[PATCH] D67974: [Dominators][AMDGPU] Don't use virtual exit node in findNearestCommonDominator

[Jakub Kuderski via Phabricator via llvm-commits]

kuhar created this revision.
kuhar added reviewers: tstellar, tpr, nhaehnle, arsenm, NutshellySima.
kuhar added a project: AMDGPU.
Herald added subscribers: hiraditya, t-tye, dstuttard, yaxunl, wdng, jvesely, kzhuravl.
Herald added a reviewer: grosser.
Herald added a project: LLVM.

This patch fixes a bug that originated from passing a virtual exit block (nullptr) to `MachinePostDominatorTee::findNearestCommonDominator` and resulted in assertion failures inside its callee.

The patch introduces a new function in PDT that given a list of `MachineBasicBlock`s finds their NCD. The new overload of `findNearestCommonDominator` handles virtual root correctly.

Note that similar handling of virtual root nodes is not necessary in (forward) `DominatorTree`s, as right now they don't use virtual roots.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D67974

Files:
  llvm/include/llvm/CodeGen/MachinePostDominators.h
  llvm/lib/CodeGen/MachinePostDominators.cpp
  llvm/lib/Target/AMDGPU/SILowerI1Copies.cpp

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