RFR: 8284579: Improve VarHandle checks for interpreter [v3]

[Mandy Chung]

On Mon, 11 Apr 2022 10:13:40 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> A few additional enhancements aiming to improve VH performance in the interpreter:
>> 
>> - Flatten `TypeAndInvokers`: adds a pointer to `VarHandle` (a small increase 40->48) but removes an object and an indirection on any instance actually used - and might avoid allocating the `MethodHandle[]` unnecessarily on some instances
>> - Have `checkExactAccessMode` return the directness of the `VarHandle` so that we can avoid some `isDirect` method calls.
>> 
>> Baseline, `-Xint`
>> 
>> Benchmark                                 Mode  Cnt    Score   Error  Units
>> VarHandleExact.exact_exactInvocation      avgt   30  478.324 ? 5.762  ns/op
>> VarHandleExact.generic_exactInvocation    avgt   30  392.114 ? 1.644  ns/op
>> VarHandleExact.generic_genericInvocation  avgt   30  822.484 ? 1.865  ns/op
>> 
>> 
>> Patched, `-Xint`
>> 
>> Benchmark                                 Mode  Cnt    Score   Error  Units
>> VarHandleExact.exact_exactInvocation      avgt   30  437.704 ? 5.320  ns/op
>> VarHandleExact.generic_exactInvocation    avgt   30  374.512 ? 3.154  ns/op
>> VarHandleExact.generic_genericInvocation  avgt   30  757.054 ? 1.237  ns/op
>> 
>> 
>> No significant performance difference in normal mode.
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   checkExactAccessMode -> checkAccessModeThenIsDirect, privatize throw method, cleanup code generator

Dropping `Exact` from `checkExactAccessMode` is good with me and it'd help future readers if you can add a javadoc what this method does.

-------------

PR: https://git.openjdk.java.net/jdk/pull/8160