Automatic verification of MIPS MSA intrinsics

[gnzlbg]

This PR adds automatic-verification of the MIPS MSA intrinsic type signatures

cc @rbirdic @wzssyqa

[alexcrichton]

This looks great to me, thanks @gnzlbg!

The only general comment I'd have is that we may want to double check for a more official source for intrinsic definitions other than a gcc header file. I know at least on x86 the __builtin_* functions all don't always map well to Intel's own names (and often don't correspond to intrinsics). I know very little about MIPS SIMD though, so if gcc is more 1:1 with upstream vendors then seems fine by me!

[gnzlbg]

The problem is that the C headers that do not include the __builtin_ use C macros to wrap those, so we can't extract any type information from them, e.g., see: https://github.com/gcc-mirror/gcc/blob/master/gcc/config/mips/msa.h#L52

[gnzlbg]

The clang header does the same: https://clang.llvm.org/doxygen/msa_8h_source.html

[alexcrichton]

Ah ok that at least means directly using the __builtin macros is probably a good idea! Seems fine by me

[gnzlbg]

FYI i tried to enable checking the instructions, but something appears to be broken in the code that parses the assert_instr macros. It only finds intrinsics in 3/100 intrinsics. I've tried a bit of code golf there, but so much has changed in syn in the last years that I'm not really sure if the approach is correct anymore.

[alexcrichton]

Ah no worries, if you want to land this an open an issue I can follow-up later poking around to see if I can enable this

[gnzlbg]

I'll wait for @rbirdic to review the proposed changes to the msa module and merge afterwards.

[rbirdic]

@gnzlbg This looks good to me. Thank you!