Messages in this thread Patch in this message | | | From | Adrian Ratiu <> | Subject | [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning | Date | Tue, 19 Jan 2021 15:17:23 +0200 |
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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
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