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Re: Compare-elim pass (was: Re: [PATCH] Fix PR 61225)
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Hans-Peter Nilsson <hp at bitrange dot com>
- Cc: Uros Bizjak <ubizjak at gmail dot com>, Eric Botcazou <ebotcazou at adacore dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Jeff Law <law at redhat dot com>, Steven Bosscher <stevenb dot gcc at gmail dot com>, Zhenqiang Chen <zhenqiang dot chen at linaro dot org>, Richard Henderson <rth at redhat dot com>
- Date: Sat, 17 Jan 2015 20:33:58 +0100
- Subject: Re: Compare-elim pass (was: Re: [PATCH] Fix PR 61225)
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- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Sat, Jan 17, 2015 at 01:18:44PM -0500, Hans-Peter Nilsson wrote:
> (Waking up an old thread with my 2 cents due to being a little
> behind on reading...)
>
> On Sat, 6 Dec 2014, Jakub Jelinek wrote:
> > On Sat, Dec 06, 2014 at 09:28:57AM +0100, Uros Bizjak wrote:
> > > > That's already what it does though, did you mean the opposite? Or did you
> > > > mean to write "combine" instead of "compare"?
> > >
> > > The above should read "... that existing RTX *combine* pass be updated
> > > ...", thanks for pointing out!
> >
> > Which target actually uses the [(operation) (set (cc) ...)] order in their
> > *.md patterns? Even aarch64 and arm use the [(set (cc) ...) (operation)]
> > order that combine expects, I thought compare-elim was written for those
> > targets? If the vast majority of mds use the order that combine expects,
> > I think it should be easier to adjust compare-elim.c and those few targets
> > that diverge.
>
> The current cc-first order happened more of an accidental
> opinion than an architectural decision as I vaguely recall, when
> asking. We also have the canonical location of a *cc clobber*,
> i.e. last in a parallel. For that reason, it then makes sense
> to have the *cc-setting* last. Changing rebelling ports doesn't
> solve that inconsistency.
Clobber is clobber, all clobbers come last, so it has nothing to do if
cc set is first or second.
Jakub