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F16C has been available for well over a decade (it was introduced in the Ivybridge uArch), and the equivalent conversions are supported on all ARMv7 CPUs since around the same time (and all ARMv8 CPUs unconditionally); most software should be able to safely assume their availability by now.

There exist some niches where this doesn’t hold, but that’s why we have software fallbacks.

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The first niche that came to mind was x86 code running under Rosetta 2; despite ARM having an equivalent to F16C, Rosetta 2 doesn’t translate AVX, and F16C doesn’t have a non-AVX encoding.

Indeed. Worth noting that Accelerate.framework provides fast and correct bulk f16 <-> f32 conversions as `vImageConvert_Planar16FtoPlanarF` and `vImageConvert_PlanarFtoPlanar16F`, and that the arm conversion instructions are unconditionally available for apps that compile for arm64 (they're part of the base ARMv8 ISA), so any _new_ code shouldn't need to worry about this.

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