RFR: 8294961: Convert java.base/java.lang.reflect.ProxyGenerator to use the Classfile API to generate proxy classes [v15]

[Chen Liang]

On Mon, 27 Mar 2023 16:43:17 GMT, Adam Sotona <asotona at openjdk.org> wrote:

>> java.base java.lang.reflect.ProxyGenerator uses ASM to generate proxy classes and this patch converts it to use Classfile API.
>> 
>> Please review.
>> 
>> Thank you,
>> Adam
>
> Adam Sotona has updated the pull request incrementally with one additional commit since the last revision:
> 
>   StackMapGenerator performance improvements

Keep-alive.

I believe the changes to cache ClassDesc symbol in ClassEntry and avoid re-computing hash in Utf8Entry can be in a separate patch delivered before the current migration patch.

For the StackMapGenerator changes, I don't agree with replacing `TOP_TYPE` with `null`: currently, top type is `0, null, 0`, which can be the default null instance after valhalla drops (so filling array will no longer be required at that point). Using `null` makes the code less readable and maintainable as well.

I also question the design to move away from `MethodTypeDesc`: `ofDescriptor` is expensive, but we can check the slots of a method type with a `MethodTypeDesc` easily than tokenizing and skipping the raw descriptor string, like 

var slots = type.parameterCount()
for (var param : type.parameterList()) // when parameterList is optimized
    if (param.isPrimitive() && (param.descriptorString.charAt(0) == 'D' || param.descriptorString.charAt(0) == 'J')) slots++;


Same for processing invoke instructions: if we can reuse the `MethodTypeDesc` at `invokeInstruction` call sites, we don't need an ad-hoc type computation either.

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PR Comment: https://git.openjdk.org/jdk/pull/10991#issuecomment-1520993443