Refactor conv 3 #5714

Job	Run time
linux (raspbian)	6m 46s
linux (aarch64-unknown-linux-gnu)	11m 53s
linux (armv6vfp-unknown-linux-gnueabihf)	10m 27s
linux (armv7-unknown-linux-gnueabihf)	10m 15s
linux (aarch64-unknown-linux-musl)	12m 24s
linux (armv7-unknown-linux-musl)	9m 39s
linux (aarch64-linux-android)	1m 11s
linux (armv7-linux-androideabi)	1m 25s
linux (i686-linux-android)	1m 13s
apple (aarch64-apple-ios)	1m 37s
linux (x86_64-linux-android)	1m 12s
apple (aarch64-apple-darwin)	6m 44s
linux (wasm32-unknown-unknown)	28s
linux (wasm32-wasi)	32s
	1h 15m 46s

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