[Webkit-unassigned] [Bug 69501] New: SpeculativeJIT::isKnownString() is wrong

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=69501

           Summary: SpeculativeJIT::isKnownString() is wrong
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: fpizlo at apple.com


It returns true if the child is a GetLocal and the local's prediction is PredictString.  But that's not right, since PredictString just means that the local is predicted to be a string, rather than it's known to be a string.

For some predictions, like array, boolean, and int32, we enforce predictions on local variables when we do a SetLocal.  But we don't do this for strings.  Hence, we can't have the same logic for strings as we have for those types.

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