[Runtime] Add entry point to canonicalize metadata.

include/swift/ABI/Metadata.h

@@ -492,6 +492,8 @@ template <typename Runtime> class TargetEnumDescriptor;
 template <typename Runtime> class TargetStructDescriptor;
 template <typename Runtime> struct TargetGenericMetadataPattern;
 
+using TypeContextDescriptor = TargetTypeContextDescriptor<InProcess>;
+
 // FIXME: https://bugs.swift.org/browse/SR-1155
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Winvalid-offsetof"
@@ -723,6 +725,10 @@ struct TargetMetadata {
 
   bool satisfiesClassConstraint() const;
 
+  const TypeContextDescriptor *getDescription() const;
+
+  bool isStaticallySpecializedGenericMetadata() const;
+
   bool isCanonicalStaticallySpecializedGenericMetadata() const;
 
 #if SWIFT_OBJC_INTEROP
@@ -1304,6 +1310,14 @@ struct TargetClassMetadata : public TargetAnyClassMetadata<Runtime> {
   }
 #endif
 
+  bool isStaticallySpecializedGenericMetadata() const {
+    auto *description = getDescription();
+    if (!description->isGeneric())
+      return false;
+
+    return this->Flags & ClassFlags::IsStaticSpecialization;
+  }
+
   bool isCanonicalStaticallySpecializedGenericMetadata() const {
     auto *description = getDescription();
     if (!description->isGeneric())
@@ -1449,6 +1463,18 @@ struct TargetStructMetadata : public TargetValueMetadata<Runtime> {
     return reinterpret_cast<const uint32_t *>(asWords + offset);
   }
 
+  bool isStaticallySpecializedGenericMetadata() const {
+    auto *description = getDescription();
+    if (!description->isGeneric())
+      return false;
+
+    auto *trailingFlags = getTrailingFlags();
+    if (trailingFlags == nullptr)
+      return false;
+
+    return trailingFlags->isStaticSpecialization();
+  }
+
   bool isCanonicalStaticallySpecializedGenericMetadata() const {
     auto *description = getDescription();
     if (!description->isGeneric())
@@ -1525,6 +1551,18 @@ struct TargetEnumMetadata : public TargetValueMetadata<Runtime> {
     return *asWords;
   }
 
+  bool isStaticallySpecializedGenericMetadata() const {
+    auto *description = getDescription();
+    if (!description->isGeneric())
+      return false;
+
+    auto *trailingFlags = getTrailingFlags();
+    if (trailingFlags == nullptr)
+      return false;
+
+    return trailingFlags->isStaticSpecialization();
+  }
+
   bool isCanonicalStaticallySpecializedGenericMetadata() const {
     auto *description = getDescription();
     if (!description->isGeneric())
@@ -3820,8 +3858,6 @@ class TargetTypeContextDescriptor
   }
 };
 
-using TypeContextDescriptor = TargetTypeContextDescriptor<InProcess>;
-
 /// Storage for class metadata bounds.  This is the variable returned
 /// by getAddrOfClassMetadataBounds in the compiler.
 ///

include/swift/AST/ASTContext.h

@@ -658,6 +658,10 @@ class ASTContext final {
   /// platform.
   AvailabilityContext getCompareProtocolConformanceDescriptorsAvailability();
 
+  /// Get the runtime availability of support for inter-module prespecialized
+  /// generic metadata.
+  AvailabilityContext getIntermodulePrespecializedGenericMetadataAvailability();
+
   /// Get the runtime availability of features introduced in the Swift 5.2
   /// compiler for the target platform.
   AvailabilityContext getSwift52Availability();

include/swift/Runtime/Metadata.h

@@ -320,6 +320,26 @@ MetadataResponse
 swift_getSingletonMetadata(MetadataRequest request,
                            const TypeContextDescriptor *description);
 
+/// Fetch a uniqued metadata object for the generic nominal type described by
+/// the provided candidate metadata, using that candidate metadata if there is
+/// not already a canonical metadata.
+///
+/// Runtime availability: Swift 5.4
+///
+/// \param candidate A prespecialized metadata record for a type which is not
+///                  statically made to be canonical which will be canonicalized
+///                  if no other canonical metadata exists for the type.
+/// \param cache A pointer to a cache which will be set to the canonical 
+///              metadata record for the type described by the candidate 
+///              metadata record.  If the cache has already been populated, its
+///              contents will be returned.
+/// \returns The canonical metadata for the specialized generic type described
+///          by the provided candidate metadata.
+SWIFT_RUNTIME_EXPORT SWIFT_CC(swift) MetadataResponse
+    swift_getCanonicalSpecializedMetadata(MetadataRequest request,
+                                          const Metadata *candidate,
+                                          const Metadata **cache);
+
 /// Fetch a uniqued metadata object for a generic nominal type.
 SWIFT_RUNTIME_EXPORT SWIFT_CC(swift)
 MetadataResponse

include/swift/Runtime/RuntimeFunctions.def

@@ -645,6 +645,14 @@ FUNCTION(GetGenericMetadata, swift_getGenericMetadata,
          ARGS(SizeTy, Int8PtrTy, TypeContextDescriptorPtrTy),
          ATTRS(NoUnwind, ReadOnly))
 
+// MetadataResponse swift_getCanonicalSpecializedMetadata(MetadataRequest request,
+//                                                        Metadata *candidate);
+FUNCTION(GetCanonicalSpecializedMetadata, swift_getCanonicalSpecializedMetadata,
+         SwiftCC, GetCanonicalSpecializedMetadataAvailability,
+         RETURNS(TypeMetadataResponseTy),
+         ARGS(SizeTy, TypeMetadataPtrTy, TypeMetadataPtrPtrTy),
+         ATTRS(NoUnwind, ReadOnly))
+
 // MetadataResponse swift_getOpaqueTypeMetadata(MetadataRequest request,
 //                                     const void * const *arguments,
 //                                     const OpaqueTypeDescriptor *descriptor,

lib/AST/Availability.cpp

@@ -318,6 +318,11 @@ ASTContext::getCompareProtocolConformanceDescriptorsAvailability() {
   return getSwiftFutureAvailability();
 }
 
+AvailabilityContext
+ASTContext::getIntermodulePrespecializedGenericMetadataAvailability() {
+  return getSwiftFutureAvailability();
+}
+
 AvailabilityContext ASTContext::getSwift52Availability() {
   auto target = LangOpts.Target;
 

lib/IRGen/IRGenModule.cpp

@@ -271,6 +271,7 @@ IRGenModule::IRGenModule(IRGenerator &irgen,
     MetadataKindTy          // MetadataKind Kind;
   });
   TypeMetadataPtrTy = TypeMetadataStructTy->getPointerTo(DefaultAS);
+  TypeMetadataPtrPtrTy = TypeMetadataPtrTy->getPointerTo(DefaultAS);
 
   TypeMetadataResponseTy = createStructType(*this, "swift.metadata_response", {
     TypeMetadataPtrTy,
@@ -670,6 +671,16 @@ namespace RuntimeConstants {
     }
     return RuntimeAvailability::AlwaysAvailable;
   }
+
+  RuntimeAvailability
+  GetCanonicalSpecializedMetadataAvailability(ASTContext &context) {
+    auto featureAvailability =
+        context.getIntermodulePrespecializedGenericMetadataAvailability();
+    if (!isDeploymentAvailabilityContainedIn(context, featureAvailability)) {
+      return RuntimeAvailability::ConditionallyAvailable;
+    }
+    return RuntimeAvailability::AlwaysAvailable;
+  }
 } // namespace RuntimeConstants
 
 // We don't use enough attributes to justify generalizing the

lib/IRGen/IRGenModule.h

@@ -635,6 +635,7 @@ class IRGenModule {
   llvm::FunctionType *DeallocatingDtorTy; /// void (%swift.refcounted*)
   llvm::StructType *TypeMetadataStructTy; /// %swift.type = type { ... }
   llvm::PointerType *TypeMetadataPtrTy;/// %swift.type*
+  llvm::PointerType *TypeMetadataPtrPtrTy; /// %swift.type**
   union {
     llvm::StructType *TypeMetadataResponseTy;   /// { %swift.type*, iSize }
     llvm::StructType *TypeMetadataDependencyTy; /// { %swift.type*, iSize }

stdlib/public/runtime/Metadata.cpp

@@ -268,6 +268,11 @@ namespace {
     GenericCacheEntry(MetadataCacheKey key, Args &&...args)
       : VariadicMetadataCacheEntryBase(key) {}
 
+    AllocationResult allocate(const Metadata *candidate) {
+      return {const_cast<Metadata *>(candidate),
+              PrivateMetadataState::Complete};
+    }
+
     AllocationResult allocate(const TypeContextDescriptor *description,
                               const void * const *arguments) {
       // Find a pattern.  Currently we always use the default pattern.
@@ -436,6 +441,28 @@ SWIFT_ALLOWED_RUNTIME_GLOBAL_CTOR_END
 extern "C" void *_objc_empty_cache;
 #endif
 
+template <> bool Metadata::isStaticallySpecializedGenericMetadata() const {
+  if (auto *metadata = dyn_cast<StructMetadata>(this))
+    return metadata->isStaticallySpecializedGenericMetadata();
+  if (auto *metadata = dyn_cast<EnumMetadata>(this))
+    return metadata->isStaticallySpecializedGenericMetadata();
+  if (auto *metadata = dyn_cast<ClassMetadata>(this))
+    return metadata->isStaticallySpecializedGenericMetadata();
+
+  return false;
+}
+
+template <> const TypeContextDescriptor *Metadata::getDescription() const {
+  if (auto *metadata = dyn_cast<StructMetadata>(this))
+    return metadata->getDescription();
+  if (auto *metadata = dyn_cast<EnumMetadata>(this))
+    return metadata->getDescription();
+  if (auto *metadata = dyn_cast<ClassMetadata>(this))
+    return metadata->getDescription();
+
+  return nullptr;
+}
+
 template <>
 bool Metadata::isCanonicalStaticallySpecializedGenericMetadata() const {
   if (auto *metadata = dyn_cast<StructMetadata>(this))
@@ -673,6 +700,40 @@ swift::swift_allocateGenericValueMetadata(const ValueTypeDescriptor *description
   return metadata;
 }
 
+MetadataResponse swift::swift_getCanonicalSpecializedMetadata(
+    MetadataRequest request, const Metadata *candidate,
+    const Metadata **cacheMetadataPtr) {
+  assert(candidate->isStaticallySpecializedGenericMetadata() &&
+         !candidate->isCanonicalStaticallySpecializedGenericMetadata());
+  auto *description = candidate->getDescription();
+  assert(description);
+
+  using CachedMetadata = std::atomic<const Metadata *>;
+  auto cachedMetadataAddr = ((CachedMetadata *)cacheMetadataPtr);
+  auto *cachedMetadata = cachedMetadataAddr->load(SWIFT_MEMORY_ORDER_CONSUME);
+  if (SWIFT_LIKELY(cachedMetadata != nullptr)) {
+    // Cached metadata pointers are always complete.
+    return MetadataResponse{(const Metadata *)cachedMetadata,
+                            MetadataState::Complete};
+  }
+
+  auto &cache = getCache(*description);
+  assert(description->getFullGenericContextHeader().Base.NumKeyArguments ==
+         cache.NumKeyParameters + cache.NumWitnessTables);
+  const void *const *arguments =
+      reinterpret_cast<const void *const *>(candidate->getGenericArgs());
+  auto key = MetadataCacheKey(cache.NumKeyParameters, cache.NumWitnessTables,
+                              arguments);
+  auto result = cache.getOrInsert(key, request, candidate);
+
+  assert(
+      !result.second.Value->isCanonicalStaticallySpecializedGenericMetadata());
+
+  cachedMetadataAddr->store(result.second.Value, std::memory_order_release);
+
+  return result.second;
+}
+
 /// The primary entrypoint.
 MetadataResponse
 swift::swift_getGenericMetadata(MetadataRequest request,