/*
This file is part of cpp-ethereum.
cpp-ethereum 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.
cpp-ethereum 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 cpp-ethereum. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* @file ExpressionClasses.cpp
* @author Christian <c@ethdev.com>
* @date 2015
* Container for equivalence classes of expressions for use in common subexpression elimination.
*/
#include <libevmasm/ExpressionClasses.h>
#include <utility>
#include <tuple>
#include <functional>
#include <boost/range/adaptor/reversed.hpp>
#include <boost/noncopyable.hpp>
#include <libevmasm/Assembly.h>
#include <libevmasm/CommonSubexpressionEliminator.h>
using namespace std;
using namespace dev;
using namespace dev::eth;
bool ExpressionClasses::Expression::operator<(ExpressionClasses::Expression const& _other) const
{
assertThrow(!!item && !!_other.item, OptimizerException, "");
auto type = item->type();
auto otherType = _other.item->type();
return std::tie(type, item->data(), arguments, sequenceNumber) <
std::tie(otherType, _other.item->data(), _other.arguments, _other.sequenceNumber);
}
ExpressionClasses::Id ExpressionClasses::find(
AssemblyItem const& _item,
Ids const& _arguments,
bool _copyItem,
unsigned _sequenceNumber
)
{
Expression exp;
exp.id = Id(-1);
exp.item = &_item;
exp.arguments = _arguments;
exp.sequenceNumber = _sequenceNumber;
if (SemanticInformation::isCommutativeOperation(_item))
sort(exp.arguments.begin(), exp.arguments.end());
if (SemanticInformation::isDeterministic(_item))
{
auto it = m_expressions.find(exp);
if (it != m_expressions.end())
return it->id;
}
if (_copyItem)
exp.item = storeItem(_item);
ExpressionClasses::Id id = tryToSimplify(exp);
if (id < m_representatives.size())
exp.id = id;
else
{
exp.id = m_representatives.size();
m_representatives.push_back(exp);
}
m_expressions.insert(exp);
return exp.id;
}
void ExpressionClasses::forceEqual(
ExpressionClasses::Id _id,
AssemblyItem const& _item,
ExpressionClasses::Ids const& _arguments,
bool _copyItem
)
{
Expression exp;
exp.id = _id;
exp.item = &_item;
exp.arguments = _arguments;
if (SemanticInformation::isCommutativeOperation(_item))
sort(exp.arguments.begin(), exp.arguments.end());
if (_copyItem)
exp.item = storeItem(_item);
m_expressions.insert(exp);
}
ExpressionClasses::Id ExpressionClasses::newClass(SourceLocation const& _location)
{
Expression exp;
exp.id = m_representatives.size();
exp.item = storeItem(AssemblyItem(UndefinedItem, (u256(1) << 255) + exp.id, _location));
m_representatives.push_back(exp);
m_expressions.insert(exp);
return exp.id;
}
bool ExpressionClasses::knownToBeDifferent(ExpressionClasses::Id _a, ExpressionClasses::Id _b)
{
// Try to simplify "_a - _b" and return true iff the value is a non-zero constant.
return knownNonZero(find(Instruction::SUB, {_a, _b}));
}
bool ExpressionClasses::knownToBeDifferentBy32(ExpressionClasses::Id _a, ExpressionClasses::Id _b)
{
// Try to simplify "_a - _b" and return true iff the value is at least 32 away from zero.
u256 const* v = knownConstant(find(Instruction::SUB, {_a, _b}));
// forbidden interval is ["-31", 31]
return v && *v + 31 > u256(62);
}
bool ExpressionClasses::knownZero(Id _c)
{
return Pattern(u256(0)).matches(representative(_c), *this);
}
bool ExpressionClasses::knownNonZero(Id _c)
{
return Pattern(u256(0)).matches(representative(find(Instruction::ISZERO, {_c})), *this);
}
u256 const* ExpressionClasses::knownConstant(Id _c)
{
map<unsigned, Expression const*> matchGroups;
Pattern constant(Push);
constant.setMatchGroup(1, matchGroups);
if (!constant.matches(representative(_c), *this))
return nullptr;
return &constant.d();
}
AssemblyItem const* ExpressionClasses::storeItem(AssemblyItem const& _item)
{
m_spareAssemblyItems.push_back(make_shared<AssemblyItem>(_item));
return m_spareAssemblyItems.back().get();
}
string ExpressionClasses::fullDAGToString(ExpressionClasses::Id _id) const
{
Expression const& expr = representative(_id);
stringstream str;
str << dec << expr.id << ":";
if (expr.item)
{
str << *expr.item << "(";
for (Id arg: expr.arguments)
str << fullDAGToString(arg) << ",";
str << ")";
}
else
str << " UNIQUE";
return str.str();
}
class Rules: public boost::noncopyable
{
public:
Rules();
void resetMatchGroups() { m_matchGroups.clear(); }
vector<pair<Pattern, function<Pattern()>>> rules() const { return m_rules; }
private:
using Expression = ExpressionClasses::Expression;
map<unsigned, Expression const*> m_matchGroups;
vector<pair<Pattern, function<Pattern()>>> m_rules;
};
template <class S> S divWorkaround(S const& _a, S const& _b)
{
return (S)(bigint(_a) / bigint(_b));
}
template <class S> S modWorkaround(S const& _a, S const& _b)
{
return (S)(bigint(_a) % bigint(_b));
}
Rules::Rules()
{
// Multiple occurences of one of these inside one rule must match the same equivalence class.
// Constants.
Pattern A(Push);
Pattern B(Push);
Pattern C(Push);
// Anything.
Pattern X;
Pattern Y;
Pattern Z;
A.setMatchGroup(1, m_matchGroups);
B.setMatchGroup(2, m_matchGroups);
C.setMatchGroup(3, m_matchGroups);
X.setMatchGroup(4, m_matchGroups);
Y.setMatchGroup(5, m_matchGroups);
Z.setMatchGroup(6, m_matchGroups);
m_rules = vector<pair<Pattern, function<Pattern()>>>{
// arithmetics on constants
{{Instruction::ADD, {A, B}}, [=]{ return A.d() + B.d(); }},
{{Instruction::MUL, {A, B}}, [=]{ return A.d() * B.d(); }},
{{Instruction::SUB, {A, B}}, [=]{ return A.d() - B.d(); }},
{{Instruction::DIV, {A, B}}, [=]{ return B.d() == 0 ? 0 : divWorkaround(A.d(), B.d()); }},
{{Instruction::SDIV, {A, B}}, [=]{ return B.d() == 0 ? 0 : s2u(divWorkaround(u2s(A.d()), u2s(B.d()))); }},
{{Instruction::MOD, {A, B}}, [=]{ return B.d() == 0 ? 0 : modWorkaround(A.d(), B.d()); }},
{{Instruction::SMOD, {A, B}}, [=]{ return B.d() == 0 ? 0 : s2u(modWorkaround(u2s(A.d()), u2s(B.d()))); }},
{{Instruction::EXP, {A, B}}, [=]{ return u256(boost::multiprecision::powm(bigint(A.d()), bigint(B.d()), bigint(1) << 256)); }},
{{Instruction::NOT, {A}}, [=]{ return ~A.d(); }},
{{Instruction::LT, {A, B}}, [=]() { return A.d() < B.d() ? u256(1) : 0; }},
{{Instruction::GT, {A, B}}, [=]() -> u256 { return A.d() > B.d() ? 1 : 0; }},
{{Instruction::SLT, {A, B}}, [=]() -> u256 { return u2s(A.d()) < u2s(B.d()) ? 1 : 0; }},
{{Instruction::SGT, {A, B}}, [=]() -> u256 { return u2s(A.d()) > u2s(B.d()) ? 1 : 0; }},
{{Instruction::EQ, {A, B}}, [=]() -> u256 { return A.d() == B.d() ? 1 : 0; }},
{{Instruction::ISZERO, {A}}, [=]() -> u256 { return A.d() == 0 ? 1 : 0; }},
{{Instruction::AND, {A, B}}, [=]{ return A.d() & B.d(); }},
{{Instruction::OR, {A, B}}, [=]{ return A.d() | B.d(); }},
{{Instruction::XOR, {A, B}}, [=]{ return A.d() ^ B.d(); }},
{{Instruction::BYTE, {A, B}}, [=]{ return A.d() >= 32 ? 0 : (B.d() >> unsigned(8 * (31 - A.d()))) & 0xff; }},
{{Instruction::ADDMOD, {A, B, C}}, [=]{ return C.d() == 0 ? 0 : u256((bigint(A.d()) + bigint(B.d())) % C.d()); }},
{{Instruction::MULMOD, {A, B, C}}, [=]{ return C.d() == 0 ? 0 : u256((bigint(A.d()) * bigint(B.d())) % C.d()); }},
{{Instruction::MULMOD, {A, B, C}}, [=]{ return A.d() * B.d(); }},
{{Instruction::SIGNEXTEND, {A, B}}, [=]() -> u256 {
if (A.d() >= 31)
return B.d();
unsigned testBit = unsigned(A.d()) * 8 + 7;
u256 mask = (u256(1) << testBit) - 1;
return u256(boost::multiprecision::bit_test(B.d(), testBit) ? B.d() | ~mask : B.d() & mask);
}},
// invariants involving known constants
{{Instruction::ADD, {X, 0}}, [=]{ return X; }},
{{Instruction::MUL, {X, 1}}, [=]{ return X; }},
{{Instruction::DIV, {X, 1}}, [=]{ return X; }},
{{Instruction::SDIV, {X, 1}}, [=]{ return X; }},
{{Instruction::OR, {X, 0}}, [=]{ return X; }},
{{Instruction::XOR, {X, 0}}, [=]{ return X; }},
{{Instruction::AND, {X, ~u256(0)}}, [=]{ return X; }},
{{Instruction::MUL, {X, 0}}, [=]{ return u256(0); }},
{{Instruction::DIV, {X, 0}}, [=]{ return u256(0); }},
{{Instruction::MOD, {X, 0}}, [=]{ return u256(0); }},
{{Instruction::MOD, {0, X}}, [=]{ return u256(0); }},
{{Instruction::AND, {X, 0}}, [=]{ return u256(0); }},
{{Instruction::OR, {X, ~u256(0)}}, [=]{ return ~u256(0); }},
// operations involving an expression and itself
{{Instruction::AND, {X, X}}, [=]{ return X; }},
{{Instruction::OR, {X, X}}, [=]{ return X; }},
{{Instruction::SUB, {X, X}}, [=]{ return u256(0); }},
{{Instruction::EQ, {X, X}}, [=]{ return u256(1); }},
{{Instruction::LT, {X, X}}, [=]{ return u256(0); }},
{{Instruction::SLT, {X, X}}, [=]{ return u256(0); }},
{{Instruction::GT, {X, X}}, [=]{ return u256(0); }},
{{Instruction::SGT, {X, X}}, [=]{ return u256(0); }},
{{Instruction::MOD, {X, X}}, [=]{ return u256(0); }},
{{Instruction::NOT, {{Instruction::NOT, {X}}}}, [=]{ return X; }},
};
// Double negation of opcodes with binary result
for (auto const& op: vector<Instruction>{
Instruction::EQ,
Instruction::LT,
Instruction::SLT,
Instruction::GT,
Instruction::SGT
})
m_rules.push_back({
{Instruction::ISZERO, {{Instruction::ISZERO, {{op, {X, Y}}}}}},
[=]() -> Pattern { return {op, {X, Y}}; }
});
m_rules.push_back({
{Instruction::ISZERO, {{Instruction::ISZERO, {{Instruction::ISZERO, {X}}}}}},
[=]() -> Pattern { return {Instruction::ISZERO, {X}}; }
});
// Associative operations
for (auto const& opFun: vector<pair<Instruction,function<u256(u256 const&,u256 const&)>>>{
{Instruction::ADD, plus<u256>()},
{Instruction::MUL, multiplies<u256>()},
{Instruction::AND, bit_and<u256>()},
{Instruction::OR, bit_or<u256>()},
{Instruction::XOR, bit_xor<u256>()}
})
{
auto op = opFun.first;
auto fun = opFun.second;
// Moving constants to the outside, order matters here!
// we need actions that return expressions (or patterns?) here, and we need also reversed rules
// (X+A)+B -> X+(A+B)
m_rules += vector<pair<Pattern, function<Pattern()>>>{{
{op, {{op, {X, A}}, B}},
[=]() -> Pattern { return {op, {X, fun(A.d(), B.d())}}; }
}, {
// X+(Y+A) -> (X+Y)+A
{op, {{op, {X, A}}, Y}},
[=]() -> Pattern { return {op, {{op, {X, Y}}, A}}; }
}, {
// For now, we still need explicit commutativity for the inner pattern
{op, {{op, {A, X}}, B}},
[=]() -> Pattern { return {op, {X, fun(A.d(), B.d())}}; }
}, {
{op, {{op, {A, X}}, Y}},
[=]() -> Pattern { return {op, {{op, {X, Y}}, A}}; }
}};
}
// move constants across subtractions
m_rules += vector<pair<Pattern, function<Pattern()>>>{
{
// X - A -> X + (-A)
{Instruction::SUB, {X, A}},
[=]() -> Pattern { return {Instruction::ADD, {X, 0 - A.d()}}; }
}, {
// (X + A) - Y -> (X - Y) + A
{Instruction::SUB, {{Instruction::ADD, {X, A}}, Y}},
[=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, A}}; }
}, {
// (A + X) - Y -> (X - Y) + A
{Instruction::SUB, {{Instruction::ADD, {A, X}}, Y}},
[=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, A}}; }
}, {
// X - (Y + A) -> (X - Y) + (-A)
{Instruction::SUB, {X, {Instruction::ADD, {Y, A}}}},
[=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, 0 - A.d()}}; }
}, {
// X - (A + Y) -> (X - Y) + (-A)
{Instruction::SUB, {X, {Instruction::ADD, {A, Y}}}},
[=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, 0 - A.d()}}; }
}
};
}
ExpressionClasses::Id ExpressionClasses::tryToSimplify(Expression const& _expr, bool _secondRun)
{
static Rules rules;
if (
!_expr.item ||
_expr.item->type() != Operation ||
!SemanticInformation::isDeterministic(*_expr.item)
)
return -1;
for (auto const& rule: rules.rules())
{
rules.resetMatchGroups();
if (rule.first.matches(_expr, *this))
{
// Debug info
//cout << "Simplifying " << *_expr.item << "(";
//for (Id arg: _expr.arguments)
// cout << fullDAGToString(arg) << ", ";
//cout << ")" << endl;
//cout << "with rule " << rule.first.toString() << endl;
//ExpressionTemplate t(rule.second());
//cout << "to " << rule.second().toString() << endl;
return rebuildExpression(ExpressionTemplate(rule.second(), _expr.item->location()));
}
}
if (!_secondRun && _expr.arguments.size() == 2 && SemanticInformation::isCommutativeOperation(*_expr.item))
{
Expression expr = _expr;
swap(expr.arguments[0], expr.arguments[1]);
return tryToSimplify(expr, true);
}
return -1;
}
ExpressionClasses::Id ExpressionClasses::rebuildExpression(ExpressionTemplate const& _template)
{
if (_template.hasId)
return _template.id;
Ids arguments;
for (ExpressionTemplate const& t: _template.arguments)
arguments.push_back(rebuildExpression(t));
return find(_template.item, arguments);
}
Pattern::Pattern(Instruction _instruction, std::vector<Pattern> const& _arguments):
m_type(Operation),
m_requireDataMatch(true),
m_data(_instruction),
m_arguments(_arguments)
{
}
void Pattern::setMatchGroup(unsigned _group, map<unsigned, Expression const*>& _matchGroups)
{
m_matchGroup = _group;
m_matchGroups = &_matchGroups;
}
bool Pattern::matches(Expression const& _expr, ExpressionClasses const& _classes) const
{
if (!matchesBaseItem(_expr.item))
return false;
if (m_matchGroup)
{
if (!m_matchGroups->count(m_matchGroup))
(*m_matchGroups)[m_matchGroup] = &_expr;
else if ((*m_matchGroups)[m_matchGroup]->id != _expr.id)
return false;
}
assertThrow(m_arguments.size() == 0 || _expr.arguments.size() == m_arguments.size(), OptimizerException, "");
for (size_t i = 0; i < m_arguments.size(); ++i)
if (!m_arguments[i].matches(_classes.representative(_expr.arguments[i]), _classes))
return false;
return true;
}
AssemblyItem Pattern::toAssemblyItem(SourceLocation const& _location) const
{
return AssemblyItem(m_type, m_data, _location);
}
string Pattern::toString() const
{
stringstream s;
switch (m_type)
{
case Operation:
s << instructionInfo(Instruction(unsigned(m_data))).name;
break;
case Push:
s << "PUSH " << hex << m_data;
break;
case UndefinedItem:
s << "ANY";
break;
default:
s << "t=" << dec << m_type << " d=" << hex << m_data;
break;
}
if (!m_requireDataMatch)
s << " ~";
if (m_matchGroup)
s << "[" << dec << m_matchGroup << "]";
s << "(";
for (Pattern const& p: m_arguments)
s << p.toString() << ", ";
s << ")";
return s.str();
}
bool Pattern::matchesBaseItem(AssemblyItem const* _item) const
{
if (m_type == UndefinedItem)
return true;
if (!_item)
return false;
if (m_type != _item->type())
return false;
if (m_requireDataMatch && m_data != _item->data())
return false;
return true;
}
Pattern::Expression const& Pattern::matchGroupValue() const
{
assertThrow(m_matchGroup > 0, OptimizerException, "");
assertThrow(!!m_matchGroups, OptimizerException, "");
assertThrow((*m_matchGroups)[m_matchGroup], OptimizerException, "");
return *(*m_matchGroups)[m_matchGroup];
}
ExpressionTemplate::ExpressionTemplate(Pattern const& _pattern, SourceLocation const& _location)
{
if (_pattern.matchGroup())
{
hasId = true;
id = _pattern.id();
}
else
{
hasId = false;
item = _pattern.toAssemblyItem(_location);
}
for (auto const& arg: _pattern.arguments())
arguments.push_back(ExpressionTemplate(arg, _location));
}
string ExpressionTemplate::toString() const
{
stringstream s;
if (hasId)
s << id;
else
s << item;
s << "(";
for (auto const& arg: arguments)
s << arg.toString();
s << ")";
return s.str();
}
