CodeGen/GlobalISel/InlineAsmLowering.cpp

//===-- lib/CodeGen/GlobalISel/InlineAsmLowering.cpp ----------------------===//
//
// 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 from LLVM IR inline asm to MIR INLINEASM
///
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/GlobalISel/InlineAsmLowering.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
#include "llvm/CodeGen/GlobalISel/Utils.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"

#define DEBUG_TYPE "inline-asm-lowering"

using namespace llvm;

void InlineAsmLowering::anchor() {}

namespace {

/// GISelAsmOperandInfo - This contains information for each constraint that we
/// are lowering.
class GISelAsmOperandInfo : public TargetLowering::AsmOperandInfo {
public:
  /// Regs - If this is a register or register class operand, this
  /// contains the set of assigned registers corresponding to the operand.
  SmallVector<Register, 1> Regs;

  explicit GISelAsmOperandInfo(const TargetLowering::AsmOperandInfo &Info)
      : TargetLowering::AsmOperandInfo(Info) {}
};

using GISelAsmOperandInfoVector = SmallVector<GISelAsmOperandInfo, 16>;

class ExtraFlags {
  unsigned Flags = 0;

public:
  explicit ExtraFlags(const CallBase &CB) {
    const InlineAsm *IA = cast<InlineAsm>(CB.getCalledOperand());
    if (IA->hasSideEffects())
      Flags |= InlineAsm::Extra_HasSideEffects;
    if (IA->isAlignStack())
      Flags |= InlineAsm::Extra_IsAlignStack;
    if (CB.isConvergent())
      Flags |= InlineAsm::Extra_IsConvergent;
    Flags |= IA->getDialect() * InlineAsm::Extra_AsmDialect;
  }

  void update(const TargetLowering::AsmOperandInfo &OpInfo) {
    // Ideally, we would only check against memory constraints.  However, the
    // meaning of an Other constraint can be target-specific and we can't easily
    // reason about it.  Therefore, be conservative and set MayLoad/MayStore
    // for Other constraints as well.
    if (OpInfo.ConstraintType == TargetLowering::C_Memory ||
        OpInfo.ConstraintType == TargetLowering::C_Other) {
      if (OpInfo.Type == InlineAsm::isInput)
        Flags |= InlineAsm::Extra_MayLoad;
      else if (OpInfo.Type == InlineAsm::isOutput)
        Flags |= InlineAsm::Extra_MayStore;
      else if (OpInfo.Type == InlineAsm::isClobber)
        Flags |= (InlineAsm::Extra_MayLoad | InlineAsm::Extra_MayStore);
    }
  }

  unsigned get() const { return Flags; }
};

} // namespace

/// Assign virtual/physical registers for the specified register operand.
static void getRegistersForValue(MachineFunction &MF,
                                 MachineIRBuilder &MIRBuilder,
                                 GISelAsmOperandInfo &OpInfo,
                                 GISelAsmOperandInfo &RefOpInfo) {

  const TargetLowering &TLI = *MF.getSubtarget().getTargetLowering();
  const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();

  // No work to do for memory operations.
  if (OpInfo.ConstraintType == TargetLowering::C_Memory)
    return;

  // If this is a constraint for a single physreg, or a constraint for a
  // register class, find it.
  Register AssignedReg;
  const TargetRegisterClass *RC;
  std::tie(AssignedReg, RC) = TLI.getRegForInlineAsmConstraint(
      &TRI, RefOpInfo.ConstraintCode, RefOpInfo.ConstraintVT);
  // RC is unset only on failure. Return immediately.
  if (!RC)
    return;

  // No need to allocate a matching input constraint since the constraint it's
  // matching to has already been allocated.
  if (OpInfo.isMatchingInputConstraint())
    return;

  // Initialize NumRegs.
  unsigned NumRegs = 1;
  if (OpInfo.ConstraintVT != MVT::Other)
    NumRegs =
        TLI.getNumRegisters(MF.getFunction().getContext(), OpInfo.ConstraintVT);

  // If this is a constraint for a specific physical register, but the type of
  // the operand requires more than one register to be passed, we allocate the
  // required amount of physical registers, starting from the selected physical
  // register.
  // For this, first retrieve a register iterator for the given register class
  TargetRegisterClass::iterator I = RC->begin();
  MachineRegisterInfo &RegInfo = MF.getRegInfo();

  // Advance the iterator to the assigned register (if set)
  if (AssignedReg) {
    for (; *I != AssignedReg; ++I)
      assert(I != RC->end() && "AssignedReg should be a member of provided RC");
  }

  // Finally, assign the registers. If the AssignedReg isn't set, create virtual
  // registers with the provided register class
  for (; NumRegs; --NumRegs, ++I) {
    assert(I != RC->end() && "Ran out of registers to allocate!");
    Register R = AssignedReg ? Register(*I) : RegInfo.createVirtualRegister(RC);
    OpInfo.Regs.push_back(R);
  }
}

/// Return an integer indicating how general CT is.
static unsigned getConstraintGenerality(TargetLowering::ConstraintType CT) {
  switch (CT) {
  case TargetLowering::C_Immediate:
  case TargetLowering::C_Other:
  case TargetLowering::C_Unknown:
    return 0;
  case TargetLowering::C_Register:
    return 1;
  case TargetLowering::C_RegisterClass:
    return 2;
  case TargetLowering::C_Memory:
    return 3;
  }
  llvm_unreachable("Invalid constraint type");
}

static void chooseConstraint(TargetLowering::AsmOperandInfo &OpInfo,
                             const TargetLowering *TLI) {
  assert(OpInfo.Codes.size() > 1 && "Doesn't have multiple constraint options");
  unsigned BestIdx = 0;
  TargetLowering::ConstraintType BestType = TargetLowering::C_Unknown;
  int BestGenerality = -1;

  // Loop over the options, keeping track of the most general one.
  for (unsigned i = 0, e = OpInfo.Codes.size(); i != e; ++i) {
    TargetLowering::ConstraintType CType =
        TLI->getConstraintType(OpInfo.Codes[i]);

    // Indirect 'other' or 'immediate' constraints are not allowed.
    if (OpInfo.isIndirect && !(CType == TargetLowering::C_Memory ||
                               CType == TargetLowering::C_Register ||
                               CType == TargetLowering::C_RegisterClass))
      continue;

    // If this is an 'other' or 'immediate' constraint, see if the operand is
    // valid for it. For example, on X86 we might have an 'rI' constraint. If
    // the operand is an integer in the range [0..31] we want to use I (saving a
    // load of a register), otherwise we must use 'r'.
    if (CType == TargetLowering::C_Other ||
        CType == TargetLowering::C_Immediate) {
      assert(OpInfo.Codes[i].size() == 1 &&
             "Unhandled multi-letter 'other' constraint");
      // FIXME: prefer immediate constraints if the target allows it
    }

    // Things with matching constraints can only be registers, per gcc
    // documentation.  This mainly affects "g" constraints.
    if (CType == TargetLowering::C_Memory && OpInfo.hasMatchingInput())
      continue;

    // This constraint letter is more general than the previous one, use it.
    int Generality = getConstraintGenerality(CType);
    if (Generality > BestGenerality) {
      BestType = CType;
      BestIdx = i;
      BestGenerality = Generality;
    }
  }

  OpInfo.ConstraintCode = OpInfo.Codes[BestIdx];
  OpInfo.ConstraintType = BestType;
}

static void computeConstraintToUse(const TargetLowering *TLI,
                                   TargetLowering::AsmOperandInfo &OpInfo) {
  assert(!OpInfo.Codes.empty() && "Must have at least one constraint");

  // Single-letter constraints ('r') are very common.
  if (OpInfo.Codes.size() == 1) {
    OpInfo.ConstraintCode = OpInfo.Codes[0];
    OpInfo.ConstraintType = TLI->getConstraintType(OpInfo.ConstraintCode);
  } else {
    chooseConstraint(OpInfo, TLI);
  }

  // 'X' matches anything.
  if (OpInfo.ConstraintCode == "X" && OpInfo.CallOperandVal) {
    // Labels and constants are handled elsewhere ('X' is the only thing
    // that matches labels).  For Functions, the type here is the type of
    // the result, which is not what we want to look at; leave them alone.
    Value *Val = OpInfo.CallOperandVal;
    if (isa<BasicBlock>(Val) || isa<ConstantInt>(Val) || isa<Function>(Val))
      return;

    // Otherwise, try to resolve it to something we know about by looking at
    // the actual operand type.
    if (const char *Repl = TLI->LowerXConstraint(OpInfo.ConstraintVT)) {
      OpInfo.ConstraintCode = Repl;
      OpInfo.ConstraintType = TLI->getConstraintType(OpInfo.ConstraintCode);
    }
  }
}

bool InlineAsmLowering::lowerInlineAsm(
    MachineIRBuilder &MIRBuilder, const CallBase &Call,
    std::function<ArrayRef<Register>(const Value &Val)> GetOrCreateVRegs)
    const {
  const InlineAsm *IA = cast<InlineAsm>(Call.getCalledOperand());

  /// ConstraintOperands - Information about all of the constraints.
  GISelAsmOperandInfoVector ConstraintOperands;

  MachineFunction &MF = MIRBuilder.getMF();
  const Function &F = MF.getFunction();
  const DataLayout &DL = F.getParent()->getDataLayout();
  const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();

  MachineRegisterInfo *MRI = MIRBuilder.getMRI();

  TargetLowering::AsmOperandInfoVector TargetConstraints =
      TLI->ParseConstraints(DL, TRI, Call);

  ExtraFlags ExtraInfo(Call);
  unsigned ResNo = 0; // ResNo - The result number of the next output.
  for (auto &T : TargetConstraints) {
    ConstraintOperands.push_back(GISelAsmOperandInfo(T));
    GISelAsmOperandInfo &OpInfo = ConstraintOperands.back();

    // Compute the value type for each operand.
    if (OpInfo.Type == InlineAsm::isInput ||
        (OpInfo.Type == InlineAsm::isOutput && OpInfo.isIndirect)) {

      LLVM_DEBUG(dbgs() << "Input operands and indirect output operands are "
                           "not supported yet\n");
      return false;

    } else if (OpInfo.Type == InlineAsm::isOutput && !OpInfo.isIndirect) {
      assert(!Call.getType()->isVoidTy() && "Bad inline asm!");
      if (StructType *STy = dyn_cast<StructType>(Call.getType())) {
        OpInfo.ConstraintVT =
            TLI->getSimpleValueType(DL, STy->getElementType(ResNo));
      } else {
        assert(ResNo == 0 && "Asm only has one result!");
        OpInfo.ConstraintVT = TLI->getSimpleValueType(DL, Call.getType());
      }
      ++ResNo;
    } else {
      OpInfo.ConstraintVT = MVT::Other;
    }

    // Compute the constraint code and ConstraintType to use.
    computeConstraintToUse(TLI, OpInfo);

    // The selected constraint type might expose new sideeffects
    ExtraInfo.update(OpInfo);
  }

  // At this point, all operand types are decided.
  // Create the MachineInstr, but don't insert it yet since input
  // operands still need to insert instructions before this one
  auto Inst = MIRBuilder.buildInstrNoInsert(TargetOpcode::INLINEASM)
                  .addExternalSymbol(IA->getAsmString().c_str())
                  .addImm(ExtraInfo.get());

  // Collects the output operands for later processing
  GISelAsmOperandInfoVector OutputOperands;

  for (auto &OpInfo : ConstraintOperands) {
    GISelAsmOperandInfo &RefOpInfo =
        OpInfo.isMatchingInputConstraint()
            ? ConstraintOperands[OpInfo.getMatchedOperand()]
            : OpInfo;

    // Assign registers for register operands
    getRegistersForValue(MF, MIRBuilder, OpInfo, RefOpInfo);

    switch (OpInfo.Type) {
    case InlineAsm::isOutput:
      if (OpInfo.ConstraintType == TargetLowering::C_Memory) {
        unsigned ConstraintID =
            TLI->getInlineAsmMemConstraint(OpInfo.ConstraintCode);
        assert(ConstraintID != InlineAsm::Constraint_Unknown &&
               "Failed to convert memory constraint code to constraint id.");

        // Add information to the INLINEASM instruction to know about this
        // output.
        unsigned OpFlags = InlineAsm::getFlagWord(InlineAsm::Kind_Mem, 1);
        OpFlags = InlineAsm::getFlagWordForMem(OpFlags, ConstraintID);
        Inst.addImm(OpFlags);
        ArrayRef<Register> SourceRegs =
            GetOrCreateVRegs(*OpInfo.CallOperandVal);
        assert(
            SourceRegs.size() == 1 &&
            "Expected the memory output to fit into a single virtual register");
        Inst.addReg(SourceRegs[0]);
      } else {
        // Otherwise, this outputs to a register (directly for C_Register /
        // C_RegisterClass. Find a register that we can use.
        assert(OpInfo.ConstraintType == TargetLowering::C_Register ||
               OpInfo.ConstraintType == TargetLowering::C_RegisterClass);

        if (OpInfo.Regs.empty()) {
          LLVM_DEBUG(dbgs()
                     << "Couldn't allocate output register for constraint\n");
          return false;
        }

        // Add information to the INLINEASM instruction to know that this
        // register is set.
        unsigned Flag = InlineAsm::getFlagWord(
            OpInfo.isEarlyClobber ? InlineAsm::Kind_RegDefEarlyClobber
                                  : InlineAsm::Kind_RegDef,
            OpInfo.Regs.size());
        if (OpInfo.Regs.front().isVirtual()) {
          // Put the register class of the virtual registers in the flag word.
          // That way, later passes can recompute register class constraints for
          // inline assembly as well as normal instructions. Don't do this for
          // tied operands that can use the regclass information from the def.
          const TargetRegisterClass *RC = MRI->getRegClass(OpInfo.Regs.front());
          Flag = InlineAsm::getFlagWordForRegClass(Flag, RC->getID());
        }

        Inst.addImm(Flag);

        for (Register Reg : OpInfo.Regs) {
          Inst.addReg(Reg,
                      RegState::Define | getImplRegState(Reg.isPhysical()));
        }

        // Remember this output operand for later processing
        OutputOperands.push_back(OpInfo);
      }

      break;
    case InlineAsm::isInput:
      return false;
    case InlineAsm::isClobber: {

      unsigned NumRegs = OpInfo.Regs.size();
      if (NumRegs > 0) {
        unsigned Flag =
            InlineAsm::getFlagWord(InlineAsm::Kind_Clobber, NumRegs);
        Inst.addImm(Flag);

        for (Register Reg : OpInfo.Regs) {
          Inst.addReg(Reg, RegState::Define | RegState::EarlyClobber |
                               getImplRegState(Reg.isPhysical()));
        }
      }
      break;
    }
    }
  }

  if (const MDNode *SrcLoc = Call.getMetadata("srcloc"))
    Inst.addMetadata(SrcLoc);

  // All inputs are handled, insert the instruction now
  MIRBuilder.insertInstr(Inst);

  // Finally, copy the output operands into the output registers
  ArrayRef<Register> ResRegs = GetOrCreateVRegs(Call);
  if (ResRegs.size() != OutputOperands.size()) {
    LLVM_DEBUG(dbgs() << "Expected the number of output registers to match the "
                         "number of destination registers\n");
    return false;
  }
  for (unsigned int i = 0, e = ResRegs.size(); i < e; i++) {
    GISelAsmOperandInfo &OpInfo = OutputOperands[i];

    if (OpInfo.Regs.empty())
      continue;

    switch (OpInfo.ConstraintType) {
    case TargetLowering::C_Register:
    case TargetLowering::C_RegisterClass: {
      if (OpInfo.Regs.size() > 1) {
        LLVM_DEBUG(dbgs() << "Output operands with multiple defining "
                             "registers are not supported yet\n");
        return false;
      }

      Register SrcReg = OpInfo.Regs[0];
      unsigned SrcSize = TRI->getRegSizeInBits(SrcReg, *MRI);
      if (MRI->getType(ResRegs[i]).getSizeInBits() < SrcSize) {
        // First copy the non-typed virtual register into a generic virtual
        // register
        Register Tmp1Reg =
            MRI->createGenericVirtualRegister(LLT::scalar(SrcSize));
        MIRBuilder.buildCopy(Tmp1Reg, SrcReg);
        // Need to truncate the result of the register
        MIRBuilder.buildTrunc(ResRegs[i], Tmp1Reg);
      } else {
        MIRBuilder.buildCopy(ResRegs[i], SrcReg);
      }
      break;
    }
    case TargetLowering::C_Immediate:
    case TargetLowering::C_Other:
      LLVM_DEBUG(
          dbgs() << "Cannot lower target specific output constraints yet\n");
      return false;
    case TargetLowering::C_Memory:
      break; // Already handled.
    case TargetLowering::C_Unknown:
      LLVM_DEBUG(dbgs() << "Unexpected unknown constraint\n");
      return false;
    }
  }

  return true;
}