[Webkit-unassigned] [Bug 283118] New: for-of loops noticeably slower than alternatives, including map

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=283118

            Bug ID: 283118
           Summary: for-of loops noticeably slower than alternatives,
                    including map
           Product: WebKit
           Version: Safari 18
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: rik at webkit.org

Created attachment 473227

  --> https://bugs.webkit.org/attachment.cgi?id=473227&action=review

Results in Safari, Firefox and Chrome

On the linked benchmark, a simple for-of loop performs noticeably worse than a forEach loop or a classic for loop.

It even performs worse than the equivalent map transformation which I find surprising because map has to do extra work (destructure the array, create a new one and replace it in the existing array).

Firefox and Chrome results are roughly what I would expect: map is the slowest, classic loop is the fastest, forEach and for-of are in between.

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