RFR: 8139457: Array bases are aligned at HeapWord granularity [v36]
Roman Kennke
rkennke at openjdk.org
Wed Jun 14 09:55:15 UTC 2023
> See [JDK-8139457](https://bugs.openjdk.org/browse/JDK-8139457) for details.
>
> Basically, when running with -XX:-UseCompressedClassPointers, arrays will have a gap between the length field and the first array element, because array elements will only start at word-aligned offsets. This is not necessary for smaller-than-word elements.
>
> Also, while it is not very important now, it will become very important with Lilliput, which eliminates the Klass field and would always put the length field at offset 8, and leave a gap between offset 12 and 16.
>
> Testing:
> - [x] runtime/FieldLayout/ArrayBaseOffsets.java (x86_64, x86_32, aarch64, arm, riscv, s390)
> - [x] bootcycle (x86_64, x86_32, aarch64, arm, riscv, s390)
> - [x] tier1 (x86_64, x86_32, aarch64, riscv)
> - [x] tier2 (x86_64, aarch64, riscv)
> - [x] tier3 (x86_64, riscv)
Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
Correctly handle oop array element aligment in 32bit builds; move method from Universe to Array
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/11044/files
- new: https://git.openjdk.org/jdk/pull/11044/files/70c05b83..f93faf5a
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=11044&range=35
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=11044&range=34-35
Stats: 20 lines in 2 files changed: 12 ins; 7 del; 1 mod
Patch: https://git.openjdk.org/jdk/pull/11044.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/11044/head:pull/11044
PR: https://git.openjdk.org/jdk/pull/11044
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