LibJS: Start fleshing out a bytecode for the JavaScript engine :^)

This patch begins the work of implementing JavaScript execution in a
bytecode VM instead of an AST tree-walk interpreter.

It's probably quite naive, but we have to start somewhere.

The basic idea is that you call Bytecode::Generator::generate() on an
AST node and it hands you back a Bytecode::Block filled with
instructions that can then be interpreted by a Bytecode::Interpreter.

This first version only implements two instructions: Load and Add. :^)

Each bytecode block has infinity registers, and the interpreter resizes
its register file to fit the block being executed.

Two new `js` options are added in this patch as well:

`-d` will dump the generated bytecode
`-b` will execute the generated bytecode

Note that unless `-d` and/or `-b` are specified, none of the bytecode
related stuff in LibJS runs at all. This is implemented in parallel
with the existing AST interpreter. :^)

Userland/Libraries/LibJS/Bytecode/Block.cpp

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/String.h>
+#include <LibJS/Bytecode/Block.h>
+#include <LibJS/Bytecode/Instruction.h>
+
+namespace JS::Bytecode {
+
+NonnullOwnPtr<Block> Block::create()
+{
+    return adopt_own(*new Block);
+}
+
+Block::Block()
+{
+}
+
+Block::~Block()
+{
+}
+
+void Block::append(Badge<Bytecode::Generator>, NonnullOwnPtr<Instruction> instruction)
+{
+    m_instructions.append(move(instruction));
+}
+
+void Block::dump() const
+{
+    for (size_t i = 0; i < m_instructions.size(); ++i) {
+        warnln("[{:3}] {}", i, m_instructions[i].to_string());
+    }
+}
+
+}

Userland/Libraries/LibJS/Bytecode/Block.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Badge.h>
+#include <AK/NonnullOwnPtrVector.h>
+#include <LibJS/Forward.h>
+
+namespace JS::Bytecode {
+
+class Block {
+public:
+    static NonnullOwnPtr<Block> create();
+    ~Block();
+
+    NonnullOwnPtrVector<Instruction> const& instructions() const { return m_instructions; }
+    void dump() const;
+
+    size_t register_count() const { return m_register_count; }
+
+    void append(Badge<Bytecode::Generator>, NonnullOwnPtr<Instruction>);
+    void set_register_count(Badge<Bytecode::Generator>, size_t count) { m_register_count = count; }
+
+private:
+    Block();
+
+    size_t m_register_count { 0 };
+    NonnullOwnPtrVector<Instruction> m_instructions;
+};
+
+}

Userland/Libraries/LibJS/Bytecode/Generator.cpp

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/OwnPtr.h>
+#include <LibJS/AST.h>
+#include <LibJS/Bytecode/Block.h>
+#include <LibJS/Bytecode/Generator.h>
+#include <LibJS/Bytecode/Instruction.h>
+#include <LibJS/Bytecode/Register.h>
+#include <LibJS/Forward.h>
+
+namespace JS::Bytecode {
+
+Generator::Generator()
+{
+    m_block = Block::create();
+}
+
+Generator::~Generator()
+{
+}
+
+OwnPtr<Block> Generator::generate(ASTNode const& node)
+{
+    Generator generator;
+    [[maybe_unused]] auto dummy = node.generate_bytecode(generator);
+    generator.m_block->set_register_count({}, generator.m_next_register);
+    return move(generator.m_block);
+}
+
+void Generator::append(NonnullOwnPtr<Instruction> instruction)
+{
+    m_block->append({}, move(instruction));
+}
+
+Register Generator::allocate_register()
+{
+    VERIFY(m_next_register != NumericLimits<u32>::max());
+    return Register { m_next_register++ };
+}
+
+}

Userland/Libraries/LibJS/Bytecode/Generator.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/OwnPtr.h>
+#include <LibJS/Forward.h>
+
+namespace JS::Bytecode {
+
+class Generator {
+public:
+    static OwnPtr<Block> generate(ASTNode const&);
+
+    Register allocate_register();
+
+    template<typename OpType, typename... Args>
+    void emit(Args&&... args)
+    {
+        auto instruction = make<OpType>(forward<Args>(args)...);
+        append(move(instruction));
+    }
+
+private:
+    Generator();
+    ~Generator();
+
+    void append(NonnullOwnPtr<Instruction>);
+
+    OwnPtr<Block> m_block;
+    u32 m_next_register { 1 };
+};
+
+}

Userland/Libraries/LibJS/Bytecode/Instruction.cpp

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Bytecode/Instruction.h>
+
+namespace JS::Bytecode {
+
+Instruction::~Instruction()
+{
+}
+
+}

Userland/Libraries/LibJS/Bytecode/Instruction.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <LibJS/Forward.h>
+
+namespace JS::Bytecode {
+
+class Instruction {
+public:
+    virtual ~Instruction();
+
+    virtual String to_string() const = 0;
+    virtual void execute(Bytecode::Interpreter&) const = 0;
+};
+
+}

Userland/Libraries/LibJS/Bytecode/Interpreter.cpp

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Bytecode/Block.h>
+#include <LibJS/Bytecode/Instruction.h>
+#include <LibJS/Bytecode/Interpreter.h>
+
+namespace JS::Bytecode {
+
+Interpreter::Interpreter(GlobalObject& global_object)
+    : m_global_object(global_object)
+{
+}
+
+Interpreter::~Interpreter()
+{
+}
+
+void Interpreter::run(Bytecode::Block const& block)
+{
+    dbgln("Bytecode::Interpreter will run block {:p}", &block);
+
+    m_registers.resize(block.register_count());
+
+    for (auto& instruction : block.instructions())
+        instruction.execute(*this);
+
+    dbgln("Bytecode::Interpreter did run block {:p}", &block);
+    for (size_t i = 0; i < m_registers.size(); ++i) {
+        String value_string;
+        if (m_registers[i].is_empty())
+            value_string = "(empty)";
+        else
+            value_string = m_registers[i].to_string_without_side_effects();
+        dbgln("[{:3}] {}", i, value_string);
+    }
+}
+
+}

Userland/Libraries/LibJS/Bytecode/Interpreter.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Bytecode/Register.h>
+#include <LibJS/Forward.h>
+#include <LibJS/Heap/Cell.h>
+#include <LibJS/Runtime/Value.h>
+
+namespace JS::Bytecode {
+
+class Interpreter {
+public:
+    explicit Interpreter(GlobalObject&);
+    ~Interpreter();
+
+    GlobalObject& global_object() { return m_global_object; }
+
+    void run(Bytecode::Block const&);
+
+    Value& reg(Register const& r) { return m_registers[r.index()]; }
+
+private:
+    GlobalObject& m_global_object;
+    Vector<Value> m_registers;
+};
+
+}

Userland/Libraries/LibJS/Bytecode/Op.cpp

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Bytecode/Interpreter.h>
+#include <LibJS/Bytecode/Op.h>
+#include <LibJS/Runtime/Value.h>
+
+namespace JS::Bytecode::Op {
+
+void Load::execute(Bytecode::Interpreter& interpreter) const
+{
+    interpreter.reg(m_dst) = m_value;
+}
+
+void Add::execute(Bytecode::Interpreter& interpreter) const
+{
+    interpreter.reg(m_dst) = add(interpreter.global_object(), interpreter.reg(m_src1), interpreter.reg(m_src2));
+}
+
+String Load::to_string() const
+{
+    return String::formatted("Load dst:r{}, value:{}", m_dst.index(), m_value.to_string_without_side_effects());
+}
+
+String Add::to_string() const
+{
+    return String::formatted("Add dst:r{}, src1:r{}, src2:r{}", m_dst.index(), m_src1.index(), m_src2.index());
+}
+
+}

Userland/Libraries/LibJS/Bytecode/Op.h

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Bytecode/Instruction.h>
+#include <LibJS/Bytecode/Register.h>
+#include <LibJS/Heap/Cell.h>
+#include <LibJS/Runtime/Value.h>
+
+namespace JS::Bytecode::Op {
+
+class Load final : public Instruction {
+public:
+    Load(Register dst, Value value)
+        : m_dst(dst)
+        , m_value(value)
+    {
+    }
+
+    virtual ~Load() override { }
+    virtual void execute(Bytecode::Interpreter&) const override;
+    virtual String to_string() const override;
+
+private:
+    Register m_dst;
+    Value m_value;
+};
+
+class Add final : public Instruction {
+public:
+    Add(Register dst, Register src1, Register src2)
+        : m_dst(dst)
+        , m_src1(src1)
+        , m_src2(src2)
+    {
+    }
+
+    virtual ~Add() override { }
+    virtual void execute(Bytecode::Interpreter&) const override;
+    virtual String to_string() const override;
+
+private:
+    Register m_dst;
+    Register m_src1;
+    Register m_src2;
+};
+
+}

Userland/Libraries/LibJS/Bytecode/Register.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+
+namespace JS::Bytecode {
+
+class Register {
+public:
+    explicit Register(u32 index)
+        : m_index(index)
+    {
+    }
+
+    u32 index() const { return m_index; }
+
+private:
+    u32 m_index { 0 };
+};
+
+}