RFR: 8335298: Fix -Wzero-as-null-pointer-constant warning in G1CardSetContainers [v2]

[Kim Barrett]

On Tue, 2 Jul 2024 07:22:25 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> gcc treats a named constant zero as a null pointer constant.  C++14 restricts that to integer literal zeros.
>> C++03 and C++11 included non-literals.  DR903 was where the change was made, and C++14 C.2.2
>> suggests that DR was supposed to apply to C++11 too, even though not in the published text.  I've found
>> some related gcc bugs, but not about exactly this warning.
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52145
>> So yeah, it's probably a gcc bug that this triggers the warning.  I think that doesn't affect the chosen
>> workaround for the warning, but maybe I should augment the comment to discuss this.
>> https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#903
>
> There is already a gcc bug about this: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114573
> I'll update the comment to refer to it.  Hopefully there aren't too many more like this in our code, or I'm going
> to suggest punting on trying to enable the warning until that bug is fixed.

I've changed the comment to refer to the gcc bug.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19955#discussion_r1661982639