RFR: 8360520: RISC-V: C1: Fix primitive array clone intrinsic regression after JDK-8333154 [v2]

[Feilong Jiang]

> Hi, please consider.
> [JDK-8333154](https://bugs.openjdk.org/browse/JDK-8333154) Implemented C1 clone intrinsic that reuses arraycopy code for primitive arrays for RISC-V.
> The new instruction flag `OmitChecksFlag` (introduced by [JDK-8302850](https://bugs.openjdk.org/browse/JDK-8302850)) is used to avoid instantiation of array copy stubs for primitive array clones.
> If `OmitChecksFlag` is set, all flags (including the `unaligned` flag) will be cleared before generating the `LIR_OpArrayCopy` node.
> This may lead to incorrect selection of the arraycopy function when `unaligned` flag for arraycopy is set.
> We observed performance regression on P550 SBC through the corresponding JMH tests when COH is enabled.
> 
> This pr adds additional checks for unaligned case on RISC-V to ensure the arraycopy function is selected correctly.
> 
> Test on linux-riscv64:
> - [x] Tier1-3
> 
> JMH data on P550 SBC for reference (w/o and w/ the patch):
> 
> Before:
> 
> Without COH:
> 
> Benchmark                 (size)  Mode  Cnt     Score   Error  Units
> ArrayClone.byteArraycopy       0  avgt   15    50.854 ± 0.379  ns/op
> ArrayClone.byteArraycopy      10  avgt   15    74.294 ± 0.449  ns/op
> ArrayClone.byteArraycopy     100  avgt   15    81.847 ± 0.082  ns/op
> ArrayClone.byteArraycopy    1000  avgt   15   480.106 ± 0.369  ns/op
> ArrayClone.byteClone           0  avgt   15    90.146 ± 0.299  ns/op
> ArrayClone.byteClone          10  avgt   15   130.525 ± 0.384  ns/op
> ArrayClone.byteClone         100  avgt   15   251.942 ± 0.122  ns/op
> ArrayClone.byteClone        1000  avgt   15   407.580 ± 0.318  ns/op
> ArrayClone.intArraycopy        0  avgt   15    49.984 ± 0.436  ns/op
> ArrayClone.intArraycopy       10  avgt   15    76.302 ± 1.388  ns/op
> ArrayClone.intArraycopy      100  avgt   15   267.487 ± 0.329  ns/op
> ArrayClone.intArraycopy     1000  avgt   15  1157.444 ± 1.588  ns/op
> ArrayClone.intClone            0  avgt   15    90.130 ± 0.257  ns/op
> ArrayClone.intClone           10  avgt   15   183.619 ± 0.588  ns/op
> ArrayClone.intClone          100  avgt   15   296.491 ± 0.246  ns/op
> ArrayClone.intClone         1000  avgt   15   828.695 ± 1.501  ns/op
> 
> -------------------------------------------------------------------------
> With COH:
> 
> Benchmark                 (size)  Mode  Cnt       Score      Error  Units
> ArrayClone.byteArraycopy       0  avgt   15      50.667 ±    0.622  ns/op
> ArrayClone.byteArraycopy      10  avgt   15      76.917 ±    0.914  ns/op
> ArrayClone.byteArraycopy     100  avgt   15      82.928 ±    0.056  n...

Feilong Jiang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' of https://github.com/openjdk/jdk into riscv-fix-c1-primitive-clone
 - check unaligned flag at LIR_OpArrayCopy to avoid using AvoidUnalignedAccesses
 - riscv: fix c1 primitive array clone intrinsic regression

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25976/files
  - new: https://git.openjdk.org/jdk/pull/25976/files/445f903b..be980424

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25976&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25976&range=00-01

  Stats: 2968 lines in 162 files changed: 639 ins; 1861 del; 468 mod
  Patch: https://git.openjdk.org/jdk/pull/25976.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25976/head:pull/25976

PR: https://git.openjdk.org/jdk/pull/25976