[CoroutineAccessors] Default overrides of new symbols.

docs/ABI/Mangling.rst

@@ -239,6 +239,7 @@ types where the metadata itself has unknown layout.)
   global ::= global 'Twb'                // back deployment thunk
   global ::= global 'TwB'                // back deployment fallback function
   global ::= global 'Twc'                // coro function pointer of a function
+  global ::= global 'Twd'                // default override of a function
   global ::= entity entity 'TV'          // vtable override thunk, derived followed by base
   global ::= type label-list? 'D'        // type mangling for the debugger with label list for function types.
   global ::= type 'TC'                   // continuation prototype (not actually used for real symbols)

include/swift/ABI/Metadata.h

@@ -654,6 +654,54 @@ using TargetRelativeProtocolRequirementPointer =
 using RelativeProtocolRequirementPointer =
   TargetRelativeProtocolRequirementPointer<InProcess>;
 
+/// An entry in the default override table, consisting of one of our methods
+/// `replacement` together with (1) another of our methods `original` which
+/// might have been overridden by a subclass and (2) an implementation of
+/// `replacement` to be used by such a subclass if it does not provide its own
+/// implementation.
+template <typename Runtime>
+struct TargetMethodDefaultOverrideDescriptor {
+  /// The method which replaced the original at call-sites.
+  TargetRelativeMethodDescriptorPointer<Runtime> Replacement;
+
+  /// The method originally called at such call sites.
+  TargetRelativeMethodDescriptorPointer<Runtime> Original;
+
+  union {
+    TargetCompactFunctionPointer<Runtime, void, /*nullable*/ true> Impl;
+    TargetRelativeDirectPointer<Runtime, void, /*nullable*/ true> AsyncImpl;
+    TargetRelativeDirectPointer<Runtime, void, /*nullable*/ true> CoroImpl;
+  };
+
+  bool isData() const {
+    auto *replacement = Replacement.get();
+    assert(replacement && "no replacement");
+    return replacement->Flags.isData();
+  }
+
+  void *getImpl() const {
+    auto *replacement = Replacement.get();
+    assert(replacement && "no replacement");
+    if (replacement->Flags.isAsync()) {
+      return AsyncImpl.get();
+    } else if (replacement->Flags.isCalleeAllocatedCoroutine()) {
+      return CoroImpl.get();
+    } else {
+      return Impl.get();
+    }
+  }
+};
+
+/// Header for a table of default override descriptors.  Such a table is a
+/// variable-sized structure whose length is stored in this header which is
+/// followed by that many TargetMethodDefaultOverrideDescriptors.
+template <typename Runtime>
+struct TargetMethodDefaultOverrideTableHeader {
+  /// The number of TargetMethodDefaultOverrideDescriptor records following this
+  /// header in the class's nominal type descriptor.
+  uint32_t NumEntries;
+};
+
 /// An entry in the method override table, referencing a method from one of our
 /// ancestor classes, together with an implementation.
 template <typename Runtime>
@@ -4205,9 +4253,11 @@ class swift_ptrauth_struct_context_descriptor(ClassDescriptor)
                               TargetCanonicalSpecializedMetadataAccessorsListEntry<Runtime>,
                               TargetCanonicalSpecializedMetadatasCachingOnceToken<Runtime>,
                               InvertibleProtocolSet,
-                              TargetSingletonMetadataPointer<Runtime>> {
+                              TargetSingletonMetadataPointer<Runtime>,
+                              TargetMethodDefaultOverrideTableHeader<Runtime>,
+                              TargetMethodDefaultOverrideDescriptor<Runtime>> {
 private:
-  using TrailingGenericContextObjects =
+  using TrailingGenericContextObjects = 
     swift::TrailingGenericContextObjects<TargetClassDescriptor<Runtime>,
                                          TargetTypeGenericContextDescriptorHeader,
                                          TargetResilientSuperclass<Runtime>,
@@ -4223,7 +4273,9 @@ class swift_ptrauth_struct_context_descriptor(ClassDescriptor)
                                          TargetCanonicalSpecializedMetadataAccessorsListEntry<Runtime>,
                                          TargetCanonicalSpecializedMetadatasCachingOnceToken<Runtime>,
                                          InvertibleProtocolSet,
-                                         TargetSingletonMetadataPointer<Runtime>>;
+                                         TargetSingletonMetadataPointer<Runtime>,
+                                         TargetMethodDefaultOverrideTableHeader<Runtime>,
+                                         TargetMethodDefaultOverrideDescriptor<Runtime>>;
 
   using TrailingObjects =
     typename TrailingGenericContextObjects::TrailingObjects;
@@ -4254,6 +4306,10 @@ class swift_ptrauth_struct_context_descriptor(ClassDescriptor)
   using MetadataCachingOnceToken =
       TargetCanonicalSpecializedMetadatasCachingOnceToken<Runtime>;
   using SingletonMetadataPointer = TargetSingletonMetadataPointer<Runtime>;
+  using DefaultOverrideTableHeader =
+      TargetMethodDefaultOverrideTableHeader<Runtime>;
+  using DefaultOverrideDescriptor =
+      TargetMethodDefaultOverrideDescriptor<Runtime>;
 
   using StoredPointer = typename Runtime::StoredPointer;
   using StoredPointerDifference = typename Runtime::StoredPointerDifference;
@@ -4399,6 +4455,16 @@ class swift_ptrauth_struct_context_descriptor(ClassDescriptor)
     return this->hasSingletonMetadataPointer() ? 1 : 0;
   }
 
+  size_t numTrailingObjects(OverloadToken<DefaultOverrideTableHeader>) const {
+    return hasDefaultOverrideTable() ? 1 : 0;
+  }
+
+  size_t numTrailingObjects(OverloadToken<DefaultOverrideDescriptor>) const {
+    if (!hasDefaultOverrideTable())
+      return 0;
+    return getDefaultOverrideTable()->NumEntries;
+  }
+
 public:
   const TargetRelativeDirectPointer<Runtime, const void, /*nullable*/true> &
   getResilientSuperclass() const {
@@ -4430,6 +4496,10 @@ class swift_ptrauth_struct_context_descriptor(ClassDescriptor)
     return FieldOffsetVectorOffset;
   }
 
+  bool hasDefaultOverrideTable() const {
+    return getTypeContextDescriptorFlags().class_hasDefaultOverrideTable();
+  }
+
   bool isActor() const {
     return this->getTypeContextDescriptorFlags().class_isActor();
   }
@@ -4476,6 +4546,20 @@ class swift_ptrauth_struct_context_descriptor(ClassDescriptor)
             numTrailingObjects(OverloadToken<MethodOverrideDescriptor>{})};
   }
 
+  const DefaultOverrideTableHeader *getDefaultOverrideTable() const {
+    if (!hasDefaultOverrideTable())
+      return nullptr;
+    return this->template getTrailingObjects<DefaultOverrideTableHeader>();
+  }
+
+  llvm::ArrayRef<DefaultOverrideDescriptor> getDefaultOverrideDescriptors()
+      const {
+    if (!hasDefaultOverrideTable())
+      return {};
+    return {this->template getTrailingObjects<DefaultOverrideDescriptor>(),
+            numTrailingObjects(OverloadToken<DefaultOverrideDescriptor>{})};
+  }
+
   /// Return the bounds of this class's metadata.
   TargetClassMetadataBounds<Runtime> getMetadataBounds() const {
     if (!hasResilientSuperclass())

include/swift/ABI/MetadataValues.h

@@ -1955,8 +1955,12 @@ class TypeContextDescriptorFlags : public FlagSet<uint16_t> {
     /// Set if the metadata contains a pointer to a layout string
     HasLayoutString = 4,
 
+    /// WARNING: 5 is the last bit!
+
     // Type-specific flags:
 
+    Class_HasDefaultOverrideTable = 6,
+
     /// Set if the class is an actor.
     ///
     /// Only meaningful for class descriptors.
@@ -2062,6 +2066,9 @@ class TypeContextDescriptorFlags : public FlagSet<uint16_t> {
   FLAGSET_DEFINE_FLAG_ACCESSORS(Class_IsActor,
                                 class_isActor,
                                 class_setIsActor)
+  FLAGSET_DEFINE_FLAG_ACCESSORS(Class_HasDefaultOverrideTable,
+                                class_hasDefaultOverrideTable,
+                                class_setHasDefaultOverrideTable)
 
   FLAGSET_DEFINE_FIELD_ACCESSORS(Class_ResilientSuperclassReferenceKind,
                                  Class_ResilientSuperclassReferenceKind_width,

include/swift/AST/DiagnosticsParse.def

@@ -763,6 +763,14 @@ ERROR(sil_witness_assoc_conf_not_found,none,
 ERROR(sil_witness_protocol_conformance_not_found,none,
       "sil protocol conformance not found", ())
 
+// SIL default override table
+ERROR(sil_default_override_func_not_found,none,
+      "sil function not found %0", (Identifier))
+ERROR(sil_default_override_class_not_found,none,
+      "sil class not found %0", (Identifier))
+ERROR(sil_default_override_decl_not_class,none,
+      "sil decl found for %0 is not a class", (Identifier))
+
 // SIL differentiability witnesses
 ERROR(sil_diff_witness_expected_token,PointsToFirstBadToken,
       "expected '%0' in differentiability witness", (StringRef))

include/swift/AST/TokenKinds.def

@@ -272,6 +272,7 @@ SIL_KEYWORD(sil_moveonlydeinit)
 SIL_KEYWORD(sil_global)
 SIL_KEYWORD(sil_witness_table)
 SIL_KEYWORD(sil_default_witness_table)
+SIL_KEYWORD(sil_default_override_table)
 SIL_KEYWORD(sil_differentiability_witness)
 SIL_KEYWORD(sil_coverage_map)
 SIL_KEYWORD(sil_scope)

include/swift/Demangling/DemangleNodes.def

@@ -411,6 +411,7 @@ NODE(Integer)
 NODE(NegativeInteger)
 NODE(DependentGenericParamValueMarker)
 NODE(CoroFunctionPointer)
+NODE(DefaultOverride)
 
 #undef CONTEXT_NODE
 #undef NODE

include/swift/Parse/ParseSILSupport.h

@@ -33,6 +33,7 @@ namespace swift {
     virtual bool parseSILGlobal(Parser &P) = 0;
     virtual bool parseSILWitnessTable(Parser &P) = 0;
     virtual bool parseSILDefaultWitnessTable(Parser &P) = 0;
+    virtual bool parseSILDefaultOverrideTable(Parser &P) = 0;
     virtual bool parseSILDifferentiabilityWitness(Parser &P) = 0;
     virtual bool parseSILCoverageMap(Parser &P) = 0;
     virtual bool parseSILProperty(Parser &P) = 0;

include/swift/SIL/Notifications.h

@@ -27,6 +27,7 @@ class SILNode;
 class ModuleDecl;
 class SILFunction;
 class SILWitnessTable;
+class SILDefaultOverrideTable;
 class SILDefaultWitnessTable;
 class SILGlobalVariable;
 class SILVTable;
@@ -50,6 +51,12 @@ class DeserializationNotificationHandlerBase {
   virtual void didDeserializeWitnessTableEntries(ModuleDecl *mod,
                                                  SILWitnessTable *wt) = 0;
 
+  /// Observe that we successfully deserialized a default override table's
+  /// entries.
+  virtual void
+  didDeserializeDefaultOverrideTableEntries(ModuleDecl *mod,
+                                            SILDefaultOverrideTable *ot) = 0;
+
   /// Observe that we successfully deserialized a default witness table's
   /// entries.
   virtual void
@@ -69,6 +76,10 @@ class DeserializationNotificationHandlerBase {
   virtual void didDeserialize(ModuleDecl *mod,
                               SILDefaultWitnessTable *wtable) = 0;
 
+  /// Observe that we deserialized a default override table declaration.
+  virtual void didDeserialize(ModuleDecl *mod,
+                              SILDefaultOverrideTable *otable) = 0;
+
   /// Observe that we deserialized a move only deinit declaration.
   virtual void didDeserialize(ModuleDecl *mod, SILMoveOnlyDeinit *deinit) = 0;
 
@@ -93,6 +104,10 @@ class DeserializationNotificationHandler
                                                  SILWitnessTable *wt) override {
   }
 
+  /// Observe that we successfully deserialized a override table's entries.
+  virtual void didDeserializeDefaultOverrideTableEntries(
+      ModuleDecl *mod, SILDefaultOverrideTable *ot) override {}
+
   /// Observe that we successfully deserialized a default witness table's
   /// entries.
   virtual void didDeserializeDefaultWitnessTableEntries(
@@ -113,6 +128,10 @@ class DeserializationNotificationHandler
   virtual void didDeserialize(ModuleDecl *mod,
                               SILDefaultWitnessTable *wtable) override {}
 
+  /// Observe that we deserialized a default override table declaration.
+  virtual void didDeserialize(ModuleDecl *mod,
+                              SILDefaultOverrideTable *otable) override {}
+
   /// Observe that we deserialized a move only deinit declaration.
   virtual void didDeserialize(ModuleDecl *mod,
                               SILMoveOnlyDeinit *deinit) override {}
@@ -242,11 +261,15 @@ class DeserializationNotificationHandlerSet final
   void
   didDeserializeDefaultWitnessTableEntries(ModuleDecl *mod,
                                            SILDefaultWitnessTable *wt) override;
+  void didDeserializeDefaultOverrideTableEntries(
+      ModuleDecl *mod, SILDefaultOverrideTable *ot) override;
   void didDeserialize(ModuleDecl *mod, SILGlobalVariable *var) override;
   void didDeserialize(ModuleDecl *mod, SILVTable *vtable) override;
   void didDeserialize(ModuleDecl *mod, SILWitnessTable *wtable) override;
   void didDeserialize(ModuleDecl *mod,
                       SILDefaultWitnessTable *wtable) override;
+  void didDeserialize(ModuleDecl *mod,
+                      SILDefaultOverrideTable *otable) override;
   void didDeserialize(ModuleDecl *mod, SILMoveOnlyDeinit *deinit) override;
 };
 } // namespace swift

include/swift/SIL/SILDeclRef.h

@@ -19,6 +19,8 @@
 #ifndef SWIFT_SIL_SILDECLREF_H
 #define SWIFT_SIL_SILDECLREF_H
 
+#include "swift/AST/Attr.h"
+#include "swift/AST/AutoDiff.h"
 #include "swift/AST/AvailabilityRange.h"
 #include "swift/AST/ClangNode.h"
 #include "swift/AST/GenericSignature.h"
@@ -36,7 +38,6 @@ namespace swift {
   enum class EffectsKind : uint8_t;
   class AbstractFunctionDecl;
   class AbstractClosureExpr;
-  class AutoDiffDerivativeFunctionIdentifier;
   class ValueDecl;
   class FuncDecl;
   class ClosureExpr;
@@ -53,7 +54,6 @@ namespace swift {
   enum class SILLinkage : uint8_t;
   class AnyFunctionRef;
   class GenericSignature;
-  class CustomAttr;
 
 /// How a method is dispatched.
 enum class MethodDispatch {