[llvm] [DAG] foldShiftToAvg - recognize sub(x, xor(y, -1)) >> 1 as avgceil[su] (#147946) (PR #156239)

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laurenmchin wrote:

@RKSimon hi! i haven’t had a chance to wrap this up yet because i’ve been focused on midterms, which wrap up next week. i’ll get back to both patches right after that - thanks for your patience and for the ping

https://github.com/llvm/llvm-project/pull/156239