[PATCH] D45173: [InstCombine] Recognize idioms for ctpop and ctlz

[Krzysztof Parzyszek via Phabricator via llvm-commits]

kparzysz added a comment.

Even back then there was some interference with the other parts of instcombine, and this code had to be put in the right place to avoid it.  The problem was that instcombine would "preprocess" this computation into a form that was no longer "recursively symmetric" and the code as is, would no longer work.

I don't know what the long-term strategy is for dealing with the interactions between pattern-recognition code and instcombine.  This is a reoccurring issue for the polynomial multiplication code in HexagonLoopIdiomRecognition and it likely to affect any code of that nature.


Repository:
  rL LLVM

https://reviews.llvm.org/D45173