RFR: 8333382: [s390x] Enhance popcnt Instruction to use Z15 facilities [v8]

[Andrew Haley]

On Tue, 11 Jun 2024 10:39:30 GMT, Amit Kumar <amitkumar at openjdk.org> wrote:

>> We need to move popcnt instruction implementation out of s390.ad file as it is required to be required some methods present in [JDK-8331126.](https://bugs.openjdk.org/browse/JDK-8331126)
>> 
>> 
>> When the miscellaneous-instruction-extensions facility 3 is not installed or bit 0 of the M3
>>  field is zero, a count of the number of one bits in each of the eight bytes of general register
>>  R2 is placed into the corresponding byte of general register R1. Each byte of general register 
>> R1 is an 8-bit binary integer in the range of 0-8.
>> 
>> 
>> 
>> When the miscellaneous-instruction-extensions facility 3 is installed and bit 0 of the M3 field
>> is one, a count of the total number of one bits in the 64-bit general register R2 is placed into 
>> general register R1. The result is a 64-bit unsigned integer in the range 0 to 64.
>> 
>> 
>> Performed tier1 test on fastdebug build and didn't see any regression.
>
> Amit Kumar has updated the pull request incrementally with one additional commit since the last revision:
> 
>   removes if and uses guarantee

src/hotspot/cpu/s390/macroAssembler_s390.hpp line 1032:

> 1030: 
> 1031:   // Up for an adventure ? use these instructions :)
> 1032:   // Should be only used when you're sure that instruction will "only" run on hardware older than z15

Suggestion:

  // For legacy (pre-z15) use, but will work on all supported s390 implementations.

src/hotspot/cpu/s390/macroAssembler_s390.hpp line 1037:

> 1035: 
> 1036:   // Should be used in a case, where you're sure that instruction will never touch a hardware older than z15
> 1037:   // it will only run on either a z15 machine or successor of it

Suggestion:

  // Only for use on z15 or later s390 implementations.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/19509#discussion_r1634716109
PR Review Comment: https://git.openjdk.org/jdk/pull/19509#discussion_r1634716972