@propagate_inbounds not working through copyto!

[vustef]

julia/base/array.jl

Line 294 in 1ebacac

copyto!(dest::Array, doffs::Integer, src::Array, soffs::Integer, n::Integer) = _copyto_impl!(dest, doffs, src, soffs, n)

invokes another function, even if I have my own function that propagates inbounds and invokes copyto!, boundscheck will actually trigger.
It seems like an oversight, but not sure if it was intentional.
I think I read somewhere that @propagate_inbounds is intended for one level of function calls, but given that, was it intentional that it invokes another function and therefore doesn't actually propagate inbounds to where it matters?

cc @NHDaly

[NHDaly]

As an example from our source code that @vustef is referring to, we have something like:

@inbounds begin
        resize!(result, len)
        copyto!(left.res_join_cols.data, 1, left.join_cols, 1, len)
        copyto!(left.res_non_join_cols.data, 1, left.non_join_cols, 1, len)
        # ...
end

and we were surprised to find that copyto!() is still performing boundschecks even though it's marked @inbounds.

Is this on-purpose?

[gbaraldi]

It's mostly intended since the boundscheck there is very cheap (It's one check for the whole operation).

[oscardssmith]

We could put a @propagate_inbounds on the copyto! and _copyto_impl! definitions to remove the check which would result in boundscheck removal.