[Webkit-unassigned] [Bug 169250] New: LowerToAir should recognize subwidth variants of Equal(StrongCAS...)

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=169250

            Bug ID: 169250
           Summary: LowerToAir should recognize subwidth variants of
                    Equal(StrongCAS...)
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: fpizlo at apple.com

We currently don't turn Equal(StrongCAS...) into a direct branch on the CAS result for Width8 and Width16.  We can do it.  We'd have to match patterns like:

Equal(SExt8(StrongCAS(@exp, ...)), SExt8(@exp))

and

Equal(SExt8(StrongCAS(BitAnd(@exp, 0xff), ...)), SExt8(@exp))

Where the right-hand SExt8 is matched with sharing.

It's not super obvious how profitable this optimization will be, particularly if we have any optimizations that turn strong CAS into weak CAS.

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