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cmd/compile: ARM: add FMA support #22400

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rasky opened this issue Oct 23, 2017 · 3 comments
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cmd/compile: ARM: add FMA support #22400

rasky opened this issue Oct 23, 2017 · 3 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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@rasky
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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
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@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
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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 the NeedsFix The path to resolution is known, but the work has not been done. label Mar 29, 2018
@ianlancetaylor ianlancetaylor added this to the Unplanned milestone Mar 29, 2018
@agnivade
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agnivade commented Nov 9, 2019

Closing this as per this comment. We have a similar code for ARM too.

Please feel free to reopen if this was a mistake.

@agnivade agnivade closed this as completed Nov 9, 2019
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