RFR: 8318217: RISC-V: C2 VectorizedHashCode [v4]

[Yuri Gaevsky]

> Hello All,
> 
> Please review these changes to support _vectorizedHashCode intrinsic on
> RISC-V platform. The patch adds the "scalar" code for the intrinsic without
> usage of any RVV instruction but provides manual unrolling of the appropriate
> loop. The code with usage of RVV instruction could be added as follow-up of
> the patch or independently.
> 
> Thanks,
> -Yuri Gaevsky
> 
> P.S. My OCA has been accepted recently (ygaevsky).
> 
> ### Correctness checks
> 
> Testing: tier1 tests successfully passed on a RISC-V StarFive JH7110 board with Linux.
> 
> ### Performance results (the numbers for non-ints are similar)
> 
> #### StarFive JH7110 board:
> 
> 
> ArraysHashCode:              without intrinsic      with intrinsic
> -------------------------------------------------------------------------------
> Benchmark  (size)  Mode  Cnt       Score     Error       Score     Error  Units
> -------------------------------------------------------------------------------
> multiints       0  avgt   30       2.658 ?   0.001       2.661 ?   0.004  ns/op
> multiints       1  avgt   30       4.881 ?   0.011       4.892 ?   0.015  ns/op
> multiints       2  avgt   30      16.109 ?   0.041      10.451 ?   0.075  ns/op
> multiints       3  avgt   30      14.873 ?   0.068      11.753 ?   0.024  ns/op
> multiints       4  avgt   30      17.283 ?   0.078      13.176 ?   0.044  ns/op
> multiints       5  avgt   30      19.691 ?   0.136      14.723 ?   0.046  ns/op
> multiints       6  avgt   30      21.727 ?   0.166      15.463 ?   0.124  ns/op
> multiints       7  avgt   30      23.790 ?   0.126      18.298 ?   0.059  ns/op
> multiints       8  avgt   30      23.527 ?   0.116      18.267 ?   0.046  ns/op
> multiints       9  avgt   30      27.981 ?   0.303      20.453 ?   0.069  ns/op
> multiints      10  avgt   30      26.947 ?   0.215      20.541 ?   0.051  ns/op
> multiints      50  avgt   30      95.373 ?   0.588      69.238 ?   0.208  ns/op
> multiints     100  avgt   30     177.109 ?   0.525     137.852 ?   0.417  ns/op
> multiints     200  avgt   30     341.074 ?   1.363     296.832 ?   0.725  ns/op
> multiints     500  avgt   30     847.993 ?   1.713     752.415 ?   1.918  ns/op
> multiints    1000  avgt   30    1610.199 ?   5.424    1426.112 ?   3.407  ns/op
> multiints   10000  avgt   30   16234.260 ?  26.789   14447.936 ?  26.345  ns/op
> multiints  100000  avgt   30  170726.025 ? 184.003  152587.649 ? 381.964  ns/op
> -------------------------------------------------------------------------------
> 
> #### T-Head RVB-ICE board:
> 
> 
> ArraysHashCode:    ...

Yuri Gaevsky has updated the pull request incrementally with eight additional commits since the last revision:

 - Temporary registers renaming.
 - Get tmp3 back and use it to hold 31^^3 constant.
 - Use t0/t1 as tmp1/tmp2.
 - Removed tmp3 register.
 - Replaced tmp3 with tmp1 in wide loop.
 - Replaced lw() of 31^^2 from memory with mv(); removed 31^^2..31^^0 constants as not needed anymore.
 - Renamed chunk -> chunks
 - Removed usage of cnt in loops for branch decisions.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16629/files
  - new: https://git.openjdk.org/jdk/pull/16629/files/86bcccee..eb4b0f87

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16629&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16629&range=02-03

  Stats: 59 lines in 4 files changed: 11 ins; 11 del; 37 mod
  Patch: https://git.openjdk.org/jdk/pull/16629.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16629/head:pull/16629

PR: https://git.openjdk.org/jdk/pull/16629