RFR: 8322174: RISC-V: C2 VectorizedHashCode RVV Version [v26]

[Fei Yang]

On Thu, 14 Aug 2025 18:39:53 GMT, Yuri Gaevsky <duke at openjdk.org> wrote:

>> The patch adds possibility to use RVV instructions for faster vectorizedHashCode calculations on RVV v1.0.0 capable hardware.
>> 
>> Testing: hotspot/jtreg/compiler/ under QEMU-8.1 with RVV v1.0.0.
>
> Yuri Gaevsky has updated the pull request incrementally with one additional commit since the last revision:
> 
>   -more updates per reviewer's suggestions.

Seems fine to me modulo some minor coding style issues. Thanks.

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp line 2009:

> 2007:   const int elsize_bytes = arrays_hashcode_elsize(eltype);
> 2008:   const int elsize_shift = exact_log2(elsize_bytes);
> 2009:   const int MAX_VEC_MASK = ~(ints_in_vec_reg * lmul - 1);

`MAX_VEC_MASK` and `ints_in_vec_reg` looks a bit confusing to me considering vector register grouping. I prefer to rename `ints_in_vec_reg` to `stride`, just like you do for the scalar version. Then we can remove this `MAX_VEC_MASK` and replace it with `~(stride - 1)` where it is used.

  const int lmul = 2;
  const int stride = MaxVectorSize / sizeof(jint) * lmul;

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp line 2053:

> 2051:   vmul_vv(v_src, v_src, v_coeffs);
> 2052:   vmadd_vx(v_sum, pow31_highest, v_src);
> 2053:   shadd(ary, consumed, ary, t0, elsize_shift);

Can you further move this `shadd` to immediately after `mulw(result, result, pow31_highest);`?
I would like to group updating of both `ary` and `cnt` together.

src/hotspot/cpu/riscv/riscv_v.ad line 4095:

> 4093:          TEMP tmp1, TEMP tmp2, TEMP tmp3, KILL cr);
> 4094: 
> 4095:   format %{ "Array HashCode array[] $ary,$cnt,$result,$basic_type -> $result\t#varrays_hashcode" %}

Suggestion:

format %{ "Array HashCode array[] $ary,$cnt,$result,$basic_type -> $result   // KILL all" %}

src/hotspot/cpu/riscv/stubDeclarations_riscv.hpp line 78:

> 76:   do_stub(compiler, arrays_hashcode_powers_of_31)                       \
> 77:   do_arch_entry(riscv, compiler, arrays_hashcode_powers_of_31,          \
> 78:                 arrays_hashcode_powers_of_31, arrays_hashcode_powers_of_31) \

Let's keep the trailing `` aligned:

  do_stub(compiler, arrays_hashcode_powers_of_31)                       \
  do_arch_entry(riscv, compiler, arrays_hashcode_powers_of_31,          \
            arrays_hashcode_powers_of_31, arrays_hashcode_powers_of_31) \

src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 6587:

> 6585:     assert(UseRVV, "sanity");
> 6586:     const int ints_in_vec_reg = MaxVectorSize / sizeof(jint);
> 6587:     const int lmul = 2;

Suggestion:

    const int lmul = 2;
    const int stride = MaxVectorSize / sizeof(jint) * lmul;

    ......

    for (int i = stride; i >= 0; i--) {

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

PR Review: https://git.openjdk.org/jdk/pull/17413#pullrequestreview-3122586012
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2278068359
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2278065225
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2278061270
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2278050015
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2278077761