[lilliput-jdk17u:lilliput] RFR: 8308956: [Lilliput/JDK17] Fix some object initialization paths

[Aleksey Shipilev]

On Fri, 26 May 2023 14:43:24 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> src/hotspot/share/gc/shared/memAllocator.cpp line 388:
>> 
>>> 386:   assert(mem != NULL, "NULL object pointer");
>>> 387:   if (UseBiasedLocking) {
>>> 388:     oopDesc::set_mark(mem, _klass->prototype_header());
>> 
>> Not enough, I think, because there is a `oopDesc::set_mark` in the block below that would overwrite it.
>
> I think this one would be cleaner:
> 
> 
> if (UseCompactObjectHeaders) {
>   oopDesc::release_set_mark(mem, _klass->prototype_header());
> } else {
>   if (UseBiasedLocking) {
>     oopDesc::set_mark(mem, _klass->prototype_header());
>   } else {
>     // May be bootstrapping
>     oopDesc::set_mark(mem, markWord::prototype());
>   }
>   // Need a release store to ensure array/class length, mark word, and
>   // object zeroing are visible before setting the klass non-NULL, for
>   // concurrent collectors.
>   if (!UseCompactObjectHeaders) {
>     oopDesc::release_set_klass(mem, _klass);
>   }
> }

Copy this to `HeapShared::copy_roots` too.

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PR Review Comment: https://git.openjdk.org/lilliput-jdk17u/pull/28#discussion_r1206897247