2 files changed, 21 insertions, 2 deletions
diff --git a/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h b/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
index 7309f6960a7..bcafda657c2 100644
--- a/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -23,6 +23,7 @@
 namespace llvm {
 
 class AliasAnalysis;
+class DominatorTree;
 class Instruction;
 class MDNode;
 class Pass;
@@ -202,9 +203,12 @@ ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
 /// If Unreachable is true, then ThenBlock ends with
 /// UnreachableInst, otherwise it branches to Tail.
 /// Returns the NewBasicBlock's terminator.
+///
+/// Updates DT if given.
 TerminatorInst *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
                                           bool Unreachable,
-                                          MDNode *BranchWeights = nullptr);
+                                          MDNode *BranchWeights = nullptr,
+                                          DominatorTree *DT = nullptr);
 
 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
 /// but also creates the ElseBlock.
diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 80b7e22baca..602e8ba5510 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -673,7 +673,8 @@ ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
 TerminatorInst *llvm::SplitBlockAndInsertIfThen(Value *Cond,
                                                 Instruction *SplitBefore,
                                                 bool Unreachable,
-                                                MDNode *BranchWeights) {
+                                                MDNode *BranchWeights,
+                                                DominatorTree *DT) {
   BasicBlock *Head = SplitBefore->getParent();
   BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
   TerminatorInst *HeadOldTerm = Head->getTerminator();
@@ -690,6 +691,20 @@ TerminatorInst *llvm::SplitBlockAndInsertIfThen(Value *Cond,
   HeadNewTerm->setDebugLoc(SplitBefore->getDebugLoc());
   HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
   ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
+
+  if (DT) {
+    if (DomTreeNode *OldNode = DT->getNode(Head)) {
+      std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
+
+      DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
+      for (auto Child : Children)
+        DT->changeImmediateDominator(Child, NewNode);
+
+      // Head dominates ThenBlock.
+      DT->addNewBlock(ThenBlock, Head);
+    }
+  }
+
   return CheckTerm;
 }