IRGen/Runtime: Use a true-const pattern to initialize non-generic resilient class metadata

Previously we would emit class metadata for classes with resilient
ancestry, and relocate it at runtime once the correct size was known.

However most of the fields were blank, so it makes more sense to
construct the metadata from scratch, and store the few bits that we
do need in a true-const pattern where we can use relative pointers.

Author: slavapestov

include/swift/ABI/Metadata.h

@@ -3085,7 +3085,7 @@ class TargetGenericMetadataPatternTrailingObjects :
   }
 };
 
-/// An instantiation pattern for class metadata.
+/// An instantiation pattern for generic class metadata.
 template <typename Runtime>
 struct TargetGenericClassMetadataPattern final :
        TargetGenericMetadataPattern<Runtime>,
@@ -3138,7 +3138,7 @@ struct TargetGenericClassMetadataPattern final :
 using GenericClassMetadataPattern =
   TargetGenericClassMetadataPattern<InProcess>;
 
-/// An instantiation pattern for value metadata.
+/// An instantiation pattern for generic value metadata.
 template <typename Runtime>
 struct TargetGenericValueMetadataPattern final :
        TargetGenericMetadataPattern<Runtime>,
@@ -3316,10 +3316,43 @@ struct TargetInPlaceValueMetadataCache {
 using InPlaceValueMetadataCache =
   TargetInPlaceValueMetadataCache<InProcess>;
 
+template <typename Runtime>
+struct TargetResilientClassMetadataPattern;
+
 /// An instantiation pattern for non-generic resilient class metadata.
 /// Used in conjunction with InPlaceValueMetadataInitialization.
 using MetadataRelocator =
-  Metadata *(const TargetTypeContextDescriptor<InProcess> *description);
+  Metadata *(const TargetTypeContextDescriptor<InProcess> *type,
+             const TargetResilientClassMetadataPattern<InProcess> *pattern);
+
+/// An instantiation pattern for non-generic resilient class metadata.
+template <typename Runtime>
+struct TargetResilientClassMetadataPattern {
+  /// If the class descriptor's hasResilientSuperclass() flag is set,
+  /// this field instead points at a function that allocates metadata
+  /// with the correct size at runtime.
+  TargetRelativeDirectPointer<Runtime, MetadataRelocator> RelocationFunction;
+
+  /// The heap-destructor function.
+  TargetRelativeDirectPointer<Runtime, HeapObjectDestroyer> Destroy;
+
+  /// The ivar-destructor function.
+  TargetRelativeDirectPointer<Runtime, ClassIVarDestroyer> IVarDestroyer;
+
+  /// The class flags.
+  ClassFlags Flags;
+
+  // The following fields are only present in ObjC interop.
+
+  /// Our ClassROData.
+  TargetRelativeDirectPointer<Runtime, void> Data;
+
+  /// Our metaclass.
+  TargetRelativeDirectPointer<Runtime, TargetAnyClassMetadata<Runtime>> Metaclass;
+};
+
+using ResilientClassMetadataPattern =
+  TargetResilientClassMetadataPattern<InProcess>;
 
 /// The control structure for performing non-trivial initialization of
 /// singleton value metadata, which is required when e.g. a non-generic
@@ -3340,8 +3373,8 @@ struct TargetInPlaceValueMetadataInitialization {
     /// If the class descriptor's hasResilientSuperclass() flag is set,
     /// this field instead points at a function that allocates metadata
     /// with the correct size at runtime.
-    TargetRelativeDirectPointer<Runtime, MetadataRelocator>
-      RelocationFunction;
+    TargetRelativeDirectPointer<Runtime, TargetResilientClassMetadataPattern<Runtime>>
+      ResilientPattern;
   };
 
   /// The completion function.  The pattern will always be null.
@@ -3358,8 +3391,10 @@ struct TargetInPlaceValueMetadataInitialization {
 
   TargetMetadata<Runtime> *allocate(
       const TargetTypeContextDescriptor<Runtime> *description) const {
-    if (hasRelocationFunction(description))
-      return RelocationFunction(description);
+    if (hasRelocationFunction(description)) {
+      return ResilientPattern->RelocationFunction(description,
+                                                  ResilientPattern.get());
+    }
     return IncompleteMetadata.get();
   }
 };

include/swift/Runtime/Metadata.h

@@ -574,15 +574,13 @@ void swift_initStructMetadata(StructMetadata *self,
                               const TypeLayout * const *fieldTypes,
                               uint32_t *fieldOffsets);
 
-/// Relocate the metadata for a class and copy fields from the given template.
-/// The final size of the metadata is calculated at runtime from the size of
-/// the superclass metadata together with the given number of immediate
-/// members.
+/// Allocate the metadata for a class and copy fields from the given pattern.
+/// The final size of the metadata is calculated at runtime from the metadata
+/// bounds in the class descriptor.
 SWIFT_RUNTIME_EXPORT
 ClassMetadata *
 swift_relocateClassMetadata(ClassDescriptor *descriptor,
-                            ClassMetadata *pattern,
-                            size_t patternSize);
+                            ResilientClassMetadataPattern *pattern);
 
 /// Initialize the field offset vector for a dependent-layout class, using the
 /// "Universal" layout strategy.

include/swift/Runtime/RuntimeFunctions.def

@@ -809,12 +809,11 @@ FUNCTION(GetExistentialMetadata,
          ATTRS(NoUnwind, ReadOnly))
 
 // Metadata *swift_relocateClassMetadata(TypeContextDescriptor *descriptor,
-//                                       Metadata *pattern,
-//                                       size_t patternSize);
+//                                       const void *pattern);
 FUNCTION(RelocateClassMetadata,
          swift_relocateClassMetadata, C_CC,
          RETURNS(TypeMetadataPtrTy),
-         ARGS(TypeContextDescriptorPtrTy, TypeMetadataPtrTy, SizeTy),
+         ARGS(TypeContextDescriptorPtrTy, Int8PtrTy),
          ATTRS(NoUnwind))
 
 // struct FieldInfo { size_t Size; size_t AlignMask; };

lib/IRGen/GenDecl.cpp

@@ -3577,6 +3577,8 @@ IRGenModule::getAddrOfTypeMetadataInstantiationFunction(NominalTypeDecl *D,
     llvm::Type *argTys[] = {
       /// Type descriptor.
       TypeContextDescriptorPtrTy,
+      /// Resilient metadata pattern.
+      Int8PtrTy
     };
 
     fnType = llvm::FunctionType::get(TypeMetadataPtrTy, argTys,