[PATCH] D49925: [SimpleLoopUnswitch] Fix DT updates for trivial branch unswitching.

[Alina Sbirlea via Phabricator via llvm-commits]

asbirlea created this revision.
asbirlea added reviewers: chandlerc, kuhar.
Herald added subscribers: jlebar, sanjoy.

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.


Repository:
  rL LLVM

https://reviews.llvm.org/D49925

Files:
  lib/Transforms/Scalar/SimpleLoopUnswitch.cpp


Index: lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
===================================================================
--- lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ 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


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