[foreign-abi] RFR: 8248331: Intrinsify downcall handles in C2

[Jorn Vernee]

Hi,

This patch adds intrinsification of down call handles.

This is done through a new method handle intrinsic called linkToNative. We create a NativeMethodHandle that calls this
intrinsic, which then replaces the leaf method handle in ProgrammableInvoker::getBoundMethodHandle, basically replacing
the call to invokeMoves. Before C2 kicks in, this intrinsic will call a fallback method handle that we pass to it. The
handle that is passed is a handle that points to ProgrammableInvoker::invokeMoves, thus simulating the current
behaviour.

However, when a call to linkToNative is inlined, C2 will instead generate either a direct call to the target function,
or a call to a wrapper stub (which is generated on demand) that also does the thread state transitions needed for long
running native functions. Information about ABI, and which registers to use are captured in a so-called 'appendix
argument' of the type NativeEntryPoint, which is passed as the last argument. This captures all the information needed
to generate the call in C2 (note that previously in the patch shared in the discussion thread this information was
split over several classes, but I've condensed the info into just NativeEntryPoint in order to reduce the amount of
code needed in the vm to be able to access the information).

With this, the overhead for downcalls is on par or slightly lower than with JNI for calls that need to do thread state
transitions, and it is even lower when the thread state transitions are omitted (see that *_trivial runs).

Benchmark                                            Mode  Cnt    Score    Error  Units
CallOverhead.jni_blank                               avgt   30    8.461 □  0.892  ns/op
CallOverhead.jni_identity                            avgt   30   12.585 □  0.066  ns/op
CallOverhead.panama_blank                            avgt   30    8.562 □  0.029  ns/op
CallOverhead.panama_blank_trivial                    avgt   30    1.372 □  0.008  ns/op
CallOverhead.panama_identity                         avgt   30   11.813 □  0.073  ns/op
CallOverhead.panama_identity_trivial                 avgt   30    6.042 □  0.024  ns/op
Finished running test 'micro:CallOverhead'

Thanks,
Jorn

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

Commit messages:
 - Rebase fixes
 - Remove RegionPtr
 - re-write RegionPtr without using std::equal
 - Add missing debug.hpp includes for files using assert
 - Patch cleanup mostly updating copyright headers
 - Reduce VM interface
 - Implement down call intrinsics

Changes: https://git.openjdk.java.net/panama-foreign/pull/219/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/219/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248331
  Stats: 1848 lines in 73 files changed: 1741 ins; 28 del; 79 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/219.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/219/head:pull/219

PR: https://git.openjdk.java.net/panama-foreign/pull/219