path: root/libevmasm/RuleList.h

/*
    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/>.
*/
/**
 * @date 2018
 * Templatized list of simplification rules.
 */

#pragma once

#include <vector>
#include <functional>

#include <libevmasm/Instruction.h>
#include <libevmasm/SimplificationRule.h>

#include <libdevcore/CommonData.h>

namespace dev
{
namespace solidity
{

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));
}

// This part of simplificationRuleList below was split out to prevent
// stack overflows in the JavaScript optimizer for emscripten builds
// that affected certain browser versions.
template <class Pattern>
std::vector<SimplificationRule<Pattern>> simplificationRuleListPart1(
    Pattern A,
    Pattern B,
    Pattern C,
    Pattern X,
    Pattern Y
)
{
    return std::vector<SimplificationRule<Pattern>> {
        // arithmetic on constants
        {{Instruction::ADD, {A, B}}, [=]{ return A.d() + B.d(); }, false},
        {{Instruction::MUL, {A, B}}, [=]{ return A.d() * B.d(); }, false},
        {{Instruction::SUB, {A, B}}, [=]{ return A.d() - B.d(); }, false},
        {{Instruction::DIV, {A, B}}, [=]{ return B.d() == 0 ? 0 : divWorkaround(A.d(), B.d()); }, false},
        {{Instruction::SDIV, {A, B}}, [=]{ return B.d() == 0 ? 0 : s2u(divWorkaround(u2s(A.d()), u2s(B.d()))); }, false},
        {{Instruction::MOD, {A, B}}, [=]{ return B.d() == 0 ? 0 : modWorkaround(A.d(), B.d()); }, false},
        {{Instruction::SMOD, {A, B}}, [=]{ return B.d() == 0 ? 0 : s2u(modWorkaround(u2s(A.d()), u2s(B.d()))); }, false},
        {{Instruction::EXP, {A, B}}, [=]{ return u256(boost::multiprecision::powm(bigint(A.d()), bigint(B.d()), bigint(1) << 256)); }, false},
        {{Instruction::NOT, {A}}, [=]{ return ~A.d(); }, false},
        {{Instruction::LT, {A, B}}, [=]() -> u256 { return A.d() < B.d() ? 1 : 0; }, false},
        {{Instruction::GT, {A, B}}, [=]() -> u256 { return A.d() > B.d() ? 1 : 0; }, false},
        {{Instruction::SLT, {A, B}}, [=]() -> u256 { return u2s(A.d()) < u2s(B.d()) ? 1 : 0; }, false},
        {{Instruction::SGT, {A, B}}, [=]() -> u256 { return u2s(A.d()) > u2s(B.d()) ? 1 : 0; }, false},
        {{Instruction::EQ, {A, B}}, [=]() -> u256 { return A.d() == B.d() ? 1 : 0; }, false},
        {{Instruction::ISZERO, {A}}, [=]() -> u256 { return A.d() == 0 ? 1 : 0; }, false},
        {{Instruction::AND, {A, B}}, [=]{ return A.d() & B.d(); }, false},
        {{Instruction::OR, {A, B}}, [=]{ return A.d() | B.d(); }, false},
        {{Instruction::XOR, {A, B}}, [=]{ return A.d() ^ B.d(); }, false},
        {{Instruction::BYTE, {A, B}}, [=]{ return A.d() >= 32 ? 0 : (B.d() >> unsigned(8 * (31 - A.d()))) & 0xff; }, false},
        {{Instruction::ADDMOD, {A, B, C}}, [=]{ return C.d() == 0 ? 0 : u256((bigint(A.d()) + bigint(B.d())) % C.d()); }, false},
        {{Instruction::MULMOD, {A, B, C}}, [=]{ return C.d() == 0 ? 0 : u256((bigint(A.d()) * bigint(B.d())) % C.d()); }, false},
        {{Instruction::MULMOD, {A, B, C}}, [=]{ return A.d() * B.d(); }, false},
        {{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);
        }, false},
        {{Instruction::SHL, {A, B}}, [=]{
            if (A.d() > 255)
                return u256(0);
            return u256(bigint(B.d()) << unsigned(A.d()));
        }, false},
        {{Instruction::SHR, {A, B}}, [=]{
            if (A.d() > 255)
                return u256(0);
            return B.d() >> unsigned(A.d());
        }, false},

        // invariants involving known constants
        {{Instruction::ADD, {X, 0}}, [=]{ return X; }, false},
        {{Instruction::ADD, {0, X}}, [=]{ return X; }, false},
        {{Instruction::SUB, {X, 0}}, [=]{ return X; }, false},
        {{Instruction::MUL, {X, 0}}, [=]{ return u256(0); }, true},
        {{Instruction::MUL, {0, X}}, [=]{ return u256(0); }, true},
        {{Instruction::MUL, {X, 1}}, [=]{ return X; }, false},
        {{Instruction::MUL, {1, X}}, [=]{ return X; }, false},
        {{Instruction::MUL, {X, u256(-1)}}, [=]() -> Pattern { return {Instruction::SUB, {0, X}}; }, false},
        {{Instruction::MUL, {u256(-1), X}}, [=]() -> Pattern { return {Instruction::SUB, {0, X}}; }, false},
        {{Instruction::DIV, {X, 0}}, [=]{ return u256(0); }, true},
        {{Instruction::DIV, {0, X}}, [=]{ return u256(0); }, true},
        {{Instruction::DIV, {X, 1}}, [=]{ return X; }, false},
        {{Instruction::SDIV, {X, 0}}, [=]{ return u256(0); }, true},
        {{Instruction::SDIV, {0, X}}, [=]{ return u256(0); }, true},
        {{Instruction::SDIV, {X, 1}}, [=]{ return X; }, false},
        {{Instruction::AND, {X, ~u256(0)}}, [=]{ return X; }, false},
        {{Instruction::AND, {~u256(0), X}}, [=]{ return X; }, false},
        {{Instruction::AND, {X, 0}}, [=]{ return u256(0); }, true},
        {{Instruction::AND, {0, X}}, [=]{ return u256(0); }, true},
        {{Instruction::OR, {X, 0}}, [=]{ return X; }, false},
        {{Instruction::OR, {0, X}}, [=]{ return X; }, false},
        {{Instruction::OR, {X, ~u256(0)}}, [=]{ return ~u256(0); }, true},
        {{Instruction::OR, {~u256(0), X}}, [=]{ return ~u256(0); }, true},
        {{Instruction::XOR, {X, 0}}, [=]{ return X; }, false},
        {{Instruction::XOR, {0, X}}, [=]{ return X; }, false},
        {{Instruction::MOD, {X, 0}}, [=]{ return u256(0); }, true},
        {{Instruction::MOD, {0, X}}, [=]{ return u256(0); }, true},
        {{Instruction::EQ, {X, 0}}, [=]() -> Pattern { return {Instruction::ISZERO, {X}}; }, false },
        {{Instruction::EQ, {0, X}}, [=]() -> Pattern { return {Instruction::ISZERO, {X}}; }, false },

        // operations involving an expression and itself
        {{Instruction::AND, {X, X}}, [=]{ return X; }, true},
        {{Instruction::OR, {X, X}}, [=]{ return X; }, true},
        {{Instruction::XOR, {X, X}}, [=]{ return u256(0); }, true},
        {{Instruction::SUB, {X, X}}, [=]{ return u256(0); }, true},
        {{Instruction::EQ, {X, X}}, [=]{ return u256(1); }, true},
        {{Instruction::LT, {X, X}}, [=]{ return u256(0); }, true},
        {{Instruction::SLT, {X, X}}, [=]{ return u256(0); }, true},
        {{Instruction::GT, {X, X}}, [=]{ return u256(0); }, true},
        {{Instruction::SGT, {X, X}}, [=]{ return u256(0); }, true},
        {{Instruction::MOD, {X, X}}, [=]{ return u256(0); }, true},

        // logical instruction combinations
        {{Instruction::NOT, {{Instruction::NOT, {X}}}}, [=]{ return X; }, false},
        {{Instruction::XOR, {X, {Instruction::XOR, {X, Y}}}}, [=]{ return Y; }, true},
        {{Instruction::XOR, {X, {Instruction::XOR, {Y, X}}}}, [=]{ return Y; }, true},
        {{Instruction::XOR, {{Instruction::XOR, {X, Y}}, X}}, [=]{ return Y; }, true},
        {{Instruction::XOR, {{Instruction::XOR, {Y, X}}, X}}, [=]{ return Y; }, true},
        {{Instruction::OR, {X, {Instruction::AND, {X, Y}}}}, [=]{ return X; }, true},
        {{Instruction::OR, {X, {Instruction::AND, {Y, X}}}}, [=]{ return X; }, true},
        {{Instruction::OR, {{Instruction::AND, {X, Y}}, X}}, [=]{ return X; }, true},
        {{Instruction::OR, {{Instruction::AND, {Y, X}}, X}}, [=]{ return X; }, true},
        {{Instruction::AND, {X, {Instruction::OR, {X, Y}}}}, [=]{ return X; }, true},
        {{Instruction::AND, {X, {Instruction::OR, {Y, X}}}}, [=]{ return X; }, true},
        {{Instruction::AND, {{Instruction::OR, {X, Y}}, X}}, [=]{ return X; }, true},
        {{Instruction::AND, {{Instruction::OR, {Y, X}}, X}}, [=]{ return X; }, true},
        {{Instruction::AND, {X, {Instruction::NOT, {X}}}}, [=]{ return u256(0); }, true},
        {{Instruction::AND, {{Instruction::NOT, {X}}, X}}, [=]{ return u256(0); }, true},
        {{Instruction::OR, {X, {Instruction::NOT, {X}}}}, [=]{ return ~u256(0); }, true},
        {{Instruction::OR, {{Instruction::NOT, {X}}, X}}, [=]{ return ~u256(0); }, true},
    };
}


// This part of simplificationRuleList below was split out to prevent
// stack overflows in the JavaScript optimizer for emscripten builds
// that affected certain browser versions.
template <class Pattern>
std::vector<SimplificationRule<Pattern>> simplificationRuleListPart2(
    Pattern A,
    Pattern B,
    Pattern,
    Pattern X,
    Pattern Y
)
{
    std::vector<SimplificationRule<Pattern>> rules;

    // Replace MOD X, <power-of-two> with AND X, <power-of-two> - 1
    for (size_t i = 0; i < 256; ++i)
    {
        u256 value = u256(1) << i;
        rules.push_back({
            {Instruction::MOD, {X, value}},
            [=]() -> Pattern { return {Instruction::AND, {X, value - 1}}; },
            false
        });
    }

    for (auto const& op: std::vector<Instruction>{
        Instruction::ADDRESS,
        Instruction::CALLER,
        Instruction::ORIGIN,
        Instruction::COINBASE
    })
    {
        u256 const mask = (u256(1) << 160) - 1;
        rules.push_back({
            {Instruction::AND, {{op, mask}}},
            [=]() -> Pattern { return op; },
            false
        });
        rules.push_back({
            {Instruction::AND, {{mask, op}}},
            [=]() -> Pattern { return op; },
            false
        });
    }

    // Double negation of opcodes with boolean result
    for (auto const& op: std::vector<Instruction>{
        Instruction::EQ,
        Instruction::LT,
        Instruction::SLT,
        Instruction::GT,
        Instruction::SGT
    })
        rules.push_back({
            {Instruction::ISZERO, {{Instruction::ISZERO, {{op, {X, Y}}}}}},
            [=]() -> Pattern { return {op, {X, Y}}; },
            false
        });

    rules.push_back({
        {Instruction::ISZERO, {{Instruction::ISZERO, {{Instruction::ISZERO, {X}}}}}},
        [=]() -> Pattern { return {Instruction::ISZERO, {X}}; },
        false
    });

    rules.push_back({
        {Instruction::ISZERO, {{Instruction::XOR, {X, Y}}}},
        [=]() -> Pattern { return { Instruction::EQ, {X, Y} }; },
        false
    });

    // Associative operations
    for (auto const& opFun: std::vector<std::pair<Instruction,std::function<u256(u256 const&,u256 const&)>>>{
        {Instruction::ADD, std::plus<u256>()},
        {Instruction::MUL, std::multiplies<u256>()},
        {Instruction::AND, std::bit_and<u256>()},
        {Instruction::OR, std::bit_or<u256>()},
        {Instruction::XOR, std::bit_xor<u256>()}
    })
    {
        auto op = opFun.first;
        auto fun = opFun.second;
        // Moving constants to the outside, order matters here - we first add rules
        // for constants and then for non-constants.
        // xa can be (X, A) or (A, X)
        for (auto xa: {std::vector<Pattern>{X, A}, std::vector<Pattern>{A, X}})
        {
            rules += std::vector<SimplificationRule<Pattern>>{{
                // (X+A)+B -> X+(A+B)
                {op, {{op, xa}, B}},
                [=]() -> Pattern { return {op, {X, fun(A.d(), B.d())}}; },
                false
            }, {
                // (X+A)+Y -> (X+Y)+A
                {op, {{op, xa}, Y}},
                [=]() -> Pattern { return {op, {{op, {X, Y}}, A}}; },
                false
            }, {
                // B+(X+A) -> X+(A+B)
                {op, {B, {op, xa}}},
                [=]() -> Pattern { return {op, {X, fun(A.d(), B.d())}}; },
                false
            }, {
                // Y+(X+A) -> (Y+X)+A
                {op, {Y, {op, xa}}},
                [=]() -> Pattern { return {op, {{op, {Y, X}}, A}}; },
                false
            }};
        }
    }

    // move constants across subtractions
    rules += std::vector<SimplificationRule<Pattern>>{
        {
            // X - A -> X + (-A)
            {Instruction::SUB, {X, A}},
            [=]() -> Pattern { return {Instruction::ADD, {X, 0 - A.d()}}; },
            false
        }, {
            // (X + A) - Y -> (X - Y) + A
            {Instruction::SUB, {{Instruction::ADD, {X, A}}, Y}},
            [=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, A}}; },
            false
        }, {
            // (A + X) - Y -> (X - Y) + A
            {Instruction::SUB, {{Instruction::ADD, {A, X}}, Y}},
            [=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, A}}; },
            false
        }, {
            // X - (Y + A) -> (X - Y) + (-A)
            {Instruction::SUB, {X, {Instruction::ADD, {Y, A}}}},
            [=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, 0 - A.d()}}; },
            false
        }, {
            // X - (A + Y) -> (X - Y) + (-A)
            {Instruction::SUB, {X, {Instruction::ADD, {A, Y}}}},
            [=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, 0 - A.d()}}; },
            false
        }
    };
    return rules;
}

/// @returns a list of simplification rules given certain match placeholders.
/// A, B and C should represent constants, X and Y arbitrary expressions.
/// The simplifications should never change the order of evaluation of
/// arbitrary operations.
template <class Pattern>
std::vector<SimplificationRule<Pattern>> simplificationRuleList(
    Pattern A,
    Pattern B,
    Pattern C,
    Pattern X,
    Pattern Y
)
{
    std::vector<SimplificationRule<Pattern>> rules;
    rules += simplificationRuleListPart1(A, B, C, X, Y);
    rules += simplificationRuleListPart2(A, B, C, X, Y);
    return rules;
}

}
}