RFR: 8306697: Add method to obtain String for CONSTANT_Class_info in ClassDesc [v2]

[Adam Sotona]

On Sat, 22 Apr 2023 18:40:45 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Add a method `internalName` to `ClassDesc`, and unifies handling of string representation of a class constant in CONSTANT_Class_info via `ofInternalName` and `internalName` APIs, documented in `ClassDesc` itself. In particular, `ofInternalName` now accepts arrays.
>> 
>> The motivation of this API is that avoiding frequent String creations via caching (enabled by this new API, will be in a separate patch) would speed up Classfile API's [writing of simple class files](https://github.com/openjdk/jdk/blob/master/test/micro/org/openjdk/bench/jdk/classfile/Write.java) by 1/3. See https://mail.openjdk.org/pipermail/classfile-api-dev/2023-April/000296.html for more context.
>> 
>> This API is futureproof: for Valhalla's Q-types, it will return their string representation in CONSTANT_Class_info, which is most likely their full descriptor string.
>> 
>> Javadoc: https://cr.openjdk.org/~liach/8306697/java.base/java/lang/constant/ClassDesc.html
>
> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Unify ofInternalName and internalName, document about CONSTANT_Class_info, remove misleading JVMS 4.4.1 links

I support this addition. Classfile API contains utility method obtaining internal name from `ClassDesc` and it is one of the core pieces.
I don't have any exact measured numbers in my hands now, however `String` conversions are significant CPU consumers in our benchmarks.
In #13671 we are targeting to support conversion-less paths for class building and transformations (by passing the original `ClassDesc` instances through the process). External utility for conversions from `ClassDesc` to internal name does not allow to effectively cache the names and so every repeated need of internal name of the same `ClassDesc` instance will produce a new substring.

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PR Comment: https://git.openjdk.org/jdk/pull/13598#issuecomment-1525168031