[lworld] RFR: 8271910: [lworld] Heap functions/callbacks should support value fields [v2]

[Alex Menkov]

> The fix implements support for flat value object by heapwalking API.
> 
> FollowReferences/IterateThroughHeap are executed at safepoint and agent callbacks may request to set/update tags for the reported object. To store tags for flattened object at safepoint a special tag table is used (entries contain strong references to holder objects), entries from the table are converted to entries in main tag table outside of safepoint.

Alex Menkov has updated the pull request incrementally with one additional commit since the last revision:

  report flattened objects from IterateThroughHeap

-------------

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1576/files
  - new: https://git.openjdk.org/valhalla/pull/1576/files/e5e14bfa..51b31dcd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1576&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1576&range=00-01

  Stats: 108 lines in 1 file changed: 88 ins; 1 del; 19 mod
  Patch: https://git.openjdk.org/valhalla/pull/1576.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1576/head:pull/1576

PR: https://git.openjdk.org/valhalla/pull/1576