[lworld+vector] RFR: 8311610: [lworld+vector] Clean-up of vector allocation in class VectorSupport [v3]

[Jatin Bhateja]

On Tue, 11 Jul 2023 10:07:45 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> PR [1] has added the vector supports for field re-assigning after object re-allocation in `deoptimization.cpp`. The similar vector
>> and vector payload re-allocation code in `vectorSupport.cpp` can be removed now.
>> 
>> Besides, there is an issue in current vector payload allocation code in `vectorSupport.cpp`, that the multi-fields are forgotten
>> to be assigned after the payload object is allocated (see [2]). This method is called separately during deoptimization (see [3]).
>> This makes several Vector API jtreg test results incorrect. And either assigning the fields by calling `Deoptimization::reassign_fields_by_klass()` after it or directly going to the normal re-allocation path in `deoptimization.cpp` can fix the issue. I prefer the latter one. Hence the similar code in `vectorSupport.cpp` is needless and can be removed.
>> 
>> This patch also fixes a crash when printing out the JVM state, which is caused by the additional multi-fields passed to a safepoint. Normally, the fields number passed to a safepoint is the same with the klass's non-static fields number. But it's different for multi-fields. Only the `multifield_base` is added to the klass's non-static field list. Hence if all the un-vectorized multi-fields are passed to a safepoint, the fields number is larger than the klass's non-static fields number. And the array access at [4] throws exception due to out of range index.
>> 
>> [1] https://github.com/openjdk/valhalla/pull/866
>> [2] https://github.com/openjdk/valhalla/blob/lworld%2Bvector/src/hotspot/share/prims/vectorSupport.cpp#L281
>> [3] https://github.com/openjdk/valhalla/blob/lworld%2Bvector/src/hotspot/share/runtime/deoptimization.cpp#L1282
>> [4] https://github.com/openjdk/valhalla/blob/lworld%2Bvector/src/hotspot/share/opto/callnode.cpp#L527
>
> Xiaohong Gong has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix deoptimize issue for un-vectorized multifields

src/hotspot/share/runtime/deoptimization.cpp line 1617:

> 1615:       ScopeValue* scope_field = sv->field_at(svIndex);
> 1616:       StackValue* value = StackValue::create_stack_value(fr, reg_map, scope_field);
> 1617:       offset += j * type2aelembytes(type);

Nice catch!!, It went in along with merge patch. Will run this through jtreg tests to ensure status quo or better validation status.

Best Regards,
Jatin

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PR Review Comment: https://git.openjdk.org/valhalla/pull/882#discussion_r1259570939