[Webkit-unassigned] [Bug 95953] New: Regressions on 32-bit platforms with revisions 125637 and 126387

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=95953

           Summary: Regressions on 32-bit platforms with revisions 125637
                    and 126387
           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: yuqiang.xian at intel.com
                CC: barraclough at apple.com, fpizlo at apple.com


Take a look at awfy.com (http://arewefastyet.com/?runs=1000&view=regress&machine=11), there are two obvious performance regressions.

The root cause is related to r125637, and it's further exposed in r126387. It's a typo in the baseline JIT compiler for op_get_by_val which causes the baseline JIT incorrectly falls back to the slow case. The value profiler knows the fact that the operation goes to the slow path, the DFG compiler then thinks it might clobber the world and the high level optimizations especially the local CSE are affected greatly.

The fix should recover both regressions. My local test indicates 5% on SunSpider, 2% on v8 and 23% on Kraken.

Patch forthcoming.

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