On Mon, 22 May 2023 at 16:36, Matthias Kretz via Libstdc++ <
libstd...@gcc.gnu.org> wrote:
> OK for trunk and backporting?
>
> regtested on x86_64-linux and aarch64-linux
>
> The constexpr API is only available with -std=gnu++XX (and proposed for
> C++26). The proposal is to have the complete simd API usable in constant
> expressions.
>
> This patch resolves several issues with using simd in constant
> expressions.
>
> Issues why constant_evaluated branches are necessary:
>
I note that using if (not __builtin_constant_evaluated()) will fail if
compiled with -fno-operator-names, which is why we don't use 'not', 'and',
etc. elsewhere in libstdc++. I don't know if (or why) anybody uses that
option though, so I don't think you need to hange anything in stdx::simd.
> * subscripting vector builtins is not allowed in constant expressions
>
Is that just because nobody made it work (yet)?
* if the implementation needs/uses memcpy
> * if the implementation would otherwise call SIMD intrinsics/builtins
>
The indentation looks off here and in the _M_set member function following
it:
operator[](size_t __i) const noexcept
{
if constexpr (_S_tuple_size == 1)
return _M_subscript_read(__i);
else
- {
#ifdef _GLIBCXX_SIMD_USE_ALIASING_LOADS
- return reinterpret_cast<const __may_alias<_Tp>*>(this)[__i];
-#else
- if constexpr (__is_scalar_abi<_Abi0>())
- {
- const _Tp* ptr = &first;
- return ptr[__i];
- }
- else
- return __i < simd_size_v<_Tp, _Abi0>
- ? _M_subscript_read(__i)
- : second[__i - simd_size_v<_Tp, _Abi0>];
+ if (not __builtin_is_constant_evaluated())
+ return reinterpret_cast<const __may_alias<_Tp>*>(this)[__i];
+ else
#endif
+ if constexpr (__is_scalar_abi<_Abi0>())
+ {
+ const _Tp* ptr = &first;
+ return ptr[__i];
}
+ else
+ return __i < simd_size_v<_Tp, _Abi0> ? _M_subscript_read(__i)
+ : second[__i - simd_size_v<_Tp, _Abi0>];
}
Are the copyright years on
testsuite/experimental/simd/pr109261_constexpr_simd.cc correct, or just
copy&paste?
