llvm/lib/Target/Xtensa/XtensaISelLowering.cpp

//===- XtensaISelLowering.cpp - Xtensa 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 Xtensa uses to lower LLVM code into a
// selection DAG.
//
//===----------------------------------------------------------------------===//

#include "XtensaISelLowering.h"
#include "XtensaConstantPoolValue.h"
#include "XtensaSubtarget.h"
#include "XtensaTargetMachine.h"
#include "llvm/CodeGen/CallingConvLower.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineJumpTableInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <deque>

using namespace llvm;

#define DEBUG_TYPE "xtensa-lower"

// Return true if we must use long (in fact, indirect) function call.
// It's simplified version, production implimentation must
// resolve a functions in ROM (usually glibc functions)
static bool isLongCall(const char *str) {
  // Currently always use long calls
  return true;
}

XtensaTargetLowering::XtensaTargetLowering(const TargetMachine &TM,
                                           const XtensaSubtarget &STI)
    : TargetLowering(TM), Subtarget(STI) {
  MVT PtrVT = MVT::i32;
  // Set up the register classes.
  addRegisterClass(MVT::i32, &Xtensa::ARRegClass);

  // Set up special registers.
  setStackPointerRegisterToSaveRestore(Xtensa::SP);

  setSchedulingPreference(Sched::RegPressure);

  setMinFunctionAlignment(Align(4));

  setOperationAction(ISD::Constant, MVT::i32, Custom);
  setOperationAction(ISD::Constant, MVT::i64, Expand);

  setBooleanContents(ZeroOrOneBooleanContent);

  setOperationAction(ISD::SIGN_EXTEND_INREG, MVT::i1, Expand);
  setOperationAction(ISD::SIGN_EXTEND_INREG, MVT::i8, Expand);
  setOperationAction(ISD::SIGN_EXTEND_INREG, MVT::i16, Expand);

  setOperationAction(ISD::BITCAST, MVT::i32, Expand);
  setOperationAction(ISD::BITCAST, MVT::f32, Expand);
  setOperationAction(ISD::UINT_TO_FP, MVT::i32, Expand);
  setOperationAction(ISD::SINT_TO_FP, MVT::i32, Expand);
  setOperationAction(ISD::FP_TO_UINT, MVT::i32, Expand);
  setOperationAction(ISD::FP_TO_SINT, MVT::i32, Expand);

  // No sign extend instructions for i1
  for (MVT VT : MVT::integer_valuetypes()) {
    setLoadExtAction(ISD::SEXTLOAD, VT, MVT::i1, Promote);
    setLoadExtAction(ISD::ZEXTLOAD, VT, MVT::i1, Promote);
    setLoadExtAction(ISD::EXTLOAD, VT, MVT::i1, Promote);
  }

  setOperationAction(ISD::ConstantPool, PtrVT, Custom);

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

//===----------------------------------------------------------------------===//
// Calling conventions
//===----------------------------------------------------------------------===//

#include "XtensaGenCallingConv.inc"

static bool CC_Xtensa_Custom(unsigned ValNo, MVT ValVT, MVT LocVT,
                             CCValAssign::LocInfo LocInfo,
                             ISD::ArgFlagsTy ArgFlags, CCState &State) {
  static const MCPhysReg IntRegs[] = {Xtensa::A2, Xtensa::A3, Xtensa::A4,
                                      Xtensa::A5, Xtensa::A6, Xtensa::A7};

  if (ArgFlags.isByVal()) {
    Align ByValAlign = ArgFlags.getNonZeroByValAlign();
    unsigned ByValSize = ArgFlags.getByValSize();
    if (ByValSize < 4) {
      ByValSize = 4;
    }
    if (ByValAlign < Align(4)) {
      ByValAlign = Align(4);
    }
    unsigned Offset = State.AllocateStack(ByValSize, ByValAlign);
    State.addLoc(CCValAssign::getMem(ValNo, ValVT, Offset, LocVT, LocInfo));
    // Mark all unused registers as allocated to avoid misuse
    // of such registers.
    while (State.AllocateReg(IntRegs))
      ;
    return false;
  }

  // Promote i8 and i16
  if (LocVT == MVT::i8 || LocVT == MVT::i16) {
    LocVT = MVT::i32;
    if (ArgFlags.isSExt())
      LocInfo = CCValAssign::SExt;
    else if (ArgFlags.isZExt())
      LocInfo = CCValAssign::ZExt;
    else
      LocInfo = CCValAssign::AExt;
  }

  unsigned Register;

  Align OrigAlign = ArgFlags.getNonZeroOrigAlign();
  bool needs64BitAlign = (ValVT == MVT::i32 && OrigAlign == Align(8));
  bool needs128BitAlign = (ValVT == MVT::i32 && OrigAlign == Align(16));

  if (ValVT == MVT::i32) {
    Register = State.AllocateReg(IntRegs);
    // If this is the first part of an i64 arg,
    // the allocated register must be either A2, A4 or A6.
    if (needs64BitAlign && (Register == Xtensa::A3 || Register == Xtensa::A5 ||
                            Register == Xtensa::A7))
      Register = State.AllocateReg(IntRegs);
    // arguments with 16byte alignment must be passed in the first register or
    // passed via stack
    if (needs128BitAlign && (Register != Xtensa::A2))
      while ((Register = State.AllocateReg(IntRegs)))
        ;
    LocVT = MVT::i32;
  } else if (ValVT == MVT::f64) {
    // Allocate int register and shadow next int register.
    Register = State.AllocateReg(IntRegs);
    if (Register == Xtensa::A3 || Register == Xtensa::A5 ||
        Register == Xtensa::A7)
      Register = State.AllocateReg(IntRegs);
    State.AllocateReg(IntRegs);
    LocVT = MVT::i32;
  } else {
    report_fatal_error("Cannot handle this ValVT.");
  }

  if (!Register) {
    unsigned Offset = State.AllocateStack(ValVT.getStoreSize(), OrigAlign);
    State.addLoc(CCValAssign::getMem(ValNo, ValVT, Offset, LocVT, LocInfo));
  } else {
    State.addLoc(CCValAssign::getReg(ValNo, ValVT, Register, LocVT, LocInfo));
  }

  return false;
}

CCAssignFn *XtensaTargetLowering::CCAssignFnForCall(CallingConv::ID CC,
                                                    bool IsVarArg) const {
  return CC_Xtensa_Custom;
}

SDValue XtensaTargetLowering::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();
  MachineFrameInfo &MFI = MF.getFrameInfo();

  // Used with vargs to acumulate store chains.
  std::vector<SDValue> OutChains;

  if (IsVarArg)
    report_fatal_error("Var arg not supported by FormalArguments Lowering");

  // Assign locations to all of the incoming arguments.
  SmallVector<CCValAssign, 16> ArgLocs;
  CCState CCInfo(CallConv, IsVarArg, DAG.getMachineFunction(), ArgLocs,
                 *DAG.getContext());

  CCInfo.AnalyzeFormalArguments(Ins, CCAssignFnForCall(CallConv, IsVarArg));

  for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i) {
    CCValAssign &VA = ArgLocs[i];
    // Arguments stored on registers
    if (VA.isRegLoc()) {
      EVT RegVT = VA.getLocVT();
      const TargetRegisterClass *RC;

      if (RegVT == MVT::i32)
        RC = &Xtensa::ARRegClass;
      else
        report_fatal_error("RegVT not supported by FormalArguments Lowering");

      // Transform the arguments stored on
      // physical registers into virtual ones
      unsigned Register = MF.addLiveIn(VA.getLocReg(), RC);
      SDValue ArgValue = DAG.getCopyFromReg(Chain, DL, Register, RegVT);

      // If this is an 8 or 16-bit value, it has been passed promoted
      // to 32 bits.  Insert an assert[sz]ext to capture this, then
      // truncate to the right size.
      if (VA.getLocInfo() != CCValAssign::Full) {
        unsigned Opcode = 0;
        if (VA.getLocInfo() == CCValAssign::SExt)
          Opcode = ISD::AssertSext;
        else if (VA.getLocInfo() == CCValAssign::ZExt)
          Opcode = ISD::AssertZext;
        if (Opcode)
          ArgValue = DAG.getNode(Opcode, DL, RegVT, ArgValue,
                                 DAG.getValueType(VA.getValVT()));
        ArgValue = DAG.getNode((VA.getValVT() == MVT::f32) ? ISD::BITCAST
                                                           : ISD::TRUNCATE,
                               DL, VA.getValVT(), ArgValue);
      }

      InVals.push_back(ArgValue);

    } else {
      assert(VA.isMemLoc());

      EVT ValVT = VA.getValVT();

      // The stack pointer offset is relative to the caller stack frame.
      int FI = MFI.CreateFixedObject(ValVT.getStoreSize(), VA.getLocMemOffset(),
                                     true);

      if (Ins[VA.getValNo()].Flags.isByVal()) {
        // Assume that in this case load operation is created
        SDValue FIN = DAG.getFrameIndex(FI, MVT::i32);
        InVals.push_back(FIN);
      } else {
        // Create load nodes to retrieve arguments from the stack
        SDValue FIN =
            DAG.getFrameIndex(FI, getFrameIndexTy(DAG.getDataLayout()));
        InVals.push_back(DAG.getLoad(
            ValVT, DL, Chain, FIN,
            MachinePointerInfo::getFixedStack(DAG.getMachineFunction(), FI)));
      }
    }
  }

  // All stores are grouped in one node to allow the matching between
  // the size of Ins and InVals. This only happens when on varg functions
  if (!OutChains.empty()) {
    OutChains.push_back(Chain);
    Chain = DAG.getNode(ISD::TokenFactor, DL, MVT::Other, OutChains);
  }

  return Chain;
}

SDValue
XtensaTargetLowering::LowerCall(CallLoweringInfo &CLI,
                                SmallVectorImpl<SDValue> &InVals) const {
  SelectionDAG &DAG = CLI.DAG;
  SDLoc &DL = CLI.DL;
  SmallVector<ISD::OutputArg, 32> &Outs = CLI.Outs;
  SmallVector<SDValue, 32> &OutVals = CLI.OutVals;
  SmallVector<ISD::InputArg, 32> &Ins = CLI.Ins;
  SDValue Chain = CLI.Chain;
  SDValue Callee = CLI.Callee;
  bool &IsTailCall = CLI.IsTailCall;
  CallingConv::ID CallConv = CLI.CallConv;
  bool IsVarArg = CLI.IsVarArg;

  MachineFunction &MF = DAG.getMachineFunction();
  EVT PtrVT = getPointerTy(DAG.getDataLayout());
  const TargetFrameLowering *TFL = Subtarget.getFrameLowering();

  // TODO: Support tail call optimization.
  IsTailCall = false;

  // Analyze the operands of the call, assigning locations to each operand.
  SmallVector<CCValAssign, 16> ArgLocs;
  CCState CCInfo(CallConv, IsVarArg, MF, ArgLocs, *DAG.getContext());

  CCAssignFn *CC = CCAssignFnForCall(CallConv, IsVarArg);

  CCInfo.AnalyzeCallOperands(Outs, CC);

  // Get a count of how many bytes are to be pushed on the stack.
  unsigned NumBytes = CCInfo.getStackSize();

  Align StackAlignment = TFL->getStackAlign();
  unsigned NextStackOffset = alignTo(NumBytes, StackAlignment);

  Chain = DAG.getCALLSEQ_START(Chain, NextStackOffset, 0, DL);

  // Copy argument values to their designated locations.
  std::deque<std::pair<unsigned, SDValue>> RegsToPass;
  SmallVector<SDValue, 8> MemOpChains;
  SDValue StackPtr;
  for (unsigned I = 0, E = ArgLocs.size(); I != E; ++I) {
    CCValAssign &VA = ArgLocs[I];
    SDValue ArgValue = OutVals[I];
    ISD::ArgFlagsTy Flags = Outs[I].Flags;

    if (VA.isRegLoc())
      // Queue up the argument copies and emit them at the end.
      RegsToPass.push_back(std::make_pair(VA.getLocReg(), ArgValue));
    else if (Flags.isByVal()) {
      assert(VA.isMemLoc());
      assert(Flags.getByValSize() &&
             "ByVal args of size 0 should have been ignored by front-end.");
      assert(!IsTailCall &&
             "Do not tail-call optimize if there is a byval argument.");

      if (!StackPtr.getNode())
        StackPtr = DAG.getCopyFromReg(Chain, DL, Xtensa::SP, PtrVT);
      unsigned Offset = VA.getLocMemOffset();
      SDValue Address = DAG.getNode(ISD::ADD, DL, PtrVT, StackPtr,
                                    DAG.getIntPtrConstant(Offset, DL));
      SDValue SizeNode = DAG.getConstant(Flags.getByValSize(), DL, MVT::i32);
      SDValue Memcpy = DAG.getMemcpy(
          Chain, DL, Address, ArgValue, SizeNode, Flags.getNonZeroByValAlign(),
          /*isVolatile=*/false, /*AlwaysInline=*/false,
          /*isTailCall=*/false, MachinePointerInfo(), MachinePointerInfo());
      MemOpChains.push_back(Memcpy);
    } else {
      assert(VA.isMemLoc() && "Argument not register or memory");

      // Work out the address of the stack slot.  Unpromoted ints and
      // floats are passed as right-justified 8-byte values.
      if (!StackPtr.getNode())
        StackPtr = DAG.getCopyFromReg(Chain, DL, Xtensa::SP, PtrVT);
      unsigned Offset = VA.getLocMemOffset();
      SDValue Address = DAG.getNode(ISD::ADD, DL, PtrVT, StackPtr,
                                    DAG.getIntPtrConstant(Offset, DL));

      // Emit the store.
      MemOpChains.push_back(
          DAG.getStore(Chain, DL, ArgValue, Address, MachinePointerInfo()));
    }
  }

  // Join the stores, which are independent of one another.
  if (!MemOpChains.empty())
    Chain = DAG.getNode(ISD::TokenFactor, DL, MVT::Other, MemOpChains);

  // Build a sequence of copy-to-reg nodes, chained and glued together.
  SDValue Glue;
  for (unsigned I = 0, E = RegsToPass.size(); I != E; ++I) {
    unsigned Reg = RegsToPass[I].first;
    Chain = DAG.getCopyToReg(Chain, DL, Reg, RegsToPass[I].second, Glue);
    Glue = Chain.getValue(1);
  }
  std::string name;
  unsigned char TF = 0;

  // Accept direct calls by converting symbolic call addresses to the
  // associated Target* opcodes.
  if (ExternalSymbolSDNode *E = dyn_cast<ExternalSymbolSDNode>(Callee)) {
    name = E->getSymbol();
    TF = E->getTargetFlags();
    if (isPositionIndependent()) {
      report_fatal_error("PIC relocations is not supported");
    } else
      Callee = DAG.getTargetExternalSymbol(E->getSymbol(), PtrVT, TF);
  } else if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
    const GlobalValue *GV = G->getGlobal();
    name = GV->getName().str();
  }

  if ((!name.empty()) && isLongCall(name.c_str())) {
    // Create a constant pool entry for the callee address
    XtensaCP::XtensaCPModifier Modifier = XtensaCP::no_modifier;

    XtensaConstantPoolValue *CPV = XtensaConstantPoolSymbol::Create(
        *DAG.getContext(), name.c_str(), 0 /* XtensaCLabelIndex */, false,
        Modifier);

    // Get the address of the callee into a register
    SDValue CPAddr = DAG.getTargetConstantPool(CPV, PtrVT, Align(4), 0, TF);
    SDValue CPWrap = getAddrPCRel(CPAddr, DAG);
    Callee = CPWrap;
  }

  // The first call operand is the chain and the second is the target address.
  SmallVector<SDValue, 8> Ops;
  Ops.push_back(Chain);
  Ops.push_back(Callee);

  // Add a register mask operand representing the call-preserved registers.
  const TargetRegisterInfo *TRI = Subtarget.getRegisterInfo();
  const uint32_t *Mask = TRI->getCallPreservedMask(MF, CallConv);
  assert(Mask && "Missing call preserved mask for calling convention");
  Ops.push_back(DAG.getRegisterMask(Mask));

  // Add argument registers to the end of the list so that they are
  // known live into the call.
  for (unsigned I = 0, E = RegsToPass.size(); I != E; ++I) {
    unsigned Reg = RegsToPass[I].first;
    Ops.push_back(DAG.getRegister(Reg, RegsToPass[I].second.getValueType()));
  }

  // Glue the call to the argument copies, if any.
  if (Glue.getNode())
    Ops.push_back(Glue);

  SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
  Chain = DAG.getNode(XtensaISD::CALL, DL, NodeTys, Ops);
  Glue = Chain.getValue(1);

  // Mark the end of the call, which is glued to the call itself.
  Chain = DAG.getCALLSEQ_END(Chain, DAG.getConstant(NumBytes, DL, PtrVT, true),
                             DAG.getConstant(0, DL, PtrVT, true), Glue, DL);
  Glue = Chain.getValue(1);

  // Assign locations to each value returned by this call.
  SmallVector<CCValAssign, 16> RetLocs;
  CCState RetCCInfo(CallConv, IsVarArg, MF, RetLocs, *DAG.getContext());
  RetCCInfo.AnalyzeCallResult(Ins, RetCC_Xtensa);

  // Copy all of the result registers out of their specified physreg.
  for (unsigned I = 0, E = RetLocs.size(); I != E; ++I) {
    CCValAssign &VA = RetLocs[I];

    // Copy the value out, gluing the copy to the end of the call sequence.
    unsigned Reg = VA.getLocReg();
    SDValue RetValue = DAG.getCopyFromReg(Chain, DL, Reg, VA.getLocVT(), Glue);
    Chain = RetValue.getValue(1);
    Glue = RetValue.getValue(2);

    InVals.push_back(RetValue);
  }
  return Chain;
}

bool XtensaTargetLowering::CanLowerReturn(
    CallingConv::ID CallConv, MachineFunction &MF, bool IsVarArg,
    const SmallVectorImpl<ISD::OutputArg> &Outs, LLVMContext &Context) const {
  SmallVector<CCValAssign, 16> RVLocs;
  CCState CCInfo(CallConv, IsVarArg, MF, RVLocs, Context);
  return CCInfo.CheckReturn(Outs, RetCC_Xtensa);
}

SDValue
XtensaTargetLowering::LowerReturn(SDValue Chain, CallingConv::ID CallConv,
                                  bool IsVarArg,
                                  const SmallVectorImpl<ISD::OutputArg> &Outs,
                                  const SmallVectorImpl<SDValue> &OutVals,
                                  const SDLoc &DL, SelectionDAG &DAG) const {
  if (IsVarArg)
    report_fatal_error("VarArg not supported");

  MachineFunction &MF = DAG.getMachineFunction();

  // Assign locations to each returned value.
  SmallVector<CCValAssign, 16> RetLocs;
  CCState RetCCInfo(CallConv, IsVarArg, MF, RetLocs, *DAG.getContext());
  RetCCInfo.AnalyzeReturn(Outs, RetCC_Xtensa);

  SDValue Glue;
  // Quick exit for void returns
  if (RetLocs.empty())
    return DAG.getNode(XtensaISD::RET, DL, MVT::Other, Chain);

  // Copy the result values into the output registers.
  SmallVector<SDValue, 4> RetOps;
  RetOps.push_back(Chain);
  for (unsigned I = 0, E = RetLocs.size(); I != E; ++I) {
    CCValAssign &VA = RetLocs[I];
    SDValue RetValue = OutVals[I];

    // Make the return register live on exit.
    assert(VA.isRegLoc() && "Can only return in registers!");

    // Chain and glue the copies together.
    unsigned Register = VA.getLocReg();
    Chain = DAG.getCopyToReg(Chain, DL, Register, RetValue, Glue);
    Glue = Chain.getValue(1);
    RetOps.push_back(DAG.getRegister(Register, VA.getLocVT()));
  }

  // Update chain and glue.
  RetOps[0] = Chain;
  if (Glue.getNode())
    RetOps.push_back(Glue);

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

SDValue XtensaTargetLowering::LowerImmediate(SDValue Op,
                                             SelectionDAG &DAG) const {
  const ConstantSDNode *CN = cast<ConstantSDNode>(Op);
  SDLoc DL(CN);
  APInt APVal = CN->getAPIntValue();
  int64_t Value = APVal.getSExtValue();
  if (Op.getValueType() == MVT::i32) {
    // Check if use node maybe lowered to the MOVI instruction
    if (Value > -2048 && Value <= 2047)
      return Op;
    // Check if use node maybe lowered to the ADDMI instruction
    SDNode &OpNode = *Op.getNode();
    if ((OpNode.hasOneUse() && OpNode.use_begin()->getOpcode() == ISD::ADD) &&
        isShiftedInt<16, 8>(Value))
      return Op;
    Type *Ty = Type::getInt32Ty(*DAG.getContext());
    Constant *CV = ConstantInt::get(Ty, Value);
    SDValue CP = DAG.getConstantPool(CV, MVT::i32);
    return CP;
  }
  return Op;
}

SDValue XtensaTargetLowering::getAddrPCRel(SDValue Op,
                                           SelectionDAG &DAG) const {
  SDLoc DL(Op);
  EVT Ty = Op.getValueType();
  return DAG.getNode(XtensaISD::PCREL_WRAPPER, DL, Ty, Op);
}

SDValue XtensaTargetLowering::LowerConstantPool(ConstantPoolSDNode *CP,
                                                SelectionDAG &DAG) const {
  EVT PtrVT = getPointerTy(DAG.getDataLayout());
  SDValue Result;
  if (!CP->isMachineConstantPoolEntry()) {
    Result = DAG.getTargetConstantPool(CP->getConstVal(), PtrVT, CP->getAlign(),
                                       CP->getOffset());
  } else {
    report_fatal_error("This constantpool type is not supported yet");
  }

  return getAddrPCRel(Result, DAG);
}

SDValue XtensaTargetLowering::LowerOperation(SDValue Op,
                                             SelectionDAG &DAG) const {
  switch (Op.getOpcode()) {
  case ISD::Constant:
    return LowerImmediate(Op, DAG);
  case ISD::ConstantPool:
    return LowerConstantPool(cast<ConstantPoolSDNode>(Op), DAG);
  default:
    report_fatal_error("Unexpected node to lower");
  }
}

const char *XtensaTargetLowering::getTargetNodeName(unsigned Opcode) const {
  switch (Opcode) {
  case XtensaISD::CALL:
    return "XtensaISD::CALL";
  case XtensaISD::PCREL_WRAPPER:
    return "XtensaISD::PCREL_WRAPPER";
  case XtensaISD::RET:
    return "XtensaISD::RET";
  }
  return nullptr;
}