[Webkit-unassigned] [Bug 16568] New: Investigate different mechanism for storing immediate numbers

[bugzilla-daemon at webkit.org]

http://bugs.webkit.org/show_bug.cgi?id=16568

           Summary: Investigate different mechanism for storing immediate
                    numbers
           Product: WebKit
           Version: 525+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Enhancement
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: oliver at apple.com
                CC: eric at webkit.org, darin at apple.com


After much discussion we feel that there is a possibility that we can gain an
improvement in the performance of immediates if we switched from storing the
low 30 bits of integer values to instead storing the high 30 bits of the
double, this reduces us to about 20 bits of integer precision, but provides a
greater range.  It also has the benefit of removing special case logic and
branches from JSImmediate::from(double), it also removes the int->double cast
needed for standard mathematical operands.

That said this may reduce the performance of bitwise operators, and array
access, but we really needed to implement it to see what happens.

We'll need to fix various immediate optimisations we make for dealing with
pairs of immediate values.


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