private BoundNode FuseNodes(BoundConditionalAccess conditionalAccess, BoundNullCoalescingOperator node)
{
var type = node.RightOperand.Type;
conditionalAccess = conditionalAccess.Update(conditionalAccess.Receiver, conditionalAccess.AccessExpression, type);
var whenNull = (BoundExpression)Visit(node.RightOperand);
if (whenNull.IsDefaultValue() && whenNull.Type.SpecialType != SpecialType.System_Decimal)
{
whenNull = null;
}
return RewriteConditionalAccess(conditionalAccess, used: true, rewrittenWhenNull: whenNull);
}
private BoundNode FuseNodes(BoundConditionalAccess conditionalAccess, BoundNullCoalescingOperator node)
{
var type = node.RightOperand.Type;
conditionalAccess = conditionalAccess.Update(conditionalAccess.Receiver, conditionalAccess.AccessExpression, type);
var whenNull = (BoundExpression)Visit(node.RightOperand);
if (whenNull.IsDefaultValue() && whenNull.Type.SpecialType != SpecialType.System_Decimal)
{
whenNull = null;
}
return(RewriteConditionalAccess(conditionalAccess, used: true, rewrittenWhenNull: whenNull));
}
// in simple cases could be left unlowered.
// IL gen can generate more compact code for unlowered conditional accesses
// by utilizing stack dup/pop instructions
public override BoundNode VisitConditionalAccess(BoundConditionalAccess node)
{
BoundExpression loweredReceiver = (BoundExpression)this.Visit(node.Receiver);
var receiverType = loweredReceiver.Type;
//TODO: if AccessExpression does not contain awaits, the node could be left unlowered (saves a temp),
// but there seem to be no way of knowing that without walking AccessExpression.
var needToLower = receiverType.IsNullableType() ||
this.inExpressionLambda ||
this.factory.CurrentMethod.IsAsync ||
node.Type.IsDynamic();
var previousConditionalAccesTarget = currentConditionalAccessTarget;
LocalSymbol temp = null;
if (needToLower)
{
if (NeedsTemp(loweredReceiver, localsMayBeAssigned: false))
{
temp = factory.SynthesizedLocal(receiverType);
currentConditionalAccessTarget = factory.Local(temp);
loweredReceiver = factory.AssignmentExpression(factory.Local(temp), loweredReceiver);
}
else
{
currentConditionalAccessTarget = loweredReceiver;
}
}
else
{
currentConditionalAccessTarget = null;
}
BoundExpression loweredAccessExpression = (BoundExpression)this.Visit(node.AccessExpression);
currentConditionalAccessTarget = previousConditionalAccesTarget;
TypeSymbol type = this.VisitType(node.Type);
TypeSymbol nodeType = node.Type;
TypeSymbol accessExpressionType = loweredAccessExpression.Type;
if (accessExpressionType != nodeType)
{
Debug.Assert(nodeType.IsNullableType() && accessExpressionType == nodeType.GetNullableUnderlyingType());
loweredAccessExpression = factory.New((NamedTypeSymbol)nodeType, loweredAccessExpression);
}
BoundExpression result;
if (!needToLower)
{
Debug.Assert(receiverType.IsReferenceType);
result = node.Update(loweredReceiver, loweredAccessExpression, type);
}
else
{
var condition = receiverType.IsReferenceType ?
factory.ObjectNotEqual(loweredReceiver, factory.Null(receiverType)) :
MakeOptimizedHasValue(loweredReceiver.Syntax, loweredReceiver);
var consequence = loweredAccessExpression;
var alternative = factory.Default(nodeType);
result = RewriteConditionalOperator(node.Syntax,
condition,
consequence,
alternative,
null,
alternative.Type);
if (temp!=null)
{
result = factory.Sequence(temp, result);
}
}
return result;
}
// in simple cases could be left unlowered.
// IL gen can generate more compact code for unlowered conditional accesses
// by utilizing stack dup/pop instructions
public override BoundNode VisitConditionalAccess(BoundConditionalAccess node)
{
BoundExpression loweredReceiver = (BoundExpression)this.Visit(node.Receiver);
var receiverType = loweredReceiver.Type;
//TODO: if AccessExpression does not contain awaits, the node could be left unlowered (saves a temp),
// but there seem to be no way of knowing that without walking AccessExpression.
var needToLower = receiverType.IsNullableType() || this.inExpressionLambda || this.factory.CurrentMethod.IsAsync;
var previousConditionalAccesTarget = currentConditionalAccessTarget;
LocalSymbol temp = null;
if (needToLower)
{
if (NeedsTemp(loweredReceiver, localsMayBeAssigned: false))
{
temp = factory.SynthesizedLocal(receiverType);
currentConditionalAccessTarget = factory.Local(temp);
loweredReceiver = factory.AssignmentExpression(factory.Local(temp), loweredReceiver);
}
else
{
currentConditionalAccessTarget = loweredReceiver;
}
}
else
{
currentConditionalAccessTarget = null;
}
BoundExpression loweredAccessExpression = (BoundExpression)this.Visit(node.AccessExpression);
currentConditionalAccessTarget = previousConditionalAccesTarget;
TypeSymbol type = this.VisitType(node.Type);
TypeSymbol nodeType = node.Type;
TypeSymbol accessExpressionType = loweredAccessExpression.Type;
if (accessExpressionType != nodeType)
{
Debug.Assert(nodeType.IsNullableType() && accessExpressionType == nodeType.GetNullableUnderlyingType());
loweredAccessExpression = factory.New((NamedTypeSymbol)nodeType, loweredAccessExpression);
}
BoundExpression result;
if (!needToLower)
{
Debug.Assert(receiverType.IsReferenceType);
result = node.Update(loweredReceiver, loweredAccessExpression, type);
}
else
{
var condition = receiverType.IsReferenceType ?
factory.ObjectNotEqual(loweredReceiver, factory.Null(receiverType)) :
MakeOptimizedHasValue(loweredReceiver.Syntax, loweredReceiver);
var consequence = loweredAccessExpression;
var alternative = factory.Default(nodeType);
result = RewriteConditionalOperator(node.Syntax,
condition,
consequence,
alternative,
null,
alternative.Type);
if (temp != null)
{
result = factory.Sequence(temp, result);
}
}
return(result);
}
// in simple cases could be left unlowered.
// IL gen can generate more compact code for unlowered conditional accesses
// by utilizing stack dup/pop instructions
internal BoundExpression RewriteConditionalAccess(BoundConditionalAccess node, bool used, BoundExpression rewrittenWhenNull = null)
{
Debug.Assert(!_inExpressionLambda);
var loweredReceiver = this.VisitExpression(node.Receiver);
var receiverType = loweredReceiver.Type;
//TODO: if AccessExpression does not contain awaits, the node could be left unlowered (saves a temp),
// but there seem to be no way of knowing that without walking AccessExpression.
// For now we will just check that we are in an async method, but it would be nice
// to have something more precise.
var isAsync = _factory.CurrentMethod.IsAsync;
ConditionalAccessLoweringKind loweringKind;
// CONSIDER: If we knew that loweredReceiver is not a captured local
// we could pass "false" for localsMayBeAssignedOrCaptured
// otherwise not capturing receiver into a temp
// could introduce additional races into the code if receiver is captured
// into a closure and is modified between null check of the receiver
// and the actual access.
//
// Nullable is special since we are not going to read any part of it twice
// we will read "HasValue" and then, conditionally will read "ValueOrDefault"
// that is no different than just reading both values unconditionally.
// As a result in the case of nullable, not reading captured local through a temp
// does not introduce any additional races so it is irrelevant whether
// the local is captured or not.
var localsMayBeAssignedOrCaptured = !receiverType.IsNullableType();
var needTemp = IntroducingReadCanBeObservable(loweredReceiver, localsMayBeAssignedOrCaptured);
if (!isAsync && !node.AccessExpression.Type.IsDynamic() && rewrittenWhenNull == null &&
(receiverType.IsReferenceType || receiverType.IsTypeParameter() && needTemp))
{
// trivial cases can be handled more efficiently in IL gen
loweringKind = ConditionalAccessLoweringKind.None;
}
else if (needTemp)
{
if (receiverType.IsReferenceType || receiverType.IsNullableType())
{
loweringKind = ConditionalAccessLoweringKind.CaptureReceiverByVal;
}
else
{
loweringKind = isAsync ?
ConditionalAccessLoweringKind.DuplicateCode :
ConditionalAccessLoweringKind.CaptureReceiverByRef;
}
}
else
{
// locals do not need to be captured
loweringKind = ConditionalAccessLoweringKind.NoCapture;
}
var previousConditionalAccesTarget = _currentConditionalAccessTarget;
LocalSymbol temp = null;
BoundExpression unconditionalAccess = null;
switch (loweringKind)
{
case ConditionalAccessLoweringKind.None:
_currentConditionalAccessTarget = null;
break;
case ConditionalAccessLoweringKind.NoCapture:
_currentConditionalAccessTarget = loweredReceiver;
break;
case ConditionalAccessLoweringKind.DuplicateCode:
_currentConditionalAccessTarget = loweredReceiver;
unconditionalAccess = used ?
this.VisitExpression(node.AccessExpression) :
this.VisitUnusedExpression(node.AccessExpression);
goto case ConditionalAccessLoweringKind.CaptureReceiverByVal;
case ConditionalAccessLoweringKind.CaptureReceiverByVal:
temp = _factory.SynthesizedLocal(receiverType);
_currentConditionalAccessTarget = _factory.Local(temp);
break;
case ConditionalAccessLoweringKind.CaptureReceiverByRef:
temp = _factory.SynthesizedLocal(receiverType, refKind: RefKind.Ref);
_currentConditionalAccessTarget = _factory.Local(temp);
break;
default:
throw ExceptionUtilities.UnexpectedValue(loweringKind);
}
BoundExpression loweredAccessExpression = used ?
this.VisitExpression(node.AccessExpression) :
this.VisitUnusedExpression(node.AccessExpression);
_currentConditionalAccessTarget = previousConditionalAccesTarget;
TypeSymbol type = this.VisitType(node.Type);
TypeSymbol nodeType = node.Type;
TypeSymbol accessExpressionType = loweredAccessExpression.Type;
if (accessExpressionType.SpecialType == SpecialType.System_Void)
{
type = nodeType = accessExpressionType;
}
if (accessExpressionType != nodeType && nodeType.IsNullableType())
{
Debug.Assert(accessExpressionType == nodeType.GetNullableUnderlyingType());
loweredAccessExpression = _factory.New((NamedTypeSymbol)nodeType, loweredAccessExpression);
if (unconditionalAccess != null)
{
unconditionalAccess = _factory.New((NamedTypeSymbol)nodeType, unconditionalAccess);
}
}
else
{
Debug.Assert(accessExpressionType == nodeType ||
(nodeType.SpecialType == SpecialType.System_Void && !used));
}
BoundExpression result;
var objectType = _compilation.GetSpecialType(SpecialType.System_Object);
rewrittenWhenNull = rewrittenWhenNull ?? _factory.Default(nodeType);
switch (loweringKind)
{
case ConditionalAccessLoweringKind.None:
Debug.Assert(!receiverType.IsValueType);
result = node.Update(loweredReceiver, loweredAccessExpression, type);
break;
case ConditionalAccessLoweringKind.CaptureReceiverByVal:
// capture the receiver into a temp
loweredReceiver = _factory.Sequence(
_factory.AssignmentExpression(_factory.Local(temp), loweredReceiver),
_factory.Local(temp));
goto case ConditionalAccessLoweringKind.NoCapture;
case ConditionalAccessLoweringKind.NoCapture:
{
// (object)r != null ? access : default(T)
var condition = receiverType.IsNullableType() ?
MakeOptimizedHasValue(loweredReceiver.Syntax, loweredReceiver) :
_factory.ObjectNotEqual(
_factory.Convert(objectType, loweredReceiver),
_factory.Null(objectType));
var consequence = loweredAccessExpression;
result = RewriteConditionalOperator(node.Syntax,
condition,
consequence,
rewrittenWhenNull,
null,
nodeType);
if (temp != null)
{
result = _factory.Sequence(temp, result);
}
}
break;
case ConditionalAccessLoweringKind.CaptureReceiverByRef:
// {ref T r; T v;
// r = ref receiver;
// (isClass && { v = r; r = ref v; v == null } ) ?
// null;
// r.Foo()}
{
var v = _factory.SynthesizedLocal(receiverType);
BoundExpression captureRef = _factory.AssignmentExpression(_factory.Local(temp), loweredReceiver, refKind: RefKind.Ref);
BoundExpression isNull = _factory.LogicalAnd(
IsClass(receiverType, objectType),
_factory.Sequence(
_factory.AssignmentExpression(_factory.Local(v), _factory.Local(temp)),
_factory.AssignmentExpression(_factory.Local(temp), _factory.Local(v), RefKind.Ref),
_factory.ObjectEqual(_factory.Convert(objectType, _factory.Local(v)), _factory.Null(objectType)))
);
result = RewriteConditionalOperator(node.Syntax,
isNull,
rewrittenWhenNull,
loweredAccessExpression,
null,
nodeType);
result = _factory.Sequence(
ImmutableArray.Create(temp, v),
captureRef,
result
);
}
break;
case ConditionalAccessLoweringKind.DuplicateCode:
{
Debug.Assert(!receiverType.IsNullableType());
// if we have a class, do regular conditional access via a val temp
loweredReceiver = _factory.AssignmentExpression(_factory.Local(temp), loweredReceiver);
BoundExpression ifClass = RewriteConditionalOperator(node.Syntax,
_factory.ObjectNotEqual(
_factory.Convert(objectType, loweredReceiver),
_factory.Null(objectType)),
loweredAccessExpression,
rewrittenWhenNull,
null,
nodeType);
if (temp != null)
{
ifClass = _factory.Sequence(temp, ifClass);
}
// if we have a struct, then just access unconditionally
BoundExpression ifStruct = unconditionalAccess;
// (object)(default(T)) != null ? ifStruct: ifClass
result = RewriteConditionalOperator(node.Syntax,
IsClass(receiverType, objectType),
ifClass,
ifStruct,
null,
nodeType);
}
break;
default:
throw ExceptionUtilities.Unreachable;
}
return(result);
}
// in simple cases could be left unlowered.
// IL gen can generate more compact code for unlowered conditional accesses
// by utilizing stack dup/pop instructions
internal BoundExpression RewriteConditionalAccess(BoundConditionalAccess node, bool used, BoundExpression rewrittenWhenNull = null)
{
Debug.Assert(!_inExpressionLambda);
var loweredReceiver = this.VisitExpression(node.Receiver);
var receiverType = loweredReceiver.Type;
//TODO: if AccessExpression does not contain awaits, the node could be left unlowered (saves a temp),
// but there seem to be no way of knowing that without walking AccessExpression.
// For now we will just check that we are in an async method, but it would be nice
// to have something more precise.
var isAsync = _factory.CurrentMethod.IsAsync;
ConditionalAccessLoweringKind loweringKind;
// CONSIDER: If we knew that loweredReceiver is not a captured local
// we could pass "false" for localsMayBeAssignedOrCaptured
// otherwise not capturing receiver into a temp
// could introduce additional races into the code if receiver is captured
// into a closure and is modified between null check of the receiver
// and the actual access.
//
// Nullable is special since we are not going to read any part of it twice
// we will read "HasValue" and then, conditionally will read "ValueOrDefault"
// that is no different than just reading both values unconditionally.
// As a result in the case of nullable, not reading captured local through a temp
// does not introduce any additional races so it is irrelevant whether
// the local is captured or not.
var localsMayBeAssignedOrCaptured = !receiverType.IsNullableType();
var needTemp = IntroducingReadCanBeObservable(loweredReceiver, localsMayBeAssignedOrCaptured);
if (!isAsync && !node.AccessExpression.Type.IsDynamic() && rewrittenWhenNull == null &&
(receiverType.IsReferenceType || receiverType.IsTypeParameter() && needTemp))
{
// trivial cases can be handled more efficiently in IL gen
loweringKind = ConditionalAccessLoweringKind.None;
}
else if (needTemp)
{
if (receiverType.IsReferenceType || receiverType.IsNullableType())
{
loweringKind = ConditionalAccessLoweringKind.CaptureReceiverByVal;
}
else
{
loweringKind = isAsync ?
ConditionalAccessLoweringKind.DuplicateCode :
ConditionalAccessLoweringKind.CaptureReceiverByRef;
}
}
else
{
// locals do not need to be captured
loweringKind = ConditionalAccessLoweringKind.NoCapture;
}
var previousConditionalAccesTarget = _currentConditionalAccessTarget;
LocalSymbol temp = null;
BoundExpression unconditionalAccess = null;
switch (loweringKind)
{
case ConditionalAccessLoweringKind.None:
_currentConditionalAccessTarget = null;
break;
case ConditionalAccessLoweringKind.NoCapture:
_currentConditionalAccessTarget = loweredReceiver;
break;
case ConditionalAccessLoweringKind.DuplicateCode:
_currentConditionalAccessTarget = loweredReceiver;
unconditionalAccess = used ?
this.VisitExpression(node.AccessExpression) :
this.VisitUnusedExpression(node.AccessExpression);
goto case ConditionalAccessLoweringKind.CaptureReceiverByVal;
case ConditionalAccessLoweringKind.CaptureReceiverByVal:
temp = _factory.SynthesizedLocal(receiverType);
_currentConditionalAccessTarget = _factory.Local(temp);
break;
case ConditionalAccessLoweringKind.CaptureReceiverByRef:
temp = _factory.SynthesizedLocal(receiverType, refKind: RefKind.Ref);
_currentConditionalAccessTarget = _factory.Local(temp);
break;
default:
throw ExceptionUtilities.UnexpectedValue(loweringKind);
}
BoundExpression loweredAccessExpression = used ?
this.VisitExpression(node.AccessExpression) :
this.VisitUnusedExpression(node.AccessExpression);
_currentConditionalAccessTarget = previousConditionalAccesTarget;
TypeSymbol type = this.VisitType(node.Type);
TypeSymbol nodeType = node.Type;
TypeSymbol accessExpressionType = loweredAccessExpression.Type;
if (accessExpressionType.SpecialType == SpecialType.System_Void)
{
type = nodeType = accessExpressionType;
}
if (accessExpressionType != nodeType && nodeType.IsNullableType())
{
Debug.Assert(accessExpressionType == nodeType.GetNullableUnderlyingType());
loweredAccessExpression = _factory.New((NamedTypeSymbol)nodeType, loweredAccessExpression);
if (unconditionalAccess != null)
{
unconditionalAccess = _factory.New((NamedTypeSymbol)nodeType, unconditionalAccess);
}
}
else
{
Debug.Assert(accessExpressionType == nodeType ||
(nodeType.SpecialType == SpecialType.System_Void && !used));
}
BoundExpression result;
var objectType = _compilation.GetSpecialType(SpecialType.System_Object);
rewrittenWhenNull = rewrittenWhenNull ?? _factory.Default(nodeType);
switch (loweringKind)
{
case ConditionalAccessLoweringKind.None:
Debug.Assert(!receiverType.IsValueType);
result = node.Update(loweredReceiver, loweredAccessExpression, type);
break;
case ConditionalAccessLoweringKind.CaptureReceiverByVal:
// capture the receiver into a temp
loweredReceiver = _factory.Sequence(
_factory.AssignmentExpression(_factory.Local(temp), loweredReceiver),
_factory.Local(temp));
goto case ConditionalAccessLoweringKind.NoCapture;
case ConditionalAccessLoweringKind.NoCapture:
{
// (object)r != null ? access : default(T)
var condition = receiverType.IsNullableType() ?
MakeOptimizedHasValue(loweredReceiver.Syntax, loweredReceiver) :
_factory.ObjectNotEqual(
_factory.Convert(objectType, loweredReceiver),
_factory.Null(objectType));
var consequence = loweredAccessExpression;
result = RewriteConditionalOperator(node.Syntax,
condition,
consequence,
rewrittenWhenNull,
null,
nodeType);
if (temp != null)
{
result = _factory.Sequence(temp, result);
}
}
break;
case ConditionalAccessLoweringKind.CaptureReceiverByRef:
// {ref T r; T v;
// r = ref receiver;
// (isClass && { v = r; r = ref v; v == null } ) ?
// null;
// r.Foo()}
{
var v = _factory.SynthesizedLocal(receiverType);
BoundExpression captureRef = _factory.AssignmentExpression(_factory.Local(temp), loweredReceiver, refKind: RefKind.Ref);
BoundExpression isNull = _factory.LogicalAnd(
IsClass(receiverType, objectType),
_factory.Sequence(
_factory.AssignmentExpression(_factory.Local(v), _factory.Local(temp)),
_factory.AssignmentExpression(_factory.Local(temp), _factory.Local(v), RefKind.Ref),
_factory.ObjectEqual(_factory.Convert(objectType, _factory.Local(v)), _factory.Null(objectType)))
);
result = RewriteConditionalOperator(node.Syntax,
isNull,
rewrittenWhenNull,
loweredAccessExpression,
null,
nodeType);
result = _factory.Sequence(
ImmutableArray.Create(temp, v),
captureRef,
result
);
}
break;
case ConditionalAccessLoweringKind.DuplicateCode:
{
Debug.Assert(!receiverType.IsNullableType());
// if we have a class, do regular conditional access via a val temp
loweredReceiver = _factory.AssignmentExpression(_factory.Local(temp), loweredReceiver);
BoundExpression ifClass = RewriteConditionalOperator(node.Syntax,
_factory.ObjectNotEqual(
_factory.Convert(objectType, loweredReceiver),
_factory.Null(objectType)),
loweredAccessExpression,
rewrittenWhenNull,
null,
nodeType);
if (temp != null)
{
ifClass = _factory.Sequence(temp, ifClass);
}
// if we have a struct, then just access unconditionally
BoundExpression ifStruct = unconditionalAccess;
// (object)(default(T)) != null ? ifStruct: ifClass
result = RewriteConditionalOperator(node.Syntax,
IsClass(receiverType, objectType),
ifClass,
ifStruct,
null,
nodeType);
}
break;
default:
throw ExceptionUtilities.Unreachable;
}
return result;
}
// in simple cases could be left unlowered.
// IL gen can generate more compact code for unlowered conditional accesses
// by utilizing stack dup/pop instructions
internal BoundExpression VisitConditionalAccess(BoundConditionalAccess node, bool used)
{
Debug.Assert(!this.inExpressionLambda);
var loweredReceiver = this.VisitExpression(node.Receiver);
var receiverType = loweredReceiver.Type;
//TODO: if AccessExpression does not contain awaits, the node could be left unlowered (saves a temp),
// but there seem to be no way of knowing that without walking AccessExpression.
// For now we will just check that we are in an async method, but it would be nice
// to have something more precise.
var isAsync = this.factory.CurrentMethod.IsAsync;
ConditionalAccessLoweringKind loweringKind;
if (!receiverType.IsValueType && !isAsync && !node.Type.IsDynamic())
{
// trivial cases can be handled more efficiently in IL gen
loweringKind = ConditionalAccessLoweringKind.None;
}
else if(NeedsTemp(loweredReceiver, localsMayBeAssigned: false))
{
if (receiverType.IsReferenceType || receiverType.IsNullableType())
{
loweringKind = ConditionalAccessLoweringKind.CaptureReceiverByVal;
}
else
{
loweringKind = isAsync ?
ConditionalAccessLoweringKind.DuplicateCode :
ConditionalAccessLoweringKind.CaptureReceiverByRef;
}
}
else
{
// locals do not need to be captured
loweringKind = ConditionalAccessLoweringKind.NoCapture;
}
var previousConditionalAccesTarget = currentConditionalAccessTarget;
LocalSymbol temp = null;
BoundExpression unconditionalAccess = null;
switch (loweringKind)
{
case ConditionalAccessLoweringKind.None:
currentConditionalAccessTarget = null;
break;
case ConditionalAccessLoweringKind.NoCapture:
currentConditionalAccessTarget = loweredReceiver;
break;
case ConditionalAccessLoweringKind.DuplicateCode:
currentConditionalAccessTarget = loweredReceiver;
unconditionalAccess = used?
this.VisitExpression(node.AccessExpression) :
this.VisitUnusedExpression(node.AccessExpression);
goto case ConditionalAccessLoweringKind.CaptureReceiverByVal;
case ConditionalAccessLoweringKind.CaptureReceiverByVal:
temp = factory.SynthesizedLocal(receiverType);
currentConditionalAccessTarget = factory.Local(temp);
break;
case ConditionalAccessLoweringKind.CaptureReceiverByRef:
temp = factory.SynthesizedLocal(receiverType, refKind: RefKind.Ref);
currentConditionalAccessTarget = factory.Local(temp);
break;
}
BoundExpression loweredAccessExpression = used ?
this.VisitExpression(node.AccessExpression) :
this.VisitUnusedExpression(node.AccessExpression);
currentConditionalAccessTarget = previousConditionalAccesTarget;
TypeSymbol type = this.VisitType(node.Type);
TypeSymbol nodeType = node.Type;
TypeSymbol accessExpressionType = loweredAccessExpression.Type;
if (accessExpressionType != nodeType && nodeType.IsNullableType())
{
Debug.Assert(accessExpressionType == nodeType.GetNullableUnderlyingType());
loweredAccessExpression = factory.New((NamedTypeSymbol)nodeType, loweredAccessExpression);
}
else
{
Debug.Assert(accessExpressionType == nodeType ||
(accessExpressionType.SpecialType == SpecialType.System_Void && !used));
}
BoundExpression result;
var objectType = compilation.GetSpecialType(SpecialType.System_Object);
switch (loweringKind)
{
case ConditionalAccessLoweringKind.None:
Debug.Assert(!receiverType.IsValueType);
result = node.Update(loweredReceiver, loweredAccessExpression, type);
break;
case ConditionalAccessLoweringKind.CaptureReceiverByVal:
// capture the receiver into a temp
loweredReceiver = factory.AssignmentExpression(factory.Local(temp), loweredReceiver);
goto case ConditionalAccessLoweringKind.NoCapture;
case ConditionalAccessLoweringKind.NoCapture:
{
// (object)r != null ? access : default(T)
var condition = receiverType.IsNullableType() ?
MakeOptimizedHasValue(loweredReceiver.Syntax, loweredReceiver) :
factory.ObjectNotEqual(
factory.Convert(objectType, loweredReceiver),
factory.Null(objectType));
var consequence = loweredAccessExpression;
var alternative = factory.Default(nodeType);
result = RewriteConditionalOperator(node.Syntax,
condition,
consequence,
alternative,
null,
nodeType);
if (temp != null)
{
result = factory.Sequence(temp, result);
}
}
break;
case ConditionalAccessLoweringKind.CaptureReceiverByRef:
// {ref T r; T v;
// r = ref receiver;
// (isClass && { v = r; r = ref v; v == null } ) ?
// null;
// r.Foo()}
{
var v = factory.SynthesizedLocal(receiverType);
BoundExpression captureRef = factory.AssignmentExpression(factory.Local(temp), loweredReceiver, refKind: RefKind.Ref);
BoundExpression isNull = factory.LogicalAnd(
IsClass(receiverType, objectType),
factory.Sequence(
factory.AssignmentExpression(factory.Local(v), factory.Local(temp)),
factory.AssignmentExpression(factory.Local(temp), factory.Local(v), RefKind.Ref),
factory.ObjectEqual(factory.Convert(objectType, factory.Local(v)), factory.Null(objectType)))
);
result = RewriteConditionalOperator(node.Syntax,
isNull,
factory.Default(nodeType),
loweredAccessExpression,
null,
nodeType);
result = factory.Sequence(
ImmutableArray.Create(temp, v),
captureRef,
result
);
}
break;
case ConditionalAccessLoweringKind.DuplicateCode:
{
Debug.Assert(!receiverType.IsNullableType());
// if we have a class, do regular conditional access via a val temp
loweredReceiver = factory.AssignmentExpression(factory.Local(temp), loweredReceiver);
BoundExpression ifClass = RewriteConditionalOperator(node.Syntax,
factory.ObjectNotEqual(
factory.Convert(objectType, loweredReceiver),
factory.Null(objectType)),
loweredAccessExpression,
factory.Default(nodeType),
null,
nodeType);
if (temp != null)
{
ifClass = factory.Sequence(temp, ifClass);
}
// if we have a struct, then just access unconditionally
BoundExpression ifStruct = unconditionalAccess;
// (object)(default(T)) != null ? ifStruct: ifClass
result = RewriteConditionalOperator(node.Syntax,
IsClass(receiverType, objectType),
ifClass,
ifStruct,
null,
nodeType);
}
break;
default:
throw ExceptionUtilities.Unreachable;
}
return result;
}