[Yul] Support conditionals

libsolidity/codegen/ir/IRGeneratorForStatements.cpp

@@ -180,6 +180,24 @@ void IRGeneratorForStatements::endVisit(VariableDeclarationStatement const& _var
 				declare(m_context.addLocalVariable(*decl));
 }
 
+bool IRGeneratorForStatements::visit(Conditional const& _conditional)
+{
+	_conditional.condition().accept(*this);
+
+	string condition = expressionAsType(_conditional.condition(), *TypeProvider::boolean());
+	declare(_conditional);
+
+	m_code << "switch " << condition << "\n" "case 0 {\n";
+	_conditional.falseExpression().accept(*this);
+	assign(_conditional, _conditional.falseExpression());
+	m_code << "}\n" "default {\n";
+	_conditional.trueExpression().accept(*this);
+	assign(_conditional, _conditional.trueExpression());
+	m_code << "}\n";
+
+	return false;
+}
+
 bool IRGeneratorForStatements::visit(Assignment const& _assignment)
 {
 	_assignment.rightHandSide().accept(*this);

libsolidity/codegen/ir/IRGeneratorForStatements.h

@@ -48,6 +48,7 @@ public:
 	void initializeStateVar(VariableDeclaration const& _varDecl);
 
 	void endVisit(VariableDeclarationStatement const& _variableDeclaration) override;
+	bool visit(Conditional const& _conditional) override;
 	bool visit(Assignment const& _assignment) override;
 	bool visit(TupleExpression const& _tuple) override;
 	bool visit(IfStatement const& _ifStatement) override;

test/libsolidity/semanticTests/viaYul/conditional/conditional_multiple.sol

@@ -0,0 +1,10 @@
+contract A {
+	function f() public pure returns (uint) {
+		uint x = 3 < 0 ? 2 > 1 ? 2 : 1 : 7 > 2 ? 7 : 6;
+		return x;
+	}
+}
+// ====
+// compileViaYul: also
+// ----
+// f() -> 7

test/libsolidity/semanticTests/viaYul/conditional/conditional_true_false_literal.sol

@@ -0,0 +1,11 @@
+contract A {
+	function f() public pure returns (uint) {
+		uint x = true ? 1 : 0;
+		uint y = false ? 0 : 1;
+		return x + y;
+	}
+}
+// ====
+// compileViaYul: also
+// ----
+// f() -> 2

test/libsolidity/semanticTests/viaYul/conditional/conditional_tuple.sol

@@ -0,0 +1,11 @@
+contract A {
+	function f(bool cond) public pure returns (uint, uint) {
+		(uint a, uint b) = cond ? (1, 2) : (3, 4);
+		return (a, b);
+	}
+}
+// ====
+// compileViaYul: also
+// ----
+// f(bool): true -> 1, 2
+// f(bool): false -> 3, 4

test/libsolidity/semanticTests/viaYul/conditional/conditional_with_assignment.sol

@@ -0,0 +1,13 @@
+contract A {
+    function f() public pure returns (uint, uint, uint, uint) {
+		uint y1 = 1;
+		uint y2 = 1;
+		uint x = 3 < 0 ? y1 = 3 : 6;
+		uint z = 3 < 10 ? y2 = 5 : 6;
+		return (x, y1, y2, z);
+	}
+}
+// ====
+// compileViaYul: also
+// ----
+// f() -> 6, 1, 5, 5

test/libsolidity/semanticTests/viaYul/conditional/conditional_with_variables.sol

@@ -0,0 +1,13 @@
+contract A {
+	function f() public pure returns (uint, uint, uint, uint) {
+		uint x = 3;
+		uint y = 1;
+		uint z = (x > y) ? x : y;
+		uint w = x < y ? x : y;
+		return (x, y, z, w);
+	}
+}
+// ====
+// compileViaYul: also
+// ----
+// f() -> 3, 1, 3, 1