llvm-project/clang/lib/Analysis/FormatString.cpp

// FormatString.cpp - Common stuff for handling printf/scanf formats -*- C++ -*-
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Shared details for processing format strings of printf and scanf
// (and friends).
//
//===----------------------------------------------------------------------===//

#include "FormatStringParsing.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/TargetInfo.h"

using clang::analyze_format_string::ArgType;
using clang::analyze_format_string::FormatStringHandler;
using clang::analyze_format_string::FormatSpecifier;
using clang::analyze_format_string::LengthModifier;
using clang::analyze_format_string::OptionalAmount;
using clang::analyze_format_string::PositionContext;
using clang::analyze_format_string::ConversionSpecifier;
using namespace clang;

// Key function to FormatStringHandler.
FormatStringHandler::~FormatStringHandler() {}

//===----------------------------------------------------------------------===//
// Functions for parsing format strings components in both printf and
// scanf format strings.
//===----------------------------------------------------------------------===//

OptionalAmount
clang::analyze_format_string::ParseAmount(const char *&Beg, const char *E) {
  const char *I = Beg;
  UpdateOnReturn <const char*> UpdateBeg(Beg, I);

  unsigned accumulator = 0;
  bool hasDigits = false;

  for ( ; I != E; ++I) {
    char c = *I;
    if (c >= '0' && c <= '9') {
      hasDigits = true;
      accumulator = (accumulator * 10) + (c - '0');
      continue;
    }

    if (hasDigits)
      return OptionalAmount(OptionalAmount::Constant, accumulator, Beg, I - Beg,
          false);

    break;
  }

  return OptionalAmount();
}

OptionalAmount
clang::analyze_format_string::ParseNonPositionAmount(const char *&Beg,
                                                     const char *E,
                                                     unsigned &argIndex) {
  if (*Beg == '*') {
    ++Beg;
    return OptionalAmount(OptionalAmount::Arg, argIndex++, Beg, 0, false);
  }

  return ParseAmount(Beg, E);
}

OptionalAmount
clang::analyze_format_string::ParsePositionAmount(FormatStringHandler &H,
                                                  const char *Start,
                                                  const char *&Beg,
                                                  const char *E,
                                                  PositionContext p) {
  if (*Beg == '*') {
    const char *I = Beg + 1;
    const OptionalAmount &Amt = ParseAmount(I, E);

    if (Amt.getHowSpecified() == OptionalAmount::NotSpecified) {
      H.HandleInvalidPosition(Beg, I - Beg, p);
      return OptionalAmount(false);
    }

    if (I == E) {
      // No more characters left?
      H.HandleIncompleteSpecifier(Start, E - Start);
      return OptionalAmount(false);
    }

    assert(Amt.getHowSpecified() == OptionalAmount::Constant);

    if (*I == '$') {
      // Handle positional arguments

      // Special case: '*0$', since this is an easy mistake.
      if (Amt.getConstantAmount() == 0) {
        H.HandleZeroPosition(Beg, I - Beg + 1);
        return OptionalAmount(false);
      }

      const char *Tmp = Beg;
      Beg = ++I;

      return OptionalAmount(OptionalAmount::Arg, Amt.getConstantAmount() - 1,
                            Tmp, 0, true);
    }

    H.HandleInvalidPosition(Beg, I - Beg, p);
    return OptionalAmount(false);
  }

  return ParseAmount(Beg, E);
}


bool
clang::analyze_format_string::ParseFieldWidth(FormatStringHandler &H,
                                              FormatSpecifier &CS,
                                              const char *Start,
                                              const char *&Beg, const char *E,
                                              unsigned *argIndex) {
  // FIXME: Support negative field widths.
  if (argIndex) {
    CS.setFieldWidth(ParseNonPositionAmount(Beg, E, *argIndex));
  }
  else {
    const OptionalAmount Amt =
      ParsePositionAmount(H, Start, Beg, E,
                          analyze_format_string::FieldWidthPos);

    if (Amt.isInvalid())
      return true;
    CS.setFieldWidth(Amt);
  }
  return false;
}

bool
clang::analyze_format_string::ParseArgPosition(FormatStringHandler &H,
                                               FormatSpecifier &FS,
                                               const char *Start,
                                               const char *&Beg,
                                               const char *E) {
  const char *I = Beg;

  const OptionalAmount &Amt = ParseAmount(I, E);

  if (I == E) {
    // No more characters left?
    H.HandleIncompleteSpecifier(Start, E - Start);
    return true;
  }

  if (Amt.getHowSpecified() == OptionalAmount::Constant && *(I++) == '$') {
    // Warn that positional arguments are non-standard.
    H.HandlePosition(Start, I - Start);

    // Special case: '%0$', since this is an easy mistake.
    if (Amt.getConstantAmount() == 0) {
      H.HandleZeroPosition(Start, I - Start);
      return true;
    }

    FS.setArgIndex(Amt.getConstantAmount() - 1);
    FS.setUsesPositionalArg();
    // Update the caller's pointer if we decided to consume
    // these characters.
    Beg = I;
    return false;
  }

  return false;
}

bool
clang::analyze_format_string::ParseLengthModifier(FormatSpecifier &FS,
                                                  const char *&I,
                                                  const char *E,
                                                  const LangOptions &LO,
                                                  bool IsScanf) {
  LengthModifier::Kind lmKind = LengthModifier::None;
  const char *lmPosition = I;
  switch (*I) {
    default:
      return false;
    case 'h':
      ++I;
      lmKind = (I != E && *I == 'h') ? (++I, LengthModifier::AsChar)
                                     : LengthModifier::AsShort;
      break;
    case 'l':
      ++I;
      lmKind = (I != E && *I == 'l') ? (++I, LengthModifier::AsLongLong)
                                     : LengthModifier::AsLong;
      break;
    case 'j': lmKind = LengthModifier::AsIntMax;     ++I; break;
    case 'z': lmKind = LengthModifier::AsSizeT;      ++I; break;
    case 't': lmKind = LengthModifier::AsPtrDiff;    ++I; break;
    case 'L': lmKind = LengthModifier::AsLongDouble; ++I; break;
    case 'q': lmKind = LengthModifier::AsQuad;       ++I; break;
    case 'a':
      if (IsScanf && !LO.C99 && !LO.CPlusPlus11) {
        // For scanf in C90, look at the next character to see if this should
        // be parsed as the GNU extension 'a' length modifier. If not, this
        // will be parsed as a conversion specifier.
        ++I;
        if (I != E && (*I == 's' || *I == 'S' || *I == '[')) {
          lmKind = LengthModifier::AsAllocate;
          break;
        }
        --I;
      }
      return false;
    case 'm':
      if (IsScanf) {
        lmKind = LengthModifier::AsMAllocate;
        ++I;
        break;
      }
      return false;
    // printf: AsInt64, AsInt32, AsInt3264
    // scanf:  AsInt64
    case 'I':
      if (I + 1 != E && I + 2 != E) {
        if (I[1] == '6' && I[2] == '4') {
          I += 3;
          lmKind = LengthModifier::AsInt64;
          break;
        }
        if (IsScanf)
          return false;

        if (I[1] == '3' && I[2] == '2') {
          I += 3;
          lmKind = LengthModifier::AsInt32;
          break;
        }
      }
      ++I;
      lmKind = LengthModifier::AsInt3264;
      break;
    case 'w':
      lmKind = LengthModifier::AsWide; ++I; break;
  }
  LengthModifier lm(lmPosition, lmKind);
  FS.setLengthModifier(lm);
  return true;
}

//===----------------------------------------------------------------------===//
// Methods on ArgType.
//===----------------------------------------------------------------------===//

bool ArgType::matchesType(ASTContext &C, QualType argTy) const {
  if (Ptr) {
    // It has to be a pointer.
    const PointerType *PT = argTy->getAs<PointerType>();
    if (!PT)
      return false;

    // We cannot write through a const qualified pointer.
    if (PT->getPointeeType().isConstQualified())
      return false;

    argTy = PT->getPointeeType();
  }

  switch (K) {
    case InvalidTy:
      llvm_unreachable("ArgType must be valid");

    case UnknownTy:
      return true;
      
    case AnyCharTy: {
      if (const EnumType *ETy = argTy->getAs<EnumType>())
        argTy = ETy->getDecl()->getIntegerType();

      if (const BuiltinType *BT = argTy->getAs<BuiltinType>())
        switch (BT->getKind()) {
          default:
            break;
          case BuiltinType::Char_S:
          case BuiltinType::SChar:
          case BuiltinType::UChar:
          case BuiltinType::Char_U:
            return true;            
        }
      return false;
    }
      
    case SpecificTy: {
      if (const EnumType *ETy = argTy->getAs<EnumType>())
        argTy = ETy->getDecl()->getIntegerType();
      argTy = C.getCanonicalType(argTy).getUnqualifiedType();

      if (T == argTy)
        return true;
      // Check for "compatible types".
      if (const BuiltinType *BT = argTy->getAs<BuiltinType>())
        switch (BT->getKind()) {
          default:
            break;
          case BuiltinType::Char_S:
          case BuiltinType::SChar:
          case BuiltinType::Char_U:
          case BuiltinType::UChar:                    
            return T == C.UnsignedCharTy || T == C.SignedCharTy;
          case BuiltinType::Short:
            return T == C.UnsignedShortTy;
          case BuiltinType::UShort:
            return T == C.ShortTy;
          case BuiltinType::Int:
            return T == C.UnsignedIntTy;
          case BuiltinType::UInt:
            return T == C.IntTy;
          case BuiltinType::Long:
            return T == C.UnsignedLongTy;
          case BuiltinType::ULong:
            return T == C.LongTy;
          case BuiltinType::LongLong:
            return T == C.UnsignedLongLongTy;
          case BuiltinType::ULongLong:
            return T == C.LongLongTy;
        }
      return false;
    }

    case CStrTy: {
      const PointerType *PT = argTy->getAs<PointerType>();
      if (!PT)
        return false;
      QualType pointeeTy = PT->getPointeeType();
      if (const BuiltinType *BT = pointeeTy->getAs<BuiltinType>())
        switch (BT->getKind()) {
          case BuiltinType::Void:
          case BuiltinType::Char_U:
          case BuiltinType::UChar:
          case BuiltinType::Char_S:
          case BuiltinType::SChar:
            return true;
          default:
            break;
        }

      return false;
    }

    case WCStrTy: {
      const PointerType *PT = argTy->getAs<PointerType>();
      if (!PT)
        return false;
      QualType pointeeTy =
        C.getCanonicalType(PT->getPointeeType()).getUnqualifiedType();
      return pointeeTy == C.getWideCharType();
    }
    
    case WIntTy: {
      
      QualType PromoArg = 
        argTy->isPromotableIntegerType()
          ? C.getPromotedIntegerType(argTy) : argTy;
      
      QualType WInt = C.getCanonicalType(C.getWIntType()).getUnqualifiedType();
      PromoArg = C.getCanonicalType(PromoArg).getUnqualifiedType();
      
      // If the promoted argument is the corresponding signed type of the
      // wint_t type, then it should match.
      if (PromoArg->hasSignedIntegerRepresentation() &&
          C.getCorrespondingUnsignedType(PromoArg) == WInt)
        return true;

      return WInt == PromoArg;
    }

    case CPointerTy:
      return argTy->isPointerType() || argTy->isObjCObjectPointerType() ||
             argTy->isBlockPointerType() || argTy->isNullPtrType();

    case ObjCPointerTy: {
      if (argTy->getAs<ObjCObjectPointerType>() ||
          argTy->getAs<BlockPointerType>())
        return true;
      
      // Handle implicit toll-free bridging.
      if (const PointerType *PT = argTy->getAs<PointerType>()) {
        // Things such as CFTypeRef are really just opaque pointers
        // to C structs representing CF types that can often be bridged
        // to Objective-C objects.  Since the compiler doesn't know which
        // structs can be toll-free bridged, we just accept them all.
        QualType pointee = PT->getPointeeType();
        if (pointee->getAsStructureType() || pointee->isVoidType())
          return true;
      }
      return false;      
    }
  }

  llvm_unreachable("Invalid ArgType Kind!");
}

QualType ArgType::getRepresentativeType(ASTContext &C) const {
  QualType Res;
  switch (K) {
    case InvalidTy:
      llvm_unreachable("No representative type for Invalid ArgType");
    case UnknownTy:
      llvm_unreachable("No representative type for Unknown ArgType");
    case AnyCharTy:
      Res = C.CharTy;
      break;
    case SpecificTy:
      Res = T;
      break;
    case CStrTy:
      Res = C.getPointerType(C.CharTy);
      break;
    case WCStrTy:
      Res = C.getPointerType(C.getWideCharType());
      break;
    case ObjCPointerTy:
      Res = C.ObjCBuiltinIdTy;
      break;
    case CPointerTy:
      Res = C.VoidPtrTy;
      break;
    case WIntTy: {
      Res = C.getWIntType();
      break;
    }
  }

  if (Ptr)
    Res = C.getPointerType(Res);
  return Res;
}

std::string ArgType::getRepresentativeTypeName(ASTContext &C) const {
  std::string S = getRepresentativeType(C).getAsString();

  std::string Alias;
  if (Name) {
    // Use a specific name for this type, e.g. "size_t".
    Alias = Name;
    if (Ptr) {
      // If ArgType is actually a pointer to T, append an asterisk.
      Alias += (Alias[Alias.size()-1] == '*') ? "*" : " *";
    }
    // If Alias is the same as the underlying type, e.g. wchar_t, then drop it.
    if (S == Alias)
      Alias.clear();
  }

  if (!Alias.empty())
    return std::string("'") + Alias + "' (aka '" + S + "')";
  return std::string("'") + S + "'";
}


//===----------------------------------------------------------------------===//
// Methods on OptionalAmount.
//===----------------------------------------------------------------------===//

ArgType
analyze_format_string::OptionalAmount::getArgType(ASTContext &Ctx) const {
  return Ctx.IntTy;
}

//===----------------------------------------------------------------------===//
// Methods on LengthModifier.
//===----------------------------------------------------------------------===//

const char *
analyze_format_string::LengthModifier::toString() const {
  switch (kind) {
  case AsChar:
    return "hh";
  case AsShort:
    return "h";
  case AsLong: // or AsWideChar
    return "l";
  case AsLongLong:
    return "ll";
  case AsQuad:
    return "q";
  case AsIntMax:
    return "j";
  case AsSizeT:
    return "z";
  case AsPtrDiff:
    return "t";
  case AsInt32:
    return "I32";
  case AsInt3264:
    return "I";
  case AsInt64:
    return "I64";
  case AsLongDouble:
    return "L";
  case AsAllocate:
    return "a";
  case AsMAllocate:
    return "m";
  case AsWide:
    return "w";
  case None:
    return "";
  }
  return nullptr;
}

//===----------------------------------------------------------------------===//
// Methods on ConversionSpecifier.
//===----------------------------------------------------------------------===//

const char *ConversionSpecifier::toString() const {
  switch (kind) {
  case dArg: return "d";
  case DArg: return "D";
  case iArg: return "i";
  case oArg: return "o";
  case OArg: return "O";
  case uArg: return "u";
  case UArg: return "U";
  case xArg: return "x";
  case XArg: return "X";
  case fArg: return "f";
  case FArg: return "F";
  case eArg: return "e";
  case EArg: return "E";
  case gArg: return "g";
  case GArg: return "G";
  case aArg: return "a";
  case AArg: return "A";
  case cArg: return "c";
  case sArg: return "s";
  case pArg: return "p";
  case nArg: return "n";
  case PercentArg:  return "%";
  case ScanListArg: return "[";
  case InvalidSpecifier: return nullptr;

  // POSIX unicode extensions.
  case CArg: return "C";
  case SArg: return "S";

  // Objective-C specific specifiers.
  case ObjCObjArg: return "@";

  // GlibC specific specifiers.
  case PrintErrno: return "m";

  // MS specific specifiers.
  case ZArg: return "Z";
  }
  return nullptr;
}

Optional<ConversionSpecifier>
ConversionSpecifier::getStandardSpecifier() const {
  ConversionSpecifier::Kind NewKind;
  
  switch (getKind()) {
  default:
    return None;
  case DArg:
    NewKind = dArg;
    break;
  case UArg:
    NewKind = uArg;
    break;
  case OArg:
    NewKind = oArg;
    break;
  }

  ConversionSpecifier FixedCS(*this);
  FixedCS.setKind(NewKind);
  return FixedCS;
}

//===----------------------------------------------------------------------===//
// Methods on OptionalAmount.
//===----------------------------------------------------------------------===//

void OptionalAmount::toString(raw_ostream &os) const {
  switch (hs) {
  case Invalid:
  case NotSpecified:
    return;
  case Arg:
    if (UsesDotPrefix)
        os << ".";
    if (usesPositionalArg())
      os << "*" << getPositionalArgIndex() << "$";
    else
      os << "*";
    break;
  case Constant:
    if (UsesDotPrefix)
        os << ".";
    os << amt;
    break;
  }
}

bool FormatSpecifier::hasValidLengthModifier(const TargetInfo &Target) const {
  switch (LM.getKind()) {
    case LengthModifier::None:
      return true;
      
    // Handle most integer flags
    case LengthModifier::AsShort:
      if (Target.getTriple().isOSMSVCRT()) {
        switch (CS.getKind()) {
          case ConversionSpecifier::cArg:
          case ConversionSpecifier::CArg:
          case ConversionSpecifier::sArg:
          case ConversionSpecifier::SArg:
          case ConversionSpecifier::ZArg:
            return true;
          default:
            break;
        }
      }
      // Fall through.
    case LengthModifier::AsChar:
    case LengthModifier::AsLongLong:
    case LengthModifier::AsQuad:
    case LengthModifier::AsIntMax:
    case LengthModifier::AsSizeT:
    case LengthModifier::AsPtrDiff:
      switch (CS.getKind()) {
        case ConversionSpecifier::dArg:
        case ConversionSpecifier::DArg:
        case ConversionSpecifier::iArg:
        case ConversionSpecifier::oArg:
        case ConversionSpecifier::OArg:
        case ConversionSpecifier::uArg:
        case ConversionSpecifier::UArg:
        case ConversionSpecifier::xArg:
        case ConversionSpecifier::XArg:
        case ConversionSpecifier::nArg:
          return true;
        default:
          return false;
      }
      
    // Handle 'l' flag
    case LengthModifier::AsLong: // or AsWideChar
      switch (CS.getKind()) {
        case ConversionSpecifier::dArg:
        case ConversionSpecifier::DArg:
        case ConversionSpecifier::iArg:
        case ConversionSpecifier::oArg:
        case ConversionSpecifier::OArg:
        case ConversionSpecifier::uArg:
        case ConversionSpecifier::UArg:
        case ConversionSpecifier::xArg:
        case ConversionSpecifier::XArg:
        case ConversionSpecifier::aArg:
        case ConversionSpecifier::AArg:
        case ConversionSpecifier::fArg:
        case ConversionSpecifier::FArg:
        case ConversionSpecifier::eArg:
        case ConversionSpecifier::EArg:
        case ConversionSpecifier::gArg:
        case ConversionSpecifier::GArg:
        case ConversionSpecifier::nArg:
        case ConversionSpecifier::cArg:
        case ConversionSpecifier::sArg:
        case ConversionSpecifier::ScanListArg:
        case ConversionSpecifier::ZArg:
          return true;
        default:
          return false;
      }
      
    case LengthModifier::AsLongDouble:
      switch (CS.getKind()) {
        case ConversionSpecifier::aArg:
        case ConversionSpecifier::AArg:
        case ConversionSpecifier::fArg:
        case ConversionSpecifier::FArg:
        case ConversionSpecifier::eArg:
        case ConversionSpecifier::EArg:
        case ConversionSpecifier::gArg:
        case ConversionSpecifier::GArg:
          return true;
        // GNU libc extension.
        case ConversionSpecifier::dArg:
        case ConversionSpecifier::iArg:
        case ConversionSpecifier::oArg:
        case ConversionSpecifier::uArg:
        case ConversionSpecifier::xArg:
        case ConversionSpecifier::XArg:
          return !Target.getTriple().isOSDarwin() &&
                 !Target.getTriple().isOSWindows();
        default:
          return false;
      }

    case LengthModifier::AsAllocate:
      switch (CS.getKind()) {
        case ConversionSpecifier::sArg:
        case ConversionSpecifier::SArg:
        case ConversionSpecifier::ScanListArg:
          return true;
        default:
          return false;
      }

    case LengthModifier::AsMAllocate:
      switch (CS.getKind()) {
        case ConversionSpecifier::cArg:
        case ConversionSpecifier::CArg:
        case ConversionSpecifier::sArg:
        case ConversionSpecifier::SArg:
        case ConversionSpecifier::ScanListArg:
          return true;
        default:
          return false;
      }
    case LengthModifier::AsInt32:
    case LengthModifier::AsInt3264:
    case LengthModifier::AsInt64:
      switch (CS.getKind()) {
        case ConversionSpecifier::dArg:
        case ConversionSpecifier::iArg:
        case ConversionSpecifier::oArg:
        case ConversionSpecifier::uArg:
        case ConversionSpecifier::xArg:
        case ConversionSpecifier::XArg:
          return Target.getTriple().isOSMSVCRT();
        default:
          return false;
      }
    case LengthModifier::AsWide:
      switch (CS.getKind()) {
        case ConversionSpecifier::cArg:
        case ConversionSpecifier::CArg:
        case ConversionSpecifier::sArg:
        case ConversionSpecifier::SArg:
        case ConversionSpecifier::ZArg:
          return Target.getTriple().isOSMSVCRT();
        default:
          return false;
      }
  }
  llvm_unreachable("Invalid LengthModifier Kind!");
}

bool FormatSpecifier::hasStandardLengthModifier() const {
  switch (LM.getKind()) {
    case LengthModifier::None:
    case LengthModifier::AsChar:
    case LengthModifier::AsShort:
    case LengthModifier::AsLong:
    case LengthModifier::AsLongLong:
    case LengthModifier::AsIntMax:
    case LengthModifier::AsSizeT:
    case LengthModifier::AsPtrDiff:
    case LengthModifier::AsLongDouble:
      return true;
    case LengthModifier::AsAllocate:
    case LengthModifier::AsMAllocate:
    case LengthModifier::AsQuad:
    case LengthModifier::AsInt32:
    case LengthModifier::AsInt3264:
    case LengthModifier::AsInt64:
    case LengthModifier::AsWide:
      return false;
  }
  llvm_unreachable("Invalid LengthModifier Kind!");
}

bool FormatSpecifier::hasStandardConversionSpecifier(const LangOptions &LangOpt) const {
  switch (CS.getKind()) {
    case ConversionSpecifier::cArg:
    case ConversionSpecifier::dArg:
    case ConversionSpecifier::iArg:
    case ConversionSpecifier::oArg:
    case ConversionSpecifier::uArg:
    case ConversionSpecifier::xArg:
    case ConversionSpecifier::XArg:
    case ConversionSpecifier::fArg:
    case ConversionSpecifier::FArg:
    case ConversionSpecifier::eArg:
    case ConversionSpecifier::EArg:
    case ConversionSpecifier::gArg:
    case ConversionSpecifier::GArg:
    case ConversionSpecifier::aArg:
    case ConversionSpecifier::AArg:
    case ConversionSpecifier::sArg:
    case ConversionSpecifier::pArg:
    case ConversionSpecifier::nArg:
    case ConversionSpecifier::ObjCObjArg:
    case ConversionSpecifier::ScanListArg:
    case ConversionSpecifier::PercentArg:
      return true;
    case ConversionSpecifier::CArg:
    case ConversionSpecifier::SArg:
      return LangOpt.ObjC1 || LangOpt.ObjC2;
    case ConversionSpecifier::InvalidSpecifier:
    case ConversionSpecifier::PrintErrno:
    case ConversionSpecifier::DArg:
    case ConversionSpecifier::OArg:
    case ConversionSpecifier::UArg:
    case ConversionSpecifier::ZArg:
      return false;
  }
  llvm_unreachable("Invalid ConversionSpecifier Kind!");
}

bool FormatSpecifier::hasStandardLengthConversionCombination() const {
  if (LM.getKind() == LengthModifier::AsLongDouble) {
    switch(CS.getKind()) {
        case ConversionSpecifier::dArg:
        case ConversionSpecifier::iArg:
        case ConversionSpecifier::oArg:
        case ConversionSpecifier::uArg:
        case ConversionSpecifier::xArg:
        case ConversionSpecifier::XArg:
          return false;
        default:
          return true;
    }
  }
  return true;
}

Optional<LengthModifier> FormatSpecifier::getCorrectedLengthModifier() const {
  if (CS.isAnyIntArg() || CS.getKind() == ConversionSpecifier::nArg) {
    if (LM.getKind() == LengthModifier::AsLongDouble ||
        LM.getKind() == LengthModifier::AsQuad) {
      LengthModifier FixedLM(LM);
      FixedLM.setKind(LengthModifier::AsLongLong);
      return FixedLM;
    }
  }

  return None;
}

bool FormatSpecifier::namedTypeToLengthModifier(QualType QT,
                                                LengthModifier &LM) {
  assert(isa<TypedefType>(QT) && "Expected a TypedefType");
  const TypedefNameDecl *Typedef = cast<TypedefType>(QT)->getDecl();

  for (;;) {
    const IdentifierInfo *Identifier = Typedef->getIdentifier();
    if (Identifier->getName() == "size_t") {
      LM.setKind(LengthModifier::AsSizeT);
      return true;
    } else if (Identifier->getName() == "ssize_t") {
      // Not C99, but common in Unix.
      LM.setKind(LengthModifier::AsSizeT);
      return true;
    } else if (Identifier->getName() == "intmax_t") {
      LM.setKind(LengthModifier::AsIntMax);
      return true;
    } else if (Identifier->getName() == "uintmax_t") {
      LM.setKind(LengthModifier::AsIntMax);
      return true;
    } else if (Identifier->getName() == "ptrdiff_t") {
      LM.setKind(LengthModifier::AsPtrDiff);
      return true;
    }

    QualType T = Typedef->getUnderlyingType();
    if (!isa<TypedefType>(T))
      break;

    Typedef = cast<TypedefType>(T)->getDecl();
  }
  return false;
}