On Sat, 17 Aug 2024 12:04:20 GMT, ExE Boss <d...@openjdk.org> wrote:
>> The current implementation of ofDescriptor puts return type and parameter
>> types together in an ArrayList, and then splits them into return type and
>> array of parameter types. This ArrayList creation is unnecessary,
>> considering most descriptors only have few parameter types.
>>
>> By splitting return type and parameter types separately and scanning the
>> descriptor first to get the number of parameters, we can just allocate an
>> exact, trusted array for the resulting MethodTypeDesc without copy.
>
> src/java.base/share/classes/jdk/internal/constant/MethodTypeDescImpl.java
> line 154:
>
>> 152: if (num >= 0) {
>> 153: int shift = num << 3;
>> 154: len = (int) ((lengths & (0xFFL << shift)) >> shift) &
>> 0xFF;
>
> The `0xFFL << shift` step is unnecessary with the trailing `& 0xFF`:
> Suggestion:
>
> len = (int) (lengths >>> shift) & 0xFF;
Under MacBook M1 Pro, the performance of running the scenario
`(Ljava/lang/Object;Ljava/lang/String;)I` multiple times is very different. The
above code is rollback verification, but it is found that the problem is not
solved.
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PR Review Comment: https://git.openjdk.org/jdk/pull/20611#discussion_r1720767948
