/*

  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

/**

 * Optimisation stage that replaces expressions of type ``sload(x)`` by the value

 * currently stored in storage, if known.

 */

#include <libyul/optimiser/LoadResolver.h>

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

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

#include <libyul/optimiser/Semantics.h>

#include <libyul/optimiser/CallGraphGenerator.h>

#include <libyul/SideEffects.h>

#include <libyul/AST.h>

#include <libyul/Utilities.h>

#include <libevmasm/GasMeter.h>

#include <libsolutil/Keccak256.h>

#include <limits>

using namespace std;

using namespace solidity;

using namespace solidity::util;

using namespace solidity::evmasm;

using namespace solidity::yul;

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

{

  bool containsMSize = MSizeFinder::containsMSize(_context.dialect, _ast);

  LoadResolver{

    _context.dialect,

    SideEffectsPropagator::sideEffects(_context.dialect, CallGraphGenerator::callGraph(_ast)),

    containsMSize,

    _context.expectedExecutionsPerDeployment

  }(_ast);

}

void LoadResolver::visit(Expression& _e)

{

  DataFlowAnalyzer::visit(_e);

  if (FunctionCall const* funCall = std::get_if<FunctionCall>(&_e))

  {

    for (auto location: { StoreLoadLocation::Memory, StoreLoadLocation::Storage })

      if (funCall->functionName.name == m_loadFunctionName[static_cast<unsigned>(location)])

      {

        tryResolve(_e, location, funCall->arguments);

        break;

      }

    if (!m_containsMSize && funCall->functionName.name == m_dialect.hashFunction({}))

      tryEvaluateKeccak(_e, funCall->arguments);

  }

}

void LoadResolver::tryResolve(

  Expression& _e,

  StoreLoadLocation _location,

  vector<Expression> const& _arguments

)

{

  if (_arguments.empty() || !holds_alternative<Identifier>(_arguments.at(0)))

    return;

  YulString key = std::get<Identifier>(_arguments.at(0)).name;

  if (_location == StoreLoadLocation::Storage)

  {

    if (auto value = storageValue(key))

      if (inScope(*value))

        _e = Identifier{debugDataOf(_e), *value};

  }

  else if (!m_containsMSize && _location == StoreLoadLocation::Memory)

    if (auto value = memoryValue(key))

      if (inScope(*value))

        _e = Identifier{debugDataOf(_e), *value};

}

void LoadResolver::tryEvaluateKeccak(

  Expression& _e,

  std::vector<Expression> const& _arguments

)

{

  yulAssert(_arguments.size() == 2, "");

  Identifier const* memoryKey = std::get_if<Identifier>(&_arguments.at(0));

  Identifier const* length = std::get_if<Identifier>(&_arguments.at(1));

  if (!memoryKey || !length)

    return;

  // The costs are only correct for hashes of 32 bytes or 1 word (when rounded up).

  GasMeter gasMeter{

    dynamic_cast<EVMDialect const&>(m_dialect),

    !m_expectedExecutionsPerDeployment,

    m_expectedExecutionsPerDeployment ? *m_expectedExecutionsPerDeployment : 1

  };

  bigint costOfKeccak = gasMeter.costs(_e);

  bigint costOfLiteral = gasMeter.costs(

    Literal{

      {},

      LiteralKind::Number,

      // a dummy 256-bit number to represent the Keccak256 hash.

      YulString{numeric_limits<u256>::max().str()},

      {}

    }

  );

  // We skip if there are no net gas savings.

  // Note that for default `m_runs = 200`, the values are

  // `costOfLiteral = 7200` and `costOfKeccak = 9000` for runtime context.

  // For creation context: `costOfLiteral = 531` and `costOfKeccak = 90`.

  if (costOfLiteral > costOfKeccak)

    return;

  optional<YulString> value = memoryValue(memoryKey->name);

  if (value && inScope(*value))

  {

    optional<u256> memoryContent = valueOfIdentifier(*value);

    optional<u256> byteLength = valueOfIdentifier(length->name);

    if (memoryContent && byteLength && *byteLength <= 32)

    {

      bytes contentAsBytes = toBigEndian(*memoryContent);

      contentAsBytes.resize(static_cast<size_t>(*byteLength));

      _e = Literal{

        debugDataOf(_e),

        LiteralKind::Number,

        YulString{u256(keccak256(contentAsBytes)).str()},

        m_dialect.defaultType

      };

    }

  }

}