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

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

OK if you close it - if we do find a need for it we'll effectively be starting from scratch anyhow

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