ssse3 `_mm_abs_pi8` : Intrinsic has incorrect return type!

[gwenn]

Try fn _mm_abs_pi8(a: i8x8) -> u8x8 patch or fn _mm_abs_pi8(a: i8x8) -> i8x8 to reproduce the error:

Intrinsic has incorrect return type!
<8 x i8> (<8 x i8>)* @llvm.x86.ssse3.pabs.b
LLVM ERROR: Broken function found, compilation aborted!
error: Could not compile `stdsimd`.

[BurntSushi]

For context, LLVM seems to think this should return an MMX type, and I've had problems getting other intrinsics with similar types to work with Rust as well. I don't quite know how to debug it though.

[alexcrichton]

According to the LLVM test for this there's a dedicated x86_mmx type for this which we're not currently using. I think this'll require compiler changes to use x86_mmx for sure?

[gwenn]

@alexcrichton You mean rustc changes ? And then we can cast i8x8 to x86_mmx ?

[alexcrichton]

I think the i8x8 type needs to be defined as x86_mmx on x86 targets similarly to how i16x8 is defined as <i16 x 8> as a type. Not sure why these are different at the LLVM layer, but something we'll have to take care of in rustc for sure.

[alexcrichton]

I've opened up an upstream PR to add this type