[Webkit-unassigned] [Bug 66747] New: There is no facility for profiling how the write barrier is used

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=66747

           Summary: There is no facility for profiling how the write
                    barrier is used
           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


Write barrier support was added to the JSC runtime in anticipation of the implementation of more sophisticated garbage collection schemes, such as possibly generational or incremental collection.  Write barrier fast paths can often be optimized for specific kinds of writes.  In some collectors, a store to a location that is in the heap can be optimized far more aggressively than a store to a location allocated outside the heap.  One example of this is the range-based generational barrier, which uses the heap address of the destination object as a quick check to see if the barrier needs to be run.

But designing such barriers requires knowing what kinds of writes programs tend to execute.  Currently, there is no way to tell the barrier what kind of write is being executed.  And there is no way to profile and report the kinds of writes encountered.

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