[llvm] [MIPS] [MSA] Widen v2i8, v216 and v2i32 vectors (PR #123040)

[Cinhi Young via llvm-commits]

Cyanoxygen wrote:

> Can we split 
> 
> ```
> 
> Widen v2i8, v2i16 and v2i32 vectors so they don't cast back and forth, and make sure that instructions with correct data unit is being used.
> 
> ```
> 
> and 
> 
> ```
> 
> Handle undef indices for VSHF when lowering VECTOR_SHUFFLE (it crashes if such index is present).
> 
> ```

No, the widened shuffle mask is guaranteed to contain UNDEFs which the VSHF must handle. Without that change the compiler simply aborts.

https://github.com/llvm/llvm-project/pull/123040