On Tue, Jun 27, 2023 at 07:23:32AM +0100, Richard Sandiford wrote:
> Andrew Carlotti via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > Many intrinsics currently depend on both an architecture version and a
> > feature, despite the corresponding instructions being available within
> > GCC at lower architecture versions.
> >
> > LLVM has already removed these explicit architecture version
> > dependences; this patch does the same for GCC, as well as removing an
> > unecessary simd dependency for the scalar fp16 intrinsics.
> >
> > Binutils does not support all of these architecture+feature combinations
> > yet, but this is an existing problem that is already reachable from GCC.
> > For example, compiling the test gcc.target/aarch64/usadv16qi-dotprod.c
> > with -O3 -march=armv8-a+dotprod has resulted in an assembler error since
> > GCC 10. I intend to patch this in binutils.
> >
> > This patch retains explicit architecture version dependencies for
> > features that do not currently have a separate feature flag.
> >
> > Ok for master, and backport to GCC 13?
> >
> > gcc/ChangeLog:
> >
> > * config/aarch64/aarch64.h (TARGET_MEMTAG): Remove armv8.5
> > dependency.
> > * config/aarch64/arm_acle.h: Remove unnecessary armv8.x
> > dependencies from target pragmas.
> > * config/aarch64/arm_fp16.h (target): Likewise.
>
> The change to this file is a bit different from the others,
> since it's removing an implicit dependency on +simd, rather
> than a dependency on an architecture level. I think it'd be
> worth mentioning that explicitly in the changelog.
>
> OK with that change, thanks.
>
> (Arguably we should add +nosimd to many of the other pragmas in
> arm_acle.h, but that's logically a separate patch.)
>
> Richard
Actually, I think I should just remove the +nosimd from the patch, because
+fp16 doesn't enable simd (unlike +bf16, which has simd as an 'explicit on'
implication).
Aside from +bf16, the only other feature with simd as an 'explicit on' is
+rdma. However, there appear to be no non-simd rdma instructions, so
+nothing+rdma+nosimd is effectively the same as +nothing.
> > ...
> >
> > diff --git a/gcc/config/aarch64/arm_fp16.h b/gcc/config/aarch64/arm_fp16.h
> > index
> > a8fa4dbbdfe1bab4aa604bb311ef66d4e1de18ac..84b2ed66f9ba19fba6ccd8be33940d7239bfa22e
> > 100644
> > --- a/gcc/config/aarch64/arm_fp16.h
> > +++ b/gcc/config/aarch64/arm_fp16.h
> > @@ -30,7 +30,7 @@
> > #include <stdint.h>
> >
> > #pragma GCC push_options
> > -#pragma GCC target ("arch=armv8.2-a+fp16")
> > +#pragma GCC target ("+nothing+fp16+nosimd")
> >
> > typedef __fp16 float16_t;
> >
