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Memoize the ObjCBridgeable conformance for Swift.String #30329

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Merged
tbkka merged 4 commits into from
Mar 11, 2020
Merged

Memoize the ObjCBridgeable conformance for Swift.String #30329

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b13fb96
Memoize the ObjCBridgeable conformance for Swift.String
tbkka Mar 10, 2020
5c536e3
Simplify this code along lines suggested by @gottesmm
tbkka Mar 10, 2020
2b93747
Try memoizing Dictionary and Array bridge witnesses as well.
tbkka Mar 10, 2020
5890c00
Revert "Try memoizing Dictionary and Array bridge witnesses as well."
tbkka Mar 10, 2020
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24 changes: 22 additions & 2 deletions stdlib/public/runtime/Casting.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2876,10 +2876,30 @@ id _bridgeAnythingNonVerbatimToObjectiveC(OpaqueValue *src,
extern "C" const _ObjectiveCBridgeableWitnessTable BRIDGING_CONFORMANCE_SYM;
#endif

/// Nominal type descriptor for Swift.String.
extern "C" const StructDescriptor NOMINAL_TYPE_DESCR_SYM(SS);

static const _ObjectiveCBridgeableWitnessTable *
swift_conformsToObjectiveCBridgeable(const Metadata *T) {
return reinterpret_cast<const _ObjectiveCBridgeableWitnessTable *>
(swift_conformsToProtocol(T, &PROTOCOL_DESCR_SYM(s21_ObjectiveCBridgeable)));
}

static const _ObjectiveCBridgeableWitnessTable *
findBridgeWitness(const Metadata *T) {
auto w = swift_conformsToProtocol(T,
&PROTOCOL_DESCR_SYM(s21_ObjectiveCBridgeable));
// 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_conformsToObjectiveCBridgeable(T);
return Swift_String_ObjectiveCBridgeable;
}
}

auto w = swift_conformsToObjectiveCBridgeable(T);
if (LLVM_LIKELY(w))
return reinterpret_cast<const _ObjectiveCBridgeableWitnessTable *>(w);
// Class and ObjC existential metatypes can be bridged, but metatypes can't
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