RFR: 8275416: G1: remove unnecessary make_referent_alive in precleaning phase

[Albert Mingkun Yang]

On Tue, 19 Oct 2021 11:02:17 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple change of removing marking work in G1 precleaning. Evaluation using a contrived example shows ~20% reduction in precleaning. 
> 
> Test: hotspot_gc

Thanks for the review.

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PR: https://git.openjdk.java.net/jdk/pull/6003