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

[Nikita Popov via llvm-commits]

nikic wrote:

> If the fold proposed in this PR isn't suitable for InstCombine, maybe we should revisit https://github.com/llvm/llvm-project/pull/135769, unless you have another suggestion?

I'm ok with that. Could you add a test that wouldn't be covered by having this patch in VectorCombine to that PR maybe?

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