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cmd/compile: ARM: add FMA support #22400

rasky opened this issue Oct 23, 2017 · 2 comments


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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).


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commented Oct 23, 2017

@benshi001 has attempted to do it on ARM32, in CL 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


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commented Oct 24, 2017

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

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

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

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