Nov 1998 12:01:19 +0100
- Cc: egcs at cygnus dot com
- References: <19981030103233.05281@horac.ta.jcu.cz> <5098.910079491@upchuck>
> Thanks. I haven't had a chance to look at it in any detail yet.
I've run into problems with recent snapshots and this patch.
It also contains the wrong fix for FP conversion bug, so I will have to
prepare updated version soon. (In fact I have it, but it runs into some
kind of weird reload problem. I will delay it for the moment.)
> > I've already split some patterns in way you describe, but I was unsure if
> > it is good idea. .info says it isn't, because reload can change register
> > to constant but keep the register version. So it says it is generally
> > better to use general addition pattern instead of inc pattern.
> > Is this still relevant?
> Most of the time tightening the predicates to more closely match the machine
> is going to win. That's become a rule of thumb for most new ports. There
> are sometimes exceptions, but they're becoming rare.
> > Can you explain me the problem in some detail?
> It's difficult to explain. Again, the general rule of thumb is to make the
> predicate match the hardware more closely. Exceptions exist, but they are
> analyzed on a case by case basis.
OK, so I will just believe you.
>
> If you have a more specific pattern, then you should put it first. Your
> general pattern may (or may not) still need to handle the case that is
> in the specific pattern -- it depends on a variety of factors.
OK, we should discuss this later once other problems are settled down.
>
> jeff
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