[llvm] [InstCombine][X86] Only demand used bits for PSHUFB mask values (PR #106377)

[Cristian Vîjdea via llvm-commits]

cvijdea-bd wrote:

@RKSimon seems great, but it seems the same thing is also missing for vperm(b|d|w|q)? They only use to lower 4, 5, 6 bits for 128, 256, and 512 size respectively. Unlike pshufb, the high bit is ignored.

https://godbolt.org/z/M1rWh7oWf



https://github.com/llvm/llvm-project/pull/106377