RFR: 8345322: RISC-V: Add concurrent gtests for cmpxchg variants [v4]

[Robbin Ehn]

On Wed, 11 Dec 2024 14:20:31 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> test/hotspot/gtest/riscv/test_assembler_riscv.cpp line 296:
>> 
>>> 294:   bool zacas = UseZacas;
>>> 295:   UseZacas = false;
>>> 296:   run_plain_cmpxchg_tests<uint32_t, Assembler::uint32>();
>> 
>> Not quite sure if we should cover `uint32` type here. `lr.w` used to implement the CAS operation loads a 32-bit word and sign-extend it.
>
> As passing uint32 as operand size is supported and done by compareAndSwapNNode.
> So we should test it ?
> 
> Which also says we should add test with max and min size of TESTSIZE, fixing that.

So one case is shenandoah CAS:ing a narrow oop.
Narrow oop are zero extended (MASM::set_narrow_oop) which means expected, exchange values should be zero extended. Hence I think we have yet another cmpxchg bug.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22574#discussion_r1880456441