From ffaed663600183b0331798bf4032208ec17bb3b3 Mon Sep 17 00:00:00 2001
From: Max Kazantsev <max.kazantsev@azul.com>
Date: Fri, 15 Feb 2019 08:18:00 +0000
Subject: [PATCH] [NFC] Tweak SplitBlockAndInsertIfThen to use existing
 ThenBlock

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354107 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../llvm/Transforms/Utils/BasicBlockUtils.h   |  6 +++--
 lib/Transforms/Utils/BasicBlockUtils.cpp      | 24 ++++++++++++-------
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h
index 4e763289cef..e997ed0cc0f 100644
--- a/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -270,7 +270,8 @@ ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
 ///   SplitBefore
 ///   Tail
 ///
-/// If Unreachable is true, then ThenBlock ends with
+/// If \p ThenBlock is not specified, a new block will be created for it.
+/// If \p Unreachable is true, the newly created block will end with
 /// UnreachableInst, otherwise it branches to Tail.
 /// Returns the NewBasicBlock's terminator.
 ///
@@ -279,7 +280,8 @@ Instruction *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
                                        bool Unreachable,
                                        MDNode *BranchWeights = nullptr,
                                        DominatorTree *DT = nullptr,
-                                       LoopInfo *LI = nullptr);
+                                       LoopInfo *LI = nullptr,
+                                       BasicBlock *ThenBlock = 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 5ca9222cf16..6f49eaec428 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -730,18 +730,23 @@ Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
                                              Instruction *SplitBefore,
                                              bool Unreachable,
                                              MDNode *BranchWeights,
-                                             DominatorTree *DT, LoopInfo *LI) {
+                                             DominatorTree *DT, LoopInfo *LI,
+                                             BasicBlock *ThenBlock) {
   BasicBlock *Head = SplitBefore->getParent();
   BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
   Instruction *HeadOldTerm = Head->getTerminator();
   LLVMContext &C = Head->getContext();
-  BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
   Instruction *CheckTerm;
-  if (Unreachable)
-    CheckTerm = new UnreachableInst(C, ThenBlock);
-  else
-    CheckTerm = BranchInst::Create(Tail, ThenBlock);
-  CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
+  bool CreateThenBlock = (ThenBlock == nullptr);
+  if (CreateThenBlock) {
+    ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
+    if (Unreachable)
+      CheckTerm = new UnreachableInst(C, ThenBlock);
+    else
+      CheckTerm = BranchInst::Create(Tail, ThenBlock);
+    CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
+  } else
+    CheckTerm = ThenBlock->getTerminator();
   BranchInst *HeadNewTerm =
     BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
   HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
@@ -756,7 +761,10 @@ Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
         DT->changeImmediateDominator(Child, NewNode);
 
       // Head dominates ThenBlock.
-      DT->addNewBlock(ThenBlock, Head);
+      if (CreateThenBlock)
+        DT->addNewBlock(ThenBlock, Head);
+      else
+        DT->changeImmediateDominator(ThenBlock, Head);
     }
   }
 
-- 
2.40.0