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Cache the last ObjC bridging conformance we looked up (#81545)

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Fixes rdar://151475392
This commit is contained in:
David Smith
2025-05-16 18:00:13 +00:00
committed by GitHub
parent 779c31aa46
commit e795eb0d13
3 changed files with 132 additions and 7 deletions
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81
stdlib/public/runtime/DynamicCast.cpp
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@@ -206,11 +206,84 @@ struct _ObjectiveCBridgeableWitnessTable : WitnessTable {
extern "C" const ProtocolDescriptor
PROTOCOL_DESCR_SYM(s21_ObjectiveCBridgeable);
#if SWIFT_OBJC_INTEROP
#define BRIDGING_CONFORMANCE_SYM \
MANGLE_SYM(s19_BridgeableMetatypeVs21_ObjectiveCBridgeablesWP)
extern "C" const _ObjectiveCBridgeableWitnessTable BRIDGING_CONFORMANCE_SYM;
#endif
/// Nominal type descriptor for Swift.String.
extern "C" const StructDescriptor NOMINAL_TYPE_DESCR_SYM(SS);
struct ObjCBridgeWitnessCacheEntry {
const Metadata *metadata;
const _ObjectiveCBridgeableWitnessTable *witness;
};
static const _ObjectiveCBridgeableWitnessTable *
swift_conformsToObjectiveCBridgeableNoCache(const Metadata *T) {
auto w = swift_conformsToProtocolCommon(
T, &PROTOCOL_DESCR_SYM(s21_ObjectiveCBridgeable));
return reinterpret_cast<const _ObjectiveCBridgeableWitnessTable *>(w);
}
static const _ObjectiveCBridgeableWitnessTable *
swift_conformsToObjectiveCBridgeable(const Metadata *T) {
static std::atomic<ObjCBridgeWitnessCacheEntry> _objcBridgeWitnessCache = {};
auto cached = _objcBridgeWitnessCache.load(SWIFT_MEMORY_ORDER_CONSUME);
if (cached.metadata == T) {
return cached.witness;
}
cached.witness = swift_conformsToObjectiveCBridgeableNoCache(T);
cached.metadata = T;
_objcBridgeWitnessCache.store(cached, std::memory_order_release);
return cached.witness;
}
static const _ObjectiveCBridgeableWitnessTable *
findBridgeWitness(const Metadata *T) {
auto w = swift_conformsToProtocolCommon(
T, &PROTOCOL_DESCR_SYM(s21_ObjectiveCBridgeable));
return reinterpret_cast<const _ObjectiveCBridgeableWitnessTable *>(w);
// Special case: Memoize the bridge witness for Swift.String.
// Swift.String is the most heavily used bridge because of the prevalence of
// string-keyed dictionaries in Obj-C. It's worth burning a few words of static
// storage to avoid repeatedly looking up this conformance.
if (T->getKind() == MetadataKind::Struct) {
auto structDescription = cast<StructMetadata>(T)->Description;
if (structDescription == &NOMINAL_TYPE_DESCR_SYM(SS)) {
static auto *Swift_String_ObjectiveCBridgeable = swift_conformsToObjectiveCBridgeableNoCache(T);
return Swift_String_ObjectiveCBridgeable;
}
}
auto w = swift_conformsToObjectiveCBridgeable(T);
if (SWIFT_LIKELY(w))
return reinterpret_cast<const _ObjectiveCBridgeableWitnessTable *>(w);
// Class and ObjC existential metatypes can be bridged, but metatypes can't
// directly conform to protocols yet. Use a stand-in conformance for a type
// that looks like a metatype value if the metatype can be bridged.
switch (T->getKind()) {
case MetadataKind::Metatype: {
#if SWIFT_OBJC_INTEROP
auto metaTy = static_cast<const MetatypeMetadata *>(T);
if (metaTy->InstanceType->isAnyClass())
return &BRIDGING_CONFORMANCE_SYM;
#endif
break;
}
case MetadataKind::ExistentialMetatype: {
#if SWIFT_OBJC_INTEROP
auto existentialMetaTy =
static_cast<const ExistentialMetatypeMetadata *>(T);
if (existentialMetaTy->isObjC())
return &BRIDGING_CONFORMANCE_SYM;
#endif
break;
}
default:
break;
}
return nullptr;
}
/// Retrieve the bridged Objective-C type for the given type that
@@ -734,7 +807,7 @@ struct ObjCBridgeMemo {
#if !NDEBUG
memo->destType = setupData->destType;
#endif
memo->destBridgeWitness = findBridgeWitness(setupData->destType);
memo->destBridgeWitness = swift_conformsToObjectiveCBridgeableNoCache(setupData->destType);
if (memo->destBridgeWitness == nullptr) {
memo->targetBridgedType = nullptr;
memo->targetBridgedObjCClass = nullptr;