|
| 1 | +//===------- RISCVPushPopOptimizer.cpp - RISCV Push/Pop opt. pass ---------===// |
| 2 | +// |
| 3 | +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | +// See https://llvm.org/LICENSE.txt for license information. |
| 5 | +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | +// |
| 7 | +//===----------------------------------------------------------------------===// |
| 8 | +// |
| 9 | +// This file contains a pass that modifies PUSH/POP instructions from Zca |
| 10 | +// standard to use their non prolog/epilog related functionalities |
| 11 | +// and generates POPRET instruction. |
| 12 | +// |
| 13 | +//===----------------------------------------------------------------------===// |
| 14 | + |
| 15 | +#include "RISCVInstrInfo.h" |
| 16 | +#include "RISCVMachineFunctionInfo.h" |
| 17 | + |
| 18 | +using namespace llvm; |
| 19 | + |
| 20 | +#define RISCV_PUSH_POP_OPT_NAME "RISC-V Zcmp Push/Pop optimization pass" |
| 21 | + |
| 22 | +namespace { |
| 23 | +struct RISCVPushPopOpt : public MachineFunctionPass { |
| 24 | + static char ID; |
| 25 | + |
| 26 | + RISCVPushPopOpt() : MachineFunctionPass(ID) { |
| 27 | + initializeRISCVPushPopOptPass(*PassRegistry::getPassRegistry()); |
| 28 | + } |
| 29 | + |
| 30 | + const RISCVInstrInfo *TII; |
| 31 | + const TargetRegisterInfo *TRI; |
| 32 | + |
| 33 | + // Track which register units have been modified and used. |
| 34 | + LiveRegUnits ModifiedRegUnits, UsedRegUnits; |
| 35 | + |
| 36 | + bool usePopRet(MachineBasicBlock::iterator &MBBI, |
| 37 | + MachineBasicBlock::iterator &NextI, bool IsReturnZero); |
| 38 | + bool adjustRetVal(MachineBasicBlock::iterator &MBBI); |
| 39 | + bool runOnMachineFunction(MachineFunction &Fn) override; |
| 40 | + |
| 41 | + StringRef getPassName() const override { return RISCV_PUSH_POP_OPT_NAME; } |
| 42 | +}; |
| 43 | + |
| 44 | +char RISCVPushPopOpt::ID = 0; |
| 45 | + |
| 46 | +} // end of anonymous namespace |
| 47 | + |
| 48 | +INITIALIZE_PASS(RISCVPushPopOpt, "riscv-push-pop-opt", RISCV_PUSH_POP_OPT_NAME, |
| 49 | + false, false) |
| 50 | + |
| 51 | +// Check if POP instruction was inserted into the MBB and return iterator to it. |
| 52 | +static MachineBasicBlock::iterator containsPop(MachineBasicBlock &MBB) { |
| 53 | + for (MachineBasicBlock::iterator MBBI = MBB.begin(); MBBI != MBB.end(); |
| 54 | + MBBI = next_nodbg(MBBI, MBB.end())) |
| 55 | + if (MBBI->getOpcode() == RISCV::CM_POP) |
| 56 | + return MBBI; |
| 57 | + |
| 58 | + return MBB.end(); |
| 59 | +} |
| 60 | + |
| 61 | +bool RISCVPushPopOpt::usePopRet(MachineBasicBlock::iterator &MBBI, |
| 62 | + MachineBasicBlock::iterator &NextI, |
| 63 | + bool IsReturnZero) { |
| 64 | + // Since Pseudo instruction lowering happen later in the pipeline, |
| 65 | + // this will detect all ret instruction. |
| 66 | + DebugLoc DL = NextI->getDebugLoc(); |
| 67 | + unsigned Opc = IsReturnZero ? RISCV::CM_POPRETZ : RISCV::CM_POPRET; |
| 68 | + BuildMI(*NextI->getParent(), NextI, DL, TII->get(Opc)) |
| 69 | + .add(MBBI->getOperand(0)) |
| 70 | + .add(MBBI->getOperand(1)); |
| 71 | + |
| 72 | + MBBI->eraseFromParent(); |
| 73 | + NextI->eraseFromParent(); |
| 74 | + return true; |
| 75 | +} |
| 76 | + |
| 77 | +// Search for last assignment to a0 and if possible use ret_val slot of POP to |
| 78 | +// store return value. |
| 79 | +bool RISCVPushPopOpt::adjustRetVal(MachineBasicBlock::iterator &MBBI) { |
| 80 | + MachineBasicBlock::reverse_iterator RE = MBBI->getParent()->rend(); |
| 81 | + // Track which register units have been modified and used between the POP |
| 82 | + // insn and the last assignment to register a0. |
| 83 | + ModifiedRegUnits.clear(); |
| 84 | + UsedRegUnits.clear(); |
| 85 | + // Since POP instruction is in Epilogue no normal instructions will follow |
| 86 | + // after it. Therefore search only previous ones to find the return value. |
| 87 | + for (MachineBasicBlock::reverse_iterator I = |
| 88 | + next_nodbg(MBBI.getReverse(), RE); |
| 89 | + I != RE; I = next_nodbg(I, RE)) { |
| 90 | + MachineInstr &MI = *I; |
| 91 | + if (auto OperandPair = TII->isCopyInstrImpl(MI)) { |
| 92 | + Register DestReg = OperandPair->Destination->getReg(); |
| 93 | + Register Source = OperandPair->Source->getReg(); |
| 94 | + if (DestReg == RISCV::X10 && Source == RISCV::X0) { |
| 95 | + MI.removeFromParent(); |
| 96 | + return true; |
| 97 | + } |
| 98 | + } |
| 99 | + // Update modified / used register units. |
| 100 | + LiveRegUnits::accumulateUsedDefed(MI, ModifiedRegUnits, UsedRegUnits, TRI); |
| 101 | + // If a0 was modified or used, there is no possibility |
| 102 | + // of using ret_val slot of POP instruction. |
| 103 | + if (!ModifiedRegUnits.available(RISCV::X10) || |
| 104 | + !UsedRegUnits.available(RISCV::X10)) |
| 105 | + return false; |
| 106 | + } |
| 107 | + return false; |
| 108 | +} |
| 109 | + |
| 110 | +bool RISCVPushPopOpt::runOnMachineFunction(MachineFunction &Fn) { |
| 111 | + if (skipFunction(Fn.getFunction())) |
| 112 | + return false; |
| 113 | + |
| 114 | + // If Zcmp extension is not supported, abort. |
| 115 | + const RISCVSubtarget *Subtarget = &Fn.getSubtarget<RISCVSubtarget>(); |
| 116 | + if (!Subtarget->hasStdExtZcmp()) |
| 117 | + return false; |
| 118 | + |
| 119 | + // If frame pointer elimination has been disabled, abort to avoid breaking the |
| 120 | + // ABI. |
| 121 | + if (Fn.getTarget().Options.DisableFramePointerElim(Fn)) |
| 122 | + return false; |
| 123 | + |
| 124 | + TII = static_cast<const RISCVInstrInfo *>(Subtarget->getInstrInfo()); |
| 125 | + TRI = Subtarget->getRegisterInfo(); |
| 126 | + // Resize the modified and used register unit trackers. We do this once |
| 127 | + // per function and then clear the register units each time we determine |
| 128 | + // correct return value for the POP. |
| 129 | + ModifiedRegUnits.init(*TRI); |
| 130 | + UsedRegUnits.init(*TRI); |
| 131 | + bool Modified = false; |
| 132 | + for (auto &MBB : Fn) { |
| 133 | + MachineBasicBlock::iterator MBBI = containsPop(MBB); |
| 134 | + MachineBasicBlock::iterator NextI = next_nodbg(MBBI, MBB.end()); |
| 135 | + if (MBBI != MBB.end() && NextI->getOpcode() == RISCV::PseudoRET) |
| 136 | + Modified |= usePopRet(MBBI, NextI, adjustRetVal(MBBI)); |
| 137 | + } |
| 138 | + return Modified; |
| 139 | +} |
| 140 | + |
| 141 | +/// createRISCVPushPopOptimizationPass - returns an instance of the |
| 142 | +/// Push/Pop optimization pass. |
| 143 | +FunctionPass *llvm::createRISCVPushPopOptimizationPass() { |
| 144 | + return new RISCVPushPopOpt(); |
| 145 | +} |
0 commit comments