[llvm] [LV] Remove common extends and selects in CSE (PR #147731)

[Sam Tebbs via llvm-commits]

SamTebbs33 wrote:

> Is the motivation for the change just removing redundant instructions in tests or unoptimized input IR?
> 
> Would be good to better understand the motivation for extending the legacy CSE, which originally was only intended to clean up some instructions related to inductions.

The motivating case was that duplicate recipes are created when `VPExpressionREcipe`  clones recipes, and this is enough to get rid of them.

https://github.com/llvm/llvm-project/pull/147731