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cmd/compile: ARM: add FMA support #22400
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
@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.