[llvm] [InstCombine] Limit canonicalization of extractelement(cast) to constant index or same basic block. (PR #166227)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon approved this pull request.

LGTM - but I think we'd be better off looking at moving this to VectorCombine at some point soon to allow it be cost driven. Also, FTR bitcasts aren't always free - fp<->int bitcasts (fp bit twiddling etc.) in particular can be a major headache.

https://github.com/llvm/llvm-project/pull/166227