RFR: 8354428: [ubsan] g1BiasedArray.hpp: pointer overflow in address calculation [v3]

[Thomas Schatzl]

> Hi all,
> 
>   please review this fix for an ubsan error related to pointer under- or overflows when using the biased array helper.
> 
> The fix is, instead of using direct address calculations that can cause these errors, use `uintptr_t` where the overflow behavior is defined in C++. Only convert to pointer at the actual access.
> 
> Testing: gha, tier1

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  * kbarrett review

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25447/files
  - new: https://git.openjdk.org/jdk/pull/25447/files/a87b3ed8..ef4b6816

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25447&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25447&range=01-02

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/25447.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25447/head:pull/25447

PR: https://git.openjdk.org/jdk/pull/25447