RFR: 8255553: [PPC64] Introduce and use setbc and setnbc P10 instructions [v7]

[Martin Doerr]

On Thu, 5 Nov 2020 13:30:11 GMT, Ziviani <github.com+670087+jrziviani at openjdk.org> wrote:

>> - setbc RT,BI: sets RT to 1 if CR(BI) is 1, otherwise 0.
>> - setnbc RT,BI: sets RT to -1 if CR(BI) is 1, otherwise 0.
>> Ref: PowerISA 3.1, page 129.
>> 
>> These instructions are particularly interesting to improve the following
>> pattern `(src1<src2)? -1: ((src1>src2)? 1: 0)`, which can be found in
>> `instruct cmpL3_reg_reg_ExEx()@ppc.ad`, by removing its branches.
>> 
>> Long.toString, that generate such pattern in getChars, has showed a
>> good performance gain by using these new instructions.
>> 
>> Example:
>> for (int i = 0; i < 200_000; i++)
>>   res = Long.toString((long)i);
>> 
>> java -Xcomp -XX:CompileThreshold=1 -XX:-TieredCompilation TestToString
>> 
>> Without setbc (average): 0.1178 seconds
>> With setbc (average): 0.0396 seconds
>
> Ziviani has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:
> 
>   8255553: [PPC64] Introduce and use setbc and setnbc P10 instructions
>   
>   - setbc RT,BI: sets RT to 1 if CR(BI) is 1, otherwise 0.
>   - setnbc RT,BI: sets RT to -1 if CR(BI) is 1, otherwise 0.
>   Ref: PowerISA 3.1, page 129.
>   
>   These instructions are particularly interesting to improve the following
>   pattern `(src1<src2)? -1: ((src1>src2)? 1: 0)`, which can be found in
>   `instruct cmpL3_reg_reg_ExEx()@ppc.ad`, by removing its branches.
>   
>   Long.toString, that generate such pattern in getChars, has showed a
>   good performance gain by using these new instructions.
>   
>   Example:
>   for (int i = 0; i < 200_000; i++)
>     res = Long.toString((long)i);
>   
>   java -Xcomp -XX:CompileThreshold=1 -XX:-TieredCompilation TestToString
>   
>   Without setbc (average): 0.1178 seconds
>   With setbc (average): 0.0396 seconds

Tests look good on Power8/9.

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

Marked as reviewed by mdoerr (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/907