RFR: 8322174: RISC-V: C2 VectorizedHashCode RVV Version [v25]

[Fei Yang]

On Wed, 13 Aug 2025 12:02:58 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:
> 
>   - addressed reviewer's comments/suggestions.

Thanks for the quick update. Some minor comments remain.

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp line 1920:

> 1918:                                         BasicType eltype)
> 1919: {
> 1920:   assert(!UseRVV, "sanity");

Although not dierectly related, can you fix indentation issue of switch-case in this function, `C2_MacroAssembler::arrays_hashcode_elsize` and `C2_MacroAssembler::arrays_hashcode_elload`?
We need add two spaces on the left of each case.

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp line 1998:

> 1996: {
> 1997:   assert(UseRVV, "sanity");
> 1998:   assert(MaxVectorSize >= 16, "sanity");

`MaxVectorSize >= 16` condition has already been ensured on JVM startup in `VM_Version::c2_initialize()`.

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp line 2005:

> 2003:   // size when check UseRVV (i.e. MaxVectorSize == VM_Version::_initial_vector_length).
> 2004:   // Let's use T_INT as all hashCode calculations eventually deal with ints.
> 2005:   const int ints_in_vec_reg = MaxVectorSize/sizeof(jint);

Please leave a space around the `/` operator.

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp line 2010:

> 2008:   const int elsize_bytes = arrays_hashcode_elsize(eltype);
> 2009:   const int elsize_shift = exact_log2(elsize_bytes);
> 2010:   const int MAX_VEC_MASK = ~(ints_in_vec_reg*lmul - 1);

Please leave a space around the `*` operator.

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp line 2024:

> 2022:   const Register pow31_highest  = tmp1;
> 2023:   const Register ary_end = tmp2;
> 2024:   const Register consumed = tmp3;

Suggestion:

  const Register pow31_highest  = tmp1;
  const Register ary_end        = tmp2;
  const Register consumed       = tmp3;

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp line 2056:

> 2054:   shadd(ary, consumed, ary, t0, elsize_shift);
> 2055:   subw(cnt, cnt, consumed);
> 2056:   andi(t1, cnt, MAX_VEC_MASK);

Can you move `subw + andi` to immediately before `bnez`?

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp line 2111:

> 2109:                                                  Register src,
> 2110:                                                  BasicType eltype) {
> 2111:   assert((T_INT == eltype) || (vdst != vtmp), "should be");

Or simply: `assert_different_registers(vdst, vtmp).` ?

src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 6586:

> 6584:   address generate_arrays_hashcode_powers_of_31() {
> 6585:     assert(UseRVV, "sanity");
> 6586:     const int ints_in_vec_reg = MaxVectorSize/sizeof(jint);

Please leave a space around the `/` operator.

src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 6591:

> 6589:     StubCodeMark mark(this, "StubRoutines", "arrays_hashcode_powers_of_31");
> 6590:     address start = __ pc();
> 6591:     for (int i = ints_in_vec_reg*lmul; i >= 0; i--) {

Please leave a space around the `*` operator.

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

PR Review: https://git.openjdk.org/jdk/pull/17413#pullrequestreview-3115969220
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2275637206
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2275645194
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2276613026
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2276615983
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2276622884
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2276591563
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2273430390
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2276613462
PR Review Comment: https://git.openjdk.org/jdk/pull/17413#discussion_r2276614023