Driver/PrintPreprocessedOutput.cpp

//===--- PrintPreprocessedOutput.cpp - Implement the -E mode --------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This code simply runs the preprocessor on the input file and prints out the
// result.  This is the traditional behavior of the -E option.
//
//===----------------------------------------------------------------------===//

#include "clang.h"
#include "clang/Lex/MacroInfo.h"
#include "clang/Lex/PPCallbacks.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Lex/Pragma.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/Diagnostic.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/System/Path.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Config/config.h"
#include "llvm/Support/raw_ostream.h"
#include <cstdio>
using namespace clang;

//===----------------------------------------------------------------------===//
// Preprocessed token printer
//===----------------------------------------------------------------------===//

static llvm::cl::opt<bool>
DisableLineMarkers("P", llvm::cl::desc("Disable linemarker output in -E mode"));
static llvm::cl::opt<bool>
EnableCommentOutput("C", llvm::cl::desc("Enable comment output in -E mode"));
static llvm::cl::opt<bool>
EnableMacroCommentOutput("CC",
                         llvm::cl::desc("Enable comment output in -E mode, "
                                        "even from macro expansions"));
static llvm::cl::opt<bool>
DumpMacros("dM", llvm::cl::desc("Print macro definitions in -E mode instead of"
                                " normal output"));


namespace {
class PrintPPOutputPPCallbacks : public PPCallbacks {
  Preprocessor &PP;
public:
  llvm::raw_ostream &OS;
private:
  unsigned CurLine;
  bool EmittedTokensOnThisLine;
  SrcMgr::CharacteristicKind FileType;
  llvm::SmallString<512> CurFilename;
  bool Initialized;
public:
  PrintPPOutputPPCallbacks(Preprocessor &pp, llvm::raw_ostream &os)
     : PP(pp), OS(os) {
    CurLine = 0;
    CurFilename += "<uninit>";
    EmittedTokensOnThisLine = false;
    FileType = SrcMgr::C_User;
    Initialized = false;
  }
  
  void SetEmittedTokensOnThisLine() { EmittedTokensOnThisLine = true; }
  bool hasEmittedTokensOnThisLine() const { return EmittedTokensOnThisLine; }
  
  virtual void FileChanged(SourceLocation Loc, FileChangeReason Reason,
                           SrcMgr::CharacteristicKind FileType);
  virtual void Ident(SourceLocation Loc, const std::string &str);
  virtual void PragmaComment(SourceLocation Loc, const IdentifierInfo *Kind, 
                             const std::string &Str);


  bool HandleFirstTokOnLine(Token &Tok);
  bool MoveToLine(SourceLocation Loc);
  bool AvoidConcat(const Token &PrevTok, const Token &Tok);
  void WriteLineInfo(unsigned LineNo, const char *Extra=0, unsigned ExtraLen=0);
};
}  // end anonymous namespace

void PrintPPOutputPPCallbacks::WriteLineInfo(unsigned LineNo,
                                             const char *Extra,
                                             unsigned ExtraLen) {
  if (EmittedTokensOnThisLine) {
    OS << '\n';
    EmittedTokensOnThisLine = false;
  }

  OS << '#' << ' ' << LineNo << ' ' << '"';
  OS.write(&CurFilename[0], CurFilename.size());
  OS << '"';
  
  if (ExtraLen)
    OS.write(Extra, ExtraLen);

  if (FileType == SrcMgr::C_System)
    OS.write(" 3", 2);
  else if (FileType == SrcMgr::C_ExternCSystem)
    OS.write(" 3 4", 4);
  OS << '\n';
}

/// MoveToLine - Move the output to the source line specified by the location
/// object.  We can do this by emitting some number of \n's, or be emitting a
/// #line directive.  This returns false if already at the specified line, true
/// if some newlines were emitted.
bool PrintPPOutputPPCallbacks::MoveToLine(SourceLocation Loc) {
  unsigned LineNo = PP.getSourceManager().getInstantiationLineNumber(Loc);

  if (DisableLineMarkers) {
    if (LineNo == CurLine) return false;
    
    CurLine = LineNo;
    
    if (!EmittedTokensOnThisLine)
      return true;
    
    OS << '\n';
    EmittedTokensOnThisLine = false;
    return true;
  }

  // If this line is "close enough" to the original line, just print newlines,
  // otherwise print a #line directive.
  if (LineNo-CurLine <= 8) {
    if (LineNo-CurLine == 1)
      OS << '\n';
    else if (LineNo == CurLine)
      return false;    // Spelling line moved, but instantiation line didn't.
    else {
      const char *NewLines = "\n\n\n\n\n\n\n\n";
      OS.write(NewLines, LineNo-CurLine);
    }
  } else {
    WriteLineInfo(LineNo, 0, 0);
  } 

  CurLine = LineNo;    
  return true;
}


/// FileChanged - Whenever the preprocessor enters or exits a #include file
/// it invokes this handler.  Update our conception of the current source
/// position.
void PrintPPOutputPPCallbacks::FileChanged(SourceLocation Loc,
                                           FileChangeReason Reason,
                                       SrcMgr::CharacteristicKind NewFileType) {
  // Unless we are exiting a #include, make sure to skip ahead to the line the
  // #include directive was at.
  SourceManager &SourceMgr = PP.getSourceManager();
  if (Reason == PPCallbacks::EnterFile) {
    SourceLocation IncludeLoc = SourceMgr.getPresumedLoc(Loc).getIncludeLoc();
    if (IncludeLoc.isValid())
      MoveToLine(IncludeLoc);
  } else if (Reason == PPCallbacks::SystemHeaderPragma) {
    MoveToLine(Loc);
    
    // TODO GCC emits the # directive for this directive on the line AFTER the
    // directive and emits a bunch of spaces that aren't needed.  Emulate this
    // strange behavior.
  }
  
  Loc = SourceMgr.getInstantiationLoc(Loc);
  CurLine = SourceMgr.getInstantiationLineNumber(Loc);

  if (DisableLineMarkers) return;

  CurFilename.clear();
  CurFilename += SourceMgr.getPresumedLoc(Loc).getFilename();
  Lexer::Stringify(CurFilename);
  FileType = NewFileType;

  if (!Initialized) {
    WriteLineInfo(CurLine);
    Initialized = true;
  }

  switch (Reason) {
  case PPCallbacks::EnterFile:
    WriteLineInfo(CurLine, " 1", 2);
    break;
  case PPCallbacks::ExitFile:
    WriteLineInfo(CurLine, " 2", 2);
    break;
  case PPCallbacks::SystemHeaderPragma: 
  case PPCallbacks::RenameFile: 
    WriteLineInfo(CurLine);
    break;
  }
}

/// Ident - Handle #ident directives when read by the preprocessor.
///
void PrintPPOutputPPCallbacks::Ident(SourceLocation Loc, const std::string &S) {
  MoveToLine(Loc);
  
  OS.write("#ident ", strlen("#ident "));
  OS.write(&S[0], S.size());
  EmittedTokensOnThisLine = true;
}

void PrintPPOutputPPCallbacks::PragmaComment(SourceLocation Loc,
                                             const IdentifierInfo *Kind, 
                                             const std::string &Str) {
  MoveToLine(Loc);
  OS << "#pragma comment(" << Kind->getName();
  
  if (!Str.empty()) {
    OS << ", \"";
    
    for (unsigned i = 0, e = Str.size(); i != e; ++i) {
      unsigned char Char = Str[i];
      if (isprint(Char) && Char != '\\' && Char != '"')
        OS << (char)Char;
      else  // Output anything hard as an octal escape.
        OS << '\\'
           << (char)('0'+ ((Char >> 6) & 7))
           << (char)('0'+ ((Char >> 3) & 7))
           << (char)('0'+ ((Char >> 0) & 7));
    }
    OS << '"';
  }
  
  OS << ')';
  EmittedTokensOnThisLine = true;
}


/// HandleFirstTokOnLine - When emitting a preprocessed file in -E mode, this
/// is called for the first token on each new line.  If this really is the start
/// of a new logical line, handle it and return true, otherwise return false.
/// This may not be the start of a logical line because the "start of line"
/// marker is set for spelling lines, not instantiation ones.
bool PrintPPOutputPPCallbacks::HandleFirstTokOnLine(Token &Tok) {
  // Figure out what line we went to and insert the appropriate number of
  // newline characters.
  if (!MoveToLine(Tok.getLocation()))
    return false;
  
  // Print out space characters so that the first token on a line is
  // indented for easy reading.
  const SourceManager &SourceMgr = PP.getSourceManager();
  unsigned ColNo = SourceMgr.getInstantiationColumnNumber(Tok.getLocation());
  
  // This hack prevents stuff like:
  // #define HASH #
  // HASH define foo bar
  // From having the # character end up at column 1, which makes it so it
  // is not handled as a #define next time through the preprocessor if in
  // -fpreprocessed mode.
  if (ColNo <= 1 && Tok.is(tok::hash))
    OS << ' ';
  
  // Otherwise, indent the appropriate number of spaces.
  for (; ColNo > 1; --ColNo)
    OS << ' ';
  
  return true;
}

namespace {
struct UnknownPragmaHandler : public PragmaHandler {
  const char *Prefix;
  PrintPPOutputPPCallbacks *Callbacks;
  
  UnknownPragmaHandler(const char *prefix, PrintPPOutputPPCallbacks *callbacks)
    : PragmaHandler(0), Prefix(prefix), Callbacks(callbacks) {}
  virtual void HandlePragma(Preprocessor &PP, Token &PragmaTok) {
    // Figure out what line we went to and insert the appropriate number of
    // newline characters.
    Callbacks->MoveToLine(PragmaTok.getLocation());
    Callbacks->OS.write(Prefix, strlen(Prefix));
    
    // Read and print all of the pragma tokens.
    while (PragmaTok.isNot(tok::eom)) {
      if (PragmaTok.hasLeadingSpace())
        Callbacks->OS << ' ';
      std::string TokSpell = PP.getSpelling(PragmaTok);
      Callbacks->OS.write(&TokSpell[0], TokSpell.size());
      PP.LexUnexpandedToken(PragmaTok);
    }
    Callbacks->OS << '\n';
  }
};
} // end anonymous namespace


enum AvoidConcatInfo {
  /// By default, a token never needs to avoid concatenation.  Most tokens (e.g.
  /// ',', ')', etc) don't cause a problem when concatenated.
  aci_never_avoid_concat = 0,

  /// aci_custom_firstchar - AvoidConcat contains custom code to handle this
  /// token's requirements, and it needs to know the first character of the
  /// token.
  aci_custom_firstchar = 1,

  /// aci_custom - AvoidConcat contains custom code to handle this token's
  /// requirements, but it doesn't need to know the first character of the
  /// token.
  aci_custom = 2,
  
  /// aci_avoid_equal - Many tokens cannot be safely followed by an '='
  /// character.  For example, "<<" turns into "<<=" when followed by an =.
  aci_avoid_equal = 4
};

/// This array contains information for each token on what action to take when
/// avoiding concatenation of tokens in the AvoidConcat method.
static char TokenInfo[tok::NUM_TOKENS];

/// InitAvoidConcatTokenInfo - Tokens that must avoid concatenation should be
/// marked by this function.
static void InitAvoidConcatTokenInfo() {
  // These tokens have custom code in AvoidConcat.
  TokenInfo[tok::identifier      ] |= aci_custom;
  TokenInfo[tok::numeric_constant] |= aci_custom_firstchar;
  TokenInfo[tok::period          ] |= aci_custom_firstchar;
  TokenInfo[tok::amp             ] |= aci_custom_firstchar;
  TokenInfo[tok::plus            ] |= aci_custom_firstchar;
  TokenInfo[tok::minus           ] |= aci_custom_firstchar;
  TokenInfo[tok::slash           ] |= aci_custom_firstchar;
  TokenInfo[tok::less            ] |= aci_custom_firstchar;
  TokenInfo[tok::greater         ] |= aci_custom_firstchar;
  TokenInfo[tok::pipe            ] |= aci_custom_firstchar;
  TokenInfo[tok::percent         ] |= aci_custom_firstchar;
  TokenInfo[tok::colon           ] |= aci_custom_firstchar;
  TokenInfo[tok::hash            ] |= aci_custom_firstchar;
  TokenInfo[tok::arrow           ] |= aci_custom_firstchar;
  
  // These tokens change behavior if followed by an '='.
  TokenInfo[tok::amp         ] |= aci_avoid_equal;           // &=
  TokenInfo[tok::plus        ] |= aci_avoid_equal;           // +=
  TokenInfo[tok::minus       ] |= aci_avoid_equal;           // -=
  TokenInfo[tok::slash       ] |= aci_avoid_equal;           // /=
  TokenInfo[tok::less        ] |= aci_avoid_equal;           // <=
  TokenInfo[tok::greater     ] |= aci_avoid_equal;           // >=
  TokenInfo[tok::pipe        ] |= aci_avoid_equal;           // |=
  TokenInfo[tok::percent     ] |= aci_avoid_equal;           // %=
  TokenInfo[tok::star        ] |= aci_avoid_equal;           // *=
  TokenInfo[tok::exclaim     ] |= aci_avoid_equal;           // !=
  TokenInfo[tok::lessless    ] |= aci_avoid_equal;           // <<=
  TokenInfo[tok::greaterequal] |= aci_avoid_equal;           // >>=
  TokenInfo[tok::caret       ] |= aci_avoid_equal;           // ^=
  TokenInfo[tok::equal       ] |= aci_avoid_equal;           // ==
}

/// StartsWithL - Return true if the spelling of this token starts with 'L'.
static bool StartsWithL(const Token &Tok, Preprocessor &PP) {
  if (!Tok.needsCleaning()) {
    SourceManager &SrcMgr = PP.getSourceManager();
    return *SrcMgr.getCharacterData(SrcMgr.getSpellingLoc(Tok.getLocation()))
               == 'L';
  }
  
  if (Tok.getLength() < 256) {
    char Buffer[256];
    const char *TokPtr = Buffer;
    PP.getSpelling(Tok, TokPtr);
    return TokPtr[0] == 'L';
  }

  return PP.getSpelling(Tok)[0] == 'L';
}

/// IsIdentifierL - Return true if the spelling of this token is literally 'L'.
static bool IsIdentifierL(const Token &Tok, Preprocessor &PP) {
  if (!Tok.needsCleaning()) {
    if (Tok.getLength() != 1)
      return false;
    SourceManager &SrcMgr = PP.getSourceManager();
    return *SrcMgr.getCharacterData(SrcMgr.getSpellingLoc(Tok.getLocation()))
               == 'L';
  }
  
  if (Tok.getLength() < 256) {
    char Buffer[256];
    const char *TokPtr = Buffer;
    if (PP.getSpelling(Tok, TokPtr) != 1) 
      return false;
    return TokPtr[0] == 'L';
  }
  
  return PP.getSpelling(Tok) == "L";
}


/// AvoidConcat - If printing PrevTok immediately followed by Tok would cause
/// the two individual tokens to be lexed as a single token, return true (which
/// causes a space to be printed between them).  This allows the output of -E
/// mode to be lexed to the same token stream as lexing the input directly
/// would.
///
/// This code must conservatively return true if it doesn't want to be 100%
/// accurate.  This will cause the output to include extra space characters, but
/// the resulting output won't have incorrect concatenations going on.  Examples
/// include "..", which we print with a space between, because we don't want to
/// track enough to tell "x.." from "...".
bool PrintPPOutputPPCallbacks::AvoidConcat(const Token &PrevTok,
                                           const Token &Tok) {
  char Buffer[256];
  
  tok::TokenKind PrevKind = PrevTok.getKind();
  if (PrevTok.getIdentifierInfo())  // Language keyword or named operator.
    PrevKind = tok::identifier;
 
  // Look up information on when we should avoid concatenation with prevtok.
  unsigned ConcatInfo = TokenInfo[PrevKind];
  
  // If prevtok never causes a problem for anything after it, return quickly.
  if (ConcatInfo == 0) return false;

  if (ConcatInfo & aci_avoid_equal) {
    // If the next token is '=' or '==', avoid concatenation.
    if (Tok.is(tok::equal) || Tok.is(tok::equalequal))
      return true;
    ConcatInfo &= ~aci_avoid_equal;
  }
  
  if (ConcatInfo == 0) return false;

  
  
  // Basic algorithm: we look at the first character of the second token, and
  // determine whether it, if appended to the first token, would form (or would
  // contribute) to a larger token if concatenated.
  char FirstChar = 0;
  if (ConcatInfo & aci_custom) {
    // If the token does not need to know the first character, don't get it.
  } else if (IdentifierInfo *II = Tok.getIdentifierInfo()) {
    // Avoid spelling identifiers, the most common form of token.
    FirstChar = II->getName()[0];
  } else if (!Tok.needsCleaning()) {
    if (Tok.isLiteral() && Tok.getLiteralData()) {
      FirstChar = *Tok.getLiteralData();
    } else {
      SourceManager &SrcMgr = PP.getSourceManager();
      FirstChar =
        *SrcMgr.getCharacterData(SrcMgr.getSpellingLoc(Tok.getLocation()));
    }
  } else if (Tok.getLength() < 256) {
    const char *TokPtr = Buffer;
    PP.getSpelling(Tok, TokPtr);
    FirstChar = TokPtr[0];
  } else {
    FirstChar = PP.getSpelling(Tok)[0];
  }
 
  switch (PrevKind) {
  default: assert(0 && "InitAvoidConcatTokenInfo built wrong");
  case tok::identifier:   // id+id or id+number or id+L"foo".
    if (Tok.is(tok::numeric_constant) || Tok.getIdentifierInfo() ||
        Tok.is(tok::wide_string_literal) /* ||
        Tok.is(tok::wide_char_literal)*/)
      return true;

    // If this isn't identifier + string, we're done.
    if (Tok.isNot(tok::char_constant) && Tok.isNot(tok::string_literal))
      return false;
      
    // FIXME: need a wide_char_constant!

    // If the string was a wide string L"foo" or wide char L'f', it would concat
    // with the previous identifier into fooL"bar".  Avoid this.
    if (StartsWithL(Tok, PP))
      return true;

    // Otherwise, this is a narrow character or string.  If the *identifier* is
    // a literal 'L', avoid pasting L "foo" -> L"foo".
    return IsIdentifierL(PrevTok, PP);
  case tok::numeric_constant:
    return isalnum(FirstChar) || Tok.is(tok::numeric_constant) ||
           FirstChar == '+' || FirstChar == '-' || FirstChar == '.';
  case tok::period:          // ..., .*, .1234
    return FirstChar == '.' || isdigit(FirstChar) ||
           (FirstChar == '*' && PP.getLangOptions().CPlusPlus);
  case tok::amp:             // &&
    return FirstChar == '&';
  case tok::plus:            // ++
    return FirstChar == '+';
  case tok::minus:           // --, ->, ->*
    return FirstChar == '-' || FirstChar == '>';
  case tok::slash:           //, /*, //
    return FirstChar == '*' || FirstChar == '/';
  case tok::less:            // <<, <<=, <:, <%
    return FirstChar == '<' || FirstChar == ':' || FirstChar == '%';
  case tok::greater:         // >>, >>=
    return FirstChar == '>';
  case tok::pipe:            // ||
    return FirstChar == '|';
  case tok::percent:         // %>, %:
    return (FirstChar == '>' || FirstChar == ':') &&
           PP.getLangOptions().Digraphs;
  case tok::colon:           // ::, :>
    return (FirstChar == ':' && PP.getLangOptions().CPlusPlus) ||
           (FirstChar == '>' && PP.getLangOptions().Digraphs);
  case tok::hash:            // ##, #@, %:%:
    return FirstChar == '#' || FirstChar == '@' || FirstChar == '%';
  case tok::arrow:           // ->*
    return FirstChar == '*';
  }
}

static void PrintPreprocessedTokens(Preprocessor &PP, Token &Tok,
                                    PrintPPOutputPPCallbacks *Callbacks,
                                    llvm::raw_ostream &OS) {
  char Buffer[256];
  Token PrevTok;
  while (1) {
    
    // If this token is at the start of a line, emit newlines if needed.
    if (Tok.isAtStartOfLine() && Callbacks->HandleFirstTokOnLine(Tok)) {
      // done.
    } else if (Tok.hasLeadingSpace() || 
               // If we haven't emitted a token on this line yet, PrevTok isn't
               // useful to look at and no concatenation could happen anyway.
               (Callbacks->hasEmittedTokensOnThisLine() &&
                // Don't print "-" next to "-", it would form "--".
                Callbacks->AvoidConcat(PrevTok, Tok))) {
      OS << ' ';
    }
    
    if (IdentifierInfo *II = Tok.getIdentifierInfo()) {
      OS.write(II->getName(), II->getLength());
    } else if (Tok.isLiteral() && !Tok.needsCleaning() &&
               Tok.getLiteralData()) {
      OS.write(Tok.getLiteralData(), Tok.getLength());
    } else if (Tok.getLength() < 256) {
      const char *TokPtr = Buffer;
      unsigned Len = PP.getSpelling(Tok, TokPtr);
      OS.write(TokPtr, Len);
    } else {
      std::string S = PP.getSpelling(Tok);
      OS.write(&S[0], S.size());
    }
    Callbacks->SetEmittedTokensOnThisLine();
    
    if (Tok.is(tok::eof)) break;
    
    PrevTok = Tok;
    PP.Lex(Tok);
  }
}

/// PrintMacroDefinition - Print a macro definition in a form that will be
/// properly accepted back as a definition.
static void PrintMacroDefinition(IdentifierInfo &II, const MacroInfo &MI,
                                 Preprocessor &PP, llvm::raw_ostream &OS) {
  // Ignore computed macros like __LINE__ and friends. 
  if (MI.isBuiltinMacro()) return;
  OS << "#define " << II.getName();

  if (MI.isFunctionLike()) {
    OS << '(';
    if (MI.arg_empty())
      ;
    else if (MI.getNumArgs() == 1) 
      OS << (*MI.arg_begin())->getName();
    else {
      MacroInfo::arg_iterator AI = MI.arg_begin(), E = MI.arg_end();
      OS << (*AI++)->getName();
      while (AI != E)
        OS << ',' << (*AI++)->getName();
    }
    
    if (MI.isVariadic()) {
      if (!MI.arg_empty())
        OS << ',';
      OS << "...";
    }
    OS << ')';
  }
  
  // GCC always emits a space, even if the macro body is empty.  However, do not
  // want to emit two spaces if the first token has a leading space.
  if (MI.tokens_empty() || !MI.tokens_begin()->hasLeadingSpace())
    OS << ' ';
  
  llvm::SmallVector<char, 128> SpellingBuffer;
  
  for (MacroInfo::tokens_iterator I = MI.tokens_begin(), E = MI.tokens_end();
       I != E; ++I) {
    if (I->hasLeadingSpace())
      OS << ' ';
    
    // Make sure we have enough space in the spelling buffer.
    if (I->getLength() < SpellingBuffer.size())
      SpellingBuffer.resize(I->getLength());
    const char *Buffer = &SpellingBuffer[0];
    unsigned SpellingLen = PP.getSpelling(*I, Buffer);
    OS.write(Buffer, SpellingLen);
  }
  OS << "\n";
}


/// DoPrintPreprocessedInput - This implements -E mode.
///
void clang::DoPrintPreprocessedInput(Preprocessor &PP, 
                                     const std::string &OutFile) {
  // Inform the preprocessor whether we want it to retain comments or not, due
  // to -C or -CC.
  PP.SetCommentRetentionState(EnableCommentOutput, EnableMacroCommentOutput);
  InitAvoidConcatTokenInfo();

  
  // Open the output buffer.
  std::string Err;
  llvm::raw_fd_ostream OS(OutFile.empty() ? "-" : OutFile.c_str(), false, Err);
  if (!Err.empty()) {
    fprintf(stderr, "%s\n", Err.c_str());
    exit(1);
  }
  
  OS.SetBufferSize(64*1024);
  
  if (DumpMacros) {
    // -dM mode just scans and ignores all tokens in the files, then dumps out
    // the macro table at the end.
    PP.EnterMainSourceFile();
    
    Token Tok;
    do PP.Lex(Tok);
    while (Tok.isNot(tok::eof));
    
    for (Preprocessor::macro_iterator I = PP.macro_begin(), E = PP.macro_end();
         I != E; ++I)
      PrintMacroDefinition(*I->first, *I->second, PP, OS);
    
  } else {
    PrintPPOutputPPCallbacks *Callbacks;
    Callbacks = new PrintPPOutputPPCallbacks(PP, OS);
    PP.AddPragmaHandler(0, new UnknownPragmaHandler("#pragma", Callbacks));
    PP.AddPragmaHandler("GCC", new UnknownPragmaHandler("#pragma GCC",
                                                        Callbacks));

    PP.setPPCallbacks(Callbacks);

    // After we have configured the preprocessor, enter the main file.
    PP.EnterMainSourceFile();

    // Consume all of the tokens that come from the predefines buffer.  Those
    // should not be emitted into the output and are guaranteed to be at the
    // start.
    const SourceManager &SourceMgr = PP.getSourceManager();
    Token Tok;
    do PP.Lex(Tok);
    while (Tok.isNot(tok::eof) && Tok.getLocation().isFileID() &&
           !strcmp(SourceMgr.getPresumedLoc(Tok.getLocation()).getFilename(),
                   "<predefines>"));

    // Read all the preprocessed tokens, printing them out to the stream.
    PrintPreprocessedTokens(PP, Tok, Callbacks, OS);
    OS << '\n';
  }
  
  // Flush the ostream.
  OS.flush();
  
  // If an error occurred, remove the output file.
  if (PP.getDiagnostics().hasErrorOccurred() && !OutFile.empty())
    llvm::sys::Path(OutFile).eraseFromDisk();
}