RFR: 8299703: GenShen: improvements in card scanning [v6]

[Y. Srinivas Ramakrishna]

On Thu, 2 Feb 2023 00:06:21 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Y. Srinivas Ramakrishna has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   guarantees to asserts (non-production), and warnings (production);
>>   review feedback.
>
> src/hotspot/share/gc/shenandoah/shenandoahScanRemembered.inline.hpp line 687:
> 
>> 685:                                    // compiler & interpreter are imprecise.
>> 686:       if (p < left && !obj->is_objArray()) {
>> 687:         if (OBJ_MARK_IMPRECISE) {
> 
> The code would be simpler if the case for handling `OBJ_MARK_IMPRECISE` were left out - perhaps moved to a descriptive comment? If we leave it in, could we name it `OBJ_MARK_ALWAYS_IMPRECISE` . The barriers do use imprecise card marks, so it's confusing to see this defined as `false`.

Yes, I agree that the naming is confusing, plus the unnecessary code clutter.

I removed that arm and associated preprocessor def'n, and fixed up the comments.

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PR: https://git.openjdk.org/shenandoah/pull/193