[vm/concurrency] Avoid calling into Dart code for evaluation of enum constants

There is no need to call from C++ into Dart code just so the Dart code
can return a constant. Instead we can get the constant directly in C++
code.

This avoids calling into Dart code during class finalization to evaluate
enum constants.

Issue https://github.com/dart-lang/sdk/issues/36097

Change-Id: Ia0b09482188be2d0ce83ce9ffc20e5c15e52d070
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/170540
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>

runtime/vm/compiler/frontend/constant_reader.cc

@@ -19,6 +19,19 @@ ConstantReader::ConstantReader(KernelReaderHelper* helper,
       script_(helper->script()),
       result_(Instance::Handle(zone_)) {}
 
+InstancePtr ConstantReader::ReadConstantInitializer() {
+  Tag tag = helper_->ReadTag();  // read tag.
+  switch (tag) {
+    case kSomething:
+      return ReadConstantExpression();
+    default:
+      H.ReportError(script_, TokenPosition::kNoSource,
+                    "Not a constant expression: unexpected kernel tag %s (%d)",
+                    Reader::TagName(tag), tag);
+  }
+  return result_.raw();
+}
+
 InstancePtr ConstantReader::ReadConstantExpression() {
   Tag tag = helper_->ReadTag();  // read tag.
   switch (tag) {

runtime/vm/compiler/frontend/constant_reader.h

@@ -23,6 +23,7 @@ class ConstantReader {
 
   virtual ~ConstantReader() {}
 
+  InstancePtr ReadConstantInitializer();
   InstancePtr ReadConstantExpression();
   ObjectPtr ReadAnnotations();
 

runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc

@@ -33,6 +33,17 @@ FlowGraph* StreamingFlowGraphBuilder::BuildGraphOfFieldInitializer() {
   FieldHelper field_helper(this);
   field_helper.ReadUntilExcluding(FieldHelper::kInitializer);
 
+  // Constants are directly accessed at use sites of Dart code. In C++ - if
+  // we need to access static constants - we do so directly using the kernel
+  // evaluation instead of invoking the initializer function in Dart code.
+  //
+  // If the field is marked as @pragma('vm:entry-point') then the embedder might
+  // invoke the getter, so we'll generate the initializer function.
+  ASSERT(!field_helper.IsConst() ||
+         Field::Handle(Z, parsed_function()->function().accessor_field())
+                 .VerifyEntryPoint(EntryPointPragma::kGetterOnly) ==
+             Error::null());
+
   Tag initializer_tag = ReadTag();  // read first part of initializer.
   if (initializer_tag != kSomething) {
     UNREACHABLE();
@@ -45,14 +56,8 @@ FlowGraph* StreamingFlowGraphBuilder::BuildGraphOfFieldInitializer() {
 
   Fragment body(normal_entry);
   body += B->CheckStackOverflowInPrologue(field_helper.position_);
-  if (field_helper.IsConst()) {
-    // This will read the initializer.
-    body += Constant(
-        Instance::ZoneHandle(Z, constant_reader_.ReadConstantExpression()));
-  } else {
-    body += SetupCapturedParameters(parsed_function()->function());
-    body += BuildExpression();  // read initializer.
-  }
+  body += SetupCapturedParameters(parsed_function()->function());
+  body += BuildExpression();  // read initializer.
   body += Return(TokenPosition::kNoSource);
 
   PrologueInfo prologue_info(-1, -1);

runtime/vm/kernel.cc

@@ -347,6 +347,38 @@ void CollectTokenPositionsFor(const Script& interesting_script) {
   script.set_debug_positions(array_object);
 }
 
+ObjectPtr EvaluateStaticConstFieldInitializer(const Field& field) {
+  ASSERT(field.is_static() && field.is_const());
+
+  LongJumpScope jump;
+  if (setjmp(*jump.Set()) == 0) {
+    Thread* thread = Thread::Current();
+    Zone* zone = thread->zone();
+    TranslationHelper helper(thread);
+    Script& script = Script::Handle(zone, field.Script());
+    helper.InitFromScript(script);
+
+    const Class& owner_class = Class::Handle(zone, field.Owner());
+    ActiveClass active_class;
+    ActiveClassScope active_class_scope(&active_class, &owner_class);
+
+    KernelReaderHelper kernel_reader(
+        zone, &helper, script,
+        ExternalTypedData::Handle(zone, field.KernelData()),
+        field.KernelDataProgramOffset());
+    kernel_reader.SetOffset(field.kernel_offset());
+    ConstantReader constant_reader(&kernel_reader, &active_class);
+
+    FieldHelper field_helper(&kernel_reader);
+    field_helper.ReadUntilExcluding(FieldHelper::kInitializer);
+    ASSERT(field_helper.IsConst());
+
+    return constant_reader.ReadConstantInitializer();
+  } else {
+    return Thread::Current()->StealStickyError();
+  }
+}
+
 class MetadataEvaluator : public KernelReaderHelper {
  public:
   MetadataEvaluator(Zone* zone,

runtime/vm/kernel.h

@@ -195,6 +195,7 @@ class KernelLineStartsReader {
 
 void CollectTokenPositionsFor(const Script& script);
 
+ObjectPtr EvaluateStaticConstFieldInitializer(const Field& field);
 ObjectPtr EvaluateMetadata(const Field& metadata_field,
                            bool is_annotations_offset);
 ObjectPtr BuildParameterDescriptor(const Function& function);

runtime/vm/object.cc

@@ -10611,6 +10611,14 @@ ErrorPtr Field::InitializeStatic() const {
 ObjectPtr Field::EvaluateInitializer() const {
   Thread* const thread = Thread::Current();
   ASSERT(thread->IsMutatorThread());
+
+#if !defined(DART_PRECOMPILED_RUNTIME)
+  if (is_static() && is_const()) {
+    ASSERT(!FLAG_precompiled_mode);
+    return kernel::EvaluateStaticConstFieldInitializer(*this);
+  }
+#endif  // !defined(DART_PRECOMPILED_RUNTIME)
+
   NoOOBMessageScope no_msg_scope(thread);
   NoReloadScope no_reload_scope(thread->isolate(), thread);
   const Function& initializer = Function::Handle(EnsureInitializerFunction());