llvm-project/llvm/lib/Target/RISCV/VentusLegalizeLoad.cpp

//===-- VentusLegalizeLoad.cpp - vlw12 instruction legalization ----------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Legalize vlw12.v instruction, in vararg function codegen, the vararg start
// index will be stored in stack, in ventus, this index will be store in private
// stack, some code example will be as below
//	               addi	sp, sp, 4         |    addi    sp, sp, -64
//	               addi	tp, tp, 80        |    addi    s0, sp, 32
//	              vsw.v	v7, -80(v8)       |    sw      a7, 28(s0)
//	              vsw.v	v6, -76(v8)       |    sw      a6, 24(s0)
//	              vsw.v	v5, -72(v8)       |    sw      a5, 20(s0)
//	              vsw.v	v4, -68(v8)       |    sw      a4, 16(s0)
//	              vsw.v	v3, -64(v8)       |    sw      a3, 12(s0)
//	              vsw.v	v2, -60(v8)       |    sw      a2, 8(s0)
//	              vsw.v	v1, -56(v8)       |    sw      a1, 4(s0)
//	              vsw.v	v0, -48(v8)       |    sw      a0, -16(s0)
//	              addi	t0, tp, -56       |    addi    a0, s0, 4
//	              vmv.v.x	v0, t0          |    sw      a0, -20(s0)
//	              vsw.v	v0, -44(v8)
//
// left hand code is generated by ventus, right hand code is generated by
// standard riscv, when load from -44(v8), vlw.v	v0, -44(v8), if need to
// load from v0, in right now ventus, the codegen will be like this vlw12.v v0,
// 0(v0), but it is actually illegal, it should be vlw.v v0, 0(v0)
//
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/RISCVMCTargetDesc.h"
#include "RISCV.h"
#include "RISCVFrameLowering.h"
#include "RISCVISelLowering.h"
#include "RISCVInstrInfo.h"
#include "RISCVSubtarget.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/Register.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Instructions.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>

#define VENTUS_LOAD_LEGALIZATION "Ventus load instruction legalization pass"
#define DEBUG_TYPE "vlw12-legalize"

using namespace llvm;

namespace {

class VentusLegalizeLoad : public MachineFunctionPass {
public:
  const RISCVInstrInfo *TII;
  static char ID;
  const RISCVRegisterInfo *MRI;
  const RISCVTargetLowering *RTI;
  const MachineRegisterInfo *MR;

  VentusLegalizeLoad() : MachineFunctionPass(ID) {
    initializeVentusLegalizeLoadPass(*PassRegistry::getPassRegistry());
  }

  bool runOnMachineFunction(MachineFunction &MF) override;

  StringRef getPassName() const override { return VENTUS_LOAD_LEGALIZATION; }

private:
  bool runOnMachineBasicBlock(MachineBasicBlock &MBB);

  bool checkVLWDependency(MachineBasicBlock &MBB, MachineInstr &MI);

  bool checkInstructionUse(MachineBasicBlock &MBB, MachineInstr &MI);

  // Check whether machine instruction is local memory load instruction or not
  bool isLocalMemLoadInstr(MachineInstr &MI) {
    switch (MI.getOpcode()) {
    case RISCV::VLWI12:
    case RISCV::VLBI12:
    case RISCV::VLBUI12:
    case RISCV::VLHI12:
    case RISCV::VLHUI12:
      return true;
    default:
      return false;
    }
  }

  unsigned getRelativePrivateMemLoadInstr(MachineInstr &MI) {
    assert(isLocalMemLoadInstr(MI) && "Illegal instruction.");
    switch (MI.getOpcode()) {
      case RISCV::VLWI12:
        return RISCV::VLW;
      case RISCV::VLBI12:
        return RISCV::VLB;
      case RISCV::VLBUI12:
        return RISCV::VLBU;
      case RISCV::VLHI12:
        return RISCV::VLH;
      case RISCV::VLHUI12:
        return RISCV::VLHU;
      default:
        llvm_unreachable("Unexpected instruction.");
    }
  }

};

bool VentusLegalizeLoad::runOnMachineFunction(MachineFunction &MF) {
  bool IsChanged = false;
  TII = static_cast<const RISCVInstrInfo *>(MF.getSubtarget().getInstrInfo());
  MRI = MF.getSubtarget<RISCVSubtarget>().getRegisterInfo();
  RTI = MF.getSubtarget<RISCVSubtarget>().getTargetLowering();
  MR = &MF.getRegInfo();
  for (auto &MBB : MF)
    IsChanged |= runOnMachineBasicBlock(MBB);
  return IsChanged;
}

bool VentusLegalizeLoad::runOnMachineBasicBlock(MachineBasicBlock &MBB) {
  bool IsMBBChanged = false;
  // Right now we only legalize vlw12.v instruction, and we need to analyze its
  // operand def-use chain
  for (auto &MI : MBB) {
    if (MI.getOpcode() == RISCV::VLW)
      IsMBBChanged |= checkVLWDependency(MBB, MI);
  }
  return IsMBBChanged;
}

bool VentusLegalizeLoad::checkVLWDependency(MachineBasicBlock &MBB,
                                            MachineInstr &MI) {
  bool IsChanged = false;

  int StoreFrameIndex = RTI->getVastartStoreFrameIndex();
  MachineOperand LoadBaseOperand = MI.getOperand(1);
  if (LoadBaseOperand.isFI() && LoadBaseOperand.getIndex() == StoreFrameIndex)
  // Check base operand has data dependency with vastart frame or not
  {
    Register VastartFrameRegister = MI.getOperand(0).getReg();
    auto UseList = MR->use_instructions(VastartFrameRegister);
    for (auto &Use : UseList) {
      // Other operation on vastart frame register
      IsChanged |= checkInstructionUse(MBB, Use);
    }
  }

  return IsChanged;
}

bool VentusLegalizeLoad::checkInstructionUse(MachineBasicBlock &MBB, MachineInstr &MI) {
  bool IsChanged = false;
  if (isLocalMemLoadInstr(MI)) {
    // Here need to change vlw12 to vlw
    LLVM_DEBUG(dbgs() << "Instruction to be changed: \n");
    LLVM_DEBUG(MI.dump());
    MI.setDesc(TII->get(getRelativePrivateMemLoadInstr(MI)));
    LLVM_DEBUG(dbgs() << "Instruction after changed: \n");
    LLVM_DEBUG(MI.dump());
    auto UseList = MR->use_instructions(MI.getOperand(0).getReg());
    // Recursive check
    // vlw.v v0, -28(v8) // vararg start frame
    // vlw.v v0, 0(v0) // should be checked too
    for (auto &Use : UseList) {
      checkInstructionUse(MBB, Use);
    }
    return IsChanged = true;
  }
  if (MI.getOpcode() == RISCV::VSW)
    return IsChanged;
  for (auto &Use : MR->use_instructions(MI.getOperand(0).getReg())) {
    IsChanged |= checkInstructionUse(MBB, Use);
  }
  return IsChanged;
}

char VentusLegalizeLoad::ID = 0;

} // end of anonymous namespace

INITIALIZE_PASS(VentusLegalizeLoad, "Ventus load instruction legalization",
                VENTUS_LOAD_LEGALIZATION, false, false)

namespace llvm {
FunctionPass *createVentusLegalizeLoadPass() {
  return new VentusLegalizeLoad();
}
} // end of namespace llvm