RFR: 8360288: Shenandoah crash at size_given_klass in op_degenerated [v3]

[William Kemper]

> Both degenerated and full GCs unload classes before reclaiming unmarked humongous objects. This may result in a null klass pointer dereference when asking humongous objects for their size.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Micro optimizations

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26256/files
  - new: https://git.openjdk.org/jdk/pull/26256/files/cb63787d..b75574da

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26256&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26256&range=01-02

  Stats: 11 lines in 2 files changed: 3 ins; 2 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/26256.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26256/head:pull/26256

PR: https://git.openjdk.org/jdk/pull/26256