RFR: 8338532: Speed up the ClassFile API MethodTypeDesc#ofDescriptor

[Shaojin Wen]

On Sun, 18 Aug 2024 21:27:44 GMT, Claes Redestad <redestad at 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/ConstantUtils.java line 309:
> 
>> 307:     private static ClassDesc resolveClassDesc(String descriptor, int start, int len) {
>> 308:         if (len == 1) {
>> 309:             return Wrapper.forPrimitiveType(descriptor.charAt(start)).basicClassDescriptor();
> 
> This was already piggy-backing on a quite fast routine. If it's a clean, significant win then I'm fine with this (untangling `Wrapper` from this is probably good, all things considered), but then we should also clean up `Wrapper` to not carry some descriptors around.

I have removed the Wrapper.forPrimitiveType(char) method. It seems that this is the only method that can be removed. Other descriptors related methods still need to be used.

> src/java.base/share/classes/jdk/internal/constant/MethodTypeDescImpl.java line 137:
> 
>> 135:         var returnType = resolveClassDesc(descriptor, rightBracket + 1, retTypeLength);
>> 136:         if (length == 3 && returnType == CD_void) {
>> 137:             return Constants.MTD_void;
> 
> Feels a bit like overfitting with quite limited data.
> 
> Could this use `ConstantDescs.MTD_void` instead or does that cause a bootstrap cycle?

Using ConstantDescs.MTD_void can also solve the bootstrap cycle, good idea, I have fixed it

> test/micro/org/openjdk/bench/java/lang/classfile/MethodTypeDescBench.java line 23:
> 
>> 21:  * questions.
>> 22:  */
>> 23: package org.openjdk.bench.java.lang.classfile;
> 
> Wrong package as the code being tested is in java.lang.constant. Also there is already a related microbenchmark in org.openjdk.bench.java.lang.constant.MethodTypeDescFactories - can you check if that covers your needs?

MethodTypeDescFactories has some illegal MethodTypeDesc, and throwing exceptions will affect the performance comparison of normal scenarios.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20611#discussion_r1721080326
PR Review Comment: https://git.openjdk.org/jdk/pull/20611#discussion_r1721064527
PR Review Comment: https://git.openjdk.org/jdk/pull/20611#discussion_r1720100307