[vm/ffi] Remove .ref VM runtime entry

After https://dart-review.googlesource.com/c/sdk/+/180190 the runtime
entry has become dead code.

This CL keeps the runtime entry itself but makes it unreachable as was
the suggestion on previous a CL removing runtime entries:
https://dart-review.googlesource.com/c/sdk/+/169406

Bug: #38648
Bug: #38721

TEST=tests/ffi/vmspecific_static_checks_test.dart
TEST=tests/ffi/*struct*test_.dart

Change-Id: I84c5c925215b9dbd999826fb390df91d8050e1dd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/182627
Reviewed-by: Aske Simon Christensen <[email protected]>
Commit-Queue: Daco Harkes <[email protected]>

Author: dcharkes

pkg/vm/lib/transformations/ffi.dart

@@ -237,7 +237,6 @@ class FfiTransformer extends Transformer {
   final Map<NativeType, Procedure> loadMethods;
   final Map<NativeType, Procedure> storeMethods;
   final Map<NativeType, Procedure> elementAtMethods;
-  final Procedure loadStructMethod;
   final Procedure memCopy;
   final Procedure allocationTearoff;
   final Procedure asFunctionTearoff;
@@ -322,7 +321,6 @@ class FfiTransformer extends Transformer {
           final name = nativeTypeClassNames[t.index];
           return index.getTopLevelMember('dart:ffi', "_elementAt$name");
         }),
-        loadStructMethod = index.getTopLevelMember('dart:ffi', '_loadStruct'),
         memCopy = index.getTopLevelMember('dart:ffi', '_memCopy'),
         allocationTearoff = index.getMember(
             'dart:ffi', 'AllocatorAlloc', LibraryIndex.tearoffPrefix + 'call'),

runtime/lib/ffi.cc

@@ -88,45 +88,8 @@ DEFINE_NATIVE_ENTRY(Ffi_loadPointer, 1, 2) {
   UNREACHABLE();
 }
 
-static ObjectPtr LoadValueStruct(Zone* zone,
-                                 const Pointer& target,
-                                 const AbstractType& instance_type_arg) {
-  // Result is a struct class -- find <class name>.#fromTypedDataBase
-  // constructor and call it.
-  const Class& cls = Class::Handle(zone, instance_type_arg.type_class());
-  const Function& constructor =
-      Function::Handle(cls.LookupFunctionAllowPrivate(String::Handle(
-          String::Concat(String::Handle(String::Concat(
-                             String::Handle(cls.Name()), Symbols::Dot())),
-                         Symbols::StructFromTypedDataBase()))));
-  ASSERT(!constructor.IsNull());
-  ASSERT(constructor.IsGenerativeConstructor());
-  ASSERT(!Object::Handle(constructor.VerifyCallEntryPoint()).IsError());
-  const Instance& new_object = Instance::Handle(Instance::New(cls));
-  ASSERT(cls.is_allocated() || Dart::vm_snapshot_kind() != Snapshot::kFullAOT);
-  const Array& args = Array::Handle(zone, Array::New(2));
-  args.SetAt(0, new_object);
-  args.SetAt(1, target);
-  const Object& constructorResult =
-      Object::Handle(DartEntry::InvokeFunction(constructor, args));
-  ASSERT(!constructorResult.IsError());
-  return new_object.ptr();
-}
-
 DEFINE_NATIVE_ENTRY(Ffi_loadStruct, 0, 2) {
-  GET_NON_NULL_NATIVE_ARGUMENT(Pointer, pointer, arguments->NativeArgAt(0));
-  const AbstractType& pointer_type_arg =
-      AbstractType::Handle(arguments->NativeTypeArgAt(0));
-  GET_NON_NULL_NATIVE_ARGUMENT(Integer, index, arguments->NativeArgAt(1));
-
-  // TODO(36370): Make representation consistent with kUnboxedFfiIntPtr.
-  const size_t address =
-      pointer.NativeAddress() + static_cast<intptr_t>(index.AsInt64Value()) *
-                                    SizeOf(zone, pointer_type_arg);
-  const Pointer& pointer_offset =
-      Pointer::Handle(zone, Pointer::New(pointer_type_arg, address));
-
-  return LoadValueStruct(zone, pointer_offset, pointer_type_arg);
+  UNREACHABLE();
 }
 
 #define DEFINE_NATIVE_ENTRY_STORE(type)                                        \

sdk/lib/_internal/vm/lib/ffi_patch.dart

@@ -204,16 +204,6 @@ double _loadDouble(Pointer pointer, int offsetInBytes) native "Ffi_loadDouble";
 Pointer<S> _loadPointer<S extends NativeType>(
     Pointer pointer, int offsetInBytes) native "Ffi_loadPointer";
 
-S _loadStructNoStruct<S extends Struct>(Pointer<S> pointer, int index) {
-  if (S == Struct) {
-    throw ArgumentError("S should be a subtype of Struct.");
-  }
-  return _loadStruct(pointer, index);
-}
-
-S _loadStruct<S extends Struct>(Pointer<S> pointer, int index)
-    native "Ffi_loadStruct";
-
 @pragma("vm:recognized", "other")
 void _storeInt8(Pointer pointer, int offsetInBytes, int value)
     native "Ffi_storeInt8";
@@ -518,10 +508,12 @@ extension PointerPointer<T extends NativeType> on Pointer<Pointer<T>> {
 
 extension StructPointer<T extends Struct> on Pointer<T> {
   @patch
-  T get ref => _loadStructNoStruct(this, 0);
+  T get ref =>
+      throw "UNREACHABLE: This case should have been rewritten in the CFE.";
 
   @patch
-  T operator [](int index) => _loadStructNoStruct(this, index);
+  T operator [](int index) =>
+      throw "UNREACHABLE: This case should have been rewritten in the CFE.";
 }
 
 extension NativePort on SendPort {