[PATCH] D76568: [InstCombine] Add CTPOP -> CTTZ simplifications (PR43513)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: spatel, lebedev.ri, nikic, xbolva00.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

As detailed on PR43513, we can simplify:

ctpop(x | -x) -> bitwidth - cttz(x, false)
Alive2: http://volta.cs.utah.edu:8080/z/caw49X

ctpop(~x & (x - 1)) -> cttz(x, false)
Alive2: http://volta.cs.utah.edu:8080/z/5zfVrx

I've tweaked the initial test cases I added at rG2d712fb75584 <https://reviews.llvm.org/rG2d712fb75584ca8a6427199ca144407155e4b9b5> to increase commutativity testing, I'm happy to pre-commit these changes if you think its useful.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D76568

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
  llvm/test/Transforms/InstCombine/ctpop-cttz.ll

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