RFR: 8276455: C2: iterative EA

[Nils Eliasson]

On Wed, 3 Nov 2021 01:44:49 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> Resolve C2 issue with nested initialization when Escape Analysis can not scalarize allocations: `new A(new B( new C)))`
> Implemented iterative EA when C2 invokes it again if there are progress and candidates.
> 
> I added JMH microbenchmark with cases which show improvements. Improvements are due to removed allocation code.
> 
> Before: 
> 
> Benchmark          Mode  Cnt     Score     Error  Units
> IterativeEA.test1  avgt    5    11.489 ±   3.037  ns/op
> IterativeEA.test2  avgt    5    16.103 ±   3.686  ns/op
> IterativeEA.test3  avgt    5  1988.827 ± 217.831  ns/op
> 
> With these changes: 
> 
> IterativeEA.test1  avgt    5    2.182 ± 0.022  ns/op
> IterativeEA.test2  avgt    5    2.375 ± 0.001  ns/op
> IterativeEA.test3  avgt    5  821.011 ± 8.268  ns/op
> 
> 
> An other JMH test:
> 
> PointerBenchmarkFlat.test      avgt   30  23.232 ± 6.507  ms/op
> 
> vs
> 
> PointerBenchmarkFlat.test      avgt   30  0.299 ±  0.001  ms/op

Looks good

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Marked as reviewed by neliasso (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6222