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  1. JDK
  2. JDK-8015417

profile pollution after call through invokestatic to shared code

    Details

    • Type: Enhancement
    • Status: Open
    • Priority: P3
    • Resolution: Unresolved
    • Affects Version/s: 9, 10
    • Fix Version/s: tbd
    • Component/s: hotspot
    • Labels:

      Description

      If M calls Objects.equals(x, y), then the call to x.equals(y) inside the Objects.equals must use a polluted profile.

      If (in addition) x and y have no inferred type in M, then even if Objects.equals is inlined, there is no way to optimistically type x.

      If M calls x.equals(y) directly, then the invokevirtual instruction in M is a profile point which can contribute the useful type information for x (but not y).

      There are two possible solutions; either or both could be taken:

      1. Add profiling to invokestatic, if the first argument is a reference. This is JDK-6919064 .

      2. Add split profiles to tiered code. This is JDK-8015416 .

      A plausible metric for success is that a micro benchmark that calls Objects.equals(x,y) is comparable in speed to one that calls x.equals(y) directly, even when the global type profile for Object.equals is polluted by warm-up calls to objects of a variety of types.

      Notes:

      The same considerations apply to invokedynamic as for invokestatic, since those two instructions have no stacked receiver argument.

      Suggestion #1 aims at the common case of a leading reference parameter, but will not help if the method takes no arguments, or if its first argument is not a reference. Suggestion #2 allows more precise collection of type information, assuming that tier-one inlining has reached all relevant invokevirtual instructions.

      The checkcast, instanceof, and aastore instructions were profiled as of JDK-6516101 and JDK-6912064 .

      Global profiling was added to tier one as of JDK-6919069 and JDK-7091764 . Split profiling is requested by /JDK-8015416 .

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              • Assignee:
                Unassigned
                Reporter:
                jrose John Rose
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                • Created:
                  Updated: