Preliminary support for function overloading

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@57909 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 903 insertions, 0 deletions

diff --git a/lib/Sema/SemaOverload.cpp b/lib/Sema/SemaOverload.cpp
new file mode 100644
index 0000000000..88c209b6e0
--- /dev/null
+++ b/lib/Sema/SemaOverload.cpp
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+//===--- SemaOverload.cpp - C++ Overloading ---------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides Sema routines for C++ overloading.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Sema.h"
+#include "clang/Basic/Diagnostic.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Expr.h"
+#include "llvm/Support/Compiler.h"
+#include <algorithm>
+
+namespace clang {
+
+/// GetConversionCategory - Retrieve the implicit conversion
+/// category corresponding to the given implicit conversion kind.
+ImplicitConversionCategory 
+GetConversionCategory(ImplicitConversionKind Kind) {
+  static const ImplicitConversionCategory
+    Category[(int)ICK_Num_Conversion_Kinds] = {
+    ICC_Identity,
+    ICC_Lvalue_Transformation,
+    ICC_Lvalue_Transformation,
+    ICC_Lvalue_Transformation,
+    ICC_Qualification_Adjustment,
+    ICC_Promotion,
+    ICC_Promotion,
+    ICC_Conversion,
+    ICC_Conversion,
+    ICC_Conversion,
+    ICC_Conversion,
+    ICC_Conversion,
+    ICC_Conversion
+  };
+  return Category[(int)Kind];
+}
+
+/// GetConversionRank - Retrieve the implicit conversion rank
+/// corresponding to the given implicit conversion kind.
+ImplicitConversionRank GetConversionRank(ImplicitConversionKind Kind) {
+  static const ImplicitConversionRank
+    Rank[(int)ICK_Num_Conversion_Kinds] = {
+    ICR_Exact_Match,
+    ICR_Exact_Match,
+    ICR_Exact_Match,
+    ICR_Exact_Match,
+    ICR_Exact_Match,
+    ICR_Promotion,
+    ICR_Promotion,
+    ICR_Conversion,
+    ICR_Conversion,
+    ICR_Conversion,
+    ICR_Conversion,
+    ICR_Conversion,
+    ICR_Conversion
+  };
+  return Rank[(int)Kind];
+}
+
+/// GetImplicitConversionName - Return the name of this kind of
+/// implicit conversion.
+const char* GetImplicitConversionName(ImplicitConversionKind Kind) {
+  static const char* Name[(int)ICK_Num_Conversion_Kinds] = {
+    "No conversion",
+    "Lvalue-to-rvalue",
+    "Array-to-pointer",
+    "Function-to-pointer",
+    "Qualification",
+    "Integral promotion",
+    "Floating point promotion",
+    "Integral conversion",
+    "Floating conversion",
+    "Floating-integral conversion",
+    "Pointer conversion",
+    "Pointer-to-member conversion",
+    "Boolean conversion"
+  };
+  return Name[Kind];
+}
+
+/// getRank - Retrieve the rank of this standard conversion sequence
+/// (C++ 13.3.3.1.1p3). The rank is the largest rank of each of the
+/// implicit conversions.
+ImplicitConversionRank StandardConversionSequence::getRank() const {
+  ImplicitConversionRank Rank = ICR_Exact_Match;
+  if  (GetConversionRank(First) > Rank)
+    Rank = GetConversionRank(First);
+  if  (GetConversionRank(Second) > Rank)
+    Rank = GetConversionRank(Second);
+  if  (GetConversionRank(Third) > Rank)
+    Rank = GetConversionRank(Third);
+  return Rank;
+}
+
+/// isPointerConversionToBool - Determines whether this conversion is
+/// a conversion of a pointer or pointer-to-member to bool. This is
+/// used as part of the ranking of standard conversion sequences 
+/// (C++ 13.3.3.2p4).
+bool StandardConversionSequence::isPointerConversionToBool() const
+{
+  QualType FromType = QualType::getFromOpaquePtr(FromTypePtr);
+  QualType ToType = QualType::getFromOpaquePtr(ToTypePtr);
+
+  // Note that FromType has not necessarily been transformed by the
+  // array-to-pointer or function-to-pointer implicit conversions, so
+  // check for their presence as well as checking whether FromType is
+  // a pointer.
+  if (ToType->isBooleanType() &&
+      (FromType->isPointerType() ||
+       First == ICK_Array_To_Pointer || First == ICK_Function_To_Pointer))
+    return true;
+
+  return false;
+}
+
+/// DebugPrint - Print this standard conversion sequence to standard
+/// error. Useful for debugging overloading issues.
+void StandardConversionSequence::DebugPrint() const {
+  bool PrintedSomething = false;
+  if (First != ICK_Identity) {
+    fprintf(stderr, "%s", GetImplicitConversionName(First));
+    PrintedSomething = true;
+  }
+
+  if (Second != ICK_Identity) {
+    if (PrintedSomething) {
+      fprintf(stderr, " -> ");
+    }
+    fprintf(stderr, "%s", GetImplicitConversionName(Second));
+    PrintedSomething = true;
+  }
+
+  if (Third != ICK_Identity) {
+    if (PrintedSomething) {
+      fprintf(stderr, " -> ");
+    }
+    fprintf(stderr, "%s", GetImplicitConversionName(Third));
+    PrintedSomething = true;
+  }
+
+  if (!PrintedSomething) {
+    fprintf(stderr, "No conversions required");
+  }
+}
+
+/// DebugPrint - Print this user-defined conversion sequence to standard
+/// error. Useful for debugging overloading issues.
+void UserDefinedConversionSequence::DebugPrint() const {
+  if (Before.First || Before.Second || Before.Third) {
+    Before.DebugPrint();
+    fprintf(stderr, " -> ");
+  }
+  fprintf(stderr, "'%s'", ConversionFunction->getName());
+  if (After.First || After.Second || After.Third) {
+    fprintf(stderr, " -> ");
+    After.DebugPrint();
+  }
+}
+
+/// DebugPrint - Print this implicit conversion sequence to standard
+/// error. Useful for debugging overloading issues.
+void ImplicitConversionSequence::DebugPrint() const {
+  switch (ConversionKind) {
+  case StandardConversion:
+    fprintf(stderr, "Standard conversion: ");
+    Standard.DebugPrint();
+    break;
+  case UserDefinedConversion:
+    fprintf(stderr, "User-defined conversion: ");
+    UserDefined.DebugPrint();
+    break;
+  case EllipsisConversion:
+    fprintf(stderr, "Ellipsis conversion");
+    break;
+  case BadConversion:
+    fprintf(stderr, "Bad conversion");
+    break;
+  }
+
+  fprintf(stderr, "\n");
+}
+
+// IsOverload - Determine whether the given New declaration is an
+// overload of the Old declaration. This routine returns false if New
+// and Old cannot be overloaded, e.g., if they are functions with the
+// same signature (C++ 1.3.10) or if the Old declaration isn't a
+// function (or overload set). When it does return false and Old is an
+// OverloadedFunctionDecl, MatchedDecl will be set to point to the
+// FunctionDecl that New cannot be overloaded with. 
+//
+// Example: Given the following input:
+//
+//   void f(int, float); // #1
+//   void f(int, int); // #2
+//   int f(int, int); // #3
+//
+// When we process #1, there is no previous declaration of "f",
+// so IsOverload will not be used. 
+//
+// When we process #2, Old is a FunctionDecl for #1.  By comparing the
+// parameter types, we see that #1 and #2 are overloaded (since they
+// have different signatures), so this routine returns false;
+// MatchedDecl is unchanged.
+//
+// When we process #3, Old is an OverloadedFunctionDecl containing #1
+// and #2. We compare the signatures of #3 to #1 (they're overloaded,
+// so we do nothing) and then #3 to #2. Since the signatures of #3 and
+// #2 are identical (return types of functions are not part of the
+// signature), IsOverload returns false and MatchedDecl will be set to
+// point to the FunctionDecl for #2.
+bool
+Sema::IsOverload(FunctionDecl *New, Decl* OldD, 
+                 OverloadedFunctionDecl::function_iterator& MatchedDecl)
+{
+  if (OverloadedFunctionDecl* Ovl = dyn_cast<OverloadedFunctionDecl>(OldD)) {
+    // Is this new function an overload of every function in the
+    // overload set?
+    OverloadedFunctionDecl::function_iterator Func = Ovl->function_begin(),
+                                           FuncEnd = Ovl->function_end();
+    for (; Func != FuncEnd; ++Func) {
+      if (!IsOverload(New, *Func, MatchedDecl)) {
+        MatchedDecl = Func;
+        return false;
+      }
+    }
+
+    // This function overloads every function in the overload set.
+    return true;
+  } else if (FunctionDecl* Old = dyn_cast<FunctionDecl>(OldD)) {
+    // Is the function New an overload of the function Old?
+    QualType OldQType = Context.getCanonicalType(Old->getType());
+    QualType NewQType = Context.getCanonicalType(New->getType());
+
+    // Compare the signatures (C++ 1.3.10) of the two functions to
+    // determine whether they are overloads. If we find any mismatch
+    // in the signature, they are overloads.
+
+    // If either of these functions is a K&R-style function (no
+    // prototype), then we consider them to have matching signatures.
+    if (isa<FunctionTypeNoProto>(OldQType.getTypePtr()) ||
+        isa<FunctionTypeNoProto>(NewQType.getTypePtr()))
+      return false;
+
+    FunctionTypeProto* OldType = cast<FunctionTypeProto>(OldQType.getTypePtr());
+    FunctionTypeProto* NewType = cast<FunctionTypeProto>(NewQType.getTypePtr());
+
+    // The signature of a function includes the types of its
+    // parameters (C++ 1.3.10), which includes the presence or absence
+    // of the ellipsis; see C++ DR 357).
+    if (OldQType != NewQType &&
+        (OldType->getNumArgs() != NewType->getNumArgs() ||
+         OldType->isVariadic() != NewType->isVariadic() ||
+         !std::equal(OldType->arg_type_begin(), OldType->arg_type_end(),
+                     NewType->arg_type_begin())))
+      return true;
+
+    // If the function is a class member, its signature includes the
+    // cv-qualifiers (if any) on the function itself.
+    //
+    // As part of this, also check whether one of the member functions
+    // is static, in which case they are not overloads (C++
+    // 13.1p2). While not part of the definition of the signature,
+    // this check is important to determine whether these functions
+    // can be overloaded.
+    CXXMethodDecl* OldMethod = dyn_cast<CXXMethodDecl>(Old);
+    CXXMethodDecl* NewMethod = dyn_cast<CXXMethodDecl>(New);
+    if (OldMethod && NewMethod && 
+        !OldMethod->isStatic() && !NewMethod->isStatic() &&
+        OldQType.getCVRQualifiers() != NewQType.getCVRQualifiers())
+      return true;
+
+    // The signatures match; this is not an overload.
+    return false;
+  } else {
+    // (C++ 13p1):
+    //   Only function declarations can be overloaded; object and type
+    //   declarations cannot be overloaded.
+    return false;
+  }
+}
+
+/// TryCopyInitialization - Attempt to copy-initialize a value of the
+/// given type (ToType) from the given expression (Expr), as one would
+/// do when copy-initializing a function parameter. This function
+/// returns an implicit conversion sequence that can be used to
+/// perform the initialization. Given
+///
+///   void f(float f);
+///   void g(int i) { f(i); }
+///
+/// this routine would produce an implicit conversion sequence to
+/// describe the initialization of f from i, which will be a standard
+/// conversion sequence containing an lvalue-to-rvalue conversion (C++
+/// 4.1) followed by a floating-integral conversion (C++ 4.9).
+//
+/// Note that this routine only determines how the conversion can be
+/// performed; it does not actually perform the conversion. As such,
+/// it will not produce any diagnostics if no conversion is available,
+/// but will instead return an implicit conversion sequence of kind
+/// "BadConversion".
+ImplicitConversionSequence
+Sema::TryCopyInitialization(Expr* From, QualType ToType)
+{
+  ImplicitConversionSequence ICS;
+
+  QualType FromType = From->getType();
+
+  // Standard conversions (C++ 4)
+  ICS.ConversionKind = ImplicitConversionSequence::StandardConversion;
+  ICS.Standard.Deprecated = false;
+  ICS.Standard.FromTypePtr = FromType.getAsOpaquePtr();
+
+  // The first conversion can be an lvalue-to-rvalue conversion,
+  // array-to-pointer conversion, or function-to-pointer conversion
+  // (C++ 4p1).
+
+  // Lvalue-to-rvalue conversion (C++ 4.1): 
+  //   An lvalue (3.10) of a non-function, non-array type T can be
+  //   converted to an rvalue.
+  Expr::isLvalueResult argIsLvalue = From->isLvalue(Context);
+  if (argIsLvalue == Expr::LV_Valid && 
+      !FromType->isFunctionType() && !FromType->isArrayType()) {
+    ICS.Standard.First = ICK_Lvalue_To_Rvalue;
+
+    // If T is a non-class type, the type of the rvalue is the
+    // cv-unqualified version of T. Otherwise, the type of the rvalue
+    // is T (C++ 4.1p1).
+    if (!FromType->isRecordType())
+      FromType = FromType.getUnqualifiedType();
+  }
+  // Array-to-pointer conversion (C++ 4.2)
+  else if (FromType->isArrayType()) {
+    ICS.Standard.First = ICK_Array_To_Pointer;
+
+    // An lvalue or rvalue of type "array of N T" or "array of unknown
+    // bound of T" can be converted to an rvalue of type "pointer to
+    // T" (C++ 4.2p1).
+    FromType = Context.getArrayDecayedType(FromType);
+
+    if (IsStringLiteralToNonConstPointerConversion(From, ToType)) {
+      // This conversion is deprecated. (C++ D.4).
+      ICS.Standard.Deprecated = true;
+
+      // For the purpose of ranking in overload resolution
+      // (13.3.3.1.1), this conversion is considered an
+      // array-to-pointer conversion followed by a qualification
+      // conversion (4.4). (C++ 4.2p2)
+      ICS.Standard.Second = ICK_Identity;
+      ICS.Standard.Third = ICK_Qualification;
+      ICS.Standard.ToTypePtr = ToType.getAsOpaquePtr();
+      return ICS;
+    }
+  }
+  // Function-to-pointer conversion (C++ 4.3).
+  else if (FromType->isFunctionType() && argIsLvalue == Expr::LV_Valid) {
+    ICS.Standard.First = ICK_Function_To_Pointer;
+
+    // An lvalue of function type T can be converted to an rvalue of
+    // type "pointer to T." The result is a pointer to the
+    // function. (C++ 4.3p1).
+    FromType = Context.getPointerType(FromType);
+
+    // FIXME: Deal with overloaded functions here (C++ 4.3p2).
+  } 
+  // We don't require any conversions for the first step.
+  else {
+    ICS.Standard.First = ICK_Identity;
+  }
+
+  // The second conversion can be an integral promotion, floating
+  // point promotion, integral conversion, floating point conversion,
+  // floating-integral conversion, pointer conversion,
+  // pointer-to-member conversion, or boolean conversion (C++ 4p1).
+  if (Context.getCanonicalType(FromType).getUnqualifiedType() ==
+      Context.getCanonicalType(ToType).getUnqualifiedType()) {
+    // The unqualified versions of the types are the same: there's no
+    // conversion to do.
+    ICS.Standard.Second = ICK_Identity;
+  }
+  // Integral promotion (C++ 4.5).  
+  else if (IsIntegralPromotion(From, FromType, ToType)) {
+    ICS.Standard.Second = ICK_Integral_Promotion;
+    FromType = ToType.getUnqualifiedType();
+  } 
+  // Floating point promotion (C++ 4.6).
+  else if (IsFloatingPointPromotion(FromType, ToType)) {
+    ICS.Standard.Second = ICK_Floating_Promotion;
+    FromType = ToType.getUnqualifiedType();
+  } 
+  // Integral conversions (C++ 4.7).
+  else if ((FromType->isIntegralType() || FromType->isEnumeralType()) &&
+           (ToType->isIntegralType() || ToType->isEnumeralType())) {
+    ICS.Standard.Second = ICK_Integral_Conversion;
+    FromType = ToType.getUnqualifiedType();
+  }
+  // Floating point conversions (C++ 4.8).
+  else if (FromType->isFloatingType() && ToType->isFloatingType()) {
+    ICS.Standard.Second = ICK_Floating_Conversion;
+    FromType = ToType.getUnqualifiedType();
+  }
+  // Floating-integral conversions (C++ 4.9).
+  else if ((FromType->isFloatingType() &&
+            ToType->isIntegralType() && !ToType->isBooleanType()) ||
+           ((FromType->isIntegralType() || FromType->isEnumeralType()) && 
+            ToType->isFloatingType())) {
+    ICS.Standard.Second = ICK_Floating_Integral;
+    FromType = ToType.getUnqualifiedType();
+  }
+  // Pointer conversions (C++ 4.10).
+  else if (IsPointerConversion(From, FromType, ToType, FromType))
+    ICS.Standard.Second = ICK_Pointer_Conversion;
+  // FIXME: Pointer to member conversions (4.11).
+  // Boolean conversions (C++ 4.12).
+  // FIXME: pointer-to-member type
+  else if (ToType->isBooleanType() &&
+           (FromType->isArithmeticType() ||
+            FromType->isEnumeralType() ||
+            FromType->isPointerType())) {
+    ICS.Standard.Second = ICK_Boolean_Conversion;
+    FromType = Context.BoolTy;
+  } else {
+    // No second conversion required.
+    ICS.Standard.Second = ICK_Identity;
+  }
+
+  // The third conversion can be a qualification conversion (C++ 4p1).
+  // FIXME: CheckPointerTypesForAssignment isn't the right way to
+  // determine whether we have a qualification conversion.
+  if (Context.getCanonicalType(FromType) != Context.getCanonicalType(ToType)
+      && CheckPointerTypesForAssignment(ToType, FromType) == Compatible) {
+    ICS.Standard.Third = ICK_Qualification;
+    FromType = ToType;
+  } else {
+    // No conversion required
+    ICS.Standard.Third = ICK_Identity;
+  }
+
+  // If we have not converted the argument type to the parameter type,
+  // this is a bad conversion sequence.
+  if (Context.getCanonicalType(FromType) != Context.getCanonicalType(ToType))
+    ICS.ConversionKind = ImplicitConversionSequence::BadConversion;
+
+  ICS.Standard.ToTypePtr = FromType.getAsOpaquePtr();
+  return ICS;
+}
+
+/// IsIntegralPromotion - Determines whether the conversion from the
+/// expression From (whose potentially-adjusted type is FromType) to
+/// ToType is an integral promotion (C++ 4.5). If so, returns true and
+/// sets PromotedType to the promoted type.
+bool Sema::IsIntegralPromotion(Expr *From, QualType FromType, QualType ToType)
+{
+  const BuiltinType *To = ToType->getAsBuiltinType();
+
+  // An rvalue of type char, signed char, unsigned char, short int, or
+  // unsigned short int can be converted to an rvalue of type int if
+  // int can represent all the values of the source type; otherwise,
+  // the source rvalue can be converted to an rvalue of type unsigned
+  // int (C++ 4.5p1).
+  if (FromType->isPromotableIntegerType() && !FromType->isBooleanType() && To) {
+    if (// We can promote any signed, promotable integer type to an int
+        (FromType->isSignedIntegerType() ||
+         // We can promote any unsigned integer type whose size is
+         // less than int to an int.
+         (!FromType->isSignedIntegerType() && 
+          Context.getTypeSize(FromType) < Context.getTypeSize(ToType))))
+      return To->getKind() == BuiltinType::Int;
+        
+    return To->getKind() == BuiltinType::UInt;
+  }
+
+  // An rvalue of type wchar_t (3.9.1) or an enumeration type (7.2)
+  // can be converted to an rvalue of the first of the following types
+  // that can represent all the values of its underlying type: int,
+  // unsigned int, long, or unsigned long (C++ 4.5p2).
+  if ((FromType->isEnumeralType() || FromType->isWideCharType())
+      && ToType->isIntegerType()) {
+    // Determine whether the type we're converting from is signed or
+    // unsigned.
+    bool FromIsSigned;
+    uint64_t FromSize = Context.getTypeSize(FromType);
+    if (const EnumType *FromEnumType = FromType->getAsEnumType()) {
+      QualType UnderlyingType = FromEnumType->getDecl()->getIntegerType();
+      FromIsSigned = UnderlyingType->isSignedIntegerType();
+    } else {
+      // FIXME: Is wchar_t signed or unsigned? We assume it's signed for now.
+      FromIsSigned = true;
+    }
+
+    // The types we'll try to promote to, in the appropriate
+    // order. Try each of these types.
+    QualType PromoteTypes[4] = { 
+      Context.IntTy, Context.UnsignedIntTy, 
+      Context.LongTy, Context.UnsignedLongTy 
+    };
+    for (int Idx = 0; Idx < 0; ++Idx) {
+      uint64_t ToSize = Context.getTypeSize(PromoteTypes[Idx]);
+      if (FromSize < ToSize ||
+          (FromSize == ToSize && 
+           FromIsSigned == PromoteTypes[Idx]->isSignedIntegerType())) {
+        // We found the type that we can promote to. If this is the
+        // type we wanted, we have a promotion. Otherwise, no
+        // promotion.
+        return Context.getCanonicalType(FromType).getUnqualifiedType()
+          == Context.getCanonicalType(PromoteTypes[Idx]).getUnqualifiedType();
+      }
+    }
+  }
+
+  // An rvalue for an integral bit-field (9.6) can be converted to an
+  // rvalue of type int if int can represent all the values of the
+  // bit-field; otherwise, it can be converted to unsigned int if
+  // unsigned int can represent all the values of the bit-field. If
+  // the bit-field is larger yet, no integral promotion applies to
+  // it. If the bit-field has an enumerated type, it is treated as any
+  // other value of that type for promotion purposes (C++ 4.5p3).
+  if (MemberExpr *MemRef = dyn_cast<MemberExpr>(From)) {
+    using llvm::APSInt;
+    FieldDecl *MemberDecl = MemRef->getMemberDecl();
+    APSInt BitWidth;
+    if (MemberDecl->isBitField() &&
+        FromType->isIntegralType() && !FromType->isEnumeralType() &&
+        From->isIntegerConstantExpr(BitWidth, Context)) {
+      APSInt ToSize(Context.getTypeSize(ToType));
+
+      // Are we promoting to an int from a bitfield that fits in an int?
+      if (BitWidth < ToSize ||
+          (FromType->isSignedIntegerType() && BitWidth <= ToSize))
+        return To->getKind() == BuiltinType::Int;
+        
+      // Are we promoting to an unsigned int from an unsigned bitfield
+      // that fits into an unsigned int?
+      if (FromType->isUnsignedIntegerType() && BitWidth <= ToSize)
+        return To->getKind() == BuiltinType::UInt;
+
+      return false;
+    }
+  }
+
+  // An rvalue of type bool can be converted to an rvalue of type int,
+  // with false becoming zero and true becoming one (C++ 4.5p4).
+  if (FromType->isBooleanType() && To && To->getKind() == BuiltinType::Int)
+    return true;
+
+  return false;
+}
+
+/// IsFloatingPointPromotion - Determines whether the conversion from
+/// FromType to ToType is a floating point promotion (C++ 4.6). If so,
+/// returns true and sets PromotedType to the promoted type.
+bool Sema::IsFloatingPointPromotion(QualType FromType, QualType ToType)
+{
+  /// An rvalue of type float can be converted to an rvalue of type
+  /// double. (C++ 4.6p1).
+  if (const BuiltinType *FromBuiltin = FromType->getAsBuiltinType())
+    if (const BuiltinType *ToBuiltin = ToType->getAsBuiltinType())
+      if (FromBuiltin->getKind() == BuiltinType::Float &&
+          ToBuiltin->getKind() == BuiltinType::Double)
+        return true;
+
+  return false;
+}
+
+/// IsPointerConversion - Determines whether the conversion of the
+/// expression From, which has the (possibly adjusted) type FromType,
+/// can be converted to the type ToType via a pointer conversion (C++
+/// 4.10). If so, returns true and places the converted type (that
+/// might differ from ToType in its cv-qualifiers at some level) into
+/// ConvertedType.
+bool Sema::IsPointerConversion(Expr *From, QualType FromType, QualType ToType,
+                               QualType& ConvertedType)
+{
+  const PointerType* ToTypePtr = ToType->getAsPointerType();
+  if (!ToTypePtr)
+    return false;
+
+  // A null pointer constant can be converted to a pointer type (C++ 4.10p1).
+  if (From->isNullPointerConstant(Context)) {
+    ConvertedType = ToType;
+    return true;
+  }
+  
+  // An rvalue of type "pointer to cv T," where T is an object type,
+  // can be converted to an rvalue of type "pointer to cv void" (C++
+  // 4.10p2).
+  if (FromType->isPointerType() &&
+      FromType->getAsPointerType()->getPointeeType()->isObjectType() &&
+      ToTypePtr->getPointeeType()->isVoidType()) {
+    // We need to produce a pointer to cv void, where cv is the same
+    // set of cv-qualifiers as we had on the incoming pointee type.
+    QualType toPointee = ToTypePtr->getPointeeType();
+    unsigned Quals = Context.getCanonicalType(FromType)->getAsPointerType()
+                   ->getPointeeType().getCVRQualifiers();
+
+    if (Context.getCanonicalType(ToTypePtr->getPointeeType()).getCVRQualifiers()
+	  == Quals) {
+      // ToType is exactly the type we want. Use it.
+      ConvertedType = ToType;
+    } else {
+      // Build a new type with the right qualifiers.
+      ConvertedType 
+	= Context.getPointerType(Context.VoidTy.getQualifiedType(Quals));
+    }
+    return true;
+  }
+
+  // FIXME: An rvalue of type "pointer to cv D," where D is a class
+  // type, can be converted to an rvalue of type "pointer to cv B,"
+  // where B is a base class (clause 10) of D (C++ 4.10p3).
+  return false;
+}
+
+/// CompareImplicitConversionSequences - Compare two implicit
+/// conversion sequences to determine whether one is better than the
+/// other or if they are indistinguishable (C++ 13.3.3.2).
+ImplicitConversionSequence::CompareKind 
+Sema::CompareImplicitConversionSequences(const ImplicitConversionSequence& ICS1,
+                                         const ImplicitConversionSequence& ICS2)
+{
+  // (C++ 13.3.3.2p2): When comparing the basic forms of implicit
+  // conversion sequences (as defined in 13.3.3.1)
+  //   -- a standard conversion sequence (13.3.3.1.1) is a better
+  //      conversion sequence than a user-defined conversion sequence or
+  //      an ellipsis conversion sequence, and
+  //   -- a user-defined conversion sequence (13.3.3.1.2) is a better
+  //      conversion sequence than an ellipsis conversion sequence
+  //      (13.3.3.1.3).
+  // 
+  if (ICS1.ConversionKind < ICS2.ConversionKind)
+    return ImplicitConversionSequence::Better;
+  else if (ICS2.ConversionKind < ICS1.ConversionKind)
+    return ImplicitConversionSequence::Worse;
+
+  // Two implicit conversion sequences of the same form are
+  // indistinguishable conversion sequences unless one of the
+  // following rules apply: (C++ 13.3.3.2p3):
+  if (ICS1.ConversionKind == ImplicitConversionSequence::StandardConversion)
+    return CompareStandardConversionSequences(ICS1.Standard, ICS2.Standard);
+  else if (ICS1.ConversionKind == 
+             ImplicitConversionSequence::UserDefinedConversion) {
+    // User-defined conversion sequence U1 is a better conversion
+    // sequence than another user-defined conversion sequence U2 if
+    // they contain the same user-defined conversion function or
+    // constructor and if the second standard conversion sequence of
+    // U1 is better than the second standard conversion sequence of
+    // U2 (C++ 13.3.3.2p3).
+    if (ICS1.UserDefined.ConversionFunction == 
+          ICS2.UserDefined.ConversionFunction)
+      return CompareStandardConversionSequences(ICS1.UserDefined.After,
+                                                ICS2.UserDefined.After);
+  }
+
+  return ImplicitConversionSequence::Indistinguishable;
+}
+
+/// CompareStandardConversionSequences - Compare two standard
+/// conversion sequences to determine whether one is better than the
+/// other or if they are indistinguishable (C++ 13.3.3.2p3).
+ImplicitConversionSequence::CompareKind 
+Sema::CompareStandardConversionSequences(const StandardConversionSequence& SCS1,
+                                         const StandardConversionSequence& SCS2)
+{
+  // Standard conversion sequence S1 is a better conversion sequence
+  // than standard conversion sequence S2 if (C++ 13.3.3.2p3):
+
+  //  -- S1 is a proper subsequence of S2 (comparing the conversion
+  //     sequences in the canonical form defined by 13.3.3.1.1,
+  //     excluding any Lvalue Transformation; the identity conversion
+  //     sequence is considered to be a subsequence of any
+  //     non-identity conversion sequence) or, if not that,
+  if (SCS1.Second == SCS2.Second && SCS1.Third == SCS2.Third)
+    // Neither is a proper subsequence of the other. Do nothing.
+    ;
+  else if ((SCS1.Second == ICK_Identity && SCS1.Third == SCS2.Third) ||
+           (SCS1.Third == ICK_Identity && SCS1.Second == SCS2.Second) ||
+           (SCS1.Second == ICK_Identity && 
+            SCS1.Third == ICK_Identity))
+    // SCS1 is a proper subsequence of SCS2.
+    return ImplicitConversionSequence::Better;
+  else if ((SCS2.Second == ICK_Identity && SCS2.Third == SCS1.Third) ||
+           (SCS2.Third == ICK_Identity && SCS2.Second == SCS1.Second) ||
+           (SCS2.Second == ICK_Identity && 
+            SCS2.Third == ICK_Identity))
+    // SCS2 is a proper subsequence of SCS1.
+    return ImplicitConversionSequence::Worse;
+
+  //  -- the rank of S1 is better than the rank of S2 (by the rules
+  //     defined below), or, if not that,
+  ImplicitConversionRank Rank1 = SCS1.getRank();
+  ImplicitConversionRank Rank2 = SCS2.getRank();
+  if (Rank1 < Rank2)
+    return ImplicitConversionSequence::Better;
+  else if (Rank2 < Rank1)
+    return ImplicitConversionSequence::Worse;
+  else {
+    // (C++ 13.3.3.2p4): Two conversion sequences with the same rank
+    // are indistinguishable unless one of the following rules
+    // applies:
+    
+    //   A conversion that is not a conversion of a pointer, or
+    //   pointer to member, to bool is better than another conversion
+    //   that is such a conversion.
+    if (SCS1.isPointerConversionToBool() != SCS2.isPointerConversionToBool())
+      return SCS2.isPointerConversionToBool()
+               ? ImplicitConversionSequence::Better
+               : ImplicitConversionSequence::Worse;
+
+    // FIXME: The other bullets in (C++ 13.3.3.2p4) require support
+    // for derived classes.
+  }
+
+  // FIXME: Handle comparison by qualifications.
+  // FIXME: Handle comparison of reference bindings.
+  return ImplicitConversionSequence::Indistinguishable;
+}
+
+/// AddOverloadCandidate - Adds the given function to the set of
+/// candidate functions, using the given function call arguments.
+void 
+Sema::AddOverloadCandidate(FunctionDecl *Function, 
+                           Expr **Args, unsigned NumArgs,
+                           OverloadCandidateSet& CandidateSet)
+{
+  const FunctionTypeProto* Proto 
+    = dyn_cast<FunctionTypeProto>(Function->getType()->getAsFunctionType());
+  assert(Proto && "Functions without a prototype cannot be overloaded");
+
+  // Add this candidate
+  CandidateSet.push_back(OverloadCandidate());
+  OverloadCandidate& Candidate = CandidateSet.back();
+  Candidate.Function = Function;
+
+  unsigned NumArgsInProto = Proto->getNumArgs();
+
+  // (C++ 13.3.2p2): A candidate function having fewer than m
+  // parameters is viable only if it has an ellipsis in its parameter
+  // list (8.3.5).
+  if (NumArgs > NumArgsInProto && !Proto->isVariadic()) {
+    Candidate.Viable = false;
+    return;
+  }
+
+  // (C++ 13.3.2p2): A candidate function having more than m parameters
+  // is viable only if the (m+1)st parameter has a default argument
+  // (8.3.6). For the purposes of overload resolution, the
+  // parameter list is truncated on the right, so that there are
+  // exactly m parameters.
+  unsigned MinRequiredArgs = Function->getMinRequiredArguments();
+  if (NumArgs < MinRequiredArgs) {
+    // Not enough arguments.
+    Candidate.Viable = false;
+    return;
+  }
+
+  // Determine the implicit conversion sequences for each of the
+  // arguments.
+  Candidate.Viable = true;
+  Candidate.Conversions.resize(NumArgs);
+  for (unsigned ArgIdx = 0; ArgIdx < NumArgs; ++ArgIdx) {
+    if (ArgIdx < NumArgsInProto) {
+      // (C++ 13.3.2p3): for F to be a viable function, there shall
+      // exist for each argument an implicit conversion sequence
+      // (13.3.3.1) that converts that argument to the corresponding
+      // parameter of F.
+      QualType ParamType = Proto->getArgType(ArgIdx);
+      Candidate.Conversions[ArgIdx] 
+        = TryCopyInitialization(Args[ArgIdx], ParamType);
+      if (Candidate.Conversions[ArgIdx].ConversionKind 
+            == ImplicitConversionSequence::BadConversion)
+        Candidate.Viable = false;
+    } else {
+      // (C++ 13.3.2p2): For the purposes of overload resolution, any
+      // argument for which there is no corresponding parameter is
+      // considered to ""match the ellipsis" (C+ 13.3.3.1.3).
+      Candidate.Conversions[ArgIdx].ConversionKind 
+        = ImplicitConversionSequence::EllipsisConversion;
+    }
+  }
+}
+
+/// AddOverloadCandidates - Add all of the function overloads in Ovl
+/// to the candidate set.
+void 
+Sema::AddOverloadCandidates(OverloadedFunctionDecl *Ovl, 
+                            Expr **Args, unsigned NumArgs,
+                            OverloadCandidateSet& CandidateSet)
+{
+  for (OverloadedFunctionDecl::function_iterator Func = Ovl->function_begin();
+       Func != Ovl->function_end(); ++Func)
+    AddOverloadCandidate(*Func, Args, NumArgs, CandidateSet);
+}
+
+/// isBetterOverloadCandidate - Determines whether the first overload
+/// candidate is a better candidate than the second (C++ 13.3.3p1).
+bool 
+Sema::isBetterOverloadCandidate(const OverloadCandidate& Cand1,
+                                const OverloadCandidate& Cand2)
+{
+  // Define viable functions to be better candidates than non-viable
+  // functions.
+  if (!Cand2.Viable)
+    return Cand1.Viable;
+  else if (!Cand1.Viable)
+    return false;
+
+  // FIXME: Deal with the implicit object parameter for static member
+  // functions. (C++ 13.3.3p1).
+
+  // (C++ 13.3.3p1): a viable function F1 is defined to be a better
+  // function than another viable function F2 if for all arguments i,
+  // ICSi(F1) is not a worse conversion sequence than ICSi(F2), and
+  // then...
+  unsigned NumArgs = Cand1.Conversions.size();
+  assert(Cand2.Conversions.size() == NumArgs && "Overload candidate mismatch");
+  bool HasBetterConversion = false;
+  for (unsigned ArgIdx = 0; ArgIdx < NumArgs; ++ArgIdx) {
+    switch (CompareImplicitConversionSequences(Cand1.Conversions[ArgIdx],
+                                               Cand2.Conversions[ArgIdx])) {
+    case ImplicitConversionSequence::Better:
+      // Cand1 has a better conversion sequence.
+      HasBetterConversion = true;
+      break;
+
+    case ImplicitConversionSequence::Worse:
+      // Cand1 can't be better than Cand2.
+      return false;
+
+    case ImplicitConversionSequence::Indistinguishable:
+      // Do nothing.
+      break;
+    }
+  }
+
+  if (HasBetterConversion)
+    return true;
+
+  // FIXME: Several other bullets in (C++ 13.3.3p1) need to be implemented.
+
+  return false;
+}
+
+/// BestViableFunction - Computes the best viable function (C++ 13.3.3) 
+/// within an overload candidate set. If overloading is successful,
+/// the result will be OR_Success and Best will be set to point to the
+/// best viable function within the candidate set. Otherwise, one of
+/// several kinds of errors will be returned; see
+/// Sema::OverloadingResult.
+Sema::OverloadingResult 
+Sema::BestViableFunction(OverloadCandidateSet& CandidateSet,
+                         OverloadCandidateSet::iterator& Best)
+{
+  // Find the best viable function.
+  Best = CandidateSet.end();
+  for (OverloadCandidateSet::iterator Cand = CandidateSet.begin();
+       Cand != CandidateSet.end(); ++Cand) {
+    if (Cand->Viable) {
+      if (Best == CandidateSet.end() || isBetterOverloadCandidate(*Cand, *Best))
+        Best = Cand;
+    }
+  }
+
+  // If we didn't find any viable functions, abort.
+  if (Best == CandidateSet.end())
+    return OR_No_Viable_Function;
+
+  // Make sure that this function is better than every other viable
+  // function. If not, we have an ambiguity.
+  for (OverloadCandidateSet::iterator Cand = CandidateSet.begin();
+       Cand != CandidateSet.end(); ++Cand) {
+    if (Cand->Viable && 
+        Cand != Best &&
+        !isBetterOverloadCandidate(*Best, *Cand))
+      return OR_Ambiguous;
+  }
+  
+  // Best is the best viable function.
+  return OR_Success;
+}
+
+/// PrintOverloadCandidates - When overload resolution fails, prints
+/// diagnostic messages containing the candidates in the candidate
+/// set. If OnlyViable is true, only viable candidates will be printed.
+void 
+Sema::PrintOverloadCandidates(OverloadCandidateSet& CandidateSet,
+                              bool OnlyViable)
+{
+  OverloadCandidateSet::iterator Cand = CandidateSet.begin(),
+                             LastCand = CandidateSet.end();
+  for (; Cand != LastCand; ++Cand) {
+    if (Cand->Viable ||!OnlyViable)
+      Diag(Cand->Function->getLocation(), diag::err_ovl_candidate);
+  }
+}
+
+} // end namespace clang