[Webkit-unassigned] [Bug 81459] New: Strength reduction, RegExp.exec -> RegExp.test

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=81459

           Summary: Strength reduction, RegExp.exec -> RegExp.test
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: barraclough at apple.com


RegExp.prototype.exec & RegExp.prototype.test can both be used to test a regular expression for a match against a string - however exec is more expensive, since it allocates a matches array object.  In cases where the result is consumed in a boolean context the allocation of the matches array can be trivially elided.

For example:
    function f()
    {
        for (i =0; i < 10000000; ++i)
            if(!/a/.exec("a"))
                err = true;
    }

This is a 2.5x speedup on this example microbenchmark loop.

In a more advanced for of this optimization, we may be able to avoid allocating the array where access to the array can be observed.

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