RFR: 8338930: StringConcatFactory static string concatenation strategy

[Shaojin Wen]

On Thu, 22 Aug 2024 11:50:02 GMT, Shaojin Wen <duke at openjdk.org> wrote:

> This is a follow-up to PR #20273, which improves performance when the number of parameters exceeds 20.
> 
> When the number of parameters is large, the possibility of reuse will be lower, so we can use the static concat method and write the length and coder directly into the bytecode to solve the performance regression problem.

Below are the performance numbers on a MacBook M1 Pro. When the number of parameters is greater than 16, the performance is significantly improved.

## Script

# baseline
git checkout 6644dd33f6f4b440105d84ef187a0ff6b1d60827
make test TEST="micro:java.lang.StringConcat."

# current
git checkout a2465a0e6011c4433833c5088ebcb5d56c6a5587
make test TEST="micro:java.lang.StringConcat."


## Performance Numbers

-# baseline
-Benchmark                                            (intValue)  Mode  Cnt     Score    Error  Units
-StringConcat.concat123String                               4711  avgt   15  1021.422 ?  5.979  ns/op
-StringConcat.concat23String                                4711  avgt   15    80.279 ?  0.338  ns/op
-StringConcat.concat23StringConst                           4711  avgt   15   103.502 ?  0.477  ns/op
-StringConcat.concat30Mix                                   4711  avgt   15   339.447 ? 14.675  ns/op

+# current
+Benchmark                                            (intValue)  Mode  Cnt     Score    Error  Units
+StringConcat.concat123String                               4711  avgt   15  1021.422 ?  5.979  ns/op
+StringConcat.concat23String                                4711  avgt   15    80.279 ?  0.338  ns/op
+StringConcat.concat23StringConst                           4711  avgt   15   103.502 ?  0.477  ns/op
+StringConcat.concat30Mix                                   4711  avgt   15   339.447 ? 14.675  ns/op


|   | baseline  | current | delta |
| --- | --- | --- | --- |
| StringConcat.concat123String | 1078.649 | 1021.422 | 5.60% |
| StringConcat.concat23String | 139.407 | 80.279 | 73.65% |
| StringConcat.concat23StringConst | 119.125 | 103.502 | 15.09% |
| StringConcat.concat30Mix | 425.278 | 339.447 | 25.29% |

-------------

PR Comment: https://git.openjdk.org/jdk/pull/20675#issuecomment-2308154069