RFR: 8278302: [s390] Implement fast-path for ASCII-compatible CharsetEncoders [v2]

[Lutz Schmidt]

On Mon, 17 Jan 2022 11:34:55 GMT, Lutz Schmidt <lucy at openjdk.org> wrote:

>> This pull request contains the s390x variant of the fast-path for ASCII-compatible CharsetEncoders. 
>> 
>> The intrinsic implementation is pretty much similar to that of PPC64. Compared to the previously existing intrinsic implementation, changes to program logic are minimal. There is a new match rule for ascii strings and the bit mask used to detect invalid bits in the string characters is set depending on the target charset: 0xff00 for ISO, 0xff80 for ascii.
>> 
>> **Request:** SAP does not maintain a full build and test infrastructure for s390x anymore. Could somebody please test this PR on s390x? At least build and tier1 tests, the more the better. Thank you!
>> 
>> With my private testing (some microbenchmarks, some SPEC benchmarks) I could not find any issues. With the fast-path active I see a 2x, sometime 2.5x, improvement of CharsetEncodeDecode.encode. 
>> 
>> **Without the fast-path patch:**
>> 
>> CharsetEncodeDecode.encode   16384        UTF-8  avgt   30  16.350 ± 0.067  us/op
>> CharsetEncodeDecode.encode   16384         BIG5  avgt   30  15.972 ± 0.136  us/op
>> CharsetEncodeDecode.encode   16384  ISO-8859-15  avgt   30  14.372 ± 0.110  us/op
>> CharsetEncodeDecode.encode   16384        ASCII  avgt   30  14.287 ± 0.051  us/op
>> 
>> 
>> **With the fast-path patch:**
>> 
>> CharsetEncodeDecode.encode   16384        UTF-8  avgt   30   6.833 ± 0.064  us/op
>> CharsetEncodeDecode.encode   16384         BIG5  avgt   30   8.195 ± 0.059  us/op
>> CharsetEncodeDecode.encode   16384  ISO-8859-15  avgt   30   6.387 ± 0.149  us/op
>> CharsetEncodeDecode.encode   16384        ASCII  avgt   30   6.321 ± 0.049  us/op
>
> Lutz Schmidt has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8278302: fix bug in us-ascii mask generation

Thank you for your comments, Claes!
As SAP has passed on responsibility for the s390 port, I would like to receive a "lead" review from the new maintainers. Then, I could recruit a "second opinion" from my direct colleagues.

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PR: https://git.openjdk.java.net/jdk/pull/6738