Restoring authorship annotation for <[email protected]>. Commit 2 of 2.

1 files changed, 2030 insertions, 2030 deletions

diff --git a/contrib/libs/llvm12/lib/CodeGen/BranchFolding.cpp b/contrib/libs/llvm12/lib/CodeGen/BranchFolding.cpp
index d53bf6dbd33..fd3f465fb39 100644
--- a/contrib/libs/llvm12/lib/CodeGen/BranchFolding.cpp
+++ b/contrib/libs/llvm12/lib/CodeGen/BranchFolding.cpp
@@ -1,2036 +1,2036 @@
-//===- BranchFolding.cpp - Fold machine code branch instructions ----------===// 
-// 
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 
-// See https://llvm.org/LICENSE.txt for license information. 
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 
-// 
-//===----------------------------------------------------------------------===// 
-// 
-// This pass forwards branches to unconditional branches to make them branch 
-// directly to the target block.  This pass often results in dead MBB's, which 
-// it then removes. 
-// 
-// Note that this pass must be run after register allocation, it cannot handle 
-// SSA form. It also must handle virtual registers for targets that emit virtual 
-// ISA (e.g. NVPTX). 
-// 
-//===----------------------------------------------------------------------===// 
- 
-#include "BranchFolding.h" 
-#include "llvm/ADT/BitVector.h" 
-#include "llvm/ADT/STLExtras.h" 
-#include "llvm/ADT/SmallSet.h" 
-#include "llvm/ADT/SmallVector.h" 
-#include "llvm/ADT/Statistic.h" 
-#include "llvm/Analysis/ProfileSummaryInfo.h" 
-#include "llvm/CodeGen/Analysis.h" 
-#include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 
-#include "llvm/CodeGen/MachineBranchProbabilityInfo.h" 
-#include "llvm/CodeGen/MachineFunction.h" 
-#include "llvm/CodeGen/MachineFunctionPass.h" 
-#include "llvm/CodeGen/MachineInstr.h" 
-#include "llvm/CodeGen/MachineInstrBuilder.h" 
-#include "llvm/CodeGen/MachineJumpTableInfo.h" 
-#include "llvm/CodeGen/MachineLoopInfo.h" 
-#include "llvm/CodeGen/MachineModuleInfo.h" 
-#include "llvm/CodeGen/MachineOperand.h" 
-#include "llvm/CodeGen/MachineRegisterInfo.h" 
-#include "llvm/CodeGen/MachineSizeOpts.h" 
-#include "llvm/CodeGen/MBFIWrapper.h" 
-#include "llvm/CodeGen/TargetInstrInfo.h" 
-#include "llvm/CodeGen/TargetOpcodes.h" 
-#include "llvm/CodeGen/TargetPassConfig.h" 
-#include "llvm/CodeGen/TargetRegisterInfo.h" 
-#include "llvm/CodeGen/TargetSubtargetInfo.h" 
-#include "llvm/IR/DebugInfoMetadata.h" 
-#include "llvm/IR/DebugLoc.h" 
-#include "llvm/IR/Function.h" 
-#include "llvm/InitializePasses.h" 
-#include "llvm/MC/LaneBitmask.h" 
-#include "llvm/MC/MCRegisterInfo.h" 
-#include "llvm/Pass.h" 
-#include "llvm/Support/BlockFrequency.h" 
-#include "llvm/Support/BranchProbability.h" 
-#include "llvm/Support/CommandLine.h" 
-#include "llvm/Support/Debug.h" 
-#include "llvm/Support/ErrorHandling.h" 
-#include "llvm/Support/raw_ostream.h" 
-#include "llvm/Target/TargetMachine.h" 
-#include <cassert> 
-#include <cstddef> 
-#include <iterator> 
-#include <numeric> 
- 
-using namespace llvm; 
- 
-#define DEBUG_TYPE "branch-folder" 
- 
-STATISTIC(NumDeadBlocks, "Number of dead blocks removed"); 
-STATISTIC(NumBranchOpts, "Number of branches optimized"); 
-STATISTIC(NumTailMerge , "Number of block tails merged"); 
-STATISTIC(NumHoist     , "Number of times common instructions are hoisted"); 
-STATISTIC(NumTailCalls,  "Number of tail calls optimized"); 
- 
-static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge", 
-                              cl::init(cl::BOU_UNSET), cl::Hidden); 
- 
-// Throttle for huge numbers of predecessors (compile speed problems) 
-static cl::opt<unsigned> 
-TailMergeThreshold("tail-merge-threshold", 
-          cl::desc("Max number of predecessors to consider tail merging"), 
-          cl::init(150), cl::Hidden); 
- 
-// Heuristic for tail merging (and, inversely, tail duplication). 
-// TODO: This should be replaced with a target query. 
-static cl::opt<unsigned> 
-TailMergeSize("tail-merge-size", 
-              cl::desc("Min number of instructions to consider tail merging"), 
-              cl::init(3), cl::Hidden); 
- 
-namespace { 
- 
-  /// BranchFolderPass - Wrap branch folder in a machine function pass. 
-  class BranchFolderPass : public MachineFunctionPass { 
-  public: 
-    static char ID; 
- 
-    explicit BranchFolderPass(): MachineFunctionPass(ID) {} 
- 
-    bool runOnMachineFunction(MachineFunction &MF) override; 
- 
-    void getAnalysisUsage(AnalysisUsage &AU) const override { 
-      AU.addRequired<MachineBlockFrequencyInfo>(); 
-      AU.addRequired<MachineBranchProbabilityInfo>(); 
-      AU.addRequired<ProfileSummaryInfoWrapperPass>(); 
-      AU.addRequired<TargetPassConfig>(); 
-      MachineFunctionPass::getAnalysisUsage(AU); 
-    } 
-  }; 
- 
-} // end anonymous namespace 
- 
-char BranchFolderPass::ID = 0; 
- 
-char &llvm::BranchFolderPassID = BranchFolderPass::ID; 
- 
-INITIALIZE_PASS(BranchFolderPass, DEBUG_TYPE, 
-                "Control Flow Optimizer", false, false) 
- 
-bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) { 
-  if (skipFunction(MF.getFunction())) 
-    return false; 
- 
-  TargetPassConfig *PassConfig = &getAnalysis<TargetPassConfig>(); 
-  // TailMerge can create jump into if branches that make CFG irreducible for 
-  // HW that requires structurized CFG. 
-  bool EnableTailMerge = !MF.getTarget().requiresStructuredCFG() && 
-                         PassConfig->getEnableTailMerge(); 
-  MBFIWrapper MBBFreqInfo( 
-      getAnalysis<MachineBlockFrequencyInfo>()); 
-  BranchFolder Folder(EnableTailMerge, /*CommonHoist=*/true, MBBFreqInfo, 
-                      getAnalysis<MachineBranchProbabilityInfo>(), 
-                      &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI()); 
-  return Folder.OptimizeFunction(MF, MF.getSubtarget().getInstrInfo(), 
-                                 MF.getSubtarget().getRegisterInfo()); 
-} 
- 
+//===- BranchFolding.cpp - Fold machine code branch instructions ----------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass forwards branches to unconditional branches to make them branch
+// directly to the target block.  This pass often results in dead MBB's, which
+// it then removes.
+//
+// Note that this pass must be run after register allocation, it cannot handle
+// SSA form. It also must handle virtual registers for targets that emit virtual
+// ISA (e.g. NVPTX).
+//
+//===----------------------------------------------------------------------===//
+
+#include "BranchFolding.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/CodeGen/Analysis.h"
+#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
+#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineJumpTableInfo.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineOperand.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/MachineSizeOpts.h"
+#include "llvm/CodeGen/MBFIWrapper.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+#include "llvm/CodeGen/TargetOpcodes.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/CodeGen/TargetRegisterInfo.h"
+#include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/DebugLoc.h"
+#include "llvm/IR/Function.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/MC/LaneBitmask.h"
+#include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/BlockFrequency.h"
+#include "llvm/Support/BranchProbability.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetMachine.h"
+#include <cassert>
+#include <cstddef>
+#include <iterator>
+#include <numeric>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "branch-folder"
+
+STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
+STATISTIC(NumBranchOpts, "Number of branches optimized");
+STATISTIC(NumTailMerge , "Number of block tails merged");
+STATISTIC(NumHoist     , "Number of times common instructions are hoisted");
+STATISTIC(NumTailCalls,  "Number of tail calls optimized");
+
+static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
+                              cl::init(cl::BOU_UNSET), cl::Hidden);
+
+// Throttle for huge numbers of predecessors (compile speed problems)
+static cl::opt<unsigned>
+TailMergeThreshold("tail-merge-threshold",
+          cl::desc("Max number of predecessors to consider tail merging"),
+          cl::init(150), cl::Hidden);
+
+// Heuristic for tail merging (and, inversely, tail duplication).
+// TODO: This should be replaced with a target query.
+static cl::opt<unsigned>
+TailMergeSize("tail-merge-size",
+              cl::desc("Min number of instructions to consider tail merging"),
+              cl::init(3), cl::Hidden);
+
+namespace {
+
+  /// BranchFolderPass - Wrap branch folder in a machine function pass.
+  class BranchFolderPass : public MachineFunctionPass {
+  public:
+    static char ID;
+
+    explicit BranchFolderPass(): MachineFunctionPass(ID) {}
+
+    bool runOnMachineFunction(MachineFunction &MF) override;
+
+    void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.addRequired<MachineBlockFrequencyInfo>();
+      AU.addRequired<MachineBranchProbabilityInfo>();
+      AU.addRequired<ProfileSummaryInfoWrapperPass>();
+      AU.addRequired<TargetPassConfig>();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+  };
+
+} // end anonymous namespace
+
+char BranchFolderPass::ID = 0;
+
+char &llvm::BranchFolderPassID = BranchFolderPass::ID;
+
+INITIALIZE_PASS(BranchFolderPass, DEBUG_TYPE,
+                "Control Flow Optimizer", false, false)
+
+bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) {
+  if (skipFunction(MF.getFunction()))
+    return false;
+
+  TargetPassConfig *PassConfig = &getAnalysis<TargetPassConfig>();
+  // TailMerge can create jump into if branches that make CFG irreducible for
+  // HW that requires structurized CFG.
+  bool EnableTailMerge = !MF.getTarget().requiresStructuredCFG() &&
+                         PassConfig->getEnableTailMerge();
+  MBFIWrapper MBBFreqInfo(
+      getAnalysis<MachineBlockFrequencyInfo>());
+  BranchFolder Folder(EnableTailMerge, /*CommonHoist=*/true, MBBFreqInfo,
+                      getAnalysis<MachineBranchProbabilityInfo>(),
+                      &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI());
+  return Folder.OptimizeFunction(MF, MF.getSubtarget().getInstrInfo(),
+                                 MF.getSubtarget().getRegisterInfo());
+}
+
 BranchFolder::BranchFolder(bool DefaultEnableTailMerge, bool CommonHoist,
-                           MBFIWrapper &FreqInfo, 
-                           const MachineBranchProbabilityInfo &ProbInfo, 
+                           MBFIWrapper &FreqInfo,
+                           const MachineBranchProbabilityInfo &ProbInfo,
                            ProfileSummaryInfo *PSI, unsigned MinTailLength)
-    : EnableHoistCommonCode(CommonHoist), MinCommonTailLength(MinTailLength), 
-      MBBFreqInfo(FreqInfo), MBPI(ProbInfo), PSI(PSI) { 
-  if (MinCommonTailLength == 0) 
-    MinCommonTailLength = TailMergeSize; 
-  switch (FlagEnableTailMerge) { 
+    : EnableHoistCommonCode(CommonHoist), MinCommonTailLength(MinTailLength),
+      MBBFreqInfo(FreqInfo), MBPI(ProbInfo), PSI(PSI) {
+  if (MinCommonTailLength == 0)
+    MinCommonTailLength = TailMergeSize;
+  switch (FlagEnableTailMerge) {
   case cl::BOU_UNSET:
     EnableTailMerge = DefaultEnableTailMerge;
     break;
-  case cl::BOU_TRUE: EnableTailMerge = true; break; 
-  case cl::BOU_FALSE: EnableTailMerge = false; break; 
-  } 
-} 
- 
-void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) { 
-  assert(MBB->pred_empty() && "MBB must be dead!"); 
-  LLVM_DEBUG(dbgs() << "\nRemoving MBB: " << *MBB); 
- 
-  MachineFunction *MF = MBB->getParent(); 
-  // drop all successors. 
-  while (!MBB->succ_empty()) 
-    MBB->removeSuccessor(MBB->succ_end()-1); 
- 
-  // Avoid matching if this pointer gets reused. 
-  TriedMerging.erase(MBB); 
- 
-  // Update call site info. 
-  std::for_each(MBB->begin(), MBB->end(), [MF](const MachineInstr &MI) { 
-    if (MI.shouldUpdateCallSiteInfo()) 
-      MF->eraseCallSiteInfo(&MI); 
-  }); 
-  // Remove the block. 
-  MF->erase(MBB); 
-  EHScopeMembership.erase(MBB); 
-  if (MLI) 
-    MLI->removeBlock(MBB); 
-} 
- 
-bool BranchFolder::OptimizeFunction(MachineFunction &MF, 
-                                    const TargetInstrInfo *tii, 
-                                    const TargetRegisterInfo *tri, 
-                                    MachineLoopInfo *mli, bool AfterPlacement) { 
-  if (!tii) return false; 
- 
-  TriedMerging.clear(); 
- 
-  MachineRegisterInfo &MRI = MF.getRegInfo(); 
-  AfterBlockPlacement = AfterPlacement; 
-  TII = tii; 
-  TRI = tri; 
-  MLI = mli; 
-  this->MRI = &MRI; 
- 
-  UpdateLiveIns = MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF); 
-  if (!UpdateLiveIns) 
-    MRI.invalidateLiveness(); 
- 
-  bool MadeChange = false; 
- 
-  // Recalculate EH scope membership. 
-  EHScopeMembership = getEHScopeMembership(MF); 
- 
-  bool MadeChangeThisIteration = true; 
-  while (MadeChangeThisIteration) { 
-    MadeChangeThisIteration    = TailMergeBlocks(MF); 
-    // No need to clean up if tail merging does not change anything after the 
-    // block placement. 
-    if (!AfterBlockPlacement || MadeChangeThisIteration) 
-      MadeChangeThisIteration |= OptimizeBranches(MF); 
-    if (EnableHoistCommonCode) 
-      MadeChangeThisIteration |= HoistCommonCode(MF); 
-    MadeChange |= MadeChangeThisIteration; 
-  } 
- 
-  // See if any jump tables have become dead as the code generator 
-  // did its thing. 
-  MachineJumpTableInfo *JTI = MF.getJumpTableInfo(); 
-  if (!JTI) 
-    return MadeChange; 
- 
-  // Walk the function to find jump tables that are live. 
-  BitVector JTIsLive(JTI->getJumpTables().size()); 
-  for (const MachineBasicBlock &BB : MF) { 
-    for (const MachineInstr &I : BB) 
-      for (const MachineOperand &Op : I.operands()) { 
-        if (!Op.isJTI()) continue; 
- 
-        // Remember that this JT is live. 
-        JTIsLive.set(Op.getIndex()); 
-      } 
-  } 
- 
-  // Finally, remove dead jump tables.  This happens when the 
-  // indirect jump was unreachable (and thus deleted). 
-  for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i) 
-    if (!JTIsLive.test(i)) { 
-      JTI->RemoveJumpTable(i); 
-      MadeChange = true; 
-    } 
- 
-  return MadeChange; 
-} 
- 
-//===----------------------------------------------------------------------===// 
-//  Tail Merging of Blocks 
-//===----------------------------------------------------------------------===// 
- 
-/// HashMachineInstr - Compute a hash value for MI and its operands. 
-static unsigned HashMachineInstr(const MachineInstr &MI) { 
-  unsigned Hash = MI.getOpcode(); 
-  for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 
-    const MachineOperand &Op = MI.getOperand(i); 
- 
-    // Merge in bits from the operand if easy. We can't use MachineOperand's 
-    // hash_code here because it's not deterministic and we sort by hash value 
-    // later. 
-    unsigned OperandHash = 0; 
-    switch (Op.getType()) { 
-    case MachineOperand::MO_Register: 
-      OperandHash = Op.getReg(); 
-      break; 
-    case MachineOperand::MO_Immediate: 
-      OperandHash = Op.getImm(); 
-      break; 
-    case MachineOperand::MO_MachineBasicBlock: 
-      OperandHash = Op.getMBB()->getNumber(); 
-      break; 
-    case MachineOperand::MO_FrameIndex: 
-    case MachineOperand::MO_ConstantPoolIndex: 
-    case MachineOperand::MO_JumpTableIndex: 
-      OperandHash = Op.getIndex(); 
-      break; 
-    case MachineOperand::MO_GlobalAddress: 
-    case MachineOperand::MO_ExternalSymbol: 
-      // Global address / external symbol are too hard, don't bother, but do 
-      // pull in the offset. 
-      OperandHash = Op.getOffset(); 
-      break; 
-    default: 
-      break; 
-    } 
- 
-    Hash += ((OperandHash << 3) | Op.getType()) << (i & 31); 
-  } 
-  return Hash; 
-} 
- 
-/// HashEndOfMBB - Hash the last instruction in the MBB. 
-static unsigned HashEndOfMBB(const MachineBasicBlock &MBB) { 
-  MachineBasicBlock::const_iterator I = MBB.getLastNonDebugInstr(); 
-  if (I == MBB.end()) 
-    return 0; 
- 
-  return HashMachineInstr(*I); 
-} 
- 
-/// Whether MI should be counted as an instruction when calculating common tail. 
-static bool countsAsInstruction(const MachineInstr &MI) { 
-  return !(MI.isDebugInstr() || MI.isCFIInstruction()); 
-} 
- 
-/// Iterate backwards from the given iterator \p I, towards the beginning of the 
-/// block. If a MI satisfying 'countsAsInstruction' is found, return an iterator 
-/// pointing to that MI. If no such MI is found, return the end iterator. 
-static MachineBasicBlock::iterator 
-skipBackwardPastNonInstructions(MachineBasicBlock::iterator I, 
-                                MachineBasicBlock *MBB) { 
-  while (I != MBB->begin()) { 
-    --I; 
-    if (countsAsInstruction(*I)) 
-      return I; 
-  } 
-  return MBB->end(); 
-} 
- 
-/// Given two machine basic blocks, return the number of instructions they 
-/// actually have in common together at their end. If a common tail is found (at 
-/// least by one instruction), then iterators for the first shared instruction 
-/// in each block are returned as well. 
-/// 
-/// Non-instructions according to countsAsInstruction are ignored. 
-static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1, 
-                                        MachineBasicBlock *MBB2, 
-                                        MachineBasicBlock::iterator &I1, 
-                                        MachineBasicBlock::iterator &I2) { 
-  MachineBasicBlock::iterator MBBI1 = MBB1->end(); 
-  MachineBasicBlock::iterator MBBI2 = MBB2->end(); 
- 
-  unsigned TailLen = 0; 
-  while (true) { 
-    MBBI1 = skipBackwardPastNonInstructions(MBBI1, MBB1); 
-    MBBI2 = skipBackwardPastNonInstructions(MBBI2, MBB2); 
-    if (MBBI1 == MBB1->end() || MBBI2 == MBB2->end()) 
-      break; 
-    if (!MBBI1->isIdenticalTo(*MBBI2) || 
-        // FIXME: This check is dubious. It's used to get around a problem where 
-        // people incorrectly expect inline asm directives to remain in the same 
-        // relative order. This is untenable because normal compiler 
-        // optimizations (like this one) may reorder and/or merge these 
-        // directives. 
-        MBBI1->isInlineAsm()) { 
-      break; 
-    } 
-    if (MBBI1->getFlag(MachineInstr::NoMerge) || 
-        MBBI2->getFlag(MachineInstr::NoMerge)) 
-      break; 
-    ++TailLen; 
-    I1 = MBBI1; 
-    I2 = MBBI2; 
-  } 
- 
-  return TailLen; 
-} 
- 
-void BranchFolder::replaceTailWithBranchTo(MachineBasicBlock::iterator OldInst, 
-                                           MachineBasicBlock &NewDest) { 
-  if (UpdateLiveIns) { 
-    // OldInst should always point to an instruction. 
-    MachineBasicBlock &OldMBB = *OldInst->getParent(); 
-    LiveRegs.clear(); 
-    LiveRegs.addLiveOuts(OldMBB); 
-    // Move backward to the place where will insert the jump. 
-    MachineBasicBlock::iterator I = OldMBB.end(); 
-    do { 
-      --I; 
-      LiveRegs.stepBackward(*I); 
-    } while (I != OldInst); 
- 
-    // Merging the tails may have switched some undef operand to non-undef ones. 
-    // Add IMPLICIT_DEFS into OldMBB as necessary to have a definition of the 
-    // register. 
-    for (MachineBasicBlock::RegisterMaskPair P : NewDest.liveins()) { 
-      // We computed the liveins with computeLiveIn earlier and should only see 
-      // full registers: 
-      assert(P.LaneMask == LaneBitmask::getAll() && 
-             "Can only handle full register."); 
-      MCPhysReg Reg = P.PhysReg; 
-      if (!LiveRegs.available(*MRI, Reg)) 
-        continue; 
-      DebugLoc DL; 
-      BuildMI(OldMBB, OldInst, DL, TII->get(TargetOpcode::IMPLICIT_DEF), Reg); 
-    } 
-  } 
- 
-  TII->ReplaceTailWithBranchTo(OldInst, &NewDest); 
-  ++NumTailMerge; 
-} 
- 
-MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, 
-                                            MachineBasicBlock::iterator BBI1, 
-                                            const BasicBlock *BB) { 
-  if (!TII->isLegalToSplitMBBAt(CurMBB, BBI1)) 
-    return nullptr; 
- 
-  MachineFunction &MF = *CurMBB.getParent(); 
- 
-  // Create the fall-through block. 
-  MachineFunction::iterator MBBI = CurMBB.getIterator(); 
-  MachineBasicBlock *NewMBB = MF.CreateMachineBasicBlock(BB); 
-  CurMBB.getParent()->insert(++MBBI, NewMBB); 
- 
-  // Move all the successors of this block to the specified block. 
-  NewMBB->transferSuccessors(&CurMBB); 
- 
-  // Add an edge from CurMBB to NewMBB for the fall-through. 
-  CurMBB.addSuccessor(NewMBB); 
- 
-  // Splice the code over. 
-  NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end()); 
- 
-  // NewMBB belongs to the same loop as CurMBB. 
-  if (MLI) 
-    if (MachineLoop *ML = MLI->getLoopFor(&CurMBB)) 
-      ML->addBasicBlockToLoop(NewMBB, MLI->getBase()); 
- 
-  // NewMBB inherits CurMBB's block frequency. 
-  MBBFreqInfo.setBlockFreq(NewMBB, MBBFreqInfo.getBlockFreq(&CurMBB)); 
- 
-  if (UpdateLiveIns) 
-    computeAndAddLiveIns(LiveRegs, *NewMBB); 
- 
-  // Add the new block to the EH scope. 
-  const auto &EHScopeI = EHScopeMembership.find(&CurMBB); 
-  if (EHScopeI != EHScopeMembership.end()) { 
-    auto n = EHScopeI->second; 
-    EHScopeMembership[NewMBB] = n; 
-  } 
- 
-  return NewMBB; 
-} 
- 
-/// EstimateRuntime - Make a rough estimate for how long it will take to run 
-/// the specified code. 
-static unsigned EstimateRuntime(MachineBasicBlock::iterator I, 
-                                MachineBasicBlock::iterator E) { 
-  unsigned Time = 0; 
-  for (; I != E; ++I) { 
-    if (!countsAsInstruction(*I)) 
-      continue; 
-    if (I->isCall()) 
-      Time += 10; 
-    else if (I->mayLoadOrStore()) 
-      Time += 2; 
-    else 
-      ++Time; 
-  } 
-  return Time; 
-} 
- 
-// CurMBB needs to add an unconditional branch to SuccMBB (we removed these 
-// branches temporarily for tail merging).  In the case where CurMBB ends 
-// with a conditional branch to the next block, optimize by reversing the 
-// test and conditionally branching to SuccMBB instead. 
-static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB, 
-                    const TargetInstrInfo *TII) { 
-  MachineFunction *MF = CurMBB->getParent(); 
-  MachineFunction::iterator I = std::next(MachineFunction::iterator(CurMBB)); 
-  MachineBasicBlock *TBB = nullptr, *FBB = nullptr; 
-  SmallVector<MachineOperand, 4> Cond; 
-  DebugLoc dl = CurMBB->findBranchDebugLoc(); 
-  if (I != MF->end() && !TII->analyzeBranch(*CurMBB, TBB, FBB, Cond, true)) { 
-    MachineBasicBlock *NextBB = &*I; 
-    if (TBB == NextBB && !Cond.empty() && !FBB) { 
-      if (!TII->reverseBranchCondition(Cond)) { 
-        TII->removeBranch(*CurMBB); 
-        TII->insertBranch(*CurMBB, SuccBB, nullptr, Cond, dl); 
-        return; 
-      } 
-    } 
-  } 
-  TII->insertBranch(*CurMBB, SuccBB, nullptr, 
-                    SmallVector<MachineOperand, 0>(), dl); 
-} 
- 
-bool 
-BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const { 
-  if (getHash() < o.getHash()) 
-    return true; 
-  if (getHash() > o.getHash()) 
-    return false; 
-  if (getBlock()->getNumber() < o.getBlock()->getNumber()) 
-    return true; 
-  if (getBlock()->getNumber() > o.getBlock()->getNumber()) 
-    return false; 
-  // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing 
-  // an object with itself. 
-#ifndef _GLIBCXX_DEBUG 
-  llvm_unreachable("Predecessor appears twice"); 
-#else 
-  return false; 
-#endif 
-} 
- 
-/// CountTerminators - Count the number of terminators in the given 
-/// block and set I to the position of the first non-terminator, if there 
-/// is one, or MBB->end() otherwise. 
-static unsigned CountTerminators(MachineBasicBlock *MBB, 
-                                 MachineBasicBlock::iterator &I) { 
-  I = MBB->end(); 
-  unsigned NumTerms = 0; 
-  while (true) { 
-    if (I == MBB->begin()) { 
-      I = MBB->end(); 
-      break; 
-    } 
-    --I; 
-    if (!I->isTerminator()) break; 
-    ++NumTerms; 
-  } 
-  return NumTerms; 
-} 
- 
-/// A no successor, non-return block probably ends in unreachable and is cold. 
-/// Also consider a block that ends in an indirect branch to be a return block, 
-/// since many targets use plain indirect branches to return. 
-static bool blockEndsInUnreachable(const MachineBasicBlock *MBB) { 
-  if (!MBB->succ_empty()) 
-    return false; 
-  if (MBB->empty()) 
-    return true; 
-  return !(MBB->back().isReturn() || MBB->back().isIndirectBranch()); 
-} 
- 
-/// ProfitableToMerge - Check if two machine basic blocks have a common tail 
-/// and decide if it would be profitable to merge those tails.  Return the 
-/// length of the common tail and iterators to the first common instruction 
-/// in each block. 
-/// MBB1, MBB2      The blocks to check 
-/// MinCommonTailLength  Minimum size of tail block to be merged. 
-/// CommonTailLen   Out parameter to record the size of the shared tail between 
-///                 MBB1 and MBB2 
-/// I1, I2          Iterator references that will be changed to point to the first 
-///                 instruction in the common tail shared by MBB1,MBB2 
-/// SuccBB          A common successor of MBB1, MBB2 which are in a canonical form 
-///                 relative to SuccBB 
-/// PredBB          The layout predecessor of SuccBB, if any. 
-/// EHScopeMembership  map from block to EH scope #. 
-/// AfterPlacement  True if we are merging blocks after layout. Stricter 
-///                 thresholds apply to prevent undoing tail-duplication. 
-static bool 
-ProfitableToMerge(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2, 
-                  unsigned MinCommonTailLength, unsigned &CommonTailLen, 
-                  MachineBasicBlock::iterator &I1, 
-                  MachineBasicBlock::iterator &I2, MachineBasicBlock *SuccBB, 
-                  MachineBasicBlock *PredBB, 
-                  DenseMap<const MachineBasicBlock *, int> &EHScopeMembership, 
-                  bool AfterPlacement, 
-                  MBFIWrapper &MBBFreqInfo, 
-                  ProfileSummaryInfo *PSI) { 
-  // It is never profitable to tail-merge blocks from two different EH scopes. 
-  if (!EHScopeMembership.empty()) { 
-    auto EHScope1 = EHScopeMembership.find(MBB1); 
-    assert(EHScope1 != EHScopeMembership.end()); 
-    auto EHScope2 = EHScopeMembership.find(MBB2); 
-    assert(EHScope2 != EHScopeMembership.end()); 
-    if (EHScope1->second != EHScope2->second) 
-      return false; 
-  } 
- 
-  CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2); 
-  if (CommonTailLen == 0) 
-    return false; 
-  LLVM_DEBUG(dbgs() << "Common tail length of " << printMBBReference(*MBB1) 
-                    << " and " << printMBBReference(*MBB2) << " is " 
-                    << CommonTailLen << '\n'); 
- 
-  // Move the iterators to the beginning of the MBB if we only got debug 
-  // instructions before the tail. This is to avoid splitting a block when we 
-  // only got debug instructions before the tail (to be invariant on -g). 
-  if (skipDebugInstructionsForward(MBB1->begin(), MBB1->end()) == I1) 
-    I1 = MBB1->begin(); 
-  if (skipDebugInstructionsForward(MBB2->begin(), MBB2->end()) == I2) 
-    I2 = MBB2->begin(); 
- 
-  bool FullBlockTail1 = I1 == MBB1->begin(); 
-  bool FullBlockTail2 = I2 == MBB2->begin(); 
- 
-  // It's almost always profitable to merge any number of non-terminator 
-  // instructions with the block that falls through into the common successor. 
-  // This is true only for a single successor. For multiple successors, we are 
-  // trading a conditional branch for an unconditional one. 
-  // TODO: Re-visit successor size for non-layout tail merging. 
-  if ((MBB1 == PredBB || MBB2 == PredBB) && 
-      (!AfterPlacement || MBB1->succ_size() == 1)) { 
-    MachineBasicBlock::iterator I; 
-    unsigned NumTerms = CountTerminators(MBB1 == PredBB ? MBB2 : MBB1, I); 
-    if (CommonTailLen > NumTerms) 
-      return true; 
-  } 
- 
-  // If these are identical non-return blocks with no successors, merge them. 
-  // Such blocks are typically cold calls to noreturn functions like abort, and 
-  // are unlikely to become a fallthrough target after machine block placement. 
-  // Tail merging these blocks is unlikely to create additional unconditional 
-  // branches, and will reduce the size of this cold code. 
-  if (FullBlockTail1 && FullBlockTail2 && 
-      blockEndsInUnreachable(MBB1) && blockEndsInUnreachable(MBB2)) 
-    return true; 
- 
-  // If one of the blocks can be completely merged and happens to be in 
-  // a position where the other could fall through into it, merge any number 
-  // of instructions, because it can be done without a branch. 
-  // TODO: If the blocks are not adjacent, move one of them so that they are? 
-  if (MBB1->isLayoutSuccessor(MBB2) && FullBlockTail2) 
-    return true; 
-  if (MBB2->isLayoutSuccessor(MBB1) && FullBlockTail1) 
-    return true; 
- 
-  // If both blocks are identical and end in a branch, merge them unless they 
-  // both have a fallthrough predecessor and successor. 
-  // We can only do this after block placement because it depends on whether 
-  // there are fallthroughs, and we don't know until after layout. 
-  if (AfterPlacement && FullBlockTail1 && FullBlockTail2) { 
-    auto BothFallThrough = [](MachineBasicBlock *MBB) { 
-      if (MBB->succ_size() != 0 && !MBB->canFallThrough()) 
-        return false; 
-      MachineFunction::iterator I(MBB); 
-      MachineFunction *MF = MBB->getParent(); 
-      return (MBB != &*MF->begin()) && std::prev(I)->canFallThrough(); 
-    }; 
-    if (!BothFallThrough(MBB1) || !BothFallThrough(MBB2)) 
-      return true; 
-  } 
- 
-  // If both blocks have an unconditional branch temporarily stripped out, 
-  // count that as an additional common instruction for the following 
-  // heuristics. This heuristic is only accurate for single-succ blocks, so to 
-  // make sure that during layout merging and duplicating don't crash, we check 
-  // for that when merging during layout. 
-  unsigned EffectiveTailLen = CommonTailLen; 
-  if (SuccBB && MBB1 != PredBB && MBB2 != PredBB && 
-      (MBB1->succ_size() == 1 || !AfterPlacement) && 
-      !MBB1->back().isBarrier() && 
-      !MBB2->back().isBarrier()) 
-    ++EffectiveTailLen; 
- 
-  // Check if the common tail is long enough to be worthwhile. 
-  if (EffectiveTailLen >= MinCommonTailLength) 
-    return true; 
- 
-  // If we are optimizing for code size, 2 instructions in common is enough if 
-  // we don't have to split a block.  At worst we will be introducing 1 new 
-  // branch instruction, which is likely to be smaller than the 2 
-  // instructions that would be deleted in the merge. 
-  MachineFunction *MF = MBB1->getParent(); 
-  bool OptForSize = 
-      MF->getFunction().hasOptSize() || 
-      (llvm::shouldOptimizeForSize(MBB1, PSI, &MBBFreqInfo) && 
-       llvm::shouldOptimizeForSize(MBB2, PSI, &MBBFreqInfo)); 
-  return EffectiveTailLen >= 2 && OptForSize && 
-         (FullBlockTail1 || FullBlockTail2); 
-} 
- 
-unsigned BranchFolder::ComputeSameTails(unsigned CurHash, 
-                                        unsigned MinCommonTailLength, 
-                                        MachineBasicBlock *SuccBB, 
-                                        MachineBasicBlock *PredBB) { 
-  unsigned maxCommonTailLength = 0U; 
-  SameTails.clear(); 
-  MachineBasicBlock::iterator TrialBBI1, TrialBBI2; 
-  MPIterator HighestMPIter = std::prev(MergePotentials.end()); 
-  for (MPIterator CurMPIter = std::prev(MergePotentials.end()), 
-                  B = MergePotentials.begin(); 
-       CurMPIter != B && CurMPIter->getHash() == CurHash; --CurMPIter) { 
-    for (MPIterator I = std::prev(CurMPIter); I->getHash() == CurHash; --I) { 
-      unsigned CommonTailLen; 
-      if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(), 
-                            MinCommonTailLength, 
-                            CommonTailLen, TrialBBI1, TrialBBI2, 
-                            SuccBB, PredBB, 
-                            EHScopeMembership, 
-                            AfterBlockPlacement, MBBFreqInfo, PSI)) { 
-        if (CommonTailLen > maxCommonTailLength) { 
-          SameTails.clear(); 
-          maxCommonTailLength = CommonTailLen; 
-          HighestMPIter = CurMPIter; 
-          SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1)); 
-        } 
-        if (HighestMPIter == CurMPIter && 
-            CommonTailLen == maxCommonTailLength) 
-          SameTails.push_back(SameTailElt(I, TrialBBI2)); 
-      } 
-      if (I == B) 
-        break; 
-    } 
-  } 
-  return maxCommonTailLength; 
-} 
- 
-void BranchFolder::RemoveBlocksWithHash(unsigned CurHash, 
-                                        MachineBasicBlock *SuccBB, 
-                                        MachineBasicBlock *PredBB) { 
-  MPIterator CurMPIter, B; 
-  for (CurMPIter = std::prev(MergePotentials.end()), 
-      B = MergePotentials.begin(); 
-       CurMPIter->getHash() == CurHash; --CurMPIter) { 
-    // Put the unconditional branch back, if we need one. 
-    MachineBasicBlock *CurMBB = CurMPIter->getBlock(); 
-    if (SuccBB && CurMBB != PredBB) 
-      FixTail(CurMBB, SuccBB, TII); 
-    if (CurMPIter == B) 
-      break; 
-  } 
-  if (CurMPIter->getHash() != CurHash) 
-    CurMPIter++; 
-  MergePotentials.erase(CurMPIter, MergePotentials.end()); 
-} 
- 
-bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB, 
-                                             MachineBasicBlock *SuccBB, 
-                                             unsigned maxCommonTailLength, 
-                                             unsigned &commonTailIndex) { 
-  commonTailIndex = 0; 
-  unsigned TimeEstimate = ~0U; 
-  for (unsigned i = 0, e = SameTails.size(); i != e; ++i) { 
-    // Use PredBB if possible; that doesn't require a new branch. 
-    if (SameTails[i].getBlock() == PredBB) { 
-      commonTailIndex = i; 
-      break; 
-    } 
-    // Otherwise, make a (fairly bogus) choice based on estimate of 
-    // how long it will take the various blocks to execute. 
-    unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(), 
-                                 SameTails[i].getTailStartPos()); 
-    if (t <= TimeEstimate) { 
-      TimeEstimate = t; 
-      commonTailIndex = i; 
-    } 
-  } 
- 
-  MachineBasicBlock::iterator BBI = 
-    SameTails[commonTailIndex].getTailStartPos(); 
-  MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); 
- 
-  LLVM_DEBUG(dbgs() << "\nSplitting " << printMBBReference(*MBB) << ", size " 
-                    << maxCommonTailLength); 
- 
-  // If the split block unconditionally falls-thru to SuccBB, it will be 
-  // merged. In control flow terms it should then take SuccBB's name. e.g. If 
-  // SuccBB is an inner loop, the common tail is still part of the inner loop. 
-  const BasicBlock *BB = (SuccBB && MBB->succ_size() == 1) ? 
-    SuccBB->getBasicBlock() : MBB->getBasicBlock(); 
-  MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI, BB); 
-  if (!newMBB) { 
-    LLVM_DEBUG(dbgs() << "... failed!"); 
-    return false; 
-  } 
- 
-  SameTails[commonTailIndex].setBlock(newMBB); 
-  SameTails[commonTailIndex].setTailStartPos(newMBB->begin()); 
- 
-  // If we split PredBB, newMBB is the new predecessor. 
-  if (PredBB == MBB) 
-    PredBB = newMBB; 
- 
-  return true; 
-} 
- 
-static void 
-mergeOperations(MachineBasicBlock::iterator MBBIStartPos, 
-                MachineBasicBlock &MBBCommon) { 
-  MachineBasicBlock *MBB = MBBIStartPos->getParent(); 
-  // Note CommonTailLen does not necessarily matches the size of 
-  // the common BB nor all its instructions because of debug 
-  // instructions differences. 
-  unsigned CommonTailLen = 0; 
-  for (auto E = MBB->end(); MBBIStartPos != E; ++MBBIStartPos) 
-    ++CommonTailLen; 
- 
-  MachineBasicBlock::reverse_iterator MBBI = MBB->rbegin(); 
-  MachineBasicBlock::reverse_iterator MBBIE = MBB->rend(); 
-  MachineBasicBlock::reverse_iterator MBBICommon = MBBCommon.rbegin(); 
-  MachineBasicBlock::reverse_iterator MBBIECommon = MBBCommon.rend(); 
- 
-  while (CommonTailLen--) { 
-    assert(MBBI != MBBIE && "Reached BB end within common tail length!"); 
-    (void)MBBIE; 
- 
-    if (!countsAsInstruction(*MBBI)) { 
-      ++MBBI; 
-      continue; 
-    } 
- 
-    while ((MBBICommon != MBBIECommon) && !countsAsInstruction(*MBBICommon)) 
-      ++MBBICommon; 
- 
-    assert(MBBICommon != MBBIECommon && 
-           "Reached BB end within common tail length!"); 
-    assert(MBBICommon->isIdenticalTo(*MBBI) && "Expected matching MIIs!"); 
- 
-    // Merge MMOs from memory operations in the common block. 
-    if (MBBICommon->mayLoadOrStore()) 
-      MBBICommon->cloneMergedMemRefs(*MBB->getParent(), {&*MBBICommon, &*MBBI}); 
-    // Drop undef flags if they aren't present in all merged instructions. 
-    for (unsigned I = 0, E = MBBICommon->getNumOperands(); I != E; ++I) { 
-      MachineOperand &MO = MBBICommon->getOperand(I); 
-      if (MO.isReg() && MO.isUndef()) { 
-        const MachineOperand &OtherMO = MBBI->getOperand(I); 
-        if (!OtherMO.isUndef()) 
-          MO.setIsUndef(false); 
-      } 
-    } 
- 
-    ++MBBI; 
-    ++MBBICommon; 
-  } 
-} 
- 
-void BranchFolder::mergeCommonTails(unsigned commonTailIndex) { 
-  MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); 
- 
-  std::vector<MachineBasicBlock::iterator> NextCommonInsts(SameTails.size()); 
-  for (unsigned int i = 0 ; i != SameTails.size() ; ++i) { 
-    if (i != commonTailIndex) { 
-      NextCommonInsts[i] = SameTails[i].getTailStartPos(); 
-      mergeOperations(SameTails[i].getTailStartPos(), *MBB); 
-    } else { 
-      assert(SameTails[i].getTailStartPos() == MBB->begin() && 
-          "MBB is not a common tail only block"); 
-    } 
-  } 
- 
-  for (auto &MI : *MBB) { 
-    if (!countsAsInstruction(MI)) 
-      continue; 
-    DebugLoc DL = MI.getDebugLoc(); 
-    for (unsigned int i = 0 ; i < NextCommonInsts.size() ; i++) { 
-      if (i == commonTailIndex) 
-        continue; 
- 
-      auto &Pos = NextCommonInsts[i]; 
-      assert(Pos != SameTails[i].getBlock()->end() && 
-          "Reached BB end within common tail"); 
-      while (!countsAsInstruction(*Pos)) { 
-        ++Pos; 
-        assert(Pos != SameTails[i].getBlock()->end() && 
-            "Reached BB end within common tail"); 
-      } 
-      assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!"); 
-      DL = DILocation::getMergedLocation(DL, Pos->getDebugLoc()); 
-      NextCommonInsts[i] = ++Pos; 
-    } 
-    MI.setDebugLoc(DL); 
-  } 
- 
-  if (UpdateLiveIns) { 
-    LivePhysRegs NewLiveIns(*TRI); 
-    computeLiveIns(NewLiveIns, *MBB); 
-    LiveRegs.init(*TRI); 
- 
-    // The flag merging may lead to some register uses no longer using the 
-    // <undef> flag, add IMPLICIT_DEFs in the predecessors as necessary. 
-    for (MachineBasicBlock *Pred : MBB->predecessors()) { 
-      LiveRegs.clear(); 
-      LiveRegs.addLiveOuts(*Pred); 
-      MachineBasicBlock::iterator InsertBefore = Pred->getFirstTerminator(); 
-      for (Register Reg : NewLiveIns) { 
-        if (!LiveRegs.available(*MRI, Reg)) 
-          continue; 
-        DebugLoc DL; 
-        BuildMI(*Pred, InsertBefore, DL, TII->get(TargetOpcode::IMPLICIT_DEF), 
-                Reg); 
-      } 
-    } 
- 
-    MBB->clearLiveIns(); 
-    addLiveIns(*MBB, NewLiveIns); 
-  } 
-} 
- 
-// See if any of the blocks in MergePotentials (which all have SuccBB as a 
-// successor, or all have no successor if it is null) can be tail-merged. 
-// If there is a successor, any blocks in MergePotentials that are not 
-// tail-merged and are not immediately before Succ must have an unconditional 
-// branch to Succ added (but the predecessor/successor lists need no 
-// adjustment). The lone predecessor of Succ that falls through into Succ, 
-// if any, is given in PredBB. 
-// MinCommonTailLength - Except for the special cases below, tail-merge if 
-// there are at least this many instructions in common. 
-bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB, 
-                                      MachineBasicBlock *PredBB, 
-                                      unsigned MinCommonTailLength) { 
-  bool MadeChange = false; 
- 
-  LLVM_DEBUG( 
-      dbgs() << "\nTryTailMergeBlocks: "; 
-      for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) dbgs() 
-      << printMBBReference(*MergePotentials[i].getBlock()) 
-      << (i == e - 1 ? "" : ", "); 
-      dbgs() << "\n"; if (SuccBB) { 
-        dbgs() << "  with successor " << printMBBReference(*SuccBB) << '\n'; 
-        if (PredBB) 
-          dbgs() << "  which has fall-through from " 
-                 << printMBBReference(*PredBB) << "\n"; 
-      } dbgs() << "Looking for common tails of at least " 
-               << MinCommonTailLength << " instruction" 
-               << (MinCommonTailLength == 1 ? "" : "s") << '\n';); 
- 
-  // Sort by hash value so that blocks with identical end sequences sort 
-  // together. 
-  array_pod_sort(MergePotentials.begin(), MergePotentials.end()); 
- 
-  // Walk through equivalence sets looking for actual exact matches. 
-  while (MergePotentials.size() > 1) { 
-    unsigned CurHash = MergePotentials.back().getHash(); 
- 
-    // Build SameTails, identifying the set of blocks with this hash code 
-    // and with the maximum number of instructions in common. 
-    unsigned maxCommonTailLength = ComputeSameTails(CurHash, 
-                                                    MinCommonTailLength, 
-                                                    SuccBB, PredBB); 
- 
-    // If we didn't find any pair that has at least MinCommonTailLength 
-    // instructions in common, remove all blocks with this hash code and retry. 
-    if (SameTails.empty()) { 
-      RemoveBlocksWithHash(CurHash, SuccBB, PredBB); 
-      continue; 
-    } 
- 
-    // If one of the blocks is the entire common tail (and is not the entry 
-    // block/an EH pad, which we can't jump to), we can treat all blocks with 
-    // this same tail at once.  Use PredBB if that is one of the possibilities, 
-    // as that will not introduce any extra branches. 
-    MachineBasicBlock *EntryBB = 
-        &MergePotentials.front().getBlock()->getParent()->front(); 
-    unsigned commonTailIndex = SameTails.size(); 
-    // If there are two blocks, check to see if one can be made to fall through 
-    // into the other. 
-    if (SameTails.size() == 2 && 
-        SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) && 
-        SameTails[1].tailIsWholeBlock() && !SameTails[1].getBlock()->isEHPad()) 
-      commonTailIndex = 1; 
-    else if (SameTails.size() == 2 && 
-             SameTails[1].getBlock()->isLayoutSuccessor( 
-                 SameTails[0].getBlock()) && 
-             SameTails[0].tailIsWholeBlock() && 
-             !SameTails[0].getBlock()->isEHPad()) 
-      commonTailIndex = 0; 
-    else { 
-      // Otherwise just pick one, favoring the fall-through predecessor if 
-      // there is one. 
-      for (unsigned i = 0, e = SameTails.size(); i != e; ++i) { 
-        MachineBasicBlock *MBB = SameTails[i].getBlock(); 
-        if ((MBB == EntryBB || MBB->isEHPad()) && 
-            SameTails[i].tailIsWholeBlock()) 
-          continue; 
-        if (MBB == PredBB) { 
-          commonTailIndex = i; 
-          break; 
-        } 
-        if (SameTails[i].tailIsWholeBlock()) 
-          commonTailIndex = i; 
-      } 
-    } 
- 
-    if (commonTailIndex == SameTails.size() || 
-        (SameTails[commonTailIndex].getBlock() == PredBB && 
-         !SameTails[commonTailIndex].tailIsWholeBlock())) { 
-      // None of the blocks consist entirely of the common tail. 
-      // Split a block so that one does. 
-      if (!CreateCommonTailOnlyBlock(PredBB, SuccBB, 
-                                     maxCommonTailLength, commonTailIndex)) { 
-        RemoveBlocksWithHash(CurHash, SuccBB, PredBB); 
-        continue; 
-      } 
-    } 
- 
-    MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); 
- 
-    // Recompute common tail MBB's edge weights and block frequency. 
-    setCommonTailEdgeWeights(*MBB); 
- 
-    // Merge debug locations, MMOs and undef flags across identical instructions 
-    // for common tail. 
-    mergeCommonTails(commonTailIndex); 
- 
-    // MBB is common tail.  Adjust all other BB's to jump to this one. 
-    // Traversal must be forwards so erases work. 
-    LLVM_DEBUG(dbgs() << "\nUsing common tail in " << printMBBReference(*MBB) 
-                      << " for "); 
-    for (unsigned int i=0, e = SameTails.size(); i != e; ++i) { 
-      if (commonTailIndex == i) 
-        continue; 
-      LLVM_DEBUG(dbgs() << printMBBReference(*SameTails[i].getBlock()) 
-                        << (i == e - 1 ? "" : ", ")); 
-      // Hack the end off BB i, making it jump to BB commonTailIndex instead. 
-      replaceTailWithBranchTo(SameTails[i].getTailStartPos(), *MBB); 
-      // BB i is no longer a predecessor of SuccBB; remove it from the worklist. 
-      MergePotentials.erase(SameTails[i].getMPIter()); 
-    } 
-    LLVM_DEBUG(dbgs() << "\n"); 
-    // We leave commonTailIndex in the worklist in case there are other blocks 
-    // that match it with a smaller number of instructions. 
-    MadeChange = true; 
-  } 
-  return MadeChange; 
-} 
- 
-bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { 
-  bool MadeChange = false; 
-  if (!EnableTailMerge) 
-    return MadeChange; 
- 
-  // First find blocks with no successors. 
-  // Block placement may create new tail merging opportunities for these blocks. 
-  MergePotentials.clear(); 
-  for (MachineBasicBlock &MBB : MF) { 
-    if (MergePotentials.size() == TailMergeThreshold) 
-      break; 
-    if (!TriedMerging.count(&MBB) && MBB.succ_empty()) 
-      MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(MBB), &MBB)); 
-  } 
- 
-  // If this is a large problem, avoid visiting the same basic blocks 
-  // multiple times. 
-  if (MergePotentials.size() == TailMergeThreshold) 
-    for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) 
-      TriedMerging.insert(MergePotentials[i].getBlock()); 
- 
-  // See if we can do any tail merging on those. 
-  if (MergePotentials.size() >= 2) 
-    MadeChange |= TryTailMergeBlocks(nullptr, nullptr, MinCommonTailLength); 
- 
-  // Look at blocks (IBB) with multiple predecessors (PBB). 
-  // We change each predecessor to a canonical form, by 
-  // (1) temporarily removing any unconditional branch from the predecessor 
-  // to IBB, and 
-  // (2) alter conditional branches so they branch to the other block 
-  // not IBB; this may require adding back an unconditional branch to IBB 
-  // later, where there wasn't one coming in.  E.g. 
-  //   Bcc IBB 
-  //   fallthrough to QBB 
-  // here becomes 
-  //   Bncc QBB 
-  // with a conceptual B to IBB after that, which never actually exists. 
-  // With those changes, we see whether the predecessors' tails match, 
-  // and merge them if so.  We change things out of canonical form and 
-  // back to the way they were later in the process.  (OptimizeBranches 
-  // would undo some of this, but we can't use it, because we'd get into 
-  // a compile-time infinite loop repeatedly doing and undoing the same 
-  // transformations.) 
- 
-  for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end(); 
-       I != E; ++I) { 
-    if (I->pred_size() < 2) continue; 
-    SmallPtrSet<MachineBasicBlock *, 8> UniquePreds; 
-    MachineBasicBlock *IBB = &*I; 
-    MachineBasicBlock *PredBB = &*std::prev(I); 
-    MergePotentials.clear(); 
-    MachineLoop *ML; 
- 
-    // Bail if merging after placement and IBB is the loop header because 
-    // -- If merging predecessors that belong to the same loop as IBB, the 
-    // common tail of merged predecessors may become the loop top if block 
-    // placement is called again and the predecessors may branch to this common 
-    // tail and require more branches. This can be relaxed if 
-    // MachineBlockPlacement::findBestLoopTop is more flexible. 
-    // --If merging predecessors that do not belong to the same loop as IBB, the 
-    // loop info of IBB's loop and the other loops may be affected. Calling the 
-    // block placement again may make big change to the layout and eliminate the 
-    // reason to do tail merging here. 
-    if (AfterBlockPlacement && MLI) { 
-      ML = MLI->getLoopFor(IBB); 
-      if (ML && IBB == ML->getHeader()) 
-        continue; 
-    } 
- 
-    for (MachineBasicBlock *PBB : I->predecessors()) { 
-      if (MergePotentials.size() == TailMergeThreshold) 
-        break; 
- 
-      if (TriedMerging.count(PBB)) 
-        continue; 
- 
-      // Skip blocks that loop to themselves, can't tail merge these. 
-      if (PBB == IBB) 
-        continue; 
- 
-      // Visit each predecessor only once. 
-      if (!UniquePreds.insert(PBB).second) 
-        continue; 
- 
-      // Skip blocks which may jump to a landing pad or jump from an asm blob. 
-      // Can't tail merge these. 
-      if (PBB->hasEHPadSuccessor() || PBB->mayHaveInlineAsmBr()) 
-        continue; 
- 
-      // After block placement, only consider predecessors that belong to the 
-      // same loop as IBB.  The reason is the same as above when skipping loop 
-      // header. 
-      if (AfterBlockPlacement && MLI) 
-        if (ML != MLI->getLoopFor(PBB)) 
-          continue; 
- 
-      MachineBasicBlock *TBB = nullptr, *FBB = nullptr; 
-      SmallVector<MachineOperand, 4> Cond; 
-      if (!TII->analyzeBranch(*PBB, TBB, FBB, Cond, true)) { 
-        // Failing case: IBB is the target of a cbr, and we cannot reverse the 
-        // branch. 
-        SmallVector<MachineOperand, 4> NewCond(Cond); 
-        if (!Cond.empty() && TBB == IBB) { 
-          if (TII->reverseBranchCondition(NewCond)) 
-            continue; 
-          // This is the QBB case described above 
-          if (!FBB) { 
-            auto Next = ++PBB->getIterator(); 
-            if (Next != MF.end()) 
-              FBB = &*Next; 
-          } 
-        } 
- 
-        // Remove the unconditional branch at the end, if any. 
-        if (TBB && (Cond.empty() || FBB)) { 
-          DebugLoc dl = PBB->findBranchDebugLoc(); 
-          TII->removeBranch(*PBB); 
-          if (!Cond.empty()) 
-            // reinsert conditional branch only, for now 
-            TII->insertBranch(*PBB, (TBB == IBB) ? FBB : TBB, nullptr, 
-                              NewCond, dl); 
-        } 
- 
-        MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(*PBB), PBB)); 
-      } 
-    } 
- 
-    // If this is a large problem, avoid visiting the same basic blocks multiple 
-    // times. 
-    if (MergePotentials.size() == TailMergeThreshold) 
-      for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) 
-        TriedMerging.insert(MergePotentials[i].getBlock()); 
- 
-    if (MergePotentials.size() >= 2) 
-      MadeChange |= TryTailMergeBlocks(IBB, PredBB, MinCommonTailLength); 
- 
-    // Reinsert an unconditional branch if needed. The 1 below can occur as a 
-    // result of removing blocks in TryTailMergeBlocks. 
-    PredBB = &*std::prev(I); // this may have been changed in TryTailMergeBlocks 
-    if (MergePotentials.size() == 1 && 
-        MergePotentials.begin()->getBlock() != PredBB) 
-      FixTail(MergePotentials.begin()->getBlock(), IBB, TII); 
-  } 
- 
-  return MadeChange; 
-} 
- 
-void BranchFolder::setCommonTailEdgeWeights(MachineBasicBlock &TailMBB) { 
-  SmallVector<BlockFrequency, 2> EdgeFreqLs(TailMBB.succ_size()); 
-  BlockFrequency AccumulatedMBBFreq; 
- 
-  // Aggregate edge frequency of successor edge j: 
-  //  edgeFreq(j) = sum (freq(bb) * edgeProb(bb, j)), 
-  //  where bb is a basic block that is in SameTails. 
-  for (const auto &Src : SameTails) { 
-    const MachineBasicBlock *SrcMBB = Src.getBlock(); 
-    BlockFrequency BlockFreq = MBBFreqInfo.getBlockFreq(SrcMBB); 
-    AccumulatedMBBFreq += BlockFreq; 
- 
-    // It is not necessary to recompute edge weights if TailBB has less than two 
-    // successors. 
-    if (TailMBB.succ_size() <= 1) 
-      continue; 
- 
-    auto EdgeFreq = EdgeFreqLs.begin(); 
- 
-    for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end(); 
-         SuccI != SuccE; ++SuccI, ++EdgeFreq) 
-      *EdgeFreq += BlockFreq * MBPI.getEdgeProbability(SrcMBB, *SuccI); 
-  } 
- 
-  MBBFreqInfo.setBlockFreq(&TailMBB, AccumulatedMBBFreq); 
- 
-  if (TailMBB.succ_size() <= 1) 
-    return; 
- 
-  auto SumEdgeFreq = 
-      std::accumulate(EdgeFreqLs.begin(), EdgeFreqLs.end(), BlockFrequency(0)) 
-          .getFrequency(); 
-  auto EdgeFreq = EdgeFreqLs.begin(); 
- 
-  if (SumEdgeFreq > 0) { 
-    for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end(); 
-         SuccI != SuccE; ++SuccI, ++EdgeFreq) { 
-      auto Prob = BranchProbability::getBranchProbability( 
-          EdgeFreq->getFrequency(), SumEdgeFreq); 
-      TailMBB.setSuccProbability(SuccI, Prob); 
-    } 
-  } 
-} 
- 
-//===----------------------------------------------------------------------===// 
-//  Branch Optimization 
-//===----------------------------------------------------------------------===// 
- 
-bool BranchFolder::OptimizeBranches(MachineFunction &MF) { 
-  bool MadeChange = false; 
- 
-  // Make sure blocks are numbered in order 
-  MF.RenumberBlocks(); 
-  // Renumbering blocks alters EH scope membership, recalculate it. 
-  EHScopeMembership = getEHScopeMembership(MF); 
- 
-  for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end(); 
-       I != E; ) { 
-    MachineBasicBlock *MBB = &*I++; 
-    MadeChange |= OptimizeBlock(MBB); 
- 
-    // If it is dead, remove it. 
-    if (MBB->pred_empty()) { 
-      RemoveDeadBlock(MBB); 
-      MadeChange = true; 
-      ++NumDeadBlocks; 
-    } 
-  } 
- 
-  return MadeChange; 
-} 
- 
-// Blocks should be considered empty if they contain only debug info; 
-// else the debug info would affect codegen. 
-static bool IsEmptyBlock(MachineBasicBlock *MBB) { 
-  return MBB->getFirstNonDebugInstr() == MBB->end(); 
-} 
- 
-// Blocks with only debug info and branches should be considered the same 
-// as blocks with only branches. 
-static bool IsBranchOnlyBlock(MachineBasicBlock *MBB) { 
-  MachineBasicBlock::iterator I = MBB->getFirstNonDebugInstr(); 
-  assert(I != MBB->end() && "empty block!"); 
-  return I->isBranch(); 
-} 
- 
-/// IsBetterFallthrough - Return true if it would be clearly better to 
-/// fall-through to MBB1 than to fall through into MBB2.  This has to return 
-/// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will 
-/// result in infinite loops. 
-static bool IsBetterFallthrough(MachineBasicBlock *MBB1, 
-                                MachineBasicBlock *MBB2) { 
-  assert(MBB1 && MBB2 && "Unknown MachineBasicBlock"); 
- 
-  // Right now, we use a simple heuristic.  If MBB2 ends with a call, and 
-  // MBB1 doesn't, we prefer to fall through into MBB1.  This allows us to 
-  // optimize branches that branch to either a return block or an assert block 
-  // into a fallthrough to the return. 
-  MachineBasicBlock::iterator MBB1I = MBB1->getLastNonDebugInstr(); 
-  MachineBasicBlock::iterator MBB2I = MBB2->getLastNonDebugInstr(); 
-  if (MBB1I == MBB1->end() || MBB2I == MBB2->end()) 
-    return false; 
- 
-  // If there is a clear successor ordering we make sure that one block 
-  // will fall through to the next 
-  if (MBB1->isSuccessor(MBB2)) return true; 
-  if (MBB2->isSuccessor(MBB1)) return false; 
- 
-  return MBB2I->isCall() && !MBB1I->isCall(); 
-} 
- 
-/// getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch 
-/// instructions on the block. 
-static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) { 
-  MachineBasicBlock::iterator I = MBB.getLastNonDebugInstr(); 
-  if (I != MBB.end() && I->isBranch()) 
-    return I->getDebugLoc(); 
-  return DebugLoc(); 
-} 
- 
-static void copyDebugInfoToPredecessor(const TargetInstrInfo *TII, 
-                                       MachineBasicBlock &MBB, 
-                                       MachineBasicBlock &PredMBB) { 
-  auto InsertBefore = PredMBB.getFirstTerminator(); 
-  for (MachineInstr &MI : MBB.instrs()) 
-    if (MI.isDebugInstr()) { 
-      TII->duplicate(PredMBB, InsertBefore, MI); 
-      LLVM_DEBUG(dbgs() << "Copied debug entity from empty block to pred: " 
-                        << MI); 
-    } 
-} 
- 
-static void copyDebugInfoToSuccessor(const TargetInstrInfo *TII, 
-                                     MachineBasicBlock &MBB, 
-                                     MachineBasicBlock &SuccMBB) { 
-  auto InsertBefore = SuccMBB.SkipPHIsAndLabels(SuccMBB.begin()); 
-  for (MachineInstr &MI : MBB.instrs()) 
-    if (MI.isDebugInstr()) { 
-      TII->duplicate(SuccMBB, InsertBefore, MI); 
-      LLVM_DEBUG(dbgs() << "Copied debug entity from empty block to succ: " 
-                        << MI); 
-    } 
-} 
- 
-// Try to salvage DBG_VALUE instructions from an otherwise empty block. If such 
-// a basic block is removed we would lose the debug information unless we have 
-// copied the information to a predecessor/successor. 
-// 
-// TODO: This function only handles some simple cases. An alternative would be 
-// to run a heavier analysis, such as the LiveDebugValues pass, before we do 
-// branch folding. 
-static void salvageDebugInfoFromEmptyBlock(const TargetInstrInfo *TII, 
-                                           MachineBasicBlock &MBB) { 
-  assert(IsEmptyBlock(&MBB) && "Expected an empty block (except debug info)."); 
-  // If this MBB is the only predecessor of a successor it is legal to copy 
-  // DBG_VALUE instructions to the beginning of the successor. 
-  for (MachineBasicBlock *SuccBB : MBB.successors()) 
-    if (SuccBB->pred_size() == 1) 
-      copyDebugInfoToSuccessor(TII, MBB, *SuccBB); 
-  // If this MBB is the only successor of a predecessor it is legal to copy the 
-  // DBG_VALUE instructions to the end of the predecessor (just before the 
-  // terminators, assuming that the terminator isn't affecting the DBG_VALUE). 
-  for (MachineBasicBlock *PredBB : MBB.predecessors()) 
-    if (PredBB->succ_size() == 1) 
-      copyDebugInfoToPredecessor(TII, MBB, *PredBB); 
-} 
- 
-bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { 
-  bool MadeChange = false; 
-  MachineFunction &MF = *MBB->getParent(); 
-ReoptimizeBlock: 
- 
-  MachineFunction::iterator FallThrough = MBB->getIterator(); 
-  ++FallThrough; 
- 
-  // Make sure MBB and FallThrough belong to the same EH scope. 
-  bool SameEHScope = true; 
-  if (!EHScopeMembership.empty() && FallThrough != MF.end()) { 
-    auto MBBEHScope = EHScopeMembership.find(MBB); 
-    assert(MBBEHScope != EHScopeMembership.end()); 
-    auto FallThroughEHScope = EHScopeMembership.find(&*FallThrough); 
-    assert(FallThroughEHScope != EHScopeMembership.end()); 
-    SameEHScope = MBBEHScope->second == FallThroughEHScope->second; 
-  } 
- 
-  // Analyze the branch in the current block. As a side-effect, this may cause 
-  // the block to become empty. 
-  MachineBasicBlock *CurTBB = nullptr, *CurFBB = nullptr; 
-  SmallVector<MachineOperand, 4> CurCond; 
-  bool CurUnAnalyzable = 
-      TII->analyzeBranch(*MBB, CurTBB, CurFBB, CurCond, true); 
- 
-  // If this block is empty, make everyone use its fall-through, not the block 
-  // explicitly.  Landing pads should not do this since the landing-pad table 
-  // points to this block.  Blocks with their addresses taken shouldn't be 
-  // optimized away. 
-  if (IsEmptyBlock(MBB) && !MBB->isEHPad() && !MBB->hasAddressTaken() && 
-      SameEHScope) { 
-    salvageDebugInfoFromEmptyBlock(TII, *MBB); 
-    // Dead block?  Leave for cleanup later. 
-    if (MBB->pred_empty()) return MadeChange; 
- 
-    if (FallThrough == MF.end()) { 
-      // TODO: Simplify preds to not branch here if possible! 
-    } else if (FallThrough->isEHPad()) { 
-      // Don't rewrite to a landing pad fallthough.  That could lead to the case 
-      // where a BB jumps to more than one landing pad. 
-      // TODO: Is it ever worth rewriting predecessors which don't already 
-      // jump to a landing pad, and so can safely jump to the fallthrough? 
-    } else if (MBB->isSuccessor(&*FallThrough)) { 
-      // Rewrite all predecessors of the old block to go to the fallthrough 
-      // instead. 
-      while (!MBB->pred_empty()) { 
-        MachineBasicBlock *Pred = *(MBB->pred_end()-1); 
-        Pred->ReplaceUsesOfBlockWith(MBB, &*FallThrough); 
-      } 
-      // If MBB was the target of a jump table, update jump tables to go to the 
-      // fallthrough instead. 
-      if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo()) 
-        MJTI->ReplaceMBBInJumpTables(MBB, &*FallThrough); 
-      MadeChange = true; 
-    } 
-    return MadeChange; 
-  } 
- 
-  // Check to see if we can simplify the terminator of the block before this 
-  // one. 
-  MachineBasicBlock &PrevBB = *std::prev(MachineFunction::iterator(MBB)); 
- 
-  MachineBasicBlock *PriorTBB = nullptr, *PriorFBB = nullptr; 
-  SmallVector<MachineOperand, 4> PriorCond; 
-  bool PriorUnAnalyzable = 
-      TII->analyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true); 
-  if (!PriorUnAnalyzable) { 
-    // If the previous branch is conditional and both conditions go to the same 
-    // destination, remove the branch, replacing it with an unconditional one or 
-    // a fall-through. 
-    if (PriorTBB && PriorTBB == PriorFBB) { 
-      DebugLoc dl = getBranchDebugLoc(PrevBB); 
-      TII->removeBranch(PrevBB); 
-      PriorCond.clear(); 
-      if (PriorTBB != MBB) 
-        TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl); 
-      MadeChange = true; 
-      ++NumBranchOpts; 
-      goto ReoptimizeBlock; 
-    } 
- 
-    // If the previous block unconditionally falls through to this block and 
-    // this block has no other predecessors, move the contents of this block 
-    // into the prior block. This doesn't usually happen when SimplifyCFG 
-    // has been used, but it can happen if tail merging splits a fall-through 
-    // predecessor of a block. 
-    // This has to check PrevBB->succ_size() because EH edges are ignored by 
-    // analyzeBranch. 
-    if (PriorCond.empty() && !PriorTBB && MBB->pred_size() == 1 && 
-        PrevBB.succ_size() == 1 && 
-        !MBB->hasAddressTaken() && !MBB->isEHPad()) { 
-      LLVM_DEBUG(dbgs() << "\nMerging into block: " << PrevBB 
-                        << "From MBB: " << *MBB); 
-      // Remove redundant DBG_VALUEs first. 
+  case cl::BOU_TRUE: EnableTailMerge = true; break;
+  case cl::BOU_FALSE: EnableTailMerge = false; break;
+  }
+}
+
+void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
+  assert(MBB->pred_empty() && "MBB must be dead!");
+  LLVM_DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
+
+  MachineFunction *MF = MBB->getParent();
+  // drop all successors.
+  while (!MBB->succ_empty())
+    MBB->removeSuccessor(MBB->succ_end()-1);
+
+  // Avoid matching if this pointer gets reused.
+  TriedMerging.erase(MBB);
+
+  // Update call site info.
+  std::for_each(MBB->begin(), MBB->end(), [MF](const MachineInstr &MI) {
+    if (MI.shouldUpdateCallSiteInfo())
+      MF->eraseCallSiteInfo(&MI);
+  });
+  // Remove the block.
+  MF->erase(MBB);
+  EHScopeMembership.erase(MBB);
+  if (MLI)
+    MLI->removeBlock(MBB);
+}
+
+bool BranchFolder::OptimizeFunction(MachineFunction &MF,
+                                    const TargetInstrInfo *tii,
+                                    const TargetRegisterInfo *tri,
+                                    MachineLoopInfo *mli, bool AfterPlacement) {
+  if (!tii) return false;
+
+  TriedMerging.clear();
+
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+  AfterBlockPlacement = AfterPlacement;
+  TII = tii;
+  TRI = tri;
+  MLI = mli;
+  this->MRI = &MRI;
+
+  UpdateLiveIns = MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF);
+  if (!UpdateLiveIns)
+    MRI.invalidateLiveness();
+
+  bool MadeChange = false;
+
+  // Recalculate EH scope membership.
+  EHScopeMembership = getEHScopeMembership(MF);
+
+  bool MadeChangeThisIteration = true;
+  while (MadeChangeThisIteration) {
+    MadeChangeThisIteration    = TailMergeBlocks(MF);
+    // No need to clean up if tail merging does not change anything after the
+    // block placement.
+    if (!AfterBlockPlacement || MadeChangeThisIteration)
+      MadeChangeThisIteration |= OptimizeBranches(MF);
+    if (EnableHoistCommonCode)
+      MadeChangeThisIteration |= HoistCommonCode(MF);
+    MadeChange |= MadeChangeThisIteration;
+  }
+
+  // See if any jump tables have become dead as the code generator
+  // did its thing.
+  MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
+  if (!JTI)
+    return MadeChange;
+
+  // Walk the function to find jump tables that are live.
+  BitVector JTIsLive(JTI->getJumpTables().size());
+  for (const MachineBasicBlock &BB : MF) {
+    for (const MachineInstr &I : BB)
+      for (const MachineOperand &Op : I.operands()) {
+        if (!Op.isJTI()) continue;
+
+        // Remember that this JT is live.
+        JTIsLive.set(Op.getIndex());
+      }
+  }
+
+  // Finally, remove dead jump tables.  This happens when the
+  // indirect jump was unreachable (and thus deleted).
+  for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i)
+    if (!JTIsLive.test(i)) {
+      JTI->RemoveJumpTable(i);
+      MadeChange = true;
+    }
+
+  return MadeChange;
+}
+
+//===----------------------------------------------------------------------===//
+//  Tail Merging of Blocks
+//===----------------------------------------------------------------------===//
+
+/// HashMachineInstr - Compute a hash value for MI and its operands.
+static unsigned HashMachineInstr(const MachineInstr &MI) {
+  unsigned Hash = MI.getOpcode();
+  for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
+    const MachineOperand &Op = MI.getOperand(i);
+
+    // Merge in bits from the operand if easy. We can't use MachineOperand's
+    // hash_code here because it's not deterministic and we sort by hash value
+    // later.
+    unsigned OperandHash = 0;
+    switch (Op.getType()) {
+    case MachineOperand::MO_Register:
+      OperandHash = Op.getReg();
+      break;
+    case MachineOperand::MO_Immediate:
+      OperandHash = Op.getImm();
+      break;
+    case MachineOperand::MO_MachineBasicBlock:
+      OperandHash = Op.getMBB()->getNumber();
+      break;
+    case MachineOperand::MO_FrameIndex:
+    case MachineOperand::MO_ConstantPoolIndex:
+    case MachineOperand::MO_JumpTableIndex:
+      OperandHash = Op.getIndex();
+      break;
+    case MachineOperand::MO_GlobalAddress:
+    case MachineOperand::MO_ExternalSymbol:
+      // Global address / external symbol are too hard, don't bother, but do
+      // pull in the offset.
+      OperandHash = Op.getOffset();
+      break;
+    default:
+      break;
+    }
+
+    Hash += ((OperandHash << 3) | Op.getType()) << (i & 31);
+  }
+  return Hash;
+}
+
+/// HashEndOfMBB - Hash the last instruction in the MBB.
+static unsigned HashEndOfMBB(const MachineBasicBlock &MBB) {
+  MachineBasicBlock::const_iterator I = MBB.getLastNonDebugInstr();
+  if (I == MBB.end())
+    return 0;
+
+  return HashMachineInstr(*I);
+}
+
+/// Whether MI should be counted as an instruction when calculating common tail.
+static bool countsAsInstruction(const MachineInstr &MI) {
+  return !(MI.isDebugInstr() || MI.isCFIInstruction());
+}
+
+/// Iterate backwards from the given iterator \p I, towards the beginning of the
+/// block. If a MI satisfying 'countsAsInstruction' is found, return an iterator
+/// pointing to that MI. If no such MI is found, return the end iterator.
+static MachineBasicBlock::iterator
+skipBackwardPastNonInstructions(MachineBasicBlock::iterator I,
+                                MachineBasicBlock *MBB) {
+  while (I != MBB->begin()) {
+    --I;
+    if (countsAsInstruction(*I))
+      return I;
+  }
+  return MBB->end();
+}
+
+/// Given two machine basic blocks, return the number of instructions they
+/// actually have in common together at their end. If a common tail is found (at
+/// least by one instruction), then iterators for the first shared instruction
+/// in each block are returned as well.
+///
+/// Non-instructions according to countsAsInstruction are ignored.
+static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
+                                        MachineBasicBlock *MBB2,
+                                        MachineBasicBlock::iterator &I1,
+                                        MachineBasicBlock::iterator &I2) {
+  MachineBasicBlock::iterator MBBI1 = MBB1->end();
+  MachineBasicBlock::iterator MBBI2 = MBB2->end();
+
+  unsigned TailLen = 0;
+  while (true) {
+    MBBI1 = skipBackwardPastNonInstructions(MBBI1, MBB1);
+    MBBI2 = skipBackwardPastNonInstructions(MBBI2, MBB2);
+    if (MBBI1 == MBB1->end() || MBBI2 == MBB2->end())
+      break;
+    if (!MBBI1->isIdenticalTo(*MBBI2) ||
+        // FIXME: This check is dubious. It's used to get around a problem where
+        // people incorrectly expect inline asm directives to remain in the same
+        // relative order. This is untenable because normal compiler
+        // optimizations (like this one) may reorder and/or merge these
+        // directives.
+        MBBI1->isInlineAsm()) {
+      break;
+    }
+    if (MBBI1->getFlag(MachineInstr::NoMerge) ||
+        MBBI2->getFlag(MachineInstr::NoMerge))
+      break;
+    ++TailLen;
+    I1 = MBBI1;
+    I2 = MBBI2;
+  }
+
+  return TailLen;
+}
+
+void BranchFolder::replaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
+                                           MachineBasicBlock &NewDest) {
+  if (UpdateLiveIns) {
+    // OldInst should always point to an instruction.
+    MachineBasicBlock &OldMBB = *OldInst->getParent();
+    LiveRegs.clear();
+    LiveRegs.addLiveOuts(OldMBB);
+    // Move backward to the place where will insert the jump.
+    MachineBasicBlock::iterator I = OldMBB.end();
+    do {
+      --I;
+      LiveRegs.stepBackward(*I);
+    } while (I != OldInst);
+
+    // Merging the tails may have switched some undef operand to non-undef ones.
+    // Add IMPLICIT_DEFS into OldMBB as necessary to have a definition of the
+    // register.
+    for (MachineBasicBlock::RegisterMaskPair P : NewDest.liveins()) {
+      // We computed the liveins with computeLiveIn earlier and should only see
+      // full registers:
+      assert(P.LaneMask == LaneBitmask::getAll() &&
+             "Can only handle full register.");
+      MCPhysReg Reg = P.PhysReg;
+      if (!LiveRegs.available(*MRI, Reg))
+        continue;
+      DebugLoc DL;
+      BuildMI(OldMBB, OldInst, DL, TII->get(TargetOpcode::IMPLICIT_DEF), Reg);
+    }
+  }
+
+  TII->ReplaceTailWithBranchTo(OldInst, &NewDest);
+  ++NumTailMerge;
+}
+
+MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
+                                            MachineBasicBlock::iterator BBI1,
+                                            const BasicBlock *BB) {
+  if (!TII->isLegalToSplitMBBAt(CurMBB, BBI1))
+    return nullptr;
+
+  MachineFunction &MF = *CurMBB.getParent();
+
+  // Create the fall-through block.
+  MachineFunction::iterator MBBI = CurMBB.getIterator();
+  MachineBasicBlock *NewMBB = MF.CreateMachineBasicBlock(BB);
+  CurMBB.getParent()->insert(++MBBI, NewMBB);
+
+  // Move all the successors of this block to the specified block.
+  NewMBB->transferSuccessors(&CurMBB);
+
+  // Add an edge from CurMBB to NewMBB for the fall-through.
+  CurMBB.addSuccessor(NewMBB);
+
+  // Splice the code over.
+  NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end());
+
+  // NewMBB belongs to the same loop as CurMBB.
+  if (MLI)
+    if (MachineLoop *ML = MLI->getLoopFor(&CurMBB))
+      ML->addBasicBlockToLoop(NewMBB, MLI->getBase());
+
+  // NewMBB inherits CurMBB's block frequency.
+  MBBFreqInfo.setBlockFreq(NewMBB, MBBFreqInfo.getBlockFreq(&CurMBB));
+
+  if (UpdateLiveIns)
+    computeAndAddLiveIns(LiveRegs, *NewMBB);
+
+  // Add the new block to the EH scope.
+  const auto &EHScopeI = EHScopeMembership.find(&CurMBB);
+  if (EHScopeI != EHScopeMembership.end()) {
+    auto n = EHScopeI->second;
+    EHScopeMembership[NewMBB] = n;
+  }
+
+  return NewMBB;
+}
+
+/// EstimateRuntime - Make a rough estimate for how long it will take to run
+/// the specified code.
+static unsigned EstimateRuntime(MachineBasicBlock::iterator I,
+                                MachineBasicBlock::iterator E) {
+  unsigned Time = 0;
+  for (; I != E; ++I) {
+    if (!countsAsInstruction(*I))
+      continue;
+    if (I->isCall())
+      Time += 10;
+    else if (I->mayLoadOrStore())
+      Time += 2;
+    else
+      ++Time;
+  }
+  return Time;
+}
+
+// CurMBB needs to add an unconditional branch to SuccMBB (we removed these
+// branches temporarily for tail merging).  In the case where CurMBB ends
+// with a conditional branch to the next block, optimize by reversing the
+// test and conditionally branching to SuccMBB instead.
+static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB,
+                    const TargetInstrInfo *TII) {
+  MachineFunction *MF = CurMBB->getParent();
+  MachineFunction::iterator I = std::next(MachineFunction::iterator(CurMBB));
+  MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
+  SmallVector<MachineOperand, 4> Cond;
+  DebugLoc dl = CurMBB->findBranchDebugLoc();
+  if (I != MF->end() && !TII->analyzeBranch(*CurMBB, TBB, FBB, Cond, true)) {
+    MachineBasicBlock *NextBB = &*I;
+    if (TBB == NextBB && !Cond.empty() && !FBB) {
+      if (!TII->reverseBranchCondition(Cond)) {
+        TII->removeBranch(*CurMBB);
+        TII->insertBranch(*CurMBB, SuccBB, nullptr, Cond, dl);
+        return;
+      }
+    }
+  }
+  TII->insertBranch(*CurMBB, SuccBB, nullptr,
+                    SmallVector<MachineOperand, 0>(), dl);
+}
+
+bool
+BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const {
+  if (getHash() < o.getHash())
+    return true;
+  if (getHash() > o.getHash())
+    return false;
+  if (getBlock()->getNumber() < o.getBlock()->getNumber())
+    return true;
+  if (getBlock()->getNumber() > o.getBlock()->getNumber())
+    return false;
+  // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing
+  // an object with itself.
+#ifndef _GLIBCXX_DEBUG
+  llvm_unreachable("Predecessor appears twice");
+#else
+  return false;
+#endif
+}
+
+/// CountTerminators - Count the number of terminators in the given
+/// block and set I to the position of the first non-terminator, if there
+/// is one, or MBB->end() otherwise.
+static unsigned CountTerminators(MachineBasicBlock *MBB,
+                                 MachineBasicBlock::iterator &I) {
+  I = MBB->end();
+  unsigned NumTerms = 0;
+  while (true) {
+    if (I == MBB->begin()) {
+      I = MBB->end();
+      break;
+    }
+    --I;
+    if (!I->isTerminator()) break;
+    ++NumTerms;
+  }
+  return NumTerms;
+}
+
+/// A no successor, non-return block probably ends in unreachable and is cold.
+/// Also consider a block that ends in an indirect branch to be a return block,
+/// since many targets use plain indirect branches to return.
+static bool blockEndsInUnreachable(const MachineBasicBlock *MBB) {
+  if (!MBB->succ_empty())
+    return false;
+  if (MBB->empty())
+    return true;
+  return !(MBB->back().isReturn() || MBB->back().isIndirectBranch());
+}
+
+/// ProfitableToMerge - Check if two machine basic blocks have a common tail
+/// and decide if it would be profitable to merge those tails.  Return the
+/// length of the common tail and iterators to the first common instruction
+/// in each block.
+/// MBB1, MBB2      The blocks to check
+/// MinCommonTailLength  Minimum size of tail block to be merged.
+/// CommonTailLen   Out parameter to record the size of the shared tail between
+///                 MBB1 and MBB2
+/// I1, I2          Iterator references that will be changed to point to the first
+///                 instruction in the common tail shared by MBB1,MBB2
+/// SuccBB          A common successor of MBB1, MBB2 which are in a canonical form
+///                 relative to SuccBB
+/// PredBB          The layout predecessor of SuccBB, if any.
+/// EHScopeMembership  map from block to EH scope #.
+/// AfterPlacement  True if we are merging blocks after layout. Stricter
+///                 thresholds apply to prevent undoing tail-duplication.
+static bool
+ProfitableToMerge(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2,
+                  unsigned MinCommonTailLength, unsigned &CommonTailLen,
+                  MachineBasicBlock::iterator &I1,
+                  MachineBasicBlock::iterator &I2, MachineBasicBlock *SuccBB,
+                  MachineBasicBlock *PredBB,
+                  DenseMap<const MachineBasicBlock *, int> &EHScopeMembership,
+                  bool AfterPlacement,
+                  MBFIWrapper &MBBFreqInfo,
+                  ProfileSummaryInfo *PSI) {
+  // It is never profitable to tail-merge blocks from two different EH scopes.
+  if (!EHScopeMembership.empty()) {
+    auto EHScope1 = EHScopeMembership.find(MBB1);
+    assert(EHScope1 != EHScopeMembership.end());
+    auto EHScope2 = EHScopeMembership.find(MBB2);
+    assert(EHScope2 != EHScopeMembership.end());
+    if (EHScope1->second != EHScope2->second)
+      return false;
+  }
+
+  CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2);
+  if (CommonTailLen == 0)
+    return false;
+  LLVM_DEBUG(dbgs() << "Common tail length of " << printMBBReference(*MBB1)
+                    << " and " << printMBBReference(*MBB2) << " is "
+                    << CommonTailLen << '\n');
+
+  // Move the iterators to the beginning of the MBB if we only got debug
+  // instructions before the tail. This is to avoid splitting a block when we
+  // only got debug instructions before the tail (to be invariant on -g).
+  if (skipDebugInstructionsForward(MBB1->begin(), MBB1->end()) == I1)
+    I1 = MBB1->begin();
+  if (skipDebugInstructionsForward(MBB2->begin(), MBB2->end()) == I2)
+    I2 = MBB2->begin();
+
+  bool FullBlockTail1 = I1 == MBB1->begin();
+  bool FullBlockTail2 = I2 == MBB2->begin();
+
+  // It's almost always profitable to merge any number of non-terminator
+  // instructions with the block that falls through into the common successor.
+  // This is true only for a single successor. For multiple successors, we are
+  // trading a conditional branch for an unconditional one.
+  // TODO: Re-visit successor size for non-layout tail merging.
+  if ((MBB1 == PredBB || MBB2 == PredBB) &&
+      (!AfterPlacement || MBB1->succ_size() == 1)) {
+    MachineBasicBlock::iterator I;
+    unsigned NumTerms = CountTerminators(MBB1 == PredBB ? MBB2 : MBB1, I);
+    if (CommonTailLen > NumTerms)
+      return true;
+  }
+
+  // If these are identical non-return blocks with no successors, merge them.
+  // Such blocks are typically cold calls to noreturn functions like abort, and
+  // are unlikely to become a fallthrough target after machine block placement.
+  // Tail merging these blocks is unlikely to create additional unconditional
+  // branches, and will reduce the size of this cold code.
+  if (FullBlockTail1 && FullBlockTail2 &&
+      blockEndsInUnreachable(MBB1) && blockEndsInUnreachable(MBB2))
+    return true;
+
+  // If one of the blocks can be completely merged and happens to be in
+  // a position where the other could fall through into it, merge any number
+  // of instructions, because it can be done without a branch.
+  // TODO: If the blocks are not adjacent, move one of them so that they are?
+  if (MBB1->isLayoutSuccessor(MBB2) && FullBlockTail2)
+    return true;
+  if (MBB2->isLayoutSuccessor(MBB1) && FullBlockTail1)
+    return true;
+
+  // If both blocks are identical and end in a branch, merge them unless they
+  // both have a fallthrough predecessor and successor.
+  // We can only do this after block placement because it depends on whether
+  // there are fallthroughs, and we don't know until after layout.
+  if (AfterPlacement && FullBlockTail1 && FullBlockTail2) {
+    auto BothFallThrough = [](MachineBasicBlock *MBB) {
+      if (MBB->succ_size() != 0 && !MBB->canFallThrough())
+        return false;
+      MachineFunction::iterator I(MBB);
+      MachineFunction *MF = MBB->getParent();
+      return (MBB != &*MF->begin()) && std::prev(I)->canFallThrough();
+    };
+    if (!BothFallThrough(MBB1) || !BothFallThrough(MBB2))
+      return true;
+  }
+
+  // If both blocks have an unconditional branch temporarily stripped out,
+  // count that as an additional common instruction for the following
+  // heuristics. This heuristic is only accurate for single-succ blocks, so to
+  // make sure that during layout merging and duplicating don't crash, we check
+  // for that when merging during layout.
+  unsigned EffectiveTailLen = CommonTailLen;
+  if (SuccBB && MBB1 != PredBB && MBB2 != PredBB &&
+      (MBB1->succ_size() == 1 || !AfterPlacement) &&
+      !MBB1->back().isBarrier() &&
+      !MBB2->back().isBarrier())
+    ++EffectiveTailLen;
+
+  // Check if the common tail is long enough to be worthwhile.
+  if (EffectiveTailLen >= MinCommonTailLength)
+    return true;
+
+  // If we are optimizing for code size, 2 instructions in common is enough if
+  // we don't have to split a block.  At worst we will be introducing 1 new
+  // branch instruction, which is likely to be smaller than the 2
+  // instructions that would be deleted in the merge.
+  MachineFunction *MF = MBB1->getParent();
+  bool OptForSize =
+      MF->getFunction().hasOptSize() ||
+      (llvm::shouldOptimizeForSize(MBB1, PSI, &MBBFreqInfo) &&
+       llvm::shouldOptimizeForSize(MBB2, PSI, &MBBFreqInfo));
+  return EffectiveTailLen >= 2 && OptForSize &&
+         (FullBlockTail1 || FullBlockTail2);
+}
+
+unsigned BranchFolder::ComputeSameTails(unsigned CurHash,
+                                        unsigned MinCommonTailLength,
+                                        MachineBasicBlock *SuccBB,
+                                        MachineBasicBlock *PredBB) {
+  unsigned maxCommonTailLength = 0U;
+  SameTails.clear();
+  MachineBasicBlock::iterator TrialBBI1, TrialBBI2;
+  MPIterator HighestMPIter = std::prev(MergePotentials.end());
+  for (MPIterator CurMPIter = std::prev(MergePotentials.end()),
+                  B = MergePotentials.begin();
+       CurMPIter != B && CurMPIter->getHash() == CurHash; --CurMPIter) {
+    for (MPIterator I = std::prev(CurMPIter); I->getHash() == CurHash; --I) {
+      unsigned CommonTailLen;
+      if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(),
+                            MinCommonTailLength,
+                            CommonTailLen, TrialBBI1, TrialBBI2,
+                            SuccBB, PredBB,
+                            EHScopeMembership,
+                            AfterBlockPlacement, MBBFreqInfo, PSI)) {
+        if (CommonTailLen > maxCommonTailLength) {
+          SameTails.clear();
+          maxCommonTailLength = CommonTailLen;
+          HighestMPIter = CurMPIter;
+          SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1));
+        }
+        if (HighestMPIter == CurMPIter &&
+            CommonTailLen == maxCommonTailLength)
+          SameTails.push_back(SameTailElt(I, TrialBBI2));
+      }
+      if (I == B)
+        break;
+    }
+  }
+  return maxCommonTailLength;
+}
+
+void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
+                                        MachineBasicBlock *SuccBB,
+                                        MachineBasicBlock *PredBB) {
+  MPIterator CurMPIter, B;
+  for (CurMPIter = std::prev(MergePotentials.end()),
+      B = MergePotentials.begin();
+       CurMPIter->getHash() == CurHash; --CurMPIter) {
+    // Put the unconditional branch back, if we need one.
+    MachineBasicBlock *CurMBB = CurMPIter->getBlock();
+    if (SuccBB && CurMBB != PredBB)
+      FixTail(CurMBB, SuccBB, TII);
+    if (CurMPIter == B)
+      break;
+  }
+  if (CurMPIter->getHash() != CurHash)
+    CurMPIter++;
+  MergePotentials.erase(CurMPIter, MergePotentials.end());
+}
+
+bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
+                                             MachineBasicBlock *SuccBB,
+                                             unsigned maxCommonTailLength,
+                                             unsigned &commonTailIndex) {
+  commonTailIndex = 0;
+  unsigned TimeEstimate = ~0U;
+  for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
+    // Use PredBB if possible; that doesn't require a new branch.
+    if (SameTails[i].getBlock() == PredBB) {
+      commonTailIndex = i;
+      break;
+    }
+    // Otherwise, make a (fairly bogus) choice based on estimate of
+    // how long it will take the various blocks to execute.
+    unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(),
+                                 SameTails[i].getTailStartPos());
+    if (t <= TimeEstimate) {
+      TimeEstimate = t;
+      commonTailIndex = i;
+    }
+  }
+
+  MachineBasicBlock::iterator BBI =
+    SameTails[commonTailIndex].getTailStartPos();
+  MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
+
+  LLVM_DEBUG(dbgs() << "\nSplitting " << printMBBReference(*MBB) << ", size "
+                    << maxCommonTailLength);
+
+  // If the split block unconditionally falls-thru to SuccBB, it will be
+  // merged. In control flow terms it should then take SuccBB's name. e.g. If
+  // SuccBB is an inner loop, the common tail is still part of the inner loop.
+  const BasicBlock *BB = (SuccBB && MBB->succ_size() == 1) ?
+    SuccBB->getBasicBlock() : MBB->getBasicBlock();
+  MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI, BB);
+  if (!newMBB) {
+    LLVM_DEBUG(dbgs() << "... failed!");
+    return false;
+  }
+
+  SameTails[commonTailIndex].setBlock(newMBB);
+  SameTails[commonTailIndex].setTailStartPos(newMBB->begin());
+
+  // If we split PredBB, newMBB is the new predecessor.
+  if (PredBB == MBB)
+    PredBB = newMBB;
+
+  return true;
+}
+
+static void
+mergeOperations(MachineBasicBlock::iterator MBBIStartPos,
+                MachineBasicBlock &MBBCommon) {
+  MachineBasicBlock *MBB = MBBIStartPos->getParent();
+  // Note CommonTailLen does not necessarily matches the size of
+  // the common BB nor all its instructions because of debug
+  // instructions differences.
+  unsigned CommonTailLen = 0;
+  for (auto E = MBB->end(); MBBIStartPos != E; ++MBBIStartPos)
+    ++CommonTailLen;
+
+  MachineBasicBlock::reverse_iterator MBBI = MBB->rbegin();
+  MachineBasicBlock::reverse_iterator MBBIE = MBB->rend();
+  MachineBasicBlock::reverse_iterator MBBICommon = MBBCommon.rbegin();
+  MachineBasicBlock::reverse_iterator MBBIECommon = MBBCommon.rend();
+
+  while (CommonTailLen--) {
+    assert(MBBI != MBBIE && "Reached BB end within common tail length!");
+    (void)MBBIE;
+
+    if (!countsAsInstruction(*MBBI)) {
+      ++MBBI;
+      continue;
+    }
+
+    while ((MBBICommon != MBBIECommon) && !countsAsInstruction(*MBBICommon))
+      ++MBBICommon;
+
+    assert(MBBICommon != MBBIECommon &&
+           "Reached BB end within common tail length!");
+    assert(MBBICommon->isIdenticalTo(*MBBI) && "Expected matching MIIs!");
+
+    // Merge MMOs from memory operations in the common block.
+    if (MBBICommon->mayLoadOrStore())
+      MBBICommon->cloneMergedMemRefs(*MBB->getParent(), {&*MBBICommon, &*MBBI});
+    // Drop undef flags if they aren't present in all merged instructions.
+    for (unsigned I = 0, E = MBBICommon->getNumOperands(); I != E; ++I) {
+      MachineOperand &MO = MBBICommon->getOperand(I);
+      if (MO.isReg() && MO.isUndef()) {
+        const MachineOperand &OtherMO = MBBI->getOperand(I);
+        if (!OtherMO.isUndef())
+          MO.setIsUndef(false);
+      }
+    }
+
+    ++MBBI;
+    ++MBBICommon;
+  }
+}
+
+void BranchFolder::mergeCommonTails(unsigned commonTailIndex) {
+  MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
+
+  std::vector<MachineBasicBlock::iterator> NextCommonInsts(SameTails.size());
+  for (unsigned int i = 0 ; i != SameTails.size() ; ++i) {
+    if (i != commonTailIndex) {
+      NextCommonInsts[i] = SameTails[i].getTailStartPos();
+      mergeOperations(SameTails[i].getTailStartPos(), *MBB);
+    } else {
+      assert(SameTails[i].getTailStartPos() == MBB->begin() &&
+          "MBB is not a common tail only block");
+    }
+  }
+
+  for (auto &MI : *MBB) {
+    if (!countsAsInstruction(MI))
+      continue;
+    DebugLoc DL = MI.getDebugLoc();
+    for (unsigned int i = 0 ; i < NextCommonInsts.size() ; i++) {
+      if (i == commonTailIndex)
+        continue;
+
+      auto &Pos = NextCommonInsts[i];
+      assert(Pos != SameTails[i].getBlock()->end() &&
+          "Reached BB end within common tail");
+      while (!countsAsInstruction(*Pos)) {
+        ++Pos;
+        assert(Pos != SameTails[i].getBlock()->end() &&
+            "Reached BB end within common tail");
+      }
+      assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!");
+      DL = DILocation::getMergedLocation(DL, Pos->getDebugLoc());
+      NextCommonInsts[i] = ++Pos;
+    }
+    MI.setDebugLoc(DL);
+  }
+
+  if (UpdateLiveIns) {
+    LivePhysRegs NewLiveIns(*TRI);
+    computeLiveIns(NewLiveIns, *MBB);
+    LiveRegs.init(*TRI);
+
+    // The flag merging may lead to some register uses no longer using the
+    // <undef> flag, add IMPLICIT_DEFs in the predecessors as necessary.
+    for (MachineBasicBlock *Pred : MBB->predecessors()) {
+      LiveRegs.clear();
+      LiveRegs.addLiveOuts(*Pred);
+      MachineBasicBlock::iterator InsertBefore = Pred->getFirstTerminator();
+      for (Register Reg : NewLiveIns) {
+        if (!LiveRegs.available(*MRI, Reg))
+          continue;
+        DebugLoc DL;
+        BuildMI(*Pred, InsertBefore, DL, TII->get(TargetOpcode::IMPLICIT_DEF),
+                Reg);
+      }
+    }
+
+    MBB->clearLiveIns();
+    addLiveIns(*MBB, NewLiveIns);
+  }
+}
+
+// See if any of the blocks in MergePotentials (which all have SuccBB as a
+// successor, or all have no successor if it is null) can be tail-merged.
+// If there is a successor, any blocks in MergePotentials that are not
+// tail-merged and are not immediately before Succ must have an unconditional
+// branch to Succ added (but the predecessor/successor lists need no
+// adjustment). The lone predecessor of Succ that falls through into Succ,
+// if any, is given in PredBB.
+// MinCommonTailLength - Except for the special cases below, tail-merge if
+// there are at least this many instructions in common.
+bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
+                                      MachineBasicBlock *PredBB,
+                                      unsigned MinCommonTailLength) {
+  bool MadeChange = false;
+
+  LLVM_DEBUG(
+      dbgs() << "\nTryTailMergeBlocks: ";
+      for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) dbgs()
+      << printMBBReference(*MergePotentials[i].getBlock())
+      << (i == e - 1 ? "" : ", ");
+      dbgs() << "\n"; if (SuccBB) {
+        dbgs() << "  with successor " << printMBBReference(*SuccBB) << '\n';
+        if (PredBB)
+          dbgs() << "  which has fall-through from "
+                 << printMBBReference(*PredBB) << "\n";
+      } dbgs() << "Looking for common tails of at least "
+               << MinCommonTailLength << " instruction"
+               << (MinCommonTailLength == 1 ? "" : "s") << '\n';);
+
+  // Sort by hash value so that blocks with identical end sequences sort
+  // together.
+  array_pod_sort(MergePotentials.begin(), MergePotentials.end());
+
+  // Walk through equivalence sets looking for actual exact matches.
+  while (MergePotentials.size() > 1) {
+    unsigned CurHash = MergePotentials.back().getHash();
+
+    // Build SameTails, identifying the set of blocks with this hash code
+    // and with the maximum number of instructions in common.
+    unsigned maxCommonTailLength = ComputeSameTails(CurHash,
+                                                    MinCommonTailLength,
+                                                    SuccBB, PredBB);
+
+    // If we didn't find any pair that has at least MinCommonTailLength
+    // instructions in common, remove all blocks with this hash code and retry.
+    if (SameTails.empty()) {
+      RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
+      continue;
+    }
+
+    // If one of the blocks is the entire common tail (and is not the entry
+    // block/an EH pad, which we can't jump to), we can treat all blocks with
+    // this same tail at once.  Use PredBB if that is one of the possibilities,
+    // as that will not introduce any extra branches.
+    MachineBasicBlock *EntryBB =
+        &MergePotentials.front().getBlock()->getParent()->front();
+    unsigned commonTailIndex = SameTails.size();
+    // If there are two blocks, check to see if one can be made to fall through
+    // into the other.
+    if (SameTails.size() == 2 &&
+        SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) &&
+        SameTails[1].tailIsWholeBlock() && !SameTails[1].getBlock()->isEHPad())
+      commonTailIndex = 1;
+    else if (SameTails.size() == 2 &&
+             SameTails[1].getBlock()->isLayoutSuccessor(
+                 SameTails[0].getBlock()) &&
+             SameTails[0].tailIsWholeBlock() &&
+             !SameTails[0].getBlock()->isEHPad())
+      commonTailIndex = 0;
+    else {
+      // Otherwise just pick one, favoring the fall-through predecessor if
+      // there is one.
+      for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
+        MachineBasicBlock *MBB = SameTails[i].getBlock();
+        if ((MBB == EntryBB || MBB->isEHPad()) &&
+            SameTails[i].tailIsWholeBlock())
+          continue;
+        if (MBB == PredBB) {
+          commonTailIndex = i;
+          break;
+        }
+        if (SameTails[i].tailIsWholeBlock())
+          commonTailIndex = i;
+      }
+    }
+
+    if (commonTailIndex == SameTails.size() ||
+        (SameTails[commonTailIndex].getBlock() == PredBB &&
+         !SameTails[commonTailIndex].tailIsWholeBlock())) {
+      // None of the blocks consist entirely of the common tail.
+      // Split a block so that one does.
+      if (!CreateCommonTailOnlyBlock(PredBB, SuccBB,
+                                     maxCommonTailLength, commonTailIndex)) {
+        RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
+        continue;
+      }
+    }
+
+    MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
+
+    // Recompute common tail MBB's edge weights and block frequency.
+    setCommonTailEdgeWeights(*MBB);
+
+    // Merge debug locations, MMOs and undef flags across identical instructions
+    // for common tail.
+    mergeCommonTails(commonTailIndex);
+
+    // MBB is common tail.  Adjust all other BB's to jump to this one.
+    // Traversal must be forwards so erases work.
+    LLVM_DEBUG(dbgs() << "\nUsing common tail in " << printMBBReference(*MBB)
+                      << " for ");
+    for (unsigned int i=0, e = SameTails.size(); i != e; ++i) {
+      if (commonTailIndex == i)
+        continue;
+      LLVM_DEBUG(dbgs() << printMBBReference(*SameTails[i].getBlock())
+                        << (i == e - 1 ? "" : ", "));
+      // Hack the end off BB i, making it jump to BB commonTailIndex instead.
+      replaceTailWithBranchTo(SameTails[i].getTailStartPos(), *MBB);
+      // BB i is no longer a predecessor of SuccBB; remove it from the worklist.
+      MergePotentials.erase(SameTails[i].getMPIter());
+    }
+    LLVM_DEBUG(dbgs() << "\n");
+    // We leave commonTailIndex in the worklist in case there are other blocks
+    // that match it with a smaller number of instructions.
+    MadeChange = true;
+  }
+  return MadeChange;
+}
+
+bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
+  bool MadeChange = false;
+  if (!EnableTailMerge)
+    return MadeChange;
+
+  // First find blocks with no successors.
+  // Block placement may create new tail merging opportunities for these blocks.
+  MergePotentials.clear();
+  for (MachineBasicBlock &MBB : MF) {
+    if (MergePotentials.size() == TailMergeThreshold)
+      break;
+    if (!TriedMerging.count(&MBB) && MBB.succ_empty())
+      MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(MBB), &MBB));
+  }
+
+  // If this is a large problem, avoid visiting the same basic blocks
+  // multiple times.
+  if (MergePotentials.size() == TailMergeThreshold)
+    for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
+      TriedMerging.insert(MergePotentials[i].getBlock());
+
+  // See if we can do any tail merging on those.
+  if (MergePotentials.size() >= 2)
+    MadeChange |= TryTailMergeBlocks(nullptr, nullptr, MinCommonTailLength);
+
+  // Look at blocks (IBB) with multiple predecessors (PBB).
+  // We change each predecessor to a canonical form, by
+  // (1) temporarily removing any unconditional branch from the predecessor
+  // to IBB, and
+  // (2) alter conditional branches so they branch to the other block
+  // not IBB; this may require adding back an unconditional branch to IBB
+  // later, where there wasn't one coming in.  E.g.
+  //   Bcc IBB
+  //   fallthrough to QBB
+  // here becomes
+  //   Bncc QBB
+  // with a conceptual B to IBB after that, which never actually exists.
+  // With those changes, we see whether the predecessors' tails match,
+  // and merge them if so.  We change things out of canonical form and
+  // back to the way they were later in the process.  (OptimizeBranches
+  // would undo some of this, but we can't use it, because we'd get into
+  // a compile-time infinite loop repeatedly doing and undoing the same
+  // transformations.)
+
+  for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
+       I != E; ++I) {
+    if (I->pred_size() < 2) continue;
+    SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
+    MachineBasicBlock *IBB = &*I;
+    MachineBasicBlock *PredBB = &*std::prev(I);
+    MergePotentials.clear();
+    MachineLoop *ML;
+
+    // Bail if merging after placement and IBB is the loop header because
+    // -- If merging predecessors that belong to the same loop as IBB, the
+    // common tail of merged predecessors may become the loop top if block
+    // placement is called again and the predecessors may branch to this common
+    // tail and require more branches. This can be relaxed if
+    // MachineBlockPlacement::findBestLoopTop is more flexible.
+    // --If merging predecessors that do not belong to the same loop as IBB, the
+    // loop info of IBB's loop and the other loops may be affected. Calling the
+    // block placement again may make big change to the layout and eliminate the
+    // reason to do tail merging here.
+    if (AfterBlockPlacement && MLI) {
+      ML = MLI->getLoopFor(IBB);
+      if (ML && IBB == ML->getHeader())
+        continue;
+    }
+
+    for (MachineBasicBlock *PBB : I->predecessors()) {
+      if (MergePotentials.size() == TailMergeThreshold)
+        break;
+
+      if (TriedMerging.count(PBB))
+        continue;
+
+      // Skip blocks that loop to themselves, can't tail merge these.
+      if (PBB == IBB)
+        continue;
+
+      // Visit each predecessor only once.
+      if (!UniquePreds.insert(PBB).second)
+        continue;
+
+      // Skip blocks which may jump to a landing pad or jump from an asm blob.
+      // Can't tail merge these.
+      if (PBB->hasEHPadSuccessor() || PBB->mayHaveInlineAsmBr())
+        continue;
+
+      // After block placement, only consider predecessors that belong to the
+      // same loop as IBB.  The reason is the same as above when skipping loop
+      // header.
+      if (AfterBlockPlacement && MLI)
+        if (ML != MLI->getLoopFor(PBB))
+          continue;
+
+      MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
+      SmallVector<MachineOperand, 4> Cond;
+      if (!TII->analyzeBranch(*PBB, TBB, FBB, Cond, true)) {
+        // Failing case: IBB is the target of a cbr, and we cannot reverse the
+        // branch.
+        SmallVector<MachineOperand, 4> NewCond(Cond);
+        if (!Cond.empty() && TBB == IBB) {
+          if (TII->reverseBranchCondition(NewCond))
+            continue;
+          // This is the QBB case described above
+          if (!FBB) {
+            auto Next = ++PBB->getIterator();
+            if (Next != MF.end())
+              FBB = &*Next;
+          }
+        }
+
+        // Remove the unconditional branch at the end, if any.
+        if (TBB && (Cond.empty() || FBB)) {
+          DebugLoc dl = PBB->findBranchDebugLoc();
+          TII->removeBranch(*PBB);
+          if (!Cond.empty())
+            // reinsert conditional branch only, for now
+            TII->insertBranch(*PBB, (TBB == IBB) ? FBB : TBB, nullptr,
+                              NewCond, dl);
+        }
+
+        MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(*PBB), PBB));
+      }
+    }
+
+    // If this is a large problem, avoid visiting the same basic blocks multiple
+    // times.
+    if (MergePotentials.size() == TailMergeThreshold)
+      for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
+        TriedMerging.insert(MergePotentials[i].getBlock());
+
+    if (MergePotentials.size() >= 2)
+      MadeChange |= TryTailMergeBlocks(IBB, PredBB, MinCommonTailLength);
+
+    // Reinsert an unconditional branch if needed. The 1 below can occur as a
+    // result of removing blocks in TryTailMergeBlocks.
+    PredBB = &*std::prev(I); // this may have been changed in TryTailMergeBlocks
+    if (MergePotentials.size() == 1 &&
+        MergePotentials.begin()->getBlock() != PredBB)
+      FixTail(MergePotentials.begin()->getBlock(), IBB, TII);
+  }
+
+  return MadeChange;
+}
+
+void BranchFolder::setCommonTailEdgeWeights(MachineBasicBlock &TailMBB) {
+  SmallVector<BlockFrequency, 2> EdgeFreqLs(TailMBB.succ_size());
+  BlockFrequency AccumulatedMBBFreq;
+
+  // Aggregate edge frequency of successor edge j:
+  //  edgeFreq(j) = sum (freq(bb) * edgeProb(bb, j)),
+  //  where bb is a basic block that is in SameTails.
+  for (const auto &Src : SameTails) {
+    const MachineBasicBlock *SrcMBB = Src.getBlock();
+    BlockFrequency BlockFreq = MBBFreqInfo.getBlockFreq(SrcMBB);
+    AccumulatedMBBFreq += BlockFreq;
+
+    // It is not necessary to recompute edge weights if TailBB has less than two
+    // successors.
+    if (TailMBB.succ_size() <= 1)
+      continue;
+
+    auto EdgeFreq = EdgeFreqLs.begin();
+
+    for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end();
+         SuccI != SuccE; ++SuccI, ++EdgeFreq)
+      *EdgeFreq += BlockFreq * MBPI.getEdgeProbability(SrcMBB, *SuccI);
+  }
+
+  MBBFreqInfo.setBlockFreq(&TailMBB, AccumulatedMBBFreq);
+
+  if (TailMBB.succ_size() <= 1)
+    return;
+
+  auto SumEdgeFreq =
+      std::accumulate(EdgeFreqLs.begin(), EdgeFreqLs.end(), BlockFrequency(0))
+          .getFrequency();
+  auto EdgeFreq = EdgeFreqLs.begin();
+
+  if (SumEdgeFreq > 0) {
+    for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end();
+         SuccI != SuccE; ++SuccI, ++EdgeFreq) {
+      auto Prob = BranchProbability::getBranchProbability(
+          EdgeFreq->getFrequency(), SumEdgeFreq);
+      TailMBB.setSuccProbability(SuccI, Prob);
+    }
+  }
+}
+
+//===----------------------------------------------------------------------===//
+//  Branch Optimization
+//===----------------------------------------------------------------------===//
+
+bool BranchFolder::OptimizeBranches(MachineFunction &MF) {
+  bool MadeChange = false;
+
+  // Make sure blocks are numbered in order
+  MF.RenumberBlocks();
+  // Renumbering blocks alters EH scope membership, recalculate it.
+  EHScopeMembership = getEHScopeMembership(MF);
+
+  for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
+       I != E; ) {
+    MachineBasicBlock *MBB = &*I++;
+    MadeChange |= OptimizeBlock(MBB);
+
+    // If it is dead, remove it.
+    if (MBB->pred_empty()) {
+      RemoveDeadBlock(MBB);
+      MadeChange = true;
+      ++NumDeadBlocks;
+    }
+  }
+
+  return MadeChange;
+}
+
+// Blocks should be considered empty if they contain only debug info;
+// else the debug info would affect codegen.
+static bool IsEmptyBlock(MachineBasicBlock *MBB) {
+  return MBB->getFirstNonDebugInstr() == MBB->end();
+}
+
+// Blocks with only debug info and branches should be considered the same
+// as blocks with only branches.
+static bool IsBranchOnlyBlock(MachineBasicBlock *MBB) {
+  MachineBasicBlock::iterator I = MBB->getFirstNonDebugInstr();
+  assert(I != MBB->end() && "empty block!");
+  return I->isBranch();
+}
+
+/// IsBetterFallthrough - Return true if it would be clearly better to
+/// fall-through to MBB1 than to fall through into MBB2.  This has to return
+/// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will
+/// result in infinite loops.
+static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
+                                MachineBasicBlock *MBB2) {
+  assert(MBB1 && MBB2 && "Unknown MachineBasicBlock");
+
+  // Right now, we use a simple heuristic.  If MBB2 ends with a call, and
+  // MBB1 doesn't, we prefer to fall through into MBB1.  This allows us to
+  // optimize branches that branch to either a return block or an assert block
+  // into a fallthrough to the return.
+  MachineBasicBlock::iterator MBB1I = MBB1->getLastNonDebugInstr();
+  MachineBasicBlock::iterator MBB2I = MBB2->getLastNonDebugInstr();
+  if (MBB1I == MBB1->end() || MBB2I == MBB2->end())
+    return false;
+
+  // If there is a clear successor ordering we make sure that one block
+  // will fall through to the next
+  if (MBB1->isSuccessor(MBB2)) return true;
+  if (MBB2->isSuccessor(MBB1)) return false;
+
+  return MBB2I->isCall() && !MBB1I->isCall();
+}
+
+/// getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch
+/// instructions on the block.
+static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) {
+  MachineBasicBlock::iterator I = MBB.getLastNonDebugInstr();
+  if (I != MBB.end() && I->isBranch())
+    return I->getDebugLoc();
+  return DebugLoc();
+}
+
+static void copyDebugInfoToPredecessor(const TargetInstrInfo *TII,
+                                       MachineBasicBlock &MBB,
+                                       MachineBasicBlock &PredMBB) {
+  auto InsertBefore = PredMBB.getFirstTerminator();
+  for (MachineInstr &MI : MBB.instrs())
+    if (MI.isDebugInstr()) {
+      TII->duplicate(PredMBB, InsertBefore, MI);
+      LLVM_DEBUG(dbgs() << "Copied debug entity from empty block to pred: "
+                        << MI);
+    }
+}
+
+static void copyDebugInfoToSuccessor(const TargetInstrInfo *TII,
+                                     MachineBasicBlock &MBB,
+                                     MachineBasicBlock &SuccMBB) {
+  auto InsertBefore = SuccMBB.SkipPHIsAndLabels(SuccMBB.begin());
+  for (MachineInstr &MI : MBB.instrs())
+    if (MI.isDebugInstr()) {
+      TII->duplicate(SuccMBB, InsertBefore, MI);
+      LLVM_DEBUG(dbgs() << "Copied debug entity from empty block to succ: "
+                        << MI);
+    }
+}
+
+// Try to salvage DBG_VALUE instructions from an otherwise empty block. If such
+// a basic block is removed we would lose the debug information unless we have
+// copied the information to a predecessor/successor.
+//
+// TODO: This function only handles some simple cases. An alternative would be
+// to run a heavier analysis, such as the LiveDebugValues pass, before we do
+// branch folding.
+static void salvageDebugInfoFromEmptyBlock(const TargetInstrInfo *TII,
+                                           MachineBasicBlock &MBB) {
+  assert(IsEmptyBlock(&MBB) && "Expected an empty block (except debug info).");
+  // If this MBB is the only predecessor of a successor it is legal to copy
+  // DBG_VALUE instructions to the beginning of the successor.
+  for (MachineBasicBlock *SuccBB : MBB.successors())
+    if (SuccBB->pred_size() == 1)
+      copyDebugInfoToSuccessor(TII, MBB, *SuccBB);
+  // If this MBB is the only successor of a predecessor it is legal to copy the
+  // DBG_VALUE instructions to the end of the predecessor (just before the
+  // terminators, assuming that the terminator isn't affecting the DBG_VALUE).
+  for (MachineBasicBlock *PredBB : MBB.predecessors())
+    if (PredBB->succ_size() == 1)
+      copyDebugInfoToPredecessor(TII, MBB, *PredBB);
+}
+
+bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
+  bool MadeChange = false;
+  MachineFunction &MF = *MBB->getParent();
+ReoptimizeBlock:
+
+  MachineFunction::iterator FallThrough = MBB->getIterator();
+  ++FallThrough;
+
+  // Make sure MBB and FallThrough belong to the same EH scope.
+  bool SameEHScope = true;
+  if (!EHScopeMembership.empty() && FallThrough != MF.end()) {
+    auto MBBEHScope = EHScopeMembership.find(MBB);
+    assert(MBBEHScope != EHScopeMembership.end());
+    auto FallThroughEHScope = EHScopeMembership.find(&*FallThrough);
+    assert(FallThroughEHScope != EHScopeMembership.end());
+    SameEHScope = MBBEHScope->second == FallThroughEHScope->second;
+  }
+
+  // Analyze the branch in the current block. As a side-effect, this may cause
+  // the block to become empty.
+  MachineBasicBlock *CurTBB = nullptr, *CurFBB = nullptr;
+  SmallVector<MachineOperand, 4> CurCond;
+  bool CurUnAnalyzable =
+      TII->analyzeBranch(*MBB, CurTBB, CurFBB, CurCond, true);
+
+  // If this block is empty, make everyone use its fall-through, not the block
+  // explicitly.  Landing pads should not do this since the landing-pad table
+  // points to this block.  Blocks with their addresses taken shouldn't be
+  // optimized away.
+  if (IsEmptyBlock(MBB) && !MBB->isEHPad() && !MBB->hasAddressTaken() &&
+      SameEHScope) {
+    salvageDebugInfoFromEmptyBlock(TII, *MBB);
+    // Dead block?  Leave for cleanup later.
+    if (MBB->pred_empty()) return MadeChange;
+
+    if (FallThrough == MF.end()) {
+      // TODO: Simplify preds to not branch here if possible!
+    } else if (FallThrough->isEHPad()) {
+      // Don't rewrite to a landing pad fallthough.  That could lead to the case
+      // where a BB jumps to more than one landing pad.
+      // TODO: Is it ever worth rewriting predecessors which don't already
+      // jump to a landing pad, and so can safely jump to the fallthrough?
+    } else if (MBB->isSuccessor(&*FallThrough)) {
+      // Rewrite all predecessors of the old block to go to the fallthrough
+      // instead.
+      while (!MBB->pred_empty()) {
+        MachineBasicBlock *Pred = *(MBB->pred_end()-1);
+        Pred->ReplaceUsesOfBlockWith(MBB, &*FallThrough);
+      }
+      // If MBB was the target of a jump table, update jump tables to go to the
+      // fallthrough instead.
+      if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
+        MJTI->ReplaceMBBInJumpTables(MBB, &*FallThrough);
+      MadeChange = true;
+    }
+    return MadeChange;
+  }
+
+  // Check to see if we can simplify the terminator of the block before this
+  // one.
+  MachineBasicBlock &PrevBB = *std::prev(MachineFunction::iterator(MBB));
+
+  MachineBasicBlock *PriorTBB = nullptr, *PriorFBB = nullptr;
+  SmallVector<MachineOperand, 4> PriorCond;
+  bool PriorUnAnalyzable =
+      TII->analyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true);
+  if (!PriorUnAnalyzable) {
+    // If the previous branch is conditional and both conditions go to the same
+    // destination, remove the branch, replacing it with an unconditional one or
+    // a fall-through.
+    if (PriorTBB && PriorTBB == PriorFBB) {
+      DebugLoc dl = getBranchDebugLoc(PrevBB);
+      TII->removeBranch(PrevBB);
+      PriorCond.clear();
+      if (PriorTBB != MBB)
+        TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl);
+      MadeChange = true;
+      ++NumBranchOpts;
+      goto ReoptimizeBlock;
+    }
+
+    // If the previous block unconditionally falls through to this block and
+    // this block has no other predecessors, move the contents of this block
+    // into the prior block. This doesn't usually happen when SimplifyCFG
+    // has been used, but it can happen if tail merging splits a fall-through
+    // predecessor of a block.
+    // This has to check PrevBB->succ_size() because EH edges are ignored by
+    // analyzeBranch.
+    if (PriorCond.empty() && !PriorTBB && MBB->pred_size() == 1 &&
+        PrevBB.succ_size() == 1 &&
+        !MBB->hasAddressTaken() && !MBB->isEHPad()) {
+      LLVM_DEBUG(dbgs() << "\nMerging into block: " << PrevBB
+                        << "From MBB: " << *MBB);
+      // Remove redundant DBG_VALUEs first.
       if (!PrevBB.empty()) {
-        MachineBasicBlock::iterator PrevBBIter = PrevBB.end(); 
-        --PrevBBIter; 
-        MachineBasicBlock::iterator MBBIter = MBB->begin(); 
-        // Check if DBG_VALUE at the end of PrevBB is identical to the 
-        // DBG_VALUE at the beginning of MBB. 
-        while (PrevBBIter != PrevBB.begin() && MBBIter != MBB->end() 
-               && PrevBBIter->isDebugInstr() && MBBIter->isDebugInstr()) { 
-          if (!MBBIter->isIdenticalTo(*PrevBBIter)) 
-            break; 
-          MachineInstr &DuplicateDbg = *MBBIter; 
-          ++MBBIter; -- PrevBBIter; 
-          DuplicateDbg.eraseFromParent(); 
-        } 
-      } 
-      PrevBB.splice(PrevBB.end(), MBB, MBB->begin(), MBB->end()); 
-      PrevBB.removeSuccessor(PrevBB.succ_begin()); 
-      assert(PrevBB.succ_empty()); 
-      PrevBB.transferSuccessors(MBB); 
-      MadeChange = true; 
-      return MadeChange; 
-    } 
- 
-    // If the previous branch *only* branches to *this* block (conditional or 
-    // not) remove the branch. 
-    if (PriorTBB == MBB && !PriorFBB) { 
-      TII->removeBranch(PrevBB); 
-      MadeChange = true; 
-      ++NumBranchOpts; 
-      goto ReoptimizeBlock; 
-    } 
- 
-    // If the prior block branches somewhere else on the condition and here if 
-    // the condition is false, remove the uncond second branch. 
-    if (PriorFBB == MBB) { 
-      DebugLoc dl = getBranchDebugLoc(PrevBB); 
-      TII->removeBranch(PrevBB); 
-      TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl); 
-      MadeChange = true; 
-      ++NumBranchOpts; 
-      goto ReoptimizeBlock; 
-    } 
- 
-    // If the prior block branches here on true and somewhere else on false, and 
-    // if the branch condition is reversible, reverse the branch to create a 
-    // fall-through. 
-    if (PriorTBB == MBB) { 
-      SmallVector<MachineOperand, 4> NewPriorCond(PriorCond); 
-      if (!TII->reverseBranchCondition(NewPriorCond)) { 
-        DebugLoc dl = getBranchDebugLoc(PrevBB); 
-        TII->removeBranch(PrevBB); 
-        TII->insertBranch(PrevBB, PriorFBB, nullptr, NewPriorCond, dl); 
-        MadeChange = true; 
-        ++NumBranchOpts; 
-        goto ReoptimizeBlock; 
-      } 
-    } 
- 
-    // If this block has no successors (e.g. it is a return block or ends with 
-    // a call to a no-return function like abort or __cxa_throw) and if the pred 
-    // falls through into this block, and if it would otherwise fall through 
-    // into the block after this, move this block to the end of the function. 
-    // 
-    // We consider it more likely that execution will stay in the function (e.g. 
-    // due to loops) than it is to exit it.  This asserts in loops etc, moving 
-    // the assert condition out of the loop body. 
-    if (MBB->succ_empty() && !PriorCond.empty() && !PriorFBB && 
-        MachineFunction::iterator(PriorTBB) == FallThrough && 
-        !MBB->canFallThrough()) { 
-      bool DoTransform = true; 
- 
-      // We have to be careful that the succs of PredBB aren't both no-successor 
-      // blocks.  If neither have successors and if PredBB is the second from 
-      // last block in the function, we'd just keep swapping the two blocks for 
-      // last.  Only do the swap if one is clearly better to fall through than 
-      // the other. 
-      if (FallThrough == --MF.end() && 
-          !IsBetterFallthrough(PriorTBB, MBB)) 
-        DoTransform = false; 
- 
-      if (DoTransform) { 
-        // Reverse the branch so we will fall through on the previous true cond. 
-        SmallVector<MachineOperand, 4> NewPriorCond(PriorCond); 
-        if (!TII->reverseBranchCondition(NewPriorCond)) { 
-          LLVM_DEBUG(dbgs() << "\nMoving MBB: " << *MBB 
-                            << "To make fallthrough to: " << *PriorTBB << "\n"); 
- 
-          DebugLoc dl = getBranchDebugLoc(PrevBB); 
-          TII->removeBranch(PrevBB); 
-          TII->insertBranch(PrevBB, MBB, nullptr, NewPriorCond, dl); 
- 
-          // Move this block to the end of the function. 
-          MBB->moveAfter(&MF.back()); 
-          MadeChange = true; 
-          ++NumBranchOpts; 
-          return MadeChange; 
-        } 
-      } 
-    } 
-  } 
- 
-  bool OptForSize = 
-      MF.getFunction().hasOptSize() || 
-      llvm::shouldOptimizeForSize(MBB, PSI, &MBBFreqInfo); 
-  if (!IsEmptyBlock(MBB) && MBB->pred_size() == 1 && OptForSize) { 
-    // Changing "Jcc foo; foo: jmp bar;" into "Jcc bar;" might change the branch 
-    // direction, thereby defeating careful block placement and regressing 
-    // performance. Therefore, only consider this for optsize functions. 
-    MachineInstr &TailCall = *MBB->getFirstNonDebugInstr(); 
-    if (TII->isUnconditionalTailCall(TailCall)) { 
-      MachineBasicBlock *Pred = *MBB->pred_begin(); 
-      MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr; 
-      SmallVector<MachineOperand, 4> PredCond; 
-      bool PredAnalyzable = 
-          !TII->analyzeBranch(*Pred, PredTBB, PredFBB, PredCond, true); 
- 
-      if (PredAnalyzable && !PredCond.empty() && PredTBB == MBB && 
-          PredTBB != PredFBB) { 
-        // The predecessor has a conditional branch to this block which consists 
-        // of only a tail call. Try to fold the tail call into the conditional 
-        // branch. 
-        if (TII->canMakeTailCallConditional(PredCond, TailCall)) { 
-          // TODO: It would be nice if analyzeBranch() could provide a pointer 
-          // to the branch instruction so replaceBranchWithTailCall() doesn't 
-          // have to search for it. 
-          TII->replaceBranchWithTailCall(*Pred, PredCond, TailCall); 
-          ++NumTailCalls; 
-          Pred->removeSuccessor(MBB); 
-          MadeChange = true; 
-          return MadeChange; 
-        } 
-      } 
-      // If the predecessor is falling through to this block, we could reverse 
-      // the branch condition and fold the tail call into that. However, after 
-      // that we might have to re-arrange the CFG to fall through to the other 
-      // block and there is a high risk of regressing code size rather than 
-      // improving it. 
-    } 
-  } 
- 
-  if (!CurUnAnalyzable) { 
-    // If this is a two-way branch, and the FBB branches to this block, reverse 
-    // the condition so the single-basic-block loop is faster.  Instead of: 
-    //    Loop: xxx; jcc Out; jmp Loop 
-    // we want: 
-    //    Loop: xxx; jncc Loop; jmp Out 
-    if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) { 
-      SmallVector<MachineOperand, 4> NewCond(CurCond); 
-      if (!TII->reverseBranchCondition(NewCond)) { 
-        DebugLoc dl = getBranchDebugLoc(*MBB); 
-        TII->removeBranch(*MBB); 
-        TII->insertBranch(*MBB, CurFBB, CurTBB, NewCond, dl); 
-        MadeChange = true; 
-        ++NumBranchOpts; 
-        goto ReoptimizeBlock; 
-      } 
-    } 
- 
-    // If this branch is the only thing in its block, see if we can forward 
-    // other blocks across it. 
-    if (CurTBB && CurCond.empty() && !CurFBB && 
-        IsBranchOnlyBlock(MBB) && CurTBB != MBB && 
-        !MBB->hasAddressTaken() && !MBB->isEHPad()) { 
-      DebugLoc dl = getBranchDebugLoc(*MBB); 
-      // This block may contain just an unconditional branch.  Because there can 
-      // be 'non-branch terminators' in the block, try removing the branch and 
-      // then seeing if the block is empty. 
-      TII->removeBranch(*MBB); 
-      // If the only things remaining in the block are debug info, remove these 
-      // as well, so this will behave the same as an empty block in non-debug 
-      // mode. 
-      if (IsEmptyBlock(MBB)) { 
-        // Make the block empty, losing the debug info (we could probably 
-        // improve this in some cases.) 
-        MBB->erase(MBB->begin(), MBB->end()); 
-      } 
-      // If this block is just an unconditional branch to CurTBB, we can 
-      // usually completely eliminate the block.  The only case we cannot 
-      // completely eliminate the block is when the block before this one 
-      // falls through into MBB and we can't understand the prior block's branch 
-      // condition. 
-      if (MBB->empty()) { 
-        bool PredHasNoFallThrough = !PrevBB.canFallThrough(); 
-        if (PredHasNoFallThrough || !PriorUnAnalyzable || 
-            !PrevBB.isSuccessor(MBB)) { 
-          // If the prior block falls through into us, turn it into an 
-          // explicit branch to us to make updates simpler. 
-          if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) && 
-              PriorTBB != MBB && PriorFBB != MBB) { 
-            if (!PriorTBB) { 
-              assert(PriorCond.empty() && !PriorFBB && 
-                     "Bad branch analysis"); 
-              PriorTBB = MBB; 
-            } else { 
-              assert(!PriorFBB && "Machine CFG out of date!"); 
-              PriorFBB = MBB; 
-            } 
-            DebugLoc pdl = getBranchDebugLoc(PrevBB); 
-            TII->removeBranch(PrevBB); 
-            TII->insertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, pdl); 
-          } 
- 
-          // Iterate through all the predecessors, revectoring each in-turn. 
-          size_t PI = 0; 
-          bool DidChange = false; 
-          bool HasBranchToSelf = false; 
-          while(PI != MBB->pred_size()) { 
-            MachineBasicBlock *PMBB = *(MBB->pred_begin() + PI); 
-            if (PMBB == MBB) { 
-              // If this block has an uncond branch to itself, leave it. 
-              ++PI; 
-              HasBranchToSelf = true; 
-            } else { 
-              DidChange = true; 
-              PMBB->ReplaceUsesOfBlockWith(MBB, CurTBB); 
-              // If this change resulted in PMBB ending in a conditional 
-              // branch where both conditions go to the same destination, 
-              // change this to an unconditional branch. 
-              MachineBasicBlock *NewCurTBB = nullptr, *NewCurFBB = nullptr; 
-              SmallVector<MachineOperand, 4> NewCurCond; 
-              bool NewCurUnAnalyzable = TII->analyzeBranch( 
-                  *PMBB, NewCurTBB, NewCurFBB, NewCurCond, true); 
-              if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) { 
-                DebugLoc pdl = getBranchDebugLoc(*PMBB); 
-                TII->removeBranch(*PMBB); 
-                NewCurCond.clear(); 
-                TII->insertBranch(*PMBB, NewCurTBB, nullptr, NewCurCond, pdl); 
-                MadeChange = true; 
-                ++NumBranchOpts; 
-              } 
-            } 
-          } 
- 
-          // Change any jumptables to go to the new MBB. 
-          if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo()) 
-            MJTI->ReplaceMBBInJumpTables(MBB, CurTBB); 
-          if (DidChange) { 
-            ++NumBranchOpts; 
-            MadeChange = true; 
-            if (!HasBranchToSelf) return MadeChange; 
-          } 
-        } 
-      } 
- 
-      // Add the branch back if the block is more than just an uncond branch. 
-      TII->insertBranch(*MBB, CurTBB, nullptr, CurCond, dl); 
-    } 
-  } 
- 
-  // If the prior block doesn't fall through into this block, and if this 
-  // block doesn't fall through into some other block, see if we can find a 
-  // place to move this block where a fall-through will happen. 
-  if (!PrevBB.canFallThrough()) { 
-    // Now we know that there was no fall-through into this block, check to 
-    // see if it has a fall-through into its successor. 
-    bool CurFallsThru = MBB->canFallThrough(); 
- 
-    if (!MBB->isEHPad()) { 
-      // Check all the predecessors of this block.  If one of them has no fall 
-      // throughs, and analyzeBranch thinks it _could_ fallthrough to this 
-      // block, move this block right after it. 
-      for (MachineBasicBlock *PredBB : MBB->predecessors()) { 
-        // Analyze the branch at the end of the pred. 
-        MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr; 
-        SmallVector<MachineOperand, 4> PredCond; 
-        if (PredBB != MBB && !PredBB->canFallThrough() && 
-            !TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true) && 
-            (PredTBB == MBB || PredFBB == MBB) && 
-            (!CurFallsThru || !CurTBB || !CurFBB) && 
-            (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) { 
-          // If the current block doesn't fall through, just move it. 
-          // If the current block can fall through and does not end with a 
-          // conditional branch, we need to append an unconditional jump to 
-          // the (current) next block.  To avoid a possible compile-time 
-          // infinite loop, move blocks only backward in this case. 
-          // Also, if there are already 2 branches here, we cannot add a third; 
-          // this means we have the case 
-          // Bcc next 
-          // B elsewhere 
-          // next: 
-          if (CurFallsThru) { 
-            MachineBasicBlock *NextBB = &*std::next(MBB->getIterator()); 
-            CurCond.clear(); 
-            TII->insertBranch(*MBB, NextBB, nullptr, CurCond, DebugLoc()); 
-          } 
-          MBB->moveAfter(PredBB); 
-          MadeChange = true; 
-          goto ReoptimizeBlock; 
-        } 
-      } 
-    } 
- 
-    if (!CurFallsThru) { 
-      // Check analyzable branch-successors to see if we can move this block 
-      // before one. 
-      if (!CurUnAnalyzable) { 
-        for (MachineBasicBlock *SuccBB : {CurFBB, CurTBB}) { 
-          if (!SuccBB) 
-            continue; 
-          // Analyze the branch at the end of the block before the succ. 
-          MachineFunction::iterator SuccPrev = --SuccBB->getIterator(); 
- 
-          // If this block doesn't already fall-through to that successor, and 
-          // if the succ doesn't already have a block that can fall through into 
-          // it, we can arrange for the fallthrough to happen. 
-          if (SuccBB != MBB && &*SuccPrev != MBB && 
-              !SuccPrev->canFallThrough()) { 
-            MBB->moveBefore(SuccBB); 
-            MadeChange = true; 
-            goto ReoptimizeBlock; 
-          } 
-        } 
-      } 
- 
-      // Okay, there is no really great place to put this block.  If, however, 
-      // the block before this one would be a fall-through if this block were 
-      // removed, move this block to the end of the function. There is no real 
-      // advantage in "falling through" to an EH block, so we don't want to 
-      // perform this transformation for that case. 
-      // 
-      // Also, Windows EH introduced the possibility of an arbitrary number of 
-      // successors to a given block.  The analyzeBranch call does not consider 
-      // exception handling and so we can get in a state where a block 
-      // containing a call is followed by multiple EH blocks that would be 
-      // rotated infinitely at the end of the function if the transformation 
-      // below were performed for EH "FallThrough" blocks.  Therefore, even if 
-      // that appears not to be happening anymore, we should assume that it is 
-      // possible and not remove the "!FallThrough()->isEHPad" condition below. 
-      MachineBasicBlock *PrevTBB = nullptr, *PrevFBB = nullptr; 
-      SmallVector<MachineOperand, 4> PrevCond; 
-      if (FallThrough != MF.end() && 
-          !FallThrough->isEHPad() && 
-          !TII->analyzeBranch(PrevBB, PrevTBB, PrevFBB, PrevCond, true) && 
-          PrevBB.isSuccessor(&*FallThrough)) { 
-        MBB->moveAfter(&MF.back()); 
-        MadeChange = true; 
-        return MadeChange; 
-      } 
-    } 
-  } 
- 
-  return MadeChange; 
-} 
- 
-//===----------------------------------------------------------------------===// 
-//  Hoist Common Code 
-//===----------------------------------------------------------------------===// 
- 
-bool BranchFolder::HoistCommonCode(MachineFunction &MF) { 
-  bool MadeChange = false; 
-  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ) { 
-    MachineBasicBlock *MBB = &*I++; 
-    MadeChange |= HoistCommonCodeInSuccs(MBB); 
-  } 
- 
-  return MadeChange; 
-} 
- 
-/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given 
-/// its 'true' successor. 
-static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB, 
-                                         MachineBasicBlock *TrueBB) { 
-  for (MachineBasicBlock *SuccBB : BB->successors()) 
-    if (SuccBB != TrueBB) 
-      return SuccBB; 
-  return nullptr; 
-} 
- 
-template <class Container> 
-static void addRegAndItsAliases(Register Reg, const TargetRegisterInfo *TRI, 
-                                Container &Set) { 
-  if (Reg.isPhysical()) { 
-    for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) 
-      Set.insert(*AI); 
-  } else { 
-    Set.insert(Reg); 
-  } 
-} 
- 
-/// findHoistingInsertPosAndDeps - Find the location to move common instructions 
-/// in successors to. The location is usually just before the terminator, 
-/// however if the terminator is a conditional branch and its previous 
-/// instruction is the flag setting instruction, the previous instruction is 
-/// the preferred location. This function also gathers uses and defs of the 
-/// instructions from the insertion point to the end of the block. The data is 
-/// used by HoistCommonCodeInSuccs to ensure safety. 
-static 
-MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB, 
-                                                  const TargetInstrInfo *TII, 
-                                                  const TargetRegisterInfo *TRI, 
-                                                  SmallSet<Register, 4> &Uses, 
-                                                  SmallSet<Register, 4> &Defs) { 
-  MachineBasicBlock::iterator Loc = MBB->getFirstTerminator(); 
-  if (!TII->isUnpredicatedTerminator(*Loc)) 
-    return MBB->end(); 
- 
-  for (const MachineOperand &MO : Loc->operands()) { 
-    if (!MO.isReg()) 
-      continue; 
-    Register Reg = MO.getReg(); 
-    if (!Reg) 
-      continue; 
-    if (MO.isUse()) { 
-      addRegAndItsAliases(Reg, TRI, Uses); 
-    } else { 
-      if (!MO.isDead()) 
-        // Don't try to hoist code in the rare case the terminator defines a 
-        // register that is later used. 
-        return MBB->end(); 
- 
-      // If the terminator defines a register, make sure we don't hoist 
-      // the instruction whose def might be clobbered by the terminator. 
-      addRegAndItsAliases(Reg, TRI, Defs); 
-    } 
-  } 
- 
-  if (Uses.empty()) 
-    return Loc; 
-  // If the terminator is the only instruction in the block and Uses is not 
-  // empty (or we would have returned above), we can still safely hoist 
-  // instructions just before the terminator as long as the Defs/Uses are not 
-  // violated (which is checked in HoistCommonCodeInSuccs). 
-  if (Loc == MBB->begin()) 
-    return Loc; 
- 
-  // The terminator is probably a conditional branch, try not to separate the 
-  // branch from condition setting instruction. 
-  MachineBasicBlock::iterator PI = prev_nodbg(Loc, MBB->begin()); 
- 
-  bool IsDef = false; 
-  for (const MachineOperand &MO : PI->operands()) { 
-    // If PI has a regmask operand, it is probably a call. Separate away. 
-    if (MO.isRegMask()) 
-      return Loc; 
-    if (!MO.isReg() || MO.isUse()) 
-      continue; 
-    Register Reg = MO.getReg(); 
-    if (!Reg) 
-      continue; 
-    if (Uses.count(Reg)) { 
-      IsDef = true; 
-      break; 
-    } 
-  } 
-  if (!IsDef) 
-    // The condition setting instruction is not just before the conditional 
-    // branch. 
-    return Loc; 
- 
-  // Be conservative, don't insert instruction above something that may have 
-  // side-effects. And since it's potentially bad to separate flag setting 
-  // instruction from the conditional branch, just abort the optimization 
-  // completely. 
-  // Also avoid moving code above predicated instruction since it's hard to 
-  // reason about register liveness with predicated instruction. 
-  bool DontMoveAcrossStore = true; 
-  if (!PI->isSafeToMove(nullptr, DontMoveAcrossStore) || TII->isPredicated(*PI)) 
-    return MBB->end(); 
- 
-  // Find out what registers are live. Note this routine is ignoring other live 
-  // registers which are only used by instructions in successor blocks. 
-  for (const MachineOperand &MO : PI->operands()) { 
-    if (!MO.isReg()) 
-      continue; 
-    Register Reg = MO.getReg(); 
-    if (!Reg) 
-      continue; 
-    if (MO.isUse()) { 
-      addRegAndItsAliases(Reg, TRI, Uses); 
-    } else { 
-      if (Uses.erase(Reg)) { 
-        if (Register::isPhysicalRegister(Reg)) { 
-          for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) 
-            Uses.erase(*SubRegs); // Use sub-registers to be conservative 
-        } 
-      } 
-      addRegAndItsAliases(Reg, TRI, Defs); 
-    } 
-  } 
- 
-  return PI; 
-} 
- 
-bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) { 
-  MachineBasicBlock *TBB = nullptr, *FBB = nullptr; 
-  SmallVector<MachineOperand, 4> Cond; 
-  if (TII->analyzeBranch(*MBB, TBB, FBB, Cond, true) || !TBB || Cond.empty()) 
-    return false; 
- 
-  if (!FBB) FBB = findFalseBlock(MBB, TBB); 
-  if (!FBB) 
-    // Malformed bcc? True and false blocks are the same? 
-    return false; 
- 
-  // Restrict the optimization to cases where MBB is the only predecessor, 
-  // it is an obvious win. 
-  if (TBB->pred_size() > 1 || FBB->pred_size() > 1) 
-    return false; 
- 
-  // Find a suitable position to hoist the common instructions to. Also figure 
-  // out which registers are used or defined by instructions from the insertion 
-  // point to the end of the block. 
-  SmallSet<Register, 4> Uses, Defs; 
-  MachineBasicBlock::iterator Loc = 
-    findHoistingInsertPosAndDeps(MBB, TII, TRI, Uses, Defs); 
-  if (Loc == MBB->end()) 
-    return false; 
- 
-  bool HasDups = false; 
-  SmallSet<Register, 4> ActiveDefsSet, AllDefsSet; 
-  MachineBasicBlock::iterator TIB = TBB->begin(); 
-  MachineBasicBlock::iterator FIB = FBB->begin(); 
-  MachineBasicBlock::iterator TIE = TBB->end(); 
-  MachineBasicBlock::iterator FIE = FBB->end(); 
-  while (TIB != TIE && FIB != FIE) { 
-    // Skip dbg_value instructions. These do not count. 
-    TIB = skipDebugInstructionsForward(TIB, TIE); 
-    FIB = skipDebugInstructionsForward(FIB, FIE); 
-    if (TIB == TIE || FIB == FIE) 
-      break; 
- 
-    if (!TIB->isIdenticalTo(*FIB, MachineInstr::CheckKillDead)) 
-      break; 
- 
-    if (TII->isPredicated(*TIB)) 
-      // Hard to reason about register liveness with predicated instruction. 
-      break; 
- 
-    bool IsSafe = true; 
-    for (MachineOperand &MO : TIB->operands()) { 
-      // Don't attempt to hoist instructions with register masks. 
-      if (MO.isRegMask()) { 
-        IsSafe = false; 
-        break; 
-      } 
-      if (!MO.isReg()) 
-        continue; 
-      Register Reg = MO.getReg(); 
-      if (!Reg) 
-        continue; 
-      if (MO.isDef()) { 
-        if (Uses.count(Reg)) { 
-          // Avoid clobbering a register that's used by the instruction at 
-          // the point of insertion. 
-          IsSafe = false; 
-          break; 
-        } 
- 
-        if (Defs.count(Reg) && !MO.isDead()) { 
-          // Don't hoist the instruction if the def would be clobber by the 
-          // instruction at the point insertion. FIXME: This is overly 
-          // conservative. It should be possible to hoist the instructions 
-          // in BB2 in the following example: 
-          // BB1: 
-          // r1, eflag = op1 r2, r3 
-          // brcc eflag 
-          // 
-          // BB2: 
-          // r1 = op2, ... 
-          //    = op3, killed r1 
-          IsSafe = false; 
-          break; 
-        } 
-      } else if (!ActiveDefsSet.count(Reg)) { 
-        if (Defs.count(Reg)) { 
-          // Use is defined by the instruction at the point of insertion. 
-          IsSafe = false; 
-          break; 
-        } 
- 
-        if (MO.isKill() && Uses.count(Reg)) 
-          // Kills a register that's read by the instruction at the point of 
-          // insertion. Remove the kill marker. 
-          MO.setIsKill(false); 
-      } 
-    } 
-    if (!IsSafe) 
-      break; 
- 
-    bool DontMoveAcrossStore = true; 
-    if (!TIB->isSafeToMove(nullptr, DontMoveAcrossStore)) 
-      break; 
- 
-    // Remove kills from ActiveDefsSet, these registers had short live ranges. 
-    for (const MachineOperand &MO : TIB->operands()) { 
-      if (!MO.isReg() || !MO.isUse() || !MO.isKill()) 
-        continue; 
-      Register Reg = MO.getReg(); 
-      if (!Reg) 
-        continue; 
-      if (!AllDefsSet.count(Reg)) { 
-        continue; 
-      } 
-      if (Reg.isPhysical()) { 
-        for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) 
-          ActiveDefsSet.erase(*AI); 
-      } else { 
-        ActiveDefsSet.erase(Reg); 
-      } 
-    } 
- 
-    // Track local defs so we can update liveins. 
-    for (const MachineOperand &MO : TIB->operands()) { 
-      if (!MO.isReg() || !MO.isDef() || MO.isDead()) 
-        continue; 
-      Register Reg = MO.getReg(); 
-      if (!Reg || Reg.isVirtual()) 
-        continue; 
-      addRegAndItsAliases(Reg, TRI, ActiveDefsSet); 
-      addRegAndItsAliases(Reg, TRI, AllDefsSet); 
-    } 
- 
-    HasDups = true; 
-    ++TIB; 
-    ++FIB; 
-  } 
- 
-  if (!HasDups) 
-    return false; 
- 
-  MBB->splice(Loc, TBB, TBB->begin(), TIB); 
-  FBB->erase(FBB->begin(), FIB); 
- 
-  if (UpdateLiveIns) { 
-    recomputeLiveIns(*TBB); 
-    recomputeLiveIns(*FBB); 
-  } 
- 
-  ++NumHoist; 
-  return true; 
-} 
+        MachineBasicBlock::iterator PrevBBIter = PrevBB.end();
+        --PrevBBIter;
+        MachineBasicBlock::iterator MBBIter = MBB->begin();
+        // Check if DBG_VALUE at the end of PrevBB is identical to the
+        // DBG_VALUE at the beginning of MBB.
+        while (PrevBBIter != PrevBB.begin() && MBBIter != MBB->end()
+               && PrevBBIter->isDebugInstr() && MBBIter->isDebugInstr()) {
+          if (!MBBIter->isIdenticalTo(*PrevBBIter))
+            break;
+          MachineInstr &DuplicateDbg = *MBBIter;
+          ++MBBIter; -- PrevBBIter;
+          DuplicateDbg.eraseFromParent();
+        }
+      }
+      PrevBB.splice(PrevBB.end(), MBB, MBB->begin(), MBB->end());
+      PrevBB.removeSuccessor(PrevBB.succ_begin());
+      assert(PrevBB.succ_empty());
+      PrevBB.transferSuccessors(MBB);
+      MadeChange = true;
+      return MadeChange;
+    }
+
+    // If the previous branch *only* branches to *this* block (conditional or
+    // not) remove the branch.
+    if (PriorTBB == MBB && !PriorFBB) {
+      TII->removeBranch(PrevBB);
+      MadeChange = true;
+      ++NumBranchOpts;
+      goto ReoptimizeBlock;
+    }
+
+    // If the prior block branches somewhere else on the condition and here if
+    // the condition is false, remove the uncond second branch.
+    if (PriorFBB == MBB) {
+      DebugLoc dl = getBranchDebugLoc(PrevBB);
+      TII->removeBranch(PrevBB);
+      TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl);
+      MadeChange = true;
+      ++NumBranchOpts;
+      goto ReoptimizeBlock;
+    }
+
+    // If the prior block branches here on true and somewhere else on false, and
+    // if the branch condition is reversible, reverse the branch to create a
+    // fall-through.
+    if (PriorTBB == MBB) {
+      SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
+      if (!TII->reverseBranchCondition(NewPriorCond)) {
+        DebugLoc dl = getBranchDebugLoc(PrevBB);
+        TII->removeBranch(PrevBB);
+        TII->insertBranch(PrevBB, PriorFBB, nullptr, NewPriorCond, dl);
+        MadeChange = true;
+        ++NumBranchOpts;
+        goto ReoptimizeBlock;
+      }
+    }
+
+    // If this block has no successors (e.g. it is a return block or ends with
+    // a call to a no-return function like abort or __cxa_throw) and if the pred
+    // falls through into this block, and if it would otherwise fall through
+    // into the block after this, move this block to the end of the function.
+    //
+    // We consider it more likely that execution will stay in the function (e.g.
+    // due to loops) than it is to exit it.  This asserts in loops etc, moving
+    // the assert condition out of the loop body.
+    if (MBB->succ_empty() && !PriorCond.empty() && !PriorFBB &&
+        MachineFunction::iterator(PriorTBB) == FallThrough &&
+        !MBB->canFallThrough()) {
+      bool DoTransform = true;
+
+      // We have to be careful that the succs of PredBB aren't both no-successor
+      // blocks.  If neither have successors and if PredBB is the second from
+      // last block in the function, we'd just keep swapping the two blocks for
+      // last.  Only do the swap if one is clearly better to fall through than
+      // the other.
+      if (FallThrough == --MF.end() &&
+          !IsBetterFallthrough(PriorTBB, MBB))
+        DoTransform = false;
+
+      if (DoTransform) {
+        // Reverse the branch so we will fall through on the previous true cond.
+        SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
+        if (!TII->reverseBranchCondition(NewPriorCond)) {
+          LLVM_DEBUG(dbgs() << "\nMoving MBB: " << *MBB
+                            << "To make fallthrough to: " << *PriorTBB << "\n");
+
+          DebugLoc dl = getBranchDebugLoc(PrevBB);
+          TII->removeBranch(PrevBB);
+          TII->insertBranch(PrevBB, MBB, nullptr, NewPriorCond, dl);
+
+          // Move this block to the end of the function.
+          MBB->moveAfter(&MF.back());
+          MadeChange = true;
+          ++NumBranchOpts;
+          return MadeChange;
+        }
+      }
+    }
+  }
+
+  bool OptForSize =
+      MF.getFunction().hasOptSize() ||
+      llvm::shouldOptimizeForSize(MBB, PSI, &MBBFreqInfo);
+  if (!IsEmptyBlock(MBB) && MBB->pred_size() == 1 && OptForSize) {
+    // Changing "Jcc foo; foo: jmp bar;" into "Jcc bar;" might change the branch
+    // direction, thereby defeating careful block placement and regressing
+    // performance. Therefore, only consider this for optsize functions.
+    MachineInstr &TailCall = *MBB->getFirstNonDebugInstr();
+    if (TII->isUnconditionalTailCall(TailCall)) {
+      MachineBasicBlock *Pred = *MBB->pred_begin();
+      MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
+      SmallVector<MachineOperand, 4> PredCond;
+      bool PredAnalyzable =
+          !TII->analyzeBranch(*Pred, PredTBB, PredFBB, PredCond, true);
+
+      if (PredAnalyzable && !PredCond.empty() && PredTBB == MBB &&
+          PredTBB != PredFBB) {
+        // The predecessor has a conditional branch to this block which consists
+        // of only a tail call. Try to fold the tail call into the conditional
+        // branch.
+        if (TII->canMakeTailCallConditional(PredCond, TailCall)) {
+          // TODO: It would be nice if analyzeBranch() could provide a pointer
+          // to the branch instruction so replaceBranchWithTailCall() doesn't
+          // have to search for it.
+          TII->replaceBranchWithTailCall(*Pred, PredCond, TailCall);
+          ++NumTailCalls;
+          Pred->removeSuccessor(MBB);
+          MadeChange = true;
+          return MadeChange;
+        }
+      }
+      // If the predecessor is falling through to this block, we could reverse
+      // the branch condition and fold the tail call into that. However, after
+      // that we might have to re-arrange the CFG to fall through to the other
+      // block and there is a high risk of regressing code size rather than
+      // improving it.
+    }
+  }
+
+  if (!CurUnAnalyzable) {
+    // If this is a two-way branch, and the FBB branches to this block, reverse
+    // the condition so the single-basic-block loop is faster.  Instead of:
+    //    Loop: xxx; jcc Out; jmp Loop
+    // we want:
+    //    Loop: xxx; jncc Loop; jmp Out
+    if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) {
+      SmallVector<MachineOperand, 4> NewCond(CurCond);
+      if (!TII->reverseBranchCondition(NewCond)) {
+        DebugLoc dl = getBranchDebugLoc(*MBB);
+        TII->removeBranch(*MBB);
+        TII->insertBranch(*MBB, CurFBB, CurTBB, NewCond, dl);
+        MadeChange = true;
+        ++NumBranchOpts;
+        goto ReoptimizeBlock;
+      }
+    }
+
+    // If this branch is the only thing in its block, see if we can forward
+    // other blocks across it.
+    if (CurTBB && CurCond.empty() && !CurFBB &&
+        IsBranchOnlyBlock(MBB) && CurTBB != MBB &&
+        !MBB->hasAddressTaken() && !MBB->isEHPad()) {
+      DebugLoc dl = getBranchDebugLoc(*MBB);
+      // This block may contain just an unconditional branch.  Because there can
+      // be 'non-branch terminators' in the block, try removing the branch and
+      // then seeing if the block is empty.
+      TII->removeBranch(*MBB);
+      // If the only things remaining in the block are debug info, remove these
+      // as well, so this will behave the same as an empty block in non-debug
+      // mode.
+      if (IsEmptyBlock(MBB)) {
+        // Make the block empty, losing the debug info (we could probably
+        // improve this in some cases.)
+        MBB->erase(MBB->begin(), MBB->end());
+      }
+      // If this block is just an unconditional branch to CurTBB, we can
+      // usually completely eliminate the block.  The only case we cannot
+      // completely eliminate the block is when the block before this one
+      // falls through into MBB and we can't understand the prior block's branch
+      // condition.
+      if (MBB->empty()) {
+        bool PredHasNoFallThrough = !PrevBB.canFallThrough();
+        if (PredHasNoFallThrough || !PriorUnAnalyzable ||
+            !PrevBB.isSuccessor(MBB)) {
+          // If the prior block falls through into us, turn it into an
+          // explicit branch to us to make updates simpler.
+          if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) &&
+              PriorTBB != MBB && PriorFBB != MBB) {
+            if (!PriorTBB) {
+              assert(PriorCond.empty() && !PriorFBB &&
+                     "Bad branch analysis");
+              PriorTBB = MBB;
+            } else {
+              assert(!PriorFBB && "Machine CFG out of date!");
+              PriorFBB = MBB;
+            }
+            DebugLoc pdl = getBranchDebugLoc(PrevBB);
+            TII->removeBranch(PrevBB);
+            TII->insertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, pdl);
+          }
+
+          // Iterate through all the predecessors, revectoring each in-turn.
+          size_t PI = 0;
+          bool DidChange = false;
+          bool HasBranchToSelf = false;
+          while(PI != MBB->pred_size()) {
+            MachineBasicBlock *PMBB = *(MBB->pred_begin() + PI);
+            if (PMBB == MBB) {
+              // If this block has an uncond branch to itself, leave it.
+              ++PI;
+              HasBranchToSelf = true;
+            } else {
+              DidChange = true;
+              PMBB->ReplaceUsesOfBlockWith(MBB, CurTBB);
+              // If this change resulted in PMBB ending in a conditional
+              // branch where both conditions go to the same destination,
+              // change this to an unconditional branch.
+              MachineBasicBlock *NewCurTBB = nullptr, *NewCurFBB = nullptr;
+              SmallVector<MachineOperand, 4> NewCurCond;
+              bool NewCurUnAnalyzable = TII->analyzeBranch(
+                  *PMBB, NewCurTBB, NewCurFBB, NewCurCond, true);
+              if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) {
+                DebugLoc pdl = getBranchDebugLoc(*PMBB);
+                TII->removeBranch(*PMBB);
+                NewCurCond.clear();
+                TII->insertBranch(*PMBB, NewCurTBB, nullptr, NewCurCond, pdl);
+                MadeChange = true;
+                ++NumBranchOpts;
+              }
+            }
+          }
+
+          // Change any jumptables to go to the new MBB.
+          if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
+            MJTI->ReplaceMBBInJumpTables(MBB, CurTBB);
+          if (DidChange) {
+            ++NumBranchOpts;
+            MadeChange = true;
+            if (!HasBranchToSelf) return MadeChange;
+          }
+        }
+      }
+
+      // Add the branch back if the block is more than just an uncond branch.
+      TII->insertBranch(*MBB, CurTBB, nullptr, CurCond, dl);
+    }
+  }
+
+  // If the prior block doesn't fall through into this block, and if this
+  // block doesn't fall through into some other block, see if we can find a
+  // place to move this block where a fall-through will happen.
+  if (!PrevBB.canFallThrough()) {
+    // Now we know that there was no fall-through into this block, check to
+    // see if it has a fall-through into its successor.
+    bool CurFallsThru = MBB->canFallThrough();
+
+    if (!MBB->isEHPad()) {
+      // Check all the predecessors of this block.  If one of them has no fall
+      // throughs, and analyzeBranch thinks it _could_ fallthrough to this
+      // block, move this block right after it.
+      for (MachineBasicBlock *PredBB : MBB->predecessors()) {
+        // Analyze the branch at the end of the pred.
+        MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
+        SmallVector<MachineOperand, 4> PredCond;
+        if (PredBB != MBB && !PredBB->canFallThrough() &&
+            !TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true) &&
+            (PredTBB == MBB || PredFBB == MBB) &&
+            (!CurFallsThru || !CurTBB || !CurFBB) &&
+            (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
+          // If the current block doesn't fall through, just move it.
+          // If the current block can fall through and does not end with a
+          // conditional branch, we need to append an unconditional jump to
+          // the (current) next block.  To avoid a possible compile-time
+          // infinite loop, move blocks only backward in this case.
+          // Also, if there are already 2 branches here, we cannot add a third;
+          // this means we have the case
+          // Bcc next
+          // B elsewhere
+          // next:
+          if (CurFallsThru) {
+            MachineBasicBlock *NextBB = &*std::next(MBB->getIterator());
+            CurCond.clear();
+            TII->insertBranch(*MBB, NextBB, nullptr, CurCond, DebugLoc());
+          }
+          MBB->moveAfter(PredBB);
+          MadeChange = true;
+          goto ReoptimizeBlock;
+        }
+      }
+    }
+
+    if (!CurFallsThru) {
+      // Check analyzable branch-successors to see if we can move this block
+      // before one.
+      if (!CurUnAnalyzable) {
+        for (MachineBasicBlock *SuccBB : {CurFBB, CurTBB}) {
+          if (!SuccBB)
+            continue;
+          // Analyze the branch at the end of the block before the succ.
+          MachineFunction::iterator SuccPrev = --SuccBB->getIterator();
+
+          // If this block doesn't already fall-through to that successor, and
+          // if the succ doesn't already have a block that can fall through into
+          // it, we can arrange for the fallthrough to happen.
+          if (SuccBB != MBB && &*SuccPrev != MBB &&
+              !SuccPrev->canFallThrough()) {
+            MBB->moveBefore(SuccBB);
+            MadeChange = true;
+            goto ReoptimizeBlock;
+          }
+        }
+      }
+
+      // Okay, there is no really great place to put this block.  If, however,
+      // the block before this one would be a fall-through if this block were
+      // removed, move this block to the end of the function. There is no real
+      // advantage in "falling through" to an EH block, so we don't want to
+      // perform this transformation for that case.
+      //
+      // Also, Windows EH introduced the possibility of an arbitrary number of
+      // successors to a given block.  The analyzeBranch call does not consider
+      // exception handling and so we can get in a state where a block
+      // containing a call is followed by multiple EH blocks that would be
+      // rotated infinitely at the end of the function if the transformation
+      // below were performed for EH "FallThrough" blocks.  Therefore, even if
+      // that appears not to be happening anymore, we should assume that it is
+      // possible and not remove the "!FallThrough()->isEHPad" condition below.
+      MachineBasicBlock *PrevTBB = nullptr, *PrevFBB = nullptr;
+      SmallVector<MachineOperand, 4> PrevCond;
+      if (FallThrough != MF.end() &&
+          !FallThrough->isEHPad() &&
+          !TII->analyzeBranch(PrevBB, PrevTBB, PrevFBB, PrevCond, true) &&
+          PrevBB.isSuccessor(&*FallThrough)) {
+        MBB->moveAfter(&MF.back());
+        MadeChange = true;
+        return MadeChange;
+      }
+    }
+  }
+
+  return MadeChange;
+}
+
+//===----------------------------------------------------------------------===//
+//  Hoist Common Code
+//===----------------------------------------------------------------------===//
+
+bool BranchFolder::HoistCommonCode(MachineFunction &MF) {
+  bool MadeChange = false;
+  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ) {
+    MachineBasicBlock *MBB = &*I++;
+    MadeChange |= HoistCommonCodeInSuccs(MBB);
+  }
+
+  return MadeChange;
+}
+
+/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
+/// its 'true' successor.
+static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
+                                         MachineBasicBlock *TrueBB) {
+  for (MachineBasicBlock *SuccBB : BB->successors())
+    if (SuccBB != TrueBB)
+      return SuccBB;
+  return nullptr;
+}
+
+template <class Container>
+static void addRegAndItsAliases(Register Reg, const TargetRegisterInfo *TRI,
+                                Container &Set) {
+  if (Reg.isPhysical()) {
+    for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+      Set.insert(*AI);
+  } else {
+    Set.insert(Reg);
+  }
+}
+
+/// findHoistingInsertPosAndDeps - Find the location to move common instructions
+/// in successors to. The location is usually just before the terminator,
+/// however if the terminator is a conditional branch and its previous
+/// instruction is the flag setting instruction, the previous instruction is
+/// the preferred location. This function also gathers uses and defs of the
+/// instructions from the insertion point to the end of the block. The data is
+/// used by HoistCommonCodeInSuccs to ensure safety.
+static
+MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB,
+                                                  const TargetInstrInfo *TII,
+                                                  const TargetRegisterInfo *TRI,
+                                                  SmallSet<Register, 4> &Uses,
+                                                  SmallSet<Register, 4> &Defs) {
+  MachineBasicBlock::iterator Loc = MBB->getFirstTerminator();
+  if (!TII->isUnpredicatedTerminator(*Loc))
+    return MBB->end();
+
+  for (const MachineOperand &MO : Loc->operands()) {
+    if (!MO.isReg())
+      continue;
+    Register Reg = MO.getReg();
+    if (!Reg)
+      continue;
+    if (MO.isUse()) {
+      addRegAndItsAliases(Reg, TRI, Uses);
+    } else {
+      if (!MO.isDead())
+        // Don't try to hoist code in the rare case the terminator defines a
+        // register that is later used.
+        return MBB->end();
+
+      // If the terminator defines a register, make sure we don't hoist
+      // the instruction whose def might be clobbered by the terminator.
+      addRegAndItsAliases(Reg, TRI, Defs);
+    }
+  }
+
+  if (Uses.empty())
+    return Loc;
+  // If the terminator is the only instruction in the block and Uses is not
+  // empty (or we would have returned above), we can still safely hoist
+  // instructions just before the terminator as long as the Defs/Uses are not
+  // violated (which is checked in HoistCommonCodeInSuccs).
+  if (Loc == MBB->begin())
+    return Loc;
+
+  // The terminator is probably a conditional branch, try not to separate the
+  // branch from condition setting instruction.
+  MachineBasicBlock::iterator PI = prev_nodbg(Loc, MBB->begin());
+
+  bool IsDef = false;
+  for (const MachineOperand &MO : PI->operands()) {
+    // If PI has a regmask operand, it is probably a call. Separate away.
+    if (MO.isRegMask())
+      return Loc;
+    if (!MO.isReg() || MO.isUse())
+      continue;
+    Register Reg = MO.getReg();
+    if (!Reg)
+      continue;
+    if (Uses.count(Reg)) {
+      IsDef = true;
+      break;
+    }
+  }
+  if (!IsDef)
+    // The condition setting instruction is not just before the conditional
+    // branch.
+    return Loc;
+
+  // Be conservative, don't insert instruction above something that may have
+  // side-effects. And since it's potentially bad to separate flag setting
+  // instruction from the conditional branch, just abort the optimization
+  // completely.
+  // Also avoid moving code above predicated instruction since it's hard to
+  // reason about register liveness with predicated instruction.
+  bool DontMoveAcrossStore = true;
+  if (!PI->isSafeToMove(nullptr, DontMoveAcrossStore) || TII->isPredicated(*PI))
+    return MBB->end();
+
+  // Find out what registers are live. Note this routine is ignoring other live
+  // registers which are only used by instructions in successor blocks.
+  for (const MachineOperand &MO : PI->operands()) {
+    if (!MO.isReg())
+      continue;
+    Register Reg = MO.getReg();
+    if (!Reg)
+      continue;
+    if (MO.isUse()) {
+      addRegAndItsAliases(Reg, TRI, Uses);
+    } else {
+      if (Uses.erase(Reg)) {
+        if (Register::isPhysicalRegister(Reg)) {
+          for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
+            Uses.erase(*SubRegs); // Use sub-registers to be conservative
+        }
+      }
+      addRegAndItsAliases(Reg, TRI, Defs);
+    }
+  }
+
+  return PI;
+}
+
+bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
+  MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
+  SmallVector<MachineOperand, 4> Cond;
+  if (TII->analyzeBranch(*MBB, TBB, FBB, Cond, true) || !TBB || Cond.empty())
+    return false;
+
+  if (!FBB) FBB = findFalseBlock(MBB, TBB);
+  if (!FBB)
+    // Malformed bcc? True and false blocks are the same?
+    return false;
+
+  // Restrict the optimization to cases where MBB is the only predecessor,
+  // it is an obvious win.
+  if (TBB->pred_size() > 1 || FBB->pred_size() > 1)
+    return false;
+
+  // Find a suitable position to hoist the common instructions to. Also figure
+  // out which registers are used or defined by instructions from the insertion
+  // point to the end of the block.
+  SmallSet<Register, 4> Uses, Defs;
+  MachineBasicBlock::iterator Loc =
+    findHoistingInsertPosAndDeps(MBB, TII, TRI, Uses, Defs);
+  if (Loc == MBB->end())
+    return false;
+
+  bool HasDups = false;
+  SmallSet<Register, 4> ActiveDefsSet, AllDefsSet;
+  MachineBasicBlock::iterator TIB = TBB->begin();
+  MachineBasicBlock::iterator FIB = FBB->begin();
+  MachineBasicBlock::iterator TIE = TBB->end();
+  MachineBasicBlock::iterator FIE = FBB->end();
+  while (TIB != TIE && FIB != FIE) {
+    // Skip dbg_value instructions. These do not count.
+    TIB = skipDebugInstructionsForward(TIB, TIE);
+    FIB = skipDebugInstructionsForward(FIB, FIE);
+    if (TIB == TIE || FIB == FIE)
+      break;
+
+    if (!TIB->isIdenticalTo(*FIB, MachineInstr::CheckKillDead))
+      break;
+
+    if (TII->isPredicated(*TIB))
+      // Hard to reason about register liveness with predicated instruction.
+      break;
+
+    bool IsSafe = true;
+    for (MachineOperand &MO : TIB->operands()) {
+      // Don't attempt to hoist instructions with register masks.
+      if (MO.isRegMask()) {
+        IsSafe = false;
+        break;
+      }
+      if (!MO.isReg())
+        continue;
+      Register Reg = MO.getReg();
+      if (!Reg)
+        continue;
+      if (MO.isDef()) {
+        if (Uses.count(Reg)) {
+          // Avoid clobbering a register that's used by the instruction at
+          // the point of insertion.
+          IsSafe = false;
+          break;
+        }
+
+        if (Defs.count(Reg) && !MO.isDead()) {
+          // Don't hoist the instruction if the def would be clobber by the
+          // instruction at the point insertion. FIXME: This is overly
+          // conservative. It should be possible to hoist the instructions
+          // in BB2 in the following example:
+          // BB1:
+          // r1, eflag = op1 r2, r3
+          // brcc eflag
+          //
+          // BB2:
+          // r1 = op2, ...
+          //    = op3, killed r1
+          IsSafe = false;
+          break;
+        }
+      } else if (!ActiveDefsSet.count(Reg)) {
+        if (Defs.count(Reg)) {
+          // Use is defined by the instruction at the point of insertion.
+          IsSafe = false;
+          break;
+        }
+
+        if (MO.isKill() && Uses.count(Reg))
+          // Kills a register that's read by the instruction at the point of
+          // insertion. Remove the kill marker.
+          MO.setIsKill(false);
+      }
+    }
+    if (!IsSafe)
+      break;
+
+    bool DontMoveAcrossStore = true;
+    if (!TIB->isSafeToMove(nullptr, DontMoveAcrossStore))
+      break;
+
+    // Remove kills from ActiveDefsSet, these registers had short live ranges.
+    for (const MachineOperand &MO : TIB->operands()) {
+      if (!MO.isReg() || !MO.isUse() || !MO.isKill())
+        continue;
+      Register Reg = MO.getReg();
+      if (!Reg)
+        continue;
+      if (!AllDefsSet.count(Reg)) {
+        continue;
+      }
+      if (Reg.isPhysical()) {
+        for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+          ActiveDefsSet.erase(*AI);
+      } else {
+        ActiveDefsSet.erase(Reg);
+      }
+    }
+
+    // Track local defs so we can update liveins.
+    for (const MachineOperand &MO : TIB->operands()) {
+      if (!MO.isReg() || !MO.isDef() || MO.isDead())
+        continue;
+      Register Reg = MO.getReg();
+      if (!Reg || Reg.isVirtual())
+        continue;
+      addRegAndItsAliases(Reg, TRI, ActiveDefsSet);
+      addRegAndItsAliases(Reg, TRI, AllDefsSet);
+    }
+
+    HasDups = true;
+    ++TIB;
+    ++FIB;
+  }
+
+  if (!HasDups)
+    return false;
+
+  MBB->splice(Loc, TBB, TBB->begin(), TIB);
+  FBB->erase(FBB->begin(), FIB);
+
+  if (UpdateLiveIns) {
+    recomputeLiveIns(*TBB);
+    recomputeLiveIns(*FBB);
+  }
+
+  ++NumHoist;
+  return true;
+}