/*

  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/>.

*/

// SPDX-License-Identifier: GPL-3.0

/**

 * 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/FunctionGrouper.h>

#include <libyul/optimiser/NameCollector.h>

#include <libyul/optimiser/OptimizerUtilities.h>

#include <libyul/Exceptions.h>

#include <libyul/AST.h>

#include <libsolutil/CommonData.h>

#include <range/v3/view/reverse.hpp>

#include <limits>

using namespace std;

using namespace solidity;

using namespace solidity::yul;

void ExpressionJoiner::run(OptimiserStepContext& _context, Block& _ast)

{

  ExpressionJoiner{_ast}(_ast);

  FunctionGrouper::run(_context, _ast);

}

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 (holds_alternative<Identifier>(_e))

  {

    Identifier const& identifier = std::get<Identifier>(_e);

    if (isLatestStatementVarDeclJoinable(identifier))

    {

      VariableDeclaration& varDecl = std::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);

}

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 | ranges::views::reverse)

  {

    --i;

    if (!holds_alternative<Identifier>(arg) && !holds_alternative<Literal>(arg))

      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 = numeric_limits<size_t>::max();

}

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 || !holds_alternative<VariableDeclaration>(*statement))

    return false;

  VariableDeclaration const& varDecl = std::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;

}