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Merged
eeckstein merged 3 commits into from
Dec 5, 2025
Merged

Embedded: allow generic class constructors #85857

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7eedc18
Swift AST: add `ConstructorDecl.isInheritable`
eeckstein Dec 5, 2025
332b253
SIL: fix vtable cache updating in `SILVTable::replaceEntries`
eeckstein Dec 5, 2025
8b496f6
Embedded: allow generic class constructors
eeckstein Dec 5, 2025
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6 changes: 4 additions & 2 deletions SwiftCompilerSources/Sources/AST/Declarations.swift
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Expand Up @@ -182,10 +182,12 @@ final public class ParamDecl: VarDecl {
final public class SubscriptDecl: AbstractStorageDecl, GenericContext {}

public class AbstractFunctionDecl: ValueDecl, GenericContext {
public var isOverridden: Bool { bridged.AbstractFunction_isOverridden() }
final public var isOverridden: Bool { bridged.AbstractFunction_isOverridden() }
}

final public class ConstructorDecl: AbstractFunctionDecl {}
final public class ConstructorDecl: AbstractFunctionDecl {
public var isInheritable: Bool { bridged.Constructor_isInheritable() }
}

final public class DestructorDecl: AbstractFunctionDecl {
final public var isIsolated: Bool { bridged.Destructor_isIsolated() }
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10 changes: 9 additions & 1 deletion SwiftCompilerSources/Sources/Optimizer/Utilities/GenericSpecialization.swift
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Expand Up @@ -82,7 +82,7 @@ private struct VTableSpecializer {
}

private func specializeEntries(of vTable: VTable, _ notifyNewFunction: (Function) -> ()) -> [VTable.Entry] {
return vTable.entries.map { entry in
return vTable.entries.compactMap { entry in
if !entry.implementation.isGeneric {
return entry
}
Expand All @@ -95,6 +95,14 @@ private struct VTableSpecializer {
let specializedMethod = context.specialize(function: entry.implementation, for: methodSubs,
convertIndirectToDirect: true, isMandatory: true)
else {
if let constructor = entry.methodDecl.decl as? ConstructorDecl,
!constructor.isInheritable
{
// For some reason, SILGen is putting constructors in the vtable, though they are never
// called through the vtable.
// Dropping those vtable entries allows using constructors with generic arguments.
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@slavapestov slavapestov Dec 5, 2025

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Instead of working around it here, is it hard to fix SILGen to not put them in the vtable? IRGen must have a similar workaround too then.

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@eeckstein eeckstein Dec 5, 2025

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Instead of working around it here, is it hard to fix SILGen to not put them in the vtable?

I don't know. We (= someone who knows SILGen) can do this as a follow-up.

IRGen must have a similar workaround too then.

No, in regular SIL it's totally fine to have a generic function in a vtable. And in embedded the compiler aborted with an error in this case.

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@DougGregor DougGregor Dec 5, 2025

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This solution seems brittle. Why not update NeedsNewVTableEntryRequest::evaluate to suppress generic initializers from the vtable in the first place? There's no way to specialize these appropriately.

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@eeckstein eeckstein Dec 8, 2025

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This solution seems brittle.

No. It does not change the vtable layout. It just marks the constructor as dead. Also, we are doing this is-generic check on the call site, too (i.e. for class_method instructions) which is the double check that we are not calling such a "dead" constructor.

Why not update NeedsNewVTableEntryRequest::evaluate to suppress generic initializers from the vtable in the first place?

I tried this but did run into assertion failures in SILGen later. It's probably a more involved thing to change the vtable layout.

return nil
}
return entry
}
notifyNewFunction(specializedMethod)
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1 change: 1 addition & 0 deletions include/swift/AST/ASTBridging.h
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Expand Up @@ -351,6 +351,7 @@ struct BridgedDeclObj {
BRIDGED_INLINE bool ProtocolDecl_requiresClass() const;
BRIDGED_INLINE bool ProtocolDecl_isMarkerProtocol() const;
BRIDGED_INLINE bool AbstractFunction_isOverridden() const;
BRIDGED_INLINE bool Constructor_isInheritable() const;
BRIDGED_INLINE bool Destructor_isIsolated() const;
BRIDGED_INLINE bool EnumElementDecl_hasAssociatedValues() const;
SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedParameterList
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4 changes: 4 additions & 0 deletions include/swift/AST/ASTBridgingImpl.h
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Expand Up @@ -272,6 +272,10 @@ bool BridgedDeclObj::AbstractFunction_isOverridden() const {
return getAs<swift::AbstractFunctionDecl>()->isOverridden();
}

bool BridgedDeclObj::Constructor_isInheritable() const {
return getAs<swift::ConstructorDecl>()->isInheritable();
}

bool BridgedDeclObj::Destructor_isIsolated() const {
auto dd = getAs<swift::DestructorDecl>();
auto ai = swift::getActorIsolation(dd);
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17 changes: 8 additions & 9 deletions lib/SIL/IR/SILVTable.cpp
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Expand Up @@ -78,15 +78,14 @@ void SILVTable::updateVTableCache(const Entry &entry) {
void SILVTable::replaceEntries(ArrayRef<Entry> newEntries) {
auto entries = getMutableEntries();
ASSERT(newEntries.size() <= entries.size());
for (unsigned i = 0; i < entries.size(); ++i) {
entries[i].getImplementation()->decrementRefCount();
if (i < newEntries.size()) {
entries[i] = newEntries[i];
entries[i].getImplementation()->incrementRefCount();
updateVTableCache(entries[i]);
} else {
removeFromVTableCache(entries[i]);
}
for (Entry &entry : getMutableEntries()) {
entry.getImplementation()->decrementRefCount();
removeFromVTableCache(entry);
}
for (unsigned i = 0; i < newEntries.size(); ++i) {
entries[i] = newEntries[i];
entries[i].getImplementation()->incrementRefCount();
updateVTableCache(entries[i]);
}
NumEntries = newEntries.size();
}
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49 changes: 40 additions & 9 deletions test/embedded/classes.swift
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Expand Up @@ -8,31 +8,57 @@
// REQUIRES: optimized_stdlib
// REQUIRES: swift_feature_Embedded

class MyClass {
public class MyClass {
init() { print("MyClass.init") }
deinit { print("MyClass.deinit") }
func foo() { print("MyClass.foo") }
}

class MySubClass: MyClass {
var x = 27
public class MySubClass: MyClass {
var x: Int

override init() {
self.x = 27
print("MySubClass.init")
}

public init(p: some P) {
self.x = p.get()
super.init()
print("MySubClass.init")
}

override init() { print("MySubClass.init") }
deinit { print("MySubClass.deinit") }
override func foo() { print("MySubClass.foo") }

override func foo() { print("MySubClass.foo: \(x)") }

func printX() {
print(x)
}
}

class MySubSubClass: MySubClass {
override init() { print("MySubSubClass.init") }
public protocol P {
func get() -> Int
}

struct S: P {
let i: Int

func get() -> Int { i }
}

public class MySubSubClass: MySubClass {
override init() {
print("MySubSubClass.init")
super.init()
}

deinit { print("MySubSubClass.deinit") }

override func foo() { print("MySubSubClass.foo") }
}

class OtherSubClass: MyClass {}
public class OtherSubClass: MyClass {}

func testCasting(_ title: StaticString, _ c: MyClass) {
print(title, terminator: "")
Expand Down Expand Up @@ -81,10 +107,15 @@ struct Main {
o.1!.foo()
o.2!.foo()
// CHECK: MyClass.foo
// CHECK: MySubClass.foo
// CHECK: MySubClass.foo: 27
// CHECK: MySubSubClass.foo
print("")

print("4b") // CHECK: 4b
o.1 = MySubClass(p: S(i: 42))
o.1!.foo()
// CHECK: MySubClass.foo: 42

print("5") // CHECK: 5
o.0 = nil
// CHECK: MyClass.deinit
Expand Down