RFR: 8318225: RISC-V: C2 UModI

[Robbin Ehn]

On Fri, 27 Oct 2023 09:15:11 GMT, Hamlin Li <mli at openjdk.org> wrote:

> Hi,
> Can you review the change to add intrinsic for UModI and UModL?
> ( This is a quite similar patch to https://github.com/openjdk/jdk/pull/16346, which addresses UDivI and UDivL, so for the performance consideration please also check the discussion in that pr. )
> Thanks!
> 
> 
> ## Tests
> 
> ### Functionality
> Run tests successfully found via `grep -nr test/jdk/ -we remainderUnsigned` and `grep -nr test/hotspot/ -we remainderUnsigned` 
> 
> ### Performance
> 
> #### Long
> **NOTE: for positive divisor, it's the common case; for negative divisor, it's a rare case**
> 
> **Before**
> 
> LongDivMod.testRemainderUnsigned                 1024          mixed  avgt   10  21222.911 ± 57.735  ns/op
> LongDivMod.testRemainderUnsigned                 1024       positive  avgt   10  28841.429 ±  6.294  ns/op
> LongDivMod.testRemainderUnsigned                 1024       negative  avgt   10   7733.038 ±  3.856  ns/op
> 
> 
> **After**
> 
> LongDivMod.testRemainderUnsigned                 1024          mixed  avgt   10  22666.448 ± 34.986  ns/op
> LongDivMod.testRemainderUnsigned                 1024       positive  avgt   10  15967.846 ± 24.805  ns/op
> LongDivMod.testRemainderUnsigned                 1024       negative  avgt   10  29507.865 ± 20.593  ns/op
> 
> 
> #### Integer
> **Before**
> 
> IntegerDivMod.testRemainderUnsigned                 1024          mixed  avgt   10  23396.475 ± 24.065  ns/op
> IntegerDivMod.testRemainderUnsigned                 1024       positive  avgt   10  16796.796 ±  3.389  ns/op
> IntegerDivMod.testRemainderUnsigned                 1024       negative  avgt   10  30159.407 ±  6.716  ns/op
> 
> 
> **After**
> 
> IntegerDivMod.testRemainderUnsigned                 1024          mixed  avgt   10  23216.710 ± 14.351  ns/op
> IntegerDivMod.testRemainderUnsigned                 1024       positive  avgt   10  16621.374 ±  3.203  ns/op
> IntegerDivMod.testRemainderUnsigned                 1024       negative  avgt   10  30002.088 ± 41.212  ns/op

Looks good, but these numbers:

LongDivMod.testRemainderUnsigned                 1024       negative  avgt   10     7733.038 ±  3.856  ns/op
IntegerDivMod.testRemainderUnsigned             1024       negative  avgt   10  30159.407 ±  6.716  ns/op


What up here ? How come in before case Long is 4-5x faster than Integer?

I don't see an explanation in other PR either ?

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

PR Comment: https://git.openjdk.org/jdk/pull/16394#issuecomment-1782602965