utils/TableGen/CodeEmitterGen.cpp

//===- CodeEmitterGen.cpp - Code Emitter Generator ------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// CodeEmitterGen uses the descriptions of instructions and their fields to
// construct an automated code emitter: a function that, given a MachineInstr,
// returns the (currently, 32-bit unsigned) value of the instruction.
//
//===----------------------------------------------------------------------===//

#include "CodeGenInstruction.h"
#include "CodeGenTarget.h"
#include "SubtargetFeatureInfo.h"
#include "Types.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/TableGen/Record.h"
#include "llvm/TableGen/TableGenBackend.h"
#include <cassert>
#include <cstdint>
#include <map>
#include <set>
#include <string>
#include <utility>
#include <vector>

using namespace llvm;

namespace {

class CodeEmitterGen {
  RecordKeeper &Records;

public:
  CodeEmitterGen(RecordKeeper &R) : Records(R) {}

  void run(raw_ostream &o);

private:
  int getVariableBit(const std::string &VarName, BitsInit *BI, int bit);
  std::string getInstructionCase(Record *R, CodeGenTarget &Target);
  std::string getInstructionCaseForEncoding(Record *R, Record *EncodingDef,
                                            CodeGenTarget &Target);
  void AddCodeToMergeInOperand(Record *R, BitsInit *BI,
                               const std::string &VarName,
                               unsigned &NumberedOp,
                               std::set<unsigned> &NamedOpIndices,
                               std::string &Case, CodeGenTarget &Target);

  void emitInstructionBaseValues(
      raw_ostream &o, ArrayRef<const CodeGenInstruction *> NumberedInstructions,
      CodeGenTarget &Target, int HwMode = -1);
  unsigned BitWidth;
  bool UseAPInt;
};

// If the VarBitInit at position 'bit' matches the specified variable then
// return the variable bit position.  Otherwise return -1.
int CodeEmitterGen::getVariableBit(const std::string &VarName,
                                   BitsInit *BI, int bit) {
  if (VarBitInit *VBI = dyn_cast<VarBitInit>(BI->getBit(bit))) {
    if (VarInit *VI = dyn_cast<VarInit>(VBI->getBitVar()))
      if (VI->getName() == VarName)
        return VBI->getBitNum();
  } else if (VarInit *VI = dyn_cast<VarInit>(BI->getBit(bit))) {
    if (VI->getName() == VarName)
      return 0;
  }

  return -1;
}

void CodeEmitterGen::
AddCodeToMergeInOperand(Record *R, BitsInit *BI, const std::string &VarName,
                        unsigned &NumberedOp,
                        std::set<unsigned> &NamedOpIndices,
                        std::string &Case, CodeGenTarget &Target) {
  CodeGenInstruction &CGI = Target.getInstruction(R);

  // Determine if VarName actually contributes to the Inst encoding.
  int bit = BI->getNumBits()-1;

  // Scan for a bit that this contributed to.
  for (; bit >= 0; ) {
    if (getVariableBit(VarName, BI, bit) != -1)
      break;

    --bit;
  }

  // If we found no bits, ignore this value, otherwise emit the call to get the
  // operand encoding.
  if (bit < 0) return;

  // If the operand matches by name, reference according to that
  // operand number. Non-matching operands are assumed to be in
  // order.
  unsigned OpIdx;
  if (CGI.Operands.hasOperandNamed(VarName, OpIdx)) {
    // Get the machine operand number for the indicated operand.
    OpIdx = CGI.Operands[OpIdx].MIOperandNo;
    assert(!CGI.Operands.isFlatOperandNotEmitted(OpIdx) &&
           "Explicitly used operand also marked as not emitted!");
  } else {
    unsigned NumberOps = CGI.Operands.size();
    /// If this operand is not supposed to be emitted by the
    /// generated emitter, skip it.
    while (NumberedOp < NumberOps &&
           (CGI.Operands.isFlatOperandNotEmitted(NumberedOp) ||
              (!NamedOpIndices.empty() && NamedOpIndices.count(
                CGI.Operands.getSubOperandNumber(NumberedOp).first)))) {
      ++NumberedOp;

      if (NumberedOp >= CGI.Operands.back().MIOperandNo +
                        CGI.Operands.back().MINumOperands) {
        errs() << "Too few operands in record " << R->getName() <<
                  " (no match for variable " << VarName << "):\n";
        errs() << *R;
        errs() << '\n';

        return;
      }
    }

    OpIdx = NumberedOp++;
  }

  std::pair<unsigned, unsigned> SO = CGI.Operands.getSubOperandNumber(OpIdx);
  std::string &EncoderMethodName = CGI.Operands[SO.first].EncoderMethodName;

  if (UseAPInt)
    Case += "      op.clearAllBits();\n";

  // If the source operand has a custom encoder, use it. This will
  // get the encoding for all of the suboperands.
  if (!EncoderMethodName.empty()) {
    // A custom encoder has all of the information for the
    // sub-operands, if there are more than one, so only
    // query the encoder once per source operand.
    if (SO.second == 0) {
      Case += "      // op: " + VarName + "\n";
      if (UseAPInt) {
        Case += "      " + EncoderMethodName + "(MI, " + utostr(OpIdx);
        Case += ", op";
      } else {
        Case += "      op = " + EncoderMethodName + "(MI, " + utostr(OpIdx);
      }
      Case += ", Fixups, STI);\n";
    }
  } else {
    Case += "      // op: " + VarName + "\n";
    if (UseAPInt) {
      Case += "      getMachineOpValue(MI, MI.getOperand(" + utostr(OpIdx) + ")";
      Case += ", op, Fixups, STI";
    } else {
      Case += "      op = getMachineOpValue(MI, MI.getOperand(" + utostr(OpIdx) + ")";
      Case += ", Fixups, STI";
    }
    Case += ");\n";
  }

  // Precalculate the number of lits this variable contributes to in the
  // operand. If there is a single lit (consecutive range of bits) we can use a
  // destructive sequence on APInt that reduces memory allocations.
  int numOperandLits = 0;
  for (int tmpBit = bit; tmpBit >= 0;) {
    int varBit = getVariableBit(VarName, BI, tmpBit);

    // If this bit isn't from a variable, skip it.
    if (varBit == -1) {
      --tmpBit;
      continue;
    }

    // Figure out the consecutive range of bits covered by this operand, in
    // order to generate better encoding code.
    int beginVarBit = varBit;
    int N = 1;
    for (--tmpBit; tmpBit >= 0;) {
      varBit = getVariableBit(VarName, BI, tmpBit);
      if (varBit == -1 || varBit != (beginVarBit - N))
        break;
      ++N;
      --tmpBit;
    }
    ++numOperandLits;
  }

  for (; bit >= 0; ) {
    int varBit = getVariableBit(VarName, BI, bit);

    // If this bit isn't from a variable, skip it.
    if (varBit == -1) {
      --bit;
      continue;
    }

    // Figure out the consecutive range of bits covered by this operand, in
    // order to generate better encoding code.
    int beginInstBit = bit;
    int beginVarBit = varBit;
    int N = 1;
    for (--bit; bit >= 0;) {
      varBit = getVariableBit(VarName, BI, bit);
      if (varBit == -1 || varBit != (beginVarBit - N)) break;
      ++N;
      --bit;
    }

    std::string maskStr;
    int opShift;

    unsigned loBit = beginVarBit - N + 1;
    unsigned hiBit = loBit + N;
    unsigned loInstBit = beginInstBit - N + 1;
    if (UseAPInt) {
      std::string extractStr;
      if (N >= 64) {
        extractStr = "op.extractBits(" + itostr(hiBit - loBit) + ", " +
                     itostr(loBit) + ")";
        Case += "      Value.insertBits(" + extractStr + ", " +
                itostr(loInstBit) + ");\n";
      } else {
        extractStr = "op.extractBitsAsZExtValue(" + itostr(hiBit - loBit) +
                     ", " + itostr(loBit) + ")";
        Case += "      Value.insertBits(" + extractStr + ", " +
                itostr(loInstBit) + ", " + itostr(hiBit - loBit) + ");\n";
      }
    } else {
      uint64_t opMask = ~(uint64_t)0 >> (64 - N);
      opShift = beginVarBit - N + 1;
      opMask <<= opShift;
      maskStr = "UINT64_C(" + utostr(opMask) + ")";
      opShift = beginInstBit - beginVarBit;

      if (numOperandLits == 1) {
        Case += "      op &= " + maskStr + ";\n";
        if (opShift > 0) {
          Case += "      op <<= " + itostr(opShift) + ";\n";
        } else if (opShift < 0) {
          Case += "      op >>= " + itostr(-opShift) + ";\n";
        }
        Case += "      Value |= op;\n";
      } else {
        if (opShift > 0) {
          Case += "      Value |= (op & " + maskStr + ") << " +
                  itostr(opShift) + ";\n";
        } else if (opShift < 0) {
          Case += "      Value |= (op & " + maskStr + ") >> " +
                  itostr(-opShift) + ";\n";
        } else {
          Case += "      Value |= (op & " + maskStr + ");\n";
        }
      }
    }
  }
}

std::string CodeEmitterGen::getInstructionCase(Record *R,
                                               CodeGenTarget &Target) {
  std::string Case;
  if (const RecordVal *RV = R->getValue("EncodingInfos")) {
    if (auto *DI = dyn_cast_or_null<DefInit>(RV->getValue())) {
      const CodeGenHwModes &HWM = Target.getHwModes();
      EncodingInfoByHwMode EBM(DI->getDef(), HWM);
      Case += "      switch (HwMode) {\n";
      Case += "      default: llvm_unreachable(\"Unhandled HwMode\");\n";
      for (auto &KV : EBM.Map) {
        Case += "      case " + itostr(KV.first) + ": {\n";
        Case += getInstructionCaseForEncoding(R, KV.second, Target);
        Case += "      break;\n";
        Case += "      }\n";
      }
      Case += "      }\n";
      return Case;
    }
  }
  return getInstructionCaseForEncoding(R, R, Target);
}

std::string CodeEmitterGen::getInstructionCaseForEncoding(Record *R, Record *EncodingDef,
                                                          CodeGenTarget &Target) {
  std::string Case;
  BitsInit *BI = EncodingDef->getValueAsBitsInit("Inst");
  unsigned NumberedOp = 0;
  std::set<unsigned> NamedOpIndices;

  // Collect the set of operand indices that might correspond to named
  // operand, and skip these when assigning operands based on position.
  if (Target.getInstructionSet()->
       getValueAsBit("noNamedPositionallyEncodedOperands")) {
    CodeGenInstruction &CGI = Target.getInstruction(R);
    for (const RecordVal &RV : R->getValues()) {
      unsigned OpIdx;
      if (!CGI.Operands.hasOperandNamed(RV.getName(), OpIdx))
        continue;

      NamedOpIndices.insert(OpIdx);
    }
  }

  // Loop over all of the fields in the instruction, determining which are the
  // operands to the instruction.
  for (const RecordVal &RV : EncodingDef->getValues()) {
    // Ignore fixed fields in the record, we're looking for values like:
    //    bits<5> RST = { ?, ?, ?, ?, ? };
    if (RV.getPrefix() || RV.getValue()->isComplete())
      continue;

    AddCodeToMergeInOperand(R, BI, RV.getName(), NumberedOp,
                            NamedOpIndices, Case, Target);
  }

  StringRef PostEmitter = R->getValueAsString("PostEncoderMethod");
  if (!PostEmitter.empty()) {
    Case += "      Value = ";
    Case += PostEmitter;
    Case += "(MI, Value";
    Case += ", STI";
    Case += ");\n";
  }

  return Case;
}

static std::string
getNameForFeatureBitset(const std::vector<Record *> &FeatureBitset) {
  std::string Name = "CEFBS";
  for (const auto &Feature : FeatureBitset)
    Name += ("_" + Feature->getName()).str();
  return Name;
}

static void emitInstBits(raw_ostream &OS, const APInt &Bits) {
  for (unsigned I = 0; I < Bits.getNumWords(); ++I)
    OS << ((I > 0) ? ", " : "") << "UINT64_C(" << utostr(Bits.getRawData()[I])
       << ")";
}

void CodeEmitterGen::emitInstructionBaseValues(
    raw_ostream &o, ArrayRef<const CodeGenInstruction *> NumberedInstructions,
    CodeGenTarget &Target, int HwMode) {
  const CodeGenHwModes &HWM = Target.getHwModes();
  if (HwMode == -1)
    o << "  static const uint64_t InstBits[] = {\n";
  else
    o << "  static const uint64_t InstBits_" << HWM.getMode(HwMode).Name
      << "[] = {\n";

  for (const CodeGenInstruction *CGI : NumberedInstructions) {
    Record *R = CGI->TheDef;

    if (R->getValueAsString("Namespace") == "TargetOpcode" ||
        R->getValueAsBit("isPseudo")) {
      o << "    "; emitInstBits(o, APInt(BitWidth, 0)); o << ",\n";
      continue;
    }

    Record *EncodingDef = R;
    if (const RecordVal *RV = R->getValue("EncodingInfos")) {
      if (auto *DI = dyn_cast_or_null<DefInit>(RV->getValue())) {
        EncodingInfoByHwMode EBM(DI->getDef(), HWM);
        EncodingDef = EBM.get(HwMode);
      }
    }
    BitsInit *BI = EncodingDef->getValueAsBitsInit("Inst");

    // Start by filling in fixed values.
    APInt Value(BitWidth, 0);
    for (unsigned i = 0, e = BI->getNumBits(); i != e; ++i) {
      if (BitInit *B = dyn_cast<BitInit>(BI->getBit(e - i - 1)))
        Value |= APInt(BitWidth, (uint64_t)B->getValue()) << (e - i - 1);
    }
    o << "    ";
    emitInstBits(o, Value);
    o << "," << '\t' << "// " << R->getName() << "\n";
  }
  o << "    UINT64_C(0)\n  };\n";
}

void CodeEmitterGen::run(raw_ostream &o) {
  CodeGenTarget Target(Records);
  std::vector<Record*> Insts = Records.getAllDerivedDefinitions("Instruction");

  // For little-endian instruction bit encodings, reverse the bit order
  Target.reverseBitsForLittleEndianEncoding();

  ArrayRef<const CodeGenInstruction*> NumberedInstructions =
    Target.getInstructionsByEnumValue();

  const CodeGenHwModes &HWM = Target.getHwModes();
  // The set of HwModes used by instruction encodings.
  std::set<unsigned> HwModes;
  BitWidth = 0;
  for (const CodeGenInstruction *CGI : NumberedInstructions) {
    Record *R = CGI->TheDef;
    if (R->getValueAsString("Namespace") == "TargetOpcode" ||
        R->getValueAsBit("isPseudo"))
      continue;

    if (const RecordVal *RV = R->getValue("EncodingInfos")) {
      if (DefInit *DI = dyn_cast_or_null<DefInit>(RV->getValue())) {
        EncodingInfoByHwMode EBM(DI->getDef(), HWM);
        for (auto &KV : EBM.Map) {
          BitsInit *BI = KV.second->getValueAsBitsInit("Inst");
          BitWidth = std::max(BitWidth, BI->getNumBits());
          HwModes.insert(KV.first);
        }
        continue;
      }
    }
    BitsInit *BI = R->getValueAsBitsInit("Inst");
    BitWidth = std::max(BitWidth, BI->getNumBits());
  }
  UseAPInt = BitWidth > 64;

  // Emit function declaration
  if (UseAPInt) {
    o << "void " << Target.getName()
      << "MCCodeEmitter::getBinaryCodeForInstr(const MCInst &MI,\n"
      << "    SmallVectorImpl<MCFixup> &Fixups,\n"
      << "    APInt &Inst,\n"
      << "    APInt &Scratch,\n"
      << "    const MCSubtargetInfo &STI) const {\n";
  } else {
    o << "uint64_t " << Target.getName();
    o << "MCCodeEmitter::getBinaryCodeForInstr(const MCInst &MI,\n"
      << "    SmallVectorImpl<MCFixup> &Fixups,\n"
      << "    const MCSubtargetInfo &STI) const {\n";
  }

  // Emit instruction base values
  if (HwModes.empty()) {
    emitInstructionBaseValues(o, NumberedInstructions, Target, -1);
  } else {
    for (unsigned HwMode : HwModes)
      emitInstructionBaseValues(o, NumberedInstructions, Target, (int)HwMode);
  }

  if (!HwModes.empty()) {
    o << "  const uint64_t *InstBits;\n";
    o << "  unsigned HwMode = STI.getHwMode();\n";
    o << "  switch (HwMode) {\n";
    o << "  default: llvm_unreachable(\"Unknown hardware mode!\"); break;\n";
    for (unsigned I : HwModes) {
      o << "  case " << I << ": InstBits = InstBits_" << HWM.getMode(I).Name
        << "; break;\n";
    }
    o << "  };\n";
  }

  // Map to accumulate all the cases.
  std::map<std::string, std::vector<std::string>> CaseMap;

  // Construct all cases statement for each opcode
  for (std::vector<Record*>::iterator IC = Insts.begin(), EC = Insts.end();
        IC != EC; ++IC) {
    Record *R = *IC;
    if (R->getValueAsString("Namespace") == "TargetOpcode" ||
        R->getValueAsBit("isPseudo"))
      continue;
    std::string InstName =
        (R->getValueAsString("Namespace") + "::" + R->getName()).str();
    std::string Case = getInstructionCase(R, Target);

    CaseMap[Case].push_back(std::move(InstName));
  }

  // Emit initial function code
  if (UseAPInt) {
    int NumWords = APInt::getNumWords(BitWidth);
    int NumBytes = (BitWidth + 7) / 8;
    o << "  const unsigned opcode = MI.getOpcode();\n"
      << "  if (Inst.getBitWidth() != " << BitWidth << ")\n"
      << "    Inst = Inst.zext(" << BitWidth << ");\n"
      << "  if (Scratch.getBitWidth() != " << BitWidth << ")\n"
      << "    Scratch = Scratch.zext(" << BitWidth << ");\n"
      << "  LoadIntFromMemory(Inst, (uint8_t*)&InstBits[opcode * " << NumWords
      << "], " << NumBytes << ");\n"
      << "  APInt &Value = Inst;\n"
      << "  APInt &op = Scratch;\n"
      << "  switch (opcode) {\n";
  } else {
    o << "  const unsigned opcode = MI.getOpcode();\n"
      << "  uint64_t Value = InstBits[opcode];\n"
      << "  uint64_t op = 0;\n"
      << "  (void)op;  // suppress warning\n"
      << "  switch (opcode) {\n";
  }

  // Emit each case statement
  std::map<std::string, std::vector<std::string>>::iterator IE, EE;
  for (IE = CaseMap.begin(), EE = CaseMap.end(); IE != EE; ++IE) {
    const std::string &Case = IE->first;
    std::vector<std::string> &InstList = IE->second;

    for (int i = 0, N = InstList.size(); i < N; i++) {
      if (i) o << "\n";
      o << "    case " << InstList[i]  << ":";
    }
    o << " {\n";
    o << Case;
    o << "      break;\n"
      << "    }\n";
  }

  // Default case: unhandled opcode
  o << "  default:\n"
    << "    std::string msg;\n"
    << "    raw_string_ostream Msg(msg);\n"
    << "    Msg << \"Not supported instr: \" << MI;\n"
    << "    report_fatal_error(Msg.str());\n"
    << "  }\n";
  if (UseAPInt)
    o << "  Inst = Value;\n";
  else
    o << "  return Value;\n";
  o << "}\n\n";

  const auto &All = SubtargetFeatureInfo::getAll(Records);
  std::map<Record *, SubtargetFeatureInfo, LessRecordByID> SubtargetFeatures;
  SubtargetFeatures.insert(All.begin(), All.end());

  o << "#ifdef ENABLE_INSTR_PREDICATE_VERIFIER\n"
    << "#undef ENABLE_INSTR_PREDICATE_VERIFIER\n"
    << "#include <sstream>\n\n";

  // Emit the subtarget feature enumeration.
  SubtargetFeatureInfo::emitSubtargetFeatureBitEnumeration(SubtargetFeatures,
                                                           o);

  // Emit the name table for error messages.
  o << "#ifndef NDEBUG\n";
  SubtargetFeatureInfo::emitNameTable(SubtargetFeatures, o);
  o << "#endif // NDEBUG\n";

  // Emit the available features compute function.
  SubtargetFeatureInfo::emitComputeAssemblerAvailableFeatures(
      Target.getName(), "MCCodeEmitter", "computeAvailableFeatures",
      SubtargetFeatures, o);

  std::vector<std::vector<Record *>> FeatureBitsets;
  for (const CodeGenInstruction *Inst : Target.getInstructionsByEnumValue()) {
    FeatureBitsets.emplace_back();
    for (Record *Predicate : Inst->TheDef->getValueAsListOfDefs("Predicates")) {
      const auto &I = SubtargetFeatures.find(Predicate);
      if (I != SubtargetFeatures.end())
        FeatureBitsets.back().push_back(I->second.TheDef);
    }
  }

  llvm::sort(FeatureBitsets, [&](const std::vector<Record *> &A,
                                 const std::vector<Record *> &B) {
    if (A.size() < B.size())
      return true;
    if (A.size() > B.size())
      return false;
    for (const auto &Pair : zip(A, B)) {
      if (std::get<0>(Pair)->getName() < std::get<1>(Pair)->getName())
        return true;
      if (std::get<0>(Pair)->getName() > std::get<1>(Pair)->getName())
        return false;
    }
    return false;
  });
  FeatureBitsets.erase(
      std::unique(FeatureBitsets.begin(), FeatureBitsets.end()),
      FeatureBitsets.end());
  o << "#ifndef NDEBUG\n"
    << "// Feature bitsets.\n"
    << "enum : " << getMinimalTypeForRange(FeatureBitsets.size()) << " {\n"
    << "  CEFBS_None,\n";
  for (const auto &FeatureBitset : FeatureBitsets) {
    if (FeatureBitset.empty())
      continue;
    o << "  " << getNameForFeatureBitset(FeatureBitset) << ",\n";
  }
  o << "};\n\n"
    << "static constexpr FeatureBitset FeatureBitsets[] = {\n"
    << "  {}, // CEFBS_None\n";
  for (const auto &FeatureBitset : FeatureBitsets) {
    if (FeatureBitset.empty())
      continue;
    o << "  {";
    for (const auto &Feature : FeatureBitset) {
      const auto &I = SubtargetFeatures.find(Feature);
      assert(I != SubtargetFeatures.end() && "Didn't import predicate?");
      o << I->second.getEnumBitName() << ", ";
    }
    o << "},\n";
  }
  o << "};\n"
    << "#endif // NDEBUG\n\n";


  // Emit the predicate verifier.
  o << "void " << Target.getName()
    << "MCCodeEmitter::verifyInstructionPredicates(\n"
    << "    const MCInst &Inst, const FeatureBitset &AvailableFeatures) const {\n"
    << "#ifndef NDEBUG\n"
    << "  static " << getMinimalTypeForRange(FeatureBitsets.size())
    << " RequiredFeaturesRefs[] = {\n";
  unsigned InstIdx = 0;
  for (const CodeGenInstruction *Inst : Target.getInstructionsByEnumValue()) {
    o << "    CEFBS";
    unsigned NumPredicates = 0;
    for (Record *Predicate : Inst->TheDef->getValueAsListOfDefs("Predicates")) {
      const auto &I = SubtargetFeatures.find(Predicate);
      if (I != SubtargetFeatures.end()) {
        o << '_' << I->second.TheDef->getName();
        NumPredicates++;
      }
    }
    if (!NumPredicates)
      o << "_None";
    o << ", // " << Inst->TheDef->getName() << " = " << InstIdx << "\n";
    InstIdx++;
  }
  o << "  };\n\n";
  o << "  assert(Inst.getOpcode() < " << InstIdx << ");\n";
  o << "  const FeatureBitset &RequiredFeatures = "
       "FeatureBitsets[RequiredFeaturesRefs[Inst.getOpcode()]];\n";
  o << "  FeatureBitset MissingFeatures =\n"
    << "      (AvailableFeatures & RequiredFeatures) ^\n"
    << "      RequiredFeatures;\n"
    << "  if (MissingFeatures.any()) {\n"
    << "    std::ostringstream Msg;\n"
    << "    Msg << \"Attempting to emit \" << "
       "MCII.getName(Inst.getOpcode()).str()\n"
    << "        << \" instruction but the \";\n"
    << "    for (unsigned i = 0, e = MissingFeatures.size(); i != e; ++i)\n"
    << "      if (MissingFeatures.test(i))\n"
    << "        Msg << SubtargetFeatureNames[i] << \" \";\n"
    << "    Msg << \"predicate(s) are not met\";\n"
    << "    report_fatal_error(Msg.str());\n"
    << "  }\n"
    << "#else\n"
    << "// Silence unused variable warning on targets that don't use MCII for "
       "other purposes (e.g. BPF).\n"
    << "(void)MCII;\n"
    << "#endif // NDEBUG\n";
  o << "}\n";
  o << "#endif\n";
}

} // end anonymous namespace

namespace llvm {

void EmitCodeEmitter(RecordKeeper &RK, raw_ostream &OS) {
  emitSourceFileHeader("Machine Code Emitter", OS);
  CodeEmitterGen(RK).run(OS);
}

} // end namespace llvm