Eliminate @_objcImpl type and field descriptors

Author: beccadax

lib/IRGen/GenDecl.cpp

@@ -4752,8 +4752,10 @@ llvm::GlobalValue *IRGenModule::defineTypeMetadata(
   unsigned adjustmentIndex = MetadataAdjustmentIndex::ValueType;
 
   if (auto nominal = concreteType->getAnyNominal()) {
-    // Keep type metadata around for all types.
-    addRuntimeResolvableType(nominal);
+    // Keep type metadata around for all types (except @_objcImplementation,
+    // since we're using ObjC metadata for that).
+    if (!isObjCImpl)
+      addRuntimeResolvableType(nominal);
 
     // Don't define the alias for foreign type metadata or prespecialized
     // generic metadata, since neither is ABI.

lib/IRGen/GenMeta.cpp

@@ -3912,6 +3912,8 @@ namespace {
       : IGM(IGM), Target(theClass), B(builder), FieldLayout(fieldLayout) {}
 
     llvm::Constant *emitNominalTypeDescriptor() {
+      if (FieldLayout.hasObjCImplementation())
+        return nullptr;
       return ClassContextDescriptorBuilder(IGM, Target, RequireMetadata).emit();
     }
 

lib/IRGen/GenReflection.cpp

@@ -844,8 +844,7 @@ class FieldTypeMetadataBuilder : public ReflectionMetadataBuilder {
     if (NTD->hasClangNode()) {
       auto *enumDecl = dyn_cast<EnumDecl>(NTD);
       // Structs and namespace-like enums are ok.
-      assert(isa<StructDecl>(NTD) || (enumDecl && !enumDecl->hasCases())
-             || !NTD->getObjCImplementationDecls().empty());
+      assert(isa<StructDecl>(NTD) || (enumDecl && !enumDecl->hasCases()));
     }
 
     PrettyStackTraceDecl DebugStack("emitting field type metadata", NTD);
@@ -1560,6 +1559,11 @@ void IRGenModule::emitFieldDescriptor(const NominalTypeDecl *D) {
       needsOpaqueDescriptor = true;
   }
 
+  if (auto *CD = dyn_cast<ClassDecl>(D)) {
+    if (!CD->getObjCImplementationDecls().empty())
+      needsFieldDescriptor = false;
+  }
+
   // If the type has custom @_alignment, emit a fixed record with the
   // alignment since remote mirrors will need to treat the type as opaque.
   //

test/IRGen/objc_implementation.swift

@@ -45,3 +45,5 @@
 // NEGATIVE-NOT: Category2
 // NEGATIVE-NOT: NoImplClass
 // NEGATIVE-NOT: OBJC_CLASS_$_ImplClass.{{[0-9]}}
+// NEGATIVE-NOT: $sSo9ImplClassCMn
+// NEGATIVE-NOT: $sSo9ImplClassCHn