[Webkit-unassigned] [Bug 171421] New: [JSC] Add @isUndefinedOrNullIgnoringMasquerade()

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Fri Apr 28 00:51:47 PDT 2017


            Bug ID: 171421
           Summary: [JSC] Add @isUndefinedOrNullIgnoringMasquerade()
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: utatane.tea at gmail.com

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.

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