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  1. JDK
  2. JDK-8245464

Shenandoah: allocate collection set bitmap at lower addresses

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    • gc
    • b25

        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.

              shade Aleksey Shipilev
              shade Aleksey Shipilev
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                Created:
                Updated:
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