Bug 171421 – [JSC] Add @isUndefinedOrNullIgnoringMasquerade()

• Status: RESOLVED
• Resolution: DUPLICATE
• Component: JavaScriptCore

[Yusuke Suzuki]

In builtin JS, we have bunch of 


if (object === null || object === @undefined)

thing. Previously, this is written as follows.

if (object == null)

However, the above one recognizes document.all as null/undefined due to its masquerade.
So, they are rewritten.

But the above thing is,

1. From JS developer, it looks very storange because it seems `== null` is better.
2. It bloats bytecodes, effectively prevents us from inlining. Keep builtin JS function small is a bit important in terms of inlining.

So, to make the meaning explicit and tighten bytecode size, we would like to introduce a new bytecode, op_is_undefined_or_null_ignoring_masquerade.

[Alexey Shvayka]

(In reply to Yusuke Suzuki from comment #0)
> So, to make the meaning explicit and tighten bytecode size, we would like to
> introduce a new bytecode, op_is_undefined_or_null_ignoring_masquerade.

OpIsUndefinedOrNull was introduced in r239761.

*** This bug has been marked as a duplicate of bug 193127 ***