RFR: JDK-8331859 : [PPC64] Remove support for Power7 and older [v4]

Thu Apr 17 17:04:10 UTC 2025

On Thu, 17 Apr 2025 08:03:02 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 with a new target base due to a merge or a rebase. The pull request now contains 27 commits:
> 
>  - Merge branch 'openjdk:master' into power8
>  - mfdscr removal
>  - indents
>  - indents
>  - mcpu flag
>  - superword
>  -  further cleanup
>  - clean of power 7 instructions
>  - Removal of older P7 Instructions
>  - Removal of older P7 Instructions
>  - ... and 17 more: https://git.openjdk.org/jdk/compare/1138a186...4aa520c2

Very nice that we can get rid of so much code!

src/hotspot/cpu/ppc/c1_LIRAssembler_ppc.cpp line 551:

> 549:         __ mtfprd(rdst, src->as_register_lo());
> 550:       }
> 551:       rsrc = rdst;

Further simplification: Remove rsrc and use `fcfid(rdst, rdst)`

src/hotspot/cpu/ppc/c1_LIRAssembler_ppc.cpp line 566:

> 564:       }
> 565:       rsrc = rdst;
> 566:       __ fcfids(rdst, rsrc);

Same here.

src/hotspot/cpu/ppc/c1_LIRAssembler_ppc.cpp line 1548:

> 1546:   }
> 1547: 
> 1548:   // Try to use isel on >=Power7.

The comment should also get removed.

src/hotspot/cpu/ppc/globals_ppc.hpp line 118:

> 116:                                                                             \
> 117:   /* special instructions */                                                \
> 118:   product(bool, SuperwordUseVSX, true,                                     \

Please add one space before ''.

src/hotspot/cpu/ppc/macroAssembler_ppc.cpp line 1574:

> 1572:   // Sub-word instructions are available since Power 8.
> 1573: 
> 1574:   const int instruction_type = size;

Maybe remove `instruction_type` and use `size` directly below?

src/hotspot/cpu/ppc/macroAssembler_ppc.cpp line 4238:

> 4236:                                      : StubRoutines::crc_table_addr()   , R0);
> 4237: 
> 4238:   kernel_crc32_vpmsum(crc, buf, len, t0, t1, t2, t3, t4, t5, t6, t7, !is_crc32c);

`kernel_crc32_1word` is now dead and should be removed completely.

src/hotspot/cpu/ppc/ppc.ad line 2070:

> 2068:       return VM_Version::has_fsqrt();
> 2069:     case Op_RoundDoubleMode:
> 2070:       return VM_Version::has_vsx();

Please remove `Op_SqrtD` and `Op_RoundDoubleMode` from this list. We should not fall through to `return UseCountLeadingZerosInstructionsPPC64;` which is wrong.

src/hotspot/cpu/ppc/ppc.ad line 10367:

> 10365: 
> 10366: // Double to Int conversion, NaN is mapped to 0.
> 10367: instruct convD2I_reg_ExEx(iRegIdst dst, regD src) %{

This `instruct` should be completely removed.

src/hotspot/cpu/ppc/ppc.ad line 10410:

> 10408: 
> 10409: // Float to Int conversion, NaN is mapped to 0.
> 10410: instruct convF2I_regF_ExEx(iRegIdst dst, regF src) %{