LibJS/Bytecode: Add Bytecode::Operand

An Operand is either a register, a local, or a constant (index into the
executable's constant table)

Userland/Libraries/LibJS/Bytecode/Instruction.cpp

@@ -42,4 +42,10 @@ RefPtr<SourceCode> InstructionStreamIterator::source_code() const
     return m_executable ? m_executable->source_code.ptr() : nullptr;
 }
 
+Operand::Operand(Register reg)
+    : m_type(Type::Register)
+    , m_index(reg.index())
+{
+}
+
 }

Userland/Libraries/LibJS/Bytecode/Instruction.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021-2024, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */

Userland/Libraries/LibJS/Bytecode/Interpreter.cpp

@@ -67,6 +67,34 @@ void Interpreter::visit_edges(Cell::Visitor& visitor)
     }
 }
 
+Value Interpreter::get(Operand op) const
+{
+    switch (op.type()) {
+    case Operand::Type::Register:
+        return reg(Register { op.index() });
+    case Operand::Type::Local:
+        return vm().running_execution_context().locals[op.index()];
+    case Operand::Type::Constant:
+        return current_executable().constants[op.index()];
+    }
+    VERIFY_NOT_REACHED();
+}
+
+void Interpreter::set(Operand op, Value value)
+{
+    switch (op.type()) {
+    case Operand::Type::Register:
+        reg(Register { op.index() }) = value;
+        return;
+    case Operand::Type::Local:
+        vm().running_execution_context().locals[op.index()] = value;
+        return;
+    case Operand::Type::Constant:
+        VERIFY_NOT_REACHED();
+    }
+    VERIFY_NOT_REACHED();
+}
+
 // 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)
 {

Userland/Libraries/LibJS/Bytecode/Interpreter.h

@@ -53,6 +53,7 @@ public:
 
     Realm& realm();
     VM& vm() { return m_vm; }
+    VM const& vm() const { return m_vm; }
 
     ThrowCompletionOr<Value> run(Script&, JS::GCPtr<Environment> lexical_environment_override = nullptr);
     ThrowCompletionOr<Value> run(SourceTextModule&);
@@ -72,6 +73,10 @@ public:
     ALWAYS_INLINE Value& accumulator() { return reg(Register::accumulator()); }
     ALWAYS_INLINE Value& saved_return_value() { return reg(Register::saved_return_value()); }
     Value& reg(Register const& r) { return registers()[r.index()]; }
+    Value reg(Register const& r) const { return registers()[r.index()]; }
+
+    [[nodiscard]] Value get(Operand) const;
+    void set(Operand, Value);
 
     auto& saved_lexical_environment_stack() { return call_frame().saved_lexical_environments; }
     auto& unwind_contexts() { return call_frame().unwind_contexts; }

Userland/Libraries/LibJS/Bytecode/Operand.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2024, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+#include <LibJS/Forward.h>
+
+namespace JS::Bytecode {
+
+class Operand {
+public:
+    enum class Type {
+        Register,
+        Local,
+        Constant,
+    };
+
+    [[nodiscard]] bool operator==(Operand const&) const = default;
+
+    explicit Operand(Type type, u32 index)
+        : m_type(type)
+        , m_index(index)
+    {
+    }
+
+    explicit Operand(Register);
+
+    [[nodiscard]] bool is_register() const { return m_type == Type::Register; }
+    [[nodiscard]] bool is_local() const { return m_type == Type::Local; }
+    [[nodiscard]] bool is_constant() const { return m_type == Type::Constant; }
+
+    [[nodiscard]] Type type() const { return m_type; }
+    [[nodiscard]] u32 index() const { return m_index; }
+
+private:
+    Type m_type {};
+    u32 m_index { 0 };
+};
+
+}