copy! is wrong for overlapping views

[stevengj]

The copy! function has special-casing to handle the case where the source and destination arrays are equal, but this machinery does not work for views:

julia> a = [1:10;]; copy!(a, 2, a, 1, 9)
10-element Array{Int64,1}:
 1
 1
 2
 3
 4
 5
 6
 7
 8
 9

julia> a = [1:10;]; v = view(a, 1:10); copy!(v, 2, v, 1, 9)
10-element SubArray{Int64,1,Array{Int64,1},Tuple{UnitRange{Int64}},true}:
 1
 1
 1
 1
 1
 1
 1
 1
 1
 1

[Keno]

@mbauman Can some of your new alias detection logic handle this case, or does it already?

[mbauman]

Nope, looks like I missed copyto! in implementing the detection. Should be as easy as adding an src′ = unalias(dest, src) line there.

[StefanKarpinski]

I'm pretty sure that it's no longer a performance trap to just reuse the src name here.

[KristofferC]

Dup of #16705