path: root/libyul/optimiser/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/>.
*/
/**
 * Module for applying replacement rules against Expressions.
 */

#include <libyul/optimiser/SimplificationRules.h>

#include <libyul/optimiser/Utilities.h>
#include <libyul/optimiser/ASTCopier.h>
#include <libyul/optimiser/Semantics.h>
#include <libyul/optimiser/SyntacticalEquality.h>
#include <libyul/AsmData.h>

#include <libevmasm/RuleList.h>

using namespace std;
using namespace dev;
using namespace langutil;
using namespace yul;


SimplificationRule<Pattern> const* SimplificationRules::findFirstMatch(
    Expression const& _expr,
    map<YulString, Expression const*> const& _ssaValues
)
{
    if (_expr.type() != typeid(FunctionalInstruction))
        return nullptr;

    static SimplificationRules rules;
    assertThrow(rules.isInitialized(), OptimizerException, "Rule list not properly initialized.");

    FunctionalInstruction const& instruction = boost::get<FunctionalInstruction>(_expr);
    for (auto const& rule: rules.m_rules[uint8_t(instruction.instruction)])
    {
        rules.resetMatchGroups();
        if (rule.pattern.matches(_expr, _ssaValues))
            return &rule;
    }
    return nullptr;
}

bool SimplificationRules::isInitialized() const
{
    return !m_rules[uint8_t(solidity::Instruction::ADD)].empty();
}

void SimplificationRules::addRules(vector<SimplificationRule<Pattern>> const& _rules)
{
    for (auto const& r: _rules)
        addRule(r);
}

void SimplificationRules::addRule(SimplificationRule<Pattern> const& _rule)
{
    m_rules[uint8_t(_rule.pattern.instruction())].push_back(_rule);
}

SimplificationRules::SimplificationRules()
{
    // Multiple occurrences of one of these inside one rule must match the same equivalence class.
    // Constants.
    Pattern A(PatternKind::Constant);
    Pattern B(PatternKind::Constant);
    Pattern C(PatternKind::Constant);
    // Anything.
    Pattern X;
    Pattern Y;
    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);

    addRules(simplificationRuleList(A, B, C, X, Y));
    assertThrow(isInitialized(), OptimizerException, "Rule list not properly initialized.");
}

Pattern::Pattern(solidity::Instruction _instruction, vector<Pattern> const& _arguments):
    m_kind(PatternKind::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, map<YulString, Expression const*> const& _ssaValues) const
{
    Expression const* expr = &_expr;

    // Resolve the variable if possible.
    // Do not do it for "Any" because we can check identity better for variables.
    if (m_kind != PatternKind::Any && _expr.type() == typeid(Identifier))
    {
        YulString varName = boost::get<Identifier>(_expr).name;
        if (_ssaValues.count(varName))
            if (Expression const* new_expr = _ssaValues.at(varName))
                expr = new_expr;
    }
    assertThrow(expr, OptimizerException, "");

    if (m_kind == PatternKind::Constant)
    {
        if (expr->type() != typeid(Literal))
            return false;
        Literal const& literal = boost::get<Literal>(*expr);
        if (literal.kind != LiteralKind::Number)
            return false;
        if (m_data && *m_data != u256(literal.value.str()))
            return false;
        assertThrow(m_arguments.empty(), OptimizerException, "");
    }
    else if (m_kind == PatternKind::Operation)
    {
        if (expr->type() != typeid(FunctionalInstruction))
            return false;
        FunctionalInstruction const& instr = boost::get<FunctionalInstruction>(*expr);
        if (m_instruction != instr.instruction)
            return false;
        assertThrow(m_arguments.size() == instr.arguments.size(), OptimizerException, "");
        for (size_t i = 0; i < m_arguments.size(); ++i)
            if (!m_arguments[i].matches(instr.arguments.at(i), _ssaValues))
                return false;
    }
    else
    {
        assertThrow(m_arguments.empty(), OptimizerException, "\"Any\" should not have arguments.");
    }

    if (m_matchGroup)
    {
        // We support matching multiple expressions that require the same value
        // based on identical ASTs, which have to be movable.

        // TODO: add tests:
        // - { let x := mload(0) let y := and(x, x) }
        // - { let x := 4 let y := and(x, y) }

        // This code uses `_expr` again for "Any", because we want the comparison to be done
        // on the variables and not their values.
        // The assumption is that CSE or local value numbering has been done prior to this step.

        if (m_matchGroups->count(m_matchGroup))
        {
            assertThrow(m_kind == PatternKind::Any, OptimizerException, "Match group repetition for non-any.");
            Expression const* firstMatch = (*m_matchGroups)[m_matchGroup];
            assertThrow(firstMatch, OptimizerException, "Match set but to null.");
            return
                SyntacticalEqualityChecker::equal(*firstMatch, _expr) &&
                MovableChecker(_expr).movable();
        }
        else if (m_kind == PatternKind::Any)
            (*m_matchGroups)[m_matchGroup] = &_expr;
        else
        {
            assertThrow(m_kind == PatternKind::Constant, OptimizerException, "Match group set for operation.");
            // We do not use _expr here, because we want the actual number.
            (*m_matchGroups)[m_matchGroup] = expr;
        }
    }
    return true;
}

solidity::Instruction Pattern::instruction() const
{
    assertThrow(m_kind == PatternKind::Operation, OptimizerException, "");
    return m_instruction;
}

Expression Pattern::toExpression(SourceLocation const& _location) const
{
    if (matchGroup())
        return ASTCopier().translate(matchGroupValue());
    if (m_kind == PatternKind::Constant)
    {
        assertThrow(m_data, OptimizerException, "No match group and no constant value given.");
        return Literal{_location, LiteralKind::Number, YulString{formatNumber(*m_data)}, {}};
    }
    else if (m_kind == PatternKind::Operation)
    {
        vector<Expression> arguments;
        for (auto const& arg: m_arguments)
            arguments.emplace_back(arg.toExpression(_location));
        return FunctionalInstruction{_location, m_instruction, std::move(arguments)};
    }
    assertThrow(false, OptimizerException, "Pattern of kind 'any', but no match group.");
}

u256 Pattern::d() const
{
    return valueOfNumberLiteral(boost::get<Literal>(matchGroupValue()));
}

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];
}