RFR: 8309044: Replace NULL with nullptr, final sweep of hotspot code [v2]

[Kim Barrett]

On Tue, 30 May 2023 19:15:38 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> A final sweep of Hotspot to remove all re-added NULLs. With only 110 changes I'd appreciate if this was considered trivial.
>
> Johan Sjölen has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Align
>  - Suggestions

I don't think `#pragma GCC poison` works for us. It would complain about a
system or library header that uses NULL and is included after the pragma.

MSVC's deprecation pragma might work for this, at least for shared and
Windows-specific code. I couldn't find a way to use it for FORBID_C_FUNCTION,
but the problems I encountered for that don't seem applicable in this case.

However, there are still a lot of NULL's left.  All of the per-cpu .ad files,
and the jvmtiXXX.xsl files contain NULL's that will appear in the associated
generated code.  Also, NULL usage in gtests doesn't seem to have been addressed
yet.

But it does look like there's been a bit of backsliding:
https://bugs.openjdk.org/browse/JDK-8324286

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PR Comment: https://git.openjdk.org/jdk/pull/14198#issuecomment-1903531104