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  1. JDK
  2. JDK-8039999

Investigate performance implications of castPP removal

    Details

    • Type: Enhancement
    • Status: Closed
    • Priority: P4
    • Resolution: Won't Fix
    • Affects Version/s: 9
    • Fix Version/s: None
    • Component/s: hotspot
    • Labels:
      None
    • Subcomponent:
    • Introduced In Version:
      9
    • CPU:
      generic
    • OS:
      generic

      Description

      JDK-8034216 eagerly removes all castPP nodes after CCP phase. This can have performance implications, since NotNull type information might be lost. See earlier concerns:


      May be we should investigate if the next performance statement about jvm98 is still true and solve it differently (in PhiNode::Ideal() for example):

      // I tried to leave the CastPP's in. This makes the graph more accurate in
      // some sense; we get to keep around the knowledge that an oop is not-null
      // after some test. Alas, the CastPP's interfere with GVN (some values are
      // the regular oop, some are the CastPP of the oop, all merge at Phi's which
      // cannot collapse, etc). This cost us 10% on SpecJVM, even when I removed
      // some of the more trivial cases in the optimizer. Removing more useless
      // Phi's started allowing Loads to illegally float above null checks. I gave
      // up on this approach. CNC 10/20/2000

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              • Assignee:
                roland Roland Westrelin
                Reporter:
                anoll Albert Noll (Inactive)
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                • Created:
                  Updated:
                  Resolved: