19 files changed, 163 insertions, 11 deletions

diff --git a/Changelog.md b/Changelog.md
index a362138e..27e72838 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -5,6 +5,7 @@ Features:
  * Syntax Checker: Turn the usage of ``callcode`` into an error as experimental 0.5.0 feature.
  * Type Checker: Improve address checksum warning.
  * Type Checker: More detailed errors for invalid array lengths (such as division by zero).
+ * Inline Assembly: ``if`` statement.
 
 Bugfixes:
 
diff --git a/docs/assembly.rst b/docs/assembly.rst
index 00bfb388..c233985b 100644
--- a/docs/assembly.rst
+++ b/docs/assembly.rst
@@ -26,6 +26,7 @@ arising when writing manual assembly by the following features:
 * access to external variables: ``function f(uint x) { assembly { x := sub(x, 1) } }``
 * labels: ``let x := 10  repeat: x := sub(x, 1) jumpi(repeat, eq(x, 0))``
 * loops: ``for { let i := 0 } lt(i, x) { i := add(i, 1) } { y := mul(2, y) }``
+* if statements: ``if slt(x, 0) { x := sub(0, x) }``
 * switch statements: ``switch x case 0 { y := mul(x, 2) } default { y := 0 }``
 * function calls: ``function f(x) -> y { switch x case 0 { y := 1 } default { y := mul(x, f(sub(x, 1))) }   }``
 
@@ -400,7 +401,7 @@ Labels
 Another problem in EVM assembly is that ``jump`` and ``jumpi`` use absolute addresses
 which can change easily. Solidity inline assembly provides labels to make the use of
 jumps easier. Note that labels are a low-level feature and it is possible to write
-efficient assembly without labels, just using assembly functions, loops and switch instructions
+efficient assembly without labels, just using assembly functions, loops, if and switch instructions
 (see below). The following code computes an element in the Fibonacci series.
 
 .. code::
@@ -523,6 +524,21 @@ is performed by replacing the variable's value on the stack by the new value.
         =: v // instruction style assignment, puts the result of sload(10) into v
     }
 
+If
+--
+
+The if statement can be used for conditionally executing code.
+There is no "else" part, consider using "switch" (see below) if
+you need multiple alternatives.
+
+.. code::
+
+    {
+        if eq(value, 0) { revert(0, 0) }
+    }
+
+The curly braces for the body are required.
+
 Switch
 ------
 
@@ -622,7 +638,7 @@ Things to Avoid
 ---------------
 
 Inline assembly might have a quite high-level look, but it actually is extremely
-low-level. Function calls, loops and switches are converted by simple
+low-level. Function calls, loops, ifs and switches are converted by simple
 rewriting rules and after that, the only thing the assembler does for you is re-arranging
 functional-style opcodes, managing jump labels, counting stack height for
 variable access and removing stack slots for assembly-local variables when the end
@@ -669,7 +685,7 @@ for the Solidity compiler. In this form, it tries to achieve several goals:
 3. Control flow should be easy to detect to help in formal verification and optimization.
 
 In order to achieve the first and last goal, assembly provides high-level constructs
-like ``for`` loops, ``switch`` statements and function calls. It should be possible
+like ``for`` loops, ``if`` and ``switch`` statements and function calls. It should be possible
 to write assembly programs that do not make use of explicit ``SWAP``, ``DUP``,
 ``JUMP`` and ``JUMPI`` statements, because the first two obfuscate the data flow
 and the last two obfuscate control flow. Furthermore, functional statements of
@@ -875,6 +891,7 @@ Grammar::
         FunctionalAssemblyAssignment |
         AssemblyAssignment |
         LabelDefinition |
+        AssemblyIf |
         AssemblySwitch |
         AssemblyFunctionDefinition |
         AssemblyFor |
@@ -891,6 +908,7 @@ Grammar::
     IdentifierList = Identifier ( ',' Identifier)*
     AssemblyAssignment = '=:' Identifier
     LabelDefinition = Identifier ':'
+    AssemblyIf = 'if' FunctionalAssemblyExpression AssemblyBlock
     AssemblySwitch = 'switch' FunctionalAssemblyExpression AssemblyCase*
         ( 'default' AssemblyBlock )?
     AssemblyCase = 'case' FunctionalAssemblyExpression AssemblyBlock
diff --git a/docs/julia.rst b/docs/julia.rst
index cf798363..309e6b36 100644
--- a/docs/julia.rst
+++ b/docs/julia.rst
@@ -15,7 +15,7 @@ future versions of the Solidity compiler will even use JULIA as intermediate
 language. It should also be easy to build high-level optimizer stages for JULIA.
 
 The core components of JULIA are functions, blocks, variables, literals,
-for-loops, switch-statements, expressions and assignments to variables.
+for-loops, if-statements, switch-statements, expressions and assignments to variables.
 
 JULIA is typed, both variables and literals must specify the type with postfix
 notation. The supported types are ``bool``, ``u8``, ``s8``, ``u32``, ``s32``,
@@ -88,6 +88,8 @@ Grammar::
         IdentifierList ':=' Expression
     Expression =
         FunctionCall | Identifier | Literal
+    If =
+        'if' Expression Block
     Switch =
         'switch' Expression Case* ( 'default' Block )?
     Case =
@@ -248,8 +250,14 @@ We will use a destructuring notation for the AST nodes.
         G, L, break
     E(G, L, continue: BreakContinue) =
         G, L, continue
+    E(G, L, <if condition body>: If) =
+        let G0, L0, v = E(G, L, condition)
+        if v is true:
+            E(G0, L0, body)
+        else:
+            G0, L0, regular
     E(G, L, <switch condition case l1:t1 st1 ... case ln:tn stn>: Switch) =
-        E(G, L, switch condition case l1:t1 st1 ... case ln:tn stn default {}) =
+        E(G, L, switch condition case l1:t1 st1 ... case ln:tn stn default {})
     E(G, L, <switch condition case l1:t1 st1 ... case ln:tn stn default st'>: Switch) =
         let G0, L0, v = E(G, L, condition)
         // i = 1 .. n
diff --git a/libjulia/backends/evm/EVMCodeTransform.cpp b/libjulia/backends/evm/EVMCodeTransform.cpp
index 66f593e8..13d9d011 100644
--- a/libjulia/backends/evm/EVMCodeTransform.cpp
+++ b/libjulia/backends/evm/EVMCodeTransform.cpp
@@ -217,6 +217,19 @@ void CodeTransform::operator()(assembly::Instruction const& _instruction)
 	checkStackHeight(&_instruction);
 }
 
+void CodeTransform::operator()(If const& _if)
+{
+	visitExpression(*_if.condition);
+	m_assembly.setSourceLocation(_if.location);
+	m_assembly.appendInstruction(solidity::Instruction::ISZERO);
+	AbstractAssembly::LabelID end = m_assembly.newLabelId();
+	m_assembly.appendJumpToIf(end);
+	(*this)(_if.body);
+	m_assembly.setSourceLocation(_if.location);
+	m_assembly.appendLabel(end);
+	checkStackHeight(&_if);
+}
+
 void CodeTransform::operator()(Switch const& _switch)
 {
 	//@TODO use JUMPV in EVM1.5?
diff --git a/libjulia/backends/evm/EVMCodeTransform.h b/libjulia/backends/evm/EVMCodeTransform.h
index 951c8a50..387720a2 100644
--- a/libjulia/backends/evm/EVMCodeTransform.h
+++ b/libjulia/backends/evm/EVMCodeTransform.h
@@ -104,6 +104,7 @@ public:
 	void operator()(solidity::assembly::StackAssignment const& _assignment);
 	void operator()(solidity::assembly::Assignment const& _assignment);
 	void operator()(solidity::assembly::VariableDeclaration const& _varDecl);
+	void operator()(solidity::assembly::If const& _if);
 	void operator()(solidity::assembly::Switch const& _switch);
 	void operator()(solidity::assembly::FunctionDefinition const&);
 	void operator()(solidity::assembly::ForLoop const&);
diff --git a/libsolidity/analysis/ViewPureChecker.cpp b/libsolidity/analysis/ViewPureChecker.cpp
index 7f28c7d2..7e41fc16 100644
--- a/libsolidity/analysis/ViewPureChecker.cpp
+++ b/libsolidity/analysis/ViewPureChecker.cpp
@@ -72,6 +72,11 @@ public:
 		for (auto const& arg: _funCall.arguments)
 			boost::apply_visitor(*this, arg);
 	}
+	void operator()(assembly::If const& _if)
+	{
+		boost::apply_visitor(*this, *_if.condition);
+		(*this)(_if.body);
+	}
 	void operator()(assembly::Switch const& _switch)
 	{
 		boost::apply_visitor(*this, *_switch.expression);
diff --git a/libsolidity/codegen/ABIFunctions.cpp b/libsolidity/codegen/ABIFunctions.cpp
index d2cbac99..bb39cbbb 100644
--- a/libsolidity/codegen/ABIFunctions.cpp
+++ b/libsolidity/codegen/ABIFunctions.cpp
@@ -168,7 +168,7 @@ string ABIFunctions::cleanupFunction(Type const& _type, bool _revertOnFailure)
 		{
 			size_t members = dynamic_cast<EnumType const&>(_type).numberOfMembers();
 			solAssert(members > 0, "empty enum should have caused a parser error.");
-			Whiskers w("switch lt(value, <members>) case 0 { <failure> } cleaned := value");
+			Whiskers w("if iszero(lt(value, <members>)) { <failure> } cleaned := value");
 			w("members", to_string(members));
 			if (_revertOnFailure)
 				w("failure", "revert(0, 0)");
@@ -988,8 +988,8 @@ string ABIFunctions::copyToMemoryFunction(bool _fromCalldata)
 					{
 						mstore(add(dst, i), mload(add(src, i)))
 					}
-					switch eq(i, length)
-					case 0 {
+					if gt(i, length)
+					{
 						// clear end
 						mstore(add(dst, length), 0)
 					}
diff --git a/libsolidity/inlineasm/AsmAnalysis.cpp b/libsolidity/inlineasm/AsmAnalysis.cpp
index e5bdc90f..2804ddfc 100644
--- a/libsolidity/inlineasm/AsmAnalysis.cpp
+++ b/libsolidity/inlineasm/AsmAnalysis.cpp
@@ -286,6 +286,22 @@ bool AsmAnalyzer::operator()(assembly::FunctionCall const& _funCall)
 	return success;
 }
 
+bool AsmAnalyzer::operator()(If const& _if)
+{
+	bool success = true;
+
+	if (!expectExpression(*_if.condition))
+		success = false;
+	m_stackHeight--;
+
+	if (!(*this)(_if.body))
+		success = false;
+
+	m_info.stackHeightInfo[&_if] = m_stackHeight;
+
+	return success;
+}
+
 bool AsmAnalyzer::operator()(Switch const& _switch)
 {
 	bool success = true;
diff --git a/libsolidity/inlineasm/AsmAnalysis.h b/libsolidity/inlineasm/AsmAnalysis.h
index 9b2a8f9c..e484b876 100644
--- a/libsolidity/inlineasm/AsmAnalysis.h
+++ b/libsolidity/inlineasm/AsmAnalysis.h
@@ -70,6 +70,7 @@ public:
 	bool operator()(assembly::VariableDeclaration const& _variableDeclaration);
 	bool operator()(assembly::FunctionDefinition const& _functionDefinition);
 	bool operator()(assembly::FunctionCall const& _functionCall);
+	bool operator()(assembly::If const& _if);
 	bool operator()(assembly::Switch const& _switch);
 	bool operator()(assembly::ForLoop const& _forLoop);
 	bool operator()(assembly::Block const& _block);
diff --git a/libsolidity/inlineasm/AsmData.h b/libsolidity/inlineasm/AsmData.h
index b0dd85ca..a792a1b8 100644
--- a/libsolidity/inlineasm/AsmData.h
+++ b/libsolidity/inlineasm/AsmData.h
@@ -68,6 +68,8 @@ struct VariableDeclaration { SourceLocation location; TypedNameList variables; s
 struct Block { SourceLocation location; std::vector<Statement> statements; };
 /// Function definition ("function f(a, b) -> (d, e) { ... }")
 struct FunctionDefinition { SourceLocation location; std::string name; TypedNameList arguments; TypedNameList returns; Block body; };
+/// Conditional execution without "else" part.
+struct If { SourceLocation location; std::shared_ptr<Statement> condition; Block body; };
 /// Switch case or default case
 struct Case { SourceLocation location; std::shared_ptr<Literal> value; Block body; };
 /// Switch statement
diff --git a/libsolidity/inlineasm/AsmDataForward.h b/libsolidity/inlineasm/AsmDataForward.h
index 4ead7ff5..d627b41a 100644
--- a/libsolidity/inlineasm/AsmDataForward.h
+++ b/libsolidity/inlineasm/AsmDataForward.h
@@ -41,11 +41,12 @@ struct VariableDeclaration;
 struct FunctionalInstruction;
 struct FunctionDefinition;
 struct FunctionCall;
+struct If;
 struct Switch;
 struct ForLoop;
 struct Block;
 
-using Statement = boost::variant<Instruction, Literal, Label, StackAssignment, Identifier, Assignment, FunctionCall, FunctionalInstruction, VariableDeclaration, FunctionDefinition, Switch, ForLoop, Block>;
+using Statement = boost::variant<Instruction, Literal, Label, StackAssignment, Identifier, Assignment, FunctionCall, FunctionalInstruction, VariableDeclaration, FunctionDefinition, If, Switch, ForLoop, Block>;
 
 }
 }
diff --git a/libsolidity/inlineasm/AsmParser.cpp b/libsolidity/inlineasm/AsmParser.cpp
index 1f4df75b..8f171005 100644
--- a/libsolidity/inlineasm/AsmParser.cpp
+++ b/libsolidity/inlineasm/AsmParser.cpp
@@ -73,13 +73,23 @@ assembly::Statement Parser::parseStatement()
 		return parseFunctionDefinition();
 	case Token::LBrace:
 		return parseBlock();
+	case Token::If:
+	{
+		assembly::If _if = createWithLocation<assembly::If>();
+		m_scanner->next();
+		_if.condition = make_shared<Statement>(parseExpression());
+		if (_if.condition->type() == typeid(assembly::Instruction))
+			fatalParserError("Instructions are not supported as conditions for if - try to append \"()\".");
+		_if.body = parseBlock();
+		return _if;
+	}
 	case Token::Switch:
 	{
 		assembly::Switch _switch = createWithLocation<assembly::Switch>();
 		m_scanner->next();
 		_switch.expression = make_shared<Statement>(parseExpression());
 		if (_switch.expression->type() == typeid(assembly::Instruction))
-			fatalParserError("Instructions are not supported as expressions for switch.");
+			fatalParserError("Instructions are not supported as expressions for switch - try to append \"()\".");
 		while (m_scanner->currentToken() == Token::Case)
 			_switch.cases.emplace_back(parseCase());
 		if (m_scanner->currentToken() == Token::Default)
diff --git a/libsolidity/inlineasm/AsmPrinter.cpp b/libsolidity/inlineasm/AsmPrinter.cpp
index a5272808..0f183244 100644
--- a/libsolidity/inlineasm/AsmPrinter.cpp
+++ b/libsolidity/inlineasm/AsmPrinter.cpp
@@ -174,6 +174,11 @@ string AsmPrinter::operator()(assembly::FunctionCall const& _functionCall)
 		")";
 }
 
+string AsmPrinter::operator()(If const& _if)
+{
+	return "if " + boost::apply_visitor(*this, *_if.condition) + "\n" + (*this)(_if.body);
+}
+
 string AsmPrinter::operator()(Switch const& _switch)
 {
 	string out = "switch " + boost::apply_visitor(*this, *_switch.expression);
diff --git a/libsolidity/inlineasm/AsmPrinter.h b/libsolidity/inlineasm/AsmPrinter.h
index 66520632..eadf81d9 100644
--- a/libsolidity/inlineasm/AsmPrinter.h
+++ b/libsolidity/inlineasm/AsmPrinter.h
@@ -48,6 +48,7 @@ public:
 	std::string operator()(assembly::VariableDeclaration const& _variableDeclaration);
 	std::string operator()(assembly::FunctionDefinition const& _functionDefinition);
 	std::string operator()(assembly::FunctionCall const& _functionCall);
+	std::string operator()(assembly::If const& _if);
 	std::string operator()(assembly::Switch const& _switch);
 	std::string operator()(assembly::ForLoop const& _forLoop);
 	std::string operator()(assembly::Block const& _block);
diff --git a/libsolidity/inlineasm/AsmScopeFiller.cpp b/libsolidity/inlineasm/AsmScopeFiller.cpp
index b70ae9ac..77ae9102 100644
--- a/libsolidity/inlineasm/AsmScopeFiller.cpp
+++ b/libsolidity/inlineasm/AsmScopeFiller.cpp
@@ -104,6 +104,11 @@ bool ScopeFiller::operator()(assembly::FunctionDefinition const& _funDef)
 	return success;
 }
 
+bool ScopeFiller::operator()(If const& _if)
+{
+	return (*this)(_if.body);
+}
+
 bool ScopeFiller::operator()(Switch const& _switch)
 {
 	bool success = true;
diff --git a/libsolidity/inlineasm/AsmScopeFiller.h b/libsolidity/inlineasm/AsmScopeFiller.h
index 80c03d2c..ed28abbf 100644
--- a/libsolidity/inlineasm/AsmScopeFiller.h
+++ b/libsolidity/inlineasm/AsmScopeFiller.h
@@ -59,6 +59,7 @@ public:
 	bool operator()(assembly::VariableDeclaration const& _variableDeclaration);
 	bool operator()(assembly::FunctionDefinition const& _functionDefinition);
 	bool operator()(assembly::FunctionCall const&) { return true; }
+	bool operator()(assembly::If const& _if);
 	bool operator()(assembly::Switch const& _switch);
 	bool operator()(assembly::ForLoop const& _forLoop);
 	bool operator()(assembly::Block const& _block);
diff --git a/test/libjulia/Parser.cpp b/test/libjulia/Parser.cpp
index f8c1aa4d..9aa325a4 100644
--- a/test/libjulia/Parser.cpp
+++ b/test/libjulia/Parser.cpp
@@ -269,6 +269,21 @@ BOOST_AUTO_TEST_CASE(multiple_assignment)
 	BOOST_CHECK(successParse(text));
 }
 
+BOOST_AUTO_TEST_CASE(if_statement)
+{
+	BOOST_CHECK(successParse("{ if true:bool {} }"));
+	BOOST_CHECK(successParse("{ if false:bool { let x:u256 := 3:u256 } }"));
+	BOOST_CHECK(successParse("{ function f() -> x:bool {} if f() { let b:bool := f() } }"));
+}
+
+BOOST_AUTO_TEST_CASE(if_statement_invalid)
+{
+	CHECK_ERROR("{ if let x:u256 {} }", ParserError, "Literal or identifier expected.");
+	CHECK_ERROR("{ if true:bool let x:u256 := 3:u256 }", ParserError, "Expected token LBrace");
+	// TODO change this to an error once we check types.
+	BOOST_CHECK(successParse("{ if 42:u256 { } }"));
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }
diff --git a/test/libsolidity/InlineAssembly.cpp b/test/libsolidity/InlineAssembly.cpp
index da3522b4..e9fb8431 100644
--- a/test/libsolidity/InlineAssembly.cpp
+++ b/test/libsolidity/InlineAssembly.cpp
@@ -251,6 +251,27 @@ BOOST_AUTO_TEST_CASE(variable_use_before_decl)
 	CHECK_PARSE_ERROR("{ let x := mul(2, x) }", DeclarationError, "Variable x used before it was declared.");
 }
 
+BOOST_AUTO_TEST_CASE(if_statement)
+{
+	BOOST_CHECK(successParse("{ if 42 {} }"));
+	BOOST_CHECK(successParse("{ if 42 { let x := 3 } }"));
+	BOOST_CHECK(successParse("{ function f() -> x {} if f() { pop(f()) } }"));
+}
+
+BOOST_AUTO_TEST_CASE(if_statement_scope)
+{
+	BOOST_CHECK(successParse("{ let x := 2 if 42 { x := 3 } }"));
+	CHECK_PARSE_ERROR("{ if 32 { let x := 3 } x := 2 }", DeclarationError, "Variable not found or variable not lvalue.");
+}
+
+BOOST_AUTO_TEST_CASE(if_statement_invalid)
+{
+	CHECK_PARSE_ERROR("{ if calldatasize {}", ParserError, "Instructions are not supported as conditions for if");
+	BOOST_CHECK("{ if calldatasize() {}");
+	CHECK_PARSE_ERROR("{ if mstore(1, 1) {} }", ParserError, "Instruction \"mstore\" not allowed in this context");
+	CHECK_PARSE_ERROR("{ if 32 let x := 3 }", ParserError, "Expected token LBrace");
+}
+
 BOOST_AUTO_TEST_CASE(switch_statement)
 {
 	BOOST_CHECK(successParse("{ switch 42 default {} }"));
@@ -275,7 +296,7 @@ BOOST_AUTO_TEST_CASE(switch_duplicate_case)
 BOOST_AUTO_TEST_CASE(switch_invalid_expression)
 {
 	CHECK_PARSE_ERROR("{ switch {} default {} }", ParserError, "Literal, identifier or instruction expected.");
-	CHECK_PARSE_ERROR("{ switch calldatasize default {} }", ParserError, "Instructions are not supported as expressions for switch.");
+	CHECK_PARSE_ERROR("{ switch calldatasize default {} }", ParserError, "Instructions are not supported as expressions for switch");
 	CHECK_PARSE_ERROR("{ switch mstore(1, 1) default {} }", ParserError, "Instruction \"mstore\" not allowed in this context");
 }
 
@@ -487,6 +508,11 @@ BOOST_AUTO_TEST_CASE(print_string_literal_unicode)
 	parsePrintCompare(parsed);
 }
 
+BOOST_AUTO_TEST_CASE(print_if)
+{
+	parsePrintCompare("{\n    if 2\n    {\n        pop(mload(0))\n    }\n}");
+}
+
 BOOST_AUTO_TEST_CASE(print_switch)
 {
 	parsePrintCompare("{\n    switch 42\n    case 1 {\n    }\n    case 2 {\n    }\n    default {\n    }\n}");
@@ -628,6 +654,11 @@ BOOST_AUTO_TEST_CASE(for_statement)
 	BOOST_CHECK(successAssemble("{ let x := calldatasize() for { let i := 0} lt(i, x) { i := add(i, 1) } { mstore(i, 2) } }"));
 }
 
+BOOST_AUTO_TEST_CASE(if_statement)
+{
+	BOOST_CHECK(successAssemble("{ if 1 {} }"));
+	BOOST_CHECK(successAssemble("{ let x := 0 if eq(calldatasize(), 0) { x := 1 } mstore(0, x) }"));
+}
 
 BOOST_AUTO_TEST_CASE(large_constant)
 {
diff --git a/test/libsolidity/SolidityEndToEndTest.cpp b/test/libsolidity/SolidityEndToEndTest.cpp
index c2f96aaa..05dc9ba3 100644
--- a/test/libsolidity/SolidityEndToEndTest.cpp
+++ b/test/libsolidity/SolidityEndToEndTest.cpp
@@ -8032,6 +8032,24 @@ BOOST_AUTO_TEST_CASE(inline_assembly_embedded_function_call)
 	ABI_CHECK(callContractFunction("f()"), encodeArgs(u256(1), u256(4), u256(7), u256(0x10)));
 }
 
+BOOST_AUTO_TEST_CASE(inline_assembly_if)
+{
+	char const* sourceCode = R"(
+		contract C {
+			function f(uint a) returns (uint b) {
+				assembly {
+					if gt(a, 1) { b := 2 }
+				}
+			}
+		}
+	)";
+	compileAndRun(sourceCode, 0, "C");
+	ABI_CHECK(callContractFunction("f(uint256)", u256(0)), encodeArgs(u256(0)));
+	ABI_CHECK(callContractFunction("f(uint256)", u256(1)), encodeArgs(u256(0)));
+	ABI_CHECK(callContractFunction("f(uint256)", u256(2)), encodeArgs(u256(2)));
+	ABI_CHECK(callContractFunction("f(uint256)", u256(3)), encodeArgs(u256(2)));
+}
+
 BOOST_AUTO_TEST_CASE(inline_assembly_switch)
 {
 	char const* sourceCode = R"(