[Webkit-unassigned] [Bug 149531] New: We should only expect a RareCaseProfile to exist if the rare case actually exists

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=149531

            Bug ID: 149531
           Summary: We should only expect a RareCaseProfile to exist if
                    the rare case actually exists
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Local Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mark.lam at apple.com

The current code that calls rareCaseProfileForBytecodeOffset() always assumes that it will always return a non-null RareCaseProfile.  As a result, op_add in the baseline JIT is forced to add a dummy slow case that will never be taken, only to ensure that the RareCaseProfile for that bytecode is created, and it will always produce a counter value of 0 (since that path will never be taken).  Instead, we'll make the callers of rareCaseProfileForBytecodeOffset() check if the profile actually exist before dereferencing it.

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