Support multiple assignment in inline assembly

libsolidity/inlineasm/AsmAnalysis.cpp

@@ -163,11 +163,25 @@ bool AsmAnalyzer::operator()(assembly::StackAssignment const& _assignment)
 
 bool AsmAnalyzer::operator()(assembly::Assignment const& _assignment)
 {
+	int const expectedItems = _assignment.variableNames.size();
+	solAssert(expectedItems >= 1, "");
 	int const stackHeight = m_stackHeight;
 	bool success = boost::apply_visitor(*this, *_assignment.value);
-	solAssert(m_stackHeight >= stackHeight, "Negative value size.");
-	if (!checkAssignment(_assignment.variableName, m_stackHeight - stackHeight))
-		success = false;
+	if ((m_stackHeight - stackHeight) != expectedItems)
+	{
+		m_errorReporter.declarationError(
+			_assignment.location,
+			"Variable count does not match number of values (" +
+			to_string(expectedItems) +
+			" vs. " +
+			to_string(m_stackHeight - stackHeight) +
+			")"
+		);
+		return false;
+	}
+	for (auto const& variableName: _assignment.variableNames)
+		if (!checkAssignment(variableName, 1))
+			success = false;
 	m_info.stackHeightInfo[&_assignment] = m_stackHeight;
 	return success;
 }

libsolidity/inlineasm/AsmData.h

@@ -54,7 +54,11 @@ struct Label { SourceLocation location; std::string name; };
 struct StackAssignment { SourceLocation location; Identifier variableName; };
 /// Assignment ("x := mload(20:u256)", expects push-1-expression on the right hand
 /// side and requires x to occupy exactly one stack slot.
-struct Assignment { SourceLocation location; Identifier variableName; std::shared_ptr<Statement> value; };
+///
+/// Multiple assignment ("x, y := f()"), where the left hand side variables each occupy
+/// a single stack slot and expects a single expression on the right hand returning
+/// the same amount of items as the number of variables.
+struct Assignment { SourceLocation location; std::vector<Identifier> variableNames; std::shared_ptr<Statement> value; };
 /// Functional instruction, e.g. "mul(mload(20:u256), add(2:u256, x))"
 struct FunctionalInstruction { SourceLocation location; Instruction instruction; std::vector<Statement> arguments; };
 struct FunctionCall { SourceLocation location; Identifier functionName; std::vector<Statement> arguments; };

libsolidity/inlineasm/AsmParser.cpp

@@ -122,6 +122,34 @@ assembly::Statement Parser::parseStatement()
 	{
 	case Token::LParen:
 		return parseCall(std::move(statement));
+	case Token::Comma:
+	{
+		// if a comma follows, a multiple assignment is assumed
+
+		if (statement.type() != typeid(assembly::Identifier))
+			fatalParserError("Label name / variable name must precede \",\" (multiple assignment).");
+		assembly::Identifier const& identifier = boost::get<assembly::Identifier>(statement);
+
+		Assignment assignment = createWithLocation<Assignment>(identifier.location);
+		assignment.variableNames.emplace_back(identifier);
+
+		do
+		{
+			expectToken(Token::Comma);
+			statement = parseElementaryOperation(false);
+			if (statement.type() != typeid(assembly::Identifier))
+				fatalParserError("Variable name expected in multiple assignemnt.");
+			assignment.variableNames.emplace_back(boost::get<assembly::Identifier>(statement));
+		}
+		while (currentToken() == Token::Comma);
+
+		expectToken(Token::Colon);
+		expectToken(Token::Assign);
+
+		assignment.value.reset(new Statement(parseExpression()));
+		assignment.location.end = locationOf(*assignment.value).end;
+		return assignment;
+	}
 	case Token::Colon:
 	{
 		if (statement.type() != typeid(assembly::Identifier))
@@ -136,7 +164,7 @@ assembly::Statement Parser::parseStatement()
 			if (!m_julia && instructions().count(identifier.name))
 				fatalParserError("Cannot use instruction names for identifier names.");
 			advance();
-			assignment.variableName = identifier;
+			assignment.variableNames.emplace_back(identifier);
 			assignment.value.reset(new Statement(parseExpression()));
 			assignment.location.end = locationOf(*assignment.value).end;
 			return assignment;

libsolidity/inlineasm/AsmPrinter.cpp

@@ -116,7 +116,11 @@ string AsmPrinter::operator()(assembly::StackAssignment const& _assignment)
 
 string AsmPrinter::operator()(assembly::Assignment const& _assignment)
 {
-	return (*this)(_assignment.variableName) + " := " + boost::apply_visitor(*this, *_assignment.value);
+	solAssert(_assignment.variableNames.size() >= 1, "");
+	string variables = (*this)(_assignment.variableNames.front());
+	for (size_t i = 1; i < _assignment.variableNames.size(); ++i)
+		variables += ", " + (*this)(_assignment.variableNames[i]);
+	return variables + " := " + boost::apply_visitor(*this, *_assignment.value);
 }
 
 string AsmPrinter::operator()(assembly::VariableDeclaration const& _variableDeclaration)