Not really in this case; Rav1e runs over blocks of image planes (like say a 16x16 block of a specific 720p color channel), so there is no continuous slice to iterate over.
I mean maybe? But I probably wouldn't anyway for this case as a slice reference is actually a "fat" pointer (ie twice the size of a normal pointer) and the length of the slice won't be used (the block size is known per kernel); LLVM might delete the length part anyway.
These are automatically generated kernels, so readability isn't the primary concern here.