[PATCH] D124119: [InstCombine] Combine instructions of type or/and where AND masks can be combined.

[Alexander Kornienko via Phabricator via llvm-commits]

alexfh added a comment.

I was wrong with the initial analysis. The patch doesn't just make the performance worse. It makes clang loop indefinitely on a certain input.

  $ cat q.cc
  int e;
  int u;
  int ag;
  void f() {
    int ak = e;
    int al((unsigned char)(ak >> 23) & 925);
    if (ak)
      al = (ak >> 23 & u) | ((unsigned char)(ak >> 23) & 925) | (u >> 23 & 157);
    ag = al;
  }
  
  $ time ./clang-15-10515 --target=x86_64--linux-gnu -O1  -c q.cc
  ^C
  
  real    0m45.072s
  user    0m0.025s
  sys     0m0.099s

This is definitely a problem that has to be fixed. If you don't have an obvious fix in mind, please revert while investigating.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D124119/new/

https://reviews.llvm.org/D124119