[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
diff --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index 34510cb..5834b61 100644
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -459,9 +459,11 @@
*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