/*
    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/>.
*/
/**
 * Optimiser component that removes assignments to variables that are not used
 * until they go out of scope or are re-assigned.
 */

#include <libyul/optimiser/RedundantAssignEliminator.h>

#include <libyul/optimiser/Semantics.h>

#include <libsolidity/inlineasm/AsmData.h>

#include <libdevcore/CommonData.h>

#include <boost/range/algorithm_ext/erase.hpp>

using namespace std;
using namespace dev;
using namespace dev::yul;
using namespace dev::solidity;

void RedundantAssignEliminator::operator()(Identifier const& _identifier)
{
    changeUndecidedTo(_identifier.name, State::Used);
}

void RedundantAssignEliminator::operator()(VariableDeclaration const& _variableDeclaration)
{
    ASTWalker::operator()(_variableDeclaration);

    for (auto const& var: _variableDeclaration.variables)
        m_declaredVariables.insert(var.name);
}

void RedundantAssignEliminator::operator()(Assignment const& _assignment)
{
    visit(*_assignment.value);
    for (auto const& var: _assignment.variableNames)
        changeUndecidedTo(var.name, State::Unused);

    if (_assignment.variableNames.size() == 1)
        // Default-construct it in "Undecided" state if it does not yet exist.
        m_assignments[_assignment.variableNames.front().name][&_assignment];
}

void RedundantAssignEliminator::operator()(If const& _if)
{
    visit(*_if.condition);

    RedundantAssignEliminator branch{*this};
    branch(_if.body);

    join(branch);
}

void RedundantAssignEliminator::operator()(Switch const& _switch)
{
    visit(*_switch.expression);

    bool hasDefault = false;
    vector<RedundantAssignEliminator> branches;
    for (auto const& c: _switch.cases)
    {
        if (!c.value)
            hasDefault = true;
        branches.emplace_back(*this);
        branches.back()(c.body);
    }

    if (hasDefault)
    {
        *this = std::move(branches.back());
        branches.pop_back();
    }
    for (auto& branch: branches)
        join(branch);
}

void RedundantAssignEliminator::operator()(FunctionDefinition const& _functionDefinition)
{
    (*this)(_functionDefinition.body);

    for (auto const& param: _functionDefinition.parameters)
        changeUndecidedTo(param.name, State::Unused);
    for (auto const& retParam: _functionDefinition.returnVariables)
        changeUndecidedTo(retParam.name, State::Used);
}

void RedundantAssignEliminator::operator()(ForLoop const& _forLoop)
{
    // This will set all variables that are declared in this
    // block to "unused" when it is destroyed.
    BlockScope scope(*this);

    // We need to visit the statements directly because of the
    // scoping rules.
    walkVector(_forLoop.pre.statements);

    // We just run the loop twice to account for the
    // back edge.
    // There need not be more runs because we only have three different states.

    visit(*_forLoop.condition);

    RedundantAssignEliminator zeroRuns{*this};

    (*this)(_forLoop.body);
    (*this)(_forLoop.post);

    visit(*_forLoop.condition);

    RedundantAssignEliminator oneRun{*this};

    (*this)(_forLoop.body);
    (*this)(_forLoop.post);

    visit(*_forLoop.condition);

    // Order does not matter because "max" is commutative and associative.
    join(oneRun);
    join(zeroRuns);
}

void RedundantAssignEliminator::operator()(Block const& _block)
{
    // This will set all variables that are declared in this
    // block to "unused" when it is destroyed.
    BlockScope scope(*this);

    ASTWalker::operator()(_block);
}

void RedundantAssignEliminator::run(Block& _ast)
{
    RedundantAssignEliminator rae;
    rae(_ast);

    std::set<Assignment const*> assignmentsToRemove;
    for (auto const& variables: rae.m_assignments)
        for (auto const& assignment: variables.second)
        {
            assertThrow(assignment.second != State::Undecided, OptimizerException, "");
            if (assignment.second == State::Unused && MovableChecker{*assignment.first->value}.movable())
                assignmentsToRemove.insert(assignment.first);
        }

    AssignmentRemover remover{assignmentsToRemove};
    remover(_ast);
}

void RedundantAssignEliminator::join(RedundantAssignEliminator& _other)
{
    for (auto& var: _other.m_assignments)
        if (m_assignments.count(var.first))
        {
            map<Assignment const*, State>& assignmentsHere = m_assignments[var.first];
            for (auto& assignment: var.second)
                assignmentsHere[assignment.first].join(assignment.second);
        }
        else
            m_assignments[var.first] = std::move(var.second);
}

void RedundantAssignEliminator::changeUndecidedTo(string const& _variable, RedundantAssignEliminator::State _newState)
{
    for (auto& assignment: m_assignments[_variable])
        if (assignment.second == State{State::Undecided})
            assignment.second = _newState;
}

void AssignmentRemover::operator()(Block& _block)
{
    boost::range::remove_erase_if(_block.statements, [=](Statement const& _statement) -> bool {
        return _statement.type() == typeid(Assignment) && m_toRemove.count(&boost::get<Assignment>(_statement));
    });

    ASTModifier::operator()(_block);
}