Indexing a SubArray without @inbounds prevents its allocation from being elided

[KristofferC]

For example:

julia> f(x) = view(x, :)[3]
f (generic function with 1 method)

julia> f2(x) = @inbounds view(x, :)[3]
f2 (generic function with 1 method)

julia> x = rand(3);

julia> @btime f($x);
  8.618 ns (1 allocation: 48 bytes)

julia> @btime f2($x);
  1.503 ns (0 allocations: 0 bytes)

Presumably, this is because it appears in a call to Base.throw_boundserror. Not surprising, but it means that many SubArrays hang around even though their only non-inlined usage is in an error branch.