allocating linearalgebra

Hi,

I am surprised by the following behavior. Can you please tell me if this is expected?

Thank you,

Best regards,

```
using BenchmarkTools

xce0 = ArrayPartition(zeros(2),[0.])
xcde0 = copy(xce0)

function foo(y, x)
	y .= y .+ 2 .* x
end

@btime foo($xcde0, $xce0)
```
which gives

```
julia> @btime foo($xcde0, $xce0)
  30.138 ns (3 allocations: 48 bytes)
```