Uploaded image for project: 'JDK'
  1. JDK
  2. JDK-8221647

[lworld] Performance regression due to the fact that check if array is array of values is not hoisted out of the loop.

    Details

    • Type: Bug
    • Status: Resolved
    • Priority: P1
    • Resolution: Fixed
    • Affects Version/s: repo-valhalla
    • Fix Version/s: repo-valhalla
    • Component/s: hotspot
    • Labels:

      Description

      Large performance regression is observed on numerous legacy (non-value) code working with Object[] arrays comparing -XX:+EnableValhalla vs -XX:-EnableValhalla

      For example:
      - Arrays.hasCode(Object[]) - 60% slowdown
      - for loop Object[] to Object[] copying - 2x times slowdown
      - pass elements of Object[] - 90% slowdown.
      - etc....

      Small set of simple benchmarks could be found here http://cr.openjdk.java.net/~skuksenko/valhalla/arrayloop/benchmarks/

      The reason of that that check if arrays is flattened value array was not hoisted out of the loop and checked on each iteration.

       asm for check (e.g.):
       mov 0x8(%r10),%r8d
       sar $0x1d,%r8d
       cmp $0xfffffffd,%r8d
       jne 0x00007f4d008cc2ad

        Attachments

          Issue Links

            Activity

              People

              • Assignee:
                roland Roland Westrelin
                Reporter:
                skuksenko Sergey Kuksenko
              • Votes:
                0 Vote for this issue
                Watchers:
                2 Start watching this issue

                Dates

                • Created:
                  Updated:
                  Resolved: