IRGen: Lower external key path components.

The key path pattern needs to include a reference to the external descriptor, along with hooks for lowering its type arguments and indices, if any. The runtime will need to instantiate and interpolate the external component when the key path object is instantiated.

While we're here, let's also reserve some more component header bytes for future expansion, since this is an ABI we're going to be living with for a while.

Author: jckarter

docs/ABI/KeyPaths.md

@@ -25,7 +25,7 @@ by previous ABI-stable versions of the Swift compiler.
 ### Buffer Header
 
 Key path objects begin with the standard Swift heap object header, followed by a
-key path object header. Relative to the start of the heap object header:
+key path object header. Relative to the end of the heap object header:
 
 Offset  | Description
 ------- | ----------------------------------------------
@@ -40,7 +40,7 @@ following bit fields:
 Bits (LSB zero) | Description
 --------------- | -----------
 0...23          | **Buffer size** in bytes
-24...29         | Reserved. Must be zero in Swift 4 runtime
+24...29         | Reserved. Must be zero in Swift 4...5 runtime
 30              | 1 = Has **reference prefix**, 0 = No reference prefix
 31              | 1 = Is **trivial**, 0 = Has destructor
 
@@ -63,8 +63,8 @@ describing the following component.
 
 Bits (LSB zero) | Description
 --------------- | -----------
-0...28          | **Payload** (meaning is dependent on component kind)
-29...30         | **Component kind**
+0...23          | **Payload** (meaning is dependent on component kind)
+24...30         | **Component kind**
 31              | 1 = **End of reference prefix**, 0 = Not end of reference prefix
 
 If the key path has a *reference prefix*, then exactly one component must have
@@ -73,27 +73,27 @@ that the component after the end of the reference prefix will initiate mutation.
 
 The following *component kinds* are recognized:
 
-Value in bit 30&29 | Description
------------------- | -----------
-0                  | Struct/tuple/self stored property
-1                  | Computed
-2                  | Class stored property
-3                  | Optional chaining/forcing/wrapping
+Value in bits 24...30 | Description
+--------------------- | -----------
+0                     | Struct/tuple/self stored property
+1                     | Computed
+2                     | Class stored property
+3                     | Optional chaining/forcing/wrapping
 
 - A **struct stored property** component, when given
   a value of the base type in memory, can project the component value in-place
   at a fixed offset within the base value. This applies for struct stored
   properties, tuple fields, and the `.self` identity component (which trivially
   projects at offset zero). The
   *payload* contains the offset in bytes of the projected field in the
-  aggregate, or the special value `0x1FFF_FFFF`, which indicates that the
+  aggregate, or the special value `0xFF_FFFF`, which indicates that the
   offset is too large to pack into the payload and is stored in the next 32 bits
   after the header.
 - A **class stored property** component, when given a reference to a class
   instance, can project the component value inside the class instance at
   a fixed offset. The *payload*
   *payload* contains the offset in bytes of the projected field from the
-  address point of the object, or the special value `0x1FFF_FFFF`, which
+  address point of the object, or the special value `0xFF_FFFF`, which
   indicates that the offset is too large to pack into the payload and is stored
   in the next 32 bits after the header.
 - An **optional** component performs an operation involving `Optional` values.

include/swift/ABI/KeyPath.h

@@ -204,6 +204,13 @@ class KeyPathComponentHeader {
                     : getResolutionStrategy(idKind)));
   }
 
+  constexpr static KeyPathComponentHeader
+  forExternalComponent() {
+    return KeyPathComponentHeader(
+      _SwiftKeyPathComponentHeader_ExternalTag
+      << _SwiftKeyPathComponentHeader_DiscriminatorShift);
+  }
+  
   constexpr uint32_t getData() const { return Data; }
 };
 

include/swift/AST/GenericEnvironment.h

@@ -29,12 +29,25 @@
 
 namespace swift {
 
+class ArchetypeType;
 class GenericSignatureBuilder;
 class ASTContext;
 class GenericTypeParamType;
 class SILModule;
 class SILType;
 
+/// Query function suitable for use as a \c TypeSubstitutionFn that queries
+/// the mapping of interface types to archetypes.
+class QueryInterfaceTypeSubstitutions {
+  const GenericEnvironment *self;
+  
+public:
+  QueryInterfaceTypeSubstitutions(const GenericEnvironment *self)
+  : self(self) { }
+  
+  Type operator()(SubstitutableType *type) const;
+};
+
 /// Describes the mapping between archetypes and interface types for the
 /// generic parameters of a DeclContext.
 ///
@@ -66,23 +79,12 @@ class alignas(1 << DeclAlignInBits) GenericEnvironment final
   GenericEnvironment(GenericSignature *signature,
                      GenericSignatureBuilder *builder);
 
-  friend class ArchetypeType;
-  friend class GenericSignatureBuilder;
+  friend ArchetypeType;
+  friend GenericSignatureBuilder;
 
   GenericSignatureBuilder *getGenericSignatureBuilder() const { return Builder; }
 
-  /// Query function suitable for use as a \c TypeSubstitutionFn that queries
-  /// the mapping of interface types to archetypes.
-  class QueryInterfaceTypeSubstitutions {
-    const GenericEnvironment *self;
-
-  public:
-    QueryInterfaceTypeSubstitutions(const GenericEnvironment *self)
-      : self(self) { }
-
-    Type operator()(SubstitutableType *type) const;
-  };
-  friend class QueryInterfaceTypeSubstitutions;
+  friend QueryInterfaceTypeSubstitutions;
 
 public:
   GenericSignature *getGenericSignature() const {

include/swift/Demangling/DemangleNodes.def

@@ -132,6 +132,7 @@ NODE(PartialApplyObjCForwarder)
 NODE(PostfixOperator)
 NODE(PrefixOperator)
 NODE(PrivateDeclName)
+NODE(PropertyDescriptor)
 CONTEXT_NODE(Protocol)
 NODE(ProtocolConformance)
 NODE(ProtocolDescriptor)

include/swift/IRGen/Linking.h

@@ -140,6 +140,10 @@ class LinkEntity {
     /// The pointer is a ClassDecl*.
     ClassMetadataBaseOffset,
 
+    /// The property descriptor for a public property or subscript.
+    /// The pointer is an AbstractStorageDecl*.
+    PropertyDescriptor,
+
     /// The nominal type descriptor for a nominal type.
     /// The pointer is a NominalTypeDecl*.
     NominalTypeDescriptor,
@@ -481,6 +485,12 @@ class LinkEntity {
     return entity;
   }
 
+  static LinkEntity forPropertyDescriptor(AbstractStorageDecl *decl) {
+    LinkEntity entity;
+    entity.setForDecl(Kind::PropertyDescriptor, decl);
+    return entity;
+  }
+
   static LinkEntity forModuleDescriptor(ModuleDecl *decl) {
     LinkEntity entity;
     entity.setForDecl(Kind::ModuleDescriptor, decl);

lib/AST/GenericEnvironment.cpp

@@ -132,8 +132,7 @@ Type TypeBase::mapTypeOutOfContext() {
     SubstFlags::AllowLoweredTypes);
 }
 
-Type GenericEnvironment::QueryInterfaceTypeSubstitutions::operator()(
-                                                SubstitutableType *type) const {
+Type QueryInterfaceTypeSubstitutions::operator()(SubstitutableType *type) const{
   if (auto gp = type->getAs<GenericTypeParamType>()) {
     // Find the index into the parallel arrays of generic parameters and
     // context types.
@@ -148,7 +147,7 @@ Type GenericEnvironment::QueryInterfaceTypeSubstitutions::operator()(
     // If the context type isn't already known, lazily create it.
     Type contextType = self->getContextTypes()[index];
     if (!contextType) {
-      assert(self->Builder && "Missing generic signature builder for lazy query");
+      assert(self->Builder &&"Missing generic signature builder for lazy query");
       auto equivClass =
         self->Builder->resolveEquivalenceClass(
                                   type,

lib/Demangling/Demangler.cpp

@@ -1464,6 +1464,9 @@ NodePointer Demangler::demangleMetatype() {
       return createWithChild(Node::Kind::ReflectionMetadataSuperclassDescriptor,
                              Ty->getChild(0));
     }
+    case 'V':
+      return createWithChild(Node::Kind::PropertyDescriptor,
+                             popNode(isEntity));
     case 'X':
       return demanglePrivateContextDescriptor();
     default:

lib/Demangling/NodePrinter.cpp

@@ -393,6 +393,7 @@ class NodePrinter {
     case Node::Kind::PostfixOperator:
     case Node::Kind::PrefixOperator:
     case Node::Kind::PrivateDeclName:
+    case Node::Kind::PropertyDescriptor:
     case Node::Kind::ProtocolConformance:
     case Node::Kind::ProtocolConformanceDescriptor:
     case Node::Kind::ProtocolDescriptor:
@@ -1467,6 +1468,10 @@ NodePointer NodePrinter::print(NodePointer Node, bool asPrefixContext) {
     Printer << "class metadata base offset for ";
     print(Node->getChild(0));
     return nullptr;
+  case Node::Kind::PropertyDescriptor:
+    Printer << "property descriptor for ";
+    print(Node->getChild(0));
+    return nullptr;
   case Node::Kind::NominalTypeDescriptor:
     Printer << "nominal type descriptor for ";
     print(Node->getChild(0));

lib/Demangling/OldRemangler.cpp

@@ -722,6 +722,10 @@ void Remangler::mangleNominalTypeDescriptor(Node *node) {
   mangleSingleChildNode(node); // type
 }
 
+void Remangler::manglePropertyDescriptor(Node *node) {
+  unreachable("not supported");
+}
+
 void Remangler::mangleTypeMetadata(Node *node) {
   Out << "M";
   mangleSingleChildNode(node); // type

lib/Demangling/Remangler.cpp

@@ -1403,6 +1403,11 @@ void Remangler::mangleNominalTypeDescriptor(Node *node) {
   Buffer << "Mn";
 }
 
+void Remangler::manglePropertyDescriptor(Node *node) {
+  mangleSingleChildNode(node);
+  Buffer << "MV";
+}
+
 void Remangler::mangleNonObjCAttribute(Node *node) {
   Buffer << "TO";
 }

lib/IRGen/GenDecl.cpp

@@ -1506,6 +1506,7 @@ SILLinkage LinkEntity::getLinkage(ForDefinition_t forDefinition) const {
   case Kind::ObjCMetaclass:
   case Kind::SwiftMetaclassStub:
   case Kind::NominalTypeDescriptor:
+  case Kind::PropertyDescriptor:
   case Kind::ClassMetadataBaseOffset:
   case Kind::ProtocolDescriptor:
     return getSILLinkage(getDeclLinkage(getDecl()), forDefinition);
@@ -1601,6 +1602,7 @@ bool LinkEntity::isAvailableExternally(IRGenModule &IGM) const {
 
   case Kind::SwiftMetaclassStub:
   case Kind::ClassMetadataBaseOffset:
+  case Kind::PropertyDescriptor:
   case Kind::NominalTypeDescriptor:
   case Kind::ProtocolDescriptor:
     return ::isAvailableExternally(IGM, getDecl());
@@ -3297,8 +3299,7 @@ IRGenModule::getAddrOfClassMetadataBaseOffset(ClassDecl *D,
                                SizeTy, DebugTypeInfo());
 }
 
-/// Return the address of a nominal type descriptor.  Right now, this
-/// must always be for purposes of defining it.
+/// Return the address of a nominal type descriptor.
 llvm::Constant *IRGenModule::getAddrOfTypeContextDescriptor(NominalTypeDecl *D,
                                                       ConstantInit definition) {
   IRGen.addLazyTypeContextDescriptor(D);
@@ -3309,6 +3310,16 @@ llvm::Constant *IRGenModule::getAddrOfTypeContextDescriptor(NominalTypeDecl *D,
                                DebugTypeInfo());
 }
 
+/// Return the address of a property descriptor.
+llvm::Constant *IRGenModule::getAddrOfPropertyDescriptor(AbstractStorageDecl *D,
+                                                      ConstantInit definition) {
+  auto entity = LinkEntity::forPropertyDescriptor(D);
+  return getAddrOfLLVMVariable(entity, Alignment(4),
+                               definition,
+                               TypeContextDescriptorTy,
+                               DebugTypeInfo());
+}
+
 llvm::Constant *IRGenModule::getAddrOfProtocolDescriptor(ProtocolDecl *D,
                                                       ConstantInit definition) {
   if (D->isObjC()) {
@@ -3442,9 +3453,9 @@ void IRGenModule::emitNestedTypeDecls(DeclRange members) {
     case DeclKind::PoundDiagnostic:
       continue;
 
-    case DeclKind::PatternBinding:
     case DeclKind::Var:
     case DeclKind::Subscript:
+    case DeclKind::PatternBinding:
     case DeclKind::Func:
     case DeclKind::Accessor:
     case DeclKind::Constructor: