RFR: 8139457: Array bases are aligned at HeapWord granularity [v8]
Roman Kennke
rkennke at openjdk.org
Fri Dec 16 10:00:12 UTC 2022
> 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 two additional commits since the last revision:
- Revert relaxation of array length
- Add guards to ArrayBaseOffsets test to allow running with -UseCompressedClassPointers
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/11044/files
- new: https://git.openjdk.org/jdk/pull/11044/files/4ec977cf..8e5c9f9f
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=11044&range=07
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=11044&range=06-07
Stats: 17 lines in 5 files changed: 2 ins; 10 del; 5 mod
Patch: https://git.openjdk.org/jdk/pull/11044.diff
Fetch: git fetch https://git.openjdk.org/jdk pull/11044/head:pull/11044
PR: https://git.openjdk.org/jdk/pull/11044
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