[PATCH] D73641: [LoopFusion] Move instructions from FC1.GuardBlock to FC0.GuardBlock and from FC0.ExitBlock to FC1.ExitBlock when proven safe.

[Whitney Tsang via Phabricator via llvm-commits]

Whitney created this revision.
Whitney added reviewers: kbarton, jdoerfert, Meinersbur, dmgreen, fhahn, hfinkel, bmahjour, etiotto.
Whitney added a project: LLVM.
Herald added subscribers: llvm-commits, hiraditya.

Currently LoopFusion give up when the second loop nest guard
block or the first loop nest exit block is not empty. For example:

  if (0 < N) {
    for (int i = 0; i < N; ++i) {}
    x+=1;
  }
  y+=1;
  if (0 < N) {
    for (int i = 0; i < N; ++i) {}
  }

The above example should be safe to fuse.
This PR moves instructions in FC1 guard block (e.g. y+=1;) to
FC0 guard block, or instructions in FC0 exit block (e.g. x+=1;) to
FC1 exit block, which then LoopFusion is able to fuse them.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73641

Files:
  llvm/lib/Transforms/Scalar/LoopFuse.cpp
  llvm/test/Transforms/LoopFusion/diagnostics_missed.ll
  llvm/test/Transforms/LoopFusion/guarded.ll

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