RFR: 8314329: AgeTable: add is_clear() & allocation spec, and relax assert to allow use of 0-index slot [v2]

[Y. Srinivas Ramakrishna]

On Fri, 19 Jan 2024 21:29:43 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> It's not obvious to me that `bool clear = _global_age_table[i]->is_clear();` is for assert-only. Looking at `ShenandoahAgeCensus::is_clear_global`, the whole methods looks like it's real/product logic.
>> 
>>> I expect that this will be used only for assertions, whenever it is, hence non-product.
>> 
>> Then, can its definition be guarded like following? My concern is that this API returns different value depending on whether it is a product build.
>> 
>> 
>> #ifdef ASSERT // or ifndef product
>> bool is_clear();
>> #endif
>> 
>> 
>> (Or, leaving it as an ordinary API seems OK as well, IMO.)
>
> Fair point. I'll fix this.

Made it #ifndef PRODUCT.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17470#discussion_r1459993014