RFR: 8315890: Attempts to load from nullptr in instanceKlass.cpp and unsafe.cpp [v2]

[Calvin Cheung]

On Mon, 30 Oct 2023 20:19:45 GMT, Matias Saavedra Silva <matsaave at openjdk.org> wrote:

>> Calls in instanceKlass.cpp and unsafe.cpp try to call an atomic load on method calls that could return nullptr. This patch ensures that nullptr is not passed into the load. Verified with tier1-5 tests.
>
> Matias Saavedra Silva has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Moved assert higher in call stack

Updated changes look good.

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Marked as reviewed by ccheung (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16405#pullrequestreview-1705152443