RFR: 8339358: Optimize TypeKind#from

[Chen Liang]

On Thu, 29 Aug 2024 05:34:37 GMT, Shaojin Wen <swen at openjdk.org> wrote:

> TypeKind.from(Class) is a frequently called method, which provides a specialized method to improve performance.
> 
> The following Compiler log shows that the call stack level is reduced and two reference accesses (descriptorString() -> String.value) are reduced, which can reduce the performance degradation caused by cache misses.
> 
> * baseline
> 
> @ 48   java.lang.classfile.TypeKind::from (25 bytes)   inline
>   @ 1   java.lang.Class::isPrimitive (0 bytes)   intrinsic
>   @ 10   java.lang.Class::descriptorString (170 bytes)   failed to inline: callee is too large
>   @ 15   java.lang.classfile.TypeKind::fromDescriptor (232 bytes)   failed to inline: callee is too large
> 
> 
> * current
> 
> @ 52   java.lang.classfile.TypeKind::from (103 bytes)   failed to inline: callee is too large

Unfortunately, I don't think this is a good API addition, as it significantly increases the complexity of this method. If we do want to be performant, we should avoid calling this `from`, as in many workloads we don't handle `void` and we just want to return the 5 computational types for the class file format. We optimize users instead of this API.

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PR Comment: https://git.openjdk.org/jdk/pull/20762#issuecomment-2371808766