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Fix code gen for some compound assignment scenarios involving extension properties. #79339

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Merged
AlekseyTs merged 1 commit into from
Jul 17, 2025
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Fix code gen for some compound assignment scenarios involving extension properties. #79339

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34 changes: 26 additions & 8 deletions ...pilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_CompoundAssignmentOperator.cs
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Expand Up @@ -226,11 +226,27 @@ BoundExpression rewriteAssignment(BoundExpression leftRead, BoundExpression righ
}

Debug.Assert(TypeSymbol.Equals(transformedLHS.Type, node.Left.Type, TypeCompareKind.AllIgnoreOptions));

if (IsNewExtensionMemberAccessWithByValPossiblyStructReceiver(transformedLHS))
{
// We need to create a tree that ensures that receiver of 'set' is evaluated after the binary operation
BoundLocal binaryResult = _factory.StoreToTemp(opFinal, out BoundAssignmentOperator assignmentToTemp, refKind: RefKind.None);
BoundExpression assignment = MakeAssignmentOperator(syntax, transformedLHS, binaryResult, used: used, isChecked: isChecked, isCompoundAssignment: true);
Debug.Assert(assignment.Type is { });
return new BoundSequence(syntax, [binaryResult.LocalSymbol], [assignmentToTemp], assignment, assignment.Type);
}
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@jcouv jcouv Jul 14, 2025 •
edited
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Just to confirm my understanding:
When handling a scenario like x.P += rhs with a struct receiver and by-value receiver parameter, we capture the receiver by reference and after local rewriting and extension rewriting we'd get:

ref S y = ref x
set_P(y, op_Binary(get_P(y), rhs))

But we want:

ref S y = ref x
var binaryResult = op_Binary(get_P(y), rhs);
set_P(y, binaryResult)

That way the derference of y for set_P is done later.
This behaves like x.P += rhs for an instance property, in that the setter can see getter or operator mutations to x.

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@AlekseyTs AlekseyTs Jul 15, 2025

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Correct.


return MakeAssignmentOperator(syntax, transformedLHS, opFinal, used: used, isChecked: isChecked, isCompoundAssignment: true);
}
}

private BoundExpression? TransformPropertyOrEventReceiver(Symbol propertyOrEvent, BoundExpression? receiverOpt, bool isRegularCompoundAssignment, ArrayBuilder<BoundExpression> stores, ArrayBuilder<LocalSymbol> temps)
private static bool IsNewExtensionMemberAccessWithByValPossiblyStructReceiver(BoundExpression transformedLHS)
{
return transformedLHS is BoundPropertyAccess { PropertySymbol: { } property } && property.GetIsNewExtensionMember() &&
property.ContainingType.ExtensionParameter is { RefKind: RefKind.None, Type.IsReferenceType: false };
}

private BoundExpression? TransformPropertyOrEventReceiver(Symbol propertyOrEvent, BoundExpression? receiverOpt, ArrayBuilder<BoundExpression> stores, ArrayBuilder<LocalSymbol> temps)
{
Debug.Assert(propertyOrEvent.Kind == SymbolKind.Property || propertyOrEvent.Kind == SymbolKind.Event);

Expand Down Expand Up @@ -272,7 +288,9 @@ BoundExpression rewriteAssignment(BoundExpression leftRead, BoundExpression righ
// SPEC VIOLATION: However, for compatibility with Dev12 we will continue treating all generic type parameters, constrained or not,
// SPEC VIOLATION: as value types.
Debug.Assert(rewrittenReceiver.Type is { });
var variableRepresentsLocation = rewrittenReceiver.Type.IsValueType || rewrittenReceiver.Type.Kind == SymbolKind.TypeParameter;
var variableRepresentsLocation = propertyOrEvent.GetIsNewExtensionMember() ?
!rewrittenReceiver.Type.IsReferenceType :
(rewrittenReceiver.Type.IsValueType || rewrittenReceiver.Type.Kind == SymbolKind.TypeParameter);

var receiverTemp = _factory.StoreToTemp(
rewrittenReceiver,
Expand All @@ -286,9 +304,10 @@ BoundExpression rewriteAssignment(BoundExpression leftRead, BoundExpression righ
stackLocalsOpt: null));
temps.Add(receiverTemp.LocalSymbol);

if (!isRegularCompoundAssignment &&
receiverTemp.LocalSymbol.IsRef &&
CodeGenerator.IsPossibleReferenceTypeReceiverOfConstrainedCall(receiverTemp) &&
if (receiverTemp.LocalSymbol.IsRef &&
(propertyOrEvent.GetIsNewExtensionMember() ?
!receiverTemp.Type.IsValueType :
CodeGenerator.IsPossibleReferenceTypeReceiverOfConstrainedCall(receiverTemp)) &&
!CodeGenerator.ReceiverIsKnownToReferToTempIfReferenceType(receiverTemp))
{
BoundAssignmentOperator? extraRefInitialization;
Expand Down Expand Up @@ -678,7 +697,7 @@ private BoundExpression TransformCompoundAssignmentLHS(BoundExpression originalL
{
// This is a temporary object that will be rewritten away before the lowering completes.
return propertyAccess.Update(TransformPropertyOrEventReceiver(propertyAccess.PropertySymbol, propertyAccess.ReceiverOpt,
isRegularCompoundAssignment, stores, temps),
stores, temps),
propertyAccess.InitialBindingReceiverIsSubjectToCloning, propertyAccess.PropertySymbol, propertyAccess.AutoPropertyAccessorKind, propertyAccess.ResultKind, propertyAccess.Type);
}
}
Expand Down Expand Up @@ -804,10 +823,9 @@ private BoundExpression TransformCompoundAssignmentLHS(BoundExpression originalL

if (eventAccess.EventSymbol.IsWindowsRuntimeEvent)
{
Debug.Assert(!isRegularCompoundAssignment);
// This is a temporary object that will be rewritten away before the lowering completes.
return eventAccess.Update(TransformPropertyOrEventReceiver(eventAccess.EventSymbol, eventAccess.ReceiverOpt,
isRegularCompoundAssignment, stores, temps),
stores, temps),
eventAccess.EventSymbol, eventAccess.IsUsableAsField, eventAccess.ResultKind, eventAccess.Type);
}

Expand Down
15 changes: 14 additions & 1 deletion .../CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_NullCoalescingAssignmentOperator.cs
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Expand Up @@ -39,7 +39,20 @@ BoundExpression rewriteNullCoalscingAssignmentStandard()
// See CodeGenNullCoalescingAssignmentTests.CoalescingAssignment_DynamicRuntimeCastFailure, which will fail if
// isCompoundAssignment is set to true. It will fail to throw a runtime binder cast exception.
Debug.Assert(TypeSymbol.Equals(transformedLHS.Type, node.LeftOperand.Type, TypeCompareKind.AllIgnoreOptions));
BoundExpression assignment = MakeAssignmentOperator(syntax, transformedLHS, loweredRight, used: true, isChecked: false, isCompoundAssignment: false);
BoundExpression assignment;

if (IsNewExtensionMemberAccessWithByValPossiblyStructReceiver(transformedLHS))
{
// We need to create a tree that ensures that receiver of 'set' is evaluated after the right hand side value
BoundLocal rightResult = _factory.StoreToTemp(loweredRight, out BoundAssignmentOperator assignmentToTemp, refKind: RefKind.None);
assignment = MakeAssignmentOperator(syntax, transformedLHS, rightResult, used: true, isChecked: false, isCompoundAssignment: false);
Debug.Assert(assignment.Type is { });
assignment = new BoundSequence(syntax, [rightResult.LocalSymbol], [assignmentToTemp], assignment, assignment.Type);
}
else
{
assignment = MakeAssignmentOperator(syntax, transformedLHS, loweredRight, used: true, isChecked: false, isCompoundAssignment: false);
}

// lhsRead ?? (transformedLHS = loweredRight)
var leftPlaceholder = new BoundValuePlaceholder(lhsRead.Syntax, lhsRead.Type);
Expand Down
20 changes: 16 additions & 4 deletions src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_UnaryOperator.cs
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Expand Up @@ -621,6 +621,7 @@ public BoundExpression VisitBuiltInOrStaticIncrementOperator(BoundIncrementOpera
//
if (isIndirectOrInstanceField(transformedLHS))
{
Debug.Assert(transformedLHS is not BoundPropertyAccess);
return rewriteWithRefOperand(isPrefix, isChecked, tempSymbols, tempInitializers, syntax, transformedLHS, boundTemp, newValue);
}
else
Expand Down Expand Up @@ -660,16 +661,27 @@ BoundExpression rewriteWithNotRefOperand(

// prefix: temp = (X)(T.Increment((T)operand))); operand = temp;
// postfix: temp = operand; operand = (X)(T.Increment((T)temp)));
ImmutableArray<BoundExpression> assignments = ImmutableArray.Create<BoundExpression>(
MakeAssignmentOperator(syntax, boundTemp, isPrefix ? newValue : MakeRValue(transformedLHS), used: false, isChecked: isChecked, isCompoundAssignment: false),
MakeAssignmentOperator(syntax, transformedLHS, isPrefix ? boundTemp : newValue, used: false, isChecked: isChecked, isCompoundAssignment: false));
tempInitializers.Add(MakeAssignmentOperator(syntax, boundTemp, isPrefix ? newValue : MakeRValue(transformedLHS), used: false, isChecked: isChecked, isCompoundAssignment: false));

if (!isPrefix && IsNewExtensionMemberAccessWithByValPossiblyStructReceiver(transformedLHS))
{
// We need to create a tree that ensures that receiver of 'set' is evaluated after the increment operation
BoundLocal incrementResult = _factory.StoreToTemp(newValue, out BoundAssignmentOperator assignmentToTemp, refKind: RefKind.None);
tempSymbols.Add(incrementResult.LocalSymbol);
tempInitializers.Add(assignmentToTemp);
tempInitializers.Add(MakeAssignmentOperator(syntax, transformedLHS, incrementResult, used: false, isChecked: isChecked, isCompoundAssignment: false));
}
else
{
tempInitializers.Add(MakeAssignmentOperator(syntax, transformedLHS, isPrefix ? boundTemp : newValue, used: false, isChecked: isChecked, isCompoundAssignment: false));
}

// prefix: Seq( operand initializers; temp = (T)(operand + 1); operand = temp; result: temp)
// postfix: Seq( operand initializers; temp = operand; operand = (T)(temp + 1); result: temp)
return new BoundSequence(
syntax: syntax,
locals: tempSymbols.ToImmutableAndFree(),
sideEffects: tempInitializers.ToImmutableAndFree().Concat(assignments),
sideEffects: tempInitializers.ToImmutableAndFree(),
value: boundTemp,
type: boundTemp.Type);
}
Expand Down
54 changes: 28 additions & 26 deletions src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenOperators.cs
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Expand Up @@ -5228,41 +5228,43 @@ public static void Repro2(T arg)
1");
compilation.VerifyIL("test<T>.Repro1(T)", @"
{
// Code size 88 (0x58)
// Code size 86 (0x56)
.maxstack 4
.locals init (T& V_0)
.locals init (T& V_0,
T V_1)
IL_0000: ldarg.0
IL_0001: box ""T""
IL_0006: dup
IL_0007: ldfld ""int c0.x""
IL_000c: ldc.i4.1
IL_000d: add
IL_000e: stfld ""int c0.x""
IL_0013: ldarga.s V_0
IL_0015: stloc.0
IL_0016: ldloc.0
IL_0017: ldobj ""T""
IL_001c: box ""T""
IL_0021: ldloc.0
IL_0022: constrained. ""T""
IL_0028: callvirt ""int c0.P1.get""
IL_002d: ldc.i4.1
IL_002e: add
IL_002f: callvirt ""void c0.P1.set""
IL_0034: ldarga.s V_0
IL_0036: stloc.0
IL_0037: ldloc.0
IL_0038: ldobj ""T""
IL_003d: box ""T""
IL_0013: ldarg.0
IL_0014: stloc.1
IL_0015: ldloca.s V_1
IL_0017: stloc.0
IL_0018: ldloc.0
IL_0019: ldloc.0
IL_001a: constrained. ""T""
IL_0020: callvirt ""int c0.P1.get""
IL_0025: ldc.i4.1
IL_0026: add
IL_0027: constrained. ""T""
IL_002d: callvirt ""void c0.P1.set""
IL_0032: ldarga.s V_0
IL_0034: stloc.0
IL_0035: ldloc.0
IL_0036: ldobj ""T""
IL_003b: box ""T""
IL_0040: ldc.i4.1
IL_0041: ldloc.0
IL_0042: ldc.i4.1
IL_0043: ldloc.0
IL_0044: ldc.i4.1
IL_0045: constrained. ""T""
IL_004b: callvirt ""int c0.this[int].get""
IL_0050: ldc.i4.1
IL_0051: add
IL_0052: callvirt ""void c0.this[int].set""
IL_0057: ret
IL_0043: constrained. ""T""
IL_0049: callvirt ""int c0.this[int].get""
IL_004e: ldc.i4.1
IL_004f: add
IL_0050: callvirt ""void c0.this[int].set""
IL_0055: ret
}
").VerifyIL("test<T>.Repro2(T)", @"
{
Expand Down
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