X86CallLowering.cpp

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//===- llvm/lib/Target/X86/X86CallLowering.cpp - Call lowering ------------===//
//
// 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 "X86CallLowering.h"
#include "X86CallingConv.h"
#include "X86ISelLowering.h"
#include "X86InstrInfo.h"
#include "X86RegisterInfo.h"
#include "X86Subtarget.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/CallingConvLower.h"
#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
#include "llvm/CodeGen/GlobalISel/Utils.h"
#include "llvm/CodeGen/LowLevelType.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/ValueTypes.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Value.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Support/LowLevelTypeImpl.h"
#include "llvm/Support/MachineValueType.h"
#include <cassert>
#include <cstdint>
 
using namespace llvm;
 
X86CallLowering::X86CallLowering(const X86TargetLowering &TLI)
    : CallLowering(&TLI) {}
 
// FIXME: This should be removed and the generic version used
bool X86CallLowering::splitToValueTypes(const ArgInfo &OrigArg,
                                        SmallVectorImpl<ArgInfo> &SplitArgs,
                                        const DataLayout &DL,
                                        MachineRegisterInfo &MRI,
                                        SplitArgTy PerformArgSplit) const {
  const X86TargetLowering &TLI = *getTLI<X86TargetLowering>();
  LLVMContext &Context = OrigArg.Ty->getContext();
 
  SmallVector<EVT, 4> SplitVTs;
  SmallVector<uint64_t, 4> Offsets;
  ComputeValueVTs(TLI, DL, OrigArg.Ty, SplitVTs, &Offsets, 0);
  assert(OrigArg.Regs.size() == 1 && "Can't handle multple regs yet");
 
  if (OrigArg.Ty->isVoidTy())
    return true;
 
  EVT VT = SplitVTs[0];
  unsigned NumParts = TLI.getNumRegisters(Context, VT);
 
  if (NumParts == 1) {
    // replace the original type ( pointer -> GPR ).
    SplitArgs.emplace_back(OrigArg.Regs[0], VT.getTypeForEVT(Context),
                           OrigArg.Flags, OrigArg.IsFixed);
    return true;
  }
 
  SmallVector<Register, 8> SplitRegs;
 
  EVT PartVT = TLI.getRegisterType(Context, VT);
  Type *PartTy = PartVT.getTypeForEVT(Context);
 
  for (unsigned i = 0; i < NumParts; ++i) {
    ArgInfo Info =
        ArgInfo{MRI.createGenericVirtualRegister(getLLTForType(*PartTy, DL)),
                PartTy, OrigArg.Flags};
    SplitArgs.push_back(Info);
    SplitRegs.push_back(Info.Regs[0]);
  }
 
  PerformArgSplit(SplitRegs);
  return true;
}
 
namespace {
 
struct X86OutgoingValueHandler : public CallLowering::OutgoingValueHandler {
  X86OutgoingValueHandler(MachineIRBuilder &MIRBuilder,
                          MachineRegisterInfo &MRI, MachineInstrBuilder &MIB,
                          CCAssignFn *AssignFn)
      : OutgoingValueHandler(MIRBuilder, MRI, AssignFn), MIB(MIB),
        DL(MIRBuilder.getMF().getDataLayout()),
        STI(MIRBuilder.getMF().getSubtarget<X86Subtarget>()) {}
 
  Register getStackAddress(uint64_t Size, int64_t Offset,
                           MachinePointerInfo &MPO,
                           ISD::ArgFlagsTy Flags) override {
    LLT p0 = LLT::pointer(0, DL.getPointerSizeInBits(0));
    LLT SType = LLT::scalar(DL.getPointerSizeInBits(0));
    auto SPReg =
        MIRBuilder.buildCopy(p0, STI.getRegisterInfo()->getStackRegister());
 
    auto OffsetReg = MIRBuilder.buildConstant(SType, Offset);
 
    auto AddrReg = MIRBuilder.buildPtrAdd(p0, SPReg, OffsetReg);
 
    MPO = MachinePointerInfo::getStack(MIRBuilder.getMF(), Offset);
    return AddrReg.getReg(0);
  }
 
  void assignValueToReg(Register ValVReg, Register PhysReg,
                        CCValAssign &VA) override {
    MIB.addUse(PhysReg, RegState::Implicit);
 
    Register ExtReg;
    // If we are copying the value to a physical register with the
    // size larger than the size of the value itself - build AnyExt
    // to the size of the register first and only then do the copy.
    // The example of that would be copying from s32 to xmm0, for which
    // case ValVT == LocVT == MVT::f32. If LocSize and ValSize are not equal
    // we expect normal extendRegister mechanism to work.
    unsigned PhysRegSize =
        MRI.getTargetRegisterInfo()->getRegSizeInBits(PhysReg, MRI);
    unsigned ValSize = VA.getValVT().getSizeInBits();
    unsigned LocSize = VA.getLocVT().getSizeInBits();
    if (PhysRegSize > ValSize && LocSize == ValSize) {
      assert((PhysRegSize == 128 || PhysRegSize == 80) &&
             "We expect that to be 128 bit");
      ExtReg =
          MIRBuilder.buildAnyExt(LLT::scalar(PhysRegSize), ValVReg).getReg(0);
    } else
      ExtReg = extendRegister(ValVReg, VA);
 
    MIRBuilder.buildCopy(PhysReg, ExtReg);
  }
 
  void assignValueToAddress(Register ValVReg, Register Addr, uint64_t Size,
                            MachinePointerInfo &MPO, CCValAssign &VA) override {
    MachineFunction &MF = MIRBuilder.getMF();
    Register ExtReg = extendRegister(ValVReg, VA);
 
    auto *MMO = MF.getMachineMemOperand(MPO, MachineMemOperand::MOStore,
                                        VA.getLocVT().getStoreSize(),
                                        inferAlignFromPtrInfo(MF, MPO));
    MIRBuilder.buildStore(ExtReg, Addr, *MMO);
  }
 
  bool assignArg(unsigned ValNo, MVT ValVT, MVT LocVT,
                 CCValAssign::LocInfo LocInfo,
                 const CallLowering::ArgInfo &Info, ISD::ArgFlagsTy Flags,
                 CCState &State) override {
    bool Res = AssignFn(ValNo, ValVT, LocVT, LocInfo, Flags, State);
    StackSize = State.getNextStackOffset();
 
    static const MCPhysReg XMMArgRegs[] = {X86::XMM0, X86::XMM1, X86::XMM2,
                                           X86::XMM3, X86::XMM4, X86::XMM5,
                                           X86::XMM6, X86::XMM7};
    if (!Info.IsFixed)
      NumXMMRegs = State.getFirstUnallocated(XMMArgRegs);
 
    return Res;
  }
 
  uint64_t getStackSize() { return StackSize; }
  uint64_t getNumXmmRegs() { return NumXMMRegs; }
 
protected:
  MachineInstrBuilder &MIB;
  uint64_t StackSize = 0;
  const DataLayout &DL;
  const X86Subtarget &STI;
  unsigned NumXMMRegs = 0;
};
 
} // end anonymous namespace
 
bool X86CallLowering::lowerReturn(MachineIRBuilder &MIRBuilder,
                                  const Value *Val, ArrayRef<Register> VRegs,
                                  FunctionLoweringInfo &FLI) const {
  assert(((Val && !VRegs.empty()) || (!Val && VRegs.empty())) &&
         "Return value without a vreg");
  auto MIB = MIRBuilder.buildInstrNoInsert(X86::RET).addImm(0);
 
  if (!VRegs.empty()) {
    MachineFunction &MF = MIRBuilder.getMF();
    const Function &F = MF.getFunction();
    MachineRegisterInfo &MRI = MF.getRegInfo();
    const DataLayout &DL = MF.getDataLayout();
    LLVMContext &Ctx = Val->getType()->getContext();
    const X86TargetLowering &TLI = *getTLI<X86TargetLowering>();
 
    SmallVector<EVT, 4> SplitEVTs;
    ComputeValueVTs(TLI, DL, Val->getType(), SplitEVTs);
    assert(VRegs.size() == SplitEVTs.size() &&
           "For each split Type there should be exactly one VReg.");
 
    SmallVector<ArgInfo, 8> SplitArgs;
    for (unsigned i = 0; i < SplitEVTs.size(); ++i) {
      ArgInfo CurArgInfo = ArgInfo{VRegs[i], SplitEVTs[i].getTypeForEVT(Ctx)};
      setArgFlags(CurArgInfo, AttributeList::ReturnIndex, DL, F);
      if (!splitToValueTypes(CurArgInfo, SplitArgs, DL, MRI,
                             [&](ArrayRef<Register> Regs) {
                               MIRBuilder.buildUnmerge(Regs, VRegs[i]);
                             }))
        return false;
    }
 
    X86OutgoingValueHandler Handler(MIRBuilder, MRI, MIB, RetCC_X86);
    if (!handleAssignments(MIRBuilder, SplitArgs, Handler, F.getCallingConv(),
                           F.isVarArg()))
      return false;
  }
 
  MIRBuilder.insertInstr(MIB);
  return true;
}
 
namespace {
 
struct X86IncomingValueHandler : public CallLowering::IncomingValueHandler {
  X86IncomingValueHandler(MachineIRBuilder &MIRBuilder,
                          MachineRegisterInfo &MRI, CCAssignFn *AssignFn)
      : IncomingValueHandler(MIRBuilder, MRI, AssignFn),
        DL(MIRBuilder.getMF().getDataLayout()) {}
 
  Register getStackAddress(uint64_t Size, int64_t Offset,
                           MachinePointerInfo &MPO,
                           ISD::ArgFlagsTy Flags) override {
    auto &MFI = MIRBuilder.getMF().getFrameInfo();
 
    // Byval is assumed to be writable memory, but other stack passed arguments
    // are not.
    const bool IsImmutable = !Flags.isByVal();
 
    int FI = MFI.CreateFixedObject(Size, Offset, IsImmutable);
    MPO = MachinePointerInfo::getFixedStack(MIRBuilder.getMF(), FI);
 
    return MIRBuilder
        .buildFrameIndex(LLT::pointer(0, DL.getPointerSizeInBits(0)), FI)
        .getReg(0);
  }
 
  void assignValueToAddress(Register ValVReg, Register Addr, uint64_t Size,
                            MachinePointerInfo &MPO, CCValAssign &VA) override {
    MachineFunction &MF = MIRBuilder.getMF();
    auto *MMO = MF.getMachineMemOperand(
        MPO, MachineMemOperand::MOLoad | MachineMemOperand::MOInvariant, Size,
        inferAlignFromPtrInfo(MF, MPO));
    MIRBuilder.buildLoad(ValVReg, Addr, *MMO);
  }
 
  void assignValueToReg(Register ValVReg, Register PhysReg,
                        CCValAssign &VA) override {
    markPhysRegUsed(PhysReg);
 
    switch (VA.getLocInfo()) {
    default: {
      // If we are copying the value from a physical register with the
      // size larger than the size of the value itself - build the copy
      // of the phys reg first and then build the truncation of that copy.
      // The example of that would be copying from xmm0 to s32, for which
      // case ValVT == LocVT == MVT::f32. If LocSize and ValSize are not equal
      // we expect this to be handled in SExt/ZExt/AExt case.
      unsigned PhysRegSize =
          MRI.getTargetRegisterInfo()->getRegSizeInBits(PhysReg, MRI);
      unsigned ValSize = VA.getValVT().getSizeInBits();
      unsigned LocSize = VA.getLocVT().getSizeInBits();
      if (PhysRegSize > ValSize && LocSize == ValSize) {
        auto Copy = MIRBuilder.buildCopy(LLT::scalar(PhysRegSize), PhysReg);
        MIRBuilder.buildTrunc(ValVReg, Copy);
        return;
      }
 
      MIRBuilder.buildCopy(ValVReg, PhysReg);
      break;
    }
    case CCValAssign::LocInfo::SExt:
    case CCValAssign::LocInfo::ZExt:
    case CCValAssign::LocInfo::AExt: {
      auto Copy = MIRBuilder.buildCopy(LLT{VA.getLocVT()}, PhysReg);
      MIRBuilder.buildTrunc(ValVReg, Copy);
      break;
    }
    }
  }
 
  /// How the physical register gets marked varies between formal
  /// parameters (it's a basic-block live-in), and a call instruction
  /// (it's an implicit-def of the BL).
  virtual void markPhysRegUsed(unsigned PhysReg) = 0;
 
protected:
  const DataLayout &DL;
};
 
struct FormalArgHandler : public X86IncomingValueHandler {
  FormalArgHandler(MachineIRBuilder &MIRBuilder, MachineRegisterInfo &MRI,
                   CCAssignFn *AssignFn)
      : X86IncomingValueHandler(MIRBuilder, MRI, AssignFn) {}
 
  void markPhysRegUsed(unsigned PhysReg) override {
    MIRBuilder.getMRI()->addLiveIn(PhysReg);
    MIRBuilder.getMBB().addLiveIn(PhysReg);
  }
};
 
struct CallReturnHandler : public X86IncomingValueHandler {
  CallReturnHandler(MachineIRBuilder &MIRBuilder, MachineRegisterInfo &MRI,
                    CCAssignFn *AssignFn, MachineInstrBuilder &MIB)
      : X86IncomingValueHandler(MIRBuilder, MRI, AssignFn), MIB(MIB) {}
 
  void markPhysRegUsed(unsigned PhysReg) override {
    MIB.addDef(PhysReg, RegState::Implicit);
  }
 
protected:
  MachineInstrBuilder &MIB;
};
 
} // end anonymous namespace
 
bool X86CallLowering::lowerFormalArguments(MachineIRBuilder &MIRBuilder,
                                           const Function &F,
                                           ArrayRef<ArrayRef<Register>> VRegs,
                                           FunctionLoweringInfo &FLI) const {
  if (F.arg_empty())
    return true;
 
  // TODO: handle variadic function
  if (F.isVarArg())
    return false;
 
  MachineFunction &MF = MIRBuilder.getMF();
  MachineRegisterInfo &MRI = MF.getRegInfo();
  auto DL = MF.getDataLayout();
 
  SmallVector<ArgInfo, 8> SplitArgs;
  unsigned Idx = 0;
  for (const auto &Arg : F.args()) {
    // TODO: handle not simple cases.
    if (Arg.hasAttribute(Attribute::ByVal) ||
        Arg.hasAttribute(Attribute::InReg) ||
        Arg.hasAttribute(Attribute::StructRet) ||
        Arg.hasAttribute(Attribute::SwiftSelf) ||
        Arg.hasAttribute(Attribute::SwiftError) ||
        Arg.hasAttribute(Attribute::Nest) || VRegs[Idx].size() > 1)
      return false;
 
    ArgInfo OrigArg(VRegs[Idx], Arg.getType());
    setArgFlags(OrigArg, Idx + AttributeList::FirstArgIndex, DL, F);
    if (!splitToValueTypes(OrigArg, SplitArgs, DL, MRI,
                           [&](ArrayRef<Register> Regs) {
                             MIRBuilder.buildMerge(VRegs[Idx][0], Regs);
                           }))
      return false;
    Idx++;
  }
 
  MachineBasicBlock &MBB = MIRBuilder.getMBB();
  if (!MBB.empty())
    MIRBuilder.setInstr(*MBB.begin());
 
  FormalArgHandler Handler(MIRBuilder, MRI, CC_X86);
  if (!handleAssignments(MIRBuilder, SplitArgs, Handler, F.getCallingConv(),
                         F.isVarArg()))
    return false;
 
  // Move back to the end of the basic block.
  MIRBuilder.setMBB(MBB);
 
  return true;
}
 
bool X86CallLowering::lowerCall(MachineIRBuilder &MIRBuilder,
                                CallLoweringInfo &Info) const {
  MachineFunction &MF = MIRBuilder.getMF();
  const Function &F = MF.getFunction();
  MachineRegisterInfo &MRI = MF.getRegInfo();
  const DataLayout &DL = F.getParent()->getDataLayout();
  const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
  const TargetInstrInfo &TII = *STI.getInstrInfo();
  const X86RegisterInfo *TRI = STI.getRegisterInfo();
 
  // Handle only Linux C, X86_64_SysV calling conventions for now.
  if (!STI.isTargetLinux() || !(Info.CallConv == CallingConv::C ||
                                Info.CallConv == CallingConv::X86_64_SysV))
    return false;
 
  unsigned AdjStackDown = TII.getCallFrameSetupOpcode();
  auto CallSeqStart = MIRBuilder.buildInstr(AdjStackDown);
 
  // Create a temporarily-floating call instruction so we can add the implicit
  // uses of arg registers.
  bool Is64Bit = STI.is64Bit();
  unsigned CallOpc = Info.Callee.isReg()
                         ? (Is64Bit ? X86::CALL64r : X86::CALL32r)
                         : (Is64Bit ? X86::CALL64pcrel32 : X86::CALLpcrel32);
 
  auto MIB = MIRBuilder.buildInstrNoInsert(CallOpc)
                 .add(Info.Callee)
                 .addRegMask(TRI->getCallPreservedMask(MF, Info.CallConv));
 
  SmallVector<ArgInfo, 8> SplitArgs;
  for (const auto &OrigArg : Info.OrigArgs) {
 
    // TODO: handle not simple cases.
    if (OrigArg.Flags[0].isByVal())
      return false;
 
    if (OrigArg.Regs.size() > 1)
      return false;
 
    if (!splitToValueTypes(OrigArg, SplitArgs, DL, MRI,
                           [&](ArrayRef<Register> Regs) {
                             MIRBuilder.buildUnmerge(Regs, OrigArg.Regs[0]);
                           }))
      return false;
  }
  // Do the actual argument marshalling.
  X86OutgoingValueHandler Handler(MIRBuilder, MRI, MIB, CC_X86);
  if (!handleAssignments(MIRBuilder, SplitArgs, Handler, Info.CallConv,
                         Info.IsVarArg))
    return false;
 
  bool IsFixed = Info.OrigArgs.empty() ? true : Info.OrigArgs.back().IsFixed;
  if (STI.is64Bit() && !IsFixed && !STI.isCallingConvWin64(Info.CallConv)) {
    // From AMD64 ABI document:
    // For calls that may call functions that use varargs or stdargs
    // (prototype-less calls or calls to functions containing ellipsis (...) in
    // the declaration) %al is used as hidden argument to specify the number
    // of SSE registers used. The contents of %al do not need to match exactly
    // the number of registers, but must be an ubound on the number of SSE
    // registers used and is in the range 0 - 8 inclusive.
 
    MIRBuilder.buildInstr(X86::MOV8ri)
        .addDef(X86::AL)
        .addImm(Handler.getNumXmmRegs());
    MIB.addUse(X86::AL, RegState::Implicit);
  }
 
  // Now we can add the actual call instruction to the correct basic block.
  MIRBuilder.insertInstr(MIB);
 
  // If Callee is a reg, since it is used by a target specific
  // instruction, it must have a register class matching the
  // constraint of that instruction.
  if (Info.Callee.isReg())
    MIB->getOperand(0).setReg(constrainOperandRegClass(
        MF, *TRI, MRI, *MF.getSubtarget().getInstrInfo(),
        *MF.getSubtarget().getRegBankInfo(), *MIB, MIB->getDesc(), Info.Callee,
        0));
 
  // Finally we can copy the returned value back into its virtual-register. In
  // symmetry with the arguments, the physical register must be an
  // implicit-define of the call instruction.
 
  if (!Info.OrigRet.Ty->isVoidTy()) {
    if (Info.OrigRet.Regs.size() > 1)
      return false;
 
    SplitArgs.clear();
    SmallVector<Register, 8> NewRegs;
 
    if (!splitToValueTypes(Info.OrigRet, SplitArgs, DL, MRI,
                           [&](ArrayRef<Register> Regs) {
                             NewRegs.assign(Regs.begin(), Regs.end());
                           }))
      return false;
 
    CallReturnHandler Handler(MIRBuilder, MRI, RetCC_X86, MIB);
    if (!handleAssignments(MIRBuilder, SplitArgs, Handler, Info.CallConv,
                           Info.IsVarArg))
      return false;
 
    if (!NewRegs.empty())
      MIRBuilder.buildMerge(Info.OrigRet.Regs[0], NewRegs);
  }
 
  CallSeqStart.addImm(Handler.getStackSize())
      .addImm(0 /* see getFrameTotalSize */)
      .addImm(0 /* see getFrameAdjustment */);
 
  unsigned AdjStackUp = TII.getCallFrameDestroyOpcode();
  MIRBuilder.buildInstr(AdjStackUp)
      .addImm(Handler.getStackSize())
      .addImm(0 /* NumBytesForCalleeToPop */);
 
  return true;
}