[llvm] d4ec8ea - [InstCombine] ctpop(X) + ctpop(Y) => ctpop(X | Y) if X and Y have no common bits (PR48999)

[Joerg Sonnenberger via llvm-commits]

On Sat, Apr 24, 2021 at 08:52:20AM -0700, Dávid Bolvanský via llvm-commits wrote:
> 
> Author: Dávid Bolvanský
> Date: 2021-04-24T17:52:10+02:00
> New Revision: d4ec8ea19cb1c944f70b584b2bdb8a12ea875261
> 
> URL: https://github.com/llvm/llvm-project/commit/d4ec8ea19cb1c944f70b584b2bdb8a12ea875261
> DIFF: https://github.com/llvm/llvm-project/commit/d4ec8ea19cb1c944f70b584b2bdb8a12ea875261.diff
> 
> LOG: [InstCombine] ctpop(X) + ctpop(Y) => ctpop(X | Y) if X and Y have no common bits (PR48999)

Would it make sense to slightly generalize this into:

  ctpop(X) + ctpop(Y) => ctpop(X|Y) - ctpop(X&Y)

if X&Y is known to be constant?

Joerg