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Extend knowledge base.

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This commit is contained in:
chriseth
2021-08-18 12:42:46 +02:00
parent 729db521a9
commit 4b038e3f02
4 changed files with 119 additions and 9 deletions
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libyul/optimiser/KnowledgeBase.cpp
+29 -9
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@@ -40,9 +40,8 @@ bool KnowledgeBase::knownToBeDifferent(YulString _a, YulString _b)
// current values to turn `sub(_a, _b)` into a nonzero constant.
// If that fails, try `eq(_a, _b)`.
Expression expr1 = simplify(FunctionCall{{}, {{}, "sub"_yulstring}, util::make_vector<Expression>(Identifier{{}, _a}, Identifier{{}, _b})});
if (holds_alternative<Literal>(expr1))
return valueOfLiteral(std::get<Literal>(expr1)) != 0;
if (optional<u256> difference = differenceIfKnownConstant(_a, _b))
return difference != 0;
Expression expr2 = simplify(FunctionCall{{}, {{}, "eq"_yulstring}, util::make_vector<Expression>(Identifier{{}, _a}, Identifier{{}, _b})});
if (holds_alternative<Literal>(expr2))
@@ -51,21 +50,42 @@ bool KnowledgeBase::knownToBeDifferent(YulString _a, YulString _b)
return false;
}
optional<u256> KnowledgeBase::differenceIfKnownConstant(YulString _a, YulString _b)
{
// Try to use the simplification rules together with the
// current values to turn `sub(_a, _b)` into a constant.
Expression expr1 = simplify(FunctionCall{{}, {{}, "sub"_yulstring}, util::make_vector<Expression>(Identifier{{}, _a}, Identifier{{}, _b})});
if (Literal const* value = get_if<Literal>(&expr1))
return valueOfLiteral(*value);
return {};
}
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}, util::make_vector<Expression>(Identifier{{}, _a}, Identifier{{}, _b})});
if (holds_alternative<Literal>(expr1))
{
u256 val = valueOfLiteral(std::get<Literal>(expr1));
return val >= 32 && val <= u256(0) - 32;
}
if (optional<u256> difference = differenceIfKnownConstant(_a, _b))
return difference >= 32 && difference <= u256(0) - 32;
return false;
}
bool KnowledgeBase::knownToBeZero(YulString _a)
{
return valueIfKnownConstant(_a) == u256{};
}
optional<u256> KnowledgeBase::valueIfKnownConstant(YulString _a)
{
if (m_variableValues.count(_a))
if (Literal const* literal = get_if<Literal>(m_variableValues.at(_a).value))
return valueOfLiteral(*literal);
return {};
}
Expression KnowledgeBase::simplify(Expression _expression)
{
bool startedRecursion = (m_recursionCounter == 0);