RFR: 8305896: Alternative full GC forwarding [v38]

[Roman Kennke]

On Tue, 9 May 2023 12:33:58 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix build
>
> src/hotspot/share/gc/shared/slidingForwarding.cpp line 68:
> 
>> 66:     _region_mask = ~((uintptr_t(1) << _region_size_bytes_shift) - 1);
>> 67: 
>> 68:     guarantee((_heap_start_region_bias << _region_size_bytes_shift) == (uintptr_t)_heap_start, "must be aligned");
> 
> This guarantee seems to blow up on Serial when the heap size isn't a power of two.

Apparently this happens when heap is not aligned properly. I integrated @tschatzl's fix and added a test config to TestSystemGCWithSerial.java which checks the situation.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13582#discussion_r1188580688