path: root/libevmasm/SimplificationRules.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 ExpressionClasses.cpp
 * @author Christian <c@ethdev.com>
 * @date 2015
 * Container for equivalence classes of expressions for use in common subexpression elimination.
 */

#include <libevmasm/ExpressionClasses.h>
#include <utility>
#include <tuple>
#include <functional>
#include <boost/range/adaptor/reversed.hpp>
#include <boost/noncopyable.hpp>
#include <libevmasm/Assembly.h>
#include <libevmasm/CommonSubexpressionEliminator.h>
#include <libevmasm/SimplificationRules.h>

using namespace std;
using namespace dev;
using namespace dev::eth;


pair<Pattern, function<Pattern()> > const* Rules::findFirstMatch(
    Expression const& _expr,
    ExpressionClasses const& _classes
)
{
    resetMatchGroups();

    assertThrow(_expr.item, OptimizerException, "");
    for (auto const& rule: m_rules[byte(_expr.item->instruction())])
    {
        if (rule.first.matches(_expr, _classes))
            return &rule;
    }
    return nullptr;
}

void Rules::addRules(std::vector<std::pair<Pattern, std::function<Pattern ()> > > const& _rules)
{
    for (auto const& r: _rules)
        addRule(r);
}

void Rules::addRule(std::pair<Pattern, std::function<Pattern()> > const& _rule)
{
    m_rules[byte(_rule.first.instruction())].push_back(_rule);
}

template <class S> S divWorkaround(S const& _a, S const& _b)
{
    return (S)(bigint(_a) / bigint(_b));
}

template <class S> S modWorkaround(S const& _a, S const& _b)
{
    return (S)(bigint(_a) % bigint(_b));
}

Rules::Rules()
{
    // Multiple occurences of one of these inside one rule must match the same equivalence class.
    // Constants.
    Pattern A(Push);
    Pattern B(Push);
    Pattern C(Push);
    // Anything.
    Pattern X;
    Pattern Y;
    Pattern Z;
    A.setMatchGroup(1, m_matchGroups);
    B.setMatchGroup(2, m_matchGroups);
    C.setMatchGroup(3, m_matchGroups);
    X.setMatchGroup(4, m_matchGroups);
    Y.setMatchGroup(5, m_matchGroups);
    Z.setMatchGroup(6, m_matchGroups);

    addRules(vector<pair<Pattern, function<Pattern()>>>{
        // arithmetics on constants
        {{Instruction::ADD, {A, B}}, [=]{ return A.d() + B.d(); }},
        {{Instruction::MUL, {A, B}}, [=]{ return A.d() * B.d(); }},
        {{Instruction::SUB, {A, B}}, [=]{ return A.d() - B.d(); }},
        {{Instruction::DIV, {A, B}}, [=]{ return B.d() == 0 ? 0 : divWorkaround(A.d(), B.d()); }},
        {{Instruction::SDIV, {A, B}}, [=]{ return B.d() == 0 ? 0 : s2u(divWorkaround(u2s(A.d()), u2s(B.d()))); }},
        {{Instruction::MOD, {A, B}}, [=]{ return B.d() == 0 ? 0 : modWorkaround(A.d(), B.d()); }},
        {{Instruction::SMOD, {A, B}}, [=]{ return B.d() == 0 ? 0 : s2u(modWorkaround(u2s(A.d()), u2s(B.d()))); }},
        {{Instruction::EXP, {A, B}}, [=]{ return u256(boost::multiprecision::powm(bigint(A.d()), bigint(B.d()), bigint(1) << 256)); }},
        {{Instruction::NOT, {A}}, [=]{ return ~A.d(); }},
        {{Instruction::LT, {A, B}}, [=]() { return A.d() < B.d() ? u256(1) : 0; }},
        {{Instruction::GT, {A, B}}, [=]() -> u256 { return A.d() > B.d() ? 1 : 0; }},
        {{Instruction::SLT, {A, B}}, [=]() -> u256 { return u2s(A.d()) < u2s(B.d()) ? 1 : 0; }},
        {{Instruction::SGT, {A, B}}, [=]() -> u256 { return u2s(A.d()) > u2s(B.d()) ? 1 : 0; }},
        {{Instruction::EQ, {A, B}}, [=]() -> u256 { return A.d() == B.d() ? 1 : 0; }},
        {{Instruction::ISZERO, {A}}, [=]() -> u256 { return A.d() == 0 ? 1 : 0; }},
        {{Instruction::AND, {A, B}}, [=]{ return A.d() & B.d(); }},
        {{Instruction::OR, {A, B}}, [=]{ return A.d() | B.d(); }},
        {{Instruction::XOR, {A, B}}, [=]{ return A.d() ^ B.d(); }},
        {{Instruction::BYTE, {A, B}}, [=]{ return A.d() >= 32 ? 0 : (B.d() >> unsigned(8 * (31 - A.d()))) & 0xff; }},
        {{Instruction::ADDMOD, {A, B, C}}, [=]{ return C.d() == 0 ? 0 : u256((bigint(A.d()) + bigint(B.d())) % C.d()); }},
        {{Instruction::MULMOD, {A, B, C}}, [=]{ return C.d() == 0 ? 0 : u256((bigint(A.d()) * bigint(B.d())) % C.d()); }},
        {{Instruction::MULMOD, {A, B, C}}, [=]{ return A.d() * B.d(); }},
        {{Instruction::SIGNEXTEND, {A, B}}, [=]() -> u256 {
            if (A.d() >= 31)
                return B.d();
            unsigned testBit = unsigned(A.d()) * 8 + 7;
            u256 mask = (u256(1) << testBit) - 1;
            return u256(boost::multiprecision::bit_test(B.d(), testBit) ? B.d() | ~mask : B.d() & mask);
        }},

        // invariants involving known constants
        {{Instruction::ADD, {X, 0}}, [=]{ return X; }},
        {{Instruction::SUB, {X, 0}}, [=]{ return X; }},
        {{Instruction::MUL, {X, 1}}, [=]{ return X; }},
        {{Instruction::DIV, {X, 1}}, [=]{ return X; }},
        {{Instruction::SDIV, {X, 1}}, [=]{ return X; }},
        {{Instruction::OR, {X, 0}}, [=]{ return X; }},
        {{Instruction::XOR, {X, 0}}, [=]{ return X; }},
        {{Instruction::AND, {X, ~u256(0)}}, [=]{ return X; }},
        {{Instruction::AND, {X, 0}}, [=]{ return u256(0); }},
        {{Instruction::MUL, {X, 0}}, [=]{ return u256(0); }},
        {{Instruction::DIV, {X, 0}}, [=]{ return u256(0); }},
        {{Instruction::DIV, {0, X}}, [=]{ return u256(0); }},
        {{Instruction::MOD, {X, 0}}, [=]{ return u256(0); }},
        {{Instruction::MOD, {0, X}}, [=]{ return u256(0); }},
        {{Instruction::OR, {X, ~u256(0)}}, [=]{ return ~u256(0); }},
        {{Instruction::EQ, {X, 0}}, [=]() -> Pattern { return {Instruction::ISZERO, {X}}; } },
        // operations involving an expression and itself
        {{Instruction::AND, {X, X}}, [=]{ return X; }},
        {{Instruction::OR, {X, X}}, [=]{ return X; }},
        {{Instruction::XOR, {X, X}}, [=]{ return u256(0); }},
        {{Instruction::SUB, {X, X}}, [=]{ return u256(0); }},
        {{Instruction::EQ, {X, X}}, [=]{ return u256(1); }},
        {{Instruction::LT, {X, X}}, [=]{ return u256(0); }},
        {{Instruction::SLT, {X, X}}, [=]{ return u256(0); }},
        {{Instruction::GT, {X, X}}, [=]{ return u256(0); }},
        {{Instruction::SGT, {X, X}}, [=]{ return u256(0); }},
        {{Instruction::MOD, {X, X}}, [=]{ return u256(0); }},

        {{Instruction::NOT, {{Instruction::NOT, {X}}}}, [=]{ return X; }},
        {{Instruction::XOR, {{{X}, {Instruction::XOR, {X, Y}}}}}, [=]{ return Y; }},
        {{Instruction::OR, {{{X}, {Instruction::AND, {X, Y}}}}}, [=]{ return X; }},
        {{Instruction::AND, {{{X}, {Instruction::OR, {X, Y}}}}}, [=]{ return X; }},
        {{Instruction::AND, {{{X}, {Instruction::NOT, {X}}}}}, [=]{ return u256(0); }},
        {{Instruction::OR, {{{X}, {Instruction::NOT, {X}}}}}, [=]{ return ~u256(0); }},
    });
    // Double negation of opcodes with binary result
    for (auto const& op: vector<Instruction>{
        Instruction::EQ,
        Instruction::LT,
        Instruction::SLT,
        Instruction::GT,
        Instruction::SGT
    })
        addRule({
            {Instruction::ISZERO, {{Instruction::ISZERO, {{op, {X, Y}}}}}},
            [=]() -> Pattern { return {op, {X, Y}}; }
        });
    addRule({
        {Instruction::ISZERO, {{Instruction::ISZERO, {{Instruction::ISZERO, {X}}}}}},
        [=]() -> Pattern { return {Instruction::ISZERO, {X}}; }
    });
    addRule({
        {Instruction::ISZERO, {{Instruction::XOR, {X, Y}}}},
        [=]() -> Pattern { return { Instruction::EQ, {X, Y} }; }
    });
    // Associative operations
    for (auto const& opFun: vector<pair<Instruction,function<u256(u256 const&,u256 const&)>>>{
        {Instruction::ADD, plus<u256>()},
        {Instruction::MUL, multiplies<u256>()},
        {Instruction::AND, bit_and<u256>()},
        {Instruction::OR, bit_or<u256>()},
        {Instruction::XOR, bit_xor<u256>()}
    })
    {
        auto op = opFun.first;
        auto fun = opFun.second;
        // Moving constants to the outside, order matters here!
        // we need actions that return expressions (or patterns?) here, and we need also reversed rules
        // (X+A)+B -> X+(A+B)
        addRules(vector<pair<Pattern, function<Pattern()>>>{{
            {op, {{op, {X, A}}, B}},
            [=]() -> Pattern { return {op, {X, fun(A.d(), B.d())}}; }
        }, {
        // X+(Y+A) -> (X+Y)+A
            {op, {{op, {X, A}}, Y}},
            [=]() -> Pattern { return {op, {{op, {X, Y}}, A}}; }
        }, {
        // For now, we still need explicit commutativity for the inner pattern
            {op, {{op, {A, X}}, B}},
            [=]() -> Pattern { return {op, {X, fun(A.d(), B.d())}}; }
        }, {
            {op, {{op, {A, X}}, Y}},
            [=]() -> Pattern { return {op, {{op, {X, Y}}, A}}; }
        }});
    }
    // move constants across subtractions
    addRules(vector<pair<Pattern, function<Pattern()>>>{
        {
            // X - A -> X + (-A)
            {Instruction::SUB, {X, A}},
            [=]() -> Pattern { return {Instruction::ADD, {X, 0 - A.d()}}; }
        }, {
            // (X + A) - Y -> (X - Y) + A
            {Instruction::SUB, {{Instruction::ADD, {X, A}}, Y}},
            [=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, A}}; }
        }, {
            // (A + X) - Y -> (X - Y) + A
            {Instruction::SUB, {{Instruction::ADD, {A, X}}, Y}},
            [=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, A}}; }
        }, {
            // X - (Y + A) -> (X - Y) + (-A)
            {Instruction::SUB, {X, {Instruction::ADD, {Y, A}}}},
            [=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, 0 - A.d()}}; }
        }, {
            // X - (A + Y) -> (X - Y) + (-A)
            {Instruction::SUB, {X, {Instruction::ADD, {A, Y}}}},
            [=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, 0 - A.d()}}; }
        }
    });
}

Pattern::Pattern(Instruction _instruction, std::vector<Pattern> const& _arguments):
    m_type(Operation),
    m_instruction(_instruction),
    m_arguments(_arguments)
{
}

void Pattern::setMatchGroup(unsigned _group, map<unsigned, Expression const*>& _matchGroups)
{
    m_matchGroup = _group;
    m_matchGroups = &_matchGroups;
}

bool Pattern::matches(Expression const& _expr, ExpressionClasses const& _classes) const
{
    if (!matchesBaseItem(_expr.item))
        return false;
    if (m_matchGroup)
    {
        if (!m_matchGroups->count(m_matchGroup))
            (*m_matchGroups)[m_matchGroup] = &_expr;
        else if ((*m_matchGroups)[m_matchGroup]->id != _expr.id)
            return false;
    }
    assertThrow(m_arguments.size() == 0 || _expr.arguments.size() == m_arguments.size(), OptimizerException, "");
    for (size_t i = 0; i < m_arguments.size(); ++i)
        if (!m_arguments[i].matches(_classes.representative(_expr.arguments[i]), _classes))
            return false;
    return true;
}

AssemblyItem Pattern::toAssemblyItem(SourceLocation const& _location) const
{
    if (m_type == Operation)
        return AssemblyItem(m_instruction, _location);
    else
        return AssemblyItem(m_type, data(), _location);
}

string Pattern::toString() const
{
    stringstream s;
    switch (m_type)
    {
    case Operation:
        s << instructionInfo(m_instruction).name;
        break;
    case Push:
        s << "PUSH " << hex << data();
        break;
    case UndefinedItem:
        s << "ANY";
        break;
    default:
        s << "t=" << dec << m_type << " d=" << hex << data();
        break;
    }
    if (!m_requireDataMatch)
        s << " ~";
    if (m_matchGroup)
        s << "[" << dec << m_matchGroup << "]";
    s << "(";
    for (Pattern const& p: m_arguments)
        s << p.toString() << ", ";
    s << ")";
    return s.str();
}

bool Pattern::matchesBaseItem(AssemblyItem const* _item) const
{
    if (m_type == UndefinedItem)
        return true;
    if (!_item)
        return false;
    if (m_type != _item->type())
        return false;
    else if (m_type == Operation)
        return m_instruction == _item->instruction();
    else if (m_requireDataMatch)
        return data() == _item->data();
    return true;
}

Pattern::Expression const& Pattern::matchGroupValue() const
{
    assertThrow(m_matchGroup > 0, OptimizerException, "");
    assertThrow(!!m_matchGroups, OptimizerException, "");
    assertThrow((*m_matchGroups)[m_matchGroup], OptimizerException, "");
    return *(*m_matchGroups)[m_matchGroup];
}

u256 const& Pattern::data() const
{
    assertThrow(m_data, OptimizerException, "");
    return *m_data;
}

ExpressionTemplate::ExpressionTemplate(Pattern const& _pattern, SourceLocation const& _location)
{
    if (_pattern.matchGroup())
    {
        hasId = true;
        id = _pattern.id();
    }
    else
    {
        hasId = false;
        item = _pattern.toAssemblyItem(_location);
    }
    for (auto const& arg: _pattern.arguments())
        arguments.push_back(ExpressionTemplate(arg, _location));
}

string ExpressionTemplate::toString() const
{
    stringstream s;
    if (hasId)
        s << id;
    else
        s << item;
    s << "(";
    for (auto const& arg: arguments)
        s << arg.toString();
    s << ")";
    return s.str();
}