RFR: 8331114: Further improve performance of MethodTypeDesc::descriptorString [v2]

[Chen Liang]

On Thu, 25 Apr 2024 13:34:50 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> When analyzing (startup) performance of the Classfile API I found this opportunity to further improve `MethodTypeDescImpl::descriptorString`.
>> 
>> Performance improves across the board in existing microbenchmarks:
>> 
>> Name                                                                 (descString) Cnt   Base   Error    Test   Error  Unit  Change
>> MethodTypeDescFactories.descriptorString  (Ljava/lang/Object;Ljava/lang/String;)I   6 55,179 ± 2,027  32,920 ± 1,189 ns/op   1,68x (p = 0,000*)
>> MethodTypeDescFactories.descriptorString                                      ()V   6 17,689 ± 1,871  11,060 ± 0,331 ns/op   1,60x (p = 0,000*)
>> MethodTypeDescFactories.descriptorString ([IJLjava/lang/String;Z)Ljava/util/List;   6 86,627 ± 1,646  41,035 ± 0,636 ns/op   2,11x (p = 0,000*)
>> MethodTypeDescFactories.descriptorString                    ()[Ljava/lang/String;   6 18,305 ± 1,974  13,110 ± 0,089 ns/op   1,40x (p = 0,000*)
>>   * = significant
>> 
>> 
>> The improvement is even more pronounced when running with `-Xint`, which is relevant for reducing startup overheads of early ClassFile API use:
>> 
>> Name                                                                 (descString) Cnt     Base      Error      Test     Error  Unit  Change
>> MethodTypeDescFactories.descriptorString  (Ljava/lang/Object;Ljava/lang/String;)I   6 5122,061 ±   81,335  2626,481 ± 101,466 ns/op   1,95x (p = 0,000*)
>> MethodTypeDescFactories.descriptorString                                      ()V   6 3481,316 ±  258,904  1489,267 ±  15,506 ns/op   2,34x (p = 0,000*)
>> MethodTypeDescFactories.descriptorString ([IJLjava/lang/String;Z)Ljava/util/List;   6 7741,081 ± 1628,244  3281,778 ±  41,892 ns/op   2,36x (p = 0,000*)
>> MethodTypeDescFactories.descriptorString                    ()[Ljava/lang/String;   6 3677,803 ±   63,432  1495,291 ±   8,995 ns/op   2,46x (p = 0,000*)
>>   * = significant
>>   ```
>>   
>>  I also applied similar approach to `MethodTypeDesc::displayDescriptor`: while not performance sensitive I think these are so inter-related that it makes sense to implement them in a similar fashion.
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   comma-separated

What if we replace `24` with a precalculated value:

int size = 2 + returnType().descriptorString().length();
for (var param : argTypes)
    size += param.descriptorString().length();

(Would be even better if we can just trust the internal array to avoid copy allocation)

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PR Comment: https://git.openjdk.org/jdk/pull/18945#issuecomment-2077600166