encoding

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();