[libcxx-commits] [PATCH] D144363: [libcxx] <experimental/simd> Added simd width functions, simd_size traits and related tests

[Yin Zhang via Phabricator via libcxx-commits]

Joy12138 added a comment.

In D144363#4504760 <https://reviews.llvm.org/D144363#4504760>, @philnik wrote:

> In D144363#4504748 <https://reviews.llvm.org/D144363#4504748>, @Joy12138 wrote:
>
>> @philnik Hi! We found that the current implementation might have an unexpected behavior. Because we do not check the template parameter of `simd_size_v`, it gives value with invalid first parameter.
>>
>> https://godbolt.org/z/o8o4fWe7n
>>
>> In the document, `simd_size` is implemented first and using `simd_size_v` as value of `simd_size`. Therefore, the template parameters of `simd_size_v` are checked by `simd_size`. Here is the behavior with GCC implementation: https://godbolt.org/z/1vYTsnbsd
>>
>> I implement in the current form because you told me earlier that implementing variable first can avoid instantiating a class every time. But it seems to have some minor issues at the moment.
>>
>> By the way, `memory_alignment_v` will also have the same issue. Do you have any suggestions for solving this?
>
> Good catch! I'm actually learning some really interesting things about template variables and how they interact with things. I think the easiest solution for now is to use the class to implement the `_v` version. It's probably not worth the effort to try to avoid the instantiation. That's more of a nice to have than an absolute need to have. Please also add a test for this. Something like
>
> name=simd_size_v.verify.cpp
>   static_assert(!std::experimental::simd_size_v<...>); // expected-error {{no member named 'value'}}
>
> should be good enough.

It seems CI not happy with

> name=simd_size_v.verify.cpp
>   static_assert(!std::experimental::simd_size_v<...>); // expected-error {{no member named 'value'}}

Can I use

> name=simd_size_v.verify.cpp
>   std::experimental::simd_size_v<...>; // expected-error {{no member named 'value'}}

instead? Or do you have any solutions?


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