LibJS: Add JumpUndefined bytecode

Userland/Libraries/LibJS/Bytecode/Instruction.h

@@ -40,6 +40,7 @@
     O(Jump)                       \
     O(JumpConditional)            \
     O(JumpNullish)                \
+    O(JumpUndefined)              \
     O(Call)                       \
     O(NewFunction)                \
     O(Return)                     \

Userland/Libraries/LibJS/Bytecode/Op.cpp

@@ -195,6 +195,17 @@ void JumpNullish::execute_impl(Bytecode::Interpreter& interpreter) const
         interpreter.jump(m_false_target.value());
 }
 
+void JumpUndefined::execute_impl(Bytecode::Interpreter& interpreter) const
+{
+    VERIFY(m_true_target.has_value());
+    VERIFY(m_false_target.has_value());
+    auto result = interpreter.accumulator();
+    if (result.is_undefined())
+        interpreter.jump(m_true_target.value());
+    else
+        interpreter.jump(m_false_target.value());
+}
+
 void Call::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     auto callee = interpreter.reg(m_callee);
@@ -439,6 +450,13 @@ String JumpNullish::to_string_impl(Bytecode::Executable const&) const
     return String::formatted("JumpNullish null:{} nonnull:{}", true_string, false_string);
 }
 
+String JumpUndefined::to_string_impl(Bytecode::Executable const&) const
+{
+    auto true_string = m_true_target.has_value() ? String::formatted("{}", *m_true_target) : "<empty>";
+    auto false_string = m_false_target.has_value() ? String::formatted("{}", *m_false_target) : "<empty>";
+    return String::formatted("JumpUndefined undefined:{} not undefined:{}", true_string, false_string);
+}
+
 String Call::to_string_impl(Bytecode::Executable const&) const
 {
     StringBuilder builder;

Userland/Libraries/LibJS/Bytecode/Op.h

@@ -377,6 +377,17 @@ public:
     String to_string_impl(Bytecode::Executable const&) const;
 };
 
+class JumpUndefined final : public Jump {
+public:
+    explicit JumpUndefined(Optional<Label> true_target = {}, Optional<Label> false_target = {})
+        : Jump(Type::JumpUndefined, move(true_target), move(false_target))
+    {
+    }
+
+    void execute_impl(Bytecode::Interpreter&) const;
+    String to_string_impl(Bytecode::Executable const&) const;
+};
+
 // NOTE: This instruction is variable-width depending on the number of arguments!
 class Call final : public Instruction {
 public:

Userland/Libraries/LibJS/Bytecode/Pass/GenerateCFG.cpp

@@ -58,7 +58,7 @@ void GenerateCFG::perform(PassPipelineExecutable& executable)
             continue;
         }
 
-        if (instruction.type() == Instruction::Type::JumpConditional || instruction.type() == Instruction::Type::JumpNullish) {
+        if (instruction.type() == Instruction::Type::JumpConditional || instruction.type() == Instruction::Type::JumpNullish || instruction.type() == Instruction::Type::JumpUndefined) {
             auto& true_target = static_cast<Op::Jump const&>(instruction).true_target();
             enter_label(true_target, current_block);
             auto& false_target = static_cast<Op::Jump const&>(instruction).false_target();