/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp

Bug Summary

File:	lib/CodeGen/BranchFolding.cpp
Warning:	line 1165, column 16 The left operand of '!=' is a garbage value
Annotated Source Code

Press '?' to see keyboard shortcuts
Show analyzer invocation
clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name BranchFolding.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-9/lib/clang/9.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-9~svn362543/build-llvm/lib/CodeGen -I /build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen -I /build/llvm-toolchain-snapshot-9~svn362543/build-llvm/include -I /build/llvm-toolchain-snapshot-9~svn362543/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward -internal-isystem /usr/include/clang/9.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-9/lib/clang/9.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-9~svn362543/build-llvm/lib/CodeGen -fdebug-prefix-map=/build/llvm-toolchain-snapshot-9~svn362543=. -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -stack-protector 2 -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2019-06-05-060531-1271-1 -x c++ /build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp -faddrsig
1//===- BranchFolding.cpp - Fold machine code branch instructions ----------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This pass forwards branches to unconditional branches to make them branch
10// directly to the target block.  This pass often results in dead MBB's, which
11// it then removes.
12//
13// Note that this pass must be run after register allocation, it cannot handle
14// SSA form. It also must handle virtual registers for targets that emit virtual
15// ISA (e.g. NVPTX).
16//
17//===----------------------------------------------------------------------===//

19#include "BranchFolding.h"
20#include "llvm/ADT/BitVector.h"
21#include "llvm/ADT/DenseMap.h"
22#include "llvm/ADT/STLExtras.h"
23#include "llvm/ADT/SmallPtrSet.h"
24#include "llvm/ADT/SmallSet.h"
25#include "llvm/ADT/SmallVector.h"
26#include "llvm/ADT/Statistic.h"
27#include "llvm/CodeGen/Analysis.h"
28#include "llvm/CodeGen/LivePhysRegs.h"
29#include "llvm/CodeGen/MachineBasicBlock.h"
30#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
31#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
32#include "llvm/CodeGen/MachineFunction.h"
33#include "llvm/CodeGen/MachineFunctionPass.h"
34#include "llvm/CodeGen/MachineInstr.h"
35#include "llvm/CodeGen/MachineInstrBuilder.h"
36#include "llvm/CodeGen/MachineJumpTableInfo.h"
37#include "llvm/CodeGen/MachineLoopInfo.h"
38#include "llvm/CodeGen/MachineModuleInfo.h"
39#include "llvm/CodeGen/MachineOperand.h"
40#include "llvm/CodeGen/MachineRegisterInfo.h"
41#include "llvm/CodeGen/TargetInstrInfo.h"
42#include "llvm/CodeGen/TargetOpcodes.h"
43#include "llvm/CodeGen/TargetPassConfig.h"
44#include "llvm/CodeGen/TargetRegisterInfo.h"
45#include "llvm/CodeGen/TargetSubtargetInfo.h"
46#include "llvm/IR/DebugInfoMetadata.h"
47#include "llvm/IR/DebugLoc.h"
48#include "llvm/IR/Function.h"
49#include "llvm/MC/LaneBitmask.h"
50#include "llvm/MC/MCRegisterInfo.h"
51#include "llvm/Pass.h"
52#include "llvm/Support/BlockFrequency.h"
53#include "llvm/Support/BranchProbability.h"
54#include "llvm/Support/CommandLine.h"
55#include "llvm/Support/Debug.h"
56#include "llvm/Support/ErrorHandling.h"
57#include "llvm/Support/raw_ostream.h"
58#include "llvm/Target/TargetMachine.h"
59#include <cassert>
60#include <cstddef>
61#include <iterator>
62#include <numeric>
63#include <vector>

65using namespace llvm;

67#define DEBUG_TYPE"branch-folder" "branch-folder"

69STATISTIC(NumDeadBlocks, "Number of dead blocks removed")static llvm::Statistic NumDeadBlocks = {"branch-folder", "NumDeadBlocks"
, "Number of dead blocks removed", {0}, {false}};
70STATISTIC(NumBranchOpts, "Number of branches optimized")static llvm::Statistic NumBranchOpts = {"branch-folder", "NumBranchOpts"
, "Number of branches optimized", {0}, {false}};
71STATISTIC(NumTailMerge , "Number of block tails merged")static llvm::Statistic NumTailMerge = {"branch-folder", "NumTailMerge"
, "Number of block tails merged", {0}, {false}};
72STATISTIC(NumHoist     , "Number of times common instructions are hoisted")static llvm::Statistic NumHoist = {"branch-folder", "NumHoist"
, "Number of times common instructions are hoisted", {0}, {false
}};
73STATISTIC(NumTailCalls,  "Number of tail calls optimized")static llvm::Statistic NumTailCalls = {"branch-folder", "NumTailCalls"
, "Number of tail calls optimized", {0}, {false}};

75static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
                            cl::init(cl::BOU_UNSET), cl::Hidden);

78// Throttle for huge numbers of predecessors (compile speed problems)
79static cl::opt<unsigned>
80TailMergeThreshold("tail-merge-threshold",
        cl::desc("Max number of predecessors to consider tail merging"),
        cl::init(150), cl::Hidden);

84// Heuristic for tail merging (and, inversely, tail duplication).
85// TODO: This should be replaced with a target query.
86static cl::opt<unsigned>
87TailMergeSize("tail-merge-size",
            cl::desc("Min number of instructions to consider tail merging"),
            cl::init(3), cl::Hidden);

91namespace {

/// 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<TargetPassConfig>();
    MachineFunctionPass::getAnalysisUsage(AU);
  }
};

110} // end anonymous namespace

112char BranchFolderPass::ID = 0;

114char &llvm::BranchFolderPassID = BranchFolderPass::ID;

116INITIALIZE_PASS(BranchFolderPass, DEBUG_TYPE,static void *initializeBranchFolderPassPassOnce(PassRegistry &
Registry) { PassInfo *PI = new PassInfo( "Control Flow Optimizer"
, "branch-folder", &BranchFolderPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<BranchFolderPass>), false, false); Registry
.registerPass(*PI, true); return PI; } static llvm::once_flag
 InitializeBranchFolderPassPassFlag; void llvm::initializeBranchFolderPassPass
(PassRegistry &Registry) { llvm::call_once(InitializeBranchFolderPassPassFlag
, initializeBranchFolderPassPassOnce, std::ref(Registry)); }
              "Control Flow Optimizer", false, false)static void *initializeBranchFolderPassPassOnce(PassRegistry &
Registry) { PassInfo *PI = new PassInfo( "Control Flow Optimizer"
, "branch-folder", &BranchFolderPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<BranchFolderPass>), false, false); Registry
.registerPass(*PI, true); return PI; } static llvm::once_flag
 InitializeBranchFolderPassPassFlag; void llvm::initializeBranchFolderPassPass
(PassRegistry &Registry) { llvm::call_once(InitializeBranchFolderPassPassFlag
, initializeBranchFolderPassPassOnce, std::ref(Registry)); }

119bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
1
Assuming the condition is false→
2
←
Taking false branch→
  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() &&
3
←
Assuming the condition is false→
                       PassConfig->getEnableTailMerge();
BranchFolder::MBFIWrapper MBBFreqInfo(
    getAnalysis<MachineBlockFrequencyInfo>());
BranchFolder Folder(EnableTailMerge, /*CommonHoist=*/true, MBBFreqInfo,
                    getAnalysis<MachineBranchProbabilityInfo>());
return Folder.OptimizeFunction(MF, MF.getSubtarget().getInstrInfo(),
4
←
Calling 'BranchFolder::OptimizeFunction'→
                               MF.getSubtarget().getRegisterInfo(),
                               getAnalysisIfAvailable<MachineModuleInfo>());
135}

137BranchFolder::BranchFolder(bool defaultEnableTailMerge, bool CommonHoist,
                         MBFIWrapper &FreqInfo,
                         const MachineBranchProbabilityInfo &ProbInfo,
                         unsigned MinTailLength)
  : EnableHoistCommonCode(CommonHoist), MinCommonTailLength(MinTailLength),
    MBBFreqInfo(FreqInfo), MBPI(ProbInfo) {
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;
}
150}

152void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
assert(MBB->pred_empty() && "MBB must be dead!")((MBB->pred_empty() && "MBB must be dead!") ? static_cast
<void> (0) : __assert_fail ("MBB->pred_empty() && \"MBB must be dead!\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 153, __PRETTY_FUNCTION__));
LLVM_DEBUG(dbgs() << "\nRemoving MBB: " << *MBB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\nRemoving MBB: " <<
 *MBB; } } while (false);

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);

// Remove the block.
MF->erase(MBB);
EHScopeMembership.erase(MBB);
if (MLI)
  MLI->removeBlock(MBB);
169}

171bool BranchFolder::OptimizeFunction(MachineFunction &MF,
                                  const TargetInstrInfo *tii,
                                  const TargetRegisterInfo *tri,
                                  MachineModuleInfo *mmi,
                                  MachineLoopInfo *mli, bool AfterPlacement) {
if (!tii) return false;
5
←
Assuming 'tii' is non-null→
6
←
Taking false branch→

TriedMerging.clear();

MachineRegisterInfo &MRI = MF.getRegInfo();
AfterBlockPlacement = AfterPlacement;
TII = tii;
TRI = tri;
MMI = mmi;
MLI = mli;
this->MRI = &MRI;

UpdateLiveIns = MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF);
if (!UpdateLiveIns)
7
←
Taking true branch→
  MRI.invalidateLiveness();

// Fix CFG.  The later algorithms expect it to be right.
bool MadeChange = false;
for (MachineBasicBlock &MBB : MF) {
  MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
  SmallVector<MachineOperand, 4> Cond;
  if (!TII->analyzeBranch(MBB, TBB, FBB, Cond, true))
    MadeChange |= MBB.CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
}

// Recalculate EH scope membership.
EHScopeMembership = getEHScopeMembership(MF);

bool MadeChangeThisIteration = true;
while (MadeChangeThisIteration) {
8
←
Loop condition is true.  Entering loop body→
  MadeChangeThisIteration    = TailMergeBlocks(MF);
9
←
Calling 'BranchFolder::TailMergeBlocks'→
  // 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;
243}

245//===----------------------------------------------------------------------===//
246//  Tail Merging of Blocks
247//===----------------------------------------------------------------------===//

249/// HashMachineInstr - Compute a hash value for MI and its operands.
250static 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;
287}

289/// HashEndOfMBB - Hash the last instruction in the MBB.
290static unsigned HashEndOfMBB(const MachineBasicBlock &MBB) {
MachineBasicBlock::const_iterator I = MBB.getLastNonDebugInstr();
if (I == MBB.end())
  return 0;

return HashMachineInstr(*I);
296}

298///  Whether MI should be counted as an instruction when calculating common tail.
299static bool countsAsInstruction(const MachineInstr &MI) {
return !(MI.isDebugInstr() || MI.isCFIInstruction());
301}

303/// ComputeCommonTailLength - Given two machine basic blocks, compute the number
304/// of instructions they actually have in common together at their end.  Return
305/// iterators for the first shared instruction in each block.
306static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
                                      MachineBasicBlock *MBB2,
                                      MachineBasicBlock::iterator &I1,
                                      MachineBasicBlock::iterator &I2) {
I1 = MBB1->end();
I2 = MBB2->end();

unsigned TailLen = 0;
while (I1 != MBB1->begin() && I2 != MBB2->begin()) {
  --I1; --I2;
  // Skip debugging pseudos; necessary to avoid changing the code.
  while (!countsAsInstruction(*I1)) {
    if (I1==MBB1->begin()) {
      while (!countsAsInstruction(*I2)) {
        if (I2==MBB2->begin()) {
          // I1==DBG at begin; I2==DBG at begin
          goto SkipTopCFIAndReturn;
        }
        --I2;
      }
      ++I2;
      // I1==DBG at begin; I2==non-DBG, or first of DBGs not at begin
      goto SkipTopCFIAndReturn;
    }
    --I1;
  }
  // I1==first (untested) non-DBG preceding known match
  while (!countsAsInstruction(*I2)) {
    if (I2==MBB2->begin()) {
      ++I1;
      // I1==non-DBG, or first of DBGs not at begin; I2==DBG at begin
      goto SkipTopCFIAndReturn;
    }
    --I2;
  }
  // I1, I2==first (untested) non-DBGs preceding known match
  if (!I1->isIdenticalTo(*I2) ||
      // 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.
      I1->isInlineAsm()) {
    ++I1; ++I2;
    break;
  }
  ++TailLen;
}
// Back past possible debugging pseudos at beginning of block.  This matters
// when one block differs from the other only by whether debugging pseudos
// are present at the beginning. (This way, the various checks later for
// I1==MBB1->begin() work as expected.)
if (I1 == MBB1->begin() && I2 != MBB2->begin()) {
  --I2;
  while (I2->isDebugInstr()) {
    if (I2 == MBB2->begin())
      return TailLen;
    --I2;
  }
  ++I2;
}
if (I2 == MBB2->begin() && I1 != MBB1->begin()) {
  --I1;
  while (I1->isDebugInstr()) {
    if (I1 == MBB1->begin())
      return TailLen;
    --I1;
  }
  ++I1;
}

377SkipTopCFIAndReturn:
// Ensure that I1 and I2 do not point to a CFI_INSTRUCTION. This can happen if
// I1 and I2 are non-identical when compared and then one or both of them ends
// up pointing to a CFI instruction after being incremented. For example:
/*
  BB1:
  ...
  INSTRUCTION_A
  ADD32ri8  <- last common instruction
  ...
  BB2:
  ...
  INSTRUCTION_B
  CFI_INSTRUCTION
  ADD32ri8  <- last common instruction
  ...
*/
// When INSTRUCTION_A and INSTRUCTION_B are compared as not equal, after
// incrementing the iterators, I1 will point to ADD, however I2 will point to
// the CFI instruction. Later on, this leads to BB2 being 'hacked off' at the
// wrong place (in ReplaceTailWithBranchTo()) which results in losing this CFI
// instruction.
while (I1 != MBB1->end() && I1->isCFIInstruction()) {
  ++I1;
}

while (I2 != MBB2->end() && I2->isCFIInstruction()) {
  ++I2;
}

return TailLen;
408}

410void 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() &&((P.LaneMask == LaneBitmask::getAll() && "Can only handle full register."
) ? static_cast<void> (0) : __assert_fail ("P.LaneMask == LaneBitmask::getAll() && \"Can only handle full register.\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 431, __PRETTY_FUNCTION__))
           "Can only handle full register.")((P.LaneMask == LaneBitmask::getAll() && "Can only handle full register."
) ? static_cast<void> (0) : __assert_fail ("P.LaneMask == LaneBitmask::getAll() && \"Can only handle full register.\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 431, __PRETTY_FUNCTION__));
    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;
442}

444MachineBasicBlock *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;
485}

487/// EstimateRuntime - Make a rough estimate for how long it will take to run
488/// the specified code.
489static 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->mayLoad() || I->mayStore())
    Time += 2;
  else
    ++Time;
}
return Time;
503}

505// CurMBB needs to add an unconditional branch to SuccMBB (we removed these
506// branches temporarily for tail merging).  In the case where CurMBB ends
507// with a conditional branch to the next block, optimize by reversing the
508// test and conditionally branching to SuccMBB instead.
509static 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);
528}

530bool
531BranchFolder::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.
542#ifndef _GLIBCXX_DEBUG
llvm_unreachable("Predecessor appears twice")::llvm::llvm_unreachable_internal("Predecessor appears twice"
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 543);
544#else
return false;
546#endif
547}

549BlockFrequency
550BranchFolder::MBFIWrapper::getBlockFreq(const MachineBasicBlock *MBB) const {
auto I = MergedBBFreq.find(MBB);

if (I != MergedBBFreq.end())
  return I->second;

return MBFI.getBlockFreq(MBB);
557}

559void BranchFolder::MBFIWrapper::setBlockFreq(const MachineBasicBlock *MBB,
                                           BlockFrequency F) {
MergedBBFreq[MBB] = F;
562}

564raw_ostream &
565BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
                                        const MachineBasicBlock *MBB) const {
return MBFI.printBlockFreq(OS, getBlockFreq(MBB));
568}

570raw_ostream &
571BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
                                        const BlockFrequency Freq) const {
return MBFI.printBlockFreq(OS, Freq);
574}

576void BranchFolder::MBFIWrapper::view(const Twine &Name, bool isSimple) {
MBFI.view(Name, isSimple);
578}

580uint64_t
581BranchFolder::MBFIWrapper::getEntryFreq() const {
return MBFI.getEntryFreq();
583}

585/// CountTerminators - Count the number of terminators in the given
586/// block and set I to the position of the first non-terminator, if there
587/// is one, or MBB->end() otherwise.
588static 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;
602}

604/// A no successor, non-return block probably ends in unreachable and is cold.
605/// Also consider a block that ends in an indirect branch to be a return block,
606/// since many targets use plain indirect branches to return.
607static bool blockEndsInUnreachable(const MachineBasicBlock *MBB) {
if (!MBB->succ_empty())
  return false;
if (MBB->empty())
  return true;
return !(MBB->back().isReturn() || MBB->back().isIndirectBranch());
613}

615/// ProfitableToMerge - Check if two machine basic blocks have a common tail
616/// and decide if it would be profitable to merge those tails.  Return the
617/// length of the common tail and iterators to the first common instruction
618/// in each block.
619/// MBB1, MBB2      The blocks to check
620/// MinCommonTailLength  Minimum size of tail block to be merged.
621/// CommonTailLen   Out parameter to record the size of the shared tail between
622///                 MBB1 and MBB2
623/// I1, I2          Iterator references that will be changed to point to the first
624///                 instruction in the common tail shared by MBB1,MBB2
625/// SuccBB          A common successor of MBB1, MBB2 which are in a canonical form
626///                 relative to SuccBB
627/// PredBB          The layout predecessor of SuccBB, if any.
628/// EHScopeMembership  map from block to EH scope #.
629/// AfterPlacement  True if we are merging blocks after layout. Stricter
630///                 thresholds apply to prevent undoing tail-duplication.
631static bool
632ProfitableToMerge(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) {
// 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())((EHScope1 != EHScopeMembership.end()) ? static_cast<void>
 (0) : __assert_fail ("EHScope1 != EHScopeMembership.end()", "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 642, __PRETTY_FUNCTION__));
  auto EHScope2 = EHScopeMembership.find(MBB2);
  assert(EHScope2 != EHScopeMembership.end())((EHScope2 != EHScopeMembership.end()) ? static_cast<void>
 (0) : __assert_fail ("EHScope2 != EHScopeMembership.end()", "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 644, __PRETTY_FUNCTION__));
  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)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "Common tail length of "
 << printMBBReference(*MBB1) << " and " << printMBBReference
(*MBB2) << " is " << CommonTailLen << '\n';
 } } while (false)
                  << " and " << printMBBReference(*MBB2) << " is "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "Common tail length of "
 << printMBBReference(*MBB1) << " and " << printMBBReference
(*MBB2) << " is " << CommonTailLen << '\n';
 } } while (false)
                  << CommonTailLen << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "Common tail length of "
 << printMBBReference(*MBB1) << " and " << printMBBReference
(*MBB2) << " is " << CommonTailLen << '\n';
 } } while (false);

// 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 (I1 == MBB1->begin() && I2 == MBB2->begin() &&
    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) && I2 == MBB2->begin())
  return true;
if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin())
  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 && I1 == MBB1->begin() && I2 == MBB2->begin()) {
  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();
return EffectiveTailLen >= 2 && MF->getFunction().hasOptSize() &&
       (I1 == MBB1->begin() || I2 == MBB2->begin());
726}

728unsigned 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)) {
      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;
762}

764void 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());
781}

783bool 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 "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\nSplitting " << printMBBReference
(*MBB) << ", size " << maxCommonTailLength; } } while
 (false)
                  << maxCommonTailLength)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\nSplitting " << printMBBReference
(*MBB) << ", size " << maxCommonTailLength; } } while
 (false);

// 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!")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "... failed!"; } } while
 (false);
  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;
831}

833static void
834mergeOperations(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!")((MBBI != MBBIE && "Reached BB end within common tail length!"
) ? static_cast<void> (0) : __assert_fail ("MBBI != MBBIE && \"Reached BB end within common tail length!\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 850, __PRETTY_FUNCTION__));
  (void)MBBIE;

  if (!countsAsInstruction(*MBBI)) {
    ++MBBI;
    continue;
  }

  while ((MBBICommon != MBBIECommon) && !countsAsInstruction(*MBBICommon))
    ++MBBICommon;

  assert(MBBICommon != MBBIECommon &&((MBBICommon != MBBIECommon && "Reached BB end within common tail length!"
) ? static_cast<void> (0) : __assert_fail ("MBBICommon != MBBIECommon && \"Reached BB end within common tail length!\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 862, __PRETTY_FUNCTION__))
         "Reached BB end within common tail length!")((MBBICommon != MBBIECommon && "Reached BB end within common tail length!"
) ? static_cast<void> (0) : __assert_fail ("MBBICommon != MBBIECommon && \"Reached BB end within common tail length!\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 862, __PRETTY_FUNCTION__));
  assert(MBBICommon->isIdenticalTo(*MBBI) && "Expected matching MIIs!")((MBBICommon->isIdenticalTo(*MBBI) && "Expected matching MIIs!"
) ? static_cast<void> (0) : __assert_fail ("MBBICommon->isIdenticalTo(*MBBI) && \"Expected matching MIIs!\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 863, __PRETTY_FUNCTION__));

  // Merge MMOs from memory operations in the common block.
  if (MBBICommon->mayLoad() || MBBICommon->mayStore())
    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;
}
881}

883void 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() &&((SameTails[i].getTailStartPos() == MBB->begin() &&
 "MBB is not a common tail only block") ? static_cast<void
> (0) : __assert_fail ("SameTails[i].getTailStartPos() == MBB->begin() && \"MBB is not a common tail only block\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 893, __PRETTY_FUNCTION__))
        "MBB is not a common tail only block")((SameTails[i].getTailStartPos() == MBB->begin() &&
 "MBB is not a common tail only block") ? static_cast<void
> (0) : __assert_fail ("SameTails[i].getTailStartPos() == MBB->begin() && \"MBB is not a common tail only block\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 893, __PRETTY_FUNCTION__));
  }
}

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() &&((Pos != SameTails[i].getBlock()->end() && "Reached BB end within common tail"
) ? static_cast<void> (0) : __assert_fail ("Pos != SameTails[i].getBlock()->end() && \"Reached BB end within common tail\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 907, __PRETTY_FUNCTION__))
        "Reached BB end within common tail")((Pos != SameTails[i].getBlock()->end() && "Reached BB end within common tail"
) ? static_cast<void> (0) : __assert_fail ("Pos != SameTails[i].getBlock()->end() && \"Reached BB end within common tail\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 907, __PRETTY_FUNCTION__));
    while (!countsAsInstruction(*Pos)) {
      ++Pos;
      assert(Pos != SameTails[i].getBlock()->end() &&((Pos != SameTails[i].getBlock()->end() && "Reached BB end within common tail"
) ? static_cast<void> (0) : __assert_fail ("Pos != SameTails[i].getBlock()->end() && \"Reached BB end within common tail\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 911, __PRETTY_FUNCTION__))
          "Reached BB end within common tail")((Pos != SameTails[i].getBlock()->end() && "Reached BB end within common tail"
) ? static_cast<void> (0) : __assert_fail ("Pos != SameTails[i].getBlock()->end() && \"Reached BB end within common tail\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 911, __PRETTY_FUNCTION__));
    }
    assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!")((MI.isIdenticalTo(*Pos) && "Expected matching MIIs!"
) ? static_cast<void> (0) : __assert_fail ("MI.isIdenticalTo(*Pos) && \"Expected matching MIIs!\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 913, __PRETTY_FUNCTION__));
    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 (unsigned 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);
}
943}

945// See if any of the blocks in MergePotentials (which all have SuccBB as a
946// successor, or all have no successor if it is null) can be tail-merged.
947// If there is a successor, any blocks in MergePotentials that are not
948// tail-merged and are not immediately before Succ must have an unconditional
949// branch to Succ added (but the predecessor/successor lists need no
950// adjustment). The lone predecessor of Succ that falls through into Succ,
951// if any, is given in PredBB.
952// MinCommonTailLength - Except for the special cases below, tail-merge if
953// there are at least this many instructions in common.
954bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
                                    MachineBasicBlock *PredBB,
                                    unsigned MinCommonTailLength) {
bool MadeChange = false;

LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
    dbgs() << "\nTryTailMergeBlocks: ";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
    for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) dbgs()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
    << printMBBReference(*MergePotentials[i].getBlock())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
    << (i == e - 1 ? "" : ", ");do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
    dbgs() << "\n"; if (SuccBB) {do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
      dbgs() << "  with successor " << printMBBReference(*SuccBB) << '\n';do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
      if (PredBB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
        dbgs() << "  which has fall-through from "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
               << printMBBReference(*PredBB) << "\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
    } dbgs() << "Looking for common tails of at least "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
             << MinCommonTailLength << " instruction"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false)
             << (MinCommonTailLength == 1 ? "" : "s") << '\n';)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { 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';; } } while (false);

// 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 not the entry
  // block, 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())
    commonTailIndex = 1;
  else if (SameTails.size() == 2 &&
           SameTails[1].getBlock()->isLayoutSuccessor(
                                                   SameTails[0].getBlock()) &&
           SameTails[0].tailIsWholeBlock())
    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 && 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)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\nUsing common tail in "
 << printMBBReference(*MBB) << " for "; } } while
 (false)
                    << " for ")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\nUsing common tail in "
 << printMBBReference(*MBB) << " for "; } } while
 (false);
  for (unsigned int i=0, e = SameTails.size(); i != e; ++i) {
    if (commonTailIndex == i)
      continue;
    LLVM_DEBUG(dbgs() << printMBBReference(*SameTails[i].getBlock())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << printMBBReference(*SameTails
[i].getBlock()) << (i == e - 1 ? "" : ", "); } } while (
false)
                      << (i == e - 1 ? "" : ", "))do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << printMBBReference(*SameTails
[i].getBlock()) << (i == e - 1 ? "" : ", "); } } while (
false);
    // 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")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\n"; } } while (false);
  // 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;
1069}

1071bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
bool MadeChange = false;
if (!EnableTailMerge) return MadeChange;
10
←
Assuming the condition is false→
11
←
Taking false branch→

// First find blocks with no successors.
// Block placement does not create new tail merging opportunities for these
// blocks.
if (!AfterBlockPlacement) {
12
←
Assuming the condition is false→
13
←
Taking false branch→
  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();
14
←
Loop condition is true.  Entering loop body→
     I != E; ++I) {
  if (I->pred_size() < 2) continue;
15
←
Assuming the condition is false→
16
←
Taking false branch→
  SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
  MachineBasicBlock *IBB = &*I;
  MachineBasicBlock *PredBB = &*std::prev(I);
  MergePotentials.clear();
  MachineLoop *ML;
17
←
'ML' declared without an initial value→

  // 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) {
18
←
Assuming the condition is false→
    ML = MLI->getLoopFor(IBB);
    if (ML && IBB == ML->getHeader())
      continue;
  }

  for (MachineBasicBlock *PBB : I->predecessors()) {
    if (MergePotentials.size() == TailMergeThreshold)
19
←
Assuming the condition is false→
20
←
Taking false branch→
34
←
Assuming the condition is false→
35
←
Taking false branch→
      break;

    if (TriedMerging.count(PBB))
21
←
Assuming the condition is false→
22
←
Taking false branch→
36
←
Assuming the condition is false→
37
←
Taking false branch→
      continue;

    // Skip blocks that loop to themselves, can't tail merge these.
    if (PBB == IBB)
23
←
Assuming 'PBB' is not equal to 'IBB'→
24
←
Taking false branch→
38
←
Assuming 'PBB' is not equal to 'IBB'→
39
←
Taking false branch→
      continue;

    // Visit each predecessor only once.
    if (!UniquePreds.insert(PBB).second)
25
←
Assuming the condition is false→
26
←
Taking false branch→
40
←
Assuming the condition is false→
41
←
Taking false branch→
      continue;

    // Skip blocks which may jump to a landing pad. Can't tail merge these.
    if (PBB->hasEHPadSuccessor())
27
←
Assuming the condition is false→
28
←
Taking false branch→
42
←
Assuming the condition is false→
43
←
Taking false branch→
      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)
44
←
Assuming the condition is true→
45
←
Assuming the condition is true→
46
←
Taking true branch→
      if (ML != MLI->getLoopFor(PBB))
47
←
The left operand of '!=' is a garbage value
        continue;

    MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
    SmallVector<MachineOperand, 4> Cond;
    if (!TII->analyzeBranch(*PBB, TBB, FBB, Cond, true)) {
29
←
Assuming the condition is true→
30
←
Taking true branch→
      // 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) {
31
←
Assuming 'TBB' is not equal to 'IBB'→
32
←
Taking false branch→
        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)) {
33
←
Assuming 'TBB' is null→
        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;
1217}

1219void 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);
  }
}
1261}

1263//===----------------------------------------------------------------------===//
1264//  Branch Optimization
1265//===----------------------------------------------------------------------===//

1267bool 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;
1289}

1291// Blocks should be considered empty if they contain only debug info;
1292// else the debug info would affect codegen.
1293static bool IsEmptyBlock(MachineBasicBlock *MBB) {
return MBB->getFirstNonDebugInstr() == MBB->end();
1295}

1297// Blocks with only debug info and branches should be considered the same
1298// as blocks with only branches.
1299static bool IsBranchOnlyBlock(MachineBasicBlock *MBB) {
MachineBasicBlock::iterator I = MBB->getFirstNonDebugInstr();
assert(I != MBB->end() && "empty block!")((I != MBB->end() && "empty block!") ? static_cast
<void> (0) : __assert_fail ("I != MBB->end() && \"empty block!\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 1301, __PRETTY_FUNCTION__));
return I->isBranch();
1303}

1305/// IsBetterFallthrough - Return true if it would be clearly better to
1306/// fall-through to MBB1 than to fall through into MBB2.  This has to return
1307/// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will
1308/// result in infinite loops.
1309static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
                              MachineBasicBlock *MBB2) {
// 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();
1326}

1328/// getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch
1329/// instructions on the block.
1330static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) {
MachineBasicBlock::iterator I = MBB.getLastNonDebugInstr();
if (I != MBB.end() && I->isBranch())
  return I->getDebugLoc();
return DebugLoc();
1335}

1337static 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: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "Copied debug entity from empty block to pred: "
 << MI; } } while (false)
                      << MI)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "Copied debug entity from empty block to pred: "
 << MI; } } while (false);
  }
1347}

1349static 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: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "Copied debug entity from empty block to succ: "
 << MI; } } while (false)
                      << MI)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "Copied debug entity from empty block to succ: "
 << MI; } } while (false);
  }
1359}

1361// Try to salvage DBG_VALUE instructions from an otherwise empty block. If such
1362// a basic block is removed we would lose the debug information unless we have
1363// copied the information to a predecessor/successor.
1364//
1365// TODO: This function only handles some simple cases. An alternative would be
1366// to run a heavier analysis, such as the LiveDebugValues pass, before we do
1367// branch folding.
1368static void salvageDebugInfoFromEmptyBlock(const TargetInstrInfo *TII,
                                         MachineBasicBlock &MBB) {
assert(IsEmptyBlock(&MBB) && "Expected an empty block (except debug info).")((IsEmptyBlock(&MBB) && "Expected an empty block (except debug info)."
) ? static_cast<void> (0) : __assert_fail ("IsEmptyBlock(&MBB) && \"Expected an empty block (except debug info).\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 1370, __PRETTY_FUNCTION__));
// 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);
1382}

1384bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
bool MadeChange = false;
MachineFunction &MF = *MBB->getParent();
1387ReoptimizeBlock:

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())((MBBEHScope != EHScopeMembership.end()) ? static_cast<void
> (0) : __assert_fail ("MBBEHScope != EHScopeMembership.end()"
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 1396, __PRETTY_FUNCTION__));
  auto FallThroughEHScope = EHScopeMembership.find(&*FallThrough);
  assert(FallThroughEHScope != EHScopeMembership.end())((FallThroughEHScope != EHScopeMembership.end()) ? static_cast
<void> (0) : __assert_fail ("FallThroughEHScope != EHScopeMembership.end()"
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 1398, __PRETTY_FUNCTION__));
  SameEHScope = MBBEHScope->second == FallThroughEHScope->second;
}

// 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 CFG for the prior block has extra edges, remove them.
  MadeChange |= PrevBB.CorrectExtraCFGEdges(PriorTBB, PriorFBB,
                                            !PriorCond.empty());

  // 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: " << PrevBBdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\nMerging into block: "
 << PrevBB << "From MBB: " << *MBB; } } while
 (false)
                      << "From MBB: " << *MBB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\nMerging into block: "
 << PrevBB << "From MBB: " << *MBB; } } while
 (false);
    // Remove redundant DBG_VALUEs first.
    if (PrevBB.begin() != PrevBB.end()) {
      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.succ_empty()) ? static_cast<void> (0) : __assert_fail
 ("PrevBB.succ_empty()", "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 1492, __PRETTY_FUNCTION__));
    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: " << *MBBdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\nMoving MBB: " <<
 *MBB << "To make fallthrough to: " << *PriorTBB <<
 "\n"; } } while (false)
                          << "To make fallthrough to: " << *PriorTBB << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("branch-folder")) { dbgs() << "\nMoving MBB: " <<
 *MBB << "To make fallthrough to: " << *PriorTBB <<
 "\n"; } } while (false);

        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;
      }
    }
  }
}

if (!IsEmptyBlock(MBB) && MBB->pred_size() == 1 &&
    MF.getFunction().hasOptSize()) {
  // 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.
  }
}

// Analyze the branch in the current block.
MachineBasicBlock *CurTBB = nullptr, *CurFBB = nullptr;
SmallVector<MachineOperand, 4> CurCond;
bool CurUnAnalyzable =
    TII->analyzeBranch(*MBB, CurTBB, CurFBB, CurCond, true);
if (!CurUnAnalyzable) {
  // If the CFG for the prior block has extra edges, remove them.
  MadeChange |= MBB->CorrectExtraCFGEdges(CurTBB, CurFBB, !CurCond.empty());

  // 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 &&((PriorCond.empty() && !PriorFBB && "Bad branch analysis"
) ? static_cast<void> (0) : __assert_fail ("PriorCond.empty() && !PriorFBB && \"Bad branch analysis\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 1672, __PRETTY_FUNCTION__))
                   "Bad branch analysis")((PriorCond.empty() && !PriorFBB && "Bad branch analysis"
) ? static_cast<void> (0) : __assert_fail ("PriorCond.empty() && !PriorFBB && \"Bad branch analysis\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 1672, __PRETTY_FUNCTION__));
            PriorTBB = MBB;
          } else {
            assert(!PriorFBB && "Machine CFG out of date!")((!PriorFBB && "Machine CFG out of date!") ? static_cast
<void> (0) : __assert_fail ("!PriorFBB && \"Machine CFG out of date!\""
, "/build/llvm-toolchain-snapshot-9~svn362543/lib/CodeGen/BranchFolding.cpp"
, 1675, __PRETTY_FUNCTION__));
            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 (and fix the CFG).
            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;
              PMBB->CorrectExtraCFGEdges(NewCurTBB, nullptr, false);
            }
          }
        }

        // 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, 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) &&
          (!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 all successors to see if we can move this block before it.
    for (MachineBasicBlock *SuccBB : MBB->successors()) {
      // 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,
      // and if the successor isn't an EH destination, we can arrange for the
      // fallthrough to happen.
      if (SuccBB != MBB && &*SuccPrev != MBB &&
          !SuccPrev->canFallThrough() && !CurUnAnalyzable &&
          !SuccBB->isEHPad()) {
        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;
1819}

1821//===----------------------------------------------------------------------===//
1822//  Hoist Common Code
1823//===----------------------------------------------------------------------===//

1825bool 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;
1833}

1835/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
1836/// its 'true' successor.
1837static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
                                       MachineBasicBlock *TrueBB) {
for (MachineBasicBlock *SuccBB : BB->successors())
  if (SuccBB != TrueBB)
    return SuccBB;
return nullptr;
1843}

1845template <class Container>
1846static void addRegAndItsAliases(unsigned Reg, const TargetRegisterInfo *TRI,
                              Container &Set) {
if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
  for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
    Set.insert(*AI);
} else {
  Set.insert(Reg);
}
1854}

1856/// findHoistingInsertPosAndDeps - Find the location to move common instructions
1857/// in successors to. The location is usually just before the terminator,
1858/// however if the terminator is a conditional branch and its previous
1859/// instruction is the flag setting instruction, the previous instruction is
1860/// the preferred location. This function also gathers uses and defs of the
1861/// instructions from the insertion point to the end of the block. The data is
1862/// used by HoistCommonCodeInSuccs to ensure safety.
1863static
1864MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB,
                                                const TargetInstrInfo *TII,
                                                const TargetRegisterInfo *TRI,
                                                SmallSet<unsigned,4> &Uses,
                                                SmallSet<unsigned,4> &Defs) {
MachineBasicBlock::iterator Loc = MBB->getFirstTerminator();
if (!TII->isUnpredicatedTerminator(*Loc))
  return MBB->end();

for (const MachineOperand &MO : Loc->operands()) {
  if (!MO.isReg())
    continue;
  unsigned 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 =
  skipDebugInstructionsBackward(std::prev(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;
  unsigned 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;
  unsigned Reg = MO.getReg();
  if (!Reg)
    continue;
  if (MO.isUse()) {
    addRegAndItsAliases(Reg, TRI, Uses);
  } else {
    if (Uses.erase(Reg)) {
      if (TargetRegisterInfo::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;
1959}

1961bool 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<unsigned, 4> Uses, Defs;
MachineBasicBlock::iterator Loc =
  findHoistingInsertPosAndDeps(MBB, TII, TRI, Uses, Defs);
if (Loc == MBB->end())
  return false;

bool HasDups = false;
SmallSet<unsigned, 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;
    unsigned 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;
    unsigned Reg = MO.getReg();
    if (!Reg)
      continue;
    if (!AllDefsSet.count(Reg)) {
      continue;
    }
    if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
      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;
    unsigned Reg = MO.getReg();
    if (!Reg || TargetRegisterInfo::isVirtualRegister(Reg))
      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;
2108}