[Webkit-unassigned] [Bug 144787] New: REGRESSION(r180595): same-callee profiling no longer works

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=144787

            Bug ID: 144787
           Summary: REGRESSION(r180595): same-callee profiling no longer
                    works
    Classification: Unclassified
           Product: WebKit
           Version: 528+ (Nightly build)
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: rniwa at webkit.org

3/2/15, 6:56 PM Phil Pizlo:
It used to be the case that if you had a constructor that wasn't inlined, we'd be able to infer that the constructor's callee was a constant if it always was the same.  This was an important optimization because it allowed us to strength-reduce CreateThis into NewObject for constructors that couldn't be inlined for whatever reason.

r180595 broke this, because it removed the use of op_get_callee.  op_get_callee was primarily there to profile whether the callee happened to always be the same.  Now, because we get the callee from "this", we have no such profiling.

Worse, that change left op_get_callee in the codebase despite it being unused.

The right solution is probably to have create_this profile whether it always sees the same callee or not.

<rdar://problem/20016842>

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