llvm/lib/Target/AArch64/AArch64CallLowering.cpp

//===-- llvm/lib/Target/AArch64/AArch64CallLowering.cpp - Call lowering ---===//
//
//                     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 lowering of LLVM calls to machine code calls for
/// GlobalISel.
///
//===----------------------------------------------------------------------===//

#include "AArch64CallLowering.h"
#include "AArch64ISelLowering.h"

#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;

#ifndef LLVM_BUILD_GLOBAL_ISEL
#error "This shouldn't be built without GISel"
#endif

AArch64CallLowering::AArch64CallLowering(const AArch64TargetLowering &TLI)
  : CallLowering(&TLI) {
}

bool AArch64CallLowering::lowerReturn(MachineIRBuilder &MIRBuilder,
                                      const Value *Val, unsigned VReg) const {
  MachineFunction &MF = MIRBuilder.getMF();
  const Function &F = *MF.getFunction();

  MachineInstrBuilder MIB = MIRBuilder.buildInstr(AArch64::RET_ReallyLR);
  assert(MIB.getInstr() && "Unable to build a return instruction?!");

  assert(((Val && VReg) || (!Val && !VReg)) && "Return value without a vreg");
  if (VReg) {
    MIRBuilder.setInstr(*MIB.getInstr(), /* Before */ true);
    const AArch64TargetLowering &TLI = *getTLI<AArch64TargetLowering>();
    CCAssignFn *AssignFn = TLI.CCAssignFnForReturn(F.getCallingConv());

    handleAssignments(
        MIRBuilder, AssignFn, MVT::getVT(Val->getType()), VReg,
        [&](MachineIRBuilder &MIRBuilder, unsigned ValReg, unsigned PhysReg) {
          MIRBuilder.buildCopy(PhysReg, ValReg);
          MIB.addUse(PhysReg, RegState::Implicit);
        });
  }
  return true;
}

bool AArch64CallLowering::handleAssignments(MachineIRBuilder &MIRBuilder,
                                            CCAssignFn *AssignFn,
                                            ArrayRef<MVT> ArgTypes,
                                            ArrayRef<unsigned> ArgRegs,
                                            AssignFnTy AssignValToReg) const {
  MachineFunction &MF = MIRBuilder.getMF();
  const Function &F = *MF.getFunction();

  SmallVector<CCValAssign, 16> ArgLocs;
  CCState CCInfo(F.getCallingConv(), F.isVarArg(), MF, ArgLocs, F.getContext());

  unsigned NumArgs = ArgTypes.size();
  auto CurVT = ArgTypes.begin();
  for (unsigned i = 0; i != NumArgs; ++i, ++CurVT) {
    bool Res = AssignFn(i, *CurVT, *CurVT, CCValAssign::Full, ISD::ArgFlagsTy(),
                        CCInfo);
    if (Res)
      return false;
  }
  assert(ArgLocs.size() == ArgTypes.size() &&
         "We have a different number of location and args?!");
  for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i) {
    CCValAssign &VA = ArgLocs[i];

    // FIXME: Support non-register argument.
    if (!VA.isRegLoc())
      return false;

    switch (VA.getLocInfo()) {
    default:
      //  Unknown loc info!
      return false;
    case CCValAssign::Full:
      break;
    case CCValAssign::BCvt:
      // We don't care about bitcast.
      break;
    case CCValAssign::AExt:
      // Existing high bits are fine for anyext (whatever they are).
      break;
    case CCValAssign::SExt:
    case CCValAssign::ZExt:
      // Zero/Sign extend the register.
      // FIXME: Not yet implemented
      return false;
    }

    // Everything checks out, tell the caller where we've decided this
    // parameter/return value should go.
    AssignValToReg(MIRBuilder, ArgRegs[i], VA.getLocReg());
  }
  return true;
}

bool AArch64CallLowering::lowerFormalArguments(
    MachineIRBuilder &MIRBuilder, const Function::ArgumentListType &Args,
    ArrayRef<unsigned> VRegs) const {
  MachineFunction &MF = MIRBuilder.getMF();
  const Function &F = *MF.getFunction();

  SmallVector<MVT, 8> ArgTys;
  for (auto &Arg : Args)
    ArgTys.push_back(MVT::getVT(Arg.getType()));

  const AArch64TargetLowering &TLI = *getTLI<AArch64TargetLowering>();
  CCAssignFn *AssignFn =
      TLI.CCAssignFnForCall(F.getCallingConv(), /*IsVarArg=*/false);

  return handleAssignments(
      MIRBuilder, AssignFn, ArgTys, VRegs,
      [](MachineIRBuilder &MIRBuilder, unsigned ValReg, unsigned PhysReg) {
        MIRBuilder.getMBB().addLiveIn(PhysReg);
        MIRBuilder.buildCopy(ValReg, PhysReg);
      });
}

bool AArch64CallLowering::lowerCall(MachineIRBuilder &MIRBuilder,
                                    const CallInst &CI, unsigned CalleeReg,
                                    unsigned ResReg,
                                    ArrayRef<unsigned> ArgRegs) const {
  MachineFunction &MF = MIRBuilder.getMF();
  const Function &F = *MF.getFunction();

  // First step is to marshall all the function's parameters into the correct
  // physregs and memory locations. Gather the sequence of argument types that
  // we'll pass to the assigner function.
  SmallVector<MVT, 8> ArgTys;
  for (auto &Arg : CI.arg_operands())
    ArgTys.push_back(MVT::getVT(Arg->getType()));

  // Find out which ABI gets to decide where things go.
  const AArch64TargetLowering &TLI = *getTLI<AArch64TargetLowering>();
  CCAssignFn *CallAssignFn =
      TLI.CCAssignFnForCall(F.getCallingConv(), /*IsVarArg=*/false);

  // And finally we can do the actual assignments. For a call we need to keep
  // track of the registers used because they'll be implicit uses of the BL.
  SmallVector<unsigned, 8> PhysRegs;
  handleAssignments(
      MIRBuilder, CallAssignFn, ArgTys, ArgRegs,
      [&](MachineIRBuilder &MIRBuilder, unsigned ValReg, unsigned PhysReg) {
        MIRBuilder.buildCopy(PhysReg, ValReg);
        PhysRegs.push_back(PhysReg);
      });

  // Now we can build the actual call instruction.
  MachineInstrBuilder MIB;
  if (CalleeReg)
    MIB = MIRBuilder.buildInstr(AArch64::BLR).addUse(CalleeReg);
  else
    MIB = MIRBuilder.buildInstr(AArch64::BL)
              .addGlobalAddress(CI.getCalledFunction());

  // Tell the call which registers are clobbered.
  auto TRI = MF.getSubtarget().getRegisterInfo();
  MIB.addRegMask(TRI->getCallPreservedMask(MF, F.getCallingConv()));

  for (auto Reg : PhysRegs)
    MIB.addUse(Reg, RegState::Implicit);

  // Finally we can copy the returned value back into its virtual-register. In
  // symmetry with the arugments, the physical register must be an
  // implicit-define of the call instruction.
  CCAssignFn *RetAssignFn = TLI.CCAssignFnForReturn(F.getCallingConv());
  if (!CI.getType()->isVoidTy())
    handleAssignments(
        MIRBuilder, RetAssignFn, MVT::getVT(CI.getType()), ResReg,
        [&](MachineIRBuilder &MIRBuilder, unsigned ValReg, unsigned PhysReg) {
          MIRBuilder.buildCopy(ValReg, PhysReg);
          MIB.addDef(PhysReg, RegState::Implicit);
        });

  return true;
}