cmd/asm, math: improve performance for math.Floor, math.Ceil, math.Trunc with asm on ppc64x

[laboger]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

tip

What operating system and processor architecture are you using (go env)?

Ubuntu 16.04 ppc64le

What did you do?

Built and ran the math package benchmark test.

What did you expect to see?

Better performance for floor, ceil, and trunc functions in math package.

What did you see instead?

Room for improvement

The Power instruction set includes frim, frip, and friz which can be used to implement the Go math package's floor, ceil, and trunc functions more efficiently. These instructions are used in the existing gccgo implementation for these math functions for ppc64x. These are compatible with power5 so can be used in both ppc64le & ppc64.

[gopherbot]

CL https://golang.org/cl/29654 mentions this issue.

[minux]

frim breaks ppc970 comparability, reopen.

[laboger]

The decision was that ppc64 would support instructions back to power5, not ppc970. This was documented in the go1.7 release notes. https://golang.org/doc/go1.7.

[bradfitz]

@laboger, I updated https://golang.org/wiki/MinimumRequirements

[laboger]

So can this be closed? Here are other issues where this was discussed #16004 #16372 and I thought this was the final decision with respect to this topic.

[bradfitz]

Yes, looks like it.