From: Adrian Ratiu <adrian.ratiu@collabora.com>
To: linux-arm-kernel@lists.infradead.org
Cc: Nathan Chancellor <natechancellor@gmail.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Arnd Bergmann <arnd@arndb.de>,
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>,
kernel@collabora.com,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning
Date: Tue, 19 Jan 2021 15:17:23 +0200 [thread overview]
Message-ID: <20210119131724.308884-2-adrian.ratiu@collabora.com> (raw)
In-Reply-To: <20210119131724.308884-1-adrian.ratiu@collabora.com>
From: Nathan Chancellor <natechancellor@gmail.com>
Drop warning because kernel now requires GCC >= v4.9 after
commit 6ec4476ac825 ("Raise gcc version requirement to 4.9")
and clarify that -ftree-vectorize now always needs enabling
for GCC by directly testing the presence of CONFIG_CC_IS_GCC.
Another reason to remove the warning is that Clang exposes
itself as GCC < 4.6 so it triggers the warning about GCC
which doesn't make much sense and misleads Clang users by
telling them to update GCC.
Because Clang is now supported by the kernel print a clear
Clang-specific warning.
Link: https://github.com/ClangBuiltLinux/linux/issues/496
Link: https://github.com/ClangBuiltLinux/linux/issues/503
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
---
arch/arm/lib/xor-neon.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
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
+
/*
* Pull in the reference implementations while instructing GCC (through
* -ftree-vectorize) to attempt to exploit implicit parallelism and emit
* NEON instructions.
*/
-#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
+#ifdef CONFIG_CC_IS_GCC
#pragma GCC optimize "tree-vectorize"
-#else
-/*
- * While older versions of GCC do not generate incorrect code, they fail to
- * recognize the parallel nature of these functions, and emit plain ARM code,
- * which is known to be slower than the optimized ARM code in asm-arm/xor.h.
- */
-#warning This code requires at least version 4.6 of GCC
#endif
#pragma GCC diagnostic ignored "-Wunused-variable"
--
2.30.0
next prev parent reply other threads:[~2021-01-19 13:30 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 ` Adrian Ratiu [this message]
2021-01-19 21:18 ` [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning Nick Desaulniers
2021-01-19 21:34 ` Arnd Bergmann
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=20210119131724.308884-2-adrian.ratiu@collabora.com \
--to=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).