/*
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 .
*/
/**
* Class that can answer questions about values of variables and their relations.
*/
#include
#include
#include
#include
#include
#include
#include
using namespace std;
using namespace yul;
using namespace dev;
bool KnowledgeBase::knownToBeDifferent(YulString _a, YulString _b)
{
// Try to use the simplification rules together with the
// current values to turn `sub(_a, _b)` into a nonzero constant.
// If that fails, try `eq(_a, _b)`.
Expression expr1 = simplify(FunctionCall{{}, {{}, "sub"_yulstring}, make_vector(Identifier{{}, _a}, Identifier{{}, _b})});
if (holds_alternative(expr1))
return valueOfLiteral(std::get(expr1)) != 0;
Expression expr2 = simplify(FunctionCall{{}, {{}, "eq"_yulstring}, make_vector(Identifier{{}, _a}, Identifier{{}, _b})});
if (holds_alternative(expr2))
return valueOfLiteral(std::get(expr2)) == 0;
return false;
}
bool KnowledgeBase::knownToBeDifferentByAtLeast32(YulString _a, YulString _b)
{
// Try to use the simplification rules together with the
// current values to turn `sub(_a, _b)` into a constant whose absolute value is at least 32.
Expression expr1 = simplify(FunctionCall{{}, {{}, "sub"_yulstring}, make_vector(Identifier{{}, _a}, Identifier{{}, _b})});
if (holds_alternative(expr1))
{
u256 val = valueOfLiteral(std::get(expr1));
return val >= 32 && val <= u256(0) - 32;
}
return false;
}
Expression KnowledgeBase::simplify(Expression _expression)
{
bool startedRecursion = (m_recursionCounter == 0);
dev::ScopeGuard{[&] { if (startedRecursion) m_recursionCounter = 0; }};
if (startedRecursion)
m_recursionCounter = 100;
else if (m_recursionCounter == 1)
return _expression;
else
--m_recursionCounter;
if (holds_alternative(_expression))
for (Expression& arg: std::get(_expression).arguments)
arg = simplify(arg);
else if (holds_alternative(_expression))
for (Expression& arg: std::get(_expression).arguments)
arg = simplify(arg);
if (auto match = SimplificationRules::findFirstMatch(_expression, m_dialect, m_variableValues))
return simplify(match->action().toExpression(locationOf(_expression)));
return _expression;
}