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[SimpleLoopUnswitch] Fix DT updates for trivial branch unswitching. 

Summary:
Fixing 2 issues with the DT update in trivial branch switching, though I don't have a case where DT update fails.
1. After splitting ParentBB->UnswitchedBB edge, new edges become: ParentBB->LoopExitBB->UnswitchedBB, so remove ParentBB->LoopExitBB edge.
2. AFAIU, for multiple CFG changes, DT should be updated using batch updates, vs consecutive addEdge and removeEdge calls.

Reviewers: chandlerc, kuhar

Subscribers: sanjoy, jlebar, llvm-commits

Differential Revision: https://reviews.llvm.org/D49925

llvm-svn: 338180
This commit is contained in:
Alina Sbirlea 2018-07-28 00:01:05 +00:00
parent 7bb4de47c9
commit 5666c7e4bd
1 changed files with 4 additions and 2 deletions
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6
llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
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@ -459,9 +459,11 @@ static bool unswitchTrivialBranch(Loop &L, BranchInst &BI, DominatorTree &DT,
*ParentBB, *OldPH, FullUnswitch);
// Now we need to update the dominator tree.
DT.insertEdge(OldPH, UnswitchedBB);
SmallVector<DominatorTree::UpdateType, 2> DTUpdates;
DTUpdates.push_back({DT.Insert, OldPH, UnswitchedBB});
if (FullUnswitch)
DT.deleteEdge(ParentBB, UnswitchedBB);
DTUpdates.push_back({DT.Delete, ParentBB, LoopExitBB});
DT.applyUpdates(DTUpdates);
// The constant we can replace all of our invariants with inside the loop
// body. If any of the invariants have a value other than this the loop won't