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Re: [PATCH] combine: Allow combining two insns to two insns
- From: Segher Boessenkool <segher at kernel dot crashing dot org>
- To: Christophe Lyon <christophe dot lyon at linaro dot org>
- Cc: gcc Patches <gcc-patches at gcc dot gnu dot org>
- Date: Wed, 1 Aug 2018 04:39:52 -0500
- Subject: Re: [PATCH] combine: Allow combining two insns to two insns
- References: <402e00c62fa533333b1e1dd69f468f7f4e43939b.1532449714.git.segher@kernel.crashing.org> <20180730160918.GY16221@gate.crashing.org> <CAKdteOZQyg8oOhp=w9h+6mMvhpd8nJpmyTVhQ=65F69wMHsgkQ@mail.gmail.com> <20180731135733.GC16221@gate.crashing.org> <CAKdteOZYc_Rb2SO3uARvDeknVESfntb1x2zJp9ZDJOZcO2tXaA@mail.gmail.com>
On Wed, Aug 01, 2018 at 10:27:31AM +0200, Christophe Lyon wrote:
> On Tue, 31 Jul 2018 at 15:57, Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
> > On Tue, Jul 31, 2018 at 02:34:06PM +0200, Christophe Lyon wrote:
> > > Since this was committed, I've noticed regressions
> > > on aarch64:
> > > FAIL: gcc.dg/zero_bits_compound-1.c scan-assembler-not \\(and:
> >
> > This went from
> > and w0, w0, 255
> > lsl w1, w0, 8
> > orr w0, w1, w0, lsl 20
> > ret
> > to
> > and w1, w0, 255
> > ubfiz w0, w0, 8, 8
> > orr w0, w0, w1, lsl 20
> > ret
> > so it's neither an improvement nor a regression, just different code.
> > The testcase wants no ANDs in the RTL.
>
> I didn't try to manually regenerate the code before and after the patch,
> but if there was "and w0, w0, 255" before the patch, why did the test pass?
It wasn't an AND in RTL (it was a ZERO_EXTEND).
> > > on arm-none-linux-gnueabi
> > > FAIL: gfortran.dg/actual_array_constructor_1.f90 -O1 execution test
> >
> > That sounds bad. Open a PR, maybe?
> >
> I've just filed PR86771
Thanks.
Segher