RFR: 8273508: Support archived heap objects in SerialGC [v2]

[Thomas Schatzl]

On Tue, 21 Sep 2021 17:35:13 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> When `-XX:+UseSerialGC is enabled`, load the CDS archived heap objects into `SerialHeap::old_gen()` during VM bootstrap. This improves VM start-up time, mostly because the module graph can be loaded from the archive.
>> 
>> 
>> $ perf stat -r 40 java -XX:+UseSerialGC -version
>> 
>> Before: 0.042484507 seconds time elapsed ( +- 0.72% )
>> After:  0.031671000 seconds time elapsed ( +- 0.72% )
>> 
>> 
>> Changes in the gc subdirectories are contributed by @tschatzl
>
> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
> 
>   @tschatzl comments

GC changes (and the bits around them) seem good to me.

We already discussed the (existing) pervasive usage of `uintptr_t` in other code calling the gc code for addresses in the java heap and using size_t/int/intx/whatever for offsets in private which I do not recommend to do. However if there is any change to be made, it's a separate issue.

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Marked as reviewed by tschatzl (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/5596