lib/CodeGen/CGCall.cpp

//===----- CGCall.h - Encapsulate calling convention details ----*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// These classes wrap the information about a call or function
// definition used to handle ABI compliancy.
//
//===----------------------------------------------------------------------===//

#include "CGCall.h"
#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclObjC.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Attributes.h"
using namespace clang;
using namespace CodeGen;

/***/

// FIXME: Use iterator and sidestep silly type array creation.

CGFunctionInfo::CGFunctionInfo(const FunctionTypeNoProto *FTNP)
  : IsVariadic(true)
{
  ArgTypes.push_back(FTNP->getResultType());
}

CGFunctionInfo::CGFunctionInfo(const FunctionTypeProto *FTP)
  : IsVariadic(FTP->isVariadic())
{
  ArgTypes.push_back(FTP->getResultType());
  for (unsigned i = 0, e = FTP->getNumArgs(); i != e; ++i)
    ArgTypes.push_back(FTP->getArgType(i));
}

// FIXME: Is there really any reason to have this still?
CGFunctionInfo::CGFunctionInfo(const FunctionDecl *FD)
{
  const FunctionType *FTy = FD->getType()->getAsFunctionType();
  const FunctionTypeProto *FTP = dyn_cast<FunctionTypeProto>(FTy);

  ArgTypes.push_back(FTy->getResultType());
  if (FTP) {
    IsVariadic = FTP->isVariadic();
    for (unsigned i = 0, e = FTP->getNumArgs(); i != e; ++i)
      ArgTypes.push_back(FTP->getArgType(i));
  } else {
    IsVariadic = true;
  }
}

CGFunctionInfo::CGFunctionInfo(const ObjCMethodDecl *MD,
                               const ASTContext &Context)
  : IsVariadic(MD->isVariadic())
{
  ArgTypes.push_back(MD->getResultType());
  ArgTypes.push_back(MD->getSelfDecl()->getType());
  ArgTypes.push_back(Context.getObjCSelType());
  for (ObjCMethodDecl::param_const_iterator i = MD->param_begin(),
         e = MD->param_end(); i != e; ++i)
    ArgTypes.push_back((*i)->getType());
}

ArgTypeIterator CGFunctionInfo::argtypes_begin() const {
  return ArgTypes.begin();
}

ArgTypeIterator CGFunctionInfo::argtypes_end() const {
  return ArgTypes.end();
}

/***/

CGCallInfo::CGCallInfo(QualType _ResultType, const CallArgList &_Args) {
  ArgTypes.push_back(_ResultType);
  for (CallArgList::const_iterator i = _Args.begin(), e = _Args.end(); i!=e; ++i)
    ArgTypes.push_back(i->second);
}

ArgTypeIterator CGCallInfo::argtypes_begin() const {
  return ArgTypes.begin();
}

ArgTypeIterator CGCallInfo::argtypes_end() const {
  return ArgTypes.end();
}

/***/

/// ABIArgInfo - Helper class to encapsulate information about how a
/// specific C type should be passed to or returned from a function.
class ABIArgInfo {
public:
  enum Kind {
    Default,
    StructRet, /// Only valid for return values. The return value
               /// should be passed through a pointer to a caller
               /// allocated location passed as an implicit first
               /// argument to the function.

    Coerce,    /// Only valid for aggregate return types, the argument
               /// should be accessed by coercion to a provided type.

    ByVal,     /// Only valid for aggregate argument types. The
               /// structure should be passed "byval" with the
               /// specified alignment (0 indicates default
               /// alignment).

    Expand,    /// Only valid for aggregate argument types. The
               /// structure should be expanded into consecutive
               /// arguments for its constituent fields. Currently
               /// expand is only allowed on structures whose fields
               /// are all scalar types or are themselves expandable
               /// types.

    KindFirst=Default, KindLast=Expand
  };

private:
  Kind TheKind;
  const llvm::Type *TypeData;
  unsigned UIntData;

  ABIArgInfo(Kind K, const llvm::Type *TD=0,
             unsigned UI=0) : TheKind(K),
                              TypeData(TD),
                              UIntData(0) {}
public:
  static ABIArgInfo getDefault() { 
    return ABIArgInfo(Default); 
  }
  static ABIArgInfo getStructRet() { 
    return ABIArgInfo(StructRet); 
  }
  static ABIArgInfo getCoerce(const llvm::Type *T) { 
    assert(T->isSingleValueType() && "Can only coerce to simple types");
    return ABIArgInfo(Coerce, T);
  }
  static ABIArgInfo getByVal(unsigned Alignment) {
    return ABIArgInfo(ByVal, 0, Alignment);
  }
  static ABIArgInfo getExpand() {
    return ABIArgInfo(Expand);
  }

  Kind getKind() const { return TheKind; }
  bool isDefault() const { return TheKind == Default; }
  bool isStructRet() const { return TheKind == StructRet; }
  bool isCoerce() const { return TheKind == Coerce; }
  bool isByVal() const { return TheKind == ByVal; }
  bool isExpand() const { return TheKind == Expand; }

  // Coerce accessors
  const llvm::Type *getCoerceToType() const {
    assert(TheKind == Coerce && "Invalid kind!");
    return TypeData;
  }

  // ByVal accessors
  unsigned getByValAlignment() const {
    assert(TheKind == ByVal && "Invalid kind!");
    return UIntData;
  }
};

/***/

/* FIXME: All of this stuff should be part of the target interface
   somehow. It is currently here because it is not clear how to factor
   the targets to support this, since the Targets currently live in a
   layer below types n'stuff.
 */

/// ABIInfo - Target specific hooks for defining how a type should be
/// passed or returned from functions.
class clang::ABIInfo {
public:
  virtual ~ABIInfo();

  virtual ABIArgInfo classifyReturnType(QualType RetTy, 
                                        ASTContext &Context) const = 0;

  virtual ABIArgInfo classifyArgumentType(QualType Ty,
                                          ASTContext &Context) const = 0;
};

ABIInfo::~ABIInfo() {}

/// isEmptyStruct - Return true iff a structure has no non-empty
/// members. Note that a structure with a flexible array member is not
/// considered empty.
static bool isEmptyStruct(QualType T) {
  const RecordType *RT = T->getAsStructureType();
  if (!RT)
    return 0;
  const RecordDecl *RD = RT->getDecl();
  if (RD->hasFlexibleArrayMember())
    return false;
  for (RecordDecl::field_iterator i = RD->field_begin(), 
         e = RD->field_end(); i != e; ++i) {
    const FieldDecl *FD = *i;
    if (!isEmptyStruct(FD->getType()))
      return false;
  }
  return true;
}

/// isSingleElementStruct - Determine if a structure is a "single
/// element struct", i.e. it has exactly one non-empty field or
/// exactly one field which is itself a single element
/// struct. Structures with flexible array members are never
/// considered single element structs.
///
/// \return The field declaration for the single non-empty field, if
/// it exists.
static const FieldDecl *isSingleElementStruct(QualType T) {
  const RecordType *RT = T->getAsStructureType();
  if (!RT)
    return 0;

  const RecordDecl *RD = RT->getDecl();
  if (RD->hasFlexibleArrayMember())
    return 0;

  const FieldDecl *Found = 0;
  for (RecordDecl::field_iterator i = RD->field_begin(), 
         e = RD->field_end(); i != e; ++i) {
    const FieldDecl *FD = *i;
    QualType FT = FD->getType();

    if (isEmptyStruct(FT)) {
      // Ignore
    } else if (Found) {
      return 0;
    } else if (!CodeGenFunction::hasAggregateLLVMType(FT)) {
      Found = FD;
    } else {
      Found = isSingleElementStruct(FT);
      if (!Found)
        return 0;
    }
  }

  return Found;
}

static bool is32Or64BitBasicType(QualType Ty, ASTContext &Context) {
  if (!Ty->getAsBuiltinType() && !Ty->isPointerType())
    return false;

  uint64_t Size = Context.getTypeSize(Ty);
  return Size == 32 || Size == 64;
}

static bool areAllFields32Or64BitBasicType(const RecordDecl *RD,
                                           ASTContext &Context) {
  for (RecordDecl::field_iterator i = RD->field_begin(), 
         e = RD->field_end(); i != e; ++i) {
    const FieldDecl *FD = *i;

    if (!is32Or64BitBasicType(FD->getType(), Context))
      return false;
    
    // If this is a bit-field we need to make sure it is still a
    // 32-bit or 64-bit type.
    if (Expr *BW = FD->getBitWidth()) {
      unsigned Width = BW->getIntegerConstantExprValue(Context).getZExtValue();
      if (Width <= 16)
        return false;
    }
  }
  return true;
}

namespace {
/// DefaultABIInfo - The default implementation for ABI specific
/// details. This implementation provides information which results in
/// sensible LLVM IR generation, but does not conform to any
/// particular ABI.
class DefaultABIInfo : public ABIInfo {
  virtual ABIArgInfo classifyReturnType(QualType RetTy, 
                                        ASTContext &Context) const;

  virtual ABIArgInfo classifyArgumentType(QualType RetTy,
                                          ASTContext &Context) const;
};

/// X86_32ABIInfo - The X86-32 ABI information.
class X86_32ABIInfo : public ABIInfo {
public:
  virtual ABIArgInfo classifyReturnType(QualType RetTy, 
                                        ASTContext &Context) const;

  virtual ABIArgInfo classifyArgumentType(QualType RetTy,
                                          ASTContext &Context) const;
};
}

ABIArgInfo X86_32ABIInfo::classifyReturnType(QualType RetTy,
                                            ASTContext &Context) const {
  assert(!RetTy->isArrayType() && 
         "Array types cannot be passed directly.");
  if (CodeGenFunction::hasAggregateLLVMType(RetTy)) {
    // Classify "single element" structs as their element type.
    const FieldDecl *SeltFD = isSingleElementStruct(RetTy);
    if (SeltFD) {
      QualType SeltTy = SeltFD->getType()->getDesugaredType();
      if (const BuiltinType *BT = SeltTy->getAsBuiltinType()) {
        // FIXME: This is gross, it would be nice if we could just
        // pass back SeltTy and have clients deal with it. Is it worth
        // supporting coerce to both LLVM and clang Types?
        if (BT->isIntegerType()) {
          uint64_t Size = Context.getTypeSize(SeltTy);
          return ABIArgInfo::getCoerce(llvm::IntegerType::get((unsigned) Size));
        } else if (BT->getKind() == BuiltinType::Float) {
          return ABIArgInfo::getCoerce(llvm::Type::FloatTy);
        } else if (BT->getKind() == BuiltinType::Double) {
          return ABIArgInfo::getCoerce(llvm::Type::DoubleTy);
        }
      } else if (SeltTy->isPointerType()) {
        // FIXME: It would be really nice if this could come out as
        // the proper pointer type.
        llvm::Type *PtrTy = 
          llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
        return ABIArgInfo::getCoerce(PtrTy);
      }
    }

    uint64_t Size = Context.getTypeSize(RetTy);
    if (Size == 8) {
      return ABIArgInfo::getCoerce(llvm::Type::Int8Ty);
    } else if (Size == 16) {
      return ABIArgInfo::getCoerce(llvm::Type::Int16Ty);
    } else if (Size == 32) {
      return ABIArgInfo::getCoerce(llvm::Type::Int32Ty);
    } else if (Size == 64) {
      return ABIArgInfo::getCoerce(llvm::Type::Int64Ty);
    } else {
      return ABIArgInfo::getStructRet();
    }
  } else {
    return ABIArgInfo::getDefault();
  }
}

ABIArgInfo X86_32ABIInfo::classifyArgumentType(QualType Ty,
                                              ASTContext &Context) const {
  assert(!Ty->isArrayType() && "Array types cannot be passed directly.");
  if (CodeGenFunction::hasAggregateLLVMType(Ty)) {
    // Structures with flexible arrays are always byval.
    if (const RecordType *RT = Ty->getAsStructureType())
      if (RT->getDecl()->hasFlexibleArrayMember())
        return ABIArgInfo::getByVal(0);

    // Expand empty structs (i.e. ignore)
    uint64_t Size = Context.getTypeSize(Ty);
    if (Ty->isStructureType() && Size == 0)
      return ABIArgInfo::getExpand();

    // Expand structs with size <= 128-bits which consist only of
    // basic types (int, long long, float, double, xxx*). This is
    // non-recursive and does not ignore empty fields.
    if (const RecordType *RT = Ty->getAsStructureType()) {
      if (Context.getTypeSize(Ty) <= 4*32 &&
          areAllFields32Or64BitBasicType(RT->getDecl(), Context))
        return ABIArgInfo::getExpand();
    }

    return ABIArgInfo::getByVal(0);
  } else {
    return ABIArgInfo::getDefault();
  }
}

ABIArgInfo DefaultABIInfo::classifyReturnType(QualType RetTy,
                                            ASTContext &Context) const {
  return ABIArgInfo::getDefault();
}

ABIArgInfo DefaultABIInfo::classifyArgumentType(QualType Ty,
                                              ASTContext &Context) const {
  assert(!Ty->isArrayType() && "Array types cannot be passed directly.");
  return ABIArgInfo::getDefault();
}

const ABIInfo &CodeGenTypes::getABIInfo() const {
  if (TheABIInfo)
    return *TheABIInfo;

  // For now we just cache this in the CodeGenTypes and don't bother
  // to free it.
  const char *TargetPrefix = getContext().Target.getTargetPrefix();
  if (strcmp(TargetPrefix, "x86") == 0) {
    if (getContext().Target.getPointerWidth(0) == 32) 
      return *(TheABIInfo = new X86_32ABIInfo());
  }

  return *(TheABIInfo = new DefaultABIInfo);
}

// getABIReturnInfo - Wrap the ABIInfo getABIReturnInfo, altering
// "default" types to StructRet when appropriate for simplicity.
static ABIArgInfo getABIReturnInfo(QualType Ty, CodeGenTypes &CGT) {
  assert(!Ty->isArrayType() && 
         "Array types cannot be passed directly.");
  ABIArgInfo Info = CGT.getABIInfo().classifyReturnType(Ty, CGT.getContext());
  // Ensure default on aggregate types is StructRet.
  if (Info.isDefault() && CodeGenFunction::hasAggregateLLVMType(Ty))
    return ABIArgInfo::getStructRet();
  return Info;
}

// getABIArgumentInfo - Wrap the ABIInfo getABIReturnInfo, altering
// "default" types to ByVal when appropriate for simplicity.
static ABIArgInfo getABIArgumentInfo(QualType Ty, CodeGenTypes &CGT) {
  assert(!Ty->isArrayType() && 
         "Array types cannot be passed directly.");
  ABIArgInfo Info = CGT.getABIInfo().classifyArgumentType(Ty, CGT.getContext());
  // Ensure default on aggregate types is ByVal.
  if (Info.isDefault() && CodeGenFunction::hasAggregateLLVMType(Ty))
    return ABIArgInfo::getByVal(0);
  return Info;  
}

/***/

void CodeGenTypes::GetExpandedTypes(QualType Ty, 
                                    std::vector<const llvm::Type*> &ArgTys) {
  const RecordType *RT = Ty->getAsStructureType();
  assert(RT && "Can only expand structure types.");
  const RecordDecl *RD = RT->getDecl();
  assert(!RD->hasFlexibleArrayMember() && 
         "Cannot expand structure with flexible array.");
  
  for (RecordDecl::field_iterator i = RD->field_begin(), 
         e = RD->field_end(); i != e; ++i) {
    const FieldDecl *FD = *i;
    assert(!FD->isBitField() && 
           "Cannot expand structure with bit-field members.");
    
    QualType FT = FD->getType();
    if (CodeGenFunction::hasAggregateLLVMType(FT)) {
      GetExpandedTypes(FT, ArgTys);
    } else {
      ArgTys.push_back(ConvertType(FT));
    }
  }
}

llvm::Function::arg_iterator 
CodeGenFunction::ExpandTypeFromArgs(QualType Ty, LValue LV,
                                    llvm::Function::arg_iterator AI) {
  const RecordType *RT = Ty->getAsStructureType();
  assert(RT && "Can only expand structure types.");

  RecordDecl *RD = RT->getDecl();
  assert(LV.isSimple() && 
         "Unexpected non-simple lvalue during struct expansion.");  
  llvm::Value *Addr = LV.getAddress();
  for (RecordDecl::field_iterator i = RD->field_begin(), 
         e = RD->field_end(); i != e; ++i) {
    FieldDecl *FD = *i;    
    QualType FT = FD->getType();

    // FIXME: What are the right qualifiers here?
    LValue LV = EmitLValueForField(Addr, FD, false, 0);
    if (CodeGenFunction::hasAggregateLLVMType(FT)) {
      AI = ExpandTypeFromArgs(FT, LV, AI);
    } else {
      EmitStoreThroughLValue(RValue::get(AI), LV, FT);
      ++AI;
    }
  }

  return AI;
}

void 
CodeGenFunction::ExpandTypeToArgs(QualType Ty, RValue RV, 
                                  llvm::SmallVector<llvm::Value*, 16> &Args) {
  const RecordType *RT = Ty->getAsStructureType();
  assert(RT && "Can only expand structure types.");

  RecordDecl *RD = RT->getDecl();
  assert(RV.isAggregate() && "Unexpected rvalue during struct expansion");
  llvm::Value *Addr = RV.getAggregateAddr();
  for (RecordDecl::field_iterator i = RD->field_begin(), 
         e = RD->field_end(); i != e; ++i) {
    FieldDecl *FD = *i;    
    QualType FT = FD->getType();
    
    // FIXME: What are the right qualifiers here?
    LValue LV = EmitLValueForField(Addr, FD, false, 0);
    if (CodeGenFunction::hasAggregateLLVMType(FT)) {
      ExpandTypeToArgs(FT, RValue::getAggregate(LV.getAddress()), Args);
    } else {
      RValue RV = EmitLoadOfLValue(LV, FT);
      assert(RV.isScalar() && 
             "Unexpected non-scalar rvalue during struct expansion.");
      Args.push_back(RV.getScalarVal());
    }
  }
}

/***/

const llvm::FunctionType *
CodeGenTypes::GetFunctionType(const CGCallInfo &CI, bool IsVariadic) {
  return GetFunctionType(CI.argtypes_begin(), CI.argtypes_end(), IsVariadic);
}

const llvm::FunctionType *
CodeGenTypes::GetFunctionType(const CGFunctionInfo &FI) {
  return GetFunctionType(FI.argtypes_begin(), FI.argtypes_end(), FI.isVariadic());
}

const llvm::FunctionType *
CodeGenTypes::GetFunctionType(ArgTypeIterator begin, ArgTypeIterator end,
                              bool IsVariadic) {
  std::vector<const llvm::Type*> ArgTys;

  const llvm::Type *ResultType = 0;

  QualType RetTy = *begin;
  ABIArgInfo RetAI = getABIReturnInfo(RetTy, *this);
  switch (RetAI.getKind()) {
  case ABIArgInfo::ByVal:
  case ABIArgInfo::Expand:
    assert(0 && "Invalid ABI kind for return argument");

  case ABIArgInfo::Default:
    if (RetTy->isVoidType()) {
      ResultType = llvm::Type::VoidTy;
    } else {
      ResultType = ConvertType(RetTy);
    }
    break;

  case ABIArgInfo::StructRet: {
    ResultType = llvm::Type::VoidTy;
    const llvm::Type *STy = ConvertType(RetTy);
    ArgTys.push_back(llvm::PointerType::get(STy, RetTy.getAddressSpace()));
    break;
  }

  case ABIArgInfo::Coerce:
    ResultType = RetAI.getCoerceToType();
    break;
  }
  
  for (++begin; begin != end; ++begin) {
    ABIArgInfo AI = getABIArgumentInfo(*begin, *this);
    const llvm::Type *Ty = ConvertType(*begin);
    
    switch (AI.getKind()) {
    case ABIArgInfo::Coerce:
    case ABIArgInfo::StructRet:
      assert(0 && "Invalid ABI kind for non-return argument");
    
    case ABIArgInfo::ByVal:
      // byval arguments are always on the stack, which is addr space #0.
      ArgTys.push_back(llvm::PointerType::getUnqual(Ty));
      assert(AI.getByValAlignment() == 0 && "FIXME: alignment unhandled");
      break;
      
    case ABIArgInfo::Default:
      ArgTys.push_back(Ty);
      break;
     
    case ABIArgInfo::Expand:
      GetExpandedTypes(*begin, ArgTys);
      break;
    }
  }

  return llvm::FunctionType::get(ResultType, ArgTys, IsVariadic);
}

bool CodeGenModule::ReturnTypeUsesSret(QualType RetTy) {
  return getABIReturnInfo(RetTy, getTypes()).isStructRet();
}

void CodeGenModule::ConstructAttributeList(const Decl *TargetDecl,
                                           ArgTypeIterator begin,
                                           ArgTypeIterator end,
                                           AttributeListType &PAL) {
  unsigned FuncAttrs = 0;
  unsigned RetAttrs = 0;

  if (TargetDecl) {
    if (TargetDecl->getAttr<NoThrowAttr>())
      FuncAttrs |= llvm::Attribute::NoUnwind;
    if (TargetDecl->getAttr<NoReturnAttr>())
      FuncAttrs |= llvm::Attribute::NoReturn;
    if (TargetDecl->getAttr<PureAttr>())
      FuncAttrs |= llvm::Attribute::ReadOnly;
    if (TargetDecl->getAttr<ConstAttr>())
      FuncAttrs |= llvm::Attribute::ReadNone;
  }

  QualType RetTy = *begin;
  unsigned Index = 1;
  ABIArgInfo RetAI = getABIReturnInfo(RetTy, getTypes());
  switch (RetAI.getKind()) {
  case ABIArgInfo::Default:
    if (RetTy->isPromotableIntegerType()) {
      if (RetTy->isSignedIntegerType()) {
        RetAttrs |= llvm::Attribute::SExt;
      } else if (RetTy->isUnsignedIntegerType()) {
        RetAttrs |= llvm::Attribute::ZExt;
      }
    }
    break;

  case ABIArgInfo::StructRet:
    PAL.push_back(llvm::AttributeWithIndex::get(Index, 
                                                  llvm::Attribute::StructRet|
                                                  llvm::Attribute::NoAlias));
    ++Index;
    break;

  case ABIArgInfo::Coerce:
    break;

  case ABIArgInfo::ByVal:
  case ABIArgInfo::Expand:
    assert(0 && "Invalid ABI kind for return argument");    
  }

  if (RetAttrs)
    PAL.push_back(llvm::AttributeWithIndex::get(0, RetAttrs));
  for (++begin; begin != end; ++begin) {
    QualType ParamType = *begin;
    unsigned Attributes = 0;
    ABIArgInfo AI = getABIArgumentInfo(ParamType, getTypes());
    
    switch (AI.getKind()) {
    case ABIArgInfo::StructRet:
    case ABIArgInfo::Coerce:
      assert(0 && "Invalid ABI kind for non-return argument");
    
    case ABIArgInfo::ByVal:
      Attributes |= llvm::Attribute::ByVal;
      assert(AI.getByValAlignment() == 0 && "FIXME: alignment unhandled");
      break;
      
    case ABIArgInfo::Default:
      if (ParamType->isPromotableIntegerType()) {
        if (ParamType->isSignedIntegerType()) {
          Attributes |= llvm::Attribute::SExt;
        } else if (ParamType->isUnsignedIntegerType()) {
          Attributes |= llvm::Attribute::ZExt;
        }
      }
      break;
     
    case ABIArgInfo::Expand: {
      std::vector<const llvm::Type*> Tys;  
      // FIXME: This is rather inefficient. Do we ever actually need
      // to do anything here? The result should be just reconstructed
      // on the other side, so extension should be a non-issue.
      getTypes().GetExpandedTypes(ParamType, Tys);
      Index += Tys.size();
      continue;
    }
    }
      
    if (Attributes)
      PAL.push_back(llvm::AttributeWithIndex::get(Index, Attributes));
    ++Index;
  }
  if (FuncAttrs)
    PAL.push_back(llvm::AttributeWithIndex::get(~0, FuncAttrs));

}

void CodeGenFunction::EmitFunctionProlog(llvm::Function *Fn,
                                         QualType RetTy, 
                                         const FunctionArgList &Args) {
  // Emit allocs for param decls.  Give the LLVM Argument nodes names.
  llvm::Function::arg_iterator AI = Fn->arg_begin();
  
  // Name the struct return argument.
  if (CGM.ReturnTypeUsesSret(RetTy)) {
    AI->setName("agg.result");
    ++AI;
  }
     
  for (FunctionArgList::const_iterator i = Args.begin(), e = Args.end();
       i != e; ++i) {
    const VarDecl *Arg = i->first;
    QualType Ty = i->second;
    ABIArgInfo ArgI = getABIArgumentInfo(Ty, CGM.getTypes());

    switch (ArgI.getKind()) {
    case ABIArgInfo::ByVal: 
    case ABIArgInfo::Default: {
      assert(AI != Fn->arg_end() && "Argument mismatch!");
      llvm::Value* V = AI;
      if (!getContext().typesAreCompatible(Ty, Arg->getType())) {
        // This must be a promotion, for something like
        // "void a(x) short x; {..."
        V = EmitScalarConversion(V, Ty, Arg->getType());
      }
      EmitParmDecl(*Arg, V);
      break;
    }
      
    case ABIArgInfo::Expand: {
      // If this was structure was expand into multiple arguments then
      // we need to create a temporary and reconstruct it from the
      // arguments.
      std::string Name = Arg->getNameAsString();
      llvm::Value *Temp = CreateTempAlloca(ConvertType(Ty), 
                                           (Name + ".addr").c_str());
      // FIXME: What are the right qualifiers here?
      llvm::Function::arg_iterator End = 
        ExpandTypeFromArgs(Ty, LValue::MakeAddr(Temp,0), AI);      
      EmitParmDecl(*Arg, Temp);

      // Name the arguments used in expansion and increment AI.
      unsigned Index = 0;
      for (; AI != End; ++AI, ++Index)
        AI->setName(Name + "." + llvm::utostr(Index));
      continue;
    }
      
    case ABIArgInfo::Coerce:
    case ABIArgInfo::StructRet:
      assert(0 && "Invalid ABI kind for non-return argument");        
    }

    ++AI;
  }
  assert(AI == Fn->arg_end() && "Argument mismatch!");
}

void CodeGenFunction::EmitFunctionEpilog(QualType RetTy, 
                                         llvm::Value *ReturnValue) {
  llvm::Value *RV = 0;

  // Functions with no result always return void.
  if (ReturnValue) { 
    ABIArgInfo RetAI = getABIReturnInfo(RetTy, CGM.getTypes());
    
    switch (RetAI.getKind()) {
    case ABIArgInfo::StructRet:
      if (RetTy->isAnyComplexType()) {
        // FIXME: Volatile
        ComplexPairTy RT = LoadComplexFromAddr(ReturnValue, false);
        StoreComplexToAddr(RT, CurFn->arg_begin(), false);
      } else if (CodeGenFunction::hasAggregateLLVMType(RetTy)) {
        EmitAggregateCopy(CurFn->arg_begin(), ReturnValue, RetTy);
      } else {
        Builder.CreateStore(Builder.CreateLoad(ReturnValue), 
                            CurFn->arg_begin());
      }
      break;

    case ABIArgInfo::Default:
      RV = Builder.CreateLoad(ReturnValue);
      break;

    case ABIArgInfo::Coerce: {
      const llvm::Type *CoerceToPTy = 
        llvm::PointerType::getUnqual(RetAI.getCoerceToType());
      RV = Builder.CreateLoad(Builder.CreateBitCast(ReturnValue, CoerceToPTy));
      break;
    }

    case ABIArgInfo::ByVal:
    case ABIArgInfo::Expand:
      assert(0 && "Invalid ABI kind for return argument");    
    }
  }
  
  if (RV) {
    Builder.CreateRet(RV);
  } else {
    Builder.CreateRetVoid();
  }
}

RValue CodeGenFunction::EmitCall(llvm::Value *Callee, 
                                 QualType RetTy, 
                                 const CallArgList &CallArgs) {
  llvm::SmallVector<llvm::Value*, 16> Args;

  // Handle struct-return functions by passing a pointer to the
  // location that we would like to return into.
  ABIArgInfo RetAI = getABIReturnInfo(RetTy, CGM.getTypes());
  switch (RetAI.getKind()) {
  case ABIArgInfo::StructRet:
    // Create a temporary alloca to hold the result of the call. :(
    Args.push_back(CreateTempAlloca(ConvertType(RetTy)));
    break;
    
  case ABIArgInfo::Default:
  case ABIArgInfo::Coerce:
    break;

  case ABIArgInfo::ByVal:
  case ABIArgInfo::Expand:
    assert(0 && "Invalid ABI kind for return argument");    
  }
  
  for (CallArgList::const_iterator I = CallArgs.begin(), E = CallArgs.end(); 
       I != E; ++I) {
    ABIArgInfo ArgInfo = getABIArgumentInfo(I->second, CGM.getTypes());
    RValue RV = I->first;

    switch (ArgInfo.getKind()) {
    case ABIArgInfo::ByVal: // Default is byval
    case ABIArgInfo::Default:      
      if (RV.isScalar()) {
        Args.push_back(RV.getScalarVal());
      } else if (RV.isComplex()) {
        // Make a temporary alloca to pass the argument.
        Args.push_back(CreateTempAlloca(ConvertType(I->second)));
        StoreComplexToAddr(RV.getComplexVal(), Args.back(), false); 
      } else {
        Args.push_back(RV.getAggregateAddr());
      }
      break;
     
    case ABIArgInfo::StructRet:
    case ABIArgInfo::Coerce:
      assert(0 && "Invalid ABI kind for non-return argument");
      break;

    case ABIArgInfo::Expand:
      ExpandTypeToArgs(I->second, RV, Args);
      break;
    }
  }
  
  llvm::CallInst *CI = Builder.CreateCall(Callee,&Args[0],&Args[0]+Args.size());
  CGCallInfo CallInfo(RetTy, CallArgs);

  // FIXME: Provide TargetDecl so nounwind, noreturn, etc, etc get set.
  CodeGen::AttributeListType AttributeList;
  CGM.ConstructAttributeList(0, 
                             CallInfo.argtypes_begin(), CallInfo.argtypes_end(),
                             AttributeList);
  CI->setAttributes(llvm::AttrListPtr::get(AttributeList.begin(), 
                                         AttributeList.size()));  

  if (const llvm::Function *F = dyn_cast<llvm::Function>(Callee))
    CI->setCallingConv(F->getCallingConv());
  if (CI->getType() != llvm::Type::VoidTy)
    CI->setName("call");

  switch (RetAI.getKind()) {
  case ABIArgInfo::StructRet:
    if (RetTy->isAnyComplexType())
      return RValue::getComplex(LoadComplexFromAddr(Args[0], false));
    else if (CodeGenFunction::hasAggregateLLVMType(RetTy))
      return RValue::getAggregate(Args[0]);
    else 
      return RValue::get(Builder.CreateLoad(Args[0]));

  case ABIArgInfo::Default:
    return RValue::get(RetTy->isVoidType() ? 0 : CI);

  case ABIArgInfo::Coerce: {
    const llvm::Type *CoerceToPTy = 
      llvm::PointerType::getUnqual(RetAI.getCoerceToType());
    llvm::Value *V = CreateTempAlloca(ConvertType(RetTy), "tmp");
    Builder.CreateStore(CI, Builder.CreateBitCast(V, CoerceToPTy));
    if (RetTy->isAnyComplexType())
      return RValue::getComplex(LoadComplexFromAddr(V, false));
    else
      return RValue::getAggregate(V);
  }

  case ABIArgInfo::ByVal:
  case ABIArgInfo::Expand:
    assert(0 && "Invalid ABI kind for return argument");    
  }

  assert(0 && "Unhandled ABIArgInfo::Kind");
  return RValue::get(0);
}