RFR: 8315856: RISC-V: Use Zacas extension for cmpxchg [v5]

[Fei Yang]

On Tue, 12 Dec 2023 21:09:45 GMT, Ludovic Henry <luhenry at openjdk.org> wrote:

>> 8315856: RISC-V: Use Zacas extension for cmpxchg
>
> Ludovic Henry has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix narrow compxchg

Two minor comments remain. What about the test coverage?

src/hotspot/cpu/riscv/macroAssembler_riscv.cpp line 2969:

> 2967:       seqz(result, t0);
> 2968:     } else {
> 2969:       if (result != expected) {

The same check is already there in `mv` [1].

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/riscv/macroAssembler_riscv.hpp#L470

src/hotspot/cpu/riscv/macroAssembler_riscv.cpp line 3096:

> 3094: #undef ATOMIC_CAS
> 3095: 
> 3096: #define ATOMIC_CASU(OP1, OP2)                                                       \

Nit: Need one extra space to keep the `` aligned.

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PR Review: https://git.openjdk.org/jdk/pull/16910#pullrequestreview-1783057607
PR Review Comment: https://git.openjdk.org/jdk/pull/16910#discussion_r1427503033
PR Review Comment: https://git.openjdk.org/jdk/pull/16910#discussion_r1427652620