From: "H.J. Lu" <hjl.tools@gmail.com>
To: Uros Bizjak <ubizjak@gmail.com>, Jakub Jelinek <jakub@redhat.com>,
Jeffrey Law <law@redhat.com>
Cc: "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>,
Jan Hubicka <hubicka@ucw.cz>
Subject: PING [PATCH] x86: Add cmpmemsi for -minline-all-stringops
Date: Wed, 19 Aug 2020 06:09:55 -0700 [thread overview]
Message-ID: <CAMe9rOq2efMDGzwe_xuVGoT7H_C00xFruOLuuTeBc48_VLiDAg@mail.gmail.com> (raw)
In-Reply-To: <CAMe9rOq9rerN2raJDFvCP2NwiQ-Ubs1Vc0m4RZ_HL=4j6yWkag@mail.gmail.com>
On Tue, May 19, 2020 at 5:14 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Tue, May 19, 2020 at 1:48 AM Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> > On Sun, May 17, 2020 at 7:06 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > >
> > > Duplicate the cmpstrn pattern for cmpmem. The only difference is that
> > > the length argument of cmpmem is guaranteed to be less than or equal to
> > > lengths of 2 memory areas. Since "repz cmpsb" can be much slower than
> > > memcmp function implemented with vector instruction, see
> > >
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43052
> > >
> > > expand cmpmem to "repz cmpsb" only with -mgeneral-regs-only.
> >
> > If there is no benefit compared to the library implementation, then
> > enable these patterns only when -minline-all-stringops is used.
>
> Fixed.
>
> > Eventually these should be reimplemented with SSE4 string instructions.
> >
> > Honza is the author of the block handling x86 system, I'll leave the
> > review to him.
>
> We used to expand memcmp to "repz cmpsb" via cmpstrnsi. It was changed
> by
>
> commit 9b0f6f5e511ca512e4faeabc81d2fd3abad9b02f
> Author: Nick Clifton <nickc@redhat.com>
> Date: Fri Aug 12 16:26:11 2011 +0000
>
> builtins.c (expand_builtin_memcmp): Do not use cmpstrnsi pattern.
>
> * builtins.c (expand_builtin_memcmp): Do not use cmpstrnsi
> pattern.
> * doc/md.texi (cmpstrn): Note that the comparison stops if both
> fetched bytes are zero.
> (cmpstr): Likewise.
> (cmpmem): Note that the comparison does not stop if both of the
> fetched bytes are zero.
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95151
>
> is a regression.
>
> Honza, can you take a look at this?
>
PING:
https://gcc.gnu.org/pipermail/gcc-patches/2020-May/546921.html
--
H.J.
next prev parent reply other threads:[~2020-08-19 13:10 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-17 17:06 [PATCH] x86: Add cmpmemsi for -mgeneral-regs-only H.J. Lu
2020-05-19 8:48 ` Uros Bizjak
2020-05-19 12:14 ` [PATCH] x86: Add cmpmemsi for -minline-all-stringops H.J. Lu
2020-08-19 13:09 ` H.J. Lu [this message]
2020-09-17 5:07 ` PING^2 " H.J. Lu
2020-10-02 13:21 ` PING^3 " H.J. Lu
2020-10-17 21:18 ` H.J. Lu
2020-10-18 15:16 ` Jan Hubicka
2020-10-18 15:27 ` H.J. Lu
2020-10-23 12:45 ` H.J. Lu
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