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

[Xiaohong Gong]

On Fri, 7 Jul 2023 06:47:07 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

Besides the vector api regressions, I met lots of crashes due to nullptr of the payload field. It looks like being caused by deoptmization as well, where the payload field is not allocated I guess. With the change in this PR, the crash cases increased. Do you have any idea about this?

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PR Comment: https://git.openjdk.org/valhalla/pull/882#issuecomment-1625004552