/src/solidity/libevmasm/PeepholeOptimiser.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/>.
*/
// SPDX-License-Identifier: GPL-3.0
/**
 * @file PeepholeOptimiser.cpp
 * Performs local optimising code changes to assembly.
 */

#include <libevmasm/PeepholeOptimiser.h>

#include <libevmasm/AssemblyItem.h>
#include <libevmasm/SemanticInformation.h>

using namespace std;
using namespace solidity;
using namespace solidity::evmasm;

// TODO: Extend this to use the tools from ExpressionClasses.cpp

namespace
{

struct OptimiserState
{
  AssemblyItems const& items;
  size_t i;
  std::back_insert_iterator<AssemblyItems> out;
};

template<typename FunctionType>
struct FunctionParameterCount;
template<typename R, typename... Args>
struct FunctionParameterCount<R(Args...)>
{
  static constexpr auto value = sizeof...(Args);
};

template <class Method>
struct SimplePeepholeOptimizerMethod
{
  template <size_t... Indices>
  static bool applyRule(AssemblyItems::const_iterator _in, back_insert_iterator<AssemblyItems> _out, index_sequence<Indices...>)
  {
    return Method::applySimple(_in[Indices]..., _out);
  }
  static bool apply(OptimiserState& _state)
  {
    static constexpr size_t WindowSize = FunctionParameterCount<decltype(Method::applySimple)>::value - 1;
    if (
      _state.i + WindowSize <= _state.items.size() &&
      applyRule(_state.items.begin() + static_cast<ptrdiff_t>(_state.i), _state.out, make_index_sequence<WindowSize>{})
    )
    {
      _state.i += WindowSize;
      return true;
    }
    else
      return false;
  }
};

struct Identity: SimplePeepholeOptimizerMethod<Identity>
{
  static bool applySimple(AssemblyItem const& _item, std::back_insert_iterator<AssemblyItems> _out)
  {
    *_out = _item;
    return true;
  }
};

struct PushPop: SimplePeepholeOptimizerMethod<PushPop>
{
  static bool applySimple(AssemblyItem const& _push, AssemblyItem const& _pop, std::back_insert_iterator<AssemblyItems>)
  {
    auto t = _push.type();
    return _pop == Instruction::POP && (
      SemanticInformation::isDupInstruction(_push) ||
      t == Push || t == PushTag || t == PushSub ||
      t == PushSubSize || t == PushProgramSize || t == PushData || t == PushLibraryAddress
    );
  }
};

struct OpPop: SimplePeepholeOptimizerMethod<OpPop>
{
  static bool applySimple(
    AssemblyItem const& _op,
    AssemblyItem const& _pop,
    std::back_insert_iterator<AssemblyItems> _out
  )
  {
    if (_pop == Instruction::POP && _op.type() == Operation)
    {
      Instruction instr = _op.instruction();
      if (instructionInfo(instr).ret == 1 && !instructionInfo(instr).sideEffects)
      {
        for (int j = 0; j < instructionInfo(instr).args; j++)
          *_out = {Instruction::POP, _op.location()};
        return true;
      }
    }
    return false;
  }
};

struct OpStop: SimplePeepholeOptimizerMethod<OpStop>
{
  static bool applySimple(
    AssemblyItem const& _op,
    AssemblyItem const& _stop,
    std::back_insert_iterator<AssemblyItems> _out
  )
  {
    if (_stop == Instruction::STOP)
    {
      if (_op.type() == Operation)
      {
        Instruction instr = _op.instruction();
        if (!instructionInfo(instr).sideEffects)
        {
          *_out = {Instruction::STOP, _op.location()};
          return true;
        }
      }
      else if (_op.type() == Push)
      {
        *_out = {Instruction::STOP, _op.location()};
        return true;
      }
    }
    return false;
  }
};

struct OpReturnRevert: SimplePeepholeOptimizerMethod<OpReturnRevert>
{
  static bool applySimple(
    AssemblyItem const& _op,
    AssemblyItem const& _push,
    AssemblyItem const& _pushOrDup,
    AssemblyItem const& _returnRevert,
    std::back_insert_iterator<AssemblyItems> _out
  )
  {
    if (
      (_returnRevert == Instruction::RETURN || _returnRevert == Instruction::REVERT) &&
      _push.type() == Push &&
      (_pushOrDup.type() == Push || _pushOrDup == dupInstruction(1))
    )
      if (
        (_op.type() == Operation && !instructionInfo(_op.instruction()).sideEffects) ||
        _op.type() == Push
      )
      {
          *_out = _push;
          *_out = _pushOrDup;
          *_out = _returnRevert;
          return true;
      }
    return false;
  }
};

struct DoubleSwap: SimplePeepholeOptimizerMethod<DoubleSwap>
{
  static size_t applySimple(AssemblyItem const& _s1, AssemblyItem const& _s2, std::back_insert_iterator<AssemblyItems>)
  {
    return _s1 == _s2 && SemanticInformation::isSwapInstruction(_s1);
  }
};

struct DoublePush: SimplePeepholeOptimizerMethod<DoublePush>
{
  static bool applySimple(AssemblyItem const& _push1, AssemblyItem const& _push2, std::back_insert_iterator<AssemblyItems> _out)
  {
    if (_push1.type() == Push && _push2.type() == Push && _push1.data() == _push2.data())
    {
      *_out = _push1;
      *_out = {Instruction::DUP1, _push2.location()};
      return true;
    }
    else
      return false;
  }
};

struct CommutativeSwap: SimplePeepholeOptimizerMethod<CommutativeSwap>
{
  static bool applySimple(AssemblyItem const& _swap, AssemblyItem const& _op, std::back_insert_iterator<AssemblyItems> _out)
  {
    // Remove SWAP1 if following instruction is commutative
    if (
      _swap == Instruction::SWAP1 &&
      SemanticInformation::isCommutativeOperation(_op)
    )
    {
      *_out = _op;
      return true;
    }
    else
      return false;
  }
};

struct SwapComparison: SimplePeepholeOptimizerMethod<SwapComparison>
{
  static bool applySimple(AssemblyItem const& _swap, AssemblyItem const& _op, std::back_insert_iterator<AssemblyItems> _out)
  {
    static map<Instruction, Instruction> const swappableOps{
      { Instruction::LT, Instruction::GT },
      { Instruction::GT, Instruction::LT },
      { Instruction::SLT, Instruction::SGT },
      { Instruction::SGT, Instruction::SLT }
    };

    if (
      _swap == Instruction::SWAP1 &&
      _op.type() == Operation &&
      swappableOps.count(_op.instruction())
    )
    {
      *_out = swappableOps.at(_op.instruction());
      return true;
    }
    else
      return false;
  }
};

/// Remove swapN after dupN
struct DupSwap: SimplePeepholeOptimizerMethod<DupSwap>
{
  static size_t applySimple(
    AssemblyItem const& _dupN,
    AssemblyItem const& _swapN,
    std::back_insert_iterator<AssemblyItems> _out
  )
  {
    if (
      SemanticInformation::isDupInstruction(_dupN) &&
      SemanticInformation::isSwapInstruction(_swapN) &&
      getDupNumber(_dupN.instruction()) == getSwapNumber(_swapN.instruction())
    )
    {
      *_out = _dupN;
      return true;
    }
    else
      return false;
  }
};


struct IsZeroIsZeroJumpI: SimplePeepholeOptimizerMethod<IsZeroIsZeroJumpI>
{
  static size_t applySimple(
    AssemblyItem const& _iszero1,
    AssemblyItem const& _iszero2,
    AssemblyItem const& _pushTag,
    AssemblyItem const& _jumpi,
    std::back_insert_iterator<AssemblyItems> _out
  )
  {
    if (
      _iszero1 == Instruction::ISZERO &&
      _iszero2 == Instruction::ISZERO &&
      _pushTag.type() == PushTag &&
      _jumpi == Instruction::JUMPI
    )
    {
      *_out = _pushTag;
      *_out = _jumpi;
      return true;
    }
    else
      return false;
  }
};

struct EqIsZeroJumpI: SimplePeepholeOptimizerMethod<EqIsZeroJumpI>
{
  static size_t applySimple(
    AssemblyItem const& _eq,
    AssemblyItem const& _iszero,
    AssemblyItem const& _pushTag,
    AssemblyItem const& _jumpi,
    std::back_insert_iterator<AssemblyItems> _out
  )
  {
    if (
      _eq == Instruction::EQ &&
      _iszero == Instruction::ISZERO &&
      _pushTag.type() == PushTag &&
      _jumpi == Instruction::JUMPI
    )
    {
      *_out = AssemblyItem(Instruction::SUB, _eq.location());
      *_out = _pushTag;
      *_out = _jumpi;
      return true;
    }
    else
      return false;
  }
};

// push_tag_1 jumpi push_tag_2 jump tag_1: -> iszero push_tag_2 jumpi tag_1:
struct DoubleJump: SimplePeepholeOptimizerMethod<DoubleJump>
{
  static size_t applySimple(
    AssemblyItem const& _pushTag1,
    AssemblyItem const& _jumpi,
    AssemblyItem const& _pushTag2,
    AssemblyItem const& _jump,
    AssemblyItem const& _tag1,
    std::back_insert_iterator<AssemblyItems> _out
  )
  {
    if (
      _pushTag1.type() == PushTag &&
      _jumpi == Instruction::JUMPI &&
      _pushTag2.type() == PushTag &&
      _jump == Instruction::JUMP &&
      _tag1.type() == Tag &&
      _pushTag1.data() == _tag1.data()
    )
    {
      *_out = AssemblyItem(Instruction::ISZERO, _jumpi.location());
      *_out = _pushTag2;
      *_out = _jumpi;
      *_out = _tag1;
      return true;
    }
    else
      return false;
  }
};

struct JumpToNext: SimplePeepholeOptimizerMethod<JumpToNext>
{
  static size_t applySimple(
    AssemblyItem const& _pushTag,
    AssemblyItem const& _jump,
    AssemblyItem const& _tag,
    std::back_insert_iterator<AssemblyItems> _out
  )
  {
    if (
      _pushTag.type() == PushTag &&
      (_jump == Instruction::JUMP || _jump == Instruction::JUMPI) &&
      _tag.type() == Tag &&
      _pushTag.data() == _tag.data()
    )
    {
      if (_jump == Instruction::JUMPI)
        *_out = AssemblyItem(Instruction::POP, _jump.location());
      *_out = _tag;
      return true;
    }
    else
      return false;
  }
};

struct TagConjunctions: SimplePeepholeOptimizerMethod<TagConjunctions>
{
  static bool applySimple(
    AssemblyItem const& _pushTag,
    AssemblyItem const& _pushConstant,
    AssemblyItem const& _and,
    std::back_insert_iterator<AssemblyItems> _out
  )
  {
    if (_and != Instruction::AND)
      return false;
    if (
      _pushTag.type() == PushTag &&
      _pushConstant.type() == Push &&
      (_pushConstant.data() & u256(0xFFFFFFFF)) == u256(0xFFFFFFFF)
    )
    {
      *_out = _pushTag;
      return true;
    }
    else if (
      // tag and constant are swapped
      _pushConstant.type() == PushTag &&
      _pushTag.type() == Push &&
      (_pushTag.data() & u256(0xFFFFFFFF)) == u256(0xFFFFFFFF)
    )
    {
      *_out = _pushConstant;
      return true;
    }
    else
      return false;
  }
};

struct TruthyAnd: SimplePeepholeOptimizerMethod<TruthyAnd>
{
  static bool applySimple(
    AssemblyItem const& _push,
    AssemblyItem const& _not,
    AssemblyItem const& _and,
    std::back_insert_iterator<AssemblyItems>
  )
  {
    return (
      _push.type() == Push && _push.data() == 0 &&
      _not == Instruction::NOT &&
      _and == Instruction::AND
    );
  }
};

/// Removes everything after a JUMP (or similar) until the next JUMPDEST.
struct UnreachableCode
{
  static bool apply(OptimiserState& _state)
  {
    auto it = _state.items.begin() + static_cast<ptrdiff_t>(_state.i);
    auto end = _state.items.end();
    if (it == end)
      return false;
    if (
      it[0] != Instruction::JUMP &&
      it[0] != Instruction::RETURN &&
      it[0] != Instruction::STOP &&
      it[0] != Instruction::INVALID &&
      it[0] != Instruction::SELFDESTRUCT &&
      it[0] != Instruction::REVERT
    )
      return false;

    ptrdiff_t i = 1;
    while (it + i != end && it[i].type() != Tag)
      i++;
    if (i > 1)
    {
      *_state.out = it[0];
      _state.i += static_cast<size_t>(i);
      return true;
    }
    else
      return false;
  }
};

void applyMethods(OptimiserState&)
{
  assertThrow(false, OptimizerException, "Peephole optimizer failed to apply identity.");
}

template <typename Method, typename... OtherMethods>
void applyMethods(OptimiserState& _state, Method, OtherMethods... _other)
{
  if (!Method::apply(_state))
    applyMethods(_state, _other...);
}

size_t numberOfPops(AssemblyItems const& _items)
{
  return static_cast<size_t>(std::count(_items.begin(), _items.end(), Instruction::POP));
}

}

bool PeepholeOptimiser::optimise()
{
  // Avoid referencing immutables too early by using approx. counting in bytesRequired()
  auto const approx = evmasm::Precision::Approximate;
  OptimiserState state {m_items, 0, std::back_inserter(m_optimisedItems)};
  while (state.i < m_items.size())
    applyMethods(
      state,
      PushPop(), OpPop(), OpStop(), OpReturnRevert(), DoublePush(), DoubleSwap(), CommutativeSwap(), SwapComparison(),
      DupSwap(), IsZeroIsZeroJumpI(), EqIsZeroJumpI(), DoubleJump(), JumpToNext(), UnreachableCode(),
      TagConjunctions(), TruthyAnd(), Identity()
    );
  if (m_optimisedItems.size() < m_items.size() || (
    m_optimisedItems.size() == m_items.size() && (
      evmasm::bytesRequired(m_optimisedItems, 3, approx) < evmasm::bytesRequired(m_items, 3, approx) ||
      numberOfPops(m_optimisedItems) > numberOfPops(m_items)
    )
  ))
  {
    m_items = std::move(m_optimisedItems);
    return true;
  }
  else
    return false;
}

Coverage Report

Created: 2022-08-24 06:39