RFR: 8315716: RISC-V: implement ChaCha20 intrinsic

[Antonios Printezis]

On Mon, 25 Sep 2023 11:47:40 GMT, Hamlin Li <mli at openjdk.org> wrote:

> Only vector version is included in this patch.
> 
> ### Test
> The patch passed the jdk tests found via `find test/jdk/ -iname *ChaCha*`

src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 4326:

> 4324:     const Register tmp_addr = t1;
> 4325:     const Register length = t2;
> 4326:     const Register avl = x28;

Can you add the rest of the tmp registers to:


// temporary register(caller-save registers)
constexpr Register t0 = x5;
constexpr Register t1 = x6;
constexpr Register t2 = x7;


so you can use `t3` / `t4` here instead of `x28` / `x29`?

src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 4338:

> 4336: 
> 4337:     RegSet saved_regs;
> 4338:     __ push_reg(saved_regs, sp);

You're only using tmp registers it looks like? Is this needed, as the `saved_regs` set is empty?

src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 4342:

> 4340:     // Put 16 here, as com.sun.crypto.providerChaCha20Cipher.KS_MAX_LEN is 1024
> 4341:     // in java level.
> 4342:     __ li(avl, 16);

It's recommended to use `__ mv(avl, 16);` to copy a constant to a register.

src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 4355:

> 4353: 
> 4354:     // Perform 10 iterations of the 8 quarter round set
> 4355:     __ li(loop, 10);

`__ mv(loop, 10);`

src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 4381:

> 4379: 
> 4380:     // Store result to key stream
> 4381:     __ li(stride, 64);

`__ mv(stride, 64);`

src/hotspot/cpu/riscv/vm_version_riscv.cpp line 251:

> 249:     FLAG_SET_DEFAULT(UseBlockZeroing, false);
> 250:   }
> 251:   if (UseRVV) {

What happens if someone enables `+UseChaCha20Intrinsics` without `+UseRVV`? Maybe check if `-UseRVV` and `+UseChaCha20Intrinsics` and disable it?

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PR Review Comment: https://git.openjdk.org/jdk/pull/15899#discussion_r1336263149
PR Review Comment: https://git.openjdk.org/jdk/pull/15899#discussion_r1336260087
PR Review Comment: https://git.openjdk.org/jdk/pull/15899#discussion_r1336247004
PR Review Comment: https://git.openjdk.org/jdk/pull/15899#discussion_r1336248783
PR Review Comment: https://git.openjdk.org/jdk/pull/15899#discussion_r1336249320
PR Review Comment: https://git.openjdk.org/jdk/pull/15899#discussion_r1336241132