RFR: 8283689: Update the foreign linker VM implementation [v7]

[Jorn Vernee]

On Wed, 11 May 2022 11:06:51 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> src/hotspot/share/opto/callGenerator.cpp line 1131:
>> 
>>> 1129: 
>>> 1130:     case vmIntrinsics::_linkToNative:
>>> 1131:     print_inlining_failure(C, callee, jvms->depth() - 1, jvms->bci(),
>> 
>> Why is it unconditionally reported as inlining failure?
>
> The call that is being processed here is `linkToNative`, and that call is not inlined, so reporting an inlining failure seems correct. We still go through the method handle trampoline stub which loads the actual target from the NativeEntryPoint appendix argument (`jump_to_native_invoker` in methodHandles_x86.cpp).
> 
> It's potentially faster here to generate a runtime call to the underlying invoker/downcall stub if the NativeEntryPoint is constant (i.e. avoid the lookup through NEP in the MH trampoline), but I hadn't gotten to investigating that yet.
> 
> From comparing the benchmark times between this and the old implementation (which generated an inline call), they are not all that different. So it seemed that doing something special here would not save that much time any ways. (but, still would be good to investigate at some point)

I've filed: https://bugs.openjdk.java.net/browse/JDK-8286588

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PR: https://git.openjdk.java.net/jdk/pull/7959