[llvm] [SeparateConstOffsetFromGEP] Decompose xor constant operand when possible (PR #195830)

[Eli Friedman via llvm-commits]

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efriedma-quic wrote:

Do we need any other profitability heuristics?

If the resulting xor simplifies, great, but there isn't any reason to expect that will happen in general

https://github.com/llvm/llvm-project/pull/195830