path: root/liblll/CodeFragment.cpp

/*
    This file is part of solidity.

    solidity is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    solidity is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with solidity.  If not, see <http://www.gnu.org/licenses/>.
*/
/** @file CodeFragment.cpp
 * @author Gav Wood <i@gavwood.com>
 * @date 2014
 */

#include "CodeFragment.h"

#include <boost/algorithm/string.hpp>

#if defined(__GNUC__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
#endif // defined(__GNUC__)

#include <boost/spirit/include/support_utree.hpp>

#if defined(__GNUC__)
#pragma GCC diagnostic pop
#endif // defined(__GNUC__)

#include <libdevcore/CommonIO.h>
#include <libevmasm/Instruction.h>
#include "CompilerState.h"
#include "Parser.h"

using namespace std;
using namespace dev;
using namespace dev::lll;

void CodeFragment::finalise(CompilerState const& _cs)
{
    // NOTE: add this as a safeguard in case the user didn't issue an
    // explicit stop at the end of the sequence
    m_asm.append(Instruction::STOP);

    if (_cs.usedAlloc && _cs.vars.size() && !m_finalised)
    {
        m_finalised = true;
        m_asm.injectStart(Instruction::MSTORE8);
        m_asm.injectStart((u256)((_cs.vars.size() + 2) * 32) - 1);
        m_asm.injectStart((u256)1);
    }
}

namespace
{
/// Returns true iff the instruction is valid in "inline assembly".
bool validAssemblyInstruction(string us)
{
    auto it = c_instructions.find(us);
    return !(
        it == c_instructions.end() ||
        solidity::isPushInstruction(it->second)
    );
}

/// Returns true iff the instruction is valid as a function.
bool validFunctionalInstruction(string us)
{
    auto it = c_instructions.find(us);
    return !(
        it == c_instructions.end() ||
        solidity::isPushInstruction(it->second) ||
        solidity::isDupInstruction(it->second) ||
        solidity::isSwapInstruction(it->second) ||
        it->second == solidity::Instruction::JUMPDEST
    );
}
}

CodeFragment::CodeFragment(sp::utree const& _t, CompilerState& _s, ReadCallback const& _readFile, bool _allowASM):
    m_readFile(_readFile)
{
/*
    std::cout << "CodeFragment. Locals:";
    for (auto const& i: _s.defs)
        std::cout << i.first << ":" << i.second.m_asm.out();
    std::cout << "Args:";
    for (auto const& i: _s.args)
        std::cout << i.first << ":" << i.second.m_asm.out();
    std::cout << "Outers:";
    for (auto const& i: _s.outers)
        std::cout << i.first << ":" << i.second.m_asm.out();
    debugOutAST(std::cout, _t);
    std::cout << endl << flush;
*/
    switch (_t.which())
    {
    case sp::utree_type::list_type:
        constructOperation(_t, _s);
        break;
    case sp::utree_type::string_type:
    {
        auto sr = _t.get<sp::basic_string<boost::iterator_range<char const*>, sp::utree_type::string_type>>();
        string s(sr.begin(), sr.end());
        m_asm.append(s);
        break;
    }
    case sp::utree_type::symbol_type:
    {
        auto sr = _t.get<sp::basic_string<boost::iterator_range<char const*>, sp::utree_type::symbol_type>>();
        string s(sr.begin(), sr.end());
        string us = boost::algorithm::to_upper_copy(s);
        if (_allowASM && c_instructions.count(us) && validAssemblyInstruction(us))
            m_asm.append(c_instructions.at(us));
        else if (_s.defs.count(s))
            m_asm.append(_s.defs.at(s).m_asm);
        else if (_s.args.count(s))
            m_asm.append(_s.args.at(s).m_asm);
        else if (_s.outers.count(s))
            m_asm.append(_s.outers.at(s).m_asm);
        else if (us.find_first_of("1234567890") != 0 && us.find_first_not_of("QWERTYUIOPASDFGHJKLZXCVBNM1234567890_-") == string::npos)
        {
            auto it = _s.vars.find(s);
            if (it == _s.vars.end())
                error<InvalidName>(std::string("Symbol not found: ") + s);
            m_asm.append((u256)it->second.first);
        }
        else
            error<BareSymbol>(s);

        break;
    }
    case sp::utree_type::any_type:
    {
        bigint i = *_t.get<bigint*>();
        if (i < 0 || i > bigint(u256(0) - 1))
            error<IntegerOutOfRange>(toString(i));
        m_asm.append((u256)i);
        break;
    }
    default:
        error<CompilerException>("Unexpected fragment type");
        break;
    }
}

void CodeFragment::constructOperation(sp::utree const& _t, CompilerState& _s)
{
    if (_t.tag() == 0 && _t.empty())
        error<EmptyList>();
    else if (_t.tag() == 0 && _t.front().which() != sp::utree_type::symbol_type)
        error<DataNotExecutable>();
    else
    {
        string s;
        string us;
        switch (_t.tag())
        {
        case 0:
        {
            auto sr = _t.front().get<sp::basic_string<boost::iterator_range<char const*>, sp::utree_type::symbol_type>>();
            s = string(sr.begin(), sr.end());
            us = boost::algorithm::to_upper_copy(s);
            break;
        }
        case 1:
            us = "MLOAD";
            break;
        case 2:
            us = "SLOAD";
            break;
        case 3:
            us = "MSTORE";
            break;
        case 4:
            us = "SSTORE";
            break;
        case 5:
            us = "SEQ";
            break;
        case 6:
            us = "CALLDATALOAD";
            break;
        default:;
        }

        auto firstAsString = [&]()
        {
            auto i = *++_t.begin();
            if (i.tag())
                error<InvalidName>(toString(i));
            if (i.which() == sp::utree_type::string_type)
            {
                auto sr = i.get<sp::basic_string<boost::iterator_range<char const*>, sp::utree_type::string_type>>();
                return string(sr.begin(), sr.end());
            }
            else if (i.which() == sp::utree_type::symbol_type)
            {
                auto sr = i.get<sp::basic_string<boost::iterator_range<char const*>, sp::utree_type::symbol_type>>();
                return _s.getDef(string(sr.begin(), sr.end())).m_asm.backString();
            }
            return string();
        };

        auto varAddress = [&](string const& n, bool createMissing = false)
        {
            if (n.empty())
                error<InvalidName>("Empty variable name not allowed");
            auto it = _s.vars.find(n);
            if (it == _s.vars.end())
            {
                if (createMissing)
                {
                    // Create new variable
                    bool ok;
                    tie(it, ok) = _s.vars.insert(make_pair(n, make_pair(_s.stackSize, 32)));
                    _s.stackSize += 32;
                }
                else
                    error<InvalidName>(std::string("Symbol not found: ") + n);
            }
            return it->second.first;
        };

        // Operations who args are not standard stack-pushers.
        bool nonStandard = true;
        if (us == "ASM")
        {
            int c = 0;
            for (auto const& i: _t)
                if (c++)
                {
                    auto fragment = CodeFragment(i, _s, m_readFile, true).m_asm;
                    if ((m_asm.deposit() + fragment.deposit()) < 0)
                        error<IncorrectParameterCount>("The assembly instruction resulted in stack underflow");
                    m_asm.append(fragment);
                }
        }
        else if (us == "INCLUDE")
        {
            if (_t.size() != 2)
                error<IncorrectParameterCount>(us);
            string fileName = firstAsString();
            if (fileName.empty())
                error<InvalidName>("Empty file name provided");
            if (!m_readFile)
                error<InvalidName>("Import callback not present");
            string contents = m_readFile(fileName);
            if (contents.empty())
                error<InvalidName>(std::string("File not found (or empty): ") + fileName);
            m_asm.append(CodeFragment::compile(contents, _s, m_readFile).m_asm);
        }
        else if (us == "SET")
        {
            // TODO: move this to be a stack variable (and not a memory variable)
            if (_t.size() != 3)
                error<IncorrectParameterCount>(us);
            int c = 0;
            for (auto const& i: _t)
                if (c++ == 2)
                    m_asm.append(CodeFragment(i, _s, m_readFile, false).m_asm);
            m_asm.append((u256)varAddress(firstAsString(), true));
            m_asm.append(Instruction::MSTORE);
        }
        else if (us == "UNSET")
        {
            // TODO: this doesn't actually free up anything, since it is a memory variable (see "SET")
            if (_t.size() != 2)
                error<IncorrectParameterCount>();
            auto it = _s.vars.find(firstAsString());
            if (it != _s.vars.end())
                _s.vars.erase(it);
        }
        else if (us == "GET")
        {
            if (_t.size() != 2)
                error<IncorrectParameterCount>(us);
            m_asm.append((u256)varAddress(firstAsString()));
            m_asm.append(Instruction::MLOAD);
        }
        else if (us == "WITH")
        {
            if (_t.size() != 4)
                error<IncorrectParameterCount>();
            string key = firstAsString();
            if (_s.vars.find(key) != _s.vars.end())
                error<InvalidName>(string("Symbol already used: ") + key);

            // Create variable
            // TODO: move this to be a stack variable (and not a memory variable)
            size_t c = 0;
            for (auto const& i: _t)
                if (c++ == 2)
                    m_asm.append(CodeFragment(i, _s, m_readFile, false).m_asm);
            m_asm.append((u256)varAddress(key, true));
            m_asm.append(Instruction::MSTORE);

            // Insert sub with variable access, but new state
            CompilerState ns = _s;
            c = 0;
            for (auto const& i: _t)
                if (c++ == 3)
                    m_asm.append(CodeFragment(i, _s, m_readFile, false).m_asm);

            // Remove variable
            auto it = _s.vars.find(key);
            if (it != _s.vars.end())
                _s.vars.erase(it);
        }
        else if (us == "REF")
            m_asm.append((u256)varAddress(firstAsString()));
        else if (us == "DEF")
        {
            string n;
            unsigned ii = 0;
            if (_t.size() != 3 && _t.size() != 4)
                error<IncorrectParameterCount>(us);
            vector<string> args;
            for (auto const& i: _t)
            {
                if (ii == 1)
                {
                    if (i.tag())
                        error<InvalidName>(toString(i));
                    if (i.which() == sp::utree_type::string_type)
                    {
                        auto sr = i.get<sp::basic_string<boost::iterator_range<char const*>, sp::utree_type::string_type>>();
                        n = string(sr.begin(), sr.end());
                    }
                    else if (i.which() == sp::utree_type::symbol_type)
                    {
                        auto sr = i.get<sp::basic_string<boost::iterator_range<char const*>, sp::utree_type::symbol_type>>();
                        n = _s.getDef(string(sr.begin(), sr.end())).m_asm.backString();
                    }
                }
                else if (ii == 2)
                    if (_t.size() == 3)
                    {
                        /// NOTE: some compilers could do the assignment first if this is done in a single line
                        CodeFragment code = CodeFragment(i, _s, m_readFile);
                        _s.defs[n] = code;
                    }
                    else
                        for (auto const& j: i)
                        {
                            if (j.tag() || j.which() != sp::utree_type::symbol_type)
                                error<InvalidMacroArgs>();
                            auto sr = j.get<sp::basic_string<boost::iterator_range<char const*>, sp::utree_type::symbol_type>>();
                            args.push_back(string(sr.begin(), sr.end()));
                        }
                else if (ii == 3)
                {
                    auto k = make_pair(n, args.size());
                    _s.macros[k].code = i;
                    _s.macros[k].env = _s.outers;
                    _s.macros[k].args = args;
                    for (auto const& i: _s.args)
                        _s.macros[k].env[i.first] = i.second;
                    for (auto const& i: _s.defs)
                        _s.macros[k].env[i.first] = i.second;
                }
                ++ii;
            }
        }
        else if (us == "LIT")
        {
            if (_t.size() < 3)
                error<IncorrectParameterCount>(us);
            unsigned ii = 0;
            CodeFragment pos;
            bytes data;
            for (auto const& i: _t)
            {
                if (ii == 0)
                {
                    ii++;
                    continue;
                }
                else if (ii == 1)
                {
                    pos = CodeFragment(i, _s, m_readFile);
                    if (pos.m_asm.deposit() != 1)
                        error<InvalidDeposit>(toString(i));
                }
                else if (i.tag() != 0)
                {
                    error<InvalidLiteral>(toString(i));
                }
                else if (i.which() == sp::utree_type::string_type)
                {
                    auto sr = i.get<sp::basic_string<boost::iterator_range<char const*>, sp::utree_type::string_type>>();
                    data.insert(data.end(), (uint8_t const *)sr.begin(), (uint8_t const*)sr.end());
                }
                else if (i.which() == sp::utree_type::any_type)
                {
                    bigint bi = *i.get<bigint*>();
                    if (bi < 0)
                        error<IntegerOutOfRange>(toString(i));
                    else
                    {
                        bytes tmp = toCompactBigEndian(bi);
                        data.insert(data.end(), tmp.begin(), tmp.end());
                    }
                }
                else
                {
                    error<InvalidLiteral>(toString(i));
                }

                ii++;
            }
            m_asm.append((u256)data.size());
            m_asm.append(Instruction::DUP1);
            m_asm.append(data);
            m_asm.append(pos.m_asm, 1);
            m_asm.append(Instruction::CODECOPY);
        }
        else
            nonStandard = false;

        if (nonStandard)
            return;

        std::map<std::string, Instruction> const c_arith = {
            { "+", Instruction::ADD },
            { "-", Instruction::SUB },
            { "*", Instruction::MUL },
            { "/", Instruction::DIV },
            { "%", Instruction::MOD },
            { "&", Instruction::AND },
            { "|", Instruction::OR },
            { "^", Instruction::XOR }
        };
        std::map<std::string, pair<Instruction, bool>> const c_binary = {
            { "<", { Instruction::LT, false } },
            { "<=", { Instruction::GT, true } },
            { ">", { Instruction::GT, false } },
            { ">=", { Instruction::LT, true } },
            { "S<", { Instruction::SLT, false } },
            { "S<=", { Instruction::SGT, true } },
            { "S>", { Instruction::SGT, false } },
            { "S>=", { Instruction::SLT, true } },
            { "=", { Instruction::EQ, false } },
            { "!=", { Instruction::EQ, true } }
        };
        std::map<std::string, Instruction> const c_unary = {
            { "!", Instruction::ISZERO },
            { "~", Instruction::NOT }
        };

        vector<CodeFragment> code;
        CompilerState ns = _s;
        ns.vars.clear();
        ns.usedAlloc = false;
        int c = _t.tag() ? 1 : 0;
        for (auto const& i: _t)
            if (c++)
            {
                if (us == "LLL" && c == 1)
                    code.push_back(CodeFragment(i, ns, m_readFile));
                else
                    code.push_back(CodeFragment(i, _s, m_readFile));
            }
        auto requireSize = [&](unsigned s) { if (code.size() != s) error<IncorrectParameterCount>(us); };
        auto requireMinSize = [&](unsigned s) { if (code.size() < s) error<IncorrectParameterCount>(us); };
        auto requireMaxSize = [&](unsigned s) { if (code.size() > s) error<IncorrectParameterCount>(us); };
        auto requireDeposit = [&](unsigned i, int s) { if (code[i].m_asm.deposit() != s) error<InvalidDeposit>(us); };

        if (_s.macros.count(make_pair(s, code.size())))
        {
            Macro const& m = _s.macros.at(make_pair(s, code.size()));
            CompilerState cs = _s;
            for (auto const& i: m.env)
                cs.outers[i.first] = i.second;
            for (auto const& i: cs.defs)
                cs.outers[i.first] = i.second;
            cs.defs.clear();
            for (unsigned i = 0; i < m.args.size(); ++i)
            {
                //requireDeposit(i, 1);
                cs.args[m.args[i]] = code[i];
            }
            m_asm.append(CodeFragment(m.code, cs, m_readFile).m_asm);
            for (auto const& i: cs.defs)
                _s.defs[i.first] = i.second;
            for (auto const& i: cs.macros)
                _s.macros.insert(i);
        }
        else if (c_instructions.count(us) && validFunctionalInstruction(us))
        {
            auto it = c_instructions.find(us);
            requireSize(instructionInfo(it->second).args);

            for (unsigned i = code.size(); i; --i)
                m_asm.append(code[i - 1].m_asm, 1);
            m_asm.append(it->second);
        }
        else if (c_arith.count(us))
        {
            auto it = c_arith.find(us);
            requireMinSize(1);
            for (unsigned i = code.size(); i; --i)
            {
                requireDeposit(i - 1, 1);
                m_asm.append(code[i - 1].m_asm, 1);
            }
            for (unsigned i = 1; i < code.size(); ++i)
                m_asm.append(it->second);
        }
        else if (c_binary.count(us))
        {
            auto it = c_binary.find(us);
            requireSize(2);
            requireDeposit(0, 1);
            requireDeposit(1, 1);
            m_asm.append(code[1].m_asm, 1);
            m_asm.append(code[0].m_asm, 1);
            m_asm.append(it->second.first);
            if (it->second.second)
                m_asm.append(Instruction::ISZERO);
        }
        else if (c_unary.count(us))
        {
            auto it = c_unary.find(us);
            requireSize(1);
            requireDeposit(0, 1);
            m_asm.append(code[0].m_asm, 1);
            m_asm.append(it->second);
        }
        else if (us == "IF")
        {
            requireSize(3);
            requireDeposit(0, 1);
            int minDep = min(code[1].m_asm.deposit(), code[2].m_asm.deposit());

            m_asm.append(code[0].m_asm);
            auto mainBranch = m_asm.appendJumpI();

            /// The else branch.
            int startDeposit = m_asm.deposit();
            m_asm.append(code[2].m_asm, minDep);
            auto end = m_asm.appendJump();
            int deposit = m_asm.deposit();
            m_asm.setDeposit(startDeposit);

            /// The main branch.
            m_asm << mainBranch.tag();
            m_asm.append(code[1].m_asm, minDep);
            m_asm << end.tag();
            if (m_asm.deposit() != deposit)
                error<InvalidDeposit>(us);
        }
        else if (us == "WHEN" || us == "UNLESS")
        {
            requireSize(2);
            requireDeposit(0, 1);

            m_asm.append(code[0].m_asm);
            if (us == "WHEN")
                m_asm.append(Instruction::ISZERO);
            auto end = m_asm.appendJumpI();
            m_asm.append(code[1].m_asm, 0);
            m_asm << end.tag();
        }
        else if (us == "WHILE" || us == "UNTIL")
        {
            requireSize(2);
            requireDeposit(0, 1);

            auto begin = m_asm.append(m_asm.newTag());
            m_asm.append(code[0].m_asm);
            if (us == "WHILE")
                m_asm.append(Instruction::ISZERO);
            auto end = m_asm.appendJumpI();
            m_asm.append(code[1].m_asm, 0);
            m_asm.appendJump(begin);
            m_asm << end.tag();
        }
        else if (us == "FOR")
        {
            requireSize(4);
            requireDeposit(1, 1);

            m_asm.append(code[0].m_asm, 0);
            auto begin = m_asm.append(m_asm.newTag());
            m_asm.append(code[1].m_asm);
            m_asm.append(Instruction::ISZERO);
            auto end = m_asm.appendJumpI();
            m_asm.append(code[3].m_asm, 0);
            m_asm.append(code[2].m_asm, 0);
            m_asm.appendJump(begin);
            m_asm << end.tag();
        }
        else if (us == "SWITCH")
        {
            requireMinSize(1);

            bool hasDefault = (code.size() % 2 == 1);
            int startDeposit = m_asm.deposit();
            int targetDeposit = hasDefault ? code[code.size() - 1].m_asm.deposit() : 0;

            // The conditions
            eth::AssemblyItems jumpTags;
            for (unsigned i = 0; i < code.size() - 1; i += 2)
            {
                requireDeposit(i, 1);
                m_asm.append(code[i].m_asm);
                jumpTags.push_back(m_asm.appendJumpI());
            }

            // The default, if present
            if (hasDefault)
                m_asm.append(code[code.size() - 1].m_asm);

            // The targets - appending in reverse makes the top case the most efficient.
            if (code.size() > 1)
            {
                auto end = m_asm.appendJump();
                for (int i = 2 * (code.size() / 2 - 1); i >= 0; i -= 2)
                {
                    m_asm << jumpTags[i / 2].tag();
                    requireDeposit(i + 1, targetDeposit);
                    m_asm.append(code[i + 1].m_asm);
                    if (i != 0)
                        m_asm.appendJump(end);
                }
                m_asm << end.tag();
            }

            m_asm.setDeposit(startDeposit + targetDeposit);
        }
        else if (us == "ALLOC")
        {
            requireSize(1);
            requireDeposit(0, 1);

            // (alloc N):
            //  - Evaluates to (msize) before the allocation - the start of the allocated memory
            //  - Does not allocate memory when N is zero
            //  - Size of memory allocated is N bytes rounded up to a multiple of 32
            //  - Uses MLOAD to expand MSIZE to avoid modifying memory.

            auto end = m_asm.newTag();
            m_asm.append(Instruction::MSIZE); // Result will be original top of memory
            m_asm.append(code[0].m_asm, 1);   // The alloc argument N
            m_asm.append(Instruction::DUP1);
            m_asm.append(Instruction::ISZERO);// (alloc 0) does not change MSIZE
            m_asm.appendJumpI(end);
            m_asm.append(u256(1));
            m_asm.append(Instruction::DUP2);  // Copy N
            m_asm.append(Instruction::SUB);   // N-1
            m_asm.append(u256(0x1f));         // Bit mask
            m_asm.append(Instruction::NOT);   // Invert
            m_asm.append(Instruction::AND);   // Align N-1 on 32 byte boundary
            m_asm.append(Instruction::MSIZE); // MSIZE is cheap
            m_asm.append(Instruction::ADD);
            m_asm.append(Instruction::MLOAD); // Updates MSIZE
            m_asm.append(Instruction::POP);   // Discard the result of the MLOAD
            m_asm.append(end);
            m_asm.append(Instruction::POP);   // Discard duplicate N

            _s.usedAlloc = true;
        }
        else if (us == "LLL")
        {
            requireMinSize(2);
            requireMaxSize(3);
            requireDeposit(1, 1);

            auto subPush = m_asm.appendSubroutine(make_shared<eth::Assembly>(code[0].assembly(ns)));
            m_asm.append(Instruction::DUP1);
            if (code.size() == 3)
            {
                requireDeposit(2, 1);
                m_asm.append(code[2].m_asm, 1);
                m_asm.append(Instruction::LT);
                m_asm.append(Instruction::ISZERO);
                m_asm.append(Instruction::MUL);
                m_asm.append(Instruction::DUP1);
            }
            m_asm.append(subPush);
            m_asm.append(code[1].m_asm, 1);
            m_asm.append(Instruction::CODECOPY);
        }
        else if (us == "&&" || us == "||")
        {
            requireMinSize(1);
            for (unsigned i = 0; i < code.size(); ++i)
                requireDeposit(i, 1);

            auto end = m_asm.newTag();
            if (code.size() > 1)
            {
                m_asm.append((u256)(us == "||" ? 1 : 0));
                for (unsigned i = 1; i < code.size(); ++i)
                {
                    // Check if true - predicate
                    m_asm.append(code[i - 1].m_asm, 1);
                    if (us == "&&")
                        m_asm.append(Instruction::ISZERO);
                    m_asm.appendJumpI(end);
                }
                m_asm.append(Instruction::POP);
            }

            // Check if true - predicate
            m_asm.append(code.back().m_asm, 1);

            // At end now.
            m_asm.append(end);
        }
        else if (us == "SEQ")
        {
            unsigned ii = 0;
            for (auto const& i: code)
                if (++ii < code.size())
                    m_asm.append(i.m_asm, 0);
                else
                    m_asm.append(i.m_asm);
        }
        else if (us == "RAW")
        {
            for (auto const& i: code)
                m_asm.append(i.m_asm);
            // Leave only the last item on stack.
            while (m_asm.deposit() > 1)
                m_asm.append(Instruction::POP);
        }
        else if (us == "BYTECODESIZE")
        {
            m_asm.appendProgramSize();
        }
        else if (us.find_first_of("1234567890") != 0 && us.find_first_not_of("QWERTYUIOPASDFGHJKLZXCVBNM1234567890_-") == string::npos)
            m_asm.append((u256)varAddress(s));
        else
            error<InvalidOperation>("Unsupported keyword: '" + us + "'");
    }
}

CodeFragment CodeFragment::compile(string const& _src, CompilerState& _s, ReadCallback const& _readFile)
{
    CodeFragment ret;
    sp::utree o;
    parseTreeLLL(_src, o);
    if (!o.empty())
        ret = CodeFragment(o, _s, _readFile);
    _s.treesToKill.push_back(o);
    return ret;
}