Merge pull request #2504 from ethereum/inlineasm-decl-empty

Support variable declarations without an assignment in assembly

Changelog.md

@@ -2,6 +2,7 @@
 
 Features:
  * Inline Assembly: Show useful error message if trying to access calldata variables.
+ * Inline Assembly: Support variable declaration without initial value (defaults to 0).
  * Type Checker: Disallow value transfers to contracts without a payable fallback function
 
 Bugfixes:

docs/assembly.rst

@@ -110,7 +110,7 @@ these curly braces, the following can be used (see the later sections for more d
  - opcodes (in "instruction style"), e.g. ``mload sload dup1 sstore``, for a list see below
  - opcodes in functional style, e.g. ``add(1, mlod(0))``
  - labels, e.g. ``name:``
- - variable declarations, e.g. ``let x := 7`` or ``let x := add(y, 3)``
+ - variable declarations, e.g. ``let x := 7``, ``let x := add(y, 3)`` or ``let x`` (initial value of empty (0) is assigned)
  - identifiers (labels or assembly-local variables and externals if used as inline assembly), e.g. ``jump(name)``, ``3 x add``
  - assignments (in "instruction style"), e.g. ``3 =: x``
  - assignments in functional style, e.g. ``x := add(y, 3)``

libjulia/backends/evm/EVMCodeTransform.cpp

@@ -37,10 +37,19 @@ void CodeTransform::operator()(VariableDeclaration const& _varDecl)
 {
 	solAssert(m_scope, "");
 
-	int expectedItems = _varDecl.variables.size();
+	int const numVariables = _varDecl.variables.size();
 	int height = m_assembly.stackHeight();
-	boost::apply_visitor(*this, *_varDecl.value);
-	expectDeposit(expectedItems, height);
+	if (_varDecl.value)
+	{
+		boost::apply_visitor(*this, *_varDecl.value);
+		expectDeposit(numVariables, height);
+	}
+	else
+	{
+		int variablesLeft = numVariables;
+		while (variablesLeft--)
+			m_assembly.appendConstant(u256(0));
+	}
 	for (auto const& variable: _varDecl.variables)
 	{
 		auto& var = boost::get<Scope::Variable>(m_scope->identifiers.at(variable.name));

libsolidity/inlineasm/AsmAnalysis.cpp

@@ -174,14 +174,20 @@ bool AsmAnalyzer::operator()(assembly::Assignment const& _assignment)
 
 bool AsmAnalyzer::operator()(assembly::VariableDeclaration const& _varDecl)
 {
-	int const expectedItems = _varDecl.variables.size();
-	int const stackHeight = m_stackHeight;
-	bool success = boost::apply_visitor(*this, *_varDecl.value);
-	if ((m_stackHeight - stackHeight) != expectedItems)
+	bool success = true;
+	int const numVariables = _varDecl.variables.size();
+	if (_varDecl.value)
 	{
-		m_errorReporter.declarationError(_varDecl.location, "Variable count mismatch.");
-		return false;
+		int const stackHeight = m_stackHeight;
+		success = boost::apply_visitor(*this, *_varDecl.value);
+		if ((m_stackHeight - stackHeight) != numVariables)
+		{
+			m_errorReporter.declarationError(_varDecl.location, "Variable count mismatch.");
+			return false;
+		}
 	}
+	else
+		m_stackHeight += numVariables;
 
 	for (auto const& variable: _varDecl.variables)
 	{

libsolidity/inlineasm/AsmParser.cpp

@@ -347,10 +347,15 @@ assembly::VariableDeclaration Parser::parseVariableDeclaration()
 		else
 			break;
 	}
-	expectToken(Token::Colon);
-	expectToken(Token::Assign);
-	varDecl.value.reset(new Statement(parseExpression()));
-	varDecl.location.end = locationOf(*varDecl.value).end;
+	if (currentToken() == Token::Colon)
+	{
+		expectToken(Token::Colon);
+		expectToken(Token::Assign);
+		varDecl.value.reset(new Statement(parseExpression()));
+		varDecl.location.end = locationOf(*varDecl.value).end;
+	}
+	else
+		varDecl.location.end = varDecl.variables.back().location.end;
 	return varDecl;
 }
 

libsolidity/inlineasm/AsmPrinter.cpp

@@ -128,8 +128,11 @@ string AsmPrinter::operator()(assembly::VariableDeclaration const& _variableDecl
 		),
 		", "
 	);
-	out += " := ";
-	out += boost::apply_visitor(*this, *_variableDeclaration.value);
+	if (_variableDeclaration.value)
+	{
+		out += " := ";
+		out += boost::apply_visitor(*this, *_variableDeclaration.value);
+	}
 	return out;
 }
 

test/libjulia/Parser.cpp

@@ -131,6 +131,11 @@ BOOST_AUTO_TEST_CASE(vardecl_bool)
 	BOOST_CHECK(successParse("{ let x:bool := false:bool }"));
 }
 
+BOOST_AUTO_TEST_CASE(vardecl_empty)
+{
+	BOOST_CHECK(successParse("{ let x:u256 }"));
+}
+
 BOOST_AUTO_TEST_CASE(assignment)
 {
 	BOOST_CHECK(successParse("{ let x:u256 := 2:u256 let y:u256 := x }"));

test/libsolidity/InlineAssembly.cpp

@@ -195,6 +195,11 @@ BOOST_AUTO_TEST_CASE(vardecl_bool)
 	CHECK_PARSE_ERROR("{ let x := false }", ParserError, "True and false are not valid literals.");
 }
 
+BOOST_AUTO_TEST_CASE(vardecl_empty)
+{
+	BOOST_CHECK(successParse("{ let x }"));
+}
+
 BOOST_AUTO_TEST_CASE(assignment)
 {
 	BOOST_CHECK(successParse("{ let x := 2 7 8 add =: x }"));

test/libsolidity/SolidityEndToEndTest.cpp

@@ -9723,6 +9723,24 @@ BOOST_AUTO_TEST_CASE(multi_modifiers)
 	BOOST_CHECK(callContractFunction("x()") == encodeArgs(u256(12)));
 }
 
+BOOST_AUTO_TEST_CASE(inlineasm_empty_let)
+{
+	char const* sourceCode = R"(
+		contract C {
+			function f() returns (uint a, uint b) {
+				assembly {
+					let x
+					let y, z
+					a := x
+					b := z
+				}
+			}
+		}
+	)";
+	compileAndRun(sourceCode, 0, "C");
+	BOOST_CHECK(callContractFunction("f()") == encodeArgs(u256(0), u256(0)));
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }