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LibJS: Avoid emptying the return value register in try/finally

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This works because at the end of the finally chunk, a
ContinuePendingUnwind is generated which copies the saved return value
register into the return value register. In cases where
ContinuePendingUnwind is not generated such as when there is a break
statement in the finally block, the fonction will return undefined which
is consistent with V8 and SpiderMonkey.
This commit is contained in:
Lucien Fiorini 2025-03-27 12:02:14 +01:00
parent 1844e10cd3
commit b684dc7134
3 changed files with 14 additions and 6 deletions
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4
Libraries/LibJS/Bytecode/Generator.h
View file

@ -274,8 +274,6 @@ public:
void emit_return(ScopedOperand value)
requires(IsOneOf<OpType, Op::Return, Op::Yield>)
{
// FIXME: Tell the call sites about the `saved_return_value` destination
// And take that into account in the movs below.
perform_needed_unwinds<OpType>();
if (must_enter_finalizer()) {
VERIFY(m_current_basic_block->finalizer() != nullptr);
@ -289,8 +287,6 @@ public:
else
emit<Bytecode::Op::Mov>(Operand(Register::saved_return_value()), value);
emit<Bytecode::Op::Mov>(Operand(Register::exception()), add_constant(Value {}));
// FIXME: Do we really need to clear the return value register here?
emit<Bytecode::Op::Mov>(Operand(Register::return_value()), add_constant(Value {}));
emit<Bytecode::Op::Jump>(Label { *m_current_basic_block->finalizer() });
return;
}

2
Libraries/LibJS/Bytecode/Interpreter.cpp
View file

@ -778,8 +778,6 @@ Interpreter::ResultAndReturnRegister Interpreter::run_executable(Executable& exe
auto return_value = js_undefined();
if (!reg(Register::return_value()).is_empty())
return_value = reg(Register::return_value());
else if (!reg(Register::saved_return_value()).is_empty())
return_value = reg(Register::saved_return_value());
auto exception = reg(Register::exception());
vm().run_queued_promise_jobs();

14
Libraries/LibJS/Tests/try-finally-break.js
View file

@ -490,3 +490,17 @@ test("Break with nested mixed try-catch/finally", () => {
expect(executionOrder).toEqual([1, 2]);
});
test("Break in finally return in try", () => {
function foo() {
do {
try {
return "bar";
} finally {
break;
}
} while (expect.fail("Continued after do-while loop"));
}
expect(foo()).toEqual(undefined);
});