From ca3c5b87220b162adb684cecebd18ba5b39997a8 Mon Sep 17 00:00:00 2001
From: Peter Collingbourne <peter@pcc.me.uk>
Date: Tue, 15 Jul 2014 04:40:27 +0000
Subject: [PATCH 1/1] Give SplitBlockAndInsertIfThen the ability to update a
 domtree.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213045 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Transforms/Utils/BasicBlockUtils.h |  6 +++++-
 lib/Transforms/Utils/BasicBlockUtils.cpp        | 17 ++++++++++++++++-
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h
index 7309f6960a7..bcafda657c2 100644
--- a/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/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/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 80b7e22baca..602e8ba5510 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/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;
 }
 
-- 
2.34.1