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Re: [PATCH] Fix up Yr constraint
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Kirill Yukhin <kirill dot yukhin at gmail dot com>, Ilya Enkovich <ilya dot enkovich at intel dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Date: Wed, 25 May 2016 08:03:32 +0200
- Subject: Re: [PATCH] Fix up Yr constraint
- Authentication-results: sourceware.org; auth=none
- References: <20160524165527 dot GM28550 at tucnak dot redhat dot com> <CAFULd4aJDh3UU6YZ+zpP_hEa4zneQUfhX9Gaw-cZya4o2Pde=Q at mail dot gmail dot com> <20160524190251 dot GP28550 at tucnak dot redhat dot com>
On Tue, May 24, 2016 at 9:02 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, May 24, 2016 at 08:35:12PM +0200, Uros Bizjak wrote:
>> On Tue, May 24, 2016 at 6:55 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>> > Hi!
>> >
>> > The Yr constraint contrary to what has been said when it has been submitted
>> > actually is always NO_REX_SSE_REGS or NO_REGS, never ALL_SSE_REGS, so
>> > the RA restriction to only the first 8 regs is done no matter what we tune
>> > for.
>> >
>> > This is because we test X86_TUNE_AVOID_4BYTE_PREFIXES, which is an enum
>> > value (59), rather than actually checking if the tune flag.
>> >
>> > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>> >
>> > 2016-05-24 Jakub Jelinek <jakub@redhat.com>
>> >
>> > * config/i386/i386.h (TARGET_AVOID_4BYTE_PREFIXES): Define.
>> > * config/i386/constraints.md (Yr): Test TARGET_AVOID_4BYTE_PREFIXES
>> > rather than X86_TUNE_AVOID_4BYTE_PREFIXES.
>>
>> Uh, another brown-paper bag bug...
>>
>> OK everywhere.
>
> I fear it might be too dangerous for -mavx512* for the branches; I went
> through all the Yr uses on the trunk, but not on the branches.
> Would you be ok with using
> "TARGET_SSE ? (TARGET_AVOID_4BYTE_PREFIXES ? NO_REX_SSE_REGS : SSE_REGS) : NO_REGS"
> on the branches instead?
> Or I guess we could use it on the trunk too, it should make no difference there
> (because on the trunk it is only used when !TARGET_AVX).
> Or maybe even
> "TARGET_SSE ? ((TARGET_AVOID_4BYTE_PREFIXES && !TARGET_AVX) ? NO_REX_SSE_REGS : SSE_REGS) : NO_REGS"
> (again, should make zero difference on the trunk, but might be better for
> the branches).
Indeed, let's play safe and go with the later version on branches.
Please also add a small comment, to avoid head-scratching in the
future.
Uros.