[llvm] r338180 - [SimpleLoopUnswitch] Fix DT updates for trivial branch unswitching.

[Alina Sbirlea via llvm-commits]

Author: asbirlea
Date: Fri Jul 27 17:01:05 2018
New Revision: 338180

URL: http://llvm.org/viewvc/llvm-project?rev=338180&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp?rev=338180&r1=338179&r2=338180&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp Fri Jul 27 17:01:05 2018
@@ -459,9 +459,11 @@ static bool unswitchTrivialBranch(Loop &
                                               *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