[llvm] [SeparateConstOffsetFromGEP] Decompose constant xor operand if possible (PR #135788)

[Shilei Tian via llvm-commits]

shiltian wrote:

> Ping! This is a P1 in downstream ticketing system.

This PR has NEVER been approved so you can't just merge it, even it is blocking anything, needless to say you basically already got request for change from two folks.

https://github.com/llvm/llvm-project/pull/135788