| //===-- PeepholeOptimizer.cpp - Peephole Optimizations --------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // Perform peephole optimizations on the machine code: |
| // |
| // - Optimize Extensions |
| // |
| // Optimization of sign / zero extension instructions. It may be extended to |
| // handle other instructions with similar properties. |
| // |
| // On some targets, some instructions, e.g. X86 sign / zero extension, may |
| // leave the source value in the lower part of the result. This optimization |
| // will replace some uses of the pre-extension value with uses of the |
| // sub-register of the results. |
| // |
| // - Optimize Comparisons |
| // |
| // Optimization of comparison instructions. For instance, in this code: |
| // |
| // sub r1, 1 |
| // cmp r1, 0 |
| // bz L1 |
| // |
| // If the "sub" instruction all ready sets (or could be modified to set) the |
| // same flag that the "cmp" instruction sets and that "bz" uses, then we can |
| // eliminate the "cmp" instruction. |
| // |
| // Another instance, in this code: |
| // |
| // sub r1, r3 | sub r1, imm |
| // cmp r3, r1 or cmp r1, r3 | cmp r1, imm |
| // bge L1 |
| // |
| // If the branch instruction can use flag from "sub", then we can replace |
| // "sub" with "subs" and eliminate the "cmp" instruction. |
| // |
| // - Optimize Bitcast pairs: |
| // |
| // v1 = bitcast v0 |
| // v2 = bitcast v1 |
| // = v2 |
| // => |
| // v1 = bitcast v0 |
| // = v0 |
| // |
| // - Optimize Loads: |
| // |
| // Loads that can be folded into a later instruction. A load is foldable |
| // if it loads to virtual registers and the virtual register defined has |
| // a single use. |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "peephole-opt" |
| #include "llvm/CodeGen/Passes.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/SmallSet.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/CodeGen/MachineDominators.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Target/TargetInstrInfo.h" |
| #include "llvm/Target/TargetRegisterInfo.h" |
| using namespace llvm; |
| |
| // Optimize Extensions |
| static cl::opt<bool> |
| Aggressive("aggressive-ext-opt", cl::Hidden, |
| cl::desc("Aggressive extension optimization")); |
| |
| static cl::opt<bool> |
| DisablePeephole("disable-peephole", cl::Hidden, cl::init(false), |
| cl::desc("Disable the peephole optimizer")); |
| |
| STATISTIC(NumReuse, "Number of extension results reused"); |
| STATISTIC(NumBitcasts, "Number of bitcasts eliminated"); |
| STATISTIC(NumCmps, "Number of compares eliminated"); |
| STATISTIC(NumImmFold, "Number of move immediate folded"); |
| STATISTIC(NumLoadFold, "Number of loads folded"); |
| STATISTIC(NumSelects, "Number of selects optimized"); |
| |
| namespace { |
| class PeepholeOptimizer : public MachineFunctionPass { |
| const TargetMachine *TM; |
| const TargetInstrInfo *TII; |
| MachineRegisterInfo *MRI; |
| MachineDominatorTree *DT; // Machine dominator tree |
| |
| public: |
| static char ID; // Pass identification |
| PeepholeOptimizer() : MachineFunctionPass(ID) { |
| initializePeepholeOptimizerPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| virtual bool runOnMachineFunction(MachineFunction &MF); |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.setPreservesCFG(); |
| MachineFunctionPass::getAnalysisUsage(AU); |
| if (Aggressive) { |
| AU.addRequired<MachineDominatorTree>(); |
| AU.addPreserved<MachineDominatorTree>(); |
| } |
| } |
| |
| private: |
| bool optimizeBitcastInstr(MachineInstr *MI, MachineBasicBlock *MBB); |
| bool optimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB); |
| bool optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB, |
| SmallPtrSet<MachineInstr*, 8> &LocalMIs); |
| bool optimizeSelect(MachineInstr *MI); |
| bool isMoveImmediate(MachineInstr *MI, |
| SmallSet<unsigned, 4> &ImmDefRegs, |
| DenseMap<unsigned, MachineInstr*> &ImmDefMIs); |
| bool foldImmediate(MachineInstr *MI, MachineBasicBlock *MBB, |
| SmallSet<unsigned, 4> &ImmDefRegs, |
| DenseMap<unsigned, MachineInstr*> &ImmDefMIs); |
| bool isLoadFoldable(MachineInstr *MI, unsigned &FoldAsLoadDefReg); |
| }; |
| } |
| |
| char PeepholeOptimizer::ID = 0; |
| char &llvm::PeepholeOptimizerID = PeepholeOptimizer::ID; |
| INITIALIZE_PASS_BEGIN(PeepholeOptimizer, "peephole-opts", |
| "Peephole Optimizations", false, false) |
| INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) |
| INITIALIZE_PASS_END(PeepholeOptimizer, "peephole-opts", |
| "Peephole Optimizations", false, false) |
| |
| /// optimizeExtInstr - If instruction is a copy-like instruction, i.e. it reads |
| /// a single register and writes a single register and it does not modify the |
| /// source, and if the source value is preserved as a sub-register of the |
| /// result, then replace all reachable uses of the source with the subreg of the |
| /// result. |
| /// |
| /// Do not generate an EXTRACT that is used only in a debug use, as this changes |
| /// the code. Since this code does not currently share EXTRACTs, just ignore all |
| /// debug uses. |
| bool PeepholeOptimizer:: |
| optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB, |
| SmallPtrSet<MachineInstr*, 8> &LocalMIs) { |
| unsigned SrcReg, DstReg, SubIdx; |
| if (!TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx)) |
| return false; |
| |
| if (TargetRegisterInfo::isPhysicalRegister(DstReg) || |
| TargetRegisterInfo::isPhysicalRegister(SrcReg)) |
| return false; |
| |
| if (MRI->hasOneNonDBGUse(SrcReg)) |
| // No other uses. |
| return false; |
| |
| // Ensure DstReg can get a register class that actually supports |
| // sub-registers. Don't change the class until we commit. |
| const TargetRegisterClass *DstRC = MRI->getRegClass(DstReg); |
| DstRC = TM->getRegisterInfo()->getSubClassWithSubReg(DstRC, SubIdx); |
| if (!DstRC) |
| return false; |
| |
| // The ext instr may be operating on a sub-register of SrcReg as well. |
| // PPC::EXTSW is a 32 -> 64-bit sign extension, but it reads a 64-bit |
| // register. |
| // If UseSrcSubIdx is Set, SubIdx also applies to SrcReg, and only uses of |
| // SrcReg:SubIdx should be replaced. |
| bool UseSrcSubIdx = TM->getRegisterInfo()-> |
| getSubClassWithSubReg(MRI->getRegClass(SrcReg), SubIdx) != 0; |
| |
| // The source has other uses. See if we can replace the other uses with use of |
| // the result of the extension. |
| SmallPtrSet<MachineBasicBlock*, 4> ReachedBBs; |
| for (MachineRegisterInfo::use_nodbg_iterator |
| UI = MRI->use_nodbg_begin(DstReg), UE = MRI->use_nodbg_end(); |
| UI != UE; ++UI) |
| ReachedBBs.insert(UI->getParent()); |
| |
| // Uses that are in the same BB of uses of the result of the instruction. |
| SmallVector<MachineOperand*, 8> Uses; |
| |
| // Uses that the result of the instruction can reach. |
| SmallVector<MachineOperand*, 8> ExtendedUses; |
| |
| bool ExtendLife = true; |
| for (MachineRegisterInfo::use_nodbg_iterator |
| UI = MRI->use_nodbg_begin(SrcReg), UE = MRI->use_nodbg_end(); |
| UI != UE; ++UI) { |
| MachineOperand &UseMO = UI.getOperand(); |
| MachineInstr *UseMI = &*UI; |
| if (UseMI == MI) |
| continue; |
| |
| if (UseMI->isPHI()) { |
| ExtendLife = false; |
| continue; |
| } |
| |
| // Only accept uses of SrcReg:SubIdx. |
| if (UseSrcSubIdx && UseMO.getSubReg() != SubIdx) |
| continue; |
| |
| // It's an error to translate this: |
| // |
| // %reg1025 = <sext> %reg1024 |
| // ... |
| // %reg1026 = SUBREG_TO_REG 0, %reg1024, 4 |
| // |
| // into this: |
| // |
| // %reg1025 = <sext> %reg1024 |
| // ... |
| // %reg1027 = COPY %reg1025:4 |
| // %reg1026 = SUBREG_TO_REG 0, %reg1027, 4 |
| // |
| // The problem here is that SUBREG_TO_REG is there to assert that an |
| // implicit zext occurs. It doesn't insert a zext instruction. If we allow |
| // the COPY here, it will give us the value after the <sext>, not the |
| // original value of %reg1024 before <sext>. |
| if (UseMI->getOpcode() == TargetOpcode::SUBREG_TO_REG) |
| continue; |
| |
| MachineBasicBlock *UseMBB = UseMI->getParent(); |
| if (UseMBB == MBB) { |
| // Local uses that come after the extension. |
| if (!LocalMIs.count(UseMI)) |
| Uses.push_back(&UseMO); |
| } else if (ReachedBBs.count(UseMBB)) { |
| // Non-local uses where the result of the extension is used. Always |
| // replace these unless it's a PHI. |
| Uses.push_back(&UseMO); |
| } else if (Aggressive && DT->dominates(MBB, UseMBB)) { |
| // We may want to extend the live range of the extension result in order |
| // to replace these uses. |
| ExtendedUses.push_back(&UseMO); |
| } else { |
| // Both will be live out of the def MBB anyway. Don't extend live range of |
| // the extension result. |
| ExtendLife = false; |
| break; |
| } |
| } |
| |
| if (ExtendLife && !ExtendedUses.empty()) |
| // Extend the liveness of the extension result. |
| std::copy(ExtendedUses.begin(), ExtendedUses.end(), |
| std::back_inserter(Uses)); |
| |
| // Now replace all uses. |
| bool Changed = false; |
| if (!Uses.empty()) { |
| SmallPtrSet<MachineBasicBlock*, 4> PHIBBs; |
| |
| // Look for PHI uses of the extended result, we don't want to extend the |
| // liveness of a PHI input. It breaks all kinds of assumptions down |
| // stream. A PHI use is expected to be the kill of its source values. |
| for (MachineRegisterInfo::use_nodbg_iterator |
| UI = MRI->use_nodbg_begin(DstReg), UE = MRI->use_nodbg_end(); |
| UI != UE; ++UI) |
| if (UI->isPHI()) |
| PHIBBs.insert(UI->getParent()); |
| |
| const TargetRegisterClass *RC = MRI->getRegClass(SrcReg); |
| for (unsigned i = 0, e = Uses.size(); i != e; ++i) { |
| MachineOperand *UseMO = Uses[i]; |
| MachineInstr *UseMI = UseMO->getParent(); |
| MachineBasicBlock *UseMBB = UseMI->getParent(); |
| if (PHIBBs.count(UseMBB)) |
| continue; |
| |
| // About to add uses of DstReg, clear DstReg's kill flags. |
| if (!Changed) { |
| MRI->clearKillFlags(DstReg); |
| MRI->constrainRegClass(DstReg, DstRC); |
| } |
| |
| unsigned NewVR = MRI->createVirtualRegister(RC); |
| MachineInstr *Copy = BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(), |
| TII->get(TargetOpcode::COPY), NewVR) |
| .addReg(DstReg, 0, SubIdx); |
| // SubIdx applies to both SrcReg and DstReg when UseSrcSubIdx is set. |
| if (UseSrcSubIdx) { |
| Copy->getOperand(0).setSubReg(SubIdx); |
| Copy->getOperand(0).setIsUndef(); |
| } |
| UseMO->setReg(NewVR); |
| ++NumReuse; |
| Changed = true; |
| } |
| } |
| |
| return Changed; |
| } |
| |
| /// optimizeBitcastInstr - If the instruction is a bitcast instruction A that |
| /// cannot be optimized away during isel (e.g. ARM::VMOVSR, which bitcast |
| /// a value cross register classes), and the source is defined by another |
| /// bitcast instruction B. And if the register class of source of B matches |
| /// the register class of instruction A, then it is legal to replace all uses |
| /// of the def of A with source of B. e.g. |
| /// %vreg0<def> = VMOVSR %vreg1 |
| /// %vreg3<def> = VMOVRS %vreg0 |
| /// Replace all uses of vreg3 with vreg1. |
| |
| bool PeepholeOptimizer::optimizeBitcastInstr(MachineInstr *MI, |
| MachineBasicBlock *MBB) { |
| unsigned NumDefs = MI->getDesc().getNumDefs(); |
| unsigned NumSrcs = MI->getDesc().getNumOperands() - NumDefs; |
| if (NumDefs != 1) |
| return false; |
| |
| unsigned Def = 0; |
| unsigned Src = 0; |
| for (unsigned i = 0, e = NumDefs + NumSrcs; i != e; ++i) { |
| const MachineOperand &MO = MI->getOperand(i); |
| if (!MO.isReg()) |
| continue; |
| unsigned Reg = MO.getReg(); |
| if (!Reg) |
| continue; |
| if (MO.isDef()) |
| Def = Reg; |
| else if (Src) |
| // Multiple sources? |
| return false; |
| else |
| Src = Reg; |
| } |
| |
| assert(Def && Src && "Malformed bitcast instruction!"); |
| |
| MachineInstr *DefMI = MRI->getVRegDef(Src); |
| if (!DefMI || !DefMI->isBitcast()) |
| return false; |
| |
| unsigned SrcSrc = 0; |
| NumDefs = DefMI->getDesc().getNumDefs(); |
| NumSrcs = DefMI->getDesc().getNumOperands() - NumDefs; |
| if (NumDefs != 1) |
| return false; |
| for (unsigned i = 0, e = NumDefs + NumSrcs; i != e; ++i) { |
| const MachineOperand &MO = DefMI->getOperand(i); |
| if (!MO.isReg() || MO.isDef()) |
| continue; |
| unsigned Reg = MO.getReg(); |
| if (!Reg) |
| continue; |
| if (!MO.isDef()) { |
| if (SrcSrc) |
| // Multiple sources? |
| return false; |
| else |
| SrcSrc = Reg; |
| } |
| } |
| |
| if (MRI->getRegClass(SrcSrc) != MRI->getRegClass(Def)) |
| return false; |
| |
| MRI->replaceRegWith(Def, SrcSrc); |
| MRI->clearKillFlags(SrcSrc); |
| MI->eraseFromParent(); |
| ++NumBitcasts; |
| return true; |
| } |
| |
| /// optimizeCmpInstr - If the instruction is a compare and the previous |
| /// instruction it's comparing against all ready sets (or could be modified to |
| /// set) the same flag as the compare, then we can remove the comparison and use |
| /// the flag from the previous instruction. |
| bool PeepholeOptimizer::optimizeCmpInstr(MachineInstr *MI, |
| MachineBasicBlock *MBB) { |
| // If this instruction is a comparison against zero and isn't comparing a |
| // physical register, we can try to optimize it. |
| unsigned SrcReg, SrcReg2; |
| int CmpMask, CmpValue; |
| if (!TII->analyzeCompare(MI, SrcReg, SrcReg2, CmpMask, CmpValue) || |
| TargetRegisterInfo::isPhysicalRegister(SrcReg) || |
| (SrcReg2 != 0 && TargetRegisterInfo::isPhysicalRegister(SrcReg2))) |
| return false; |
| |
| // Attempt to optimize the comparison instruction. |
| if (TII->optimizeCompareInstr(MI, SrcReg, SrcReg2, CmpMask, CmpValue, MRI)) { |
| ++NumCmps; |
| return true; |
| } |
| |
| return false; |
| } |
| |
| /// Optimize a select instruction. |
| bool PeepholeOptimizer::optimizeSelect(MachineInstr *MI) { |
| unsigned TrueOp = 0; |
| unsigned FalseOp = 0; |
| bool Optimizable = false; |
| SmallVector<MachineOperand, 4> Cond; |
| if (TII->analyzeSelect(MI, Cond, TrueOp, FalseOp, Optimizable)) |
| return false; |
| if (!Optimizable) |
| return false; |
| if (!TII->optimizeSelect(MI)) |
| return false; |
| MI->eraseFromParent(); |
| ++NumSelects; |
| return true; |
| } |
| |
| /// isLoadFoldable - Check whether MI is a candidate for folding into a later |
| /// instruction. We only fold loads to virtual registers and the virtual |
| /// register defined has a single use. |
| bool PeepholeOptimizer::isLoadFoldable(MachineInstr *MI, |
| unsigned &FoldAsLoadDefReg) { |
| if (!MI->canFoldAsLoad() || !MI->mayLoad()) |
| return false; |
| const MCInstrDesc &MCID = MI->getDesc(); |
| if (MCID.getNumDefs() != 1) |
| return false; |
| |
| unsigned Reg = MI->getOperand(0).getReg(); |
| // To reduce compilation time, we check MRI->hasOneUse when inserting |
| // loads. It should be checked when processing uses of the load, since |
| // uses can be removed during peephole. |
| if (!MI->getOperand(0).getSubReg() && |
| TargetRegisterInfo::isVirtualRegister(Reg) && |
| MRI->hasOneUse(Reg)) { |
| FoldAsLoadDefReg = Reg; |
| return true; |
| } |
| return false; |
| } |
| |
| bool PeepholeOptimizer::isMoveImmediate(MachineInstr *MI, |
| SmallSet<unsigned, 4> &ImmDefRegs, |
| DenseMap<unsigned, MachineInstr*> &ImmDefMIs) { |
| const MCInstrDesc &MCID = MI->getDesc(); |
| if (!MI->isMoveImmediate()) |
| return false; |
| if (MCID.getNumDefs() != 1) |
| return false; |
| unsigned Reg = MI->getOperand(0).getReg(); |
| if (TargetRegisterInfo::isVirtualRegister(Reg)) { |
| ImmDefMIs.insert(std::make_pair(Reg, MI)); |
| ImmDefRegs.insert(Reg); |
| return true; |
| } |
| |
| return false; |
| } |
| |
| /// foldImmediate - Try folding register operands that are defined by move |
| /// immediate instructions, i.e. a trivial constant folding optimization, if |
| /// and only if the def and use are in the same BB. |
| bool PeepholeOptimizer::foldImmediate(MachineInstr *MI, MachineBasicBlock *MBB, |
| SmallSet<unsigned, 4> &ImmDefRegs, |
| DenseMap<unsigned, MachineInstr*> &ImmDefMIs) { |
| for (unsigned i = 0, e = MI->getDesc().getNumOperands(); i != e; ++i) { |
| MachineOperand &MO = MI->getOperand(i); |
| if (!MO.isReg() || MO.isDef()) |
| continue; |
| unsigned Reg = MO.getReg(); |
| if (!TargetRegisterInfo::isVirtualRegister(Reg)) |
| continue; |
| if (ImmDefRegs.count(Reg) == 0) |
| continue; |
| DenseMap<unsigned, MachineInstr*>::iterator II = ImmDefMIs.find(Reg); |
| assert(II != ImmDefMIs.end()); |
| if (TII->FoldImmediate(MI, II->second, Reg, MRI)) { |
| ++NumImmFold; |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) { |
| DEBUG(dbgs() << "********** PEEPHOLE OPTIMIZER **********\n"); |
| DEBUG(dbgs() << "********** Function: " << MF.getName() << '\n'); |
| |
| if (DisablePeephole) |
| return false; |
| |
| TM = &MF.getTarget(); |
| TII = TM->getInstrInfo(); |
| MRI = &MF.getRegInfo(); |
| DT = Aggressive ? &getAnalysis<MachineDominatorTree>() : 0; |
| |
| bool Changed = false; |
| |
| SmallPtrSet<MachineInstr*, 8> LocalMIs; |
| SmallSet<unsigned, 4> ImmDefRegs; |
| DenseMap<unsigned, MachineInstr*> ImmDefMIs; |
| unsigned FoldAsLoadDefReg; |
| for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) { |
| MachineBasicBlock *MBB = &*I; |
| |
| bool SeenMoveImm = false; |
| LocalMIs.clear(); |
| ImmDefRegs.clear(); |
| ImmDefMIs.clear(); |
| FoldAsLoadDefReg = 0; |
| |
| for (MachineBasicBlock::iterator |
| MII = I->begin(), MIE = I->end(); MII != MIE; ) { |
| MachineInstr *MI = &*MII; |
| // We may be erasing MI below, increment MII now. |
| ++MII; |
| LocalMIs.insert(MI); |
| |
| // If there exists an instruction which belongs to the following |
| // categories, we will discard the load candidate. |
| if (MI->isLabel() || MI->isPHI() || MI->isImplicitDef() || |
| MI->isKill() || MI->isInlineAsm() || MI->isDebugValue() || |
| MI->hasUnmodeledSideEffects()) { |
| FoldAsLoadDefReg = 0; |
| continue; |
| } |
| if (MI->mayStore() || MI->isCall()) |
| FoldAsLoadDefReg = 0; |
| |
| if ((MI->isBitcast() && optimizeBitcastInstr(MI, MBB)) || |
| (MI->isCompare() && optimizeCmpInstr(MI, MBB)) || |
| (MI->isSelect() && optimizeSelect(MI))) { |
| // MI is deleted. |
| LocalMIs.erase(MI); |
| Changed = true; |
| continue; |
| } |
| |
| if (isMoveImmediate(MI, ImmDefRegs, ImmDefMIs)) { |
| SeenMoveImm = true; |
| } else { |
| Changed |= optimizeExtInstr(MI, MBB, LocalMIs); |
| // optimizeExtInstr might have created new instructions after MI |
| // and before the already incremented MII. Adjust MII so that the |
| // next iteration sees the new instructions. |
| MII = MI; |
| ++MII; |
| if (SeenMoveImm) |
| Changed |= foldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs); |
| } |
| |
| // Check whether MI is a load candidate for folding into a later |
| // instruction. If MI is not a candidate, check whether we can fold an |
| // earlier load into MI. |
| if (!isLoadFoldable(MI, FoldAsLoadDefReg) && FoldAsLoadDefReg) { |
| // We need to fold load after optimizeCmpInstr, since optimizeCmpInstr |
| // can enable folding by converting SUB to CMP. |
| MachineInstr *DefMI = 0; |
| MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI, |
| FoldAsLoadDefReg, DefMI); |
| if (FoldMI) { |
| // Update LocalMIs since we replaced MI with FoldMI and deleted DefMI. |
| DEBUG(dbgs() << "Replacing: " << *MI); |
| DEBUG(dbgs() << " With: " << *FoldMI); |
| LocalMIs.erase(MI); |
| LocalMIs.erase(DefMI); |
| LocalMIs.insert(FoldMI); |
| MI->eraseFromParent(); |
| DefMI->eraseFromParent(); |
| ++NumLoadFold; |
| |
| // MI is replaced with FoldMI. |
| Changed = true; |
| continue; |
| } |
| } |
| } |
| } |
| |
| return Changed; |
| } |
