On Thursday, 28 April 2022 08:09:54 CEST Alexandre Oliva via Gcc-patches
wrote:
> libstdc++'s bits/simd.h section for PPC (Altivec) defines various
> intrinsic vector types that are only available along with VSX: 64-bit
> long double, double, (un)signed long long, and 64-bit (un)signed long.
Oh, so uttering `__vector double` is ill-formed (now) without VSX? I'm fairly
certain I tested without VSX and the __intrinsic_type_impl definitions were
fine.
> experimental/simd/standard_abi_usable{,_2}.cc tests error out reporting
> the unmet requirements when the target cpu doesn't enable VSX. Make the
> reported instrinsic types conditional on VSX so that <experimental/simd>
> can be used on ppc variants that do not have VSX support.
IIRC this will break other valid uses. You'd have to run `make check-simd`
(see libstdc++-v3/testsuite/experimental/simd/README.md) to be certain nothing
breaks. I will also take a look.
> Regstrapped on powerpc64el-linux-gnu. Ok to install?
>
> This is also relevant for gcc-11. Tested with
> x86_64-linux-gnu-x-ppc64-vx7r2. Ok for gcc-11?
>
>
> for libstdc++-v3/ChangeLog
>
> * include/experimental/bits/simd.h [__ALTIVEC__]: Require VSX
> for double, long long, and 64-bit long and 64-bit long double
> intrinsic types.
> ---
> libstdc++-v3/include/experimental/bits/simd.h | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/libstdc++-v3/include/experimental/bits/simd.h
> b/libstdc++-v3/include/experimental/bits/simd.h index
> 82e9841195e1d..66c07127ec435 100644
> --- a/libstdc++-v3/include/experimental/bits/simd.h
> +++ b/libstdc++-v3/include/experimental/bits/simd.h
> @@ -2430,17 +2430,23 @@ template <typename _Tp>
> template <>
> \ struct __intrinsic_type_impl<_Tp> { using type = __vector _Tp; }
> _GLIBCXX_SIMD_PPC_INTRIN(float);
> +# ifdef __VSX__
> _GLIBCXX_SIMD_PPC_INTRIN(double);
> +# endif
> _GLIBCXX_SIMD_PPC_INTRIN(signed char);
> _GLIBCXX_SIMD_PPC_INTRIN(unsigned char);
> _GLIBCXX_SIMD_PPC_INTRIN(signed short);
> _GLIBCXX_SIMD_PPC_INTRIN(unsigned short);
> _GLIBCXX_SIMD_PPC_INTRIN(signed int);
> _GLIBCXX_SIMD_PPC_INTRIN(unsigned int);
> +# if defined __VSX__ || __LONG_WIDTH__ == 32
> _GLIBCXX_SIMD_PPC_INTRIN(signed long);
> _GLIBCXX_SIMD_PPC_INTRIN(unsigned long);
> +# endif
> +# ifdef __VSX__
> _GLIBCXX_SIMD_PPC_INTRIN(signed long long);
> _GLIBCXX_SIMD_PPC_INTRIN(unsigned long long);
> +# endif
> #undef _GLIBCXX_SIMD_PPC_INTRIN
>
> template <typename _Tp, size_t _Bytes>
> @@ -2452,8 +2458,9 @@ template <typename _Tp, size_t _Bytes>
> static_assert(!(_S_is_ldouble && sizeof(long double) > sizeof(double)),
> "no __intrinsic_type support for long double on PPC");
> #ifndef __VSX__
> - static_assert(!is_same_v<_Tp, double>,
> - "no __intrinsic_type support for double on PPC w/o VSX");
> + static_assert(!(is_same_v<_Tp, double>
> + || (_S_is_ldouble && sizeof(long double) ==
sizeof(double))),
> + "no __intrinsic_type support for [long] double on PPC w/o
VSX");
The missing condition here was an incorrect omission. With -mlong-double-64
and without VSX no assertion caught the issue.
IIRC, a user won't get to see this error message unless there's a bug in the
simd library implementation, so the error message is good enough for me. (It's
talking about __intrinsic_type, the user would be lost in any case.)
> #endif
> using type =
> typename __intrinsic_type_impl<
--
──────────────────────────────────────────────────────────────────────────
Dr. Matthias Kretz https://mattkretz.github.io
GSI Helmholtz Centre for Heavy Ion Research https://gsi.de
stdₓ::simd
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