RFR: 8339642: Reduce overheads in InvokerBytecodeGenerator

[Claes Redestad]

On Fri, 6 Sep 2024 10:42:54 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> - A small portion (~5%) of the instrumented overhead when spinning MH/LF classes in `InvokeBytecodeGenerator` comes from creating the exact same `RuntimeVisibleAnnotationsAttribute` for every method. Introducing a couple of constants has a small but measurable impact.
>> - `classDesc(MemberName.class)` is called ~8000 times during an OpenJDK build, `classDesc(MethodType.class)` ~900 - special casing looks profitable
>> - Class name validation narrowed down, use ReferenceClassDescImpl.ofValidated
>> - Various minor optimizations helping reduce bytecode size and speed up interpreter execution
>
> src/java.base/share/classes/java/lang/invoke/InvokerBytecodeGenerator.java line 149:
> 
>> 147:         localsMap[0] = 0; // localsMap has at least one element
>> 148:         for (int i = 1, index = 0; i < localsMap.length; i++) {
>> 149:             Class<?> cl = mt.parameterType(i - 1);
> 
> Can we use var?
> 
> var cl = mt.parameterType(i - 1);

I'm not too keen on `var` when it's not immediately obvious what the type is. For these two places I think `var` would make type information slightly less obvious when reading the code, so I'll opt to leave it as-is.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20887#discussion_r1747032114