LibJS/Bytecode: Make Bytecode::Interpreter participate in GC marking

Since the relationship between VM and Bytecode::Interpreter is now
clear, we can have VM ask the Interpreter for roots in the GC marking
pass. This avoids having to register and unregister handles and
MarkedVectors over and over.

Since GeneratorObject can also own a RegisterWindow, we share the code
in a RegisterWindow::visit_edges() helper.

~4% speed-up on Kraken/stanford-crypto-ccm.js :^)

Userland/Libraries/LibJS/Bytecode/BasicBlock.h

@@ -18,8 +18,8 @@ struct UnwindInfo {
     BasicBlock const* handler;
     BasicBlock const* finalizer;
 
-    Handle<Environment> lexical_environment;
+    JS::GCPtr<Environment> lexical_environment;
-    Handle<Environment> variable_environment;
+    JS::GCPtr<Environment> variable_environment;
 };
 
 class BasicBlock {

Userland/Libraries/LibJS/Bytecode/Interpreter.cpp

@@ -50,6 +50,19 @@ Interpreter::~Interpreter()
 {
 }
 
+void Interpreter::visit_edges(Cell::Visitor& visitor)
+{
+    if (m_return_value.has_value())
+        visitor.visit(*m_return_value);
+    if (m_saved_return_value.has_value())
+        visitor.visit(*m_saved_return_value);
+    if (m_saved_exception.has_value())
+        visitor.visit(*m_saved_exception);
+    for (auto& window : m_register_windows) {
+        window.visit([&](auto& value) { value->visit_edges(visitor); });
+    }
+}
+
 // 16.1.6 ScriptEvaluation ( scriptRecord ), https://tc39.es/ecma262/#sec-runtime-semantics-scriptevaluation
 ThrowCompletionOr<Value> Interpreter::run(Script& script_record, JS::GCPtr<Environment> lexical_environment_override)
 {
@@ -223,7 +236,7 @@ Interpreter::ValueAndFrame Interpreter::run_and_return_frame(Realm& realm, Execu
             auto ran_or_error = instruction.execute(*this);
             if (ran_or_error.is_error()) {
                 auto exception_value = *ran_or_error.throw_completion().value();
-                m_saved_exception = make_handle(exception_value);
+                m_saved_exception = exception_value;
                 if (unwind_contexts().is_empty())
                     break;
                 auto& unwind_context = unwind_contexts().last();
@@ -254,7 +267,7 @@ Interpreter::ValueAndFrame Interpreter::run_and_return_frame(Realm& realm, Execu
                 will_jump = true;
                 break;
             }
-            if (!m_return_value.is_empty()) {
+            if (m_return_value.has_value()) {
                 will_return = true;
                 // Note: A `yield` statement will not go through a finally statement,
                 //       hence we need to set a flag to not do so,
@@ -273,7 +286,7 @@ Interpreter::ValueAndFrame Interpreter::run_and_return_frame(Realm& realm, Execu
         if (!unwind_contexts().is_empty() && !will_yield) {
             auto& unwind_context = unwind_contexts().last();
             if (unwind_context.executable == m_current_executable && unwind_context.finalizer) {
-                m_saved_return_value = make_handle(m_return_value);
+                m_saved_return_value = m_return_value;
                 m_return_value = {};
                 m_current_block = unwind_context.finalizer;
                 // the unwind_context will be pop'ed when entering the finally block
@@ -284,7 +297,7 @@ Interpreter::ValueAndFrame Interpreter::run_and_return_frame(Realm& realm, Execu
         if (pc.at_end())
             break;
 
-        if (!m_saved_exception.is_null())
+        if (m_saved_exception.has_value())
             break;
 
         if (will_return)
@@ -307,12 +320,10 @@ Interpreter::ValueAndFrame Interpreter::run_and_return_frame(Realm& realm, Execu
     auto frame = pop_register_window();
 
     Value return_value = js_undefined();
-    if (!m_return_value.is_empty()) {
+    if (m_return_value.has_value()) {
-        return_value = m_return_value;
+        return_value = m_return_value.release_value();
-        m_return_value = {};
+    } else if (m_saved_return_value.has_value() && !m_saved_exception.has_value()) {
-    } else if (!m_saved_return_value.is_null() && m_saved_exception.is_null()) {
+        return_value = m_saved_return_value.release_value();
-        return_value = m_saved_return_value.value();
-        m_saved_return_value = {};
     }
 
     // NOTE: The return value from a called function is put into $0 in the caller context.
@@ -330,7 +341,7 @@ Interpreter::ValueAndFrame Interpreter::run_and_return_frame(Realm& realm, Execu
 
     vm().finish_execution_generation();
 
-    if (!m_saved_exception.is_null()) {
+    if (m_saved_exception.has_value()) {
         Value thrown_value = m_saved_exception.value();
         m_saved_exception = {};
         m_saved_return_value = {};
@@ -361,15 +372,12 @@ void Interpreter::leave_unwind_context()
 
 ThrowCompletionOr<void> Interpreter::continue_pending_unwind(Label const& resume_label)
 {
-    if (!m_saved_exception.is_null()) {
+    if (m_saved_exception.has_value()) {
-        auto result = throw_completion(m_saved_exception.value());
+        return throw_completion(m_saved_exception.release_value());
-        m_saved_exception = {};
-        return result;
     }
 
-    if (!m_saved_return_value.is_null()) {
+    if (m_saved_return_value.has_value()) {
-        do_return(m_saved_return_value.value());
+        do_return(m_saved_return_value.release_value());
-        m_saved_return_value = {};
         return {};
     }
 

Userland/Libraries/LibJS/Bytecode/Interpreter.h

@@ -10,7 +10,6 @@
 #include <LibJS/Bytecode/Register.h>
 #include <LibJS/Forward.h>
 #include <LibJS/Heap/Cell.h>
-#include <LibJS/Heap/Handle.h>
 #include <LibJS/Runtime/FunctionKind.h>
 #include <LibJS/Runtime/VM.h>
 #include <LibJS/Runtime/Value.h>
@@ -21,9 +20,22 @@ class InstructionStreamIterator;
 class PassManager;
 
 struct RegisterWindow {
-    MarkedVector<Value> registers;
+    void visit_edges(Cell::Visitor& visitor)
-    MarkedVector<GCPtr<Environment>> saved_lexical_environments;
+    {
-    MarkedVector<GCPtr<Environment>> saved_variable_environments;
+        for (auto const& value : registers)
+            visitor.visit(value);
+        for (auto const& environment : saved_lexical_environments)
+            visitor.visit(environment);
+        for (auto const& environment : saved_variable_environments)
+            visitor.visit(environment);
+        for (auto& context : unwind_contexts) {
+            visitor.visit(context.lexical_environment);
+            visitor.visit(context.variable_environment);
+        }
+    }
+    Vector<Value> registers;
+    Vector<GCPtr<Environment>> saved_lexical_environments;
+    Vector<GCPtr<Environment>> saved_variable_environments;
     Vector<UnwindInfo> unwind_contexts;
 };
 
@@ -90,6 +102,8 @@ public:
 
     VM::InterpreterExecutionScope ast_interpreter_scope(Realm&);
 
+    void visit_edges(Cell::Visitor&);
+
 private:
     RegisterWindow& window()
     {
@@ -112,10 +126,10 @@ private:
     Span<Value> m_current_register_window;
     Optional<BasicBlock const*> m_pending_jump;
     BasicBlock const* m_scheduled_jump { nullptr };
-    Value m_return_value;
+    Optional<Value> m_return_value;
-    Handle<Value> m_saved_return_value;
+    Optional<Value> m_saved_return_value;
+    Optional<Value> m_saved_exception;
     Executable const* m_current_executable { nullptr };
-    Handle<Value> m_saved_exception;
     OwnPtr<JS::Interpreter> m_ast_interpreter;
     BasicBlock const* m_current_block { nullptr };
     InstructionStreamIterator* m_pc { nullptr };

Userland/Libraries/LibJS/Heap/Heap.cpp

@@ -10,6 +10,7 @@
 #include <AK/StackInfo.h>
 #include <AK/TemporaryChange.h>
 #include <LibCore/ElapsedTimer.h>
+#include <LibJS/Bytecode/Interpreter.h>
 #include <LibJS/Heap/CellAllocator.h>
 #include <LibJS/Heap/Handle.h>
 #include <LibJS/Heap/Heap.h>
@@ -270,6 +271,10 @@ void Heap::mark_live_cells(HashTable<Cell*> const& roots)
     dbgln_if(HEAP_DEBUG, "mark_live_cells:");
 
     MarkingVisitor visitor(roots);
+
+    if (auto* bytecode_interpreter = vm().bytecode_interpreter_if_exists())
+        bytecode_interpreter->visit_edges(visitor);
+
     visitor.mark_all_live_cells();
 
     for (auto& inverse_root : m_uprooted_cells)

Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp

@@ -52,6 +52,8 @@ void GeneratorObject::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_generating_function);
     visitor.visit(m_previous_value);
     m_execution_context.visit_edges(visitor);
+    if (m_frame.has_value())
+        m_frame->visit_edges(visitor);
 }
 
 // 27.5.3.2 GeneratorValidate ( generator, generatorBrand ), https://tc39.es/ecma262/#sec-generatorvalidate