[PATCH] D151403: [LoopPeel] Peel iterations based on and, or conditions

[Joshua Cao via Phabricator via llvm-commits]

caojoshua created this revision.
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caojoshua added reviewers: nikic, fhahn.
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This patch looks at ALL and/or's in the loop. In https://reviews.llvm.org/D151052, @nikic recommended that we only look at and/or's that are used by selects and branches. I think its beneficial to look at the ALL and/or's for the following reasons:

1. We can look at nested and/or's, which won't be used directly by branch/select.
2. We can look at and/or's used in other ways. For example, it can be passed to a function.

I have some examples in https://godbolt.org/z/WzE5P1jca.


This allows us to peel this loop with a `and`:

  for (int i = 0; i < N; ++i) {
    if (i % 2 == 0 && i < 3) // can peel based on || as well
      f1();
    f2();

into:

  for (int i = 0; i < 3; ++i) { // peel three iterations
    if (i % 2 == 0)
      f1();
    f2();
  }
  for (int i = 3; i < N; ++i)
    f2();


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D151403

Files:
  llvm/lib/Transforms/Utils/LoopPeel.cpp
  llvm/test/Transforms/LoopUnroll/peel-loop-conditions.ll

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