//=- LoongArchISelLowering.cpp - LoongArch DAG Lowering Implementation  ---===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file defines the interfaces that LoongArch uses to lower LLVM code into
// a selection DAG.
//
//===----------------------------------------------------------------------===//

#include "LoongArchISelLowering.h"
#include "LoongArch.h"
#include "LoongArchMachineFunctionInfo.h"
#include "LoongArchRegisterInfo.h"
#include "LoongArchSubtarget.h"
#include "LoongArchTargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"

using namespace llvm;

#define DEBUG_TYPE "loongarch-isel-lowering"

LoongArchTargetLowering::LoongArchTargetLowering(const TargetMachine &TM,
                                                 const LoongArchSubtarget &STI)
    : TargetLowering(TM), Subtarget(STI) {

  MVT GRLenVT = Subtarget.getGRLenVT();
  // Set up the register classes.
  addRegisterClass(GRLenVT, &LoongArch::GPRRegClass);

  // TODO: add necessary setOperationAction calls later.

  // Compute derived properties from the register classes.
  computeRegisterProperties(STI.getRegisterInfo());

  setStackPointerRegisterToSaveRestore(LoongArch::R3);

  // Function alignments.
  const Align FunctionAlignment(4);
  setMinFunctionAlignment(FunctionAlignment);
}

const char *LoongArchTargetLowering::getTargetNodeName(unsigned Opcode) const {
  switch ((LoongArchISD::NodeType)Opcode) {
  case LoongArchISD::FIRST_NUMBER:
    break;

#define NODE_NAME_CASE(node)                                                   \
  case LoongArchISD::node:                                                     \
    return "LoongArchISD::" #node;

    // TODO: Add more target-dependent nodes later.
    NODE_NAME_CASE(RET)
  }
#undef NODE_NAME_CASE
  return nullptr;
}

//===----------------------------------------------------------------------===//
//                     Calling Convention Implementation
//===----------------------------------------------------------------------===//
// FIXME: Now, we only support CallingConv::C with fixed arguments which are
// passed with integer registers.
static const MCPhysReg ArgGPRs[] = {
    LoongArch::R4, LoongArch::R5, LoongArch::R6,  LoongArch::R7,
    LoongArch::R8, LoongArch::R9, LoongArch::R10, LoongArch::R11};

// Implements the LoongArch calling convention. Returns true upon failure.
static bool CC_LoongArch(unsigned ValNo, MVT ValVT,
                         CCValAssign::LocInfo LocInfo, CCState &State) {
  // Allocate to a register if possible.
  Register Reg = State.AllocateReg(ArgGPRs);
  if (Reg) {
    State.addLoc(CCValAssign::getReg(ValNo, ValVT, Reg, ValVT, LocInfo));
    return false;
  }

  // TODO: Handle arguments passed without register.
  return true;
}

void LoongArchTargetLowering::analyzeInputArgs(
    CCState &CCInfo, const SmallVectorImpl<ISD::InputArg> &Ins,
    LoongArchCCAssignFn Fn) const {
  for (unsigned i = 0, e = Ins.size(); i != e; ++i) {
    MVT ArgVT = Ins[i].VT;

    if (Fn(i, ArgVT, CCValAssign::Full, CCInfo)) {
      LLVM_DEBUG(dbgs() << "InputArg #" << i << " has unhandled type "
                        << EVT(ArgVT).getEVTString() << '\n');
      llvm_unreachable("");
    }
  }
}

void LoongArchTargetLowering::analyzeOutputArgs(
    CCState &CCInfo, const SmallVectorImpl<ISD::OutputArg> &Outs,
    LoongArchCCAssignFn Fn) const {
  for (unsigned i = 0, e = Outs.size(); i != e; ++i) {
    MVT ArgVT = Outs[i].VT;

    if (Fn(i, ArgVT, CCValAssign::Full, CCInfo)) {
      LLVM_DEBUG(dbgs() << "OutputArg #" << i << " has unhandled type "
                        << EVT(ArgVT).getEVTString() << "\n");
      llvm_unreachable("");
    }
  }
}

static SDValue unpackFromRegLoc(SelectionDAG &DAG, SDValue Chain,
                                const CCValAssign &VA, const SDLoc &DL,
                                const LoongArchTargetLowering &TLI) {
  MachineFunction &MF = DAG.getMachineFunction();
  MachineRegisterInfo &RegInfo = MF.getRegInfo();
  EVT LocVT = VA.getLocVT();
  const TargetRegisterClass *RC = TLI.getRegClassFor(LocVT.getSimpleVT());
  Register VReg = RegInfo.createVirtualRegister(RC);
  RegInfo.addLiveIn(VA.getLocReg(), VReg);

  return DAG.getCopyFromReg(Chain, DL, VReg, LocVT);
}

// Transform physical registers into virtual registers.
SDValue LoongArchTargetLowering::LowerFormalArguments(
    SDValue Chain, CallingConv::ID CallConv, bool IsVarArg,
    const SmallVectorImpl<ISD::InputArg> &Ins, const SDLoc &DL,
    SelectionDAG &DAG, SmallVectorImpl<SDValue> &InVals) const {

  MachineFunction &MF = DAG.getMachineFunction();

  switch (CallConv) {
  default:
    llvm_unreachable("Unsupported calling convention");
  case CallingConv::C:
    break;
  }

  // Assign locations to all of the incoming arguments.
  SmallVector<CCValAssign> ArgLocs;
  CCState CCInfo(CallConv, IsVarArg, MF, ArgLocs, *DAG.getContext());

  analyzeInputArgs(CCInfo, Ins, CC_LoongArch);

  for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i)
    InVals.push_back(unpackFromRegLoc(DAG, Chain, ArgLocs[i], DL, *this));

  return Chain;
}

bool LoongArchTargetLowering::CanLowerReturn(
    CallingConv::ID CallConv, MachineFunction &MF, bool IsVarArg,
    const SmallVectorImpl<ISD::OutputArg> &Outs, LLVMContext &Context) const {
  // Any return value split in to more than two values can't be returned
  // directly.
  return Outs.size() <= 2;
}

SDValue LoongArchTargetLowering::LowerReturn(
    SDValue Chain, CallingConv::ID CallConv, bool IsVarArg,
    const SmallVectorImpl<ISD::OutputArg> &Outs,
    const SmallVectorImpl<SDValue> &OutVals, const SDLoc &DL,
    SelectionDAG &DAG) const {
  // Stores the assignment of the return value to a location.
  SmallVector<CCValAssign> RVLocs;

  // Info about the registers and stack slot.
  CCState CCInfo(CallConv, IsVarArg, DAG.getMachineFunction(), RVLocs,
                 *DAG.getContext());

  analyzeOutputArgs(CCInfo, Outs, CC_LoongArch);

  SDValue Glue;
  SmallVector<SDValue, 4> RetOps(1, Chain);

  // Copy the result values into the output registers.
  for (unsigned i = 0, e = RVLocs.size(); i < e; ++i) {
    CCValAssign &VA = RVLocs[i];
    assert(VA.isRegLoc() && "Can only return in registers!");

    // Handle a 'normal' return.
    Chain = DAG.getCopyToReg(Chain, DL, VA.getLocReg(), OutVals[i], Glue);

    // Guarantee that all emitted copies are stuck together.
    Glue = Chain.getValue(1);
    RetOps.push_back(DAG.getRegister(VA.getLocReg(), VA.getLocVT()));
  }

  RetOps[0] = Chain; // Update chain.

  // Add the glue node if we have it.
  if (Glue.getNode())
    RetOps.push_back(Glue);

  return DAG.getNode(LoongArchISD::RET, DL, MVT::Other, RetOps);
}