C++ LValue类代码示例

static void EmitOMPAtomicReadExpr(CodeGenFunction &CGF, bool IsSeqCst,
                                  const Expr *X, const Expr *V,
                                  SourceLocation Loc) {
  // v = x;
  assert(V->isLValue() && "V of 'omp atomic read' is not lvalue");
  assert(X->isLValue() && "X of 'omp atomic read' is not lvalue");
  LValue XLValue = CGF.EmitLValue(X);
  LValue VLValue = CGF.EmitLValue(V);
  RValue Res = XLValue.isGlobalReg() ? CGF.EmitLoadOfLValue(XLValue, Loc)
                                     : CGF.EmitAtomicLoad(XLValue, Loc);
  // OpenMP, 2.12.6, atomic Construct
  // Any atomic construct with a seq_cst clause forces the atomically
  // performed operation to include an implicit flush operation without a
  // list.
  if (IsSeqCst)
    CGF.CGM.getOpenMPRuntime().EmitOMPFlush(CGF, llvm::None, Loc);
  switch (CGF.getEvaluationKind(V->getType())) {
  case TEK_Scalar:
    CGF.EmitStoreOfScalar(
        convertToScalarValue(CGF, Res, X->getType(), V->getType()), VLValue);
    break;
  case TEK_Complex:
    CGF.EmitStoreOfComplex(
        convertToComplexValue(CGF, Res, X->getType(), V->getType()), VLValue,
        /*isInit=*/false);
    break;
  case TEK_Aggregate:
    llvm_unreachable("Must be a scalar or complex.");
  }
}

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");

  // FIXME:  __block variables need the RHS evaluated first!
  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()) {
    AggValueSlot Slot = EnsureSlot(E->getRHS()->getType());
    CGF.EmitAggExpr(E->getRHS(), Slot);
    CGF.EmitStoreThroughPropertyRefLValue(Slot.asRValue(), LHS);
  } else {
    bool GCollection = false;
    if (CGF.getContext().getLangOptions().getGCMode())
      GCollection = TypeRequiresGCollection(E->getLHS()->getType());

    // Codegen the RHS so that it stores directly into the LHS.
    AggValueSlot LHSSlot = AggValueSlot::forLValue(LHS, true, 
                                                   GCollection);
    CGF.EmitAggExpr(E->getRHS(), LHSSlot, false);
    EmitFinalDestCopy(E, LHS, true);
  }
}

llvm::Value* CodeGenFunction::EmitAsmInput(const AsmStmt &S,
                                         const TargetInfo::ConstraintInfo &Info,
                                           const Expr *InputExpr,
                                           std::string &ConstraintStr) {
  llvm::Value *Arg;
  if (Info.allowsRegister() || !Info.allowsMemory()) { 
    const llvm::Type *Ty = ConvertType(InputExpr->getType());
    
    if (Ty->isSingleValueType()) {
      Arg = EmitScalarExpr(InputExpr);
    } else {
      InputExpr = InputExpr->IgnoreParenNoopCasts(getContext());
      LValue Dest = EmitLValue(InputExpr);

      uint64_t Size = CGM.getTargetData().getTypeSizeInBits(Ty);
      if (Size <= 64 && llvm::isPowerOf2_64(Size)) {
        Ty = llvm::IntegerType::get(VMContext, Size);
        Ty = llvm::PointerType::getUnqual(Ty);
        
        Arg = Builder.CreateLoad(Builder.CreateBitCast(Dest.getAddress(), Ty));
      } else {
        Arg = Dest.getAddress();
        ConstraintStr += '*';
      }
    }
  } else {
    InputExpr = InputExpr->IgnoreParenNoopCasts(getContext());
    LValue Dest = EmitLValue(InputExpr);
    Arg = Dest.getAddress();
    ConstraintStr += '*';
  }
  
  return Arg;
}

/// 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);
}

static void EmitDeclInit(CodeGenFunction &CGF, const VarDecl &D,
                         llvm::Constant *DeclPtr) {
  assert(D.hasGlobalStorage() && "VarDecl must have global storage!");
  assert(!D.getType()->isReferenceType() && 
         "Should not call EmitDeclInit on a reference!");
  
  ASTContext &Context = CGF.getContext();

  CharUnits alignment = Context.getDeclAlign(&D);
  QualType type = D.getType();
  LValue lv = CGF.MakeAddrLValue(DeclPtr, type, alignment);

  const Expr *Init = D.getInit();
  if (!CGF.hasAggregateLLVMType(type)) {
    CodeGenModule &CGM = CGF.CGM;
    if (lv.isObjCStrong())
      CGM.getObjCRuntime().EmitObjCGlobalAssign(CGF, CGF.EmitScalarExpr(Init),
                                                DeclPtr, D.isThreadSpecified());
    else if (lv.isObjCWeak())
      CGM.getObjCRuntime().EmitObjCWeakAssign(CGF, CGF.EmitScalarExpr(Init),
                                              DeclPtr);
    else
      CGF.EmitScalarInit(Init, &D, lv, false);
  } else if (type->isAnyComplexType()) {
    CGF.EmitComplexExprIntoAddr(Init, DeclPtr, lv.isVolatile());
  } else {
    CGF.EmitAggExpr(Init, AggValueSlot::forLValue(lv,AggValueSlot::IsDestructed,
                                          AggValueSlot::DoesNotNeedGCBarriers,
                                                  AggValueSlot::IsNotAliased));
  }
}

// If an l-value is found, return it. Otherwise, return an r-value.
bool
SemanticAnalysis::svalue(Expression *expr, SValue *outp)
{
  // Demand only RValues.
  SaveAndSet<ValueContext> context(&value_context_, kLValue);

  LValue lval;

  // Between setting the "outparams" and returning, nothing should call us.
  assert(!outp_ && !hir_);
  outp_ = &lval;
  expr->accept(this);
  outp_ = nullptr;

  // We should not have received both an r-value and an l-value.
  assert(!hir_ || lval.kind() == LValue::Error);
  if (!hir_ && lval.kind() == LValue::Error)
    return false;

  if (hir_)
    *outp = SValue(ReturnAndVoid(hir_));
  else
    *outp = SValue(lval);
  return true;
}

static void EmitDeclInit(CodeGenFunction &CGF, const VarDecl &D,
                         ConstantAddress DeclPtr) {
  assert(D.hasGlobalStorage() && "VarDecl must have global storage!");
  assert(!D.getType()->isReferenceType() && 
         "Should not call EmitDeclInit on a reference!");
  
  QualType type = D.getType();
  LValue lv = CGF.MakeAddrLValue(DeclPtr, type);

  const Expr *Init = D.getInit();
  switch (CGF.getEvaluationKind(type)) {
  case TEK_Scalar: {
    CodeGenModule &CGM = CGF.CGM;
    if (lv.isObjCStrong())
      CGM.getObjCRuntime().EmitObjCGlobalAssign(CGF, CGF.EmitScalarExpr(Init),
                                                DeclPtr, D.getTLSKind());
    else if (lv.isObjCWeak())
      CGM.getObjCRuntime().EmitObjCWeakAssign(CGF, CGF.EmitScalarExpr(Init),
                                              DeclPtr);
    else
      CGF.EmitScalarInit(Init, &D, lv, false);
    return;
  }
  case TEK_Complex:
    CGF.EmitComplexExprIntoLValue(Init, lv, /*isInit*/ true);
    return;
  case TEK_Aggregate:
    CGF.EmitAggExpr(Init, AggValueSlot::forLValue(lv,AggValueSlot::IsDestructed,
                                          AggValueSlot::DoesNotNeedGCBarriers,
                                                  AggValueSlot::IsNotAliased));
    return;
  }
  llvm_unreachable("bad evaluation kind");
}

/// Copy an r-value into memory as part of storing to an atomic type.
/// This needs to create a bit-pattern suitable for atomic operations.
void AtomicInfo::emitCopyIntoMemory(RValue rvalue, LValue dest) const {
  // If we have an r-value, the rvalue should be of the atomic type,
  // which means that the caller is responsible for having zeroed
  // any padding.  Just do an aggregate copy of that type.
  if (rvalue.isAggregate()) {
    CGF.EmitAggregateCopy(dest.getAddress(),
                          rvalue.getAggregateAddr(),
                          getAtomicType(),
                          (rvalue.isVolatileQualified()
                           || dest.isVolatileQualified()),
                          dest.getAlignment());
    return;
  }

  // Okay, otherwise we're copying stuff.

  // Zero out the buffer if necessary.
  emitMemSetZeroIfNecessary(dest);

  // Drill past the padding if present.
  dest = projectValue(dest);

  // Okay, store the rvalue in.
  if (rvalue.isScalar()) {
    CGF.EmitStoreOfScalar(rvalue.getScalarVal(), dest, /*init*/ true);
  } else {
    CGF.EmitStoreOfComplex(rvalue.getComplexVal(), dest, /*init*/ true);
  }
}

void 
AggExprEmitter::EmitInitializationToLValue(Expr* E, LValue LV) {
  QualType type = LV.getType();
  // FIXME: Ignore result?
  // FIXME: Are initializers affected by volatile?
  if (Dest.isZeroed() && isSimpleZero(E, CGF)) {
    // Storing "i32 0" to a zero'd memory location is a noop.
  } else if (isa<ImplicitValueInitExpr>(E)) {
    EmitNullInitializationToLValue(LV);
  } else if (type->isReferenceType()) {
    RValue RV = CGF.EmitReferenceBindingToExpr(E, /*InitializedDecl=*/0);
    CGF.EmitStoreThroughLValue(RV, LV);
  } else if (type->isAnyComplexType()) {
    CGF.EmitComplexExprIntoAddr(E, LV.getAddress(), false);
  } else if (CGF.hasAggregateLLVMType(type)) {
    CGF.EmitAggExpr(E, AggValueSlot::forLValue(LV,
                                               AggValueSlot::IsDestructed,
                                      AggValueSlot::DoesNotNeedGCBarriers,
                                               AggValueSlot::IsNotAliased,
                                               Dest.isZeroed()));
  } else if (LV.isSimple()) {
    CGF.EmitScalarInit(E, /*D=*/0, LV, /*Captured=*/false);
  } else {
    CGF.EmitStoreThroughLValue(RValue::get(CGF.EmitScalarExpr(E)), LV);
  }
}

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;
}

LValue CGObjCRuntime::EmitValueForIvarAtOffset(CodeGen::CodeGenFunction &CGF,
                                               const ObjCInterfaceDecl *OID,
                                               llvm::Value *BaseValue,
                                               const ObjCIvarDecl *Ivar,
                                               unsigned CVRQualifiers,
                                               llvm::Value *Offset) {
  // Compute (type*) ( (char *) BaseValue + Offset)
  QualType IvarTy = Ivar->getType();
  llvm::Type *LTy = CGF.CGM.getTypes().ConvertTypeForMem(IvarTy);
  llvm::Value *V = CGF.Builder.CreateBitCast(BaseValue, CGF.Int8PtrTy);
  V = CGF.Builder.CreateInBoundsGEP(V, Offset, "add.ptr");

  if (!Ivar->isBitField()) {
    V = CGF.Builder.CreateBitCast(V, llvm::PointerType::getUnqual(LTy));
    LValue LV = CGF.MakeNaturalAlignAddrLValue(V, IvarTy);
    LV.getQuals().addCVRQualifiers(CVRQualifiers);
    return LV;
  }

  // We need to compute an access strategy for this bit-field. We are given the
  // offset to the first byte in the bit-field, the sub-byte offset is taken
  // from the original layout. We reuse the normal bit-field access strategy by
  // treating this as an access to a struct where the bit-field is in byte 0,
  // and adjust the containing type size as appropriate.
  //
  // FIXME: Note that currently we make a very conservative estimate of the
  // alignment of the bit-field, because (a) it is not clear what guarantees the
  // runtime makes us, and (b) we don't have a way to specify that the struct is
  // at an alignment plus offset.
  //
  // Note, there is a subtle invariant here: we can only call this routine on
  // non-synthesized ivars but we may be called for synthesized ivars.  However,
  // a synthesized ivar can never be a bit-field, so this is safe.
  uint64_t FieldBitOffset = LookupFieldBitOffset(CGF.CGM, OID, nullptr, Ivar);
  uint64_t BitOffset = FieldBitOffset % CGF.CGM.getContext().getCharWidth();
  uint64_t AlignmentBits = CGF.CGM.getTarget().getCharAlign();
  uint64_t BitFieldSize = Ivar->getBitWidthValue(CGF.getContext());
  CharUnits StorageSize =
    CGF.CGM.getContext().toCharUnitsFromBits(
      llvm::RoundUpToAlignment(BitOffset + BitFieldSize, AlignmentBits));
  CharUnits Alignment = CGF.CGM.getContext().toCharUnitsFromBits(AlignmentBits);

  // Allocate a new CGBitFieldInfo object to describe this access.
  //
  // FIXME: This is incredibly wasteful, these should be uniqued or part of some
  // layout object. However, this is blocked on other cleanups to the
  // Objective-C code, so for now we just live with allocating a bunch of these
  // objects.
  CGBitFieldInfo *Info = new (CGF.CGM.getContext()) CGBitFieldInfo(
    CGBitFieldInfo::MakeInfo(CGF.CGM.getTypes(), Ivar, BitOffset, BitFieldSize,
                             CGF.CGM.getContext().toBits(StorageSize),
                             CharUnits::fromQuantity(0)));

  V = CGF.Builder.CreateBitCast(V,
                                llvm::Type::getIntNPtrTy(CGF.getLLVMContext(),
                                                         Info->StorageSize));
  return LValue::MakeBitfield(V, *Info,
                              IvarTy.withCVRQualifiers(CVRQualifiers),
                              Alignment);
}

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

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

  case 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 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 CK_DerivedToBase:
  case CK_BaseToDerived:
  case 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 CK_Unknown:
  case CK_NoOp:
  case CK_UserDefinedConversion:
  case CK_ConstructorConversion:
    assert(CGF.getContext().hasSameUnqualifiedType(E->getSubExpr()->getType(),
                                                   E->getType()) &&
           "Implicit cast types must be compatible");
    Visit(E->getSubExpr());
    break;

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

void AtomicInfo::emitMemSetZeroIfNecessary(LValue dest) const {
  llvm::Value *addr = dest.getAddress();
  if (!requiresMemSetZero(addr->getType()->getPointerElementType()))
    return;

  CGF.Builder.CreateMemSet(addr, llvm::ConstantInt::get(CGF.Int8Ty, 0),
                           AtomicSizeInBits / 8,
                           dest.getAlignment().getQuantity());
}

/// Emit a materializeForSet callback that stores the value from the
/// result buffer back into the l-value.
SILFunction *
MaterializeForSetEmitter::createSetterCallback(SILFunction &F,
                                               const TypeLowering *indicesTL,
                                               CanType indicesFormalType) {
  return createCallback(F, [&](SILGenFunction &SGF, SILLocation loc,
                            SILValue value, SILValue callbackBuffer,
                            SILValue self) {
    // If this is a subscript, we need to handle the indices in the
    // callback storage.
    RValue indices;
    if (indicesTL) {
      assert(isa<SubscriptDecl>(WitnessStorage));
      SILType indicesTy = indicesTL->getLoweredType();

      // Enter a cleanup to deallocate the callback storage.
      SGF.Cleanups.pushCleanup<DeallocateValueBuffer>(indicesTy,
                                                      callbackBuffer);

      // Project the value out, loading if necessary, and take
      // ownership of it.
      SILValue indicesV =
        SGF.B.createProjectValueBuffer(loc, indicesTy, callbackBuffer);
      if (indicesTL->isLoadable() || !SGF.silConv.useLoweredAddresses())
        indicesV = indicesTL->emitLoad(SGF.B, loc, indicesV,
                                       LoadOwnershipQualifier::Take);
      ManagedValue mIndices =
        SGF.emitManagedRValueWithCleanup(indicesV, *indicesTL);

      // Explode as an r-value.
      indices = RValue(SGF, loc, indicesFormalType, mIndices);
    }

    // The callback gets the address of 'self' at +0.
    ManagedValue mSelf = ManagedValue::forLValue(self);

    // That's enough to build the l-value.
    LValue lvalue = buildLValue(SGF, loc, mSelf, std::move(indices),
                                AccessKind::Write);

    // The callback gets the value at +1.
    auto &valueTL = SGF.getTypeLowering(lvalue.getTypeOfRValue());
    value = SGF.B.createPointerToAddress(
      loc, value, valueTL.getLoweredType().getAddressType(),
      /*isStrict*/ true, /*isInvariant*/ false);
    if (valueTL.isLoadable() || !SGF.silConv.useLoweredAddresses())
      value = valueTL.emitLoad(SGF.B, loc, value, LoadOwnershipQualifier::Take);
    ManagedValue mValue = SGF.emitManagedRValueWithCleanup(value, valueTL);
    RValue rvalue(SGF, loc, lvalue.getSubstFormalType(), mValue);

    // Finally, call the setter.
    SGF.emitAssignToLValue(loc, std::move(rvalue), std::move(lvalue));
  });
}

void
SemanticAnalysis::visitAssignment(Assignment *node)
{
  LValue lval;
  if (!lvalue(node->lvalue(), &lval))
    return;

  HIR *hir = rvalue(node->expression());
  if ((hir = coerce(hir, lval.type(), Coerce_Assign)) == nullptr)
    return;

  hir_ = new (pool_) HStore(node, lval.type(), node->token(), lval, hir);
}