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Re: [PATCH] x86-64: Compile branred.c with -mprefer-vector-width=128 [BZ #24603]
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: Joseph Myers <joseph at codesourcery dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Tue, 11 Jun 2019 09:07:06 -0700
- Subject: Re: [PATCH] x86-64: Compile branred.c with -mprefer-vector-width=128 [BZ #24603]
- References: <CAMe9rOoP_293SM=sYpuqx5Yg9K1a-F9GtN6g0DDFjHTZM5OkcA@mail.gmail.com> <alpine.DEB.2.21.1906101545000.29610@digraph.polyomino.org.uk> <CAMe9rOoyj_b=zWkUgcSKLxPLEuBA0Y9-75v+xqg0yT4HDXy56Q@mail.gmail.com> <87sgsg3yax.fsf@oldenburg2.str.redhat.com>
On Tue, Jun 11, 2019 at 9:02 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > Fixed. I also added check for -mprefer-vector-width=128 which is new in GCC 8.
> > GCC 7 doesn't have this problem since it doesn't vectorize the second loop.
> >
> > Here is the updated patch.
> >
> > OK for master?
>
> I still don't understand why we need a workaround for a GCC performance
> bug in glibc. Is there any precedent for this?
>
I don't know if we ever investigated performance impacts of different GCC
optimizations on glibc.
--
H.J.