AST/ASTContext.cpp

//===--- ASTContext.cpp - Context to hold long-lived AST nodes ------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Chris Lattner and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file implements the ASTContext interface.
//
//===----------------------------------------------------------------------===//

#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Basic/TargetInfo.h"
#include "llvm/ADT/SmallVector.h"
using namespace clang;

enum FloatingRank {
  FloatRank, DoubleRank, LongDoubleRank
};

ASTContext::~ASTContext() {
  // Deallocate all the types.
  while (!Types.empty()) {
    if (FunctionTypeProto *FT = dyn_cast<FunctionTypeProto>(Types.back())) {
      // Destroy the object, but don't call delete.  These are malloc'd.
      FT->~FunctionTypeProto();
      free(FT);
    } else {
      delete Types.back();
    }
    Types.pop_back();
  }
}

void ASTContext::PrintStats() const {
  fprintf(stderr, "*** AST Context Stats:\n");
  fprintf(stderr, "  %d types total.\n", (int)Types.size());
  unsigned NumBuiltin = 0, NumPointer = 0, NumArray = 0, NumFunctionP = 0;
  unsigned NumFunctionNP = 0, NumTypeName = 0, NumTagged = 0, NumReference = 0;
  
  unsigned NumTagStruct = 0, NumTagUnion = 0, NumTagEnum = 0, NumTagClass = 0;
  
  for (unsigned i = 0, e = Types.size(); i != e; ++i) {
    Type *T = Types[i];
    if (isa<BuiltinType>(T))
      ++NumBuiltin;
    else if (isa<PointerType>(T))
      ++NumPointer;
    else if (isa<ReferenceType>(T))
      ++NumReference;
    else if (isa<ArrayType>(T))
      ++NumArray;
    else if (isa<FunctionTypeNoProto>(T))
      ++NumFunctionNP;
    else if (isa<FunctionTypeProto>(T))
      ++NumFunctionP;
    else if (isa<TypedefType>(T))
      ++NumTypeName;
    else if (TagType *TT = dyn_cast<TagType>(T)) {
      ++NumTagged;
      switch (TT->getDecl()->getKind()) {
      default: assert(0 && "Unknown tagged type!");
      case Decl::Struct: ++NumTagStruct; break;
      case Decl::Union:  ++NumTagUnion; break;
      case Decl::Class:  ++NumTagClass; break; 
      case Decl::Enum:   ++NumTagEnum; break;
      }
    } else {
      assert(0 && "Unknown type!");
    }
  }

  fprintf(stderr, "    %d builtin types\n", NumBuiltin);
  fprintf(stderr, "    %d pointer types\n", NumPointer);
  fprintf(stderr, "    %d reference types\n", NumReference);
  fprintf(stderr, "    %d array types\n", NumArray);
  fprintf(stderr, "    %d function types with proto\n", NumFunctionP);
  fprintf(stderr, "    %d function types with no proto\n", NumFunctionNP);
  fprintf(stderr, "    %d typename (typedef) types\n", NumTypeName);
  fprintf(stderr, "    %d tagged types\n", NumTagged);
  fprintf(stderr, "      %d struct types\n", NumTagStruct);
  fprintf(stderr, "      %d union types\n", NumTagUnion);
  fprintf(stderr, "      %d class types\n", NumTagClass);
  fprintf(stderr, "      %d enum types\n", NumTagEnum);
  fprintf(stderr, "Total bytes = %d\n", int(NumBuiltin*sizeof(BuiltinType)+
    NumPointer*sizeof(PointerType)+NumArray*sizeof(ArrayType)+
    NumFunctionP*sizeof(FunctionTypeProto)+
    NumFunctionNP*sizeof(FunctionTypeNoProto)+
    NumTypeName*sizeof(TypedefType)+NumTagged*sizeof(TagType)));
}


void ASTContext::InitBuiltinType(QualType &R, BuiltinType::Kind K) {
  Types.push_back((R = QualType(new BuiltinType(K),0)).getTypePtr());
}


void ASTContext::InitBuiltinTypes() {
  assert(VoidTy.isNull() && "Context reinitialized?");
  
  // C99 6.2.5p19.
  InitBuiltinType(VoidTy,              BuiltinType::Void);
  
  // C99 6.2.5p2.
  InitBuiltinType(BoolTy,              BuiltinType::Bool);
  // C99 6.2.5p3.
  if (Target.isCharSigned(SourceLocation()))
    InitBuiltinType(CharTy,            BuiltinType::Char_S);
  else
    InitBuiltinType(CharTy,            BuiltinType::Char_U);
  // C99 6.2.5p4.
  InitBuiltinType(SignedCharTy,        BuiltinType::SChar);
  InitBuiltinType(ShortTy,             BuiltinType::Short);
  InitBuiltinType(IntTy,               BuiltinType::Int);
  InitBuiltinType(LongTy,              BuiltinType::Long);
  InitBuiltinType(LongLongTy,          BuiltinType::LongLong);
  
  // C99 6.2.5p6.
  InitBuiltinType(UnsignedCharTy,      BuiltinType::UChar);
  InitBuiltinType(UnsignedShortTy,     BuiltinType::UShort);
  InitBuiltinType(UnsignedIntTy,       BuiltinType::UInt);
  InitBuiltinType(UnsignedLongTy,      BuiltinType::ULong);
  InitBuiltinType(UnsignedLongLongTy,  BuiltinType::ULongLong);
  
  // C99 6.2.5p10.
  InitBuiltinType(FloatTy,             BuiltinType::Float);
  InitBuiltinType(DoubleTy,            BuiltinType::Double);
  InitBuiltinType(LongDoubleTy,        BuiltinType::LongDouble);
  
  // C99 6.2.5p11.
  FloatComplexTy      = getComplexType(FloatTy);
  DoubleComplexTy     = getComplexType(DoubleTy);
  LongDoubleComplexTy = getComplexType(LongDoubleTy);
}


/// getTypeSize - Return the size of the specified type, in bits.  This method
/// does not work on incomplete types.
unsigned ASTContext::getTypeSize(QualType T) {
  T = T.getCanonicalType();
  switch (T->getTypeClass()) {
  default:
  case Type::Complex:
  case Type::Array:
  case Type::Vector:
  case Type::TypeName:
  case Type::Tagged:
    assert(0 && "Unimplemented type sizes!");
  case Type::FunctionNoProto:
  case Type::FunctionProto:
    assert(0 && "Incomplete types have no size!");
  case Type::Builtin: {
    // FIXME: need to use TargetInfo to derive the target specific sizes. This
    // implementation will suffice for play with vector support.
    switch (cast<BuiltinType>(T)->getKind()) {
    default: assert(0 && "Unknown builtin type!");
    case BuiltinType::Void:       assert(0 && "Incomplete types have no size!");
    case BuiltinType::Bool:       return Target.getBoolWidth(SourceLocation());
    case BuiltinType::Char_S:
    case BuiltinType::Char_U:
    case BuiltinType::UChar:
    case BuiltinType::SChar:      return Target.getCharWidth(SourceLocation());
    case BuiltinType::UShort:
    case BuiltinType::Short:      return Target.getShortWidth(SourceLocation());
    case BuiltinType::UInt:
    case BuiltinType::Int:        return Target.getIntWidth(SourceLocation());
    case BuiltinType::ULong:
    case BuiltinType::Long:       return Target.getLongWidth(SourceLocation());
    case BuiltinType::ULongLong:
    case BuiltinType::LongLong:return Target.getLongLongWidth(SourceLocation());
    case BuiltinType::Float:    return Target.getFloatWidth(SourceLocation());
    case BuiltinType::Double:   return Target.getDoubleWidth(SourceLocation());
    case BuiltinType::LongDouble:
      return Target.getLongDoubleWidth(SourceLocation());
    }
  }
  case Type::Pointer:
    return Target.getPointerWidth(SourceLocation());
  case Type::Reference:
    // "When applied to a reference or a reference type, the result is the size
    // of the referenced type." C++98 5.3.3p2: expr.sizeof
    return getTypeSize(cast<ReferenceType>(T)->getReferenceeType());
  }
}

//===----------------------------------------------------------------------===//
//                   Type creation/memoization methods
//===----------------------------------------------------------------------===//


/// getComplexType - Return the uniqued reference to the type for a complex
/// number with the specified element type.
QualType ASTContext::getComplexType(QualType T) {
  // Unique pointers, to guarantee there is only one pointer of a particular
  // structure.
  llvm::FoldingSetNodeID ID;
  ComplexType::Profile(ID, T);
  
  void *InsertPos = 0;
  if (ComplexType *CT = ComplexTypes.FindNodeOrInsertPos(ID, InsertPos))
    return QualType(CT, 0);
  
  // If the pointee type isn't canonical, this won't be a canonical type either,
  // so fill in the canonical type field.
  QualType Canonical;
  if (!T->isCanonical()) {
    Canonical = getComplexType(T.getCanonicalType());
    
    // Get the new insert position for the node we care about.
    ComplexType *NewIP = ComplexTypes.FindNodeOrInsertPos(ID, InsertPos);
    assert(NewIP == 0 && "Shouldn't be in the map!");
  }
  ComplexType *New = new ComplexType(T, Canonical);
  Types.push_back(New);
  ComplexTypes.InsertNode(New, InsertPos);
  return QualType(New, 0);
}


/// getPointerType - Return the uniqued reference to the type for a pointer to
/// the specified type.
QualType ASTContext::getPointerType(QualType T) {
  // Unique pointers, to guarantee there is only one pointer of a particular
  // structure.
  llvm::FoldingSetNodeID ID;
  PointerType::Profile(ID, T);
  
  void *InsertPos = 0;
  if (PointerType *PT = PointerTypes.FindNodeOrInsertPos(ID, InsertPos))
    return QualType(PT, 0);
  
  // If the pointee type isn't canonical, this won't be a canonical type either,
  // so fill in the canonical type field.
  QualType Canonical;
  if (!T->isCanonical()) {
    Canonical = getPointerType(T.getCanonicalType());
   
    // Get the new insert position for the node we care about.
    PointerType *NewIP = PointerTypes.FindNodeOrInsertPos(ID, InsertPos);
    assert(NewIP == 0 && "Shouldn't be in the map!");
  }
  PointerType *New = new PointerType(T, Canonical);
  Types.push_back(New);
  PointerTypes.InsertNode(New, InsertPos);
  return QualType(New, 0);
}

/// getReferenceType - Return the uniqued reference to the type for a reference
/// to the specified type.
QualType ASTContext::getReferenceType(QualType T) {
  // Unique pointers, to guarantee there is only one pointer of a particular
  // structure.
  llvm::FoldingSetNodeID ID;
  ReferenceType::Profile(ID, T);

  void *InsertPos = 0;
  if (ReferenceType *RT = ReferenceTypes.FindNodeOrInsertPos(ID, InsertPos))
    return QualType(RT, 0);
  
  // If the referencee type isn't canonical, this won't be a canonical type
  // either, so fill in the canonical type field.
  QualType Canonical;
  if (!T->isCanonical()) {
    Canonical = getReferenceType(T.getCanonicalType());
   
    // Get the new insert position for the node we care about.
    ReferenceType *NewIP = ReferenceTypes.FindNodeOrInsertPos(ID, InsertPos);
    assert(NewIP == 0 && "Shouldn't be in the map!");
  }

  ReferenceType *New = new ReferenceType(T, Canonical);
  Types.push_back(New);
  ReferenceTypes.InsertNode(New, InsertPos);
  return QualType(New, 0);
}

/// getArrayType - Return the unique reference to the type for an array of the
/// specified element type.
QualType ASTContext::getArrayType(QualType EltTy,ArrayType::ArraySizeModifier ASM,
                                  unsigned EltTypeQuals, Expr *NumElts) {
  // Unique array types, to guarantee there is only one array of a particular
  // structure.
  llvm::FoldingSetNodeID ID;
  ArrayType::Profile(ID, ASM, EltTypeQuals, EltTy, NumElts);
      
  void *InsertPos = 0;
  if (ArrayType *ATP = ArrayTypes.FindNodeOrInsertPos(ID, InsertPos))
    return QualType(ATP, 0);
  
  // If the element type isn't canonical, this won't be a canonical type either,
  // so fill in the canonical type field.
  QualType Canonical;
  if (!EltTy->isCanonical()) {
    Canonical = getArrayType(EltTy.getCanonicalType(), ASM, EltTypeQuals,
                             NumElts);
    
    // Get the new insert position for the node we care about.
    ArrayType *NewIP = ArrayTypes.FindNodeOrInsertPos(ID, InsertPos);
    assert(NewIP == 0 && "Shouldn't be in the map!");
  }
  
  ArrayType *New = new ArrayType(EltTy, ASM, EltTypeQuals, Canonical, NumElts);
  ArrayTypes.InsertNode(New, InsertPos);
  Types.push_back(New);
  return QualType(New, 0);
}

/// convertToVectorType - Return the unique reference to a vector type of
/// the specified element type and size. VectorType can be a pointer, array,
/// function, or built-in type (i.e. _Bool, integer, or float).
QualType ASTContext::convertToVectorType(QualType vecType, unsigned NumElts) {
  BuiltinType *baseType;
  
  baseType = dyn_cast<BuiltinType>(vecType.getCanonicalType().getTypePtr());
  assert(baseType != 0 && 
         "convertToVectorType(): Complex vector types unimplemented");
         
  // Check if we've already instantiated a vector of this type.
  llvm::FoldingSetNodeID ID;
  VectorType::Profile(ID, vecType, NumElts);      
  void *InsertPos = 0;
  if (VectorType *VTP = VectorTypes.FindNodeOrInsertPos(ID, InsertPos))
    return QualType(VTP, 0);

  // If the element type isn't canonical, this won't be a canonical type either,
  // so fill in the canonical type field.
  QualType Canonical;
  if (!vecType->isCanonical()) {
    Canonical = convertToVectorType(vecType.getCanonicalType(), NumElts);
    
    // Get the new insert position for the node we care about.
    VectorType *NewIP = VectorTypes.FindNodeOrInsertPos(ID, InsertPos);
    assert(NewIP == 0 && "Shouldn't be in the map!");
  }
  VectorType *New = new VectorType(vecType, NumElts, Canonical);
  VectorTypes.InsertNode(New, InsertPos);
  Types.push_back(New);
  return QualType(New, 0);
}

/// getFunctionTypeNoProto - Return a K&R style C function type like 'int()'.
///
QualType ASTContext::getFunctionTypeNoProto(QualType ResultTy) {
  // Unique functions, to guarantee there is only one function of a particular
  // structure.
  llvm::FoldingSetNodeID ID;
  FunctionTypeNoProto::Profile(ID, ResultTy);
  
  void *InsertPos = 0;
  if (FunctionTypeNoProto *FT = 
        FunctionTypeNoProtos.FindNodeOrInsertPos(ID, InsertPos))
    return QualType(FT, 0);
  
  QualType Canonical;
  if (!ResultTy->isCanonical()) {
    Canonical = getFunctionTypeNoProto(ResultTy.getCanonicalType());
    
    // Get the new insert position for the node we care about.
    FunctionTypeNoProto *NewIP =
      FunctionTypeNoProtos.FindNodeOrInsertPos(ID, InsertPos);
    assert(NewIP == 0 && "Shouldn't be in the map!");
  }
  
  FunctionTypeNoProto *New = new FunctionTypeNoProto(ResultTy, Canonical);
  Types.push_back(New);
  FunctionTypeProtos.InsertNode(New, InsertPos);
  return QualType(New, 0);
}

/// getFunctionType - Return a normal function type with a typed argument
/// list.  isVariadic indicates whether the argument list includes '...'.
QualType ASTContext::getFunctionType(QualType ResultTy, QualType *ArgArray,
                                     unsigned NumArgs, bool isVariadic) {
  // Unique functions, to guarantee there is only one function of a particular
  // structure.
  llvm::FoldingSetNodeID ID;
  FunctionTypeProto::Profile(ID, ResultTy, ArgArray, NumArgs, isVariadic);

  void *InsertPos = 0;
  if (FunctionTypeProto *FTP = 
        FunctionTypeProtos.FindNodeOrInsertPos(ID, InsertPos))
    return QualType(FTP, 0);
    
  // Determine whether the type being created is already canonical or not.  
  bool isCanonical = ResultTy->isCanonical();
  for (unsigned i = 0; i != NumArgs && isCanonical; ++i)
    if (!ArgArray[i]->isCanonical())
      isCanonical = false;

  // If this type isn't canonical, get the canonical version of it.
  QualType Canonical;
  if (!isCanonical) {
    llvm::SmallVector<QualType, 16> CanonicalArgs;
    CanonicalArgs.reserve(NumArgs);
    for (unsigned i = 0; i != NumArgs; ++i)
      CanonicalArgs.push_back(ArgArray[i].getCanonicalType());
    
    Canonical = getFunctionType(ResultTy.getCanonicalType(),
                                &CanonicalArgs[0], NumArgs,
                                isVariadic);
    
    // Get the new insert position for the node we care about.
    FunctionTypeProto *NewIP =
      FunctionTypeProtos.FindNodeOrInsertPos(ID, InsertPos);
    assert(NewIP == 0 && "Shouldn't be in the map!");
  }
  
  // FunctionTypeProto objects are not allocated with new because they have a
  // variable size array (for parameter types) at the end of them.
  FunctionTypeProto *FTP = 
    (FunctionTypeProto*)malloc(sizeof(FunctionTypeProto) + 
                               (NumArgs-1)*sizeof(QualType));
  new (FTP) FunctionTypeProto(ResultTy, ArgArray, NumArgs, isVariadic,
                              Canonical);
  Types.push_back(FTP);
  FunctionTypeProtos.InsertNode(FTP, InsertPos);
  return QualType(FTP, 0);
}

/// getTypedefType - Return the unique reference to the type for the
/// specified typename decl.
QualType ASTContext::getTypedefType(TypedefDecl *Decl) {
  if (Decl->TypeForDecl) return QualType(Decl->TypeForDecl, 0);
  
  QualType Canonical = Decl->getUnderlyingType().getCanonicalType();
  Decl->TypeForDecl = new TypedefType(Decl, Canonical);
  Types.push_back(Decl->TypeForDecl);
  return QualType(Decl->TypeForDecl, 0);
}

/// getTagDeclType - Return the unique reference to the type for the
/// specified TagDecl (struct/union/class/enum) decl.
QualType ASTContext::getTagDeclType(TagDecl *Decl) {
  // The decl stores the type cache.
  if (Decl->TypeForDecl) return QualType(Decl->TypeForDecl, 0);
  
  Decl->TypeForDecl = new TagType(Decl, QualType());
  Types.push_back(Decl->TypeForDecl);
  return QualType(Decl->TypeForDecl, 0);
}

/// getSizeType - Return the unique type for "size_t" (C99 7.17), the result 
/// of the sizeof operator (C99 6.5.3.4p4). The value is target dependent and 
/// needs to agree with the definition in <stddef.h>. 
QualType ASTContext::getSizeType() const {
  // On Darwin, size_t is defined as a "long unsigned int". 
  // FIXME: should derive from "Target".
  return UnsignedLongTy; 
}

/// getPointerDiffType - Return the unique type for "ptrdiff_t" (ref?)
/// defined in <stddef.h>. Pointer - pointer requires this (C99 6.5.6p9).
QualType ASTContext::getPointerDiffType() const {
  // On Darwin, ptrdiff_t is defined as a "int". This seems like a bug...
  // FIXME: should derive from "Target".
  return IntTy; 
}

/// getIntegerBitwidth - Return the bitwidth of the specified integer type
/// according to the target.  'Loc' specifies the source location that
/// requires evaluation of this property.
unsigned ASTContext::getIntegerBitwidth(QualType T, SourceLocation Loc) {
  if (const TagType *TT = dyn_cast<TagType>(T.getCanonicalType())) {
    assert(TT->getDecl()->getKind() == Decl::Enum && "not an int or enum");
    assert(0 && "FIXME: getIntegerBitwidth(enum) unimplemented!");
  }
  
  const BuiltinType *BT = cast<BuiltinType>(T.getCanonicalType());
  switch (BT->getKind()) {
  default: assert(0 && "getIntegerBitwidth(): not a built-in integer");
  case BuiltinType::Bool:      return Target.getBoolWidth(Loc);
  case BuiltinType::Char_S:
  case BuiltinType::Char_U:
  case BuiltinType::SChar:
  case BuiltinType::UChar:     return Target.getCharWidth(Loc);
  case BuiltinType::Short:
  case BuiltinType::UShort:    return Target.getShortWidth(Loc);
  case BuiltinType::Int:
  case BuiltinType::UInt:      return Target.getIntWidth(Loc);
  case BuiltinType::Long:
  case BuiltinType::ULong:     return Target.getLongWidth(Loc);
  case BuiltinType::LongLong:
  case BuiltinType::ULongLong: return Target.getLongLongWidth(Loc);
  }
}

/// getIntegerRank - Return an integer conversion rank (C99 6.3.1.1p1). This
/// routine will assert if passed a built-in type that isn't an integer or enum.
static int getIntegerRank(QualType t) {
  if (const TagType *TT = dyn_cast<TagType>(t.getCanonicalType())) {
    assert(TT->getDecl()->getKind() == Decl::Enum && "not an int or enum");
    return 4;
  }
  
  const BuiltinType *BT = cast<BuiltinType>(t.getCanonicalType());
  switch (BT->getKind()) {
  default:
    assert(0 && "getIntegerRank(): not a built-in integer");
  case BuiltinType::Bool:
    return 1;
  case BuiltinType::Char_S:
  case BuiltinType::Char_U:
  case BuiltinType::SChar:
  case BuiltinType::UChar:
    return 2;
  case BuiltinType::Short:
  case BuiltinType::UShort:
    return 3;
  case BuiltinType::Int:
  case BuiltinType::UInt:
    return 4;
  case BuiltinType::Long:
  case BuiltinType::ULong:
    return 5;
  case BuiltinType::LongLong:
  case BuiltinType::ULongLong:
    return 6;
  }
}

/// getFloatingRank - Return a relative rank for floating point types.
/// This routine will assert if passed a built-in type that isn't a float.
static int getFloatingRank(QualType T) {
  T = T.getCanonicalType();
  if (ComplexType *CT = dyn_cast<ComplexType>(T))
    return getFloatingRank(CT->getElementType());
  
  switch (cast<BuiltinType>(T)->getKind()) {
  default:  assert(0 && "getFloatingPointRank(): not a floating type");
  case BuiltinType::Float:      return FloatRank;
  case BuiltinType::Double:     return DoubleRank;
  case BuiltinType::LongDouble: return LongDoubleRank;
  }
}

// maxComplexType - the following code handles 3 different combinations:
// complex/complex, complex/float, float/complex. 
// When both operands are complex, the shorter operand is converted to the 
// type of the longer, and that is the type of the result. This corresponds 
// to what is done when combining two real floating-point operands. 
// The fun begins when size promotion occur across type domains. g
// getFloatingRank & convertFloatingRankToComplexType handle this without 
// enumerating all permutations. 
// It also allows us to add new types without breakage.
// From H&S 6.3.4: When one operand is complex and the other is a real
// floating-point type, the less precise type is converted, within it's 
// real or complex domain, to the precision of the other type. For example,
// when combining a "long double" with a "double _Complex", the 
// "double _Complex" is promoted to "long double _Complex".

QualType ASTContext::maxComplexType(QualType lt, QualType rt) const {
  switch (std::max(getFloatingRank(lt), getFloatingRank(rt))) {
  default: assert(0 && "convertRankToComplex(): illegal value for rank");
  case FloatRank:      return FloatComplexTy;
  case DoubleRank:     return DoubleComplexTy;
  case LongDoubleRank: return LongDoubleComplexTy;
  }
}

// maxFloatingType - handles the simple case, both operands are floats.
QualType ASTContext::maxFloatingType(QualType lt, QualType rt) {
  return getFloatingRank(lt) > getFloatingRank(rt) ? lt : rt;
}

// maxIntegerType - Returns the highest ranked integer type. Handles 3 case:
// unsigned/unsigned, signed/signed, signed/unsigned. C99 6.3.1.8p1.
QualType ASTContext::maxIntegerType(QualType lhs, QualType rhs) {
  if (lhs == rhs) return lhs;
  
  bool t1Unsigned = lhs->isUnsignedIntegerType();
  bool t2Unsigned = rhs->isUnsignedIntegerType();
  
  if ((t1Unsigned && t2Unsigned) || (!t1Unsigned && !t2Unsigned))
    return getIntegerRank(lhs) >= getIntegerRank(rhs) ? lhs : rhs; 
  
  // We have two integer types with differing signs
  QualType unsignedType = t1Unsigned ? lhs : rhs;
  QualType signedType = t1Unsigned ? rhs : lhs;
  
  if (getIntegerRank(unsignedType) >= getIntegerRank(signedType))
    return unsignedType;
  else {
    // FIXME: Need to check if the signed type can represent all values of the 
    // unsigned type. If it can, then the result is the signed type. 
    // If it can't, then the result is the unsigned version of the signed type.  
    // Should probably add a helper that returns a signed integer type from 
    // an unsigned (and vice versa). C99 6.3.1.8.
    return signedType; 
  }
}