[PATCH] D58500: [DO NOT MERGE] Explore MSSA behavior in LoopSimplifyCFG

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: asbirlea, rtereshin.
Herald added subscribers: llvm-commits, george.burgess.iv, hiraditya, Prazek.
Herald added a project: LLVM.

With this patch, test `test/Transforms/LoopSimplifyCFG/lcssa.ll` hits the assertion

  opt: /home/mkazantsev/work/llvm/llvm/lib/Analysis/MemorySSAUpdater.cpp:848: void llvm::MemorySSAUpdater::applyInsertUpdates(llvm::ArrayRef<llvm::cfg::Update<llvm::BasicBlock*> >, llvm::DominatorTree&, const llvm::GraphDiff<llvm::BasicBlock*, false>*): Assertion `DT.dominates(NewIDom, PrevIDom) && "New idom should dominate old idom"' failed.

when we try to apply updates to MSSA. The very same updates have updated DT correctly (it passes verification).
It must be something fishy around how MSSA updater works which I don't understand.


https://reviews.llvm.org/D58500

Files:
  llvm/lib/Analysis/MemorySSAUpdater.cpp
  llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
  llvm/test/Transforms/LoopSimplifyCFG/lcssa.ll

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