[aarch64-port-dev ] [16] RFR(S): 8251525: AARCH64: Faster Math.signum(fp)

[Andrew Haley]

On 31/08/2020 15:28, Dmitry Chuyko wrote:
> Here is another version of intrinsics. It is an extension of webrev.03.
> Additional thing is that constants 0 and 1 that are used internally by
> intrinics are constructed as nodes. This is somehow similar to what is
> done for passing pointers to tables.
>
> webrev: http://cr.openjdk.java.net/~dchuyko/8251525/webrev.04/
> results:
> http://cr.openjdk.java.net/~dchuyko/8251525/webrev.04/benchmarks/signum-facgt_ir-copysign.ods

Hi,

Thank you. That certainly looks better.

It's unfortunate that signum doesn't help in all cases, but I'm happy
that we have something positive in general. Certainly the code looks
nice. I'm still rather baffled that an intrinsification of copySign
actually makes things much worse on blackhole on Neoverse N1, but it
doesn't really matter because the copySign intrinsic isn't enabled by
default. So please go ahead with this version.

Having said all of that, it's a fairly minor improvement for some
considerable complexity. And it depends terribly on the
micorarchitecture of a particular part, albeit an important one.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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