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Assume that push will not overflow

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This commit is contained in:
Leonardo Alt
2020-05-18 16:35:56 +02:00
parent 82db35e563
commit d4d26c02e4
8 changed files with 88 additions and 6 deletions
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libsolidity/formal/SMTEncoder.cpp
+6 -6
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@@ -1085,6 +1085,11 @@ void SMTEncoder::arrayPush(FunctionCall const& _funCall)
auto symbArray = dynamic_pointer_cast<smt::SymbolicArrayVariable>(m_context.expression(memberAccess->expression()));
solAssert(symbArray, "");
auto oldLength = symbArray->length();
m_context.addAssertion(oldLength >= 0);
// Real world assumption: the array length is assumed to not overflow.
// This assertion guarantees that both the current and updated lengths have the above property.
m_context.addAssertion(oldLength + 1 < (smt::maxValue(*TypeProvider::uint256()) - 1));
auto const& arguments = _funCall.arguments();
smt::Expression element = arguments.empty() ?
smt::zeroValue(_funCall.annotation().type) :
@@ -1096,12 +1101,7 @@ void SMTEncoder::arrayPush(FunctionCall const& _funCall)
);
symbArray->increaseIndex();
m_context.addAssertion(symbArray->elements() == store);
auto newLength = smt::Expression::ite(
oldLength == smt::maxValue(*TypeProvider::uint256()),
0,
oldLength + 1
);
m_context.addAssertion(symbArray->length() == newLength);
m_context.addAssertion(symbArray->length() == oldLength + 1);
if (arguments.empty())
defineExpr(_funCall, element);