encoding

libsolutil/BooleanLP.cpp

@@ -97,9 +97,32 @@ void BooleanLPSolver::declareVariable(string const& _name, SortPointer const& _s
 
 void BooleanLPSolver::addAssertion(Expression const& _expr)
 {
+	solAssert(_expr.sort->kind == Kind::Bool);
 	if (_expr.arguments.empty())
-		state().clauses.emplace_back(Clause{vector<Literal>{*parseLiteral(_expr)}});
+	{
+		solAssert(isBooleanVariable(_expr.name));
+		state().clauses.emplace_back(Clause{Literal{
+			true,
+			state().variables.at(_expr.name)
+		}});
+	}
 	else if (_expr.name == "=")
+	{
+		solAssert(_expr.arguments.at(0).sort->kind == _expr.arguments.at(1).sort->kind);
+		if (_expr.arguments.at(0).sort->kind == Kind::Bool)
+		{
+			if (_expr.arguments.at(0).arguments.empty() && isBooleanVariable(_expr.arguments.at(0).name))
+				addBooleanEquality(*parseLiteral(_expr.arguments.at(0)), _expr.arguments.at(1));
+			else if (_expr.arguments.at(1).arguments.empty() && isBooleanVariable(_expr.arguments.at(1).name))
+				addBooleanEquality(*parseLiteral(_expr.arguments.at(1)), _expr.arguments.at(0));
+			else
+			{
+				Literal newBoolean = *parseLiteral(declareInternalVariable(true));
+				addBooleanEquality(newBoolean, _expr.arguments.at(0));
+				addBooleanEquality(newBoolean, _expr.arguments.at(1));
+			}
+		}
+		else if (_expr.arguments.at(0).sort->kind == Kind::Int)
 		{
 			// Try to see if both sides are linear.
 			optional<LinearExpression> left = parseLinearSum(_expr.arguments.at(0));
@@ -112,17 +135,16 @@ void BooleanLPSolver::addAssertion(Expression const& _expr)
 				if (!tryAddDirectBounds(c))
 					state().fixedConstraints.emplace_back(move(c));
 			}
-		else if (_expr.arguments.at(0).arguments.empty() && isBooleanVariable(_expr.arguments.at(0).name))
-			addBooleanEquality(*parseLiteral(_expr.arguments.at(0)), _expr.arguments.at(1));
-		else if (_expr.arguments.at(1).arguments.empty() && isBooleanVariable(_expr.arguments.at(1).name))
-			addBooleanEquality(*parseLiteral(_expr.arguments.at(1)), _expr.arguments.at(0));
 			else
 			{
-			Literal newBoolean = *parseLiteral(declareInternalBoolean());
+				Expression left = parseLinearSumOrReturnEqualVariable(_expr.arguments.at(0));
-			addBooleanEquality(newBoolean, _expr.arguments.at(0));
+				Expression right = parseLinearSumOrReturnEqualVariable(_expr.arguments.at(1));
-			addBooleanEquality(newBoolean, _expr.arguments.at(1));
+				addAssertion(left == right);
 			}
 		}
+		else
+			solAssert(false);
+	}
 	else if (_expr.name == "and")
 	{
 		addAssertion(_expr.arguments.at(0));
@@ -137,7 +159,7 @@ void BooleanLPSolver::addAssertion(Expression const& _expr)
 		{
 			// We cannot have more than one constraint per clause.
 			// TODO Why?
-			right = *parseLiteral(declareInternalBoolean());
+			right = *parseLiteral(declareInternalVariable(true));
 			addBooleanEquality(right, _expr.arguments.at(1));
 		}
 		state().clauses.emplace_back(Clause{vector<Literal>{left, right}});
@@ -152,19 +174,21 @@ void BooleanLPSolver::addAssertion(Expression const& _expr)
 	{
 		optional<LinearExpression> left = parseLinearSum(_expr.arguments.at(0));
 		optional<LinearExpression> right = parseLinearSum(_expr.arguments.at(1));
-		if (!left || !right)
+		if (left && right)
 		{
-			cout << "Unable to parse expression" << endl;
-			// TODO fail in some way
-			return;
-		}
-
 			LinearExpression data = *left - *right;
 			data[0] *= -1;
 			Constraint c{move(data), _expr.name == "=", {}};
 			if (!tryAddDirectBounds(c))
 				state().fixedConstraints.emplace_back(move(c));
 		}
+		else
+		{
+			Expression left = parseLinearSumOrReturnEqualVariable(_expr.arguments.at(0));
+			Expression right = parseLinearSumOrReturnEqualVariable(_expr.arguments.at(1));
+			addAssertion(left <= right);
+		}
+	}
 	else if (_expr.name == ">=")
 		addAssertion(_expr.arguments.at(1) <= _expr.arguments.at(0));
 	else if (_expr.name == "<")
@@ -275,11 +299,11 @@ string BooleanLPSolver::toString() const
 	return result;
 }
 
-Expression BooleanLPSolver::declareInternalBoolean()
+Expression BooleanLPSolver::declareInternalVariable(bool _boolean)
 {
 	string name = "$" + to_string(state().variables.size() + 1);
-	declareVariable(name, true);
+	declareVariable(name, _boolean);
-	return smtutil::Expression(name, {}, SortProvider::boolSort);
+	return smtutil::Expression(name, {}, _boolean ? SortProvider::boolSort : SortProvider::uintSort);
 }
 
 void BooleanLPSolver::declareVariable(string const& _name, bool _boolean)
@@ -350,17 +374,42 @@ Literal BooleanLPSolver::negate(Literal const& _lit)
 
 Literal BooleanLPSolver::parseLiteralOrReturnEqualBoolean(Expression const& _expr)
 {
-	// TODO hen can this fail?
+	solAssert(_expr.sort->kind == Kind::Bool);
+	// TODO when can this fail?
 	if (optional<Literal> literal = parseLiteral(_expr))
 		return *literal;
 	else
 	{
-		Literal newBoolean = *parseLiteral(declareInternalBoolean());
+		Literal newBoolean = *parseLiteral(declareInternalVariable(true));
 		addBooleanEquality(newBoolean, _expr);
 		return newBoolean;
 	}
 }
 
+Expression BooleanLPSolver::parseLinearSumOrReturnEqualVariable(Expression const& _expr)
+{
+	solAssert(_expr.sort->kind == Kind::Int);
+	if (_expr.name == "ite")
+	{
+		Literal condition = parseLiteralOrReturnEqualBoolean(_expr.arguments.at(0));
+		// TODO this adds too many variables
+		Expression conditionBoolean = declareInternalVariable(true);
+		addBooleanEquality(condition, conditionBoolean);
+		Expression trueValue = parseLinearSumOrReturnEqualVariable(_expr.arguments.at(1));
+		Expression falseValue = parseLinearSumOrReturnEqualVariable(_expr.arguments.at(2));
+		Expression result = declareInternalVariable(false);
+		addAssertion(conditionBoolean || (result == trueValue));
+		addAssertion(!conditionBoolean || (result == falseValue));
+		return result;
+	}
+	if (_expr.arguments.empty())
+		return _expr;
+	solAssert(parseLinearSum(_expr));
+	Expression result = declareInternalVariable(false);
+	addAssertion(result == _expr);
+	return result;
+}
+
 optional<LinearExpression> BooleanLPSolver::parseLinearSum(smtutil::Expression const& _expr) const
 {
 	if (_expr.arguments.empty() || _expr.name == "*")
@@ -374,7 +423,12 @@ optional<LinearExpression> BooleanLPSolver::parseLinearSum(smtutil::Expression c
 		return _expr.name == "+" ? *left + *right : *left - *right;
 	}
 	else
+	{
+			// TOOD This should just resort to parseLinearSumOrReturn...
+			// and then use that variable
+		cout << "Invalid operator " << _expr.name << endl;
 		return std::nullopt;
+	}
 }
 
 optional<LinearExpression> BooleanLPSolver::parseProduct(smtutil::Expression const& _expr) const
@@ -477,6 +531,7 @@ size_t BooleanLPSolver::addConditionalConstraint(Constraint _constraint)
 
 void BooleanLPSolver::addBooleanEquality(Literal const& _left, smtutil::Expression const& _right)
 {
+	solAssert(_right.sort->kind == Kind::Bool);
 	if (optional<Literal> right = parseLiteral(_right))
 	{
 		// includes: not, <=, <, >=, >, boolean variables.
@@ -501,7 +556,7 @@ void BooleanLPSolver::addBooleanEquality(Literal const& _left, smtutil::Expressi
 		{
 			// We cannot have more than one constraint per clause.
 			// TODO Why?
-			b = *parseLiteral(declareInternalBoolean());
+			b = *parseLiteral(declareInternalVariable(true));
 			addBooleanEquality(b, _right.arguments.at(1));
 		}
 

libsolutil/BooleanLP.h

@@ -47,12 +47,14 @@ struct State
 };
 
 /**
- * Component that satisfies the SMT SolverInterface and uses an LP solver plus the DPLL
+ * Component that satisfies the SMT SolverInterface and uses an LP solver plus the CDCL
  * algorithm internally.
  * It uses a rational relaxation of the integer program and thus will not be able to answer
  * "satisfiable", but its answers are still correct.
  *
- * TODO are integers always non-negative?
+ * Contrary to the usual SMT type system, it adds an implicit constraint for all variables
+ * and sub-expressions to be non-negative.
+ * TODO this does not apply to e.g. `x + y - something`
  *
  * Integers are unbounded.
  */
@@ -77,13 +79,15 @@ public:
 private:
 	using rational = boost::rational<bigint>;
 
-	smtutil::Expression declareInternalBoolean();
+	smtutil::Expression declareInternalVariable(bool _boolean);
 	void declareVariable(std::string const& _name, bool _boolean);
 
+	/// Parses an expression of sort bool and returns a literal.
 	std::optional<Literal> parseLiteral(smtutil::Expression const& _expr);
 	Literal negate(Literal const& _lit);
 
 	Literal parseLiteralOrReturnEqualBoolean(smtutil::Expression const& _expr);
+	smtutil::Expression parseLinearSumOrReturnEqualVariable(smtutil::Expression const& _expr);
 
 	/// Parses the expression and expects a linear sum of variables.
 	/// Returns a vector with the first element being the constant and the

libyul/optimiser/ReasoningBasedSimplifier.cpp

@@ -28,6 +28,8 @@
 
 #include <libsolutil/CommonData.h>
 
+#include <libsolutil/BooleanLP.h>
+
 #include <utility>
 #include <memory>
 
@@ -40,7 +42,10 @@ using namespace solidity::smtutil;
 void ReasoningBasedSimplifier::run(OptimiserStepContext& _context, Block& _ast)
 {
 	set<YulString> ssaVars = SSAValueTracker::ssaVariables(_ast);
-	ReasoningBasedSimplifier{_context.dialect, ssaVars}(_ast);
+	ReasoningBasedSimplifier simpl{_context.dialect, ssaVars};
+	// Hack to inject the boolean lp solver.
+	simpl.m_solver = make_unique<BooleanLPSolver>();
+	simpl(_ast);
 }
 
 std::optional<string> ReasoningBasedSimplifier::invalidInCurrentEnvironment()
@@ -120,12 +125,21 @@ smtutil::Expression ReasoningBasedSimplifier::encodeEVMBuiltin(
 	switch (_instruction)
 	{
 	case evmasm::Instruction::ADD:
-		return wrap(arguments.at(0) + arguments.at(1));
+	{
+		auto result = arguments.at(0) + arguments.at(1) - (bigint(1) << 256) * newZeroOneVariable();
+		restrictToEVMWord(result);
+		return result;
+	}
 	case evmasm::Instruction::MUL:
 		return wrap(arguments.at(0) * arguments.at(1));
 	case evmasm::Instruction::SUB:
-		return wrap(arguments.at(0) - arguments.at(1));
+	{
+		auto result = arguments.at(0) - arguments.at(1) + (bigint(1) << 256) * newZeroOneVariable();
+		restrictToEVMWord(result);
+		return result;
+	}
 	case evmasm::Instruction::DIV:
+		// TODO add assertion that result is <= input
 		return smtutil::Expression::ite(
 			arguments.at(1) == constantValue(0),
 			constantValue(0),
@@ -224,3 +238,15 @@ smtutil::Expression ReasoningBasedSimplifier::encodeEVMBuiltin(
 	}
 	return newRestrictedVariable();
 }
+
+smtutil::Expression ReasoningBasedSimplifier::newZeroOneVariable()
+{
+	smtutil::Expression var = newVariable();
+	m_solver->addAssertion(var == 0 || var == 1);
+	return var;
+}
+
+void ReasoningBasedSimplifier::restrictToEVMWord(smtutil::Expression _value)
+{
+	m_solver->addAssertion(0 <= _value && _value < bigint(1) << 256);
+}

libyul/optimiser/ReasoningBasedSimplifier.h

@@ -69,6 +69,9 @@ private:
 		std::vector<Expression> const& _arguments
 	) override;
 
+	smtutil::Expression newZeroOneVariable();
+	void restrictToEVMWord(smtutil::Expression _value);
+
 	Dialect const& m_dialect;
 };
 

libyul/optimiser/SMTSolver.cpp

@@ -81,6 +81,11 @@ smtutil::Expression SMTSolver::newVariable()
 	return m_solver->newVariable(uniqueName(), defaultSort());
 }
 
+smtutil::Expression SMTSolver::newBooleanVariable()
+{
+	return m_solver->newVariable(uniqueName(), SortProvider::boolSort);
+}
+
 smtutil::Expression SMTSolver::newRestrictedVariable(bigint _maxValue)
 {
 	smtutil::Expression var = newVariable();
@@ -100,6 +105,7 @@ shared_ptr<Sort> SMTSolver::defaultSort() const
 
 smtutil::Expression SMTSolver::booleanValue(smtutil::Expression _value)
 {
+	// TODO should not use ite
 	return smtutil::Expression::ite(_value, constantValue(1), constantValue(0));
 }
 
@@ -115,6 +121,7 @@ smtutil::Expression SMTSolver::literalValue(Literal const& _literal)
 
 smtutil::Expression SMTSolver::twosComplementToSigned(smtutil::Expression _value)
 {
+	// TODO will that work for LP?
 	return smtutil::Expression::ite(
 		_value < smtutil::Expression(bigint(1) << 255),
 		_value,
@@ -136,6 +143,7 @@ smtutil::Expression SMTSolver::wrap(smtutil::Expression _value)
 	smtutil::Expression rest = newRestrictedVariable();
 	smtutil::Expression multiplier = newVariable();
 	m_solver->addAssertion(_value == multiplier * smtutil::Expression(bigint(1) << 256) + rest);
+	m_solver->addAssertion(0 <= rest && rest < bigint(1) << 256);
 	return rest;
 }
 

libyul/optimiser/SMTSolver.h

@@ -68,6 +68,7 @@ protected:
 	static smtutil::Expression bv2int(smtutil::Expression _arg);
 
 	smtutil::Expression newVariable();
+	smtutil::Expression newBooleanVariable();
 	virtual smtutil::Expression newRestrictedVariable(bigint _maxValue = (bigint(1) << 256) - 1);
 	std::string uniqueName();
 

test/libyul/YulOptimizerTest.cpp

@@ -53,12 +53,13 @@ YulOptimizerTest::YulOptimizerTest(string const& _filename):
 		BOOST_THROW_EXCEPTION(runtime_error("Filename path has to contain a directory: \"" + _filename + "\"."));
 	m_optimizerStep = std::prev(std::prev(path.end()))->string();
 
+	/*
 	if (m_optimizerStep == "reasoningBasedSimplifier" && (
 		solidity::test::CommonOptions::get().disableSMT ||
 		ReasoningBasedSimplifier::invalidInCurrentEnvironment()
 	))
 		m_shouldRun = false;
-
+*/
 	m_source = m_reader.source();
 
 	auto dialectName = m_reader.stringSetting("dialect", "evm");