RFR: 8261847: performace of java.lang.Record::toString should be improved [v3]

[Claes Redestad]

On Sat, 20 Nov 2021 04:40:22 GMT, Stuart Marks <smarks at openjdk.org> wrote:

>> Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   adding the benchmark
>
> Regarding the slot limit in `StringConcatFactory`, it's not clear to me the limit of 200 is normative or is merely an implementation note. The limit of 200 slots seems to be arbitrary and shouldn't be baked into the spec. Perhaps this limit can be removed if the splitting logic is moved into `StringConcatFactory`.

@stuart-marks yes, a general purpose splitting logic moved into the `StringConcatFactory` would be able to get rid of the arbitrary 200 slot limit (we would hit a harder but less arbitrary limit at around 253 instead).

@JimLaskey I don't see why it wouldn't work generally from the point of view of the `StringConcatFactory`: Vicente's code operates on a `MethodHandle[]` with getters as inputs to the `SCF` bootstrap method, whereas `SCF` would deal with arguments directly (retrieved from an `Object[]`). I think the code changes from the patch here after moving the logic into `SCF` should be pretty minimal and straightforward: if I'm not missing anything we'd only conceptually be replacing the `filterArguments` on line 313 with an `insertArguments`.

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PR: https://git.openjdk.java.net/jdk/pull/6403