On Mon, 27 Apr 2026 17:03:33 GMT, Axel Boldt-Christmas <[email protected]> wrote:
>> Hello, >> >> Embdedded flat contended fields might not be included in the class' OopMap >> if there are no other oop fields in the holder class. >> >> Flat fields are handled separately in fieldLayoutBuilder.cpp, resulting in >> the current `_oop_count` not being updated if a flat field contains oops. >> This is OK, since the oop fields are handled at a later point in time. >> However, for contended fields, which are part of the contended group, >> embedded oop fields are only tracked if: `cg->oop_count() > 0`, which is not >> guaranteed to be true. >> >> I've written a test to see if the oop field is included in the class' OopMap >> and also changed the `_oop_count` field `_has_embedded_oops`, and changed >> that to a boolean property, which is how we've used it so far. >> >> Since embedded fields in flat paylods are not tracked in `cg->oop_fields()`, >> we can't do the assert that is currently there, so I just removed that. >> >> Testing: >> * New test fails without the fixes in fieldLayoutBuilder and passes with >> fixes >> * Running Oracle's tier1-3 >> >> --------- >> - [x] I confirm that I make this contribution in accordance with the >> [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). > > src/hotspot/share/classfile/fieldLayoutBuilder.cpp line 178: > >> 176: _oop_fields(nullptr), >> 177: _contended_group(contended_group), // -1 means no contended group, 0 >> means default contended group >> 178: _has_embedded_oops(false) {} > > I wonder if we should just remove the `_has_embedded_oops` completely. And > just unconditionally call `register_embedded_oops`. It already handles an > empty (no embedded oops) list of sub-blocks. > > It makes the code less complex, but we miss an optimisation in the case where > we have flattened a lot of values where no fields contains oops. > > But seems like the better optimization if this was a problem would be to > create a list of each raw block with oops, so we only walk those, rather than > all if one happens to contain an oop. I think this is a good idea and it does make the code a bit easier to reason about. ------------- PR Review Comment: https://git.openjdk.org/valhalla/pull/2371#discussion_r3153691169
