RFR: 8256011: Shenandoah: Don't resurrect finalizably reachable objects [v8]

[Aleksey Shipilev]

On Wed, 11 Nov 2020 15:55:19 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> In the weak-LRB we currently return referents when it is 'marked', that is when it's either reachable strongly or through a finalizable object. This means a finalizable object can be resurrected by Reference.get(), which is wrong. Only truly strongly reachable objects should be returned by Reference.get() during weak-reference-processing. 
>> 
>> I had to reconsider the way we call into runtime-LRBs from generated code for these reasons:
>>  - We need to distinguish phantom, weak and strong reference strength, and native vs in-heap access. Those are two orthogonal dimensions
>>  - We can have strong and phantom native referents, and strong and weak in-heap referents
>>  - Native referents are never compressed
>> 
>> Note that this depends on PR#1140.
>> 
>> Testing:
>>  - [x] hotspot_gc_shenandoah (x86_64, x64_32, aarch64)
>>  - [x] tier1 +UseShenandoahGC +ShenandoahVerify
>>  - [x] tier2 +UseShenandoahGC +ShenandoahVerify
>
> Roman Kennke has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 18 additional commits since the last revision:
> 
>  - Fix/invert condition in CmpP optimization
>  - Fix after merge
>  - Merge branch 'master' into JDK-8256011
>  - Merge branch 'master' into JDK-8256011
>  - Don't make phantom-access narrow (mistake when doing 32bit parts
>  - Remove superfluous LP64 in aarch64 part
>  - Fixes/missing parts for x86_64
>  - Aarch64 parts
>  - Whitespace changes
>  - Mask decorators in hash/cmp, not in ctor
>  - ... and 8 more: https://git.openjdk.java.net/jdk/compare/682e0e24...c0ee9346

This looks fine to me. Good to go, assuming the tests pass.

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Marked as reviewed by shade (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1109