/*(

  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/>.

*/

/**

 * Optimisation stage that aggressively rematerializes certain variables ina a function to free

 * space on the stack until it is compilable.

 */

#include <libyul/optimiser/StackCompressor.h>

#include <libyul/optimiser/NameCollector.h>

#include <libyul/optimiser/Rematerialiser.h>

#include <libyul/optimiser/UnusedPruner.h>

#include <libyul/optimiser/Metrics.h>

#include <libyul/optimiser/Semantics.h>

#include <libyul/backends/evm/ControlFlowGraphBuilder.h>

#include <libyul/backends/evm/StackHelpers.h>

#include <libyul/backends/evm/StackLayoutGenerator.h>

#include <libyul/AsmAnalysis.h>

#include <libyul/AsmAnalysisInfo.h>

#include <libyul/CompilabilityChecker.h>

#include <libyul/AST.h>

#include <libsolutil/CommonData.h>

using namespace std;

using namespace solidity;

using namespace solidity::yul;

namespace

{

/**

 * Class that discovers all variables that can be fully eliminated by rematerialization,

 * and the corresponding approximate costs.

 *

 * Prerequisite: Disambiguator, Function Grouper

 */

class RematCandidateSelector: public DataFlowAnalyzer

{

public:

  explicit RematCandidateSelector(Dialect const& _dialect): DataFlowAnalyzer(_dialect, MemoryAndStorage::Ignore) {}

  /// @returns a map from function name to rematerialisation costs to a vector of variables to rematerialise

  /// and variables that occur in their expression.

  /// While the map is sorted by cost, the contained vectors are sorted by the order of occurrence.

  map<YulString, map<size_t, vector<YulString>>> candidates()

  {

    map<YulString, map<size_t, vector<YulString>>> cand;

    for (auto const& [functionName, candidate]: m_candidates)

    {

      if (size_t const* cost = util::valueOrNullptr(m_expressionCodeCost, candidate))

      {

        size_t numRef = m_numReferences[candidate];

        cand[functionName][*cost * numRef].emplace_back(candidate);

      }

    }

    return cand;

  }

  using DataFlowAnalyzer::operator();

  void operator()(FunctionDefinition& _function) override

  {

    yulAssert(m_currentFunctionName.empty());

    m_currentFunctionName = _function.name;

    DataFlowAnalyzer::operator()(_function);

    m_currentFunctionName = {};

  }

  void operator()(VariableDeclaration& _varDecl) override

  {

    DataFlowAnalyzer::operator()(_varDecl);

    if (_varDecl.variables.size() == 1)

    {

      YulString varName = _varDecl.variables.front().name;

      if (AssignedValue const* value = variableValue(varName))

      {

        yulAssert(!m_expressionCodeCost.count(varName), "");

        m_candidates.emplace_back(m_currentFunctionName, varName);

        m_expressionCodeCost[varName] = CodeCost::codeCost(m_dialect, *value->value);

      }

    }

  }

  void operator()(Assignment& _assignment) override

  {

    for (auto const& var: _assignment.variableNames)

      rematImpossible(var.name);

    DataFlowAnalyzer::operator()(_assignment);

  }

  // We use visit(Expression) because operator()(Identifier) would also

  // get called on left-hand-sides of assignments.

  void visit(Expression& _e) override

  {

    if (holds_alternative<Identifier>(_e))

    {

      YulString name = std::get<Identifier>(_e).name;

      if (m_expressionCodeCost.count(name))

      {

        if (!variableValue(name))

          rematImpossible(name);

        else

          ++m_numReferences[name];

      }

    }

    DataFlowAnalyzer::visit(_e);

  }

  /// Remove the variable from the candidate set.

  void rematImpossible(YulString _variable)

  {

    m_numReferences.erase(_variable);

    m_expressionCodeCost.erase(_variable);

  }

  YulString m_currentFunctionName = {};

  /// All candidate variables by function name, in order of occurrence.

  vector<pair<YulString, YulString>> m_candidates;

  /// Candidate variables and the code cost of their value.

  map<YulString, size_t> m_expressionCodeCost;

  /// Number of references to each candidate variable.

  map<YulString, size_t> m_numReferences;

};

/// Selects at most @a _numVariables among @a _candidates.

set<YulString> chooseVarsToEliminate(

  map<size_t, vector<YulString>> const& _candidates,

  size_t _numVariables

)

{

  set<YulString> varsToEliminate;

  for (auto&& [cost, candidates]: _candidates)

    for (auto&& candidate: candidates)

    {

      if (varsToEliminate.size() >= _numVariables)

        return varsToEliminate;

      varsToEliminate.insert(candidate);

    }

  return varsToEliminate;

}

void eliminateVariables(

  Dialect const& _dialect,

  Block& _ast,

  map<YulString, int> const& _numVariables,

  bool _allowMSizeOptimization

)

{

  RematCandidateSelector selector{_dialect};

  selector(_ast);

  map<YulString, map<size_t, vector<YulString>>> candidates = selector.candidates();

  set<YulString> varsToEliminate;

  for (auto const& [functionName, numVariables]: _numVariables)

  {

    yulAssert(numVariables > 0);

    varsToEliminate += chooseVarsToEliminate(candidates[functionName], static_cast<size_t>(numVariables));

  }

  Rematerialiser::run(_dialect, _ast, move(varsToEliminate));

  // Do not remove functions.

  set<YulString> allFunctions = NameCollector{_ast, NameCollector::OnlyFunctions}.names();

  UnusedPruner::runUntilStabilised(_dialect, _ast, _allowMSizeOptimization, nullptr, allFunctions);

}

void eliminateVariablesOptimizedCodegen(

  Dialect const& _dialect,

  Block& _ast,

  map<YulString, vector<StackLayoutGenerator::StackTooDeep>> const& _unreachables,

  bool _allowMSizeOptimization

)

{

  if (std::all_of(_unreachables.begin(), _unreachables.end(), [](auto const& _item) { return _item.second.empty(); }))

    return;

  RematCandidateSelector selector{_dialect};

  selector(_ast);

  map<YulString, size_t> candidates;

  for (auto const& [functionName, candidatesInFunction]: selector.candidates())

    for (auto [cost, candidatesWithCost]: candidatesInFunction)

      for (auto candidate: candidatesWithCost)

        candidates[candidate] = cost;

  set<YulString> varsToEliminate;

  // TODO: this currently ignores the fact that variables may reference other variables we want to eliminate.

  for (auto const& [functionName, unreachables]: _unreachables)

    for (auto const& unreachable: unreachables)

    {

      map<size_t, vector<YulString>> suitableCandidates;

      size_t neededSlots = unreachable.deficit;

      for (auto varName: unreachable.variableChoices)

      {

        if (varsToEliminate.count(varName))

          --neededSlots;

        else if (size_t* cost = util::valueOrNullptr(candidates, varName))

          if (!util::contains(suitableCandidates[*cost], varName))

            suitableCandidates[*cost].emplace_back(varName);

      }

      for (auto candidatesByCost: suitableCandidates)

      {

        for (auto candidate: candidatesByCost.second)

          if (neededSlots--)

            varsToEliminate.emplace(candidate);

          else

            break;

        if (!neededSlots)

          break;

      }

    }

  Rematerialiser::run(_dialect, _ast, std::move(varsToEliminate), true);

  // Do not remove functions.

  set<YulString> allFunctions = NameCollector{_ast, NameCollector::OnlyFunctions}.names();

  UnusedPruner::runUntilStabilised(_dialect, _ast, _allowMSizeOptimization, nullptr, allFunctions);

}

}

bool StackCompressor::run(

  Dialect const& _dialect,

  Object& _object,

  bool _optimizeStackAllocation,

  size_t _maxIterations

)

{

  yulAssert(

    _object.code &&

    _object.code->statements.size() > 0 && holds_alternative<Block>(_object.code->statements.at(0)),

    "Need to run the function grouper before the stack compressor."

  );

  bool usesOptimizedCodeGenerator = false;

  if (auto evmDialect = dynamic_cast<EVMDialect const*>(&_dialect))

    usesOptimizedCodeGenerator =

      _optimizeStackAllocation &&

      evmDialect->evmVersion().canOverchargeGasForCall() &&

      evmDialect->providesObjectAccess();

  bool allowMSizeOptimzation = !MSizeFinder::containsMSize(_dialect, *_object.code);

  if (usesOptimizedCodeGenerator)

  {

    yul::AsmAnalysisInfo analysisInfo = yul::AsmAnalyzer::analyzeStrictAssertCorrect(_dialect, _object);

    unique_ptr<CFG> cfg = ControlFlowGraphBuilder::build(analysisInfo, _dialect, *_object.code);

    eliminateVariablesOptimizedCodegen(

      _dialect,

      *_object.code,

      StackLayoutGenerator::reportStackTooDeep(*cfg),

      allowMSizeOptimzation

    );

  }

  else

    for (size_t iterations = 0; iterations < _maxIterations; iterations++)

    {

      map<YulString, int> stackSurplus = CompilabilityChecker(_dialect, _object, _optimizeStackAllocation).stackDeficit;

      if (stackSurplus.empty())

        return true;

      eliminateVariables(

        _dialect,

        *_object.code,

        stackSurplus,

        allowMSizeOptimzation

      );

    }

  return false;

}