RFR: 8331920: ubsan: g1CardSetContainers.inline.hpp:266:5: runtime error: index 2 out of bounds for type 'G1CardSetHowl::ContainerPtr [2]' reported [v3]

[Ivan Walulya]

> Hi all,
> 
> Please review this change to improve access to G1CardSetContainer VLA elements. Instead of  straightforward indexing, we obscure access through a base pointer and offsets to reduce the possibility of UB. 
> 
> Testing: Tier 1-3
>               - Local testing on Mac with `--enable-ubsan`.

Ivan Walulya has updated the pull request incrementally with one additional commit since the last revision:

  add const

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19300/files
  - new: https://git.openjdk.org/jdk/pull/19300/files/13652dc7..9b8b940f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19300&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19300&range=01-02

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/19300.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19300/head:pull/19300

PR: https://git.openjdk.org/jdk/pull/19300