| //===--------- PPCPreEmitPeephole.cpp - Late peephole optimizations -------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // A pre-emit peephole for catching opportunities introduced by late passes such |
| // as MachineBlockPlacement. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "PPC.h" |
| #include "PPCInstrInfo.h" |
| #include "PPCSubtarget.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/CodeGen/LivePhysRegs.h" |
| #include "llvm/CodeGen/MachineBasicBlock.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Support/Debug.h" |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "ppc-pre-emit-peephole" |
| |
| STATISTIC(NumRRConvertedInPreEmit, |
| "Number of r+r instructions converted to r+i in pre-emit peephole"); |
| STATISTIC(NumRemovedInPreEmit, |
| "Number of instructions deleted in pre-emit peephole"); |
| STATISTIC(NumberOfSelfCopies, |
| "Number of self copy instructions eliminated"); |
| |
| static cl::opt<bool> |
| RunPreEmitPeephole("ppc-late-peephole", cl::Hidden, cl::init(true), |
| cl::desc("Run pre-emit peephole optimizations.")); |
| |
| namespace { |
| class PPCPreEmitPeephole : public MachineFunctionPass { |
| public: |
| static char ID; |
| PPCPreEmitPeephole() : MachineFunctionPass(ID) { |
| initializePPCPreEmitPeepholePass(*PassRegistry::getPassRegistry()); |
| } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| MachineFunctionPass::getAnalysisUsage(AU); |
| } |
| |
| MachineFunctionProperties getRequiredProperties() const override { |
| return MachineFunctionProperties().set( |
| MachineFunctionProperties::Property::NoVRegs); |
| } |
| |
| // This function removes any redundant load immediates. It has two level |
| // loops - The outer loop finds the load immediates BBI that could be used |
| // to replace following redundancy. The inner loop scans instructions that |
| // after BBI to find redundancy and update kill/dead flags accordingly. If |
| // AfterBBI is the same as BBI, it is redundant, otherwise any instructions |
| // that modify the def register of BBI would break the scanning. |
| // DeadOrKillToUnset is a pointer to the previous operand that had the |
| // kill/dead flag set. It keeps track of the def register of BBI, the use |
| // registers of AfterBBIs and the def registers of AfterBBIs. |
| bool removeRedundantLIs(MachineBasicBlock &MBB, |
| const TargetRegisterInfo *TRI) { |
| LLVM_DEBUG(dbgs() << "Remove redundant load immediates from MBB:\n"; |
| MBB.dump(); dbgs() << "\n"); |
| |
| DenseSet<MachineInstr *> InstrsToErase; |
| for (auto BBI = MBB.instr_begin(); BBI != MBB.instr_end(); ++BBI) { |
| // Skip load immediate that is marked to be erased later because it |
| // cannot be used to replace any other instructions. |
| if (InstrsToErase.find(&*BBI) != InstrsToErase.end()) |
| continue; |
| // Skip non-load immediate. |
| unsigned Opc = BBI->getOpcode(); |
| if (Opc != PPC::LI && Opc != PPC::LI8 && Opc != PPC::LIS && |
| Opc != PPC::LIS8) |
| continue; |
| // Skip load immediate, where the operand is a relocation (e.g., $r3 = |
| // LI target-flags(ppc-lo) %const.0). |
| if (!BBI->getOperand(1).isImm()) |
| continue; |
| assert(BBI->getOperand(0).isReg() && |
| "Expected a register for the first operand"); |
| |
| LLVM_DEBUG(dbgs() << "Scanning after load immediate: "; BBI->dump();); |
| |
| Register Reg = BBI->getOperand(0).getReg(); |
| int64_t Imm = BBI->getOperand(1).getImm(); |
| MachineOperand *DeadOrKillToUnset = nullptr; |
| if (BBI->getOperand(0).isDead()) { |
| DeadOrKillToUnset = &BBI->getOperand(0); |
| LLVM_DEBUG(dbgs() << " Kill flag of " << *DeadOrKillToUnset |
| << " from load immediate " << *BBI |
| << " is a unsetting candidate\n"); |
| } |
| // This loop scans instructions after BBI to see if there is any |
| // redundant load immediate. |
| for (auto AfterBBI = std::next(BBI); AfterBBI != MBB.instr_end(); |
| ++AfterBBI) { |
| // Track the operand that kill Reg. We would unset the kill flag of |
| // the operand if there is a following redundant load immediate. |
| int KillIdx = AfterBBI->findRegisterUseOperandIdx(Reg, true, TRI); |
| if (KillIdx != -1) { |
| assert(!DeadOrKillToUnset && "Shouldn't kill same register twice"); |
| DeadOrKillToUnset = &AfterBBI->getOperand(KillIdx); |
| LLVM_DEBUG(dbgs() |
| << " Kill flag of " << *DeadOrKillToUnset << " from " |
| << *AfterBBI << " is a unsetting candidate\n"); |
| } |
| |
| if (!AfterBBI->modifiesRegister(Reg, TRI)) |
| continue; |
| // Finish scanning because Reg is overwritten by a non-load |
| // instruction. |
| if (AfterBBI->getOpcode() != Opc) |
| break; |
| assert(AfterBBI->getOperand(0).isReg() && |
| "Expected a register for the first operand"); |
| // Finish scanning because Reg is overwritten by a relocation or a |
| // different value. |
| if (!AfterBBI->getOperand(1).isImm() || |
| AfterBBI->getOperand(1).getImm() != Imm) |
| break; |
| |
| // It loads same immediate value to the same Reg, which is redundant. |
| // We would unset kill flag in previous Reg usage to extend live range |
| // of Reg first, then remove the redundancy. |
| if (DeadOrKillToUnset) { |
| LLVM_DEBUG(dbgs() |
| << " Unset dead/kill flag of " << *DeadOrKillToUnset |
| << " from " << *DeadOrKillToUnset->getParent()); |
| if (DeadOrKillToUnset->isDef()) |
| DeadOrKillToUnset->setIsDead(false); |
| else |
| DeadOrKillToUnset->setIsKill(false); |
| } |
| DeadOrKillToUnset = |
| AfterBBI->findRegisterDefOperand(Reg, true, true, TRI); |
| if (DeadOrKillToUnset) |
| LLVM_DEBUG(dbgs() |
| << " Dead flag of " << *DeadOrKillToUnset << " from " |
| << *AfterBBI << " is a unsetting candidate\n"); |
| InstrsToErase.insert(&*AfterBBI); |
| LLVM_DEBUG(dbgs() << " Remove redundant load immediate: "; |
| AfterBBI->dump()); |
| } |
| } |
| |
| for (MachineInstr *MI : InstrsToErase) { |
| MI->eraseFromParent(); |
| } |
| NumRemovedInPreEmit += InstrsToErase.size(); |
| return !InstrsToErase.empty(); |
| } |
| |
| bool runOnMachineFunction(MachineFunction &MF) override { |
| if (skipFunction(MF.getFunction()) || !RunPreEmitPeephole) |
| return false; |
| bool Changed = false; |
| const PPCInstrInfo *TII = MF.getSubtarget<PPCSubtarget>().getInstrInfo(); |
| const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo(); |
| SmallVector<MachineInstr *, 4> InstrsToErase; |
| for (MachineBasicBlock &MBB : MF) { |
| Changed |= removeRedundantLIs(MBB, TRI); |
| for (MachineInstr &MI : MBB) { |
| unsigned Opc = MI.getOpcode(); |
| // Detect self copies - these can result from running AADB. |
| if (PPCInstrInfo::isSameClassPhysRegCopy(Opc)) { |
| const MCInstrDesc &MCID = TII->get(Opc); |
| if (MCID.getNumOperands() == 3 && |
| MI.getOperand(0).getReg() == MI.getOperand(1).getReg() && |
| MI.getOperand(0).getReg() == MI.getOperand(2).getReg()) { |
| NumberOfSelfCopies++; |
| LLVM_DEBUG(dbgs() << "Deleting self-copy instruction: "); |
| LLVM_DEBUG(MI.dump()); |
| InstrsToErase.push_back(&MI); |
| continue; |
| } |
| else if (MCID.getNumOperands() == 2 && |
| MI.getOperand(0).getReg() == MI.getOperand(1).getReg()) { |
| NumberOfSelfCopies++; |
| LLVM_DEBUG(dbgs() << "Deleting self-copy instruction: "); |
| LLVM_DEBUG(MI.dump()); |
| InstrsToErase.push_back(&MI); |
| continue; |
| } |
| } |
| MachineInstr *DefMIToErase = nullptr; |
| if (TII->convertToImmediateForm(MI, &DefMIToErase)) { |
| Changed = true; |
| NumRRConvertedInPreEmit++; |
| LLVM_DEBUG(dbgs() << "Converted instruction to imm form: "); |
| LLVM_DEBUG(MI.dump()); |
| if (DefMIToErase) { |
| InstrsToErase.push_back(DefMIToErase); |
| } |
| } |
| } |
| |
| // Eliminate conditional branch based on a constant CR bit by |
| // CRSET or CRUNSET. We eliminate the conditional branch or |
| // convert it into an unconditional branch. Also, if the CR bit |
| // is not used by other instructions, we eliminate CRSET as well. |
| auto I = MBB.getFirstInstrTerminator(); |
| if (I == MBB.instr_end()) |
| continue; |
| MachineInstr *Br = &*I; |
| if (Br->getOpcode() != PPC::BC && Br->getOpcode() != PPC::BCn) |
| continue; |
| MachineInstr *CRSetMI = nullptr; |
| Register CRBit = Br->getOperand(0).getReg(); |
| unsigned CRReg = getCRFromCRBit(CRBit); |
| bool SeenUse = false; |
| MachineBasicBlock::reverse_iterator It = Br, Er = MBB.rend(); |
| for (It++; It != Er; It++) { |
| if (It->modifiesRegister(CRBit, TRI)) { |
| if ((It->getOpcode() == PPC::CRUNSET || |
| It->getOpcode() == PPC::CRSET) && |
| It->getOperand(0).getReg() == CRBit) |
| CRSetMI = &*It; |
| break; |
| } |
| if (It->readsRegister(CRBit, TRI)) |
| SeenUse = true; |
| } |
| if (!CRSetMI) continue; |
| |
| unsigned CRSetOp = CRSetMI->getOpcode(); |
| if ((Br->getOpcode() == PPC::BCn && CRSetOp == PPC::CRSET) || |
| (Br->getOpcode() == PPC::BC && CRSetOp == PPC::CRUNSET)) { |
| // Remove this branch since it cannot be taken. |
| InstrsToErase.push_back(Br); |
| MBB.removeSuccessor(Br->getOperand(1).getMBB()); |
| } |
| else { |
| // This conditional branch is always taken. So, remove all branches |
| // and insert an unconditional branch to the destination of this. |
| MachineBasicBlock::iterator It = Br, Er = MBB.end(); |
| for (; It != Er; It++) { |
| if (It->isDebugInstr()) continue; |
| assert(It->isTerminator() && "Non-terminator after a terminator"); |
| InstrsToErase.push_back(&*It); |
| } |
| if (!MBB.isLayoutSuccessor(Br->getOperand(1).getMBB())) { |
| ArrayRef<MachineOperand> NoCond; |
| TII->insertBranch(MBB, Br->getOperand(1).getMBB(), nullptr, |
| NoCond, Br->getDebugLoc()); |
| } |
| for (auto &Succ : MBB.successors()) |
| if (Succ != Br->getOperand(1).getMBB()) { |
| MBB.removeSuccessor(Succ); |
| break; |
| } |
| } |
| |
| // If the CRBit is not used by another instruction, we can eliminate |
| // CRSET/CRUNSET instruction. |
| if (!SeenUse) { |
| // We need to check use of the CRBit in successors. |
| for (auto &SuccMBB : MBB.successors()) |
| if (SuccMBB->isLiveIn(CRBit) || SuccMBB->isLiveIn(CRReg)) { |
| SeenUse = true; |
| break; |
| } |
| if (!SeenUse) |
| InstrsToErase.push_back(CRSetMI); |
| } |
| } |
| for (MachineInstr *MI : InstrsToErase) { |
| LLVM_DEBUG(dbgs() << "PPC pre-emit peephole: erasing instruction: "); |
| LLVM_DEBUG(MI->dump()); |
| MI->eraseFromParent(); |
| NumRemovedInPreEmit++; |
| } |
| return Changed; |
| } |
| }; |
| } |
| |
| INITIALIZE_PASS(PPCPreEmitPeephole, DEBUG_TYPE, "PowerPC Pre-Emit Peephole", |
| false, false) |
| char PPCPreEmitPeephole::ID = 0; |
| |
| FunctionPass *llvm::createPPCPreEmitPeepholePass() { |
| return new PPCPreEmitPeephole(); |
| } |
