RFR: 8345177: RISC-V: Add gtests for cmpxchg

[Fei Yang]

On Thu, 28 Nov 2024 12:30:12 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

> Hi, please consider.
> 
> This adds tests to some of the base cases.
> Focusing on the cases when we pass in same register in some of the argument. (variant 0,1,2,3)
> 
> Note: Google Test filter = *RiscV.cmpxchg*
> [==========] Running 4 tests from 1 test suite.
> [----------] Global test environment set-up.
> [----------] 4 tests from RiscV
> [ RUN      ] RiscV.cmpxchg_int64_plain_lr_sc_vm
> [       OK ] RiscV.cmpxchg_int64_plain_lr_sc_vm (2 ms)
> [ RUN      ] RiscV.cmpxchg_int64_plain_maybe_zacas_vm
> [       OK ] RiscV.cmpxchg_int64_plain_maybe_zacas_vm (0 ms)
> [ RUN      ] RiscV.cmpxchg_int32_plain_lr_sc_vm
> [       OK ] RiscV.cmpxchg_int32_plain_lr_sc_vm (0 ms)
> [ RUN      ] RiscV.cmpxchg_int32_plain_maybe_zacas_vm
> [       OK ] RiscV.cmpxchg_int32_plain_maybe_zacas_vm (0 ms)
> [----------] 4 tests from RiscV (20806 ms total)
> 
> [----------] Global test environment tear-down
> [==========] 4 tests from 1 test suite ran. (20809 ms total)
> [  PASSED  ] 4 tests.
> 
> 
> Executed with `-XX:+UnlockExperimentalVMOptions -XX:+UseZacas`
> 
> Thanks, Robbin

Nice tests! I only have one minor question. Thanks.

test/hotspot/gtest/riscv/test_assembler_riscv.cpp line 153:

> 151:     }
> 152:     _masm.flush();
> 153:     OrderAccess::cross_modify_fence();

Do we need this `cross_modify_fence`? Seems to me the preceding `_masm.flush()` which delegates work to `riscv_flush_icache` syscall will do here. Same question for the `CmovTester` case.

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PR Review: https://git.openjdk.org/jdk/pull/22437#pullrequestreview-2468987523
PR Review Comment: https://git.openjdk.org/jdk/pull/22437#discussion_r1862858193