text: //===--- PPExpressions.cpp - Preprocessor Expression Evaluation -----------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements the Preprocessor::EvaluateDirectiveExpression method,
  // which parses and evaluates integer constant expressions for #if directives.
  //
  //===----------------------------------------------------------------------===//
  //
  // FIXME: implement testing for #assert's.
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/Lex/Preprocessor.h"
  #include "clang/Basic/TargetInfo.h"
  #include "clang/Lex/CodeCompletionHandler.h"
  #include "clang/Lex/LexDiagnostic.h"
  #include "clang/Lex/LiteralSupport.h"
  #include "clang/Lex/MacroInfo.h"
  #include "llvm/ADT/APSInt.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/SaveAndRestore.h"
  using namespace clang;
  
  namespace {
  
  /// PPValue - Represents the value of a subexpression of a preprocessor
  /// conditional and the source range covered by it.
  class PPValue {
    SourceRange Range;
  public:
    llvm::APSInt Val;
  
    // Default ctor - Construct an 'invalid' PPValue.
    PPValue(unsigned BitWidth) : Val(BitWidth) {}
  
    unsigned getBitWidth() const { return Val.getBitWidth(); }
    bool isUnsigned() const { return Val.isUnsigned(); }
  
    SourceRange getRange() const { return Range; }
  
    void setRange(SourceLocation L) { Range.setBegin(L); Range.setEnd(L); }
    void setRange(SourceLocation B, SourceLocation E) {
      Range.setBegin(B); Range.setEnd(E);
    }
    void setBegin(SourceLocation L) { Range.setBegin(L); }
    void setEnd(SourceLocation L) { Range.setEnd(L); }
  };
  
  }
  
  static bool EvaluateDirectiveSubExpr(PPValue &LHS, unsigned MinPrec,
                                       Token &PeekTok, bool ValueLive,
                                       Preprocessor &PP);
  
  /// DefinedTracker - This struct is used while parsing expressions to keep track
  /// of whether !defined(X) has been seen.
  ///
  /// With this simple scheme, we handle the basic forms:
  ///    !defined(X)   and !defined X
  /// but we also trivially handle (silly) stuff like:
  ///    !!!defined(X) and +!defined(X) and !+!+!defined(X) and !(defined(X)).
  struct DefinedTracker {
    /// Each time a Value is evaluated, it returns information about whether the
    /// parsed value is of the form defined(X), !defined(X) or is something else.
    enum TrackerState {
      DefinedMacro,        // defined(X)
      NotDefinedMacro,     // !defined(X)
      Unknown              // Something else.
    } State;
    /// TheMacro - When the state is DefinedMacro or NotDefinedMacro, this
    /// indicates the macro that was checked.
    IdentifierInfo *TheMacro;
  };
  
  /// EvaluateDefined - Process a 'defined(sym)' expression.
  static bool EvaluateDefined(PPValue &Result, Token &PeekTok, DefinedTracker &DT,
                              bool ValueLive, Preprocessor &PP) {
    SourceLocation beginLoc(PeekTok.getLocation());
    Result.setBegin(beginLoc);
  
    // Get the next token, don't expand it.
    PP.LexUnexpandedNonComment(PeekTok);
  
    // Two options, it can either be a pp-identifier or a (.
    SourceLocation LParenLoc;
    if (PeekTok.is(tok::l_paren)) {
      // Found a paren, remember we saw it and skip it.
      LParenLoc = PeekTok.getLocation();
      PP.LexUnexpandedNonComment(PeekTok);
    }
  
    if (PeekTok.is(tok::code_completion)) {
      if (PP.getCodeCompletionHandler())
        PP.getCodeCompletionHandler()->CodeCompleteMacroName(false);
      PP.setCodeCompletionReached();
      PP.LexUnexpandedNonComment(PeekTok);
    }
  
    // If we don't have a pp-identifier now, this is an error.
    if (PP.CheckMacroName(PeekTok, MU_Other))
      return true;
  
    // Otherwise, we got an identifier, is it defined to something?
    IdentifierInfo *II = PeekTok.getIdentifierInfo();
    MacroDefinition Macro = PP.getMacroDefinition(II);
    Result.Val = !!Macro;
    Result.Val.setIsUnsigned(false); // Result is signed intmax_t.
  
    // If there is a macro, mark it used.
    if (Result.Val != 0 && ValueLive)
      PP.markMacroAsUsed(Macro.getMacroInfo());
  
    // Save macro token for callback.
    Token macroToken(PeekTok);
  
    // If we are in parens, ensure we have a trailing ).
    if (LParenLoc.isValid()) {
      // Consume identifier.
      Result.setEnd(PeekTok.getLocation());
      PP.LexUnexpandedNonComment(PeekTok);
  
      if (PeekTok.isNot(tok::r_paren)) {
        PP.Diag(PeekTok.getLocation(), diag::err_pp_expected_after)
            << "'defined'" << tok::r_paren;
        PP.Diag(LParenLoc, diag::note_matching) << tok::l_paren;
        return true;
      }
      // Consume the ).
      Result.setEnd(PeekTok.getLocation());
      PP.LexNonComment(PeekTok);
    } else {
      // Consume identifier.
      Result.setEnd(PeekTok.getLocation());
      PP.LexNonComment(PeekTok);
    }
  
    // Invoke the 'defined' callback.
    if (PPCallbacks *Callbacks = PP.getPPCallbacks()) {
      Callbacks->Defined(macroToken, Macro,
                         SourceRange(beginLoc, PeekTok.getLocation()));
    }
  
    // Success, remember that we saw defined(X).
    DT.State = DefinedTracker::DefinedMacro;
    DT.TheMacro = II;
    return false;
  }
  
  /// EvaluateValue - Evaluate the token PeekTok (and any others needed) and
  /// return the computed value in Result.  Return true if there was an error
  /// parsing.  This function also returns information about the form of the
  /// expression in DT.  See above for information on what DT means.
  ///
  /// If ValueLive is false, then this value is being evaluated in a context where
  /// the result is not used.  As such, avoid diagnostics that relate to
  /// evaluation.
  static bool EvaluateValue(PPValue &Result, Token &PeekTok, DefinedTracker &DT,
                            bool ValueLive, Preprocessor &PP) {
    DT.State = DefinedTracker::Unknown;
  
    if (PeekTok.is(tok::code_completion)) {
      if (PP.getCodeCompletionHandler())
        PP.getCodeCompletionHandler()->CodeCompletePreprocessorExpression();
      PP.setCodeCompletionReached();
      PP.LexNonComment(PeekTok);
    }
        
    // If this token's spelling is a pp-identifier, check to see if it is
    // 'defined' or if it is a macro.  Note that we check here because many
    // keywords are pp-identifiers, so we can't check the kind.
    if (IdentifierInfo *II = PeekTok.getIdentifierInfo()) {
      // Handle "defined X" and "defined(X)".
      if (II->isStr("defined"))
        return(EvaluateDefined(Result, PeekTok, DT, ValueLive, PP));
      
      // If this identifier isn't 'defined' or one of the special
      // preprocessor keywords and it wasn't macro expanded, it turns
      // into a simple 0, unless it is the C++ keyword "true", in which case it
      // turns into "1".
      if (ValueLive &&
          II->getTokenID() != tok::kw_true &&
          II->getTokenID() != tok::kw_false)
        PP.Diag(PeekTok, diag::warn_pp_undef_identifier) << II;
      Result.Val = II->getTokenID() == tok::kw_true;
      Result.Val.setIsUnsigned(false);  // "0" is signed intmax_t 0.
      Result.setRange(PeekTok.getLocation());
      PP.LexNonComment(PeekTok);
      return false;
    }
  
    switch (PeekTok.getKind()) {
    default:  // Non-value token.
      PP.Diag(PeekTok, diag::err_pp_expr_bad_token_start_expr);
      return true;
    case tok::eod:
    case tok::r_paren:
      // If there is no expression, report and exit.
      PP.Diag(PeekTok, diag::err_pp_expected_value_in_expr);
      return true;
    case tok::numeric_constant: {
      SmallString<64> IntegerBuffer;
      bool NumberInvalid = false;
      StringRef Spelling = PP.getSpelling(PeekTok, IntegerBuffer, 
                                                &NumberInvalid);
      if (NumberInvalid)
        return true; // a diagnostic was already reported
  
      NumericLiteralParser Literal(Spelling, PeekTok.getLocation(), PP);
      if (Literal.hadError)
        return true; // a diagnostic was already reported.
  
      if (Literal.isFloatingLiteral() || Literal.isImaginary) {
        PP.Diag(PeekTok, diag::err_pp_illegal_floating_literal);
        return true;
      }
      assert(Literal.isIntegerLiteral() && "Unknown ppnumber");
  
      // Complain about, and drop, any ud-suffix.
      if (Literal.hasUDSuffix())
        PP.Diag(PeekTok, diag::err_pp_invalid_udl) << /*integer*/1;
  
      // 'long long' is a C99 or C++11 feature.
      if (!PP.getLangOpts().C99 && Literal.isLongLong) {
        if (PP.getLangOpts().CPlusPlus)
          PP.Diag(PeekTok,
               PP.getLangOpts().CPlusPlus11 ?
               diag::warn_cxx98_compat_longlong : diag::ext_cxx11_longlong);
        else
          PP.Diag(PeekTok, diag::ext_c99_longlong);
      }
  
      // Parse the integer literal into Result.
      if (Literal.GetIntegerValue(Result.Val)) {
        // Overflow parsing integer literal.
        if (ValueLive)
          PP.Diag(PeekTok, diag::err_integer_literal_too_large)
              << /* Unsigned */ 1;
        Result.Val.setIsUnsigned(true);
      } else {
        // Set the signedness of the result to match whether there was a U suffix
        // or not.
        Result.Val.setIsUnsigned(Literal.isUnsigned);
  
        // Detect overflow based on whether the value is signed.  If signed
        // and if the value is too large, emit a warning "integer constant is so
        // large that it is unsigned" e.g. on 12345678901234567890 where intmax_t
        // is 64-bits.
        if (!Literal.isUnsigned && Result.Val.isNegative()) {
          // Octal, hexadecimal, and binary literals are implicitly unsigned if
          // the value does not fit into a signed integer type.
          if (ValueLive && Literal.getRadix() == 10)
            PP.Diag(PeekTok, diag::ext_integer_literal_too_large_for_signed);
          Result.Val.setIsUnsigned(true);
        }
      }
  
      // Consume the token.
      Result.setRange(PeekTok.getLocation());
      PP.LexNonComment(PeekTok);
      return false;
    }
    case tok::char_constant:          // 'x'
    case tok::wide_char_constant:     // L'x'
    case tok::utf8_char_constant:     // u8'x'
    case tok::utf16_char_constant:    // u'x'
    case tok::utf32_char_constant: {  // U'x'
      // Complain about, and drop, any ud-suffix.
      if (PeekTok.hasUDSuffix())
        PP.Diag(PeekTok, diag::err_pp_invalid_udl) << /*character*/0;
  
      SmallString<32> CharBuffer;
      bool CharInvalid = false;
      StringRef ThisTok = PP.getSpelling(PeekTok, CharBuffer, &CharInvalid);
      if (CharInvalid)
        return true;
  
      CharLiteralParser Literal(ThisTok.begin(), ThisTok.end(),
                                PeekTok.getLocation(), PP, PeekTok.getKind());
      if (Literal.hadError())
        return true;  // A diagnostic was already emitted.
  
      // Character literals are always int or wchar_t, expand to intmax_t.
      const TargetInfo &TI = PP.getTargetInfo();
      unsigned NumBits;
      if (Literal.isMultiChar())
        NumBits = TI.getIntWidth();
      else if (Literal.isWide())
        NumBits = TI.getWCharWidth();
      else if (Literal.isUTF16())
        NumBits = TI.getChar16Width();
      else if (Literal.isUTF32())
        NumBits = TI.getChar32Width();
      else
        NumBits = TI.getCharWidth();
  
      // Set the width.
      llvm::APSInt Val(NumBits);
      // Set the value.
      Val = Literal.getValue();
      // Set the signedness. UTF-16 and UTF-32 are always unsigned
      if (Literal.isWide())
        Val.setIsUnsigned(!TargetInfo::isTypeSigned(TI.getWCharType()));
      else if (!Literal.isUTF16() && !Literal.isUTF32())
        Val.setIsUnsigned(!PP.getLangOpts().CharIsSigned);
  
      if (Result.Val.getBitWidth() > Val.getBitWidth()) {
        Result.Val = Val.extend(Result.Val.getBitWidth());
      } else {
        assert(Result.Val.getBitWidth() == Val.getBitWidth() &&
               "intmax_t smaller than char/wchar_t?");
        Result.Val = Val;
      }
  
      // Consume the token.
      Result.setRange(PeekTok.getLocation());
      PP.LexNonComment(PeekTok);
      return false;
    }
    case tok::l_paren: {
      SourceLocation Start = PeekTok.getLocation();
      PP.LexNonComment(PeekTok);  // Eat the (.
      // Parse the value and if there are any binary operators involved, parse
      // them.
      if (EvaluateValue(Result, PeekTok, DT, ValueLive, PP)) return true;
  
      // If this is a silly value like (X), which doesn't need parens, check for
      // !(defined X).
      if (PeekTok.is(tok::r_paren)) {
        // Just use DT unmodified as our result.
      } else {
        // Otherwise, we have something like (x+y), and we consumed '(x'.
        if (EvaluateDirectiveSubExpr(Result, 1, PeekTok, ValueLive, PP))
          return true;
  
        if (PeekTok.isNot(tok::r_paren)) {
          PP.Diag(PeekTok.getLocation(), diag::err_pp_expected_rparen)
            << Result.getRange();
          PP.Diag(Start, diag::note_matching) << tok::l_paren;
          return true;
        }
        DT.State = DefinedTracker::Unknown;
      }
      Result.setRange(Start, PeekTok.getLocation());
      PP.LexNonComment(PeekTok);  // Eat the ).
      return false;
    }
    case tok::plus: {
      SourceLocation Start = PeekTok.getLocation();
      // Unary plus doesn't modify the value.
      PP.LexNonComment(PeekTok);
      if (EvaluateValue(Result, PeekTok, DT, ValueLive, PP)) return true;
      Result.setBegin(Start);
      return false;
    }
    case tok::minus: {
      SourceLocation Loc = PeekTok.getLocation();
      PP.LexNonComment(PeekTok);
      if (EvaluateValue(Result, PeekTok, DT, ValueLive, PP)) return true;
      Result.setBegin(Loc);
  
      // C99 6.5.3.3p3: The sign of the result matches the sign of the operand.
      Result.Val = -Result.Val;
  
      // -MININT is the only thing that overflows.  Unsigned never overflows.
      bool Overflow = !Result.isUnsigned() && Result.Val.isMinSignedValue();
  
      // If this operator is live and overflowed, report the issue.
      if (Overflow && ValueLive)
        PP.Diag(Loc, diag::warn_pp_expr_overflow) << Result.getRange();
  
      DT.State = DefinedTracker::Unknown;
      return false;
    }
  
    case tok::tilde: {
      SourceLocation Start = PeekTok.getLocation();
      PP.LexNonComment(PeekTok);
      if (EvaluateValue(Result, PeekTok, DT, ValueLive, PP)) return true;
      Result.setBegin(Start);
  
      // C99 6.5.3.3p4: The sign of the result matches the sign of the operand.
      Result.Val = ~Result.Val;
      DT.State = DefinedTracker::Unknown;
      return false;
    }
  
    case tok::exclaim: {
      SourceLocation Start = PeekTok.getLocation();
      PP.LexNonComment(PeekTok);
      if (EvaluateValue(Result, PeekTok, DT, ValueLive, PP)) return true;
      Result.setBegin(Start);
      Result.Val = !Result.Val;
      // C99 6.5.3.3p5: The sign of the result is 'int', aka it is signed.
      Result.Val.setIsUnsigned(false);
  
      if (DT.State == DefinedTracker::DefinedMacro)
        DT.State = DefinedTracker::NotDefinedMacro;
      else if (DT.State == DefinedTracker::NotDefinedMacro)
        DT.State = DefinedTracker::DefinedMacro;
      return false;
    }
  
    // FIXME: Handle #assert
    }
  }
  
  
  
  /// getPrecedence - Return the precedence of the specified binary operator
  /// token.  This returns:
  ///   ~0 - Invalid token.
  ///   14 -> 3 - various operators.
  ///    0 - 'eod' or ')'
  static unsigned getPrecedence(tok::TokenKind Kind) {
    switch (Kind) {
    default: return ~0U;
    case tok::percent:
    case tok::slash:
    case tok::star:                 return 14;
    case tok::plus:
    case tok::minus:                return 13;
    case tok::lessless:
    case tok::greatergreater:       return 12;
    case tok::lessequal:
    case tok::less:
    case tok::greaterequal:
    case tok::greater:              return 11;
    case tok::exclaimequal:
    case tok::equalequal:           return 10;
    case tok::amp:                  return 9;
    case tok::caret:                return 8;
    case tok::pipe:                 return 7;
    case tok::ampamp:               return 6;
    case tok::pipepipe:             return 5;
    case tok::question:             return 4;
    case tok::comma:                return 3;
    case tok::colon:                return 2;
    case tok::r_paren:              return 0;// Lowest priority, end of expr.
    case tok::eod:                  return 0;// Lowest priority, end of directive.
    }
  }
  
  
  /// EvaluateDirectiveSubExpr - Evaluate the subexpression whose first token is
  /// PeekTok, and whose precedence is PeekPrec.  This returns the result in LHS.
  ///
  /// If ValueLive is false, then this value is being evaluated in a context where
  /// the result is not used.  As such, avoid diagnostics that relate to
  /// evaluation, such as division by zero warnings.
  static bool EvaluateDirectiveSubExpr(PPValue &LHS, unsigned MinPrec,
                                       Token &PeekTok, bool ValueLive,
                                       Preprocessor &PP) {
    unsigned PeekPrec = getPrecedence(PeekTok.getKind());
    // If this token isn't valid, report the error.
    if (PeekPrec == ~0U) {
      PP.Diag(PeekTok.getLocation(), diag::err_pp_expr_bad_token_binop)
        << LHS.getRange();
      return true;
    }
  
    while (1) {
      // If this token has a lower precedence than we are allowed to parse, return
      // it so that higher levels of the recursion can parse it.
      if (PeekPrec < MinPrec)
        return false;
  
      tok::TokenKind Operator = PeekTok.getKind();
  
      // If this is a short-circuiting operator, see if the RHS of the operator is
      // dead.  Note that this cannot just clobber ValueLive.  Consider
      // "0 && 1 ? 4 : 1 / 0", which is parsed as "(0 && 1) ? 4 : (1 / 0)".  In
      // this example, the RHS of the && being dead does not make the rest of the
      // expr dead.
      bool RHSIsLive;
      if (Operator == tok::ampamp && LHS.Val == 0)
        RHSIsLive = false;   // RHS of "0 && x" is dead.
      else if (Operator == tok::pipepipe && LHS.Val != 0)
        RHSIsLive = false;   // RHS of "1 || x" is dead.
      else if (Operator == tok::question && LHS.Val == 0)
        RHSIsLive = false;   // RHS (x) of "0 ? x : y" is dead.
      else
        RHSIsLive = ValueLive;
  
      // Consume the operator, remembering the operator's location for reporting.
      SourceLocation OpLoc = PeekTok.getLocation();
      PP.LexNonComment(PeekTok);
  
      PPValue RHS(LHS.getBitWidth());
      // Parse the RHS of the operator.
      DefinedTracker DT;
      if (EvaluateValue(RHS, PeekTok, DT, RHSIsLive, PP)) return true;
  
      // Remember the precedence of this operator and get the precedence of the
      // operator immediately to the right of the RHS.
      unsigned ThisPrec = PeekPrec;
      PeekPrec = getPrecedence(PeekTok.getKind());
  
      // If this token isn't valid, report the error.
      if (PeekPrec == ~0U) {
        PP.Diag(PeekTok.getLocation(), diag::err_pp_expr_bad_token_binop)
          << RHS.getRange();
        return true;
      }
  
      // Decide whether to include the next binop in this subexpression.  For
      // example, when parsing x+y*z and looking at '*', we want to recursively
      // handle y*z as a single subexpression.  We do this because the precedence
      // of * is higher than that of +.  The only strange case we have to handle
      // here is for the ?: operator, where the precedence is actually lower than
      // the LHS of the '?'.  The grammar rule is:
      //
      // conditional-expression ::=
      //    logical-OR-expression ? expression : conditional-expression
      // where 'expression' is actually comma-expression.
      unsigned RHSPrec;
      if (Operator == tok::question)
        // The RHS of "?" should be maximally consumed as an expression.
        RHSPrec = getPrecedence(tok::comma);
      else  // All others should munch while higher precedence.
        RHSPrec = ThisPrec+1;
  
      if (PeekPrec >= RHSPrec) {
        if (EvaluateDirectiveSubExpr(RHS, RHSPrec, PeekTok, RHSIsLive, PP))
          return true;
        PeekPrec = getPrecedence(PeekTok.getKind());
      }
      assert(PeekPrec <= ThisPrec && "Recursion didn't work!");
  
      // Usual arithmetic conversions (C99 6.3.1.8p1): result is unsigned if
      // either operand is unsigned.
      llvm::APSInt Res(LHS.getBitWidth());
      switch (Operator) {
      case tok::question:       // No UAC for x and y in "x ? y : z".
      case tok::lessless:       // Shift amount doesn't UAC with shift value.
      case tok::greatergreater: // Shift amount doesn't UAC with shift value.
      case tok::comma:          // Comma operands are not subject to UACs.
      case tok::pipepipe:       // Logical || does not do UACs.
      case tok::ampamp:         // Logical && does not do UACs.
        break;                  // No UAC
      default:
        Res.setIsUnsigned(LHS.isUnsigned()|RHS.isUnsigned());
        // If this just promoted something from signed to unsigned, and if the
        // value was negative, warn about it.
        if (ValueLive && Res.isUnsigned()) {
          if (!LHS.isUnsigned() && LHS.Val.isNegative())
            PP.Diag(OpLoc, diag::warn_pp_convert_lhs_to_positive)
              << LHS.Val.toString(10, true) + " to " +
                 LHS.Val.toString(10, false)
              << LHS.getRange() << RHS.getRange();
          if (!RHS.isUnsigned() && RHS.Val.isNegative())
            PP.Diag(OpLoc, diag::warn_pp_convert_rhs_to_positive)
              << RHS.Val.toString(10, true) + " to " +
                 RHS.Val.toString(10, false)
              << LHS.getRange() << RHS.getRange();
        }
        LHS.Val.setIsUnsigned(Res.isUnsigned());
        RHS.Val.setIsUnsigned(Res.isUnsigned());
      }
  
      bool Overflow = false;
      switch (Operator) {
      default: llvm_unreachable("Unknown operator token!");
      case tok::percent:
        if (RHS.Val != 0)
          Res = LHS.Val % RHS.Val;
        else if (ValueLive) {
          PP.Diag(OpLoc, diag::err_pp_remainder_by_zero)
            << LHS.getRange() << RHS.getRange();
          return true;
        }
        break;
      case tok::slash:
        if (RHS.Val != 0) {
          if (LHS.Val.isSigned())
            Res = llvm::APSInt(LHS.Val.sdiv_ov(RHS.Val, Overflow), false);
          else
            Res = LHS.Val / RHS.Val;
        } else if (ValueLive) {
          PP.Diag(OpLoc, diag::err_pp_division_by_zero)
            << LHS.getRange() << RHS.getRange();
          return true;
        }
        break;
  
      case tok::star:
        if (Res.isSigned())
          Res = llvm::APSInt(LHS.Val.smul_ov(RHS.Val, Overflow), false);
        else
          Res = LHS.Val * RHS.Val;
        break;
      case tok::lessless: {
        // Determine whether overflow is about to happen.
        if (LHS.isUnsigned())
          Res = LHS.Val.ushl_ov(RHS.Val, Overflow);
        else
          Res = llvm::APSInt(LHS.Val.sshl_ov(RHS.Val, Overflow), false);
        break;
      }
      case tok::greatergreater: {
        // Determine whether overflow is about to happen.
        unsigned ShAmt = static_cast<unsigned>(RHS.Val.getLimitedValue());
        if (ShAmt >= LHS.getBitWidth())
          Overflow = true, ShAmt = LHS.getBitWidth()-1;
        Res = LHS.Val >> ShAmt;
        break;
      }
      case tok::plus:
        if (LHS.isUnsigned())
          Res = LHS.Val + RHS.Val;
        else
          Res = llvm::APSInt(LHS.Val.sadd_ov(RHS.Val, Overflow), false);
        break;
      case tok::minus:
        if (LHS.isUnsigned())
          Res = LHS.Val - RHS.Val;
        else
          Res = llvm::APSInt(LHS.Val.ssub_ov(RHS.Val, Overflow), false);
        break;
      case tok::lessequal:
        Res = LHS.Val <= RHS.Val;
        Res.setIsUnsigned(false);  // C99 6.5.8p6, result is always int (signed)
        break;
      case tok::less:
        Res = LHS.Val < RHS.Val;
        Res.setIsUnsigned(false);  // C99 6.5.8p6, result is always int (signed)
        break;
      case tok::greaterequal:
        Res = LHS.Val >= RHS.Val;
        Res.setIsUnsigned(false);  // C99 6.5.8p6, result is always int (signed)
        break;
      case tok::greater:
        Res = LHS.Val > RHS.Val;
        Res.setIsUnsigned(false);  // C99 6.5.8p6, result is always int (signed)
        break;
      case tok::exclaimequal:
        Res = LHS.Val != RHS.Val;
        Res.setIsUnsigned(false);  // C99 6.5.9p3, result is always int (signed)
        break;
      case tok::equalequal:
        Res = LHS.Val == RHS.Val;
        Res.setIsUnsigned(false);  // C99 6.5.9p3, result is always int (signed)
        break;
      case tok::amp:
        Res = LHS.Val & RHS.Val;
        break;
      case tok::caret:
        Res = LHS.Val ^ RHS.Val;
        break;
      case tok::pipe:
        Res = LHS.Val | RHS.Val;
        break;
      case tok::ampamp:
        Res = (LHS.Val != 0 && RHS.Val != 0);
        Res.setIsUnsigned(false);  // C99 6.5.13p3, result is always int (signed)
        break;
      case tok::pipepipe:
        Res = (LHS.Val != 0 || RHS.Val != 0);
        Res.setIsUnsigned(false);  // C99 6.5.14p3, result is always int (signed)
        break;
      case tok::comma:
        // Comma is invalid in pp expressions in c89/c++ mode, but is valid in C99
        // if not being evaluated.
        if (!PP.getLangOpts().C99 || ValueLive)
          PP.Diag(OpLoc, diag::ext_pp_comma_expr)
            << LHS.getRange() << RHS.getRange();
        Res = RHS.Val; // LHS = LHS,RHS -> RHS.
        break;
      case tok::question: {
        // Parse the : part of the expression.
        if (PeekTok.isNot(tok::colon)) {
          PP.Diag(PeekTok.getLocation(), diag::err_expected)
              << tok::colon << LHS.getRange() << RHS.getRange();
          PP.Diag(OpLoc, diag::note_matching) << tok::question;
          return true;
        }
        // Consume the :.
        PP.LexNonComment(PeekTok);
  
        // Evaluate the value after the :.
        bool AfterColonLive = ValueLive && LHS.Val == 0;
        PPValue AfterColonVal(LHS.getBitWidth());
        DefinedTracker DT;
        if (EvaluateValue(AfterColonVal, PeekTok, DT, AfterColonLive, PP))
          return true;
  
        // Parse anything after the : with the same precedence as ?.  We allow
        // things of equal precedence because ?: is right associative.
        if (EvaluateDirectiveSubExpr(AfterColonVal, ThisPrec,
                                     PeekTok, AfterColonLive, PP))
          return true;
  
        // Now that we have the condition, the LHS and the RHS of the :, evaluate.
        Res = LHS.Val != 0 ? RHS.Val : AfterColonVal.Val;
        RHS.setEnd(AfterColonVal.getRange().getEnd());
  
        // Usual arithmetic conversions (C99 6.3.1.8p1): result is unsigned if
        // either operand is unsigned.
        Res.setIsUnsigned(RHS.isUnsigned() | AfterColonVal.isUnsigned());
  
        // Figure out the precedence of the token after the : part.
        PeekPrec = getPrecedence(PeekTok.getKind());
        break;
      }
      case tok::colon:
        // Don't allow :'s to float around without being part of ?: exprs.
        PP.Diag(OpLoc, diag::err_pp_colon_without_question)
          << LHS.getRange() << RHS.getRange();
        return true;
      }
  
      // If this operator is live and overflowed, report the issue.
      if (Overflow && ValueLive)
        PP.Diag(OpLoc, diag::warn_pp_expr_overflow)
          << LHS.getRange() << RHS.getRange();
  
      // Put the result back into 'LHS' for our next iteration.
      LHS.Val = Res;
      LHS.setEnd(RHS.getRange().getEnd());
    }
  }
  
  /// EvaluateDirectiveExpression - Evaluate an integer constant expression that
  /// may occur after a #if or #elif directive.  If the expression is equivalent
  /// to "!defined(X)" return X in IfNDefMacro.
  bool Preprocessor::EvaluateDirectiveExpression(IdentifierInfo *&IfNDefMacro) {
    SaveAndRestore<bool> PPDir(ParsingIfOrElifDirective, true);
    // Save the current state of 'DisableMacroExpansion' and reset it to false. If
    // 'DisableMacroExpansion' is true, then we must be in a macro argument list
    // in which case a directive is undefined behavior.  We want macros to be able
    // to recursively expand in order to get more gcc-list behavior, so we force
    // DisableMacroExpansion to false and restore it when we're done parsing the
    // expression.
    bool DisableMacroExpansionAtStartOfDirective = DisableMacroExpansion;
    DisableMacroExpansion = false;
    
    // Peek ahead one token.
    Token Tok;
    LexNonComment(Tok);
    
    // C99 6.10.1p3 - All expressions are evaluated as intmax_t or uintmax_t.
    unsigned BitWidth = getTargetInfo().getIntMaxTWidth();
  
    PPValue ResVal(BitWidth);
    DefinedTracker DT;
    if (EvaluateValue(ResVal, Tok, DT, true, *this)) {
      // Parse error, skip the rest of the macro line.
      if (Tok.isNot(tok::eod))
        DiscardUntilEndOfDirective();
      
      // Restore 'DisableMacroExpansion'.
      DisableMacroExpansion = DisableMacroExpansionAtStartOfDirective;
      return false;
    }
  
    // If we are at the end of the expression after just parsing a value, there
    // must be no (unparenthesized) binary operators involved, so we can exit
    // directly.
    if (Tok.is(tok::eod)) {
      // If the expression we parsed was of the form !defined(macro), return the
      // macro in IfNDefMacro.
      if (DT.State == DefinedTracker::NotDefinedMacro)
        IfNDefMacro = DT.TheMacro;
  
      // Restore 'DisableMacroExpansion'.
      DisableMacroExpansion = DisableMacroExpansionAtStartOfDirective;
      return ResVal.Val != 0;
    }
  
    // Otherwise, we must have a binary operator (e.g. "#if 1 < 2"), so parse the
    // operator and the stuff after it.
    if (EvaluateDirectiveSubExpr(ResVal, getPrecedence(tok::question),
                                 Tok, true, *this)) {
      // Parse error, skip the rest of the macro line.
      if (Tok.isNot(tok::eod))
        DiscardUntilEndOfDirective();
      
      // Restore 'DisableMacroExpansion'.
      DisableMacroExpansion = DisableMacroExpansionAtStartOfDirective;
      return false;
    }
  
    // If we aren't at the tok::eod token, something bad happened, like an extra
    // ')' token.
    if (Tok.isNot(tok::eod)) {
      Diag(Tok, diag::err_pp_expected_eol);
      DiscardUntilEndOfDirective();
    }
  
    // Restore 'DisableMacroExpansion'.
    DisableMacroExpansion = DisableMacroExpansionAtStartOfDirective;
    return ResVal.Val != 0;
  }
  