Preliminary SILGen support for subclass existentials (SE-0156)

docs/ABI.rst

@@ -1044,6 +1044,7 @@ Types
   type ::= associated-type
   type ::= nominal-type
   type ::= protocol-list 'p'                 // existential type
+  type ::= protocol-list superclass 'XE'     // existential type with superclass
   type ::= type-list 't'                     // tuple
   type ::= type generic-signature 'u'        // generic type
   type ::= 'x'                               // generic param, depth=0, idx=0

include/swift/AST/DiagnosticsSema.def

@@ -3093,7 +3093,11 @@ ERROR(function_type_no_parens,none,
 NOTE(not_objc_empty_protocol_composition,none,
      "'Any' is not considered '@objc'; use 'AnyObject' instead", ())
 NOTE(not_objc_protocol,none,
-     "protocol %0 is not '@objc'", (Type))
+     "protocol-constrained type containing protocol %0 cannot be represented "
+     "in Objective-C", (Type))
+NOTE(not_objc_class_constraint,none,
+     "protocol-constrained type containing class %0 cannot be represented "
+     "in Objective-C", (Type))
 NOTE(not_objc_error_protocol_composition,none,
      "protocol-constrained type containing 'Error' cannot be represented "
      "in Objective-C", ())

include/swift/AST/ExistentialLayout.h

@@ -58,8 +58,13 @@ struct ExistentialLayout {
     return requiresClass && !containsNonObjCProtocol;
   }
 
+  // Does this existential contain the Error protocol?
   bool isExistentialWithError(ASTContext &ctx) const;
 
+  // Does this existential consist of an Error protocol only with no other
+  // constraints?
+  bool isErrorExistential() const;
+
   ArrayRef<ProtocolType *> getProtocols() const {
     if (singleProtocol)
       return ArrayRef<ProtocolType *>{&singleProtocol, 1};

include/swift/AST/Types.h

@@ -4552,21 +4552,6 @@ inline CanType CanType::getNominalParent() const {
   }
 }
 
-inline bool TypeBase::mayHaveSuperclass() {
-  if (getClassOrBoundGenericClass())
-    return true;
-
-  // FIXME: requiresClass() is not the same as having an explicit superclass;
-  // is this wrong?
-  if (auto archetype = getAs<ArchetypeType>())
-    return (bool)archetype->requiresClass();
-
-  if (isExistentialType())
-    return (bool)getSuperclass(nullptr);
-
-  return is<DynamicSelfType>();
-}
-
 inline TupleTypeElt::TupleTypeElt(Type ty, Identifier name, bool isVariadic,
                                   bool isAutoClosure, bool isEscaping)
     : Name(name), ElementType(ty),

include/swift/Demangling/DemangleNodes.def

@@ -123,6 +123,7 @@ CONTEXT_NODE(Protocol)
 NODE(ProtocolConformance)
 NODE(ProtocolDescriptor)
 NODE(ProtocolList)
+NODE(ProtocolListWithClass)
 NODE(ProtocolWitness)
 NODE(ProtocolWitnessTable)
 NODE(ProtocolWitnessTableAccessor)

lib/AST/ASTMangler.cpp

@@ -17,6 +17,7 @@
 #include "swift/AST/ASTMangler.h"
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/ASTVisitor.h"
+#include "swift/AST/ExistentialLayout.h"
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/Initializer.h"
 #include "swift/AST/Module.h"
@@ -631,16 +632,32 @@ void ASTMangler::appendType(Type type) {
       appendTypeList(type);
       return appendOperator("t");
 
-    case TypeKind::Protocol:
+    case TypeKind::Protocol: {
+      bool First = true;
+      appendProtocolName(cast<ProtocolType>(tybase)->getDecl());
+      appendListSeparator(First);
+      return appendOperator("p");
+    }
+
     case TypeKind::ProtocolComposition: {
       // We mangle ProtocolType and ProtocolCompositionType using the
       // same production:
       bool First = true;
-      appendProtocolList(type, First);
+      auto layout = type->getExistentialLayout();
+      for (Type protoTy : layout.getProtocols()) {
+        appendProtocolName(protoTy->castTo<ProtocolType>()->getDecl());
+        appendListSeparator(First);
+      }
       if (First)
         appendOperator("y");
+
+      if (layout.superclass) {
+        appendType(layout.superclass);
+        return appendOperator("XE");
+      }
       return appendOperator("p");
     }
+
     case TypeKind::UnboundGeneric:
     case TypeKind::Class:
     case TypeKind::Enum:

lib/AST/Type.cpp

@@ -273,6 +273,8 @@ ExistentialLayout::ExistentialLayout(ProtocolCompositionType *type) {
       isa<ClassDecl>(members[0]->getAnyNominal())) {
     superclass = members[0];
     members = members.slice(1);
+    requiresClass = true;
+    requiresClassImplied = true;
   }
 
   for (auto member : members) {
@@ -600,6 +602,13 @@ bool TypeBase::isAnyObject() {
   return canTy.getExistentialLayout().isAnyObject();
 }
 
+bool ExistentialLayout::isErrorExistential() const {
+  auto protocols = getProtocols();
+  return (!requiresClass &&
+          protocols.size() == 1 &&
+          protocols[0]->getDecl()->isSpecificProtocol(KnownProtocolKind::Error));
+}
+
 bool ExistentialLayout::isExistentialWithError(ASTContext &ctx) const {
   auto errorProto = ctx.getProtocol(KnownProtocolKind::Error);
   if (!errorProto) return false;
@@ -1562,6 +1571,16 @@ LayoutConstraint TypeBase::getLayoutConstraint() {
   return LayoutConstraint();
 }
 
+bool TypeBase::mayHaveSuperclass() {
+  if (getClassOrBoundGenericClass())
+    return true;
+
+  if (auto archetype = getAs<ArchetypeType>())
+    return (bool)archetype->requiresClass();
+
+  return is<DynamicSelfType>();
+}
+
 Type TypeBase::getSuperclass(LazyResolver *resolver) {
   auto *nominalDecl = getAnyNominal();
   auto *classDecl = dyn_cast_or_null<ClassDecl>(nominalDecl);
@@ -1987,10 +2006,18 @@ getObjCObjectRepresentable(Type type, const DeclContext *dc) {
       return ForeignRepresentableKind::Object;
   }
 
-  // Objective-C existential types.
-  if (type->isObjCExistentialType())
-    return ForeignRepresentableKind::Object;
-
+  // Objective-C existential types are trivially representable if
+  // they don't have a superclass constraint, or if the superclass
+  // constraint is an @objc class.
+  if (type->isExistentialType()) {
+    auto layout = type->getExistentialLayout();
+    if (layout.isObjC() &&
+        (!layout.superclass ||
+         getObjCObjectRepresentable(layout.superclass, dc) ==
+           ForeignRepresentableKind::Object))
+      return ForeignRepresentableKind::Object;
+  }
+
   // Any can be bridged to id.
   if (type->isAny()) {
     return ForeignRepresentableKind::Bridged;

lib/Demangling/Demangler.cpp

@@ -1583,6 +1583,12 @@ NodePointer Demangler::demangleSpecialType() {
     case 'p':
       return createType(createWithChild(Node::Kind::ExistentialMetatype,
                                         popNode(Node::Kind::Type)));
+    case 'E': {
+      NodePointer Superclass = popNode(Node::Kind::Type);
+      NodePointer Protocols = demangleProtocolListType();
+      return createType(createWithChildren(Node::Kind::ProtocolListWithClass,
+                                           Protocols, Superclass));
+    }
     case 'X':
     case 'x': {
       // SIL box types.

lib/Demangling/NodePrinter.cpp

@@ -267,6 +267,7 @@ class NodePrinter {
         return true;
       return false;
 
+    case Node::Kind::ProtocolListWithClass:
     case Node::Kind::Allocator:
     case Node::Kind::ArgumentTuple:
     case Node::Kind::AssociatedTypeMetadataAccessor:
@@ -578,7 +579,8 @@ class NodePrinter {
 
 static bool isExistentialType(NodePointer node) {
   return (node->getKind() == Node::Kind::ExistentialMetatype ||
-          node->getKind() == Node::Kind::ProtocolList);
+          node->getKind() == Node::Kind::ProtocolList ||
+          node->getKind() == Node::Kind::ProtocolListWithClass);
 }
 
 /// Print the relevant parameters and return the new index.
@@ -1388,6 +1390,16 @@ void NodePrinter::print(NodePointer pointer, bool asContext, bool suppressType)
       printChildren(type_list, " & ");
     return;
   }
+  case Node::Kind::ProtocolListWithClass: {
+    if (pointer->getNumChildren() < 2)
+      return;
+    NodePointer protocols = pointer->getChild(0);
+    NodePointer superclass = pointer->getChild(1);
+    print(superclass);
+    Printer << " & ";
+    printChildren(protocols, " & ");
+    return;
+  }
   case Node::Kind::AssociatedType:
     // Don't print for now.
     return;

lib/Demangling/Remangler.cpp

@@ -249,6 +249,8 @@ class Remangler {
     mangleChildNodes(Proto);
   }
 
+  void mangleProtocolList(Node *protocols, Node *superclass);
+
   bool trySubstitution(Node *node, SubstitutionEntry &entry,
                        bool treatAsIdentifier = false);
   void addSubstitution(const SubstitutionEntry &entry);
@@ -1401,17 +1403,31 @@ void Remangler::mangleProtocolDescriptor(Node *node) {
   Buffer << "Mp";
 }
 
-void Remangler::mangleProtocolList(Node *node) {
-  node = getSingleChild(node, Node::Kind::TypeList);
+void Remangler::mangleProtocolList(Node *node, Node *superclass) {
   bool FirstElem = true;
   for (NodePointer Child : *node) {
     manglePureProtocol(Child);
     mangleListSeparator(FirstElem);
   }
   mangleEndOfList(FirstElem);
+  if (superclass) {
+    mangleType(superclass);
+    Buffer << "XE";
+    return;
+  }
   Buffer << 'p';
 }
 
+void Remangler::mangleProtocolList(Node *node) {
+  auto *protocols = getSingleChild(node, Node::Kind::TypeList);
+  mangleProtocolList(protocols, nullptr);
+}
+
+void Remangler::mangleProtocolListWithClass(Node *node) {
+  mangleProtocolList(node->getChild(0),
+                     node->getChild(1));
+}
+
 void Remangler::mangleProtocolWitness(Node *node) {
   mangleChildNodes(node);
   Buffer << "TW";

lib/SIL/SILType.cpp

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "swift/SIL/SILType.h"
+#include "swift/AST/ExistentialLayout.h"
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/Type.h"
 #include "swift/SIL/SILModule.h"
@@ -473,16 +474,9 @@ static bool isBridgedErrorClass(SILModule &M,
   return false;
 }
 
-static bool isErrorExistential(ArrayRef<ProtocolDecl*> protocols) {
-  return protocols.size() == 1
-    && protocols[0]->isSpecificProtocol(KnownProtocolKind::Error);
-}
-
 ExistentialRepresentation
 SILType::getPreferredExistentialRepresentation(SILModule &M,
                                                Type containedType) const {
-  SmallVector<ProtocolDecl *, 4> protocols;
-
   // Existential metatypes always use metatype representation.
   if (is<ExistentialMetatypeType>())
     return ExistentialRepresentation::Metatype;
@@ -491,11 +485,9 @@ SILType::getPreferredExistentialRepresentation(SILModule &M,
   if (!isExistentialType())
     return ExistentialRepresentation::None;
 
-  // Get the list of existential constraints.
-  getSwiftRValueType()->getExistentialTypeProtocols(protocols);
+  auto layout = getSwiftRValueType().getExistentialLayout();
 
-  // The (uncomposed) Error existential uses a special boxed representation.
-  if (isErrorExistential(protocols)) {
+  if (layout.isErrorExistential()) {
     // NSError or CFError references can be adopted directly as Error
     // existentials.
     if (isBridgedErrorClass(M, containedType)) {
@@ -507,10 +499,8 @@ SILType::getPreferredExistentialRepresentation(SILModule &M,
 
   // A class-constrained protocol composition can adopt the conforming
   // class reference directly.
-  for (auto proto : protocols) {
-    if (proto->requiresClass())
-      return ExistentialRepresentation::Class;
-  }
+  if (layout.requiresClass)
+    return ExistentialRepresentation::Class;
 
   // Otherwise, we need to use a fixed-sized buffer.
   return ExistentialRepresentation::Opaque;
@@ -529,23 +519,22 @@ SILType::canUseExistentialRepresentation(SILModule &M,
     // Look at the protocols to see what representation is appropriate.
     if (!getSwiftRValueType().isExistentialType())
       return false;
-    SmallVector<ProtocolDecl *, 4> protocols;
-    getSwiftRValueType().getExistentialTypeProtocols(protocols);
+
+    auto layout = getSwiftRValueType().getExistentialLayout();
 
     // The (uncomposed) Error existential uses a special boxed
     // representation. It can also adopt class references of bridged error types
     // directly.
-    if (isErrorExistential(protocols))
+    if (layout.isErrorExistential())
       return repr == ExistentialRepresentation::Boxed
         || (repr == ExistentialRepresentation::Class
             && isBridgedErrorClass(M, containedType));
 
     // A class-constrained composition uses ClassReference representation;
-    // otherwise, we use a fixed-sized buffer
-    for (auto *proto : protocols) {
-      if (proto->requiresClass())
-        return repr == ExistentialRepresentation::Class;
-    }
+    // otherwise, we use a fixed-sized buffer.
+    if (layout.requiresClass)
+      return repr == ExistentialRepresentation::Class;
+
     return repr == ExistentialRepresentation::Opaque;
   }
   case ExistentialRepresentation::Metatype: