[llvm] [VectorCombine] Fold Deinterleave/Interleave Pairs (PR #211022)

[Gaëtan Bossu via llvm-commits]

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gbossu wrote:

Or poison/undef? (Note it might already be supported by `getSplatValue()`, but I guess if the first instruction uses poison and the next one use a proper splat, then we won't consider all operands as identical)

https://github.com/llvm/llvm-project/pull/211022