RFR: 8278568: Consolidate filler objects

[Thomas Schatzl]

On Mon, 13 Dec 2021 11:42:42 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

Lgtm.

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Marked as reviewed by tschatzl (Reviewer).

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