llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp

//===- llvm/CodeGen/GlobalISel/InstructionSelector.cpp --------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \file
/// This file implements the InstructionSelector class.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
#include "llvm/CodeGen/GlobalISel/Utils.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include <cassert>

#define DEBUG_TYPE "instructionselector"

using namespace llvm;

InstructionSelector::MatcherState::MatcherState(unsigned MaxRenderers)
    : Renderers(MaxRenderers), MIs() {}

InstructionSelector::InstructionSelector() = default;

bool InstructionSelector::constrainOperandRegToRegClass(
    MachineInstr &I, unsigned OpIdx, const TargetRegisterClass &RC,
    const TargetInstrInfo &TII, const TargetRegisterInfo &TRI,
    const RegisterBankInfo &RBI) const {
  MachineBasicBlock &MBB = *I.getParent();
  MachineFunction &MF = *MBB.getParent();
  MachineRegisterInfo &MRI = MF.getRegInfo();

  return
      constrainRegToClass(MRI, TII, RBI, I, I.getOperand(OpIdx).getReg(), RC);
}

bool InstructionSelector::constrainSelectedInstRegOperands(
    MachineInstr &I, const TargetInstrInfo &TII, const TargetRegisterInfo &TRI,
    const RegisterBankInfo &RBI) const {
  MachineBasicBlock &MBB = *I.getParent();
  MachineFunction &MF = *MBB.getParent();
  MachineRegisterInfo &MRI = MF.getRegInfo();

  for (unsigned OpI = 0, OpE = I.getNumExplicitOperands(); OpI != OpE; ++OpI) {
    MachineOperand &MO = I.getOperand(OpI);

    // There's nothing to be done on non-register operands.
    if (!MO.isReg())
      continue;

    DEBUG(dbgs() << "Converting operand: " << MO << '\n');
    assert(MO.isReg() && "Unsupported non-reg operand");

    unsigned Reg = MO.getReg();
    // Physical registers don't need to be constrained.
    if (TRI.isPhysicalRegister(Reg))
      continue;

    // Register operands with a value of 0 (e.g. predicate operands) don't need
    // to be constrained.
    if (Reg == 0)
      continue;

    // If the operand is a vreg, we should constrain its regclass, and only
    // insert COPYs if that's impossible.
    // constrainOperandRegClass does that for us.
    MO.setReg(constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, I.getDesc(),
                                       Reg, OpI));

    // Tie uses to defs as indicated in MCInstrDesc if this hasn't already been
    // done.
    if (MO.isUse()) {
      int DefIdx = I.getDesc().getOperandConstraint(OpI, MCOI::TIED_TO);
      if (DefIdx != -1 && !I.isRegTiedToUseOperand(DefIdx))
        I.tieOperands(DefIdx, OpI);
    }
  }
  return true;
}

bool InstructionSelector::isOperandImmEqual(
    const MachineOperand &MO, int64_t Value,
    const MachineRegisterInfo &MRI) const {
  if (MO.isReg() && MO.getReg())
    if (auto VRegVal = getConstantVRegVal(MO.getReg(), MRI))
      return *VRegVal == Value;
  return false;
}

bool InstructionSelector::isBaseWithConstantOffset(
    const MachineOperand &Root, const MachineRegisterInfo &MRI) const {
  if (!Root.isReg())
    return false;

  MachineInstr *RootI = MRI.getVRegDef(Root.getReg());
  if (RootI->getOpcode() != TargetOpcode::G_GEP)
    return false;

  MachineOperand &RHS = RootI->getOperand(2);
  MachineInstr *RHSI = MRI.getVRegDef(RHS.getReg());
  if (RHSI->getOpcode() != TargetOpcode::G_CONSTANT)
    return false;

  return true;
}

bool InstructionSelector::isObviouslySafeToFold(MachineInstr &MI,
                                                MachineInstr &IntoMI) const {
  // Immediate neighbours are already folded.
  if (MI.getParent() == IntoMI.getParent() &&
      std::next(MI.getIterator()) == IntoMI.getIterator())
    return true;

  return !MI.mayLoadOrStore() && !MI.hasUnmodeledSideEffects() &&
         MI.implicit_operands().begin() == MI.implicit_operands().end();
}