[llvm] [InstCombine][NFC] Pre-commit tests for #125935 (PR #144111)

[Abhishek Kaushik via llvm-commits]

abhishek-kaushik22 wrote:

> You can set the known bits for a scalar, then create a vector splat: https://alive2.llvm.org/ce/z/oBQx2e It is clearer than and+shift+or sequence.

I tried but this triggers a different instcombine simplification than what we are looking for

https://github.com/llvm/llvm-project/pull/144111