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[SMTChecker] Variables are merged after branches (ite variables)

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This commit is contained in:
Leonardo Alt 2017-12-18 19:43:15 +01:00
parent 6a9a4e2bb8
commit d0abc5359b
3 changed files with 76 additions and 21 deletions
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32
libsolidity/formal/SMTChecker.cpp
View File

@ -91,15 +91,16 @@ bool SMTChecker::visit(IfStatement const& _node)
checkBooleanNotConstant(_node.condition(), "Condition is always $VALUE.");
visitBranch(_node.trueStatement(), expr(_node.condition()));
auto countersEndFalse = m_currentSequenceCounter;
auto countersEndTrue = visitBranch(_node.trueStatement(), expr(_node.condition()));
vector<Declaration const*> touchedVariables = m_variableUsage->touchedVariables(_node.trueStatement());
if (_node.falseStatement())
{
visitBranch(*_node.falseStatement(), !expr(_node.condition()));
countersEndFalse = visitBranch(*_node.falseStatement(), !expr(_node.condition()));
touchedVariables += m_variableUsage->touchedVariables(*_node.falseStatement());
}
resetVariables(touchedVariables);
mergeVariables(touchedVariables, expr(_node.condition()), countersEndTrue, countersEndFalse);
return false;
}
@ -506,12 +507,12 @@ void SMTChecker::assignment(Declaration const& _variable, smt::Expression const&
m_interface->addAssertion(newValue(_variable) == _value);
}
void SMTChecker::visitBranch(Statement const& _statement, smt::Expression _condition)
SMTChecker::VariableSequenceCounters SMTChecker::visitBranch(Statement const& _statement, smt::Expression _condition)
{
visitBranch(_statement, &_condition);
return visitBranch(_statement, &_condition);
}
void SMTChecker::visitBranch(Statement const& _statement, smt::Expression const* _condition)
SMTChecker::VariableSequenceCounters SMTChecker::visitBranch(Statement const& _statement, smt::Expression const* _condition)
{
VariableSequenceCounters sequenceCountersStart = m_currentSequenceCounter;
@ -522,7 +523,8 @@ void SMTChecker::visitBranch(Statement const& _statement, smt::Expression const*
popPathCondition();
m_conditionalExecutionHappened = true;
m_currentSequenceCounter = sequenceCountersStart;
std::swap(sequenceCountersStart, m_currentSequenceCounter);
return sequenceCountersStart;
}
void SMTChecker::checkCondition(
@ -702,6 +704,22 @@ void SMTChecker::resetVariables(vector<Declaration const*> _variables)
}
}
void SMTChecker::mergeVariables(vector<Declaration const*> const& _variables, smt::Expression const& _condition, VariableSequenceCounters const& _countersEndTrue, VariableSequenceCounters const& _countersEndFalse)
{
set<Declaration const*> uniqueVars(_variables.begin(), _variables.end());
for (auto const* decl: uniqueVars)
{
int trueCounter = _countersEndTrue.at(decl);
int falseCounter = _countersEndFalse.at(decl);
solAssert(trueCounter != falseCounter, "");
m_interface->addAssertion(newValue(*decl) == smt::Expression::ite(
_condition,
valueAtSequence(*decl, trueCounter),
valueAtSequence(*decl, falseCounter))
);
}
}
bool SMTChecker::createVariable(VariableDeclaration const& _varDecl)
{
if (dynamic_cast<IntegerType const*>(_varDecl.type().get()))

18
libsolidity/formal/SMTChecker.h
View File

@ -75,10 +75,14 @@ private:
void assignment(Declaration const& _variable, Expression const& _value, SourceLocation const& _location);
void assignment(Declaration const& _variable, smt::Expression const& _value, SourceLocation const& _location);
// Visits the branch given by the statement, pushes and pops the SMT checker.
// @param _condition if present, asserts that this condition is true within the branch.
void visitBranch(Statement const& _statement, smt::Expression const* _condition = nullptr);
void visitBranch(Statement const& _statement, smt::Expression _condition);
/// Maps a variable to an SSA index.
using VariableSequenceCounters = std::map<Declaration const*, int>;
/// Visits the branch given by the statement, pushes and pops the current path conditions.
/// @param _condition if present, asserts that this condition is true within the branch.
/// @returns the variable sequence counter after visiting the branch.
VariableSequenceCounters visitBranch(Statement const& _statement, smt::Expression const* _condition = nullptr);
VariableSequenceCounters visitBranch(Statement const& _statement, smt::Expression _condition);
/// Check that a condition can be satisfied.
void checkCondition(
@ -106,6 +110,10 @@ private:
void initializeLocalVariables(FunctionDefinition const& _function);
void resetVariables(std::vector<Declaration const*> _variables);
/// Given two different branches and the touched variables,
/// merge the touched variables into after-branch ite variables
/// using the branch condition as guard.
void mergeVariables(std::vector<Declaration const*> const& _variables, smt::Expression const& _condition, VariableSequenceCounters const& _countersEndTrue, VariableSequenceCounters const& _countersEndFalse);
/// Tries to create an uninitialized variable and returns true on success.
/// This fails if the type is not supported.
bool createVariable(VariableDeclaration const& _varDecl);
@ -134,8 +142,6 @@ private:
static smt::Expression minValue(IntegerType const& _t);
static smt::Expression maxValue(IntegerType const& _t);
using VariableSequenceCounters = std::map<Declaration const*, int>;
/// Returns the expression corresponding to the AST node. Throws if the expression does not exist.
smt::Expression expr(Expression const& _e);
/// Creates the expression (value can be arbitrary)

47
test/libsolidity/SMTChecker.cpp
View File

@ -168,9 +168,9 @@ BOOST_AUTO_TEST_CASE(function_call_does_not_clear_local_vars)
CHECK_SUCCESS_NO_WARNINGS(text);
}
BOOST_AUTO_TEST_CASE(branches_clear_variables)
BOOST_AUTO_TEST_CASE(branches_merge_variables)
{
// Only clears accessed variables
// Branch does not touch variable a
string text = R"(
contract C {
function f(uint x) public pure {
@ -182,7 +182,7 @@ BOOST_AUTO_TEST_CASE(branches_clear_variables)
}
)";
CHECK_SUCCESS_NO_WARNINGS(text);
// It is just a plain clear and will not combine branches.
// Positive branch touches variable a, but assertion should still hold.
text = R"(
contract C {
function f(uint x) public pure {
@ -194,8 +194,8 @@ BOOST_AUTO_TEST_CASE(branches_clear_variables)
}
}
)";
CHECK_WARNING(text, "Assertion violation happens here");
// Clear also works on the else branch
CHECK_SUCCESS_NO_WARNINGS(text);
// Negative branch touches variable a, but assertion should still hold.
text = R"(
contract C {
function f(uint x) public pure {
@ -208,8 +208,8 @@ BOOST_AUTO_TEST_CASE(branches_clear_variables)
}
}
)";
CHECK_WARNING(text, "Assertion violation happens here");
// Variable is not cleared, if it is only read.
CHECK_SUCCESS_NO_WARNINGS(text);
// Variable is not merged, if it is only read.
text = R"(
contract C {
function f(uint x) public pure {
@ -224,6 +224,36 @@ BOOST_AUTO_TEST_CASE(branches_clear_variables)
}
)";
CHECK_SUCCESS_NO_WARNINGS(text);
// Variable is reset in both branches
text = R"(
contract C {
function f(uint x) public pure {
uint a = 2;
if (x > 10) {
a = 3;
} else {
a = 3;
}
assert(a == 3);
}
}
)";
CHECK_SUCCESS_NO_WARNINGS(text);
// Variable is reset in both branches
text = R"(
contract C {
function f(uint x) public pure {
uint a = 2;
if (x > 10) {
a = 3;
} else {
a = 4;
}
assert(a >= 3);
}
}
)";
CHECK_SUCCESS_NO_WARNINGS(text);
}
BOOST_AUTO_TEST_CASE(branches_assert_condition)
@ -262,7 +292,7 @@ BOOST_AUTO_TEST_CASE(branches_assert_condition)
CHECK_SUCCESS_NO_WARNINGS(text);
}
BOOST_AUTO_TEST_CASE(ways_to_clear_variables)
BOOST_AUTO_TEST_CASE(ways_to_merge_variables)
{
string text = R"(
contract C {
@ -275,6 +305,7 @@ BOOST_AUTO_TEST_CASE(ways_to_clear_variables)
}
}
)";
CHECK_WARNING(text, "Assertion violation happens here");
text = R"(
contract C {
function f(uint x) public pure {