Add Kokkos::mdspan

[Swiftb0y]

mdspan will be in C++23 and could greatly help with making the audio engine more flexible. It allows to interpret a contiguous chunk of memory as a multidimensional std::span. The result is that the iteration logic can be separate from the memory access logic (and thus the memory layout), allowing us to write generic audio algorithms which can easily adapt to different channel layouts (consider surround audio and STEMs).
This PR contains a demo commit to confirm the changes to the build actually work, no meaningful work has yet been done in any mixxx-related audio code.

[JoergAtGithub]

Sounds good to me!

[daschuer]

Nice.

It would be interesting if auto vectorization is still done when we for instance use it for:

mixxx/src/util/sample.cpp

Line 178 in f36cd4f

void SampleUtil::applyAlternatingGain(CSAMPLE* pBuffer, CSAMPLE gain1,

Unfortunatly MSVC 2019 is not able to compile it:

Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(67): error C7568: argument list missing after assumed function template 'is_empty_v'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(67): error C2059: syntax error: '!'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(67): error C7568: argument list missing after assumed function template 'is_empty_v'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(68): error C2332: 'struct': missing tag name
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(68): error C3306: 'Kokkos::detail::<unnamed-tag>': unnamed class template is not allowed
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(82): error C2639: trailing return type 'int' of deduction guide should be a specialization of 'Kokkos::detail::__compressed_pair'
D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(98): note: see reference to class template instantiation 'Kokkos::detail::<unnamed-tag><_T,_U>' being compiled
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(82): error C2643: deduction guide should be declared in the same scope as the corresponding class template 'Kokkos::detail::__compressed_pair'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(82): error C2178: 'Kokkos::detail::<unnamed-tag><_T,_U>::__compressed_pair' cannot be declared with 'constexpr' specifier
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(82): error C2610: 'int Kokkos::detail::<unnamed-tag><_T,_U>::__compressed_pair(void) noexcept': is not a special member function or comparison operator which can be defaulted
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(84): error C2061: syntax error: identifier '__compressed_pair'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(84): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(84): error C2610: 'int Kokkos::detail::<unnamed-tag><_T,_U>::__compressed_pair(void) noexcept': is not a special member function or comparison operator which can be defaulted
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(86): error C2061: syntax error: identifier '__compressed_pair'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(86): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(86): error C2610: 'int Kokkos::detail::<unnamed-tag><_T,_U>::__compressed_pair(void) noexcept': is not a special member function or comparison operator which can be defaulted
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(88): error C2143: syntax error: missing ';' before '&'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(88): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(88): error C2178: 'Kokkos::detail::<unnamed-tag><_T,_U>::__compressed_pair' cannot be declared with 'constexpr' specifier
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(89): error C2238: unexpected token(s) preceding ';'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(91): error C2143: syntax error: missing ';' before '&'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(91): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(91): error C2178: 'Kokkos::detail::<unnamed-tag><_T,_U>::__compressed_pair' cannot be declared with 'constexpr' specifier
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(92): error C2238: unexpected token(s) preceding ';'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(94): error C2523: 'Kokkos::detail::<unnamed-tag><_T,_U>::~__compressed_pair': destructor tag mismatch
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(97): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(104): error C7568: argument list missing after assumed function template 'is_empty_v'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(104): error C2062: type 'unknown-type' unexpected
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(104): error C7568: argument list missing after assumed function template 'is_empty_v'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(105): error C2332: 'struct': missing tag name
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(136): error C2953: 'Kokkos::detail::<unnamed-tag>': class template has already been defined
D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(105): note: see declaration of 'Kokkos::detail::<unnamed-tag>'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(142): error C7568: argument list missing after assumed function template 'is_empty_v'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(142): error C7568: argument list missing after assumed function template 'is_empty_v'
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(142): error C2062: type 'unknown-type' unexpected
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(148): error C2332: 'struct': missing tag name
Error: D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(190): error C2953: 'Kokkos::detail::<unnamed-tag>': class template has already been defined
D:\a\mixxx\mixxx\lib\mdspan\include\experimental\__p0009_bits\compressed_pair.hpp(148): note: see declaration of 'Kokkos::detail::<unnamed-tag>'
[242/870] Building CXX object CMakeFiles\mixxx-lib.dir\src\analyzer\analyzerwaveform.cpp.obj
ninja: build stopped: subcommand failed.
Error: Process completed with exit code 1.

[Swiftb0y]

It would be interesting if auto vectorization is still done when we for instance use it for:

Yes, I'm quite certain though it probably depends on the complexity of layout and the accessor implementation. Unfortunately there is not much accessible documentation for mdspan yet. These are probably the best:

• https://github.com/kokkos/mdspan/wiki/A-Gentle-Introduction-to-mdspan
• https://www.youtube.com/watch?v=lvylnaqB96U

Unfortunatly MSVC 2019 is not able to compile it:

They seem to be aware but not doing particularly much about it. kokkos/mdspan#26

We could conditionally use the vcpkg port on MSVC, though I don't really want to look into this right now.

[JoergAtGithub]

If it compiles with VS2022, it should be OK for the Main branch. This is because Qt6 requires Windows 10 (build 1809 or later) and on these newer Windows10 versions, VS2022 is supported as well.

[github-actions]

This PR is marked as stale because it has been open 90 days with no activity.

[Swiftb0y]

It builds. I'll remove the demo commit and remove draft now.

[daschuer]

LGTM.

However let's keep it as draft to not merge an unused library to our lib folder.
If one starts to refactor our code using mdspan they can base on this PR.

[Swiftb0y]

Fine for me.

[github-actions]

This PR is marked as stale because it has been open 90 days with no activity.