lib/CodeGen/CGExprAgg.cpp

//===--- CGExprAgg.cpp - Emit LLVM Code from Aggregate Expressions --------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code to emit Aggregate Expr nodes as LLVM code.
//
//===----------------------------------------------------------------------===//

#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "CGObjCRuntime.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/StmtVisitor.h"
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Intrinsics.h"
using namespace clang;
using namespace CodeGen;

//===----------------------------------------------------------------------===//
//                        Aggregate Expression Emitter
//===----------------------------------------------------------------------===//

namespace  {
class AggExprEmitter : public StmtVisitor<AggExprEmitter> {
  CodeGenFunction &CGF;
  CGBuilderTy &Builder;
  llvm::Value *DestPtr;
  bool VolatileDest;
  bool IgnoreResult;
  bool IsInitializer;
  bool RequiresGCollection;

  ReturnValueSlot getReturnValueSlot() const {
    // If the destination slot requires garbage collection, we can't
    // use the real return value slot, because we have to use the GC
    // API.
    if (RequiresGCollection) return ReturnValueSlot();

    return ReturnValueSlot(DestPtr, VolatileDest);
  }

public:
  AggExprEmitter(CodeGenFunction &cgf, llvm::Value *destPtr, bool v,
                 bool ignore, bool isinit, bool requiresGCollection)
    : CGF(cgf), Builder(CGF.Builder),
      DestPtr(destPtr), VolatileDest(v), IgnoreResult(ignore),
      IsInitializer(isinit), RequiresGCollection(requiresGCollection) {
  }

  //===--------------------------------------------------------------------===//
  //                               Utilities
  //===--------------------------------------------------------------------===//

  /// EmitAggLoadOfLValue - Given an expression with aggregate type that
  /// represents a value lvalue, this method emits the address of the lvalue,
  /// then loads the result into DestPtr.
  void EmitAggLoadOfLValue(const Expr *E);

  /// EmitFinalDestCopy - Perform the final copy to DestPtr, if desired.
  void EmitFinalDestCopy(const Expr *E, LValue Src, bool Ignore = false);
  void EmitFinalDestCopy(const Expr *E, RValue Src, bool Ignore = false);

  void EmitGCMove(const Expr *E, RValue Src);

  bool TypeRequiresGCollection(QualType T);

  //===--------------------------------------------------------------------===//
  //                            Visitor Methods
  //===--------------------------------------------------------------------===//

  void VisitStmt(Stmt *S) {
    CGF.ErrorUnsupported(S, "aggregate expression");
  }
  void VisitParenExpr(ParenExpr *PE) { Visit(PE->getSubExpr()); }
  void VisitUnaryExtension(UnaryOperator *E) { Visit(E->getSubExpr()); }

  // l-values.
  void VisitDeclRefExpr(DeclRefExpr *DRE) { EmitAggLoadOfLValue(DRE); }
  void VisitMemberExpr(MemberExpr *ME) { EmitAggLoadOfLValue(ME); }
  void VisitUnaryDeref(UnaryOperator *E) { EmitAggLoadOfLValue(E); }
  void VisitStringLiteral(StringLiteral *E) { EmitAggLoadOfLValue(E); }
  void VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
    EmitAggLoadOfLValue(E);
  }
  void VisitArraySubscriptExpr(ArraySubscriptExpr *E) {
    EmitAggLoadOfLValue(E);
  }
  void VisitBlockDeclRefExpr(const BlockDeclRefExpr *E) {
    EmitAggLoadOfLValue(E);
  }
  void VisitPredefinedExpr(const PredefinedExpr *E) {
    EmitAggLoadOfLValue(E);
  }

  // Operators.
  void VisitCastExpr(CastExpr *E);
  void VisitCallExpr(const CallExpr *E);
  void VisitStmtExpr(const StmtExpr *E);
  void VisitBinaryOperator(const BinaryOperator *BO);
  void VisitPointerToDataMemberBinaryOperator(const BinaryOperator *BO);
  void VisitBinAssign(const BinaryOperator *E);
  void VisitBinComma(const BinaryOperator *E);

  void VisitObjCMessageExpr(ObjCMessageExpr *E);
  void VisitObjCIvarRefExpr(ObjCIvarRefExpr *E) {
    EmitAggLoadOfLValue(E);
  }
  void VisitObjCPropertyRefExpr(ObjCPropertyRefExpr *E);
  void VisitObjCImplicitSetterGetterRefExpr(ObjCImplicitSetterGetterRefExpr *E);

  void VisitConditionalOperator(const ConditionalOperator *CO);
  void VisitChooseExpr(const ChooseExpr *CE);
  void VisitInitListExpr(InitListExpr *E);
  void VisitImplicitValueInitExpr(ImplicitValueInitExpr *E);
  void VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
    Visit(DAE->getExpr());
  }
  void VisitCXXBindTemporaryExpr(CXXBindTemporaryExpr *E);
  void VisitCXXConstructExpr(const CXXConstructExpr *E);
  void VisitCXXExprWithTemporaries(CXXExprWithTemporaries *E);
  void VisitCXXScalarValueInitExpr(CXXScalarValueInitExpr *E);
  void VisitCXXTypeidExpr(CXXTypeidExpr *E) { EmitAggLoadOfLValue(E); }

  void VisitVAArgExpr(VAArgExpr *E);

  void EmitInitializationToLValue(Expr *E, LValue Address, QualType T);
  void EmitNullInitializationToLValue(LValue Address, QualType T);
  //  case Expr::ChooseExprClass:
  void VisitCXXThrowExpr(const CXXThrowExpr *E) { CGF.EmitCXXThrowExpr(E); }
};
}  // end anonymous namespace.

//===----------------------------------------------------------------------===//
//                                Utilities
//===----------------------------------------------------------------------===//

/// EmitAggLoadOfLValue - Given an expression with aggregate type that
/// represents a value lvalue, this method emits the address of the lvalue,
/// then loads the result into DestPtr.
void AggExprEmitter::EmitAggLoadOfLValue(const Expr *E) {
  LValue LV = CGF.EmitLValue(E);
  EmitFinalDestCopy(E, LV);
}

/// \brief True if the given aggregate type requires special GC API calls.
bool AggExprEmitter::TypeRequiresGCollection(QualType T) {
  // Only record types have members that might require garbage collection.
  const RecordType *RecordTy = T->getAs<RecordType>();
  if (!RecordTy) return false;

  // Don't mess with non-trivial C++ types.
  RecordDecl *Record = RecordTy->getDecl();
  if (isa<CXXRecordDecl>(Record) &&
      (!cast<CXXRecordDecl>(Record)->hasTrivialCopyConstructor() ||
       !cast<CXXRecordDecl>(Record)->hasTrivialDestructor()))
    return false;

  // Check whether the type has an object member.
  return Record->hasObjectMember();
}

/// \brief Perform the final move to DestPtr if RequiresGCollection is set.
///
/// The idea is that you do something like this:
///   RValue Result = EmitSomething(..., getReturnValueSlot());
///   EmitGCMove(E, Result);
/// If GC doesn't interfere, this will cause the result to be emitted
/// directly into the return value slot.  If GC does interfere, a final
/// move will be performed.
void AggExprEmitter::EmitGCMove(const Expr *E, RValue Src) {
  if (RequiresGCollection) {
    std::pair<uint64_t, unsigned> TypeInfo = 
      CGF.getContext().getTypeInfo(E->getType());
    unsigned long size = TypeInfo.first/8;
    const llvm::Type *SizeTy = CGF.ConvertType(CGF.getContext().getSizeType());
    llvm::Value *SizeVal = llvm::ConstantInt::get(SizeTy, size);
    CGF.CGM.getObjCRuntime().EmitGCMemmoveCollectable(CGF, DestPtr,
                                                    Src.getAggregateAddr(),
                                                    SizeVal);
  }
}

/// EmitFinalDestCopy - Perform the final copy to DestPtr, if desired.
void AggExprEmitter::EmitFinalDestCopy(const Expr *E, RValue Src, bool Ignore) {
  assert(Src.isAggregate() && "value must be aggregate value!");

  // If the result is ignored, don't copy from the value.
  if (DestPtr == 0) {
    if (!Src.isVolatileQualified() || (IgnoreResult && Ignore))
      return;
    // If the source is volatile, we must read from it; to do that, we need
    // some place to put it.
    DestPtr = CGF.CreateMemTemp(E->getType(), "agg.tmp");
  }

  if (RequiresGCollection) {
    std::pair<uint64_t, unsigned> TypeInfo = 
    CGF.getContext().getTypeInfo(E->getType());
    unsigned long size = TypeInfo.first/8;
    const llvm::Type *SizeTy = CGF.ConvertType(CGF.getContext().getSizeType());
    llvm::Value *SizeVal = llvm::ConstantInt::get(SizeTy, size);
    CGF.CGM.getObjCRuntime().EmitGCMemmoveCollectable(CGF,
                                              DestPtr, Src.getAggregateAddr(),
                                              SizeVal);
    return;
  }
  // If the result of the assignment is used, copy the LHS there also.
  // FIXME: Pass VolatileDest as well.  I think we also need to merge volatile
  // from the source as well, as we can't eliminate it if either operand
  // is volatile, unless copy has volatile for both source and destination..
  CGF.EmitAggregateCopy(DestPtr, Src.getAggregateAddr(), E->getType(),
                        VolatileDest|Src.isVolatileQualified());
}

/// EmitFinalDestCopy - Perform the final copy to DestPtr, if desired.
void AggExprEmitter::EmitFinalDestCopy(const Expr *E, LValue Src, bool Ignore) {
  assert(Src.isSimple() && "Can't have aggregate bitfield, vector, etc");

  EmitFinalDestCopy(E, RValue::getAggregate(Src.getAddress(),
                                            Src.isVolatileQualified()),
                    Ignore);
}

//===----------------------------------------------------------------------===//
//                            Visitor Methods
//===----------------------------------------------------------------------===//

void AggExprEmitter::VisitCastExpr(CastExpr *E) {
  if (!DestPtr && E->getCastKind() != CastExpr::CK_Dynamic) {
    Visit(E->getSubExpr());
    return;
  }

  switch (E->getCastKind()) {
  default: assert(0 && "Unhandled cast kind!");

  case CastExpr::CK_Dynamic: {
    assert(isa<CXXDynamicCastExpr>(E) && "CK_Dynamic without a dynamic_cast?");
    LValue LV = CGF.EmitCheckedLValue(E->getSubExpr());
    // FIXME: Do we also need to handle property references here?
    if (LV.isSimple())
      CGF.EmitDynamicCast(LV.getAddress(), cast<CXXDynamicCastExpr>(E));
    else
      CGF.CGM.ErrorUnsupported(E, "non-simple lvalue dynamic_cast");
    
    if (DestPtr)
      CGF.CGM.ErrorUnsupported(E, "lvalue dynamic_cast with a destination");      
    break;
  }
      
  case CastExpr::CK_ToUnion: {
    // GCC union extension
    QualType Ty = E->getSubExpr()->getType();
    QualType PtrTy = CGF.getContext().getPointerType(Ty);
    llvm::Value *CastPtr = Builder.CreateBitCast(DestPtr,
                                                 CGF.ConvertType(PtrTy));
    EmitInitializationToLValue(E->getSubExpr(), CGF.MakeAddrLValue(CastPtr, Ty),
                               Ty);
    break;
  }

  case CastExpr::CK_DerivedToBase:
  case CastExpr::CK_BaseToDerived:
  case CastExpr::CK_UncheckedDerivedToBase: {
    assert(0 && "cannot perform hierarchy conversion in EmitAggExpr: "
                "should have been unpacked before we got here");
    break;
  }

  // FIXME: Remove the CK_Unknown check here.
  case CastExpr::CK_Unknown:
  case CastExpr::CK_NoOp:
  case CastExpr::CK_UserDefinedConversion:
  case CastExpr::CK_ConstructorConversion:
    assert(CGF.getContext().hasSameUnqualifiedType(E->getSubExpr()->getType(),
                                                   E->getType()) &&
           "Implicit cast types must be compatible");
    Visit(E->getSubExpr());
    break;

  case CastExpr::CK_LValueBitCast:
    llvm_unreachable("there are no lvalue bit-casts on aggregates");
    break;
  }
}

void AggExprEmitter::VisitCallExpr(const CallExpr *E) {
  if (E->getCallReturnType()->isReferenceType()) {
    EmitAggLoadOfLValue(E);
    return;
  }

  RValue RV = CGF.EmitCallExpr(E, getReturnValueSlot());
  EmitGCMove(E, RV);
}

void AggExprEmitter::VisitObjCMessageExpr(ObjCMessageExpr *E) {
  RValue RV = CGF.EmitObjCMessageExpr(E, getReturnValueSlot());
  EmitGCMove(E, RV);
}

void AggExprEmitter::VisitObjCPropertyRefExpr(ObjCPropertyRefExpr *E) {
  RValue RV = CGF.EmitObjCPropertyGet(E, getReturnValueSlot());
  EmitGCMove(E, RV);
}

void AggExprEmitter::VisitObjCImplicitSetterGetterRefExpr(
                                   ObjCImplicitSetterGetterRefExpr *E) {
  RValue RV = CGF.EmitObjCPropertyGet(E, getReturnValueSlot());
  EmitGCMove(E, RV);
}

void AggExprEmitter::VisitBinComma(const BinaryOperator *E) {
  CGF.EmitAnyExpr(E->getLHS(), 0, false, true);
  CGF.EmitAggExpr(E->getRHS(), DestPtr, VolatileDest,
                  /*IgnoreResult=*/false, IsInitializer);
}

void AggExprEmitter::VisitStmtExpr(const StmtExpr *E) {
  CGF.EmitCompoundStmt(*E->getSubStmt(), true, DestPtr, VolatileDest);
}

void AggExprEmitter::VisitBinaryOperator(const BinaryOperator *E) {
  if (E->getOpcode() == BinaryOperator::PtrMemD ||
      E->getOpcode() == BinaryOperator::PtrMemI)
    VisitPointerToDataMemberBinaryOperator(E);
  else
    CGF.ErrorUnsupported(E, "aggregate binary expression");
}

void AggExprEmitter::VisitPointerToDataMemberBinaryOperator(
                                                    const BinaryOperator *E) {
  LValue LV = CGF.EmitPointerToDataMemberBinaryExpr(E);
  EmitFinalDestCopy(E, LV);
}

void AggExprEmitter::VisitBinAssign(const BinaryOperator *E) {
  // For an assignment to work, the value on the right has
  // to be compatible with the value on the left.
  assert(CGF.getContext().hasSameUnqualifiedType(E->getLHS()->getType(),
                                                 E->getRHS()->getType())
         && "Invalid assignment");
  LValue LHS = CGF.EmitLValue(E->getLHS());

  // We have to special case property setters, otherwise we must have
  // a simple lvalue (no aggregates inside vectors, bitfields).
  if (LHS.isPropertyRef()) {
    llvm::Value *AggLoc = DestPtr;
    if (!AggLoc)
      AggLoc = CGF.CreateMemTemp(E->getRHS()->getType());
    CGF.EmitAggExpr(E->getRHS(), AggLoc, VolatileDest);
    CGF.EmitObjCPropertySet(LHS.getPropertyRefExpr(),
                            RValue::getAggregate(AggLoc, VolatileDest));
  } else if (LHS.isKVCRef()) {
    llvm::Value *AggLoc = DestPtr;
    if (!AggLoc)
      AggLoc = CGF.CreateMemTemp(E->getRHS()->getType());
    CGF.EmitAggExpr(E->getRHS(), AggLoc, VolatileDest);
    CGF.EmitObjCPropertySet(LHS.getKVCRefExpr(),
                            RValue::getAggregate(AggLoc, VolatileDest));
  } else {
    bool RequiresGCollection = false;
    if (CGF.getContext().getLangOptions().getGCMode())
      RequiresGCollection = TypeRequiresGCollection(E->getLHS()->getType());

    // Codegen the RHS so that it stores directly into the LHS.
    CGF.EmitAggExpr(E->getRHS(), LHS.getAddress(), LHS.isVolatileQualified(),
                    false, false, RequiresGCollection);
    EmitFinalDestCopy(E, LHS, true);
  }
}

void AggExprEmitter::VisitConditionalOperator(const ConditionalOperator *E) {
  if (!E->getLHS()) {
    CGF.ErrorUnsupported(E, "conditional operator with missing LHS");
    return;
  }

  llvm::BasicBlock *LHSBlock = CGF.createBasicBlock("cond.true");
  llvm::BasicBlock *RHSBlock = CGF.createBasicBlock("cond.false");
  llvm::BasicBlock *ContBlock = CGF.createBasicBlock("cond.end");

  CGF.EmitBranchOnBoolExpr(E->getCond(), LHSBlock, RHSBlock);

  CGF.BeginConditionalBranch();
  CGF.EmitBlock(LHSBlock);

  // Handle the GNU extension for missing LHS.
  assert(E->getLHS() && "Must have LHS for aggregate value");

  Visit(E->getLHS());
  CGF.EndConditionalBranch();
  CGF.EmitBranch(ContBlock);

  CGF.BeginConditionalBranch();
  CGF.EmitBlock(RHSBlock);

  Visit(E->getRHS());
  CGF.EndConditionalBranch();
  CGF.EmitBranch(ContBlock);

  CGF.EmitBlock(ContBlock);
}

void AggExprEmitter::VisitChooseExpr(const ChooseExpr *CE) {
  Visit(CE->getChosenSubExpr(CGF.getContext()));
}

void AggExprEmitter::VisitVAArgExpr(VAArgExpr *VE) {
  llvm::Value *ArgValue = CGF.EmitVAListRef(VE->getSubExpr());
  llvm::Value *ArgPtr = CGF.EmitVAArg(ArgValue, VE->getType());

  if (!ArgPtr) {
    CGF.ErrorUnsupported(VE, "aggregate va_arg expression");
    return;
  }

  EmitFinalDestCopy(VE, CGF.MakeAddrLValue(ArgPtr, VE->getType()));
}

void AggExprEmitter::VisitCXXBindTemporaryExpr(CXXBindTemporaryExpr *E) {
  llvm::Value *Val = DestPtr;

  if (!Val) {
    // Create a temporary variable.
    Val = CGF.CreateMemTemp(E->getType(), "tmp");

    // FIXME: volatile
    CGF.EmitAggExpr(E->getSubExpr(), Val, false);
  } else
    Visit(E->getSubExpr());

  // Don't make this a live temporary if we're emitting an initializer expr.
  if (!IsInitializer)
    CGF.EmitCXXTemporary(E->getTemporary(), Val);
}

void
AggExprEmitter::VisitCXXConstructExpr(const CXXConstructExpr *E) {
  llvm::Value *Val = DestPtr;

  if (!Val) // Create a temporary variable.
    Val = CGF.CreateMemTemp(E->getType(), "tmp");

  if (E->requiresZeroInitialization())
    EmitNullInitializationToLValue(CGF.MakeAddrLValue(Val, E->getType()),
                                   E->getType());

  CGF.EmitCXXConstructExpr(Val, E);
}

void AggExprEmitter::VisitCXXExprWithTemporaries(CXXExprWithTemporaries *E) {
  llvm::Value *Val = DestPtr;

  CGF.EmitCXXExprWithTemporaries(E, Val, VolatileDest, IsInitializer);
}

void AggExprEmitter::VisitCXXScalarValueInitExpr(CXXScalarValueInitExpr *E) {
  llvm::Value *Val = DestPtr;

  if (!Val) {
    // Create a temporary variable.
    Val = CGF.CreateMemTemp(E->getType(), "tmp");
  }
  EmitNullInitializationToLValue(CGF.MakeAddrLValue(Val, E->getType()),
                                 E->getType());
}

void AggExprEmitter::VisitImplicitValueInitExpr(ImplicitValueInitExpr *E) {
  llvm::Value *Val = DestPtr;

  if (!Val) {
    // Create a temporary variable.
    Val = CGF.CreateMemTemp(E->getType(), "tmp");
  }
  EmitNullInitializationToLValue(CGF.MakeAddrLValue(Val, E->getType()),
                                 E->getType());
}

void 
AggExprEmitter::EmitInitializationToLValue(Expr* E, LValue LV, QualType T) {
  // FIXME: Ignore result?
  // FIXME: Are initializers affected by volatile?
  if (isa<ImplicitValueInitExpr>(E)) {
    EmitNullInitializationToLValue(LV, T);
  } else if (T->isReferenceType()) {
    RValue RV = CGF.EmitReferenceBindingToExpr(E, /*InitializedDecl=*/0);
    CGF.EmitStoreThroughLValue(RV, LV, T);
  } else if (T->isAnyComplexType()) {
    CGF.EmitComplexExprIntoAddr(E, LV.getAddress(), false);
  } else if (CGF.hasAggregateLLVMType(T)) {
    CGF.EmitAnyExpr(E, LV.getAddress(), false);
  } else {
    CGF.EmitStoreThroughLValue(CGF.EmitAnyExpr(E), LV, T);
  }
}

void AggExprEmitter::EmitNullInitializationToLValue(LValue LV, QualType T) {
  if (!CGF.hasAggregateLLVMType(T)) {
    // For non-aggregates, we can store zero
    llvm::Value *Null = llvm::Constant::getNullValue(CGF.ConvertType(T));
    CGF.EmitStoreThroughLValue(RValue::get(Null), LV, T);
  } else {
    // There's a potential optimization opportunity in combining
    // memsets; that would be easy for arrays, but relatively
    // difficult for structures with the current code.
    CGF.EmitNullInitialization(LV.getAddress(), T);
  }
}

void AggExprEmitter::VisitInitListExpr(InitListExpr *E) {
#if 0
  // FIXME: Assess perf here?  Figure out what cases are worth optimizing here
  // (Length of globals? Chunks of zeroed-out space?).
  //
  // If we can, prefer a copy from a global; this is a lot less code for long
  // globals, and it's easier for the current optimizers to analyze.
  if (llvm::Constant* C = CGF.CGM.EmitConstantExpr(E, E->getType(), &CGF)) {
    llvm::GlobalVariable* GV =
    new llvm::GlobalVariable(CGF.CGM.getModule(), C->getType(), true,
                             llvm::GlobalValue::InternalLinkage, C, "");
    EmitFinalDestCopy(E, CGF.MakeAddrLValue(GV, E->getType()));
    return;
  }
#endif
  if (E->hadArrayRangeDesignator()) {
    CGF.ErrorUnsupported(E, "GNU array range designator extension");
  }

  // Handle initialization of an array.
  if (E->getType()->isArrayType()) {
    const llvm::PointerType *APType =
      cast<llvm::PointerType>(DestPtr->getType());
    const llvm::ArrayType *AType =
      cast<llvm::ArrayType>(APType->getElementType());

    uint64_t NumInitElements = E->getNumInits();

    if (E->getNumInits() > 0) {
      QualType T1 = E->getType();
      QualType T2 = E->getInit(0)->getType();
      if (CGF.getContext().hasSameUnqualifiedType(T1, T2)) {
        EmitAggLoadOfLValue(E->getInit(0));
        return;
      }
    }

    uint64_t NumArrayElements = AType->getNumElements();
    QualType ElementType = CGF.getContext().getCanonicalType(E->getType());
    ElementType = CGF.getContext().getAsArrayType(ElementType)->getElementType();

    // FIXME: were we intentionally ignoring address spaces and GC attributes?

    for (uint64_t i = 0; i != NumArrayElements; ++i) {
      llvm::Value *NextVal = Builder.CreateStructGEP(DestPtr, i, ".array");
      LValue LV = CGF.MakeAddrLValue(NextVal, ElementType);
      if (i < NumInitElements)
        EmitInitializationToLValue(E->getInit(i), LV, ElementType);

      else
        EmitNullInitializationToLValue(LV, ElementType);
    }
    return;
  }

  assert(E->getType()->isRecordType() && "Only support structs/unions here!");

  // Do struct initialization; this code just sets each individual member
  // to the approprate value.  This makes bitfield support automatic;
  // the disadvantage is that the generated code is more difficult for
  // the optimizer, especially with bitfields.
  unsigned NumInitElements = E->getNumInits();
  RecordDecl *SD = E->getType()->getAs<RecordType>()->getDecl();
  unsigned CurInitVal = 0;

  if (E->getType()->isUnionType()) {
    // Only initialize one field of a union. The field itself is
    // specified by the initializer list.
    if (!E->getInitializedFieldInUnion()) {
      // Empty union; we have nothing to do.

#ifndef NDEBUG
      // Make sure that it's really an empty and not a failure of
      // semantic analysis.
      for (RecordDecl::field_iterator Field = SD->field_begin(),
                                   FieldEnd = SD->field_end();
           Field != FieldEnd; ++Field)
        assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
#endif
      return;
    }

    // FIXME: volatility
    FieldDecl *Field = E->getInitializedFieldInUnion();
    LValue FieldLoc = CGF.EmitLValueForFieldInitialization(DestPtr, Field, 0);

    if (NumInitElements) {
      // Store the initializer into the field
      EmitInitializationToLValue(E->getInit(0), FieldLoc, Field->getType());
    } else {
      // Default-initialize to null
      EmitNullInitializationToLValue(FieldLoc, Field->getType());
    }

    return;
  }
  
  // If we're initializing the whole aggregate, just do it in place.
  // FIXME: This is a hack around an AST bug (PR6537).
  if (NumInitElements == 1 && E->getType() == E->getInit(0)->getType()) {
    EmitInitializationToLValue(E->getInit(0),
                               CGF.MakeAddrLValue(DestPtr, E->getType()),
                               E->getType());
    return;
  }
  

  // Here we iterate over the fields; this makes it simpler to both
  // default-initialize fields and skip over unnamed fields.
  for (RecordDecl::field_iterator Field = SD->field_begin(),
                               FieldEnd = SD->field_end();
       Field != FieldEnd; ++Field) {
    // We're done once we hit the flexible array member
    if (Field->getType()->isIncompleteArrayType())
      break;

    if (Field->isUnnamedBitfield())
      continue;

    // FIXME: volatility
    LValue FieldLoc = CGF.EmitLValueForFieldInitialization(DestPtr, *Field, 0);
    // We never generate write-barries for initialized fields.
    FieldLoc.setNonGC(true);
    if (CurInitVal < NumInitElements) {
      // Store the initializer into the field.
      EmitInitializationToLValue(E->getInit(CurInitVal++), FieldLoc,
                                 Field->getType());
    } else {
      // We're out of initalizers; default-initialize to null
      EmitNullInitializationToLValue(FieldLoc, Field->getType());
    }
  }
}

//===----------------------------------------------------------------------===//
//                        Entry Points into this File
//===----------------------------------------------------------------------===//

/// EmitAggExpr - Emit the computation of the specified expression of aggregate
/// type.  The result is computed into DestPtr.  Note that if DestPtr is null,
/// the value of the aggregate expression is not needed.  If VolatileDest is
/// true, DestPtr cannot be 0.
//
// FIXME: Take Qualifiers object.
void CodeGenFunction::EmitAggExpr(const Expr *E, llvm::Value *DestPtr,
                                  bool VolatileDest, bool IgnoreResult,
                                  bool IsInitializer,
                                  bool RequiresGCollection) {
  assert(E && hasAggregateLLVMType(E->getType()) &&
         "Invalid aggregate expression to emit");
  assert ((DestPtr != 0 || VolatileDest == false)
          && "volatile aggregate can't be 0");

  AggExprEmitter(*this, DestPtr, VolatileDest, IgnoreResult, IsInitializer,
                 RequiresGCollection)
    .Visit(const_cast<Expr*>(E));
}

LValue CodeGenFunction::EmitAggExprToLValue(const Expr *E) {
  assert(hasAggregateLLVMType(E->getType()) && "Invalid argument!");
  llvm::Value *Temp = CreateMemTemp(E->getType());
  LValue LV = MakeAddrLValue(Temp, E->getType());
  EmitAggExpr(E, Temp, LV.isVolatileQualified());
  return LV;
}

void CodeGenFunction::EmitAggregateCopy(llvm::Value *DestPtr,
                                        llvm::Value *SrcPtr, QualType Ty,
                                        bool isVolatile) {
  assert(!Ty->isAnyComplexType() && "Shouldn't happen for complex");

  if (getContext().getLangOptions().CPlusPlus) {
    if (const RecordType *RT = Ty->getAs<RecordType>()) {
      CXXRecordDecl *Record = cast<CXXRecordDecl>(RT->getDecl());
      assert((Record->hasTrivialCopyConstructor() || 
              Record->hasTrivialCopyAssignment()) &&
             "Trying to aggregate-copy a type without a trivial copy "
             "constructor or assignment operator");
      // Ignore empty classes in C++.
      if (Record->isEmpty())
        return;
    }
  }
  
  // Aggregate assignment turns into llvm.memcpy.  This is almost valid per
  // C99 6.5.16.1p3, which states "If the value being stored in an object is
  // read from another object that overlaps in anyway the storage of the first
  // object, then the overlap shall be exact and the two objects shall have
  // qualified or unqualified versions of a compatible type."
  //
  // memcpy is not defined if the source and destination pointers are exactly
  // equal, but other compilers do this optimization, and almost every memcpy
  // implementation handles this case safely.  If there is a libc that does not
  // safely handle this, we can add a target hook.

  // Get size and alignment info for this aggregate.
  std::pair<uint64_t, unsigned> TypeInfo = getContext().getTypeInfo(Ty);

  // FIXME: Handle variable sized types.

  // FIXME: If we have a volatile struct, the optimizer can remove what might
  // appear to be `extra' memory ops:
  //
  // volatile struct { int i; } a, b;
  //
  // int main() {
  //   a = b;
  //   a = b;
  // }
  //
  // we need to use a different call here.  We use isVolatile to indicate when
  // either the source or the destination is volatile.

  const llvm::PointerType *DPT = cast<llvm::PointerType>(DestPtr->getType());
  const llvm::Type *DBP =
    llvm::Type::getInt8PtrTy(VMContext, DPT->getAddressSpace());
  DestPtr = Builder.CreateBitCast(DestPtr, DBP, "tmp");

  const llvm::PointerType *SPT = cast<llvm::PointerType>(SrcPtr->getType());
  const llvm::Type *SBP =
    llvm::Type::getInt8PtrTy(VMContext, SPT->getAddressSpace());
  SrcPtr = Builder.CreateBitCast(SrcPtr, SBP, "tmp");

  if (const RecordType *RecordTy = Ty->getAs<RecordType>()) {
    RecordDecl *Record = RecordTy->getDecl();
    if (Record->hasObjectMember()) {
      unsigned long size = TypeInfo.first/8;
      const llvm::Type *SizeTy = ConvertType(getContext().getSizeType());
      llvm::Value *SizeVal = llvm::ConstantInt::get(SizeTy, size);
      CGM.getObjCRuntime().EmitGCMemmoveCollectable(*this, DestPtr, SrcPtr, 
                                                    SizeVal);
      return;
    }
  } else if (getContext().getAsArrayType(Ty)) {
    QualType BaseType = getContext().getBaseElementType(Ty);
    if (const RecordType *RecordTy = BaseType->getAs<RecordType>()) {
      if (RecordTy->getDecl()->hasObjectMember()) {
        unsigned long size = TypeInfo.first/8;
        const llvm::Type *SizeTy = ConvertType(getContext().getSizeType());
        llvm::Value *SizeVal = llvm::ConstantInt::get(SizeTy, size);
        CGM.getObjCRuntime().EmitGCMemmoveCollectable(*this, DestPtr, SrcPtr, 
                                                      SizeVal);
        return;
      }
    }
  }
  
  Builder.CreateCall5(CGM.getMemCpyFn(DestPtr->getType(), SrcPtr->getType(),
                                      IntPtrTy),
                      DestPtr, SrcPtr,
                      // TypeInfo.first describes size in bits.
                      llvm::ConstantInt::get(IntPtrTy, TypeInfo.first/8),
                      Builder.getInt32(TypeInfo.second/8),
                      Builder.getInt1(isVolatile));
}