[lworld] RFR: 8364191: [lworld] Accesses to atomic flat fields prevent scalar replacement
Quan Anh Mai
qamai at openjdk.org
Mon Jul 28 14:52:32 UTC 2025
Hi,
Flat accesses prevent scalar replacement because they are mismatched accesses. It is also generally not possible to look through them, because the payload may contain an oop in the form of raw bits. As a result, this PR adds `LoadFlatNode` and `StoreFlatNode`, which act as high-level abstractions for atomic accesses on flat fields. When it is determined that there is no racing access on the flat field (e.g. because the holder object does not escape), these flat access nodes can be expanded into multiple accesses to each flattened fields, otherwise, they will be expanded into a sequence of inferring a payload and accessing memory with that payload.
I also fix an issue with deoptimization reallocation where we miss assigning the null marker of elements in a nullable flat array.
Please take a look and leave your reviews, thanks a lot.
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Commit messages:
- add LoadFlatNode and StoreFlatNode
Changes: https://git.openjdk.org/valhalla/pull/1518/files
Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1518&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8364191
Stats: 955 lines in 13 files changed: 746 ins; 187 del; 22 mod
Patch: https://git.openjdk.org/valhalla/pull/1518.diff
Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1518/head:pull/1518
PR: https://git.openjdk.org/valhalla/pull/1518
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