[Webkit-unassigned] [Bug 20814] New: V8 tests spend fair amount of time in property lookup cache misses

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=20814

           Summary: V8 tests spend fair amount of time in property lookup
                    cache misses
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Macintosh
        OS/Version: Mac OS X 10.5
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: mjs at apple.com


A number of the V8 tests spend significant time in cti_op_get_by_id_generic,
indicating misses of the polymorphic inline cache. Some of the causes include:

- Math object properties being accessed in a pattern that makes the structure
ID change (since the function properties are created on demand). We might want
to pre-populate all at once, perhaps, or at least prebuild the structure ID and
leave "placeholder" values of some kind.
- Legitimate polymorphism, which we could handle either by making the generic
case faster, or by making the polymorphic inline cache truly polymorphic up to
some limit.
- Unknown causes perhaps due to bugs in our cache logic.

This most heavily affects DeltaBlue (to the tune of 23.2%) but Richards (6.4%),
Raytrace (3.2%), and Crypto(1.9%) are also somewhat affected. See bug 20813 for
profiles.


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