[llvm] [InstCombine] Do not perform binop-of-shuffle when mask is poison (PR #82185)

[via llvm-commits]

goldsteinn wrote:

> > It looks like only your third test is problematic: https://alive2.llvm.org/ce/z/WrH49f
> > can the fix be made more precise?
> 
> Wouldn't that require to know right / left demanded of the mask of the use of the operand passed to `SimplifyDemandedVectorElts` (`%msplat`)? Not sure if there's a better / worth way to do this.

+ 1

https://github.com/llvm/llvm-project/pull/82185