RFR: 8278568: Consolidate filler objects [v2]

[Thomas Schatzl]

On Thu, 16 Dec 2021 14:33:28 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> In PSPromotionLAB exists some code that fills unused tails of promotion LABs, which is semantically the same as the CollectedHeap::fill* family of methods. They can be consolidated.
>> 
>> We also have ContiguousSpace::allocate_temporary_filler() which does the same, but is unused and can be removed. 
>> 
>> Testing:
>>  - [x] hotspot_gc
>>  - [x] tier1
>>  - [ ] tier2
>>  - [ ] tier3
>
> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Make min_dummy_object_size() constexpr, use trueInDebug

Still good.

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Marked as reviewed by tschatzl (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6814