From: Segher Boessenkool <segher@kernel.crashing.org>
To: Oleg Endo <oleg.endo@t-online.de>
Cc: gcc-patches@gcc.gnu.org, Nicholas Krause <xerofoify@gmail.com>,
richard.sandiford@arm.com
Subject: Re: Add a new combine pass
Date: Fri, 06 Dec 2019 22:51:00 -0000 [thread overview]
Message-ID: <20191206225130.GS3152@gate.crashing.org> (raw)
In-Reply-To: <bd91f885d1ae6b0303ac9c6f434512b3bcfb6085.camel@t-online.de>
On Wed, Dec 04, 2019 at 07:43:30PM +0900, Oleg Endo wrote:
> On Tue, 2019-12-03 at 12:05 -0600, Segher Boessenkool wrote:
> > > Hmm ... the R0 problem ... SH doesn't override class_likely_spilled
> > > explicitly, but it's got a R0_REGS class with only one said reg in it.
> > > So the default impl of class_likely_spilled should do its thing.
> >
> > Yes, good point. So what happened here?
>
> "Something, somewhere, went terribly wrong"...
>
> insn 18 wants to do
>
> mov.l @(r4,r6),r0
>
> But it can't because the reg+reg address mode has a R0 constraint
> itself. So it needs to be changed to
>
> mov r4,r0
> mov.l @(r0,r6),r0
>
> And it can't handle that. Or only sometimes? Don't remember.
>
> > Is it just RA messing things
> > up, unrelated to the new pass?
>
> Yep, I think so. The additional pass seems to create "tougher" code so
> reload passes out earlier than usual. We've had the same issue when
> trying address mode selection optimization. In fact that was one huge
> showstopper.
So maybe you should have a define_insn_and_split that allows any two
regs and replaces one by r0 if neither is (and a move to r0 before the
load)? Split after reload of course.
It may be admitting defeat, but it may even result in better code as
well ;-)
Segher
next prev parent reply other threads:[~2019-12-06 22:51 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-18 0:21 Richard Sandiford
2019-11-18 2:04 ` Andrew Pinski
2019-11-18 17:58 ` Richard Sandiford
2019-11-23 23:01 ` Segher Boessenkool
2019-11-23 23:09 ` Nicholas Krause
2019-11-23 23:43 ` Segher Boessenkool
2019-11-24 0:11 ` Nicholas Krause
2019-11-25 22:09 ` Richard Sandiford
2019-11-25 22:52 ` Segher Boessenkool
2019-12-03 13:33 ` Oleg Endo
2019-12-03 18:05 ` Segher Boessenkool
2019-12-04 10:43 ` Oleg Endo
2019-12-06 22:51 ` Segher Boessenkool [this message]
2019-12-06 23:47 ` Oleg Endo
2019-11-19 0:11 ` Segher Boessenkool
2019-11-19 11:36 ` Richard Sandiford
2019-11-19 21:13 ` Segher Boessenkool
2019-11-20 18:29 ` Richard Sandiford
2019-11-20 20:49 ` Segher Boessenkool
2019-11-21 21:12 ` Richard Sandiford
2019-11-22 16:39 ` Segher Boessenkool
2019-11-25 21:25 ` Richard Sandiford
2019-11-25 22:17 ` Segher Boessenkool
2019-11-25 23:26 ` Richard Sandiford
2019-11-26 1:44 ` Segher Boessenkool
2019-11-27 8:32 ` Richard Biener
2019-11-27 10:18 ` Richard Sandiford
2019-11-27 19:36 ` Segher Boessenkool
2019-11-21 19:02 ` Nicholas Krause
2019-11-21 19:47 ` Richard Sandiford
2019-11-22 16:27 ` Segher Boessenkool
2019-12-05 10:17 ` Richard Sandiford
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