RFR: 8332602: [s390x] Improve itable_stub [v4]

[Amit Kumar]

> s390x Port similar to [JDK-8305959 (x86)](https://bugs.openjdk.org/browse/JDK-8305959) and [JDK-8307352(aarch64)](https://bugs.openjdk.org/browse/JDK-8307352)
> 
> Testing: I ran `tier1` test on fastdebug & release VM; I didn't see any regression there;
> 
> Benchmarking: 
> 
> Without Patch: 
> Benchmark                        Mode  Cnt   Score    Error  Units
> InterfaceCalls.test1stInt2Types  avgt   12   1.924 ±  0.001  ns/op
> InterfaceCalls.test1stInt3Types  avgt   12  13.925 ±  0.014  ns/op
> InterfaceCalls.test1stInt5Types  avgt   12  16.591 ±  0.045  ns/op
> InterfaceCalls.test2ndInt2Types  avgt   12   2.028 ±  0.013  ns/op
> InterfaceCalls.test2ndInt3Types  avgt   12   7.634 ±  0.049  ns/op
> InterfaceCalls.test2ndInt5Types  avgt   12  16.231 ±  1.222  ns/op
> InterfaceCalls.testIfaceCall     avgt   12  16.587 ±  0.058  ns/op
> InterfaceCalls.testIfaceExtCall  avgt   12  17.532 ±  0.024  ns/op
> InterfaceCalls.testMonomorphic   avgt   12   0.746 ±  0.001  ns/op
> Finished running test 'micro:vm.compiler.InterfaceCalls'
> 
> 
> With Patch: 
> 
> Benchmark                        Mode  Cnt   Score    Error  Units
> InterfaceCalls.test1stInt2Types  avgt   12   1.929 ±  0.012  ns/op
> InterfaceCalls.test1stInt3Types  avgt   12  13.280 ±  0.093  ns/op
> InterfaceCalls.test1stInt5Types  avgt   12  16.169 ±  0.364  ns/op
> InterfaceCalls.test2ndInt2Types  avgt   12   6.758 ±  4.473  ns/op
> InterfaceCalls.test2ndInt3Types  avgt   12  11.772 ±  2.411  ns/op
> InterfaceCalls.test2ndInt5Types  avgt   12  15.099 ±  0.081  ns/op
> InterfaceCalls.testIfaceCall     avgt   12  15.972 ±  0.021  ns/op
> InterfaceCalls.testIfaceExtCall  avgt   12  16.600 ±  0.322  ns/op
> InterfaceCalls.testMonomorphic   avgt   12   0.746 ±  0.001  ns/op
> Finished running test 'micro:vm.compiler.InterfaceCalls'

Amit Kumar has updated the pull request incrementally with one additional commit since the last revision:

  Update src/hotspot/cpu/s390/macroAssembler_s390.cpp

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19698/files
  - new: https://git.openjdk.org/jdk/pull/19698/files/19c3673c..22e33189

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19698&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19698&range=02-03

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19698.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19698/head:pull/19698

PR: https://git.openjdk.org/jdk/pull/19698