| Message ID | 20201112212457.2042105-2-adrian.ratiu@collabora.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xor-neon: Remove GCC warn & pragmas | expand |
On Thu, Nov 12, 2020 at 1:23 PM Adrian Ratiu <adrian.ratiu@collabora.com> wrote: > > 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"). > > Reported-by: Nick Desaulniers <ndesaulniers@google.com> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> Link: https://github.com/ClangBuiltLinux/linux/issues/496 Link: https://github.com/ClangBuiltLinux/linux/issues/503 Reviewed-by: Nick Desaulniers <ndesaulniers@google.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" > -- > 2.29.2 >
On Thu, 12 Nov 2020 at 22:23, Adrian Ratiu <adrian.ratiu@collabora.com> wrote: > > 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"). > > Reported-by: Nick Desaulniers <ndesaulniers@google.com> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> Again, this does not do what it says on the tin. If you want to disable the pragma for Clang, call that out in the commit log, and don't hide it under a GCC version change. Without the pragma, the generated code is the same as the generic code, so it makes no sense to build xor-neon.ko at all, right? > --- > 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" > -- > 2.29.2 >
Hi Ard, On Fri, 13 Nov 2020, Ard Biesheuvel <ardb@kernel.org> wrote: > On Thu, 12 Nov 2020 at 22:23, Adrian Ratiu > <adrian.ratiu@collabora.com> wrote: >> >> 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"). >> >> Reported-by: Nick Desaulniers <ndesaulniers@google.com> >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> >> Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> > > Again, this does not do what it says on the tin. > > If you want to disable the pragma for Clang, call that out in > the commit log, and don't hide it under a GCC version change. I am not doing anything for Clang in this series. The option to auto-vectorize in Clang is enabled by default but doesn't work for some reason (likely to do with how it computes the cost model, so maybe not even a bug at all) and if we enable it explicitely (eg via a Clang specific pragma) we get some warnings we currently do not understand, so I am not changing the Clang behaviour at the recommendation of Nick. So this is only for GCC as the "tin" says :) We can fix clang separately as the Clang bug has always been present and is unrelated. > > Without the pragma, the generated code is the same as the > generic code, so it makes no sense to build xor-neon.ko at all, > right? > Yes that is correct and that is the reason why in v1 I opted to not build xor-neon.ko for Clang anymore, but that got NACKed, so here I'm fixing the low hanging fruit: the very obvious & clear GCC problems. >> --- >> 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" >> -- >> 2.29.2 >>
On Fri, 13 Nov 2020 at 12:05, Adrian Ratiu <adrian.ratiu@collabora.com> wrote: > > Hi Ard, > > On Fri, 13 Nov 2020, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Thu, 12 Nov 2020 at 22:23, Adrian Ratiu > > <adrian.ratiu@collabora.com> wrote: > >> > >> 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"). > >> > >> Reported-by: Nick Desaulniers <ndesaulniers@google.com> > >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > >> Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> > > > > Again, this does not do what it says on the tin. > > > > If you want to disable the pragma for Clang, call that out in > > the commit log, and don't hide it under a GCC version change. > > I am not doing anything for Clang in this series. > > The option to auto-vectorize in Clang is enabled by default but > doesn't work for some reason (likely to do with how it computes > the cost model, so maybe not even a bug at all) and if we enable > it explicitely (eg via a Clang specific pragma) we get some > warnings we currently do not understand, so I am not changing the > Clang behaviour at the recommendation of Nick. > > So this is only for GCC as the "tin" says :) We can fix clang > separately as the Clang bug has always been present and is > unrelated. > But you are adding the IS_GCC check here, no? Is that equivalent? IOW, does Clang today identify as GCC <= 4.6? > > > > Without the pragma, the generated code is the same as the > > generic code, so it makes no sense to build xor-neon.ko at all, > > right? > > > > Yes that is correct and that is the reason why in v1 I opted to > not build xor-neon.ko for Clang anymore, but that got NACKed, so > here I'm fixing the low hanging fruit: the very obvious & clear > GCC problems. > > Fair enough. > >> --- > >> 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" > >> -- > >> 2.29.2 > >>
On Fri, 13 Nov 2020, Ard Biesheuvel <ardb@kernel.org> wrote: > On Fri, 13 Nov 2020 at 12:05, Adrian Ratiu > <adrian.ratiu@collabora.com> wrote: >> >> Hi Ard, >> >> On Fri, 13 Nov 2020, Ard Biesheuvel <ardb@kernel.org> wrote: >> > On Thu, 12 Nov 2020 at 22:23, Adrian Ratiu >> > <adrian.ratiu@collabora.com> wrote: >> >> >> >> 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"). >> >> >> >> Reported-by: Nick Desaulniers <ndesaulniers@google.com> >> >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> >> >> Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> >> > >> > Again, this does not do what it says on the tin. >> > >> > If you want to disable the pragma for Clang, call that out in >> > the commit log, and don't hide it under a GCC version change. >> >> I am not doing anything for Clang in this series. >> >> The option to auto-vectorize in Clang is enabled by default but >> doesn't work for some reason (likely to do with how it computes >> the cost model, so maybe not even a bug at all) and if we >> enable it explicitely (eg via a Clang specific pragma) we get >> some warnings we currently do not understand, so I am not >> changing the Clang behaviour at the recommendation of Nick. >> >> So this is only for GCC as the "tin" says :) We can fix clang >> separately as the Clang bug has always been present and is >> unrelated. >> > > But you are adding the IS_GCC check here, no? Is that > equivalent? IOW, does Clang today identify as GCC <= 4.6? > I see what you mean now. Thanks. Clang identifies as GCC <= 4.6 yes, so the code is not strictly speaking equivalent. The warning to upgrade GCC doesn't make sense for Clang but I should mention removing it in the commit message as well. >> > >> > Without the pragma, the generated code is the same as the >> > generic code, so it makes no sense to build xor-neon.ko at all, >> > right? >> > >> >> Yes that is correct and that is the reason why in v1 I opted to >> not build xor-neon.ko for Clang anymore, but that got NACKed, so >> here I'm fixing the low hanging fruit: the very obvious & clear >> GCC problems. >> >> > > Fair enough. > >> >> --- >> >> 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" >> >> -- >> >> 2.29.2 >> >>
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"