RFR: 8294961: Convert java.base/java.lang.reflect.ProxyGenerator to use the Classfile API to generate proxy classes [v5]

[Adam Sotona]

On Sun, 7 Jan 2024 18:16:05 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Original code has been significant in profiler.
>> 
>> 
>> MethodTypeDesc desc = MethodTypeDesc.of(toClassDesc(returnType),
>>                     Arrays.stream(parameterTypes).map(ProxyGenerator::toClassDesc).toArray(ClassDesc[]::new));
>> 
>> 
>> 1. each `toClassDesc` builds `descriptorString` and parses/validates it while constructing `ClassDesc`
>> 2. `Arrays.stream(...).map(...).toArray(...)` allocates an array
>> 3. `MethodTypeDesc.of(...)` clones the array and iterates params to check for void
>> 4. `desc.descriptorString()` then finally use the `StringJoiner` 
>> 
>> Optimized code only joins `descriptorString`, no validations, no streaming, no arrays, no cloning.
>> 
>> 
>> I suggest this patch as this code is considered as performance critical.
>> However we can go through `ClassDesc` and `MethodTypeDesc` if not performance critical or if the conversions would be optimized.
>> 
>> For example better (trusted) paths from `MethodType` to `MethodTypeDescriptor` and from `Class` to `ClassDesc`, avoiding at least validations.
>
> Turns out your approach to avoid MTD here is apparently useless; `MethodTypeDesc` is still created for initializing the local tracker `topLocal` in `DirectCodeBuilder`. In addition, `StackMapDecoder` also uses `methodTypeSymbol` to compute the initial frame.
> 
> IMO we should just stay with MTD; the descriptor breakdown happens too often and, from previous benchmarks, descriptor breakdown is actually slow (which gives CF API a small edge over ASM here). But we can still replace the `parameterList()` iteration with index-based iteration to avoid array copies.

Right, there are still so many conversions.
I'll revert the custom code to simplify further optimizations.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17121#discussion_r1444690465