Recommit r343993: [X86] condition branches folding for three-way conditional codes
Fix the memory issue exposed by sanitizer.
llvm-svn: 344085
diff --git a/llvm/lib/Target/X86/X86CondBrFolding.cpp b/llvm/lib/Target/X86/X86CondBrFolding.cpp
new file mode 100644
index 0000000..9a5ae70
--- /dev/null
+++ b/llvm/lib/Target/X86/X86CondBrFolding.cpp
@@ -0,0 +1,579 @@
+//===---- X86CondBrFolding.cpp - optimize conditional branches ------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// This file defines a pass that optimizes condition branches on x86 by taking
+// advantage of the three-way conditional code generated by compare
+// instructions.
+// Currently, it tries to hoisting EQ and NE conditional branch to a dominant
+// conditional branch condition where the same EQ/NE conditional code is
+// computed. An example:
+// bb_0:
+// cmp %0, 19
+// jg bb_1
+// jmp bb_2
+// bb_1:
+// cmp %0, 40
+// jg bb_3
+// jmp bb_4
+// bb_4:
+// cmp %0, 20
+// je bb_5
+// jmp bb_6
+// Here we could combine the two compares in bb_0 and bb_4 and have the
+// following code:
+// bb_0:
+// cmp %0, 20
+// jg bb_1
+// jl bb_2
+// jmp bb_5
+// bb_1:
+// cmp %0, 40
+// jg bb_3
+// jmp bb_6
+// For the case of %0 == 20 (bb_5), we eliminate two jumps, and the control
+// height for bb_6 is also reduced. bb_4 is gone after the optimization.
+//
+// There are plenty of this code patterns, especially from the switch case
+// lowing where we generate compare of "pivot-1" for the inner nodes in the
+// binary search tree.
+//===----------------------------------------------------------------------===//
+
+#include "X86.h"
+#include "X86InstrInfo.h"
+#include "X86Subtarget.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/BranchProbability.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "x86-condbr-folding"
+
+STATISTIC(NumFixedCondBrs, "Number of x86 condbr folded");
+
+namespace {
+class X86CondBrFoldingPass : public MachineFunctionPass {
+public:
+ X86CondBrFoldingPass() : MachineFunctionPass(ID) {}
+
+ StringRef getPassName() const override { return "X86 CondBr Folding"; }
+
+ bool runOnMachineFunction(MachineFunction &MF) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ MachineFunctionPass::getAnalysisUsage(AU);
+ AU.addRequired<MachineBranchProbabilityInfo>();
+ }
+
+private:
+ static char ID;
+};
+
+char X86CondBrFoldingPass::ID = 0;
+} // namespace
+
+FunctionPass *llvm::createX86CondBrFolding() {
+ return new X86CondBrFoldingPass();
+}
+
+// A class the stores the auxiliary information for each MBB.
+struct TargetMBBInfo {
+ MachineBasicBlock *TBB;
+ MachineBasicBlock *FBB;
+ MachineInstr *BrInstr;
+ MachineInstr *CmpInstr;
+ X86::CondCode BranchCode;
+ unsigned SrcReg;
+ int CmpValue;
+ bool Modified;
+ bool CmpBrOnly;
+};
+
+// A class that optimizes the conditional branch by hoisting and merge CondCode.
+class X86CondBrFolding {
+public:
+ X86CondBrFolding(const X86InstrInfo *TII,
+ const MachineBranchProbabilityInfo *MBPI,
+ MachineFunction &MF)
+ : TII(TII), MBPI(MBPI), MF(MF) {}
+ bool optimize();
+
+private:
+ const X86InstrInfo *TII;
+ const MachineBranchProbabilityInfo *MBPI;
+ MachineFunction &MF;
+ std::vector<std::unique_ptr<TargetMBBInfo>> MBBInfos;
+ SmallVector<MachineBasicBlock *, 4> RemoveList;
+
+ void optimizeCondBr(MachineBasicBlock &MBB,
+ SmallVectorImpl<MachineBasicBlock *> &BranchPath);
+ void fixBranchProb(MachineBasicBlock *NextMBB, MachineBasicBlock *RootMBB,
+ SmallVectorImpl<MachineBasicBlock *> &BranchPath);
+ void replaceBrDest(MachineBasicBlock *MBB, MachineBasicBlock *OrigDest,
+ MachineBasicBlock *NewDest);
+ void fixupModifiedCond(MachineBasicBlock *MBB);
+ std::unique_ptr<TargetMBBInfo> analyzeMBB(MachineBasicBlock &MBB);
+ static bool analyzeCompare(const MachineInstr &MI, unsigned &SrcReg,
+ int &CmpValue);
+ bool findPath(MachineBasicBlock *MBB,
+ SmallVectorImpl<MachineBasicBlock *> &BranchPath);
+ TargetMBBInfo *getMBBInfo(MachineBasicBlock *MBB) const {
+ return MBBInfos[MBB->getNumber()].get();
+ }
+};
+
+// Find a valid path that we can reuse the CondCode.
+// The resulted path (if return true) is stored in BranchPath.
+// Return value:
+// false: is no valid path is found.
+// true: a valid path is found and the targetBB can be reached.
+bool X86CondBrFolding::findPath(
+ MachineBasicBlock *MBB, SmallVectorImpl<MachineBasicBlock *> &BranchPath) {
+ TargetMBBInfo *MBBInfo = getMBBInfo(MBB);
+ assert(MBBInfo && "Expecting a candidate MBB");
+ int CmpValue = MBBInfo->CmpValue;
+
+ MachineBasicBlock *PredMBB = *MBB->pred_begin();
+ MachineBasicBlock *SaveMBB = MBB;
+ while (PredMBB) {
+ TargetMBBInfo *PredMBBInfo = getMBBInfo(PredMBB);
+ if (!PredMBBInfo || PredMBBInfo->SrcReg != MBBInfo->SrcReg)
+ return false;
+
+ assert(SaveMBB == PredMBBInfo->TBB || SaveMBB == PredMBBInfo->FBB);
+ bool IsFalseBranch = (SaveMBB == PredMBBInfo->FBB);
+
+ X86::CondCode CC = PredMBBInfo->BranchCode;
+ assert(CC == X86::COND_L || CC == X86::COND_G || CC == X86::COND_E);
+ int PredCmpValue = PredMBBInfo->CmpValue;
+ bool ValueCmpTrue = ((CmpValue < PredCmpValue && CC == X86::COND_L) ||
+ (CmpValue > PredCmpValue && CC == X86::COND_G) ||
+ (CmpValue == PredCmpValue && CC == X86::COND_E));
+ // Check if both the result of value compare and the branch target match.
+ if (!(ValueCmpTrue ^ IsFalseBranch)) {
+ LLVM_DEBUG(dbgs() << "Dead BB detected!\n");
+ return false;
+ }
+
+ BranchPath.push_back(PredMBB);
+ // These are the conditions on which we could combine the compares.
+ if ((CmpValue == PredCmpValue) ||
+ (CmpValue == PredCmpValue - 1 && CC == X86::COND_L) ||
+ (CmpValue == PredCmpValue + 1 && CC == X86::COND_G))
+ return true;
+
+ // If PredMBB has more than on preds, or not a pure cmp and br, we bailout.
+ if (PredMBB->pred_size() != 1 || !PredMBBInfo->CmpBrOnly)
+ return false;
+
+ SaveMBB = PredMBB;
+ PredMBB = *PredMBB->pred_begin();
+ }
+ return false;
+}
+
+// Fix up any PHI node in the successor of MBB.
+static void fixPHIsInSucc(MachineBasicBlock *MBB, MachineBasicBlock *OldMBB,
+ MachineBasicBlock *NewMBB) {
+ if (NewMBB == OldMBB)
+ return;
+ for (auto MI = MBB->instr_begin(), ME = MBB->instr_end();
+ MI != ME && MI->isPHI(); ++MI)
+ for (unsigned i = 2, e = MI->getNumOperands() + 1; i != e; i += 2) {
+ MachineOperand &MO = MI->getOperand(i);
+ if (MO.getMBB() == OldMBB)
+ MO.setMBB(NewMBB);
+ }
+}
+
+// Utility function to set branch probability for edge MBB->SuccMBB.
+static inline bool setBranchProb(MachineBasicBlock *MBB,
+ MachineBasicBlock *SuccMBB,
+ BranchProbability Prob) {
+ auto MBBI = std::find(MBB->succ_begin(), MBB->succ_end(), SuccMBB);
+ if (MBBI == MBB->succ_end())
+ return false;
+ MBB->setSuccProbability(MBBI, Prob);
+ return true;
+}
+
+// Utility function to find the unconditional br instruction in MBB.
+static inline MachineBasicBlock::iterator
+findUncondBrI(MachineBasicBlock *MBB) {
+ return std::find_if(MBB->begin(), MBB->end(), [](MachineInstr &MI) -> bool {
+ return MI.getOpcode() == X86::JMP_1;
+ });
+}
+
+// Replace MBB's original successor, OrigDest, with NewDest.
+// Also update the MBBInfo for MBB.
+void X86CondBrFolding::replaceBrDest(MachineBasicBlock *MBB,
+ MachineBasicBlock *OrigDest,
+ MachineBasicBlock *NewDest) {
+ TargetMBBInfo *MBBInfo = getMBBInfo(MBB);
+ MachineInstr *BrMI;
+ if (MBBInfo->TBB == OrigDest) {
+ BrMI = MBBInfo->BrInstr;
+ unsigned JNCC = GetCondBranchFromCond(MBBInfo->BranchCode);
+ MachineInstrBuilder MIB =
+ BuildMI(*MBB, BrMI, MBB->findDebugLoc(BrMI), TII->get(JNCC))
+ .addMBB(NewDest);
+ MBBInfo->TBB = NewDest;
+ MBBInfo->BrInstr = MIB.getInstr();
+ } else { // Should be the unconditional jump stmt.
+ MachineBasicBlock::iterator UncondBrI = findUncondBrI(MBB);
+ BuildMI(*MBB, UncondBrI, MBB->findDebugLoc(UncondBrI), TII->get(X86::JMP_1))
+ .addMBB(NewDest);
+ MBBInfo->FBB = NewDest;
+ BrMI = &*UncondBrI;
+ }
+ fixPHIsInSucc(NewDest, OrigDest, MBB);
+ BrMI->eraseFromParent();
+ MBB->addSuccessor(NewDest);
+ setBranchProb(MBB, NewDest, MBPI->getEdgeProbability(MBB, OrigDest));
+ MBB->removeSuccessor(OrigDest);
+}
+
+// Change the CondCode and BrInstr according to MBBInfo.
+void X86CondBrFolding::fixupModifiedCond(MachineBasicBlock *MBB) {
+ TargetMBBInfo *MBBInfo = getMBBInfo(MBB);
+ if (!MBBInfo->Modified)
+ return;
+
+ MachineInstr *BrMI = MBBInfo->BrInstr;
+ X86::CondCode CC = MBBInfo->BranchCode;
+ MachineInstrBuilder MIB = BuildMI(*MBB, BrMI, MBB->findDebugLoc(BrMI),
+ TII->get(GetCondBranchFromCond(CC)))
+ .addMBB(MBBInfo->TBB);
+ BrMI->eraseFromParent();
+ MBBInfo->BrInstr = MIB.getInstr();
+
+ MachineBasicBlock::iterator UncondBrI = findUncondBrI(MBB);
+ BuildMI(*MBB, UncondBrI, MBB->findDebugLoc(UncondBrI), TII->get(X86::JMP_1))
+ .addMBB(MBBInfo->FBB);
+ MBB->erase(UncondBrI);
+ MBBInfo->Modified = false;
+}
+
+//
+// Apply the transformation:
+// RootMBB -1-> ... PredMBB -3-> MBB -5-> TargetMBB
+// \-2-> \-4-> \-6-> FalseMBB
+// ==>
+// RootMBB -1-> ... PredMBB -7-> FalseMBB
+// TargetMBB <-8-/ \-2-> \-4->
+//
+// Note that PredMBB and RootMBB could be the same.
+// And in the case of dead TargetMBB, we will not have TargetMBB and edge 8.
+//
+// There are some special handling where the RootMBB is COND_E in which case
+// we directly short-cycle the brinstr.
+//
+void X86CondBrFolding::optimizeCondBr(
+ MachineBasicBlock &MBB, SmallVectorImpl<MachineBasicBlock *> &BranchPath) {
+
+ X86::CondCode CC;
+ TargetMBBInfo *MBBInfo = getMBBInfo(&MBB);
+ assert(MBBInfo && "Expecting a candidate MBB");
+ MachineBasicBlock *TargetMBB = MBBInfo->TBB;
+ BranchProbability TargetProb = MBPI->getEdgeProbability(&MBB, MBBInfo->TBB);
+
+ // Forward the jump from MBB's predecessor to MBB's false target.
+ MachineBasicBlock *PredMBB = BranchPath.front();
+ TargetMBBInfo *PredMBBInfo = getMBBInfo(PredMBB);
+ assert(PredMBBInfo && "Expecting a candidate MBB");
+ if (PredMBBInfo->Modified)
+ fixupModifiedCond(PredMBB);
+ CC = PredMBBInfo->BranchCode;
+ // Don't do this if depth of BranchPath is 1 and PredMBB is of COND_E.
+ // We will short-cycle directly for this case.
+ if (!(CC == X86::COND_E && BranchPath.size() == 1))
+ replaceBrDest(PredMBB, &MBB, MBBInfo->FBB);
+
+ MachineBasicBlock *RootMBB = BranchPath.back();
+ TargetMBBInfo *RootMBBInfo = getMBBInfo(RootMBB);
+ assert(RootMBBInfo && "Expecting a candidate MBB");
+ if (RootMBBInfo->Modified)
+ fixupModifiedCond(RootMBB);
+ CC = RootMBBInfo->BranchCode;
+
+ if (CC != X86::COND_E) {
+ MachineBasicBlock::iterator UncondBrI = findUncondBrI(RootMBB);
+ // RootMBB: Cond jump to the original not-taken MBB.
+ X86::CondCode NewCC;
+ switch (CC) {
+ case X86::COND_L:
+ NewCC = X86::COND_G;
+ break;
+ case X86::COND_G:
+ NewCC = X86::COND_L;
+ break;
+ default:
+ llvm_unreachable("unexpected condtional code.");
+ }
+ BuildMI(*RootMBB, UncondBrI, RootMBB->findDebugLoc(UncondBrI),
+ TII->get(GetCondBranchFromCond(NewCC)))
+ .addMBB(RootMBBInfo->FBB);
+
+ // RootMBB: Jump to TargetMBB
+ BuildMI(*RootMBB, UncondBrI, RootMBB->findDebugLoc(UncondBrI),
+ TII->get(X86::JMP_1))
+ .addMBB(TargetMBB);
+ RootMBB->addSuccessor(TargetMBB);
+ fixPHIsInSucc(TargetMBB, &MBB, RootMBB);
+ RootMBB->erase(UncondBrI);
+ } else {
+ replaceBrDest(RootMBB, RootMBBInfo->TBB, TargetMBB);
+ }
+
+ // Fix RootMBB's CmpValue to MBB's CmpValue to TargetMBB. Don't set Imm
+ // directly. Move MBB's stmt to here as the opcode might be different.
+ if (RootMBBInfo->CmpValue != MBBInfo->CmpValue) {
+ MachineInstr *NewCmp = MBBInfo->CmpInstr;
+ NewCmp->removeFromParent();
+ RootMBB->insert(RootMBBInfo->CmpInstr, NewCmp);
+ RootMBBInfo->CmpInstr->eraseFromParent();
+ }
+
+ // Fix branch Probabilities.
+ auto fixBranchProb = [&](MachineBasicBlock *NextMBB) {
+ BranchProbability Prob;
+ for (auto &I : BranchPath) {
+ MachineBasicBlock *ThisMBB = I;
+ if (!ThisMBB->hasSuccessorProbabilities() ||
+ !ThisMBB->isSuccessor(NextMBB))
+ break;
+ Prob = MBPI->getEdgeProbability(ThisMBB, NextMBB);
+ if (Prob.isUnknown())
+ break;
+ TargetProb = Prob * TargetProb;
+ Prob = Prob - TargetProb;
+ setBranchProb(ThisMBB, NextMBB, Prob);
+ if (ThisMBB == RootMBB) {
+ setBranchProb(ThisMBB, TargetMBB, TargetProb);
+ }
+ ThisMBB->normalizeSuccProbs();
+ if (ThisMBB == RootMBB)
+ break;
+ NextMBB = ThisMBB;
+ }
+ return true;
+ };
+ if (CC != X86::COND_E && !TargetProb.isUnknown())
+ fixBranchProb(MBBInfo->FBB);
+
+ if (CC != X86::COND_E)
+ RemoveList.push_back(&MBB);
+
+ // Invalidate MBBInfo just in case.
+ MBBInfos[MBB.getNumber()] = nullptr;
+ MBBInfos[RootMBB->getNumber()] = nullptr;
+
+ LLVM_DEBUG(dbgs() << "After optimization:\nRootMBB is: " << *RootMBB << "\n");
+ if (BranchPath.size() > 1)
+ LLVM_DEBUG(dbgs() << "PredMBB is: " << *(BranchPath[0]) << "\n");
+}
+
+// Driver function for optimization: find the valid candidate and apply
+// the transformation.
+bool X86CondBrFolding::optimize() {
+ bool Changed = false;
+ LLVM_DEBUG(dbgs() << "***** X86CondBr Folding on Function: " << MF.getName()
+ << " *****\n");
+ // Setup data structures.
+ MBBInfos.resize(MF.getNumBlockIDs());
+ for (auto &MBB : MF)
+ MBBInfos[MBB.getNumber()] = analyzeMBB(MBB);
+
+ for (auto &MBB : MF) {
+ TargetMBBInfo *MBBInfo = getMBBInfo(&MBB);
+ if (!MBBInfo || !MBBInfo->CmpBrOnly)
+ continue;
+ if (MBB.pred_size() != 1)
+ continue;
+ LLVM_DEBUG(dbgs() << "Work on MBB." << MBB.getNumber()
+ << " CmpValue: " << MBBInfo->CmpValue << "\n");
+ SmallVector<MachineBasicBlock *, 4> BranchPath;
+ if (!findPath(&MBB, BranchPath))
+ continue;
+
+#ifndef NDEBUG
+ LLVM_DEBUG(dbgs() << "Found one path (len=" << BranchPath.size() << "):\n");
+ int Index = 1;
+ LLVM_DEBUG(dbgs() << "Target MBB is: " << MBB << "\n");
+ for (auto I = BranchPath.rbegin(); I != BranchPath.rend(); ++I, ++Index) {
+ MachineBasicBlock *PMBB = *I;
+ TargetMBBInfo *PMBBInfo = getMBBInfo(PMBB);
+ LLVM_DEBUG(dbgs() << "Path MBB (" << Index << " of " << BranchPath.size()
+ << ") is " << *PMBB);
+ LLVM_DEBUG(dbgs() << "CC=" << PMBBInfo->BranchCode
+ << " Val=" << PMBBInfo->CmpValue
+ << " CmpBrOnly=" << PMBBInfo->CmpBrOnly << "\n\n");
+ }
+#endif
+ optimizeCondBr(MBB, BranchPath);
+ Changed = true;
+ }
+ NumFixedCondBrs += RemoveList.size();
+ for (auto MBBI : RemoveList) {
+ for (auto *Succ : MBBI->successors())
+ MBBI->removeSuccessor(Succ);
+ MBBI->eraseFromParent();
+ }
+
+ return Changed;
+}
+
+// Analyze instructions that generate CondCode and extract information.
+bool X86CondBrFolding::analyzeCompare(const MachineInstr &MI, unsigned &SrcReg,
+ int &CmpValue) {
+ unsigned SrcRegIndex = 0;
+ unsigned ValueIndex = 0;
+ switch (MI.getOpcode()) {
+ // TODO: handle test instructions.
+ default:
+ return false;
+ case X86::CMP64ri32:
+ case X86::CMP64ri8:
+ case X86::CMP32ri:
+ case X86::CMP32ri8:
+ case X86::CMP16ri:
+ case X86::CMP16ri8:
+ case X86::CMP8ri:
+ SrcRegIndex = 0;
+ ValueIndex = 1;
+ break;
+ case X86::SUB64ri32:
+ case X86::SUB64ri8:
+ case X86::SUB32ri:
+ case X86::SUB32ri8:
+ case X86::SUB16ri:
+ case X86::SUB16ri8:
+ case X86::SUB8ri:
+ SrcRegIndex = 1;
+ ValueIndex = 2;
+ break;
+ }
+ SrcReg = MI.getOperand(SrcRegIndex).getReg();
+ assert(MI.getOperand(ValueIndex).isImm() && "Expecting Imm operand");
+ CmpValue = MI.getOperand(ValueIndex).getImm();
+ return true;
+}
+
+// Analyze a candidate MBB and set the extract all the information needed.
+// The valid candidate will have two successors.
+// It also should have a sequence of
+// Branch_instr,
+// CondBr,
+// UnCondBr.
+// Return TargetMBBInfo if MBB is a valid candidate and nullptr otherwise.
+std::unique_ptr<TargetMBBInfo>
+X86CondBrFolding::analyzeMBB(MachineBasicBlock &MBB) {
+ MachineBasicBlock *TBB;
+ MachineBasicBlock *FBB;
+ MachineInstr *BrInstr;
+ MachineInstr *CmpInstr;
+ X86::CondCode CC;
+ unsigned SrcReg;
+ int CmpValue;
+ bool Modified;
+ bool CmpBrOnly;
+
+ if (MBB.succ_size() != 2)
+ return nullptr;
+
+ CmpBrOnly = true;
+ FBB = TBB = nullptr;
+ CmpInstr = nullptr;
+ MachineBasicBlock::iterator I = MBB.end();
+ while (I != MBB.begin()) {
+ --I;
+ if (I->isDebugValue())
+ continue;
+ if (I->getOpcode() == X86::JMP_1) {
+ if (FBB)
+ return nullptr;
+ FBB = I->getOperand(0).getMBB();
+ continue;
+ }
+ if (I->isBranch()) {
+ if (TBB)
+ return nullptr;
+ CC = X86::getCondFromBranchOpc(I->getOpcode());
+ switch (CC) {
+ default:
+ return nullptr;
+ case X86::COND_E:
+ case X86::COND_L:
+ case X86::COND_G:
+ case X86::COND_NE:
+ case X86::COND_LE:
+ case X86::COND_GE:
+ break;
+ }
+ TBB = I->getOperand(0).getMBB();
+ BrInstr = &*I;
+ continue;
+ }
+ if (analyzeCompare(*I, SrcReg, CmpValue)) {
+ if (CmpInstr)
+ return nullptr;
+ CmpInstr = &*I;
+ continue;
+ }
+ CmpBrOnly = false;
+ break;
+ }
+
+ if (!TBB || !FBB || !CmpInstr)
+ return nullptr;
+
+ // Simplify CondCode. Note this is only to simplify the findPath logic
+ // and will not change the instruction here.
+ switch (CC) {
+ case X86::COND_NE:
+ CC = X86::COND_E;
+ std::swap(TBB, FBB);
+ Modified = true;
+ break;
+ case X86::COND_LE:
+ if (CmpValue == INT_MAX)
+ return nullptr;
+ CC = X86::COND_L;
+ CmpValue += 1;
+ Modified = true;
+ break;
+ case X86::COND_GE:
+ if (CmpValue == INT_MIN)
+ return nullptr;
+ CC = X86::COND_G;
+ CmpValue -= 1;
+ Modified = true;
+ break;
+ default:
+ Modified = false;
+ break;
+ }
+ return llvm::make_unique<TargetMBBInfo>(TargetMBBInfo{
+ TBB, FBB, BrInstr, CmpInstr, CC, SrcReg, CmpValue, Modified, CmpBrOnly});
+}
+
+bool X86CondBrFoldingPass::runOnMachineFunction(MachineFunction &MF) {
+ const X86Subtarget &ST = MF.getSubtarget<X86Subtarget>();
+ if (!ST.threewayBranchProfitable())
+ return false;
+ const X86InstrInfo *TII = ST.getInstrInfo();
+ const MachineBranchProbabilityInfo *MBPI =
+ &getAnalysis<MachineBranchProbabilityInfo>();
+
+ X86CondBrFolding CondBr(TII, MBPI, MF);
+ return CondBr.optimize();
+}