RFR: 8318159: RISC-V: Improve itable_stub

[Fei Yang]

On Tue, 14 Nov 2023 15:01:51 GMT, Yuri Gaevsky <duke at openjdk.org> wrote:

> Please review the change for RISC-V similar to #13792(AARCH64) and #13460(X86).
> 
> From #13792:
> The change replaces two separate iterations over the itable with new algorithm
> consisting of two loops. First, we look for a match with resolved_klass,
> checking for a match with holder_klass along the way. Then we continue iterating
> (not starting over) the itable using the second loop, checking only for a match
> with holder_klass.
> 
> ### Correctness checks
> 
> Testing: tier1 tests successfully passed on HiFive Unmatched board.
> 
> #### Performance results on RISC-V StarFive JH7110 board:
> 
> 
> InterfaceCalls:                  before fix        after fix
> -------------------------------------------------------------------
> Benchmark         Mode  Cnt   Score   Error    Score   Error  Units
> -------------------------------------------------------------------
> test1stInt2Types  avgt  100  14.380 ? 0.017 | 14.370 ? 0.014  ns/op
> test1stInt3Types  avgt  100  72.724 ? 0.552 | 66.290 ? 0.080  ns/op
> test1stInt5Types  avgt  100  73.948 ? 0.524 | 68.781 ? 0.377  ns/op
> test2ndInt2Types  avgt  100  15.705 ? 0.016 | 15.707 ? 0.018  ns/op
> test2ndInt3Types  avgt  100  82.370 ? 0.453 | 75.363 ? 0.156  ns/op
> test2ndInt5Types  avgt  100  85.266 ? 0.466 | 80.969 ? 0.752  ns/op
> testIfaceCall     avgt  100  75.684 ? 0.648 | 72.603 ? 0.460  ns/op
> testIfaceExtCall  avgt  100  86.293 ? 0.567 | 77.939 ? 0.340  ns/op
> testMonomorphic   avgt  100  11.357 ? 0.007 | 11.359 ? 0.009  ns/op
> -------------------------------------------------------------------
> 
> 
> #### Performance results on RISC-V HiFive Unmatched board:
> 
> 
> InterfaceCalls:                   before fix         after fix
> ---------------------------------------------------------------------
> Benchmark         Mode  Cnt    Score   Error     Score   Error  Units
> ---------------------------------------------------------------------
> test1stInt2Types  avgt  100   24.432 ? 1.811 |  23.205 ? 1.512  ns/op
> test1stInt3Types  avgt  100  135.800 ? 3.991 | 127.112 ? 2.299  ns/op
> test1stInt5Types  avgt  100  141.746 ? 4.272 | 136.069 ? 4.919  ns/op
> test2ndInt2Types  avgt  100   31.474 ? 2.468 |  26.978 ? 1.951  ns/op
> test2ndInt3Types  avgt  100  146.410 ? 3.575 | 139.443 ? 3.677  ns/op
> test2ndInt5Types  avgt  100  156.083 ? 3.617 | 150.583 ? 2.909  ns/op
> testIfaceCall     avgt  100  136.392 ? 2.546 | 129.632 ? 1.662  ns/op
> testIfaceExtCall  avgt  100  155.602 ? 3.836 | 138.058 ? 2.147  ns/op
> testMonomorphic   avgt  100   24.018 ? 1.888 |  21.522 ? 1.662  ns/op
> ---------...

Changes requested by fyang (Reviewer).

src/hotspot/cpu/riscv/macroAssembler_riscv.cpp line 2562:

> 2560:   mv(holder_offset, zr);
> 2561:   // scan_temp = &(itable[0]._interface)
> 2562:   la(scan_temp, Address(scan_temp));

The `la` call here won't emit any code on riscv [1]. So I think we can simply remove it and apply the code comment at L2561 to the preceding `shadd` call.

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/riscv/macroAssembler_riscv.cpp#L745

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

PR Review: https://git.openjdk.org/jdk/pull/16657#pullrequestreview-1733407682
PR Review Comment: https://git.openjdk.org/jdk/pull/16657#discussion_r1395092707