[metadata prespecialization] Support for classes.

When generic metadata for a class is requested in the same module where
the class is defined, rather than a call to the generic metadata
accessor or to a variant of typeForMangledNode, a call to a new
accessor--a canonical specialized generic metadata accessor--is emitted.
The new function is defined schematically as follows:

    MetadataResponse `canonical specialized metadata accessor for C<K>`(MetadataRequest request) {
      (void)`canonical specialized metadata accessor for superclass(C<K>)`(::Complete)
      (void)`canonical specialized metadata accessor for generic_argument_class(C<K>, 1)`(::Complete)
      ...
      (void)`canonical specialized metadata accessor for generic_argument_class(C<K>, count)`(::Complete)
      auto *metadata = objc_opt_self(`canonical specialized metadata for C<K>`);
      return {metadata, MetadataState::Complete};
    }

where generic_argument_class(C<K>, N) denotes the Nth generic argument
which is both (1) itself a specialized generic type and is also (2) a
class.  These calls to the specialized metadata accessors for these
related types ensure that all generic class types are registered with
the Objective-C runtime.

To enable these new canonical specialized generic metadata accessors,
metadata for generic classes is prespecialized as needed. So are the
metaclasses and the corresponding rodata.

Previously, the lazy objc naming hook was registered during process
execution when the first generic class metadata was instantiated. Since
that instantiation may occur "before process launch" (i.e. if the
generic metadata is prespecialized), the lazy naming hook is now
installed at process launch.

Author: nate-chandler

include/swift/ABI/Metadata.h

@@ -1025,7 +1025,7 @@ struct TargetAnyClassMetadata : public TargetHeapMetadata<Runtime> {
   using TargetMetadata<Runtime>::setClassISA;
 #endif
 
-  // Note that ObjC classes does not have a metadata header.
+  // Note that ObjC classes do not have a metadata header.
 
   /// The metadata for the superclass.  This is null for the root class.
   ConstTargetMetadataPointer<Runtime, swift::TargetClassMetadata> Superclass;

include/swift/AST/Types.h

@@ -852,7 +852,17 @@ class alignas(1 << TypeAlignInBits) TypeBase {
   /// \returns The superclass of this type, or a null type if it has no
   ///          superclass.
   Type getSuperclass(bool useArchetypes = true);
-  
+
+  /// Retrieve the root class of this type by repeatedly retrieving the
+  /// superclass.
+  ///
+  /// \param useArchetypes Whether to use context archetypes for outer generic
+  /// parameters if the class is nested inside a generic function.
+  ///
+  /// \returns The base class of this type, or this type itself if it has no
+  ///          superclasses.
+  Type getRootClass(bool useArchetypes = true);
+
   /// True if this type is the exact superclass of another type.
   ///
   /// \param ty       The potential subclass.

include/swift/Demangling/DemangleNodes.def

@@ -287,5 +287,9 @@ NODE(OpaqueTypeDescriptorAccessorVar)
 NODE(OpaqueReturnType)
 CONTEXT_NODE(OpaqueReturnTypeOf)
 
+// Added in Swift 5.3
+NODE(CanonicalSpecializedGenericMetaclass)
+NODE(CanonicalSpecializedGenericTypeMetadataAccessFunction)
+
 #undef CONTEXT_NODE
 #undef NODE

include/swift/IRGen/Linking.h

@@ -193,7 +193,7 @@ class LinkEntity {
     /// The nominal type descriptor for a nominal type.
     /// The pointer is a NominalTypeDecl*.
     NominalTypeDescriptor,
-    
+
     /// The descriptor for an opaque type.
     /// The pointer is an OpaqueTypeDecl*.
     OpaqueTypeDescriptor,
@@ -295,12 +295,12 @@ class LinkEntity {
     /// The descriptor for an extension.
     /// The pointer is an ExtensionDecl*.
     ExtensionDescriptor,
-    
+
     /// The descriptor for a runtime-anonymous context.
     /// The pointer is the DeclContext* of a child of the context that should
     /// be considered private.
     AnonymousDescriptor,
-    
+
     /// A SIL global variable. The pointer is a SILGlobalVariable*.
     SILGlobalVariable,
 
@@ -384,6 +384,15 @@ class LinkEntity {
 
     /// A global function pointer for dynamically replaceable functions.
     DynamicallyReplaceableFunctionVariable,
+
+    /// A reference to a metaclass-stub for a statically specialized generic
+    /// class.
+    /// The pointer is a canonical TypeBase*.
+    CanonicalSpecializedGenericSwiftMetaclassStub,
+
+    /// An access function for prespecialized type metadata.
+    /// The pointer is a canonical TypeBase*.
+    CanonicalSpecializedGenericTypeMetadataAccessFunction,
   };
   friend struct llvm::DenseMapInfo<LinkEntity>;
 
@@ -1020,6 +1029,22 @@ class LinkEntity {
     return entity;
   }
 
+  static LinkEntity
+  forSpecializedGenericSwiftMetaclassStub(CanType concreteType) {
+    LinkEntity entity;
+    entity.setForType(Kind::CanonicalSpecializedGenericSwiftMetaclassStub,
+                      concreteType);
+    return entity;
+  }
+
+  static LinkEntity
+  forPrespecializedTypeMetadataAccessFunction(CanType theType) {
+    LinkEntity entity;
+    entity.setForType(
+        Kind::CanonicalSpecializedGenericTypeMetadataAccessFunction, theType);
+    return entity;
+  }
+
   void mangle(llvm::raw_ostream &out) const;
   void mangle(SmallVectorImpl<char> &buffer) const;
   std::string mangleAsString() const;

lib/AST/Type.cpp

@@ -1546,6 +1546,17 @@ Type TypeBase::getSuperclass(bool useArchetypes) {
   return superclassTy.subst(subMap);
 }
 
+Type TypeBase::getRootClass(bool useArchetypes) {
+  Type iterator = this;
+  assert(iterator);
+
+  while (auto superclass = iterator->getSuperclass(useArchetypes)) {
+    iterator = superclass;
+  }
+
+  return iterator;
+}
+
 bool TypeBase::isExactSuperclassOf(Type ty) {
   // For there to be a superclass relationship, we must be a class, and
   // the potential subtype must be a class, superclass-bounded archetype,

lib/Demangling/Demangler.cpp

@@ -1874,6 +1874,9 @@ NodePointer Demangler::demangleMetatype() {
     case 'A':
       return createWithChild(Node::Kind::ReflectionMetadataAssocTypeDescriptor,
                              popProtocolConformance());
+    case 'b':
+      return createWithPoppedType(
+          Node::Kind::CanonicalSpecializedGenericTypeMetadataAccessFunction);
     case 'B':
       return createWithChild(Node::Kind::ReflectionMetadataBuiltinDescriptor,
                                popNode(Node::Kind::Type));
@@ -1917,6 +1920,9 @@ NodePointer Demangler::demangleMetatype() {
       return createWithPoppedType(Node::Kind::TypeMetadataLazyCache);
     case 'm':
       return createWithPoppedType(Node::Kind::Metaclass);
+    case 'M':
+      return createWithPoppedType(
+          Node::Kind::CanonicalSpecializedGenericMetaclass);
     case 'n':
       return createWithPoppedType(Node::Kind::NominalTypeDescriptor);
     case 'o':

lib/Demangling/NodePrinter.cpp

@@ -540,6 +540,8 @@ class NodePrinter {
     case Node::Kind::OpaqueTypeDescriptorSymbolicReference:
     case Node::Kind::OpaqueReturnType:
     case Node::Kind::OpaqueReturnTypeOf:
+    case Node::Kind::CanonicalSpecializedGenericMetaclass:
+    case Node::Kind::CanonicalSpecializedGenericTypeMetadataAccessFunction:
       return false;
     }
     printer_unreachable("bad node kind");
@@ -2418,6 +2420,14 @@ NodePointer NodePrinter::print(NodePointer Node, bool asPrefixContext) {
   case Node::Kind::AccessorFunctionReference:
     Printer << "accessor function at " << Node->getIndex();
     return nullptr;
+  case Node::Kind::CanonicalSpecializedGenericMetaclass:
+    Printer << "specialized generic metaclass for ";
+    print(Node->getFirstChild());
+    return nullptr;
+  case Node::Kind::CanonicalSpecializedGenericTypeMetadataAccessFunction:
+    Printer << "canonical specialized generic type metadata accessor for ";
+    print(Node->getChild(0));
+    return nullptr;
   }
   printer_unreachable("bad node kind!");
 }

lib/Demangling/OldRemangler.cpp

@@ -2133,6 +2133,17 @@ void Remangler::mangleAccessorFunctionReference(Node *node) {
   unreachable("can't remangle");
 }
 
+void Remangler::mangleCanonicalSpecializedGenericMetaclass(Node *node) {
+  Buffer << "MM";
+  mangleSingleChildNode(node); // type
+}
+
+void Remangler::mangleCanonicalSpecializedGenericTypeMetadataAccessFunction(
+    Node *node) {
+  mangleSingleChildNode(node);
+  Buffer << "Mb";
+}
+
 /// The top-level interface to the remangler.
 std::string Demangle::mangleNodeOld(NodePointer node) {
   if (!node) return "";

lib/Demangling/Remangler.cpp

@@ -2533,6 +2533,17 @@ void Remangler::mangleAccessorFunctionReference(Node *node) {
   unreachable("can't remangle");
 }
 
+void Remangler::mangleCanonicalSpecializedGenericMetaclass(Node *node) {
+  mangleChildNodes(node);
+  Buffer << "MM";
+}
+
+void Remangler::mangleCanonicalSpecializedGenericTypeMetadataAccessFunction(
+    Node *node) {
+  mangleSingleChildNode(node);
+  Buffer << "Mb";
+}
+
 } // anonymous namespace
 
 /// The top-level interface to the remangler.

lib/IRGen/ClassTypeInfo.h

@@ -0,0 +1,66 @@
+//===--- ClassTypeInfo.h - The layout info for class types. -----*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file contains layout information for class types.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_IRGEN_CLASSTYPEINFO_H
+#define SWIFT_IRGEN_CLASSTYPEINFO_H
+
+#include "ClassLayout.h"
+#include "HeapTypeInfo.h"
+
+namespace swift {
+namespace irgen {
+
+/// Layout information for class types.
+class ClassTypeInfo : public HeapTypeInfo<ClassTypeInfo> {
+  ClassDecl *TheClass;
+
+  // The resilient layout of the class, without making any assumptions
+  // that violate resilience boundaries. This is used to allocate
+  // and deallocate instances of the class, and to access fields.
+  mutable Optional<ClassLayout> ResilientLayout;
+
+  // A completely fragile layout, used for metadata emission.
+  mutable Optional<ClassLayout> FragileLayout;
+
+  /// Can we use swift reference-counting, or do we have to use
+  /// objc_retain/release?
+  const ReferenceCounting Refcount;
+
+  ClassLayout generateLayout(IRGenModule &IGM, SILType classType,
+                             bool forBackwardDeployment) const;
+
+public:
+  ClassTypeInfo(llvm::PointerType *irType, Size size, SpareBitVector spareBits,
+                Alignment align, ClassDecl *theClass,
+                ReferenceCounting refcount)
+      : HeapTypeInfo(irType, size, std::move(spareBits), align),
+        TheClass(theClass), Refcount(refcount) {}
+
+  ReferenceCounting getReferenceCounting() const { return Refcount; }
+
+  ClassDecl *getClass() const { return TheClass; }
+
+  const ClassLayout &getClassLayout(IRGenModule &IGM, SILType type,
+                                    bool forBackwardDeployment) const;
+
+  StructLayout *createLayoutWithTailElems(IRGenModule &IGM, SILType classType,
+                                          ArrayRef<SILType> tailTypes) const;
+};
+
+} // namespace irgen
+} // namespace swift
+
+#endif