RFR: 8279523: Parallel: Remove unnecessary PSScavenge::_to_space_top_before_gc

[Kim Barrett]

On Wed, 5 Jan 2022 16:09:01 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple change of removing an unnecessary field.
> 
> Test: hotspot_gc

Looks good.  I wonder if this is a leftover from something since discarded, like UseAdaptiveGCBoundary.

As further evidence that this change is okay, `save_to_space_top_before_gc()` was called immediately after `young_gen->to_space()->clear()`.

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6968