[llvm] [InstCombine] Fold bitcast (extelt (bitcast X), Idx) into bitcast+shufflevector. (PR #136998)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

I think so - the extra bonus is you might be able to drop the one use checks, assuming you can account for the old/new cases in the costs.

https://github.com/llvm/llvm-project/pull/136998