Merge pull request #8958 from slavapestov/subclass-existentials-runtime

More runtime support for subclass existentials

Author: slavapestov

include/swift/ABI/MetadataValues.h

@@ -404,7 +404,8 @@ class ExistentialTypeFlags {
   enum : int_type {
     NumWitnessTablesMask  = 0x00FFFFFFU,
     ClassConstraintMask   = 0x80000000U,
-    SpecialProtocolMask   = 0x7F000000U,
+    HasSuperclassMask     = 0x40000000U,
+    SpecialProtocolMask   = 0x3F000000U,
     SpecialProtocolShift  = 24U,
   };
   int_type Data;
@@ -421,6 +422,11 @@ class ExistentialTypeFlags {
                                   | (bool(c) ? ClassConstraintMask : 0));
   }
   constexpr ExistentialTypeFlags
+  withHasSuperclass(bool hasSuperclass) const {
+    return ExistentialTypeFlags((Data & ~HasSuperclassMask)
+                                  | (hasSuperclass ? HasSuperclassMask : 0));
+  }
+  constexpr ExistentialTypeFlags
   withSpecialProtocol(SpecialProtocol sp) const {
     return ExistentialTypeFlags((Data & ~SpecialProtocolMask)
                                   | (int_type(sp) << SpecialProtocolShift));
@@ -433,7 +439,11 @@ class ExistentialTypeFlags {
   ProtocolClassConstraint getClassConstraint() const {
     return ProtocolClassConstraint(bool(Data & ClassConstraintMask));
   }
-  
+
+  bool hasSuperclassConstraint() const {
+    return bool(Data & HasSuperclassMask);
+  }
+
   /// Return whether this existential type represents an uncomposed special
   /// protocol.
   SpecialProtocol getSpecialProtocol() const {

include/swift/Runtime/Metadata.h

@@ -2445,9 +2445,16 @@ struct TargetExistentialTypeMetadata : public TargetMetadata<Runtime> {
     return Flags.getClassConstraint() == ProtocolClassConstraint::Class;
   }
 
-  const Metadata *getSuperclassConstraint() const {
-    // FIXME
-    return nullptr;
+  const TargetMetadata<Runtime> *getSuperclassConstraint() const {
+    if (!Flags.hasSuperclassConstraint())
+      return nullptr;
+
+    // Get a pointer to tail-allocated storage for this metadata record.
+    auto Pointer = reinterpret_cast<
+      ConstTargetMetadataPointer<Runtime, TargetMetadata> const *>(this + 1);
+
+    // The superclass immediately follows the list of protocol descriptors.
+    return Pointer[Protocols.NumProtocols];
   }
 
   static bool classof(const TargetMetadata<Runtime> *metadata) {

lib/IRGen/GenCast.cpp

@@ -291,21 +291,34 @@ llvm::Value *irgen::emitReferenceToObjCProtocol(IRGenFunction &IGF,
 /// Emit a helper function to look up \c numProtocols witness tables given
 /// a value and a type metadata reference.
 ///
-/// The function's input type is (value, metadataValue, protocol...)
+/// If \p checkClassConstraint is true, we must emit an explicit check that the
+/// instance is a class.
+///
+/// If \p checkSuperclassConstraint is true, we are given an additional parameter
+/// with a superclass type in it, and must emit a check that the instance is a
+/// subclass of the given class.
+///
+/// The function's input type is (value, metadataValue, superclass?, protocol...)
 /// The function's output type is (value, witnessTable...)
 ///
 /// The value is NULL if the cast failed.
-static llvm::Function *emitExistentialScalarCastFn(IRGenModule &IGM,
-                                                   unsigned numProtocols,
-                                                   CheckedCastMode mode,
-                                                   bool checkClassConstraint) {
+static llvm::Function *
+emitExistentialScalarCastFn(IRGenModule &IGM,
+                            unsigned numProtocols,
+                            CheckedCastMode mode,
+                            bool checkClassConstraint,
+                            bool checkSuperclassConstraint) {
+  assert(!checkSuperclassConstraint || checkClassConstraint);
+
   // Build the function name.
   llvm::SmallString<32> name;
   {
     llvm::raw_svector_ostream os(name);
     os << "dynamic_cast_existential_";
     os << numProtocols;
-    if (checkClassConstraint)
+    if (checkSuperclassConstraint)
+      os << "_superclass";
+    else if (checkClassConstraint)
       os << "_class";
     switch (mode) {
     case CheckedCastMode::Unconditional:
@@ -329,6 +342,8 @@ static llvm::Function *emitExistentialScalarCastFn(IRGenModule &IGM,
   argTys.push_back(IGM.Int8PtrTy);
   argTys.push_back(IGM.TypeMetadataPtrTy);
   returnTys.push_back(IGM.Int8PtrTy);
+  if (checkSuperclassConstraint)
+    argTys.push_back(IGM.TypeMetadataPtrTy);
   for (unsigned i = 0; i < numProtocols; ++i) {
     argTys.push_back(IGM.ProtocolDescriptorPtrTy);
     returnTys.push_back(IGM.WitnessTablePtrTy);
@@ -355,7 +370,26 @@ static llvm::Function *emitExistentialScalarCastFn(IRGenModule &IGM,
   rets.add(value);
 
   // Check the class constraint if necessary.
-  if (checkClassConstraint) {
+  if (checkSuperclassConstraint) {
+    auto superclassMetadata = args.claimNext();
+    auto castFn = IGF.IGM.getDynamicCastMetatypeFn();
+    auto castResult = IGF.Builder.CreateCall(castFn, {ref,
+                                                      superclassMetadata});
+
+    auto cc = cast<llvm::Function>(castFn)->getCallingConv();
+
+    // FIXME: Eventually, we may want to throw.
+    castResult->setCallingConv(cc);
+    castResult->setDoesNotThrow();
+
+    auto isClass = IGF.Builder.CreateICmpNE(
+        castResult,
+        llvm::ConstantPointerNull::get(IGF.IGM.TypeMetadataPtrTy));
+
+    auto contBB = IGF.createBasicBlock("cont");
+    IGF.Builder.CreateCondBr(isClass, contBB, failBB);
+    IGF.Builder.emitBlock(contBB);
+  } else if (checkClassConstraint) {
     auto isClass = IGF.Builder.CreateCall(IGM.getIsClassTypeFn(), ref);
     auto contBB = IGF.createBasicBlock("cont");
     IGF.Builder.CreateCondBr(isClass, contBB, failBB);
@@ -374,7 +408,7 @@ static llvm::Function *emitExistentialScalarCastFn(IRGenModule &IGM,
     IGF.Builder.emitBlock(contBB);
     rets.add(witness);
   }
-  
+
   // If we succeeded, return the witnesses.
   IGF.emitScalarReturn(returnTy, rets);
 
@@ -472,11 +506,15 @@ void irgen::emitScalarExistentialDowncast(IRGenFunction &IGF,
                                   CheckedCastMode mode,
                                   Optional<MetatypeRepresentation> metatypeKind,
                                   Explosion &ex) {
-  auto instanceType = destType.getSwiftRValueType();
-  while (auto metatypeType = dyn_cast<ExistentialMetatypeType>(instanceType))
-    instanceType = metatypeType.getInstanceType();
+  auto srcInstanceType = srcType.getSwiftRValueType();
+  auto destInstanceType = destType.getSwiftRValueType();
+  while (auto metatypeType = dyn_cast<ExistentialMetatypeType>(
+           destInstanceType)) {
+    destInstanceType = metatypeType.getInstanceType();
+    srcInstanceType = cast<AnyMetatypeType>(srcInstanceType).getInstanceType();
+  }
 
-  auto layout = instanceType.getExistentialLayout();
+  auto layout = destInstanceType.getExistentialLayout();
 
   // Look up witness tables for the protocols that need them and get
   // references to the ObjC Protocol* values for the objc protocols.
@@ -486,7 +524,7 @@ void irgen::emitScalarExistentialDowncast(IRGenFunction &IGF,
   bool hasClassConstraint = layout.requiresClass;
   bool hasClassConstraintByProtocol = false;
 
-  assert(!layout.superclass && "Subclass existentials not supported yet");
+  bool hasSuperclassConstraint = bool(layout.superclass);
 
   for (auto protoTy : layout.getProtocols()) {
     auto *protoDecl = protoTy->getDecl();
@@ -532,10 +570,34 @@ void irgen::emitScalarExistentialDowncast(IRGenFunction &IGF,
     auto schema = IGF.getTypeInfo(destType).getSchema();
     resultType = schema[0].getScalarType();
   }
-  // We only need to check the class constraint for metatype casts where
-  // no protocol conformance indirectly requires the constraint for us.
-  bool checkClassConstraint =
-    (bool)metatypeKind && hasClassConstraint && !hasClassConstraintByProtocol;
+
+  // The source of a scalar cast is statically known to be a class or a
+  // metatype, so we only have to check the class constraint in two cases:
+  //
+  // 1) The destination type has an explicit superclass constraint that is
+  //    more derived than what the source type is known to be.
+  //
+  // 2) We are casting between metatypes, in which case the source might
+  //    be a non-class metatype.
+  bool checkClassConstraint = false;
+  if ((bool)metatypeKind &&
+      hasClassConstraint &&
+      !hasClassConstraintByProtocol &&
+      !srcInstanceType->mayHaveSuperclass())
+    checkClassConstraint = true;
+
+  // If the source has an equal or more derived superclass constraint than
+  // the destination, we can elide the superclass check.
+  //
+  // Note that destInstanceType is always an existential type, so calling
+  // getSuperclass() returns the superclass constraint of the existential,
+  // not the superclass of some concrete class.
+  bool checkSuperclassConstraint =
+    hasSuperclassConstraint &&
+    !destInstanceType->getSuperclass()->isExactSuperclassOf(srcInstanceType);
+
+  if (checkSuperclassConstraint)
+    checkClassConstraint = true;
 
   llvm::Value *resultValue = value;
 
@@ -671,8 +733,11 @@ void irgen::emitScalarExistentialDowncast(IRGenFunction &IGF,
   }
 
   // Look up witness tables for the protocols that need them.
-  auto fn = emitExistentialScalarCastFn(IGF.IGM, witnessTableProtos.size(),
-                                        mode, checkClassConstraint);
+  auto fn = emitExistentialScalarCastFn(IGF.IGM,
+                                        witnessTableProtos.size(),
+                                        mode,
+                                        checkClassConstraint,
+                                        checkSuperclassConstraint);
 
   llvm::SmallVector<llvm::Value *, 4> args;
 
@@ -681,6 +746,10 @@ void irgen::emitScalarExistentialDowncast(IRGenFunction &IGF,
   args.push_back(resultValue);
 
   args.push_back(metadataValue);
+
+  if (checkSuperclassConstraint)
+    args.push_back(IGF.emitTypeMetadataRef(CanType(layout.superclass)));
+
   for (auto proto : witnessTableProtos)
     args.push_back(proto);
 

lib/IRGen/GenReflection.cpp

@@ -601,6 +601,7 @@ class CaptureDescriptorBuilder : public ReflectionMetadataBuilder {
   CanSILFunctionType SubstCalleeType;
   SubstitutionList Subs;
   const HeapLayout &Layout;
+
 public:
   CaptureDescriptorBuilder(IRGenModule &IGM,
                            SILFunction &Caller,
@@ -630,6 +631,35 @@ class CaptureDescriptorBuilder : public ReflectionMetadataBuilder {
     }
   }
 
+  /// Give up if we captured an opened existential type. Eventually we
+  /// should figure out how to represent this.
+  static bool hasOpenedExistential(CanSILFunctionType OrigCalleeType,
+                                   const HeapLayout &Layout) {
+    if (!OrigCalleeType->isPolymorphic() ||
+        OrigCalleeType->isPseudogeneric())
+      return false;
+
+    auto &Bindings = Layout.getBindings();
+    for (unsigned i = 0; i < Bindings.size(); ++i) {
+      // Skip protocol requirements (FIXME: for now?)
+      if (Bindings[i].Protocol != nullptr)
+        continue;
+
+      if (Bindings[i].TypeParameter->hasOpenedExistential())
+        return true;
+    }
+
+    auto ElementTypes = Layout.getElementTypes().slice(
+        Layout.hasBindings() ? 1 : 0);
+    for (auto ElementType : ElementTypes) {
+      auto SwiftType = ElementType.getSwiftRValueType();
+      if (SwiftType->hasOpenedExistential())
+        return true;
+    }
+
+    return false;
+  }
+
   /// Slice off the NecessaryBindings struct at the beginning, if it's there.
   /// We'll keep track of how many things are in the bindings struct with its
   /// own count in the capture descriptor.
@@ -660,8 +690,9 @@ class CaptureDescriptorBuilder : public ReflectionMetadataBuilder {
         continue;
 
       auto Source = SourceBuilder.createClosureBinding(i);
-      auto BindingType = Caller.mapTypeOutOfContext(Bindings[i].TypeParameter);
-      SourceMap.push_back({BindingType->getCanonicalType(), Source});
+      auto BindingType = Bindings[i].TypeParameter;
+      auto InterfaceType = Caller.mapTypeOutOfContext(BindingType);
+      SourceMap.push_back({InterfaceType->getCanonicalType(), Source});
     }
 
     // Check if any requirements were fulfilled by metadata stored inside a
@@ -701,10 +732,9 @@ class CaptureDescriptorBuilder : public ReflectionMetadataBuilder {
       // parameters.
       auto Src = Path.getMetadataSource(SourceBuilder, Root);
 
-      auto SubstType =
-        Caller.mapTypeOutOfContext(
-            GenericParam.subst(SubstMap, None));
-      SourceMap.push_back({SubstType->getCanonicalType(), Src});
+      auto SubstType = GenericParam.subst(SubstMap);
+      auto InterfaceType = Caller.mapTypeOutOfContext(SubstType);
+      SourceMap.push_back({InterfaceType->getCanonicalType(), Src});
     });
 
     return SourceMap;
@@ -872,11 +902,13 @@ IRGenModule::getAddrOfCaptureDescriptor(SILFunction &Caller,
   if (!IRGen.Opts.EnableReflectionMetadata)
     return llvm::Constant::getNullValue(CaptureDescriptorPtrTy);
 
+  if (CaptureDescriptorBuilder::hasOpenedExistential(OrigCalleeType, Layout))
+    return llvm::Constant::getNullValue(CaptureDescriptorPtrTy);
+
   CaptureDescriptorBuilder builder(*this, Caller,
                                    OrigCalleeType, SubstCalleeType, Subs,
                                    Layout);
   auto var = builder.emit();
-
   return llvm::ConstantExpr::getBitCast(var, CaptureDescriptorPtrTy);
 }
 

lib/IRGen/GenType.cpp

@@ -1531,8 +1531,9 @@ llvm::StructType *IRGenModule::createNominalType(CanType type) {
   assert(type.getNominalOrBoundGenericNominal());
 
   // We share type infos for different instantiations of a generic type
-  // when the archetypes have the same exemplars.  Mangling the archetypes
-  // in this case can be very misleading, so we just mangle the base name.
+  // when the archetypes have the same exemplars.  We cannot mangle
+  // archetypes, and the mangling does not have to be unique, so we just
+  // mangle the unbound generic form of the type.
   if (type->hasArchetype())
     type = type.getNominalOrBoundGenericNominal()->getDeclaredType()
                                                  ->getCanonicalType();

lib/IRGen/IRGenMangler.cpp

@@ -94,7 +94,18 @@ mangleProtocolForLLVMTypeName(ProtocolCompositionType *type) {
         appendOperator("_");
     }
     if (layout.superclass) {
-      appendType(layout.superclass);
+      auto superclassTy = layout.superclass;
+
+      // We share type infos for different instantiations of a generic type
+      // when the archetypes have the same exemplars.  We cannot mangle
+      // archetypes, and the mangling does not have to be unique, so we just
+      // mangle the unbound generic form of the type.
+      if (superclassTy->hasArchetype()) {
+        superclassTy = superclassTy->getClassOrBoundGenericClass()
+          ->getDeclaredType();
+      }
+
+      appendType(CanType(superclassTy));
       appendOperator("Xc");
     } else if (layout.getLayoutConstraint()) {
       appendOperator("Xl");