| //===--------- 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"); | |
| STATISTIC(NumFrameOffFoldInPreEmit, | |
| "Number of folding frame offset by using r+r in pre-emit peephole"); | |
| 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) { | |
| // Remove UNENCODED_NOP even when this pass is disabled. | |
| // This needs to be done unconditionally so we don't emit zeros | |
| // in the instruction stream. | |
| SmallVector<MachineInstr *, 4> InstrsToErase; | |
| for (MachineBasicBlock &MBB : MF) | |
| for (MachineInstr &MI : MBB) | |
| if (MI.getOpcode() == PPC::UNENCODED_NOP) | |
| InstrsToErase.push_back(&MI); | |
| for (MachineInstr *MI : InstrsToErase) | |
| MI->eraseFromParent(); | |
| 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(); | |
| if (Opc == PPC::UNENCODED_NOP) { | |
| InstrsToErase.push_back(&MI); | |
| continue; | |
| } | |
| // 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); | |
| } | |
| } | |
| if (TII->foldFrameOffset(MI)) { | |
| Changed = true; | |
| NumFrameOffFoldInPreEmit++; | |
| LLVM_DEBUG(dbgs() << "Frame offset folding by using index form: "); | |
| LLVM_DEBUG(MI.dump()); | |
| } | |
| } | |
| // 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(); | |
| } |