From: Jakub Jelinek <jakub@redhat.com>
To: Jan Hubicka <jh@suse.cz>
Cc: gcc@gcc.gnu.org
Subject: Re: SUBREGs and modes
Date: Wed, 02 Aug 2000 05:58:00 -0000 [thread overview]
Message-ID: <20000802150417.K26939@sunsite.ms.mff.cuni.cz> (raw)
In-Reply-To: <20000802144916.L22797@atrey.karlin.mff.cuni.cz>
On Wed, Aug 02, 2000 at 02:49:16PM +0200, Jan Hubicka wrote:
> Hi
> (except for many other cases), my checker pointed out
> weird usage of SUBREGs. According to my uderstanding the docs, when
> WORDNUM is nonzero, the innermode must be greater than word and
> the outer mode must be word.
>
> My checker has caught occurences of subregs not matching these constraints
> such as:
> (subreg:HI (reg:DI ) 1)
> in i386.
>
> These happends in early stages of RTL generation and seems to be results of
> combining two SUBREGS together. Simplifiers in recog.c and combine.c can't deal
> with such SUBREGS when they get constant insode so we at least miss
> optimizations.
>
> So the question is, whether are such subregs correct, if so we
> should probably docuemnt their semantics and add optimizations, if not,
> how to avoid these?
>
> Jakub: Does your (and Davids) SUBREG_BYTE work touch this issue somehow?
Yes, things are quite different.
First of all, one big endian subreg_lowpart_p has nonzero BYTENUM.
(subreg:QI (reg:SI %eax) 1) is legal e.g. on i386, that's %ah.
I hope SUBREG_BYTE will be integrated soon and thus am not sure how much is
it worth of regoing the SUBREG_WORD stuff now (it would definitely be much
more work for me to keep up with the patches).
Jakub
next prev parent reply other threads:[~2000-08-02 5:58 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-08-02 5:49 Jan Hubicka
2000-08-02 5:58 ` Jakub Jelinek [this message]
2000-08-02 8:39 ` Joern Rennecke
2000-08-02 8:49 ` Jan Hubicka
2000-08-02 9:13 ` Joern Rennecke
2000-08-02 9:30 ` Jan Hubicka
2000-08-02 12:40 ` Geoff Keating
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