Generic metadata prespecialization, part 1

include/swift/ABI/Metadata.h

@@ -697,6 +697,8 @@ struct TargetMetadata {
 
   bool satisfiesClassConstraint() const;
 
+  bool isCanonicalStaticallySpecializedGenericMetadata() const;
+
 #if SWIFT_OBJC_INTEROP
   /// Get the ObjC class object for this type if it has one, or return null if
   /// the type is not a class (or not a class with a class object).
@@ -1348,6 +1350,34 @@ struct TargetStructMetadata : public TargetValueMetadata<Runtime> {
     return reinterpret_cast<const uint32_t *>(asWords + offset);
   }
 
+  bool isCanonicalStaticallySpecializedGenericMetadata() const {
+    auto *description = getDescription();
+    if (!description->isGeneric())
+      return false;
+
+    auto *trailingFlags = getTrailingFlags();
+    if (trailingFlags == nullptr)
+      return false;
+
+    return trailingFlags->isCanonicalStaticSpecialization();
+  }
+
+  const MetadataTrailingFlags *getTrailingFlags() const {
+    auto description = getDescription();
+    auto flags = description->getFullGenericContextHeader()
+                     .DefaultInstantiationPattern->PatternFlags;
+    if (!flags.hasTrailingFlags())
+      return nullptr;
+    auto fieldOffset = description->FieldOffsetVectorOffset;
+    auto offset =
+        fieldOffset +
+        // Pad to the nearest pointer.
+        ((description->NumFields * sizeof(uint32_t) + sizeof(void *) - 1) /
+         sizeof(void *));
+    auto asWords = reinterpret_cast<const void *const *>(this);
+    return reinterpret_cast<const MetadataTrailingFlags *>(asWords + offset);
+  }
+
   static constexpr int32_t getGenericArgumentOffset() {
     return sizeof(TargetStructMetadata<Runtime>) / sizeof(StoredPointer);
   }
@@ -3575,7 +3605,7 @@ struct TargetSingletonMetadataInitialization {
   }
 
   /// This method can only be called from the runtime itself. It is defined
-  /// in MetadataCache.h.
+  /// in Metadata.cpp.
   TargetMetadata<Runtime> *allocate(
       const TargetTypeContextDescriptor<Runtime> *description) const;
 };

include/swift/ABI/MetadataValues.h

@@ -1511,6 +1511,10 @@ class GenericMetadataPatternFlags : public FlagSet<uint32_t> {
     /// Does this pattern have an extra-data pattern?
     HasExtraDataPattern = 0,
 
+    /// Do instances of this pattern have a bitset of flags that occur at the
+    /// end of the metadata, after the extra data if there is any?
+    HasTrailingFlags = 1,
+
     // Class-specific flags.
 
     /// Does this pattern have an immediate-members pattern?
@@ -1535,6 +1539,10 @@ class GenericMetadataPatternFlags : public FlagSet<uint32_t> {
                                 hasExtraDataPattern,
                                 setHasExtraDataPattern)
 
+  FLAGSET_DEFINE_FLAG_ACCESSORS(HasTrailingFlags,
+                                hasTrailingFlags,
+                                setHasTrailingFlags)
+
   FLAGSET_DEFINE_FIELD_ACCESSORS(Value_MetadataKind,
                                  Value_MetadataKind_width,
                                  MetadataKind,
@@ -1667,6 +1675,30 @@ class MetadataRequest : public FlagSet<size_t> {
   }
 };
 
+struct MetadataTrailingFlags : public FlagSet<uint64_t> {
+  enum {
+    /// Whether this metadata is a specialization of a generic metadata pattern
+    /// which was created during compilation.
+    IsStaticSpecialization = 0,
+
+    /// Whether this metadata is a specialization of a generic metadata pattern
+    /// which was created during compilation and made to be canonical by
+    /// modifying the metadata accessor.
+    IsCanonicalStaticSpecialization = 1,
+  };
+
+  explicit MetadataTrailingFlags(uint64_t bits) : FlagSet(bits) {}
+  constexpr MetadataTrailingFlags() {}
+
+  FLAGSET_DEFINE_FLAG_ACCESSORS(IsStaticSpecialization,
+                                isStaticSpecialization,
+                                setIsStaticSpecialization)
+
+  FLAGSET_DEFINE_FLAG_ACCESSORS(IsCanonicalStaticSpecialization,
+                                isCanonicalStaticSpecialization,
+                                setIsCanonicalStaticSpecialization)
+};
+
 /// Flags for Builtin.IntegerLiteral values.
 class IntegerLiteralFlags {
 public:

include/swift/AST/ASTContext.h

@@ -614,6 +614,14 @@ class ASTContext final {
   /// swift_getTypeByMangledNameInContextInMetadataState.
   AvailabilityContext getTypesInAbstractMetadataStateAvailability();
 
+  /// Get the runtime availability of support for prespecialized generic 
+  /// metadata.
+  AvailabilityContext getPrespecializedGenericMetadataAvailability();
+
+  /// Get the runtime availability of features introduced in the Swift 5.2
+  /// compiler for the target platform.
+  AvailabilityContext getSwift52Availability();
+
 
   //===--------------------------------------------------------------------===//
   // Diagnostics Helper functions

include/swift/AST/Decl.h

@@ -2862,7 +2862,7 @@ class GenericTypeDecl : public GenericContext, public TypeDecl {
 /// code. One is formed implicitly when a declaration is written with an opaque
 /// result type, as in:
 ///
-/// func foo() -> opaque SignedInteger { return 1 }
+/// func foo() -> some SignedInteger { return 1 }
 ///
 /// The declared type is a special kind of ArchetypeType representing the
 /// abstracted underlying type.

include/swift/AST/IRGenOptions.h

@@ -190,6 +190,10 @@ class IRGenOptions {
   /// Passing this flag completely disables this behavior.
   unsigned DisableLegacyTypeInfo : 1;
 
+  /// Create metadata specializations for generic types at statically known type
+  /// arguments.
+  unsigned PrespecializeGenericMetadata : 1;
+
   /// The path to load legacy type layouts from.
   StringRef ReadLegacyTypeInfoPath;
 
@@ -255,8 +259,9 @@ class IRGenOptions {
         EnableAnonymousContextMangledNames(false), ForcePublicLinkage(false),
         LazyInitializeClassMetadata(false),
         LazyInitializeProtocolConformances(false), DisableLegacyTypeInfo(false),
-        UseIncrementalLLVMCodeGen(true), UseSwiftCall(false),
-        GenerateProfile(false), EnableDynamicReplacementChaining(false),
+        PrespecializeGenericMetadata(false), UseIncrementalLLVMCodeGen(true),
+        UseSwiftCall(false), GenerateProfile(false),
+        EnableDynamicReplacementChaining(false),
         DisableRoundTripDebugTypes(false), DisableDebuggerShadowCopies(false),
         CmdArgs(), SanitizeCoverage(llvm::SanitizerCoverageOptions()),
         TypeInfoFilter(TypeInfoDumpFilter::All) {}

include/swift/IRGen/Linking.h

@@ -65,7 +65,7 @@ class UniversalLinkageInfo {
   bool shouldAllPrivateDeclsBeVisibleFromOtherFiles() const {
     return HasMultipleIGMs;
   }
-  /// In case of multipe llvm modules, private lazy protocol
+  /// In case of multiple llvm modules, private lazy protocol
   /// witness table accessors could be emitted by two different IGMs during
   /// IRGen into different object files and the linker would complain about
   /// duplicate symbols.

include/swift/Option/FrontendOptions.td

@@ -644,6 +644,10 @@ def disable_verify_exclusivity : Flag<["-"], "disable-verify-exclusivity">,
 def disable_legacy_type_info : Flag<["-"], "disable-legacy-type-info">,
   HelpText<"Completely disable legacy type layout">;
 
+def prespecialize_generic_metadata : Flag<["-"], "prespecialize-generic-metadata">,
+  HelpText<"Statically specialize metadata for generic types at types that "
+           "are known to be used in source.">;
+
 def read_legacy_type_info_path_EQ : Joined<["-"], "read-legacy-type-info-path=">,
   HelpText<"Read legacy type layout from the given path instead of default path">;
 

lib/AST/Availability.cpp

@@ -239,14 +239,25 @@ AvailabilityContext ASTContext::getSwift51Availability() {
 }
 
 AvailabilityContext ASTContext::getTypesInAbstractMetadataStateAvailability() {
+  return getSwift52Availability();
+}
+
+AvailabilityContext ASTContext::getPrespecializedGenericMetadataAvailability() {
+  return getSwift52Availability();
+}
+
+AvailabilityContext ASTContext::getSwift52Availability() {
   auto target = LangOpts.Target;
 
   if (target.isMacOSX() ) {
     return AvailabilityContext(
         VersionRange::allGTE(llvm::VersionTuple(10, 99, 0)));
-  } else if (target.isiOS() || target.isWatchOS()) {
+  } else if (target.isiOS()) {
+    return AvailabilityContext(
+        VersionRange::allGTE(llvm::VersionTuple(99, 0, 0)));
+  } else if (target.isWatchOS()) {
     return AvailabilityContext(
-        VersionRange::allGTE(llvm::VersionTuple(9999, 0, 0)));
+        VersionRange::allGTE(llvm::VersionTuple(9, 99, 0)));
   } else {
     return AvailabilityContext::alwaysAvailable();
   }

lib/Frontend/CompilerInvocation.cpp

@@ -1249,6 +1249,10 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
     Opts.DisableLegacyTypeInfo = true;
   }
 
+  if (Args.hasArg(OPT_prespecialize_generic_metadata)) {
+    Opts.PrespecializeGenericMetadata = true;
+  }
+
   if (const Arg *A = Args.getLastArg(OPT_read_legacy_type_info_path_EQ)) {
     Opts.ReadLegacyTypeInfoPath = A->getValue();
   }

lib/IRGen/ClassMetadataVisitor.h

@@ -204,8 +204,13 @@ class ClassMetadataScanner : public ClassMetadataVisitor<Impl> {
       addPointer();
     }
   }
-  void addGenericArgument(ClassDecl *forClass) { addPointer(); }
-  void addGenericWitnessTable(ClassDecl *forClass) { addPointer(); }
+  void addGenericArgument(GenericRequirement requirement, ClassDecl *forClass) {
+    addPointer();
+  }
+  void addGenericWitnessTable(GenericRequirement requirement,
+                              ClassDecl *forClass) {
+    addPointer();
+  }
   void addPlaceholder(MissingMemberDecl *MMD) {
     for (auto i : range(MMD->getNumberOfVTableEntries())) {
       (void)i;

lib/IRGen/EnumMetadataVisitor.h

@@ -82,8 +82,8 @@ class EnumMetadataScanner : public EnumMetadataVisitor<Impl> {
   void addMetadataFlags() { addPointer(); }
   void addValueWitnessTable() { addPointer(); }
   void addNominalTypeDescriptor() { addPointer(); }
-  void addGenericArgument() { addPointer(); }
-  void addGenericWitnessTable() { addPointer(); }
+  void addGenericArgument(GenericRequirement requirement) { addPointer(); }
+  void addGenericWitnessTable(GenericRequirement requirement) { addPointer(); }
   void addPayloadSize() { addPointer(); }
   void noteStartOfTypeSpecificMembers() {}
 

lib/IRGen/GenDecl.cpp

@@ -1129,6 +1129,7 @@ void IRGenerator::emitTypeMetadataRecords() {
 /// else) that we require.
 void IRGenerator::emitLazyDefinitions() {
   while (!LazyTypeMetadata.empty() ||
+         !LazySpecializedTypeMetadataRecords.empty() ||
          !LazyTypeContextDescriptors.empty() ||
          !LazyOpaqueTypeDescriptors.empty() ||
          !LazyFieldDescriptors.empty() ||
@@ -1145,6 +1146,12 @@ void IRGenerator::emitLazyDefinitions() {
       CurrentIGMPtr IGM = getGenModule(type->getDeclContext());
       emitLazyTypeMetadata(*IGM.get(), type);
     }
+    while (!LazySpecializedTypeMetadataRecords.empty()) {
+      CanType type = LazySpecializedTypeMetadataRecords.pop_back_val();
+      auto *nominal = type->getNominalOrBoundGenericNominal();
+      CurrentIGMPtr IGM = getGenModule(nominal->getDeclContext());
+      emitLazySpecializedGenericTypeMetadata(*IGM.get(), type);
+    }
     while (!LazyTypeContextDescriptors.empty()) {
       NominalTypeDecl *type = LazyTypeContextDescriptors.pop_back_val();
       auto &entry = LazyTypeGlobals.find(type)->second;
@@ -1185,6 +1192,12 @@ void IRGenerator::emitLazyDefinitions() {
     }
   }
 
+  while (!LazyMetadataAccessors.empty()) {
+    NominalTypeDecl *nominal = LazyMetadataAccessors.pop_back_val();
+    CurrentIGMPtr IGM = getGenModule(nominal->getDeclContext());
+    emitLazyMetadataAccessor(*IGM.get(), nominal);
+  }
+
   FinishedEmittingLazyDefinitions = true;
 }
 
@@ -1362,6 +1375,18 @@ void IRGenerator::noteUseOfFieldDescriptor(NominalTypeDecl *type) {
   LazyFieldDescriptors.push_back(type);
 }
 
+void IRGenerator::noteUseOfSpecializedGenericTypeMetadata(CanType type) {
+  auto key = type->getAnyNominal();
+  assert(key);
+  auto &enqueuedSpecializedTypes = this->SpecializationsForGenericTypes[key];
+  if (llvm::all_of(enqueuedSpecializedTypes,
+                   [&](CanType enqueued) { return enqueued != type; })) {
+    assert(!FinishedEmittingLazyDefinitions);
+    this->LazySpecializedTypeMetadataRecords.push_back(type);
+    enqueuedSpecializedTypes.push_back(type);
+  }
+}
+
 void IRGenerator::noteUseOfOpaqueTypeDescriptor(OpaqueTypeDecl *opaque) {
   if (!opaque)
     return;
@@ -3646,8 +3671,11 @@ llvm::GlobalValue *IRGenModule::defineTypeMetadata(CanType concreteType,
   if (nominal)
     addRuntimeResolvableType(nominal);
 
-  // Don't define the alias for foreign type metadata, since it's not ABI.
-  if (nominal && requiresForeignTypeMetadata(nominal))
+  // Don't define the alias for foreign type metadata or prespecialized generic
+  // metadata, since neither is ABI.
+  if ((nominal && requiresForeignTypeMetadata(nominal)) ||
+      (concreteType->getAnyGeneric() &&
+       concreteType->getAnyGeneric()->isGenericContext()))
     return var;
 
   // For concrete metadata, declare the alias to its address point.
@@ -3682,9 +3710,13 @@ ConstantReference IRGenModule::getAddrOfTypeMetadata(CanType concreteType,
 
   llvm::Type *defaultVarTy;
   unsigned adjustmentIndex;
-
+
+  bool fullMetadata = (nominal && requiresForeignTypeMetadata(nominal)) ||
+                      (concreteType->getAnyGeneric() &&
+                       concreteType->getAnyGeneric()->isGenericContext());
+
   // Foreign classes reference the full metadata with a GEP.
-  if (nominal && requiresForeignTypeMetadata(nominal)) {
+  if (fullMetadata) {
     defaultVarTy = FullTypeMetadataStructTy;
     adjustmentIndex = MetadataAdjustmentIndex::ValueType;
   // The symbol for other nominal type metadata is generated at the address
@@ -3709,10 +3741,18 @@ ConstantReference IRGenModule::getAddrOfTypeMetadata(CanType concreteType,
     IRGen.noteUseOfTypeMetadata(nominal);
   }
 
+  if (shouldPrespecializeGenericMetadata()) {
+    if (auto nominal = concreteType->getAnyNominal()) {
+      if (nominal->isGenericContext()) {
+        IRGen.noteUseOfSpecializedGenericTypeMetadata(concreteType);
+      }
+    }
+  }
+
   Optional<LinkEntity> entity;
   DebugTypeInfo DbgTy;
 
-  if (nominal && requiresForeignTypeMetadata(nominal)) {
+  if (fullMetadata) {
     entity = LinkEntity::forTypeMetadata(concreteType,
                                          TypeMetadataAddress::FullMetadata);
     DbgTy = DebugTypeInfo::getMetadata(MetatypeType::get(concreteType),
@@ -4029,10 +4069,6 @@ Optional<llvm::Function*> IRGenModule::getAddrOfIVarInitDestroy(
 llvm::Function *IRGenModule::getAddrOfValueWitness(CanType abstractType,
                                                    ValueWitness index,
                                                 ForDefinition_t forDefinition) {
-  // We shouldn't emit value witness symbols for generic type instances.
-  assert(!isa<BoundGenericType>(abstractType) &&
-         "emitting value witness for generic type instance?!");
-
   LinkEntity entity = LinkEntity::forValueWitness(abstractType, index);
 
   llvm::Function *&entry = GlobalFuncs[entity];