RFR: 8364588: Export the NPE backtracking functionality to general null-checking APIs [v4]

[David Holmes]

On Tue, 5 Aug 2025 16:04:08 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Provide a general facility for our null check APIs like Objects::requireNonNull or future Checks::nullCheck (void), converting the existing infrastructure to start tracking from a given stack site (depth offset) and a given stack slot (offset value).
>> 
>> This is a necessary prerequisite for https://bugs.openjdk.org/browse/JDK-8233268, which proposes enhanced null messages to `Objects::requireNonNull`.
>
> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update NPE per roger review

src/hotspot/share/interpreter/bytecodeUtils.cpp line 205:

> 203:     // A slot is found
> 204:     FOUND
> 205:   };

So you define an ENUM to capture the negative cases but then you can use any int >= 0 and pretend it is a member of the enum. ?? Is that typical C++ enum usage?

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PR Review Comment: https://git.openjdk.org/jdk/pull/26600#discussion_r2373618080