serenity/Userland/Libraries/LibJS/Bytecode/Generator.h

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

#pragma once

#include <AK/NonnullOwnPtrVector.h>
#include <AK/OwnPtr.h>
#include <AK/SinglyLinkedList.h>
#include <LibJS/Bytecode/BasicBlock.h>
#include <LibJS/Bytecode/Label.h>
#include <LibJS/Bytecode/Op.h>
#include <LibJS/Bytecode/Register.h>
#include <LibJS/Bytecode/StringTable.h>
#include <LibJS/Forward.h>

namespace JS::Bytecode {

struct Executable {
    NonnullOwnPtrVector<BasicBlock> basic_blocks;
    NonnullOwnPtr<StringTable> string_table;
    size_t number_of_registers { 0 };

    String const& get_string(StringTableIndex index) const { return string_table->get(index); }
};

class Generator {
public:
    static Executable generate(ASTNode const&, bool is_in_generator_function = false);

    Register allocate_register();

    void ensure_enough_space(size_t size)
    {
        // Make sure there's always enough space for a single jump at the end.
        if (!m_current_basic_block->can_grow(size + sizeof(Op::Jump))) {
            auto& new_block = make_block();
            emit<Op::Jump>().set_targets(
                Label { new_block },
                {});
            switch_to_basic_block(new_block);
        }
    }

    template<typename OpType, typename... Args>
    OpType& emit(Args&&... args)
    {
        VERIFY(!is_current_block_terminated());
        // If the block doesn't have enough space, switch to another block
        if constexpr (!OpType::IsTerminator)
            ensure_enough_space(sizeof(OpType));

        void* slot = next_slot();
        grow(sizeof(OpType));
        new (slot) OpType(forward<Args>(args)...);
        if constexpr (OpType::IsTerminator)
            m_current_basic_block->terminate({});
        return *static_cast<OpType*>(slot);
    }

    template<typename OpType, typename... Args>
    OpType& emit_with_extra_register_slots(size_t extra_register_slots, Args&&... args)
    {
        VERIFY(!is_current_block_terminated());
        // If the block doesn't have enough space, switch to another block
        if constexpr (!OpType::IsTerminator)
            ensure_enough_space(sizeof(OpType) + extra_register_slots * sizeof(Register));

        void* slot = next_slot();
        grow(sizeof(OpType) + extra_register_slots * sizeof(Register));
        new (slot) OpType(forward<Args>(args)...);
        if constexpr (OpType::IsTerminator)
            m_current_basic_block->terminate({});
        return *static_cast<OpType*>(slot);
    }

    void begin_continuable_scope(Label continue_target);
    void end_continuable_scope();
    void begin_breakable_scope(Label breakable_target);
    void end_breakable_scope();

    [[nodiscard]] Label nearest_continuable_scope() const;
    [[nodiscard]] Label nearest_breakable_scope() const;

    void switch_to_basic_block(BasicBlock& block)
    {
        m_current_basic_block = &block;
    }

    [[nodiscard]] BasicBlock& current_block() { return *m_current_basic_block; }

    BasicBlock& make_block(String name = {})
    {
        if (name.is_empty())
            name = String::number(m_next_block++);
        m_root_basic_blocks.append(BasicBlock::create(name));
        return m_root_basic_blocks.last();
    }

    bool is_current_block_terminated() const
    {
        return m_current_basic_block->is_terminated();
    }

    StringTableIndex intern_string(StringView const& string)
    {
        return m_string_table->insert(string);
    }

    bool is_in_generator_function() const { return m_is_in_generator_function; }
    void enter_generator_context() { m_is_in_generator_function = true; }
    void leave_generator_context() { m_is_in_generator_function = false; }

private:
    Generator();
    ~Generator();

    void grow(size_t);
    void* next_slot();

    BasicBlock* m_current_basic_block { nullptr };
    NonnullOwnPtrVector<BasicBlock> m_root_basic_blocks;
    NonnullOwnPtr<StringTable> m_string_table;

    u32 m_next_register { 2 };
    u32 m_next_block { 1 };
    bool m_is_in_generator_function { false };
    Vector<Label> m_continuable_scopes;
    Vector<Label> m_breakable_scopes;
};

}