New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

cmd/compile: ARM: add FMA support #22400

Open
rasky opened this Issue Oct 23, 2017 · 2 comments

Comments

Projects
None yet
4 participants
@rasky
Member

rasky commented Oct 23, 2017

Tracking bug for missing FMA (fused multiply-add) support on ARM/ARM64 backends.

I think that, for 32-bit ARM, part of the problem is that FMA support is sparse; it requires a specific FPU type, so it doesn't even correctly map to a specific architecture (as identified by the current GOARM environment variable).

@cherrymui

This comment has been minimized.

Contributor

cherrymui commented Oct 23, 2017

@benshi001 has attempted to do it on ARM32, in CL https://go-review.googlesource.com/c/go/+/63770. It turns out that even GOARM=7 machine may not support fused multiply-add. That CL then added and made use of (non-fused) multiply-add instruction.

Given that we already do multiply-add in one instruction, and the fused version is not widely available (and not sure how much faster it is compared to non-fused version), I'm not sure what we want to do here.

cc @benshi001

@benshi001

This comment has been minimized.

Member

benshi001 commented Oct 24, 2017

the fused mul-add was introduced in VFP-4, which GOARM=7 does not imply.

@ianlancetaylor ianlancetaylor changed the title from ARM: add FMA support to cmd/compile: ARM: add FMA support Mar 29, 2018

@ianlancetaylor ianlancetaylor added this to the Unplanned milestone Mar 29, 2018

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment