[PATCH] D71821: [LoopFusion] Move instructions from FC1.Preheader to FC0.Preheader when proven safe.

[Whitney Tsang via Phabricator via llvm-commits]

Whitney created this revision.
Whitney added reviewers: kbarton, Meinersbur, jdoerfert, dmgreen, fhahn, hfinkel, bmahjour, etiotto.
Whitney added a project: LLVM.
Herald added subscribers: llvm-commits, hiraditya.
Whitney added a parent revision: D71578: [CodeMoverUtils] Improve IsControlFlowEquivalent..

Currently LoopFusion give up when the second loop nest preheader is
not empty. For example:

  for (int i = 0; i < 100; ++i) {}
  x+=1;
  for (int i = 0; i < 100; ++i) {}

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


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D71821

Files:
  llvm/include/llvm/Transforms/Utils/CodeMoverUtils.h
  llvm/lib/Transforms/Scalar/LoopFuse.cpp
  llvm/lib/Transforms/Utils/CodeMoverUtils.cpp
  llvm/test/Transforms/LoopFusion/cannot_fuse.ll
  llvm/test/Transforms/LoopFusion/diagnostics_missed.ll
  llvm/test/Transforms/LoopFusion/guarded.ll
  llvm/test/Transforms/LoopFusion/simple.ll

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