C++ Sema::UnwrapSimilarPointerTypes方法代码示例

/// CastsAwayConstness - Check if the pointer conversion from SrcType to
/// DestType casts away constness as defined in C++ 5.2.11p8ff. This is used by
/// the cast checkers.  Both arguments must denote pointer (possibly to member)
/// types.
bool
CastsAwayConstness(Sema &Self, QualType SrcType, QualType DestType)
{
  // Casting away constness is defined in C++ 5.2.11p8 with reference to
  // C++ 4.4. We piggyback on Sema::IsQualificationConversion for this, since
  // the rules are non-trivial. So first we construct Tcv *...cv* as described
  // in C++ 5.2.11p8.
  assert((SrcType->isPointerType() || SrcType->isMemberPointerType()) &&
         "Source type is not pointer or pointer to member.");
  assert((DestType->isPointerType() || DestType->isMemberPointerType()) &&
         "Destination type is not pointer or pointer to member.");

  QualType UnwrappedSrcType = SrcType, UnwrappedDestType = DestType;
  llvm::SmallVector<unsigned, 8> cv1, cv2;

  // Find the qualifications.
  while (Self.UnwrapSimilarPointerTypes(UnwrappedSrcType, UnwrappedDestType)) {
    cv1.push_back(UnwrappedSrcType.getCVRQualifiers());
    cv2.push_back(UnwrappedDestType.getCVRQualifiers());
  }
  assert(cv1.size() > 0 && "Must have at least one pointer level.");

  // Construct void pointers with those qualifiers (in reverse order of
  // unwrapping, of course).
  QualType SrcConstruct = Self.Context.VoidTy;
  QualType DestConstruct = Self.Context.VoidTy;
  for (llvm::SmallVector<unsigned, 8>::reverse_iterator i1 = cv1.rbegin(),
                                                        i2 = cv2.rbegin();
       i1 != cv1.rend(); ++i1, ++i2)
  {
    SrcConstruct = Self.Context.getPointerType(
      SrcConstruct.getQualifiedType(*i1));
    DestConstruct = Self.Context.getPointerType(
      DestConstruct.getQualifiedType(*i2));
  }

  // Test if they're compatible.
  return SrcConstruct != DestConstruct &&
    !Self.IsQualificationConversion(SrcConstruct, DestConstruct);
}

/// CheckConstCast - Check that a const_cast\<DestType\>(SrcExpr) is valid.
/// Refer to C++ 5.2.11 for details. const_cast is typically used in code
/// like this:
/// const char *str = "literal";
/// legacy_function(const_cast\<char*\>(str));
void
CheckConstCast(Sema &Self, Expr *&SrcExpr, QualType DestType,
               const SourceRange &OpRange, const SourceRange &DestRange)
{
  QualType OrigDestType = DestType, OrigSrcType = SrcExpr->getType();

  DestType = Self.Context.getCanonicalType(DestType);
  QualType SrcType = SrcExpr->getType();
  if (const LValueReferenceType *DestTypeTmp =
        DestType->getAsLValueReferenceType()) {
    if (SrcExpr->isLvalue(Self.Context) != Expr::LV_Valid) {
      // Cannot cast non-lvalue to lvalue reference type.
      Self.Diag(OpRange.getBegin(), diag::err_bad_cxx_cast_rvalue)
        << "const_cast" << OrigDestType << SrcExpr->getSourceRange();
      return;
    }

    // C++ 5.2.11p4: An lvalue of type T1 can be [cast] to an lvalue of type T2
    //   [...] if a pointer to T1 can be [cast] to the type pointer to T2.
    DestType = Self.Context.getPointerType(DestTypeTmp->getPointeeType());
    SrcType = Self.Context.getPointerType(SrcType);
  } else {
    // C++ 5.2.11p1: Otherwise, the result is an rvalue and the
    //   lvalue-to-rvalue, array-to-pointer, and function-to-pointer standard
    //   conversions are performed on the expression.
    Self.DefaultFunctionArrayConversion(SrcExpr);
    SrcType = SrcExpr->getType();
  }

  // C++ 5.2.11p5: For a const_cast involving pointers to data members [...]
  //   the rules for const_cast are the same as those used for pointers.

  if (!DestType->isPointerType() && !DestType->isMemberPointerType()) {
    // Cannot cast to non-pointer, non-reference type. Note that, if DestType
    // was a reference type, we converted it to a pointer above.
    // The status of rvalue references isn't entirely clear, but it looks like
    // conversion to them is simply invalid.
    // C++ 5.2.11p3: For two pointer types [...]
    Self.Diag(OpRange.getBegin(), diag::err_bad_const_cast_dest)
      << OrigDestType << DestRange;
    return;
  }
  if (DestType->isFunctionPointerType() ||
      DestType->isMemberFunctionPointerType()) {
    // Cannot cast direct function pointers.
    // C++ 5.2.11p2: [...] where T is any object type or the void type [...]
    // T is the ultimate pointee of source and target type.
    Self.Diag(OpRange.getBegin(), diag::err_bad_const_cast_dest)
      << OrigDestType << DestRange;
    return;
  }
  SrcType = Self.Context.getCanonicalType(SrcType);

  // Unwrap the pointers. Ignore qualifiers. Terminate early if the types are
  // completely equal.
  // FIXME: const_cast should probably not be able to convert between pointers
  // to different address spaces.
  // C++ 5.2.11p3 describes the core semantics of const_cast. All cv specifiers
  // in multi-level pointers may change, but the level count must be the same,
  // as must be the final pointee type.
  while (SrcType != DestType &&
         Self.UnwrapSimilarPointerTypes(SrcType, DestType)) {
    SrcType = SrcType.getUnqualifiedType();
    DestType = DestType.getUnqualifiedType();
  }

  // Doug Gregor said to disallow this until users complain.
#if 0
  // If we end up with constant arrays of equal size, unwrap those too. A cast
  // from const int [N] to int (&)[N] is invalid by my reading of the
  // standard, but g++ accepts it even with -ansi -pedantic.
  // No more than one level, though, so don't embed this in the unwrap loop
  // above.
  const ConstantArrayType *SrcTypeArr, *DestTypeArr;
  if ((SrcTypeArr = Self.Context.getAsConstantArrayType(SrcType)) &&
     (DestTypeArr = Self.Context.getAsConstantArrayType(DestType)))
  {
    if (SrcTypeArr->getSize() != DestTypeArr->getSize()) {
      // Different array sizes.
      Self.Diag(OpRange.getBegin(), diag::err_bad_cxx_cast_generic)
        << "const_cast" << OrigDestType << OrigSrcType << OpRange;
      return;
    }
    SrcType = SrcTypeArr->getElementType().getUnqualifiedType();
    DestType = DestTypeArr->getElementType().getUnqualifiedType();
  }
#endif

  // Since we're dealing in canonical types, the remainder must be the same.
  if (SrcType != DestType) {
    // Cast between unrelated types.
    Self.Diag(OpRange.getBegin(), diag::err_bad_cxx_cast_generic)
      << "const_cast" << OrigDestType << OrigSrcType << OpRange;
    return;
  }
//.........这里部分代码省略.........

/// TryConstCast - See if a const_cast from source to destination is allowed,
/// and perform it if it is.
static TryCastResult TryConstCast(Sema &Self, Expr *SrcExpr, QualType DestType,
                                  bool CStyle, unsigned &msg) {
  DestType = Self.Context.getCanonicalType(DestType);
  QualType SrcType = SrcExpr->getType();
  if (const LValueReferenceType *DestTypeTmp =
        DestType->getAs<LValueReferenceType>()) {
    if (SrcExpr->isLvalue(Self.Context) != Expr::LV_Valid) {
      // Cannot const_cast non-lvalue to lvalue reference type. But if this
      // is C-style, static_cast might find a way, so we simply suggest a
      // message and tell the parent to keep searching.
      msg = diag::err_bad_cxx_cast_rvalue;
      return TC_NotApplicable;
    }

    // C++ 5.2.11p4: An lvalue of type T1 can be [cast] to an lvalue of type T2
    //   [...] if a pointer to T1 can be [cast] to the type pointer to T2.
    DestType = Self.Context.getPointerType(DestTypeTmp->getPointeeType());
    SrcType = Self.Context.getPointerType(SrcType);
  }

  // C++ 5.2.11p5: For a const_cast involving pointers to data members [...]
  //   the rules for const_cast are the same as those used for pointers.

  if (!DestType->isPointerType() && !DestType->isMemberPointerType()) {
    // Cannot cast to non-pointer, non-reference type. Note that, if DestType
    // was a reference type, we converted it to a pointer above.
    // The status of rvalue references isn't entirely clear, but it looks like
    // conversion to them is simply invalid.
    // C++ 5.2.11p3: For two pointer types [...]
    if (!CStyle)
      msg = diag::err_bad_const_cast_dest;
    return TC_NotApplicable;
  }
  if (DestType->isFunctionPointerType() ||
      DestType->isMemberFunctionPointerType()) {
    // Cannot cast direct function pointers.
    // C++ 5.2.11p2: [...] where T is any object type or the void type [...]
    // T is the ultimate pointee of source and target type.
    if (!CStyle)
      msg = diag::err_bad_const_cast_dest;
    return TC_NotApplicable;
  }
  SrcType = Self.Context.getCanonicalType(SrcType);

  // Unwrap the pointers. Ignore qualifiers. Terminate early if the types are
  // completely equal.
  // FIXME: const_cast should probably not be able to convert between pointers
  // to different address spaces.
  // C++ 5.2.11p3 describes the core semantics of const_cast. All cv specifiers
  // in multi-level pointers may change, but the level count must be the same,
  // as must be the final pointee type.
  while (SrcType != DestType &&
         Self.UnwrapSimilarPointerTypes(SrcType, DestType)) {
    SrcType = SrcType.getUnqualifiedType();
    DestType = DestType.getUnqualifiedType();
  }

  // Since we're dealing in canonical types, the remainder must be the same.
  if (SrcType != DestType)
    return TC_NotApplicable;

  return TC_Success;
}