RFR: 8307495: Specialize atomic bitset functions for aix-ppc [v6]

[Richard Reingruber]

On Fri, 10 Oct 2025 09:15:35 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> src/hotspot/cpu/ppc/atomicAccess_ppc.hpp line 186:
>> 
>>> 184:     : [dest]            "b"     (dest),
>>> 185:       [exchange_value]  "r"     (exchange_value),
>>> 186:                         "m"     (*dest)
>> 
>> The memory operands with constraint 'm' are unused. I think the intent was to express that `dest` is dereferenced to read and write memory at that location. But that's expressed with `memory` in the `clobber` section.
>> These operands should be removed.
>
> Do you know what "b" means? We use "r" at other places.

It means base register (R0 not allowed). See PowerPC section in https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html

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PR Review Comment: https://git.openjdk.org/jdk/pull/27650#discussion_r2419042661