llvm-project/llvm/lib/Target/RISCV/GISel/RISCVCallLowering.cpp

//===-- RISCVCallLowering.cpp - Call lowering -------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
/// \file
/// This file implements the lowering of LLVM calls to machine code calls for
/// GlobalISel.
//
//===----------------------------------------------------------------------===//

#include "RISCVCallLowering.h"
#include "RISCVISelLowering.h"
#include "RISCVSubtarget.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"

using namespace llvm;

namespace {

struct RISCVOutgoingValueAssigner : public CallLowering::OutgoingValueAssigner {
private:
  // The function used internally to assign args - we ignore the AssignFn stored
  // by OutgoingValueAssigner since RISC-V implements its CC using a custom
  // function with a different signature.
  RISCVTargetLowering::RISCVCCAssignFn *RISCVAssignFn;

  // Whether this is assigning args for a return.
  bool IsRet;

public:
  RISCVOutgoingValueAssigner(
      RISCVTargetLowering::RISCVCCAssignFn *RISCVAssignFn_, bool IsRet)
      : CallLowering::OutgoingValueAssigner(nullptr),
        RISCVAssignFn(RISCVAssignFn_), IsRet(IsRet) {}

  bool assignArg(unsigned ValNo, EVT OrigVT, MVT ValVT, MVT LocVT,
                 CCValAssign::LocInfo LocInfo,
                 const CallLowering::ArgInfo &Info, ISD::ArgFlagsTy Flags,
                 CCState &State) override {
    MachineFunction &MF = State.getMachineFunction();
    const DataLayout &DL = MF.getDataLayout();
    const RISCVSubtarget &Subtarget = MF.getSubtarget<RISCVSubtarget>();

    return RISCVAssignFn(DL, Subtarget.getTargetABI(), ValNo, ValVT, LocVT,
                         LocInfo, Flags, State, /*IsFixed=*/true, IsRet,
                         Info.Ty, *Subtarget.getTargetLowering(),
                         /*FirstMaskArgument=*/std::nullopt);
  }
};

struct RISCVOutgoingValueHandler : public CallLowering::OutgoingValueHandler {
  RISCVOutgoingValueHandler(MachineIRBuilder &B, MachineRegisterInfo &MRI,
                            MachineInstrBuilder MIB)
      : OutgoingValueHandler(B, MRI), MIB(MIB) {}

  MachineInstrBuilder MIB;

  Register getStackAddress(uint64_t MemSize, int64_t Offset,
                           MachinePointerInfo &MPO,
                           ISD::ArgFlagsTy Flags) override {
    llvm_unreachable("not implemented");
  }

  void assignValueToAddress(Register ValVReg, Register Addr, LLT MemTy,
                            MachinePointerInfo &MPO, CCValAssign &VA) override {
    llvm_unreachable("not implemented");
  }

  void assignValueToReg(Register ValVReg, Register PhysReg,
                        CCValAssign VA) override {
    Register ExtReg = extendRegister(ValVReg, VA);
    MIRBuilder.buildCopy(PhysReg, ExtReg);
    MIB.addUse(PhysReg, RegState::Implicit);
  }
};

struct RISCVIncomingValueAssigner : public CallLowering::IncomingValueAssigner {
private:
  // The function used internally to assign args - we ignore the AssignFn stored
  // by IncomingValueAssigner since RISC-V implements its CC using a custom
  // function with a different signature.
  RISCVTargetLowering::RISCVCCAssignFn *RISCVAssignFn;

  // Whether this is assigning args from a return.
  bool IsRet;

public:
  RISCVIncomingValueAssigner(
      RISCVTargetLowering::RISCVCCAssignFn *RISCVAssignFn_, bool IsRet)
      : CallLowering::IncomingValueAssigner(nullptr),
        RISCVAssignFn(RISCVAssignFn_), IsRet(IsRet) {}

  bool assignArg(unsigned ValNo, EVT OrigVT, MVT ValVT, MVT LocVT,
                 CCValAssign::LocInfo LocInfo,
                 const CallLowering::ArgInfo &Info, ISD::ArgFlagsTy Flags,
                 CCState &State) override {
    MachineFunction &MF = State.getMachineFunction();
    const DataLayout &DL = MF.getDataLayout();
    const RISCVSubtarget &Subtarget = MF.getSubtarget<RISCVSubtarget>();

    return RISCVAssignFn(DL, Subtarget.getTargetABI(), ValNo, ValVT, LocVT,
                         LocInfo, Flags, State, /*IsFixed=*/true, IsRet,
                         Info.Ty, *Subtarget.getTargetLowering(),
                         /*FirstMaskArgument=*/std::nullopt);
  }
};

struct RISCVIncomingValueHandler : public CallLowering::IncomingValueHandler {
  RISCVIncomingValueHandler(MachineIRBuilder &B, MachineRegisterInfo &MRI)
      : IncomingValueHandler(B, MRI) {}

  Register getStackAddress(uint64_t MemSize, int64_t Offset,
                           MachinePointerInfo &MPO,
                           ISD::ArgFlagsTy Flags) override {
    llvm_unreachable("not implemented");
  }

  void assignValueToAddress(Register ValVReg, Register Addr, LLT MemTy,
                            MachinePointerInfo &MPO, CCValAssign &VA) override {
    llvm_unreachable("not implemented");
  }

  void assignValueToReg(Register ValVReg, Register PhysReg,
                        CCValAssign VA) override {
    // Copy argument received in physical register to desired VReg.
    MIRBuilder.getMBB().addLiveIn(PhysReg);
    MIRBuilder.buildCopy(ValVReg, PhysReg);
  }
};

struct RISCVCallReturnHandler : public RISCVIncomingValueHandler {
  RISCVCallReturnHandler(MachineIRBuilder &B, MachineRegisterInfo &MRI,
                         MachineInstrBuilder &MIB)
      : RISCVIncomingValueHandler(B, MRI), MIB(MIB) {}

  MachineInstrBuilder MIB;

  void assignValueToReg(Register ValVReg, Register PhysReg,
                        CCValAssign VA) override {
    // Copy argument received in physical register to desired VReg.
    MIB.addDef(PhysReg, RegState::Implicit);
    MIRBuilder.buildCopy(ValVReg, PhysReg);
  }
};

} // namespace

RISCVCallLowering::RISCVCallLowering(const RISCVTargetLowering &TLI)
    : CallLowering(&TLI) {}

bool RISCVCallLowering::lowerReturnVal(MachineIRBuilder &MIRBuilder,
                                       const Value *Val,
                                       ArrayRef<Register> VRegs,
                                       MachineInstrBuilder &Ret) const {
  if (!Val)
    return true;

  // TODO: Only integer, pointer and aggregate types are supported now.
  if (!Val->getType()->isIntOrPtrTy() && !Val->getType()->isAggregateType())
    return false;

  MachineFunction &MF = MIRBuilder.getMF();
  const DataLayout &DL = MF.getDataLayout();
  const Function &F = MF.getFunction();
  CallingConv::ID CC = F.getCallingConv();

  ArgInfo OrigRetInfo(VRegs, Val->getType(), 0);
  setArgFlags(OrigRetInfo, AttributeList::ReturnIndex, DL, F);

  SmallVector<ArgInfo, 4> SplitRetInfos;
  splitToValueTypes(OrigRetInfo, SplitRetInfos, DL, CC);

  RISCVOutgoingValueAssigner Assigner(
      CC == CallingConv::Fast ? RISCV::CC_RISCV_FastCC : RISCV::CC_RISCV,
      /*IsRet=*/true);
  RISCVOutgoingValueHandler Handler(MIRBuilder, MF.getRegInfo(), Ret);
  return determineAndHandleAssignments(Handler, Assigner, SplitRetInfos,
                                       MIRBuilder, CC, F.isVarArg());
}

bool RISCVCallLowering::lowerReturn(MachineIRBuilder &MIRBuilder,
                                    const Value *Val, ArrayRef<Register> VRegs,
                                    FunctionLoweringInfo &FLI) const {
  assert(!Val == VRegs.empty() && "Return value without a vreg");
  MachineInstrBuilder Ret = MIRBuilder.buildInstrNoInsert(RISCV::PseudoRET);

  if (!lowerReturnVal(MIRBuilder, Val, VRegs, Ret))
    return false;

  MIRBuilder.insertInstr(Ret);
  return true;
}

bool RISCVCallLowering::lowerFormalArguments(MachineIRBuilder &MIRBuilder,
                                             const Function &F,
                                             ArrayRef<ArrayRef<Register>> VRegs,
                                             FunctionLoweringInfo &FLI) const {
  // Early exit if there are no arguments.
  if (F.arg_empty())
    return true;

  // TODO: Support vararg functions.
  if (F.isVarArg())
    return false;

  // TODO: Support all argument types.
  for (auto &Arg : F.args()) {
    if (Arg.getType()->isIntegerTy())
      continue;
    if (Arg.getType()->isPointerTy())
      continue;
    return false;
  }

  MachineFunction &MF = MIRBuilder.getMF();
  const DataLayout &DL = MF.getDataLayout();
  CallingConv::ID CC = F.getCallingConv();

  SmallVector<ArgInfo, 32> SplitArgInfos;
  unsigned Index = 0;
  for (auto &Arg : F.args()) {
    // Construct the ArgInfo object from destination register and argument type.
    ArgInfo AInfo(VRegs[Index], Arg.getType(), Index);
    setArgFlags(AInfo, Index + AttributeList::FirstArgIndex, DL, F);

    // Handle any required merging from split value types from physical
    // registers into the desired VReg. ArgInfo objects are constructed
    // correspondingly and appended to SplitArgInfos.
    splitToValueTypes(AInfo, SplitArgInfos, DL, CC);

    ++Index;
  }

  RISCVIncomingValueAssigner Assigner(
      CC == CallingConv::Fast ? RISCV::CC_RISCV_FastCC : RISCV::CC_RISCV,
      /*IsRet=*/false);
  RISCVIncomingValueHandler Handler(MIRBuilder, MF.getRegInfo());

  return determineAndHandleAssignments(Handler, Assigner, SplitArgInfos,
                                       MIRBuilder, CC, F.isVarArg());
}

bool RISCVCallLowering::lowerCall(MachineIRBuilder &MIRBuilder,
                                  CallLoweringInfo &Info) const {
  MachineFunction &MF = MIRBuilder.getMF();
  const DataLayout &DL = MF.getDataLayout();
  const Function &F = MF.getFunction();
  CallingConv::ID CC = F.getCallingConv();

  // TODO: Support vararg functions.
  if (Info.IsVarArg)
    return false;

  // TODO: Support all argument types.
  for (auto &AInfo : Info.OrigArgs) {
    if (AInfo.Ty->isIntegerTy())
      continue;
    if (AInfo.Ty->isPointerTy())
      continue;
    if (AInfo.Ty->isFloatingPointTy())
      continue;
    return false;
  }

  SmallVector<ArgInfo, 32> SplitArgInfos;
  SmallVector<ISD::OutputArg, 8> Outs;
  for (auto &AInfo : Info.OrigArgs) {
    // Handle any required unmerging of split value types from a given VReg into
    // physical registers. ArgInfo objects are constructed correspondingly and
    // appended to SplitArgInfos.
    splitToValueTypes(AInfo, SplitArgInfos, DL, CC);
  }

  // TODO: Support tail calls.
  Info.IsTailCall = false;

  if (!Info.Callee.isReg())
    Info.Callee.setTargetFlags(RISCVII::MO_CALL);

  MachineInstrBuilder Call =
      MIRBuilder
          .buildInstrNoInsert(Info.Callee.isReg() ? RISCV::PseudoCALLIndirect
                                                  : RISCV::PseudoCALL)
          .add(Info.Callee);

  RISCVOutgoingValueAssigner ArgAssigner(
      CC == CallingConv::Fast ? RISCV::CC_RISCV_FastCC : RISCV::CC_RISCV,
      /*IsRet=*/false);
  RISCVOutgoingValueHandler ArgHandler(MIRBuilder, MF.getRegInfo(), Call);
  if (!determineAndHandleAssignments(ArgHandler, ArgAssigner, SplitArgInfos,
                                     MIRBuilder, CC, Info.IsVarArg))
    return false;

  MIRBuilder.insertInstr(Call);

  if (Info.OrigRet.Ty->isVoidTy())
    return true;

  // TODO: Only integer, pointer and aggregate types are supported now.
  if (!Info.OrigRet.Ty->isIntOrPtrTy() && !Info.OrigRet.Ty->isAggregateType())
    return false;

  SmallVector<ArgInfo, 4> SplitRetInfos;
  splitToValueTypes(Info.OrigRet, SplitRetInfos, DL, CC);

  // Assignments should be handled *before* the merging of values takes place.
  // To ensure this, the insert point is temporarily adjusted to just after the
  // call instruction.
  MachineBasicBlock::iterator CallInsertPt = Call;
  MIRBuilder.setInsertPt(MIRBuilder.getMBB(), std::next(CallInsertPt));

  RISCVIncomingValueAssigner RetAssigner(
      CC == CallingConv::Fast ? RISCV::CC_RISCV_FastCC : RISCV::CC_RISCV,
      /*IsRet=*/true);
  RISCVCallReturnHandler RetHandler(MIRBuilder, MF.getRegInfo(), Call);
  if (!determineAndHandleAssignments(RetHandler, RetAssigner, SplitRetInfos,
                                     MIRBuilder, CC, Info.IsVarArg))
    return false;

  // Readjust insert point to end of basic block.
  MIRBuilder.setMBB(MIRBuilder.getMBB());

  return true;
}