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

[Ricardo Jesus via llvm-commits]

rj-jesus wrote:

Yeah, that came up in one of the comments in #135769. Avoiding the vector extract and scalar->vector bitcast seemed generally useful, but I'm happy to move this to VectorCombine if you think that would be better. Shall I do so?

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