On Mon, 18 Nov 2024 14:31:52 GMT, Emanuel Peter <epe...@openjdk.org> wrote:
>>> @rkennke Ok, fair enough. As far as I know, we at Oracle do not super care >>> about strict alignment `AlignVector`. But maybe other people care, and have >>> to make that tradeoff between vectorization and small object headers. >> >> BTW, this problem is not specific to UseCompactObjectHeaders - I think the >> same problem would happen with -UseCompressedClassPointers. With >> uncompressed class-pointers, byte[] would start at offset 20, while long[] >> start at offset 24. But nobody cares about -UCCP I think. >> >> What is the failure mode, though? When running with -UCOH and +AlignVector, >> would it crash or misbehave? Or would it (silently?) not vectorize? I think >> we could live with the latter, but not with the former. > > @rkennke >> BTW, this problem is not specific to UseCompactObjectHeaders - I think the >> same problem would happen with -UseCompressedClassPointers. With >> uncompressed class-pointers, byte[] would start at offset 20, while long[] >> start at offset 24. But nobody cares about -UCCP I think. > > Sure. But I guess some people will want to run both `AlignVector` and > `UseCompactObjectHeaders` in the future. Some machines simply do require > strict alignment. So they will have to live with that tradeoff. @eme64 Tbh I don't see how `AlignVector` can mitigate the issue if strict alignment is required unless the object base is guaranteed to be aligned at least as much as the vector length. ------------- PR Comment: https://git.openjdk.org/jdk/pull/20677#issuecomment-2483230986
