From: Arnd Bergmann <arnd@kernel.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Adrian Ratiu <adrian.ratiu@collabora.com>,
Arnd Bergmann <arnd@arndb.de>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Nathan Chancellor <natechancellor@gmail.com>,
Russell King <linux@armlinux.org.uk>,
Ard Biesheuvel <ardb@kernel.org>,
Arvind Sankar <nivedita@alum.mit.edu>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Collabora Kernel ML <kernel@collabora.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning
Date: Tue, 19 Jan 2021 22:34:45 +0100 [thread overview]
Message-ID: <CAK8P3a0XWVu-oG3YaGppZDedRL=SA37Gr8YM4cojVap5Bwk2TA@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdkNZ09kkzi+A8diaxViqSufxrHizuBu-7quG6an3Z8iDA@mail.gmail.com>
On Tue, Jan 19, 2021 at 10:18 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@googlegroups.com> wrote:
>
> On Tue, Jan 19, 2021 at 5:17 AM Adrian Ratiu <adrian.ratiu@collabora.com> wrote:
> > diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c
> > index b99dd8e1c93f..f9f3601cc2d1 100644
> > --- a/arch/arm/lib/xor-neon.c
> > +++ b/arch/arm/lib/xor-neon.c
> > @@ -14,20 +14,22 @@ MODULE_LICENSE("GPL");
> > #error You should compile this file with '-march=armv7-a -mfloat-abi=softfp -mfpu=neon'
> > #endif
> >
> > +/*
> > + * TODO: Even though -ftree-vectorize is enabled by default in Clang, the
> > + * compiler does not produce vectorized code due to its cost model.
> > + * See: https://github.com/ClangBuiltLinux/linux/issues/503
> > + */
> > +#ifdef CONFIG_CC_IS_CLANG
> > +#warning Clang does not vectorize code in this file.
> > +#endif
>
> Arnd, remind me again why it's a bug that the compiler's cost model
> says it's faster to not produce a vectorized version of these loops?
> I stand by my previous comment: https://bugs.llvm.org/show_bug.cgi?id=40976#c8
The point is that without vectorizing the code, there is no point in building
both the default xor code and a "neon" version that has to save/restore
the neon registers but doesn't actually use them.
Arnd
next prev parent reply other threads:[~2021-01-19 21:37 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 13:17 [PATCH v4 0/2] xor-neon: Remove GCC warn & pragmas Adrian Ratiu
2021-01-19 13:17 ` [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning Adrian Ratiu
2021-01-19 21:18 ` Nick Desaulniers
2021-01-19 21:34 ` Arnd Bergmann [this message]
2021-01-19 22:04 ` Nick Desaulniers
2021-01-19 23:10 ` Nick Desaulniers
2021-01-20 23:09 ` Nick Desaulniers
2021-01-20 23:15 ` Nick Desaulniers
2021-01-21 4:13 ` Arvind Sankar
2021-01-21 4:24 ` Nick Desaulniers
2021-01-21 8:46 ` Ard Biesheuvel
2021-01-20 13:11 ` Adrian Ratiu
2021-01-19 21:54 ` Nathan Chancellor
2021-01-20 13:18 ` Adrian Ratiu
2021-01-19 22:04 ` David Laight
2021-01-19 22:05 ` Nick Desaulniers
2021-01-19 13:17 ` [PATCH v4 2/2] arm: lib: xor-neon: move pragma options to makefile Adrian Ratiu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAK8P3a0XWVu-oG3YaGppZDedRL=SA37Gr8YM4cojVap5Bwk2TA@mail.gmail.com' \
--to=arnd@kernel.org \
--cc=adrian.ratiu@collabora.com \
--cc=ardb@kernel.org \
--cc=arnd@arndb.de \
--cc=clang-built-linux@googlegroups.com \
--cc=kernel@collabora.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@armlinux.org.uk \
--cc=natechancellor@gmail.com \
--cc=ndesaulniers@google.com \
--cc=nivedita@alum.mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).