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

[Suchismith Roy]

On Wed, 2 Apr 2025 20:36:38 GMT, Martin Doerr <mdoerr 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.
>
> src/hotspot/cpu/ppc/vm_version_ppc.hpp line 113:
> 
>> 111:   static bool has_fcfids()  { return (_features & fcfids_m) != 0; }
>> 112:   static bool has_vand()    { return (_features & vand_m) != 0; }
>> 113:   static bool has_lqarx()   { return (_features & lqarx_m) != 0; }
> 
> Why are the other Power7 and older instruction checks not removed?

Hi @TheRealMDoerr  I removed the instructions mentioned in the issue. How can I determine which instructions were older ? Is there a file where it is mentioned specifically ?

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PR Review Comment: https://git.openjdk.org/jdk/pull/20262#discussion_r2030708128