RFR: JDK-8331859 : [PPC64] Remove support for Power7 and older [v14]

[Martin Doerr]

On Tue, 20 May 2025 14:48:07 GMT, Suchismith Roy <sroy at openjdk.org> wrote:

>> JBS Issue: [JDK-8331859](https://bugs.openjdk.org/browse/JDK-8331859) 
>> Linux PPC64le requires Power8 since the beginning.
>> AIX requires Power8 with the new OpenXL based build ([JDK-8307520](https://bugs.openjdk.org/browse/JDK-8307520)). The old build has been removed in JDK 23 ([JDK-8327701](https://bugs.openjdk.org/browse/JDK-8327701)).
>> Linux PPC64 Big Endian is no longer officially supported (only kept alive for development, debugging and testing purposes).
>> 
>> The following checks for old processors are no longer needed:
>> 8: VM_Version::has_lqarx()
>> 7: VM_Version::has_popcntw()
>> 6: VM_Version::has_cmpb()
>> 5: VM_Version::has_popcntb()
>> These ones and some more checks for old instructions are no longer needed. All code which is no longer reachable when removing them should also get removed.
>> Checks like "PowerArchitecturePPC64 >= 8" (or older) can be removed.
>> 
>> Atomic::PlatformCmpxchg<1>::operator() can be simplified by using sub-word instructions (lharx, lbarx).
>> 
>> Temp registers can be removed from cmpxchgb and cmpxchgh.
>> 
>> Build flags "-mcpu=powerpc64 -mtune=power5" for Big Endian linux should get replaced by "-mcpu=power8 -mtune=power8" as already used for linux PPC64le.
>
> Suchismith Roy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove costly operations

src/hotspot/cpu/ppc/ppc.ad line 3398:

> 3396:     __ li($dst$$Register, $src$$constant);
> 3397:     __ bind(done);
> 3398:   %}

Now, you have a lot of empty lines! Also at other places where you removed code.

src/hotspot/cpu/ppc/vm_version_ppc.cpp line 168:

> 166:                "ppc64%s%s%s%s",
> 167:                (" sha"),
> 168:                (" aes"),

Why did you revert this part?

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PR Review Comment: https://git.openjdk.org/jdk/pull/20262#discussion_r2098240930
PR Review Comment: https://git.openjdk.org/jdk/pull/20262#discussion_r2098242766