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  1. JDK
  2. JDK-8245464

Shenandoah: allocate collection set bitmap at lower addresses

    Details

    • Type: Enhancement
    • Status: Resolved
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: 8-shenandoah, 11-shenandoah, 14, 15
    • Fix Version/s: 15
    • Component/s: hotspot
    • Subcomponent:
      gc
    • Resolved In Build:
      b25

      Description

      LRB midpath has the in-cset check that tests the address against cset bitmap. The default address for that bitmap is quite huge, so we end up emitting a large address immediate for it:

        ...65: mov %rax,%r10
        ...68: shr $0x17,%r10
        ...6c: movabs $0x7f3c5533d000,%r11
        ...76: cmpb $0x0,(%r11,%r10,1)
        ...7b: je 0x00007f3c408f4e55

      We can help it if we put cset bitmap at lower addresses.

      For example with:
        https://cr.openjdk.java.net/~shade/8245464/webrev.01/

        ...65: mov %rax,%r10
        ...68: shr $0x17,%r10
        ...6c: mov $0x10000,%r11d
        ...72: cmpb $0x0,(%r11,%r10,1)
        ...77: je 0x00007f868c8ef355

      Immediate used to take 10 bytes, now it takes 6 bytes.

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              • Assignee:
                shade Aleksey Shipilev
                Reporter:
                shade Aleksey Shipilev
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                • Created:
                  Updated:
                  Resolved: