RFR: 8262885: Shenandoah: FullGC prologue does not need to save/restore heap has_forwarded_object flag [v2]

[Zhengyu Gu]

On Wed, 3 Mar 2021 13:27:12 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Zhengyu Gu has updated the pull request incrementally with three additional commits since the last revision:
>> 
>>  - Aleksey's comment
>>  - Removed whitespaces
>>  - Aleksey's comment
>
> Good!

> Yeah, but this code protects from some downstream code we are calling from the prologue to accidentally drop the flag. At least it should be asserted that `has_forwarded_objects` has the same value at the end of the prologue as it was at the beginning. Or better just leave this for safety?

Okay, I added assert. The restore code led me to search where it got overwritten, a bit confusing.

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PR: https://git.openjdk.java.net/jdk/pull/2797