[PATCH] D43293: [SimplifyCFG] Don't remove preheaders when we need canonical loops.

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: eli.friedman, pacxx, skatkov.

Commit https://reviews.llvm.org/rL324208 loosened a restriction on removing basic blocks
in the intent to remove empty back edge blocks, but also started
removing preheaders in the process. This prevents the preheaders
from being removed when we want to keep loop simple form.


https://reviews.llvm.org/D43293

Files:
  include/llvm/Transforms/Utils/Local.h
  lib/Transforms/Scalar/SimplifyCFGPass.cpp
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/LoopUnswitch/2015-06-17-Metadata.ll
  test/Transforms/LoopUnswitch/infinite-loop.ll
  test/Transforms/SimplifyCFG/UncondBranchToHeader.ll

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