From: Alan Modra <amodra@gmail.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: Combine simplify_set WORD_REGISTER_OPERATIONS
Date: Mon, 01 Feb 2016 01:13:00 -0000 [thread overview]
Message-ID: <20160201011316.GZ17028@bubble.grove.modra.org> (raw)
In-Reply-To: <20160201000235.GA11814@gate.crashing.org>
On Sun, Jan 31, 2016 at 06:02:35PM -0600, Segher Boessenkool wrote:
> On Mon, Feb 01, 2016 at 08:46:42AM +1030, Alan Modra wrote:
> > The comment says this test is supposed to prevent "a narrower
> > operation than requested", but it actually only allows a larger
> > subreg, not one the same size. Fix that.
> >
> > Bootstrapped and regression tested powerpc64-linux. OK for stage1?
> >
> > Note that this bug was found when investigating why gcc-6 does not
> > suffer from pr69548, ie. this bug was masking a powerpc backend bug.
>
> It sounds like you have a testcase, can we see it please?
The testcase in pr69548 will show changes in rtl..
> And, just a missed optimisation, not a bug, right?
Yes, not a bug, and only presumed a missed optimisation. I don't
actually have a testcase that shows worse code. All I have is a
comment that makes sense to me, that doesn't agree exactly with the
code, and some understanding how the code may have been accidentally
written the way it is.
--
Alan Modra
Australia Development Lab, IBM
next prev parent reply other threads:[~2016-02-01 1:13 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-31 22:16 Alan Modra
2016-02-01 0:02 ` Segher Boessenkool
2016-02-01 1:13 ` Alan Modra [this message]
2016-02-08 16:27 ` Jeff Law
2016-02-09 11:18 ` Alan Modra
2016-02-09 17:37 ` Segher Boessenkool
2016-04-26 21:02 ` Jeff Law
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