RFR: 8300979: Lazily initialize (byte, char)arr in java.io.DataInputStream [v3]

[Eirik Bjorsnos]

On Thu, 23 Mar 2023 14:00:40 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

>> I cannot explain why, but the changes suggested in this PR seem to introduce a small, but significant performance regression on the `DataInputStreamTest.readInt` benchmark:
>> 
>> Baseline:
>> 
>> 
>> Benchmark                    Mode  Cnt  Score   Error  Units
>> DataInputStreamTest.readInt  avgt   20  5.563 ± 0.037  us/op
>> 
>> 
>> PR:
>> 
>> 
>> Benchmark                    Mode  Cnt  Score   Error  Units
>> DataInputStreamTest.readInt  avgt   20  6.021 ± 0.020  us/op
>> 
>> 
>> The reason this puzzles me is that the `readInt` benchmark don't involve the UTF code paths at all. So why would it become slower, just because two fields are no longer initialized with the default arrays?
>
>> The reason this puzzles me is that the `readInt` benchmark don't involve the UTF code paths at all. So why would it become slower, just because two fields are no longer initialized with the default arrays?
> 
> Could there be some JIT optimizations not being possible because the fields are no longer 'never null'?

> @eirbjo I've updated the PR so we hold zero-length arrays rather than null arrays. Please re-run your benchmark to see if there is any change.

@minborg I ran the test now after your integration and I no longer observe the regression I did before.

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PR Comment: https://git.openjdk.org/jdk/pull/13121#issuecomment-1487396449