RFR: 8331187: Optimize MethodTypeDesc and ClassDesc.ofDescriptor for primitive types [v3]

[Mandy Chung]

On Fri, 26 Apr 2024 11:51:51 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> This PR makes ClassDesc.ofDescriptor return the shared constant for primitive descriptor strings ("I" etc..), and leverages this further by refactoring `MethodTypeDescImpl.ofDescriptor` to avoid the intermediate substring for primitives. 
>> 
>> Microbenchmarks results look good with expected speedups and allocation reductions any time a primitive is part of the descriptor string, and a non-significant cost otherwise:
>> 
>> 
>> Name                                                             (descString) Cnt     Base     Error       Test     Error   Unit  Change
>> ClassDescFactories.ofDescriptor                            Ljava/lang/Object;   6   13,941 ±   1,643     14,071 ±   1,333  ns/op   0,99x (p = 0,681 )
>>   :gc.alloc.rate.norm                                                               16,000 ±   0,000     16,000 ±   0,000   B/op   1,00x (p = 0,617 )
>> ClassDescFactories.ofDescriptor                                             V   6    9,212 ±   1,045      1,405 ±   0,049  ns/op   6,55x (p = 0,000*)
>>   :gc.alloc.rate.norm                                                               48,000 ±   0,000      0,000 ±   0,000   B/op   0,00x (p = 0,000*)
>> ClassDescFactories.ofDescriptor                                             I   6    9,009 ±   0,035      1,431 ±   0,192  ns/op   6,30x (p = 0,000*)
>>   :gc.alloc.rate.norm                                                               48,000 ±   0,000      0,000 ±   0,000   B/op   0,00x (p = 0,000*)
>> MethodTypeDescFactories.ofDescriptor  (Ljava/lang/Object;Ljava/lang/String;)I   6  182,050 ±   4,333    141,644 ±   2,685  ns/op   1,29x (p = 0,000*)
>>   :gc.alloc.rate.norm                                                              360,001 ±   0,000    264,001 ±   0,000   B/op   0,73x (p = 0,000*)
>> MethodTypeDescFactories.ofDescriptor                                      ()V   6   17,169 ±   2,008      9,915 ±   0,018  ns/op   1,73x (p = 0,000*)
>>   :gc.alloc.rate.norm                                                              120,000 ±   0,000    104,000 ±   0,000   B/op   0,87x (p = 0,000*)
>> MethodTypeDescFactories.ofDescriptor ([IJLjava/lang/String;Z)Ljava/util/List;   6  270,372 ±   3,624    217,050 ±   3,170  ns/op   1,25x (p = 0,000*)
>>   :gc.alloc.rate.norm                                                              520,002 ±   0,000    328,001 ±   0,000   B/op   0,63x (p = 0,000*)
>> MethodTypeDescFactories.ofDescriptor                    ()[Ljava/lang/String;   6   35,036 ±   0,351     36...
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Copyrights and other comments from @JornVernee

src/java.base/share/classes/sun/invoke/util/Wrapper.java line 384:

> 382: 
> 383:     /** A nominal descriptor of the primitive type */
> 384:     public ClassDesc primitiveClassDescriptor() { return primitiveTypeDesc; }

As this method is named as `primitiveClassDescriptor`, I expect this should either throw or return null for `OBJECT` and even `VOID` wrapper.   Or should be named "classDescriptor".

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

PR Review Comment: https://git.openjdk.org/jdk/pull/18971#discussion_r1581352160