The @effects attribute?

[Jens]

@Joe_Groff

readnone , and the other LLVM-level effects, is too low-level of a concept to be generally useful for Swift code.

Yes, my interest was sparked by this post from another thread:

@scanon

Yeah. nextUp is actually slightly more efficient than the C nextafter function, because it doesn't need to figure out what direction to move. It's right around the size threshold where inlining would make sense in general contexts. And, yes, we should be able to mark it readnone .

And looking at nextUp's implementation as well as eg that of the new hashing, I sometimes need to write code at that level, so I thought it would be good to know more about @effects as part of my ongoing quest to get better at writing performance critical code (both in general and in Swift).

@Joe_Groff

readnone means that a function does not read or write memory at all. Unspecialized generic functions pass their arguments through memory so can never be readnone .

Does this mean that a generic function can never be marked @effects(readnone), or that it works only together with some other attribute(s) like @_specialize or @_transparent?