RFR: 8332189: Enable -Wzero-as-null-pointer-constant for gcc/clang [v2]

[Afshin Zafari]

On Tue, 10 Feb 2026 05:44:09 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Please review this change which enables `-Wzero-as-null-pointer-constant`
>> warnings in HotSpot code when building with gcc or clang.
>> 
>> There are three parts to this change.
>> 
>> The first part augments the warning flags setup to support adding warning
>> options that are only applied to HotSpot, rather than the JDK as a whole.
>> There was previously some unused and possibly incomplete support for this when
>> using gcc. Note that the Windows/Visual Studio support hasn't been tested
>> much, and I think might not be working yet. I'm going to investigate that
>> further in followup work.
>> 
>> The second part enables `-Wzero-as-null-pointer-constant` for HotSpot code.
>> This follows the guidance to avoid such in the HotSpot Style Guide.
>> 
>> The third part removes a note in the HotSpot Style Guide about lingering uses
>> of literal 0 as a null pointer constant.  Those have been removed, and this
>> change will block backsliding.
>> 
>> Testing: mach5 tier1, GHA Sanity tests
>> 
>> Integration of this change needs to wait for JDK-8376758.
>
> Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update copyright

Thanks.
LGTM.

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Marked as reviewed by azafari (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/29497#pullrequestreview-3777769510