RFR: 8297914: Remove java_lang_Class::process_archived_mirror()

[David Holmes]

On Wed, 4 Jan 2023 21:01:28 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> This is another prerequisite for [JDK-8296344](https://bugs.openjdk.org/browse/JDK-8296344).
> 
> Before this PR, when archiving mirror objects (i.e., instances of `java.lang.Class`):
> - We first allocate a copy of the mirror inside a safepoint. 
> - We then reinitialize the contents of the copy to the desired state (so that it can be used by `Klass::restore_unshareable_info()`
> 
> This copy-and-modify operation inside the safepoint makes it difficult to implement [JDK-8296344](https://bugs.openjdk.org/browse/JDK-8296344). It violates the requirements [1] and [2] as stated in [JDK-8298600](https://bugs.openjdk.org/browse/JDK-8298600). Also, the reinitialization code is complicated.
> 
> After this PR:
> - During the creation of each regular mirror object, we allocate a "scratch mirror" object, which has the states as expected by `Klass::restore_unshareable_info()`. See `java_lang_Class::create_scratch_mirror()`.
> - When the archive heap is dumped inside a safepoint, we use the scratch mirror, so we can avoid the copy-and-modify operation. See `HeapShared::archive_java_mirrors()`.
> 
> Testing: tiers 1-4

src/hotspot/share/classfile/javaClasses.cpp line 1062:

> 1060: //
> 1061: // Note: we archive the "scratch mirror" instead of k->java_mirror(), because the
> 1062: // later may contain dumptime-specific information that cannot be archived

s/later/latter/

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PR: https://git.openjdk.org/jdk/pull/11853