Bug 176473

Summary: pdfjs performance regresses if OSR exit uses arrayModeFromStructure() for observing ArrayModes.
Product: WebKit Reporter: Mark Lam <mark.lam>
Component: JavaScriptCoreAssignee: Nobody <webkit-unassigned>
Status: NEW    
Severity: Normal CC: fpizlo, jfbastien, keith_miller, msaboff, rmorisset, saam
Priority: P2    
Version: WebKit Nightly Build   
Hardware: Unspecified   
OS: Unspecified   

Mark Lam
Reported 2017-09-06 11:59:08 PDT
While working on https://bugs.webkit.org/show_bug.cgi?id=175144, we saw a 18-20% regression in pdfjs. This regression due to my changing the new OSR exit code to use arrayModeFromStructure() to compute the observed ArrayMode. Logging shows that the observed cell is a TypeUint8 array. Hence, arrayModeFromStructure() should have returned a more accurate ArrayMode profile, which should be better for performance. Instead, it resulted in a performance regression.
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