RFR: 8299807: String.newStringUTF8NoRepl and getBytesUTF8NoRepl always copy arrays

[Glavo]

On Mon, 9 Jan 2023 03:34:55 GMT, Glavo <duke at openjdk.org> wrote:

> `JavaLangAccess::newStringUTF8NoRepl` and `JavaLangAccess::getBytesUTF8NoRepl` are not implemented correctly. They always copy arrays, rather than avoiding copying as much as possible as javadoc says.
> 
> I ran the tier1 test without any new errors.

I noticed that the baseline had a high variance in the above test results, so I added the warm-up and running time to retest. 

Here are the new results:

baseline:

Benchmark             (length)  Mode  Cnt         Score       Error  Units
NoRepl.testReadAscii         0  avgt    5       209.602 ±     2.982  ns/op
NoRepl.testReadAscii      1024  avgt    5       291.026 ±     0.266  ns/op
NoRepl.testReadAscii      8192  avgt    5       416.418 ±     1.083  ns/op
NoRepl.testReadAscii   1048576  avgt    5     29678.103 ±   119.644  ns/op
NoRepl.testReadAscii  33554432  avgt    5   1136507.598 ±  2597.706  ns/op
NoRepl.testReadUTF8          0  avgt    5       205.729 ±     1.229  ns/op
NoRepl.testReadUTF8       1024  avgt    5      1295.330 ±     4.092  ns/op
NoRepl.testReadUTF8       8192  avgt    5      9352.954 ±   126.249  ns/op
NoRepl.testReadUTF8    1048576  avgt    5   1202516.789 ±  2876.660  ns/op
NoRepl.testReadUTF8   33554432  avgt    5  44475835.218 ± 80173.497  ns/op


This PR:

Benchmark             (length)  Mode  Cnt         Score        Error  Units
NoRepl.testReadAscii         0  avgt    5       212.301 ±      1.002  ns/op
NoRepl.testReadAscii      1024  avgt    5       284.751 ±      1.685  ns/op
NoRepl.testReadAscii      8192  avgt    5       353.243 ±      2.501  ns/op
NoRepl.testReadAscii   1048576  avgt    5     19740.869 ±    137.207  ns/op
NoRepl.testReadAscii  33554432  avgt    5    853450.226 ±   7765.001  ns/op
NoRepl.testReadUTF8          0  avgt    5       200.015 ±      3.930  ns/op
NoRepl.testReadUTF8       1024  avgt    5      1281.397 ±     16.402  ns/op
NoRepl.testReadUTF8       8192  avgt    5      9333.988 ±      9.603  ns/op
NoRepl.testReadUTF8    1048576  avgt    5   1202822.719 ±   3187.910  ns/op
NoRepl.testReadUTF8   33554432  avgt    5  44579793.940 ± 106239.604  ns/op


The conclusion is basically unchanged.

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PR: https://git.openjdk.org/jdk/pull/11897