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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 v3 RESEND 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning
Date: Mon, 18 Jan 2021 12:55:56 +0200	[thread overview]
Message-ID: <20210118105557.186614-2-adrian.ratiu@collabora.com> (raw)
In-Reply-To: <20210118105557.186614-1-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 risks misleading users.

As a side-note remark, -fttree-vectorize is on by default in
Clang, but it currently does not work (see linked issues).

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 | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c
index b99dd8e1c93f..e1e76186ec23 100644
--- a/arch/arm/lib/xor-neon.c
+++ b/arch/arm/lib/xor-neon.c
@@ -19,15 +19,8 @@ MODULE_LICENSE("GPL");
  * -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


WARNING: multiple messages have this Message-ID (diff)
From: Adrian Ratiu <adrian.ratiu@collabora.com>
To: linux-arm-kernel@lists.infradead.org
Cc: Arnd Bergmann <arnd@arndb.de>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Russell King <linux@armlinux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Nathan Chancellor <natechancellor@gmail.com>,
	kernel@collabora.com, Ard Biesheuvel <ardb@kernel.org>
Subject: [PATCH v3 RESEND 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning
Date: Mon, 18 Jan 2021 12:55:56 +0200	[thread overview]
Message-ID: <20210118105557.186614-2-adrian.ratiu@collabora.com> (raw)
In-Reply-To: <20210118105557.186614-1-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 risks misleading users.

As a side-note remark, -fttree-vectorize is on by default in
Clang, but it currently does not work (see linked issues).

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 | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c
index b99dd8e1c93f..e1e76186ec23 100644
--- a/arch/arm/lib/xor-neon.c
+++ b/arch/arm/lib/xor-neon.c
@@ -19,15 +19,8 @@ MODULE_LICENSE("GPL");
  * -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


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  reply	other threads:[~2021-01-18 10:58 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-18 10:55 [PATCH v3 RESEND 0/2] xor-neon: Remove GCC warn & pragmas Adrian Ratiu
2021-01-18 10:55 ` Adrian Ratiu
2021-01-18 10:55 ` Adrian Ratiu [this message]
2021-01-18 10:55   ` [PATCH v3 RESEND 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning Adrian Ratiu
2021-01-18 11:06   ` Arnd Bergmann
2021-01-18 11:06     ` Arnd Bergmann
2021-01-18 11:28     ` Adrian Ratiu
2021-01-18 11:28       ` Adrian Ratiu
2021-01-18 11:33       ` Arnd Bergmann
2021-01-18 11:33         ` Arnd Bergmann
2021-01-18 10:55 ` [PATCH v3 RESEND 2/2] arm: lib: xor-neon: move pragma options to makefile Adrian Ratiu
2021-01-18 10:55   ` Adrian Ratiu

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