Index: lib/Target/X86/CMakeLists.txt =================================================================== --- lib/Target/X86/CMakeLists.txt +++ lib/Target/X86/CMakeLists.txt @@ -27,6 +27,7 @@ X86CallingConv.cpp X86CallLowering.cpp X86CmovConversion.cpp + X86CondBrFolding.cpp X86DomainReassignment.cpp X86ExpandPseudo.cpp X86FastISel.cpp Index: lib/Target/X86/X86.h =================================================================== --- lib/Target/X86/X86.h +++ lib/Target/X86/X86.h @@ -75,6 +75,9 @@ /// Return a pass that transforms setcc + movzx pairs into xor + setcc. FunctionPass *createX86FixupSetCC(); +/// Return a pass that folds conditional branch jumps. +FunctionPass *createX86CondBrFolding(); + /// Return a pass that avoids creating store forward block issues in the hardware. FunctionPass *createX86AvoidStoreForwardingBlocks(); Index: lib/Target/X86/X86CondBrFolding.cpp =================================================================== --- /dev/null +++ lib/Target/X86/X86CondBrFolding.cpp @@ -0,0 +1,576 @@ +//===---- 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/DenseMap.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"); + +struct TargetMBBInfo; + +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(); + } + +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 { + TargetMBBInfo(MachineBasicBlock &MBB) : MBB(MBB) {} + MachineBasicBlock &MBB; + MachineBasicBlock *TBB; + MachineBasicBlock *FBB; + MachineInstr *BrInstr; + MachineInstr *CmpInstr; + X86::CondCode BranchCode; + unsigned SrcReg; + int CmpValue; + bool Modified; + bool CmpBrOnly; + + bool analyzeMBB(); + static bool analyzeCompare(const MachineInstr &MI, unsigned &SrcReg, + int &CmpValue); +}; + +// Analyze instruction that generates CondCode and extract information. +bool TargetMBBInfo::analyzeCompare(const MachineInstr &MI, unsigned &SrcReg, + int &CmpValue) { + int SrcRegIndex = 0; + int ValueIndex = 0; + switch (MI.getOpcode()) { + // TODO: handle test. + 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(); + if (!MI.getOperand(ValueIndex).isImm()) + return false; + 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 should has a sequence of +// Brand_instr, +// CondBr, +// UnCondBr. +// Return true if MBB is a valid candidate and false otherwise. +bool TargetMBBInfo::analyzeMBB() { + if (MBB.succ_size() != 2) + return false; + + CmpBrOnly = true; + FBB = TBB = nullptr; + CmpInstr = nullptr; + X86::CondCode CC; + MachineBasicBlock::iterator I = MBB.end(); + while (I != MBB.begin()) { + --I; + if (I->isDebugValue()) + continue; + if (I->getOpcode() == X86::JMP_1) { + if (FBB) + return false; + FBB = I->getOperand(0).getMBB(); + continue; + } + if (I->isBranch()) { + if (TBB) + return false; + CC = X86::getCondFromBranchOpc(I->getOpcode()); + switch (CC) { + default: + return false; + 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 false; + CmpInstr = &*I; + continue; + } + CmpBrOnly = false; + break; + } + + if (!TBB || !FBB || !CmpInstr) + return false; + + // 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 false; + CC = X86::COND_L; + CmpValue += 1; + Modified = true; + break; + case X86::COND_GE: + if (CmpValue == INT_MIN) + return false; + CC = X86::COND_G; + CmpValue -= 1; + Modified = true; + break; + default: + Modified = false; + break; + } + BranchCode = CC; + return true; +} + +// 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; + DenseMap> MBBInfos; + SmallVector RemoveList; + + void optimizeCondBr(MachineBasicBlock &MBB, + SmallVectorImpl &BranchPath); + void fixBranchProb(MachineBasicBlock *NextMBB, MachineBasicBlock *RootMBB, + SmallVectorImpl &BranchPath); + void replaceBrDest(MachineBasicBlock *MBB, MachineBasicBlock *OrigDest, + MachineBasicBlock *NewDest); + void fixupModifiedCond(MachineBasicBlock *MBB); +}; + +// 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. +static bool findPath(MachineBasicBlock *MBB, + const DenseMap> &MBBInfos, + SmallVectorImpl &BranchPath) { + TargetMBBInfo *MBBInfo = &*(MBBInfos.find(MBB)->second.get()); + int CmpValue = MBBInfo->CmpValue; + assert(MBBInfo); + + MachineBasicBlock *PredMBB = *MBB->pred_begin(); + MachineBasicBlock *SaveMBB = MBB; + while (PredMBB) { + TargetMBBInfo *PredMBBInfo = &*(MBBInfos.find(PredMBB)->second.get()); + 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 = &*(MBBInfos.find(MBB)->second.get()); + 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 = &*(MBBInfos.find(MBB)->second.get()); + 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 &BranchPath) { + + X86::CondCode CC; + TargetMBBInfo *MBBInfo = &*(MBBInfos.find(&MBB)->second.get()); + MachineBasicBlock *TargetMBB = MBBInfo->TBB; + assert(MBBInfo); + 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 = &*(MBBInfos.find(PredMBB)->second.get()); + assert(PredMBBInfo); + 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 = &*(MBBInfos.find(RootMBB)->second.get()); + assert(RootMBBInfo); + 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 CmpVlaue 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(); + } + + // Invalidate MBBInfo just in case. + MBBInfos.find(&MBB)->second = nullptr; + MBBInfos.find(RootMBB)->second = nullptr; + + // 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); + + 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. + for (auto &MBB : MF) { + auto MBBInfoP = llvm::make_unique(MBB); + if (!MBBInfoP->analyzeMBB()) { + MBBInfos.insert(std::make_pair(&MBB, nullptr)); + continue; + } + MBBInfos.insert(std::make_pair(&MBB, std::move(MBBInfoP))); + } + + for (auto &MBB : MF) { + auto It = MBBInfos.find(&MBB); + TargetMBBInfo *MBBInfo = &(*It->second.get()); + if (!MBBInfo || !MBBInfo->CmpBrOnly) + continue; + if (MBB.pred_size() != 1) + continue; + LLVM_DEBUG(dbgs() << "Work on MBB." << MBB.getNumber() + << " CmpValue: " << MBBInfo->CmpValue << "\n"); + SmallVector BranchPath; + if (!findPath(&MBB, MBBInfos, 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 = &*(MBBInfos.find(PMBB)->second.get()); + 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; +} +bool X86CondBrFoldingPass::runOnMachineFunction(MachineFunction &MF) { + const X86InstrInfo *TII; + const MachineBranchProbabilityInfo *MBPI; + TII = MF.getSubtarget().getInstrInfo(); + MBPI = &getAnalysis(); + + X86CondBrFolding CondBr(TII, MBPI, MF); + return CondBr.optimize(); +} Index: lib/Target/X86/X86TargetMachine.cpp =================================================================== --- lib/Target/X86/X86TargetMachine.cpp +++ lib/Target/X86/X86TargetMachine.cpp @@ -54,6 +54,11 @@ cl::desc("Enable the machine combiner pass"), cl::init(true), cl::Hidden); +static cl::opt EnableCondBrFoldingPass("x86-condbr-folding", + cl::desc("Enable the conditional branch " + "folding pass"), + cl::init(true), cl::Hidden); + namespace llvm { void initializeWinEHStatePassPass(PassRegistry &); @@ -447,6 +452,8 @@ } bool X86PassConfig::addILPOpts() { + if (EnableCondBrFoldingPass) + addPass(createX86CondBrFolding()); addPass(&EarlyIfConverterID); if (EnableMachineCombinerPass) addPass(&MachineCombinerID); Index: test/CodeGen/X86/2007-02-16-BranchFold.ll =================================================================== --- test/CodeGen/X86/2007-02-16-BranchFold.ll +++ test/CodeGen/X86/2007-02-16-BranchFold.ll @@ -1,5 +1,5 @@ ; PR 1200 -; RUN: llc < %s -enable-tail-merge=0 | not grep jmp +; RUN: llc < %s -enable-tail-merge=0 -x86-condbr-folding=false | not grep jmp ; ModuleID = '' target datalayout = "e-p:32:32" Index: test/CodeGen/X86/O3-pipeline.ll =================================================================== --- test/CodeGen/X86/O3-pipeline.ll +++ test/CodeGen/X86/O3-pipeline.ll @@ -70,6 +70,7 @@ ; CHECK-NEXT: Merge disjoint stack slots ; CHECK-NEXT: Local Stack Slot Allocation ; CHECK-NEXT: Remove dead machine instructions +; CHECK-NEXT: X86 CondBr Folding ; CHECK-NEXT: MachineDominator Tree Construction ; CHECK-NEXT: Machine Natural Loop Construction ; CHECK-NEXT: Machine Trace Metrics Index: test/CodeGen/X86/condbr_if.ll =================================================================== --- /dev/null +++ test/CodeGen/X86/condbr_if.ll @@ -0,0 +1,157 @@ +; RUN: llc -mtriple=x86_64-linux-gnu %s -o - -verify-machineinstrs | FileCheck %s + +define dso_local i32 @length2_1(i32) { + %2 = icmp slt i32 %0, 3 + br i1 %2, label %3, label %5 + +;