[PATCH] x86-64: Compile branred.c with -mprefer-vector-width=128

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Re: [PATCH] x86-64: Compile branred.c with -mprefer-vector-width=128 [BZ #24603]

Jeff Law
On 6/17/19 3:37 PM, Joseph Myers wrote:

> On Mon, 17 Jun 2019, H.J. Lu wrote:
>
>> On Mon, Jun 17, 2019 at 12:12 PM Florian Weimer <[hidden email]> wrote:
>>>
>>> * Jeff Law:
>>>
>>>> ISTM that 8, 9, 10 would use the new flag.  11 would issue an error
>>>> which would trigger a reinvestigation roughly a year from now.
>>>
>>> Do you suggest to put in a #warning for GCC 11, so that people can
>>> configure with --disable-werror and still build with GCC 11?
>>>
>>> Given that GCC 11 will probably add other warnings that break the build,
>>> this proposal isn't entirely unreasonable (even though I generally
>>> dislike such time bombs).
>>>
>>
>> Since there is no issue in source, this requires an artificial warning
>> purely based on GCC version.   We can place GCC version check in
>> configure script with explicit -mprefer-vector-width=128 support.
>>
>> --enable-mprefer-vector-width:
>>
>> 1.  Default.  For GCC 8, 9, 10, use -mprefer-vector-width=128.
>> For GCC 11 and above, issue a configure error.
>
> I don't think anything causing the build to break with newer GCC versions
> is appropriate.
Fair enough -- hence a bit of a step away from the decision process in
my prior message on this subject.  I threw it out as a way to address
the issue Florian raised, but I strongly believe it's up to the glibc
team to decide how they want to go forward.

jeff

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Re: [PATCH] x86-64: Compile branred.c with -mprefer-vector-width=128 [BZ #24603]

H.J. Lu-30
On Mon, Jun 17, 2019 at 2:41 PM Jeff Law <[hidden email]> wrote:

>
> On 6/17/19 3:37 PM, Joseph Myers wrote:
> > On Mon, 17 Jun 2019, H.J. Lu wrote:
> >
> >> On Mon, Jun 17, 2019 at 12:12 PM Florian Weimer <[hidden email]> wrote:
> >>>
> >>> * Jeff Law:
> >>>
> >>>> ISTM that 8, 9, 10 would use the new flag.  11 would issue an error
> >>>> which would trigger a reinvestigation roughly a year from now.
> >>>
> >>> Do you suggest to put in a #warning for GCC 11, so that people can
> >>> configure with --disable-werror and still build with GCC 11?
> >>>
> >>> Given that GCC 11 will probably add other warnings that break the build,
> >>> this proposal isn't entirely unreasonable (even though I generally
> >>> dislike such time bombs).
> >>>
> >>
> >> Since there is no issue in source, this requires an artificial warning
> >> purely based on GCC version.   We can place GCC version check in
> >> configure script with explicit -mprefer-vector-width=128 support.
> >>
> >> --enable-mprefer-vector-width:
> >>
> >> 1.  Default.  For GCC 8, 9, 10, use -mprefer-vector-width=128.
> >> For GCC 11 and above, issue a configure error.
> >
> > I don't think anything causing the build to break with newer GCC versions
> > is appropriate.
> Fair enough -- hence a bit of a step away from the decision process in
> my prior message on this subject.  I threw it out as a way to address
> the issue Florian raised, but I strongly believe it's up to the glibc
> team to decide how they want to go forward.
>

I'd like to check in my patch to close the 40% performance gap with GCC
8, 9 and 10.  We will monitor performance changes in the future GCC.

Thanks.

--
H.J.
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Re: [PATCH] x86-64: Compile branred.c with -mprefer-vector-width=128 [BZ #24603]

H.J. Lu-30
On Thu, Jun 20, 2019 at 9:30 AM H.J. Lu <[hidden email]> wrote:

>
> On Mon, Jun 17, 2019 at 2:41 PM Jeff Law <[hidden email]> wrote:
> >
> > On 6/17/19 3:37 PM, Joseph Myers wrote:
> > > On Mon, 17 Jun 2019, H.J. Lu wrote:
> > >
> > >> On Mon, Jun 17, 2019 at 12:12 PM Florian Weimer <[hidden email]> wrote:
> > >>>
> > >>> * Jeff Law:
> > >>>
> > >>>> ISTM that 8, 9, 10 would use the new flag.  11 would issue an error
> > >>>> which would trigger a reinvestigation roughly a year from now.
> > >>>
> > >>> Do you suggest to put in a #warning for GCC 11, so that people can
> > >>> configure with --disable-werror and still build with GCC 11?
> > >>>
> > >>> Given that GCC 11 will probably add other warnings that break the build,
> > >>> this proposal isn't entirely unreasonable (even though I generally
> > >>> dislike such time bombs).
> > >>>
> > >>
> > >> Since there is no issue in source, this requires an artificial warning
> > >> purely based on GCC version.   We can place GCC version check in
> > >> configure script with explicit -mprefer-vector-width=128 support.
> > >>
> > >> --enable-mprefer-vector-width:
> > >>
> > >> 1.  Default.  For GCC 8, 9, 10, use -mprefer-vector-width=128.
> > >> For GCC 11 and above, issue a configure error.
> > >
> > > I don't think anything causing the build to break with newer GCC versions
> > > is appropriate.
> > Fair enough -- hence a bit of a step away from the decision process in
> > my prior message on this subject.  I threw it out as a way to address
> > the issue Florian raised, but I strongly believe it's up to the glibc
> > team to decide how they want to go forward.
> >
>
> I'd like to check in my patch to close the 40% performance gap with GCC
> 8, 9 and 10.  We will monitor performance changes in the future GCC.
>
> Thanks.
>

I will check in my patch tomorrow.

Thanks.

--
H.J.
12