[foreign-preview] RFR: 8281595: ASM-ify scope acquire/release for down call parameters [v2]

[Jorn Vernee]

> Hi,
> 
> This patch rewrites the scope acquire/release logic that we do for downcalls inside ASM, in the generated specialized binding class. This also drops the fallback path we had for more than 5 scopes. The new code now always checks to see if every scope is unique. (I think that should be okay, but please let me know if otherwise).
> 
> I've also added a benchmark by Maurizio to this patch, which was showing a failure to scalar replace some scoped arguments with the old MH logic (reason discussed in [JDK-8281387](https://bugs.openjdk.java.net/browse/JDK-8281387)). With the new ASM-based logic, there is no sign of allocations (other than some noise):
> 
> 
> Benchmark                                                     Mode  Cnt   Score    Error   Units
> PointerInvoke.panama_call_as_address                          avgt   30  13.181 ±  0.320   ns/op
> PointerInvoke.panama_call_as_address:·gc.alloc.rate           avgt   30   0.043 ±  0.049  MB/sec
> PointerInvoke.panama_call_as_address:·gc.alloc.rate.norm      avgt   30   0.001 ±  0.001    B/op
> PointerInvoke.panama_call_as_address:·gc.count                avgt   30     ≈ 0           counts
> PointerInvoke.panama_call_as_long                             avgt   30  12.943 ±  0.287   ns/op
> PointerInvoke.panama_call_as_long:·gc.alloc.rate              avgt   30   0.065 ±  0.054  MB/sec
> PointerInvoke.panama_call_as_long:·gc.alloc.rate.norm         avgt   30   0.002 ±  0.001    B/op
> PointerInvoke.panama_call_as_long:·gc.count                   avgt   30     ≈ 0           counts
> PointerInvoke.panama_call_as_new_segment                      avgt   30  14.309 ±  0.177   ns/op
> PointerInvoke.panama_call_as_new_segment:·gc.alloc.rate       avgt   30   0.173 ±  0.144  MB/sec
> PointerInvoke.panama_call_as_new_segment:·gc.alloc.rate.norm  avgt   30   0.005 ±  0.004    B/op
> PointerInvoke.panama_call_as_new_segment:·gc.count            avgt   30     ≈ 0           counts
> PointerInvoke.panama_call_as_segment                          avgt   30  13.273 ±  0.191   ns/op
> PointerInvoke.panama_call_as_segment:·gc.alloc.rate           avgt   30  ≈ 10??           MB/sec
> PointerInvoke.panama_call_as_segment:·gc.alloc.rate.norm      avgt   30  ≈ 10??             B/op
> PointerInvoke.panama_call_as_segment:·gc.count                avgt   30     ≈ 0           counts
> 
> 
> Thanks,
> Jorn

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  Use local variable for inital scope slots array (instead of storing it in the scopeSlots field)

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/640/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/640/files/1ec239ea..078e77e9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=640&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=640&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/640.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/640/head:pull/640

PR: https://git.openjdk.java.net/panama-foreign/pull/640