RFR: 8306842: Classfile API performance improvements [v7]

[Claes Redestad]

On Tue, 16 May 2023 08:17:02 GMT, Adam Sotona <asotona at openjdk.org> wrote:

>> Following improvements implemented:
>> - Switch over `String` replaced with switch single char
>> - Binary search for frames in `StackMapGenerator`
>> - `StackMapGenerator.rawHandlers` with pre-calculated offsets
>> - `ClassEntry` is caching `ClassDesc` symbol
>> - Caching of type symbols in `NameAndTypeEntry` and `MethodTypeEntry`
>> - Caching `MethodTypeDesc` in `MethodInfo` implementations
>> - `StackMapGenerator` and `Utils` delegating to cached `MethodTypeDesc` instead of custom parsing
>> 
>> No API change.
>> 
>> Benchmarks show stack map generation improved by 21% and code generation from symbols improved by 30%.
>> 
>> 
>> Benchmark                     Mode  Cnt       Score       Error  Units
>> GenerateStackMaps.benchmark  thrpt   10  407931.202 ± 13101.023  ops/s
>> RebuildMethodBodies.shared   thrpt    4   10258.597 ±   383.699  ops/s
>> RebuildMethodBodies.unshared thrpt    4    7224.543 ±   256.800  ops/s
>> 
>> 
>> 
>> Benchmark                     Mode  Cnt       Score      Error  Units
>> GenerateStackMaps.benchmark  thrpt   10  495101.110 ± 2389.628  ops/s
>> RebuildMethodBodies.shared    thrpt   4   13380.272 ±  810.113  ops/s
>> RebuildMethodBodies.unshared  thrpt   4    9399.863 ±  557.060  ops/s
>
> Adam Sotona has updated the pull request incrementally with one additional commit since the last revision:
> 
>   LinkedList replaced with ArrayList in benchmarks

Looks like a good set of improvements for throughput cases. 

For the future I think we should probably add something that measures startup/warmup overheads of the classfile API, since it's likely that usage pattern in many applications will be heavy during bootstrap and then subside (similar to how ASM usage can be startup sensitive but will then disappear from sight once an application is up and running)

src/java.base/share/classes/jdk/internal/classfile/impl/StackMapDecoder.java line 83:

> 81:             vtis = new VerificationTypeInfo[methodType.parameterCount()];
> 82:         }
> 83:         for(var arg : methodType.parameterList()) {

`MethodTypeDesc::parameterList` copies the internal `ClassDesc[]`, so desugaring loop from `0` to `mdesc.parameterCount()` might be a small improvement for this and a few other cases.

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Marked as reviewed by redestad (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13671#pullrequestreview-1428657206
PR Review Comment: https://git.openjdk.org/jdk/pull/13671#discussion_r1195248228