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Re: [PATCH] x86-64: Compile branred.c with -mprefer-vector-width=128 [BZ #24603]
On Tue, Jun 11, 2019 at 9:07 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> 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.
>
I found:
sysdeps/powerpc/powerpc64/power4/Makefile:CFLAGS-memmove.c += --param
max-variable-expansions-in-unroller=2 --param max-unroll-times=2
-funroll-loops -fpeel-loops
--
H.J.