RFR: 8256046: Shenandoah: Mix-in NULL_PTR in non-strong ShLRBNode's type [v3]

[Aleksey Shipilev]

On Tue, 10 Nov 2020 13:15:17 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> Testing found this problem (very rare/hard to reproduce):
>> 
>> # Internal Error (d:/a/jdk/jdk/jdk/src/hotspot/cpu/x86/macroAssembler_x86.cpp:880), pid=6160, tid=5828
>> # fatal error: DEBUG MESSAGE: unexpected null in intrinsic
>> 
>> I believe this may be caused by non-strong LRB reporting a non-NULL type by passing-through its input's type, even though it may actually return NULL on non-NULL inputs. If this serves as input to an intrinsic, it may lead to elimination of surrounding null-check, and thus end up passing a NULL to the intrinsic even thought it should not. 
>> 
>> Testing:
>>  - [x] hotspot_gc_shenandoah
>>  - [ ] tier1+Shenandoah
>>  - [ ] tier2+Shenandoah
>
> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Shuffle new code-paths to match rest of methods

Thanks. Looks fine to me.

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Marked as reviewed by shade (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1120