libyul/optimiser/ExpressionJoiner.cpp


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/*
    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 undoes what the ExpressionSplitter did, i.e.
 * it more or less inlines variable declarations.
 */

#include <libyul/optimiser/ExpressionJoiner.h>

#include <libyul/optimiser/NameCollector.h>
#include <libyul/optimiser/Utilities.h>
#include <libyul/Exceptions.h>

#include <libyul/AsmData.h>

#include <libdevcore/CommonData.h>

#include <boost/range/adaptor/reversed.hpp>

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

void ExpressionJoiner::operator()(FunctionalInstruction& _instruction)
{
    handleArguments(_instruction.arguments);
}

void ExpressionJoiner::operator()(FunctionCall& _funCall)
{
    handleArguments(_funCall.arguments);
}

void ExpressionJoiner::operator()(Block& _block)
{
    resetLatestStatementPointer();
    for (size_t i = 0; i < _block.statements.size(); ++i)
    {
        visit(_block.statements[i]);
        m_currentBlock = &_block;
        m_latestStatementInBlock = i;
    }

    removeEmptyBlocks(_block);
    resetLatestStatementPointer();
}

void ExpressionJoiner::visit(Expression& _e)
{
    if (_e.type() == typeid(Identifier))
    {
        Identifier const& identifier = boost::get<Identifier>(_e);
        if (isLatestStatementVarDeclJoinable(identifier))
        {
            VariableDeclaration& varDecl = boost::get<VariableDeclaration>(*latestStatement());
            _e = std::move(*varDecl.value);

            // Delete the variable declaration (also get the moved-from structure back into a sane state)
            *latestStatement() = Block();

            decrementLatestStatementPointer();
        }
    }
    else
        ASTModifier::visit(_e);
}

void ExpressionJoiner::run(Block& _ast)
{
    ExpressionJoiner{_ast}(_ast);
}

ExpressionJoiner::ExpressionJoiner(Block& _ast)
{
    m_references = ReferencesCounter::countReferences(_ast);
}

void ExpressionJoiner::handleArguments(vector<Expression>& _arguments)
{
    // We have to fill from left to right, but we can only
    // fill if everything to the right is just an identifier
    // or a literal.
    // Also we only descend into function calls if everything
    // on the right is an identifier or literal.

    size_t i = _arguments.size();
    for (Expression const& arg: _arguments | boost::adaptors::reversed)
    {
        --i;
        if (arg.type() != typeid(Identifier) && arg.type() != typeid(Literal))
            break;
    }
    // i points to the last element that is neither an identifier nor a literal,
    // or to the first element if all of them are identifiers or literals.

    for (; i < _arguments.size(); ++i)
        visit(_arguments.at(i));
}

void ExpressionJoiner::decrementLatestStatementPointer()
{
    if (!m_currentBlock)
        return;
    if (m_latestStatementInBlock > 0)
        --m_latestStatementInBlock;
    else
        resetLatestStatementPointer();
}

void ExpressionJoiner::resetLatestStatementPointer()
{
    m_currentBlock = nullptr;
    m_latestStatementInBlock = size_t(-1);
}

Statement* ExpressionJoiner::latestStatement()
{
    if (!m_currentBlock)
        return nullptr;
    else
        return &m_currentBlock->statements.at(m_latestStatementInBlock);
}

bool ExpressionJoiner::isLatestStatementVarDeclJoinable(Identifier const& _identifier)
{
    Statement const* statement = latestStatement();
    if (!statement || statement->type() != typeid(VariableDeclaration))
        return false;
    VariableDeclaration const& varDecl = boost::get<VariableDeclaration>(*statement);
    if (varDecl.variables.size() != 1 || !varDecl.value)
        return false;
    assertThrow(varDecl.variables.size() == 1, OptimizerException, "");
    assertThrow(varDecl.value, OptimizerException, "");
    return varDecl.variables.at(0).name == _identifier.name && m_references[_identifier.name] == 1;
}