Bye bye MMX!

[mati865]

Fixes #823

[rust-highfive]

r? @Amanieu

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[bjorn3]

There is also special casing in the compiler to give the mmx vector type the right LLVM type. That should also be removed.

[mati865]

@bjorn3 sure, after this is merged I'm going to grep mmx on Rust repo.

[Amanieu]

I'm a bit concerned about the number of functions we're removing from SSE, SSE2, etc. Are we sure that all of these are MMX-only?

EDIT: Apparently just removing anything that uses __m64 seems to be correct. See MSVC docs:

The __m64 data type is not supported on x64 processors. Applications that use __m64 as part of MMX intrinsics must be rewritten to use equivalent SSE and SSE2 intrinsics.

[mati865]

I'm a bit concerned about the number of functions we're removing from SSE, SSE2, etc. Are we sure that all of these are MMX-only?

EDIT: Apparently just removing anything that uses __m64 seems to be correct. See MSVC docs:

The __m64 data type is not supported on x64 processors. Applications that use __m64 as part of MMX intrinsics must be rewritten to use equivalent SSE and SSE2 intrinsics.

I wasn't sure whether we want to just remove MMX instructions or all the instructions involving MMX registers.
Went for the latter but I can bring back __m64 and SSE{,2} instructions using MMX registers.

[Amanieu]

Make sure to tag with relnotes when updating the submodule in rust-lang/rust.

[Amanieu]

Hmm actually this is only unstable code, so we don't want it in the release notes.

[danieldjewell]

It would appear that this change has broken compilation of rust-lang/packed_simd (see referenced issues). I assume that it was this pull that broke things as the "_mm_movemask_pi8" macro appears to have been removed?

Could someone who is more versed in this than I perhaps take a look?

@Amanieu It would appear that your concerns were well founded.

Edit:

MSVC docs

@Amanieu I'm not sure it's a good idea for a programming language to reference another programming language's documentation unless it's written in that language.... (Correct me if I'm wrong but Rust is written in Rust?) Perhaps the best reference on what is and is not supported by x86 would be: https://software.intel.com/content/www/us/en/develop/articles/intel-sdm.html

PDF: https://software.intel.com/content/www/us/en/develop/download/intel-64-and-ia-32-architectures-sdm-combined-volumes-1-2a-2b-2c-2d-3a-3b-3c-3d-and-4.html (5000! pages! wow!)