# Tracking the cause of allocation in the presence of a generated function

**URL:** <https://discourse.julialang.org/t/tracking-the-cause-of-allocation-in-the-presence-of-a-generated-function/98215>\
**Category:** Performance\
**Tags:** performance, arrays, staticarrays\
**Created:** [May 2, 2023, 5:25pm UTC](https://discourse.julialang.org/t/tracking-the-cause-of-allocation-in-the-presence-of-a-generated-function/98215 "2023-05-02T17:25:35Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![mateuszbaran](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mateuszbaran/32/221842_2.png) [@mateuszbaran](https://discourse.julialang.org/u/mateuszbaran)\
**Post date:** [May 2, 2023, 5:25pm UTC](https://discourse.julialang.org/t/tracking-the-cause-of-allocation-in-the-presence-of-a-generated-function/98215/1 "2023-05-02T17:25:35Z")

</div>

I have some trouble tracking why the following code allocates:

```julia
julia> using HybridArrays, StaticArrays
[Info: Precompiling HybridArrays [1baab800-613f-4b0a-84e4-9cd3431bfbb9]

julia> using BenchmarkTools

julia> H = HybridArray{Tuple{2,2,StaticArrays.Dynamic()}}(randn(2,2,2))
2×2×2 HybridArray{Tuple{2, 2, StaticArraysCore.Dynamic()}, Float64, 3, 3, Array{Float64, 3}} with indices SOneTo(2)×SOneTo(2)×Base.OneTo(2):
[:, :, 1] =
^[[B 0.363275 -1.4971
 -0.380408 0.34421

[:, :, 2] =
 0.191441 0.681372
 0.667848 0.128238

julia> H2 = HybridArray{Tuple{2,2,StaticArrays.Dynamic()}}(Array{Float64}(undef, 2, 2, 4))
2×2×4 HybridArray{Tuple{2, 2, StaticArraysCore.Dynamic()}, Float64, 3, 3, Array{Float64, 3}} with indices SOneTo(2)×SOneTo(2)×Base.OneTo(4):
[:, :, 1] =
 6.90494e-310 6.90494e-310
 0.0 0.0

[:, :, 2] =
 6.90494e-310 6.90494e-310
 0.0 0.0

[:, :, 3] =
 6.90503e-310 6.90503e-310
 0.0 0.0

[:, :, 4] =
 6.90503e-310 6.90503e-310
 0.0 0.0

julia> f2(H, H2) = copyto!(view(H2,:,:,1:2), H)
f2 (generic function with 1 method)

julia> @btime f2($H, $H2)
  187.921 ns (16 allocations: 512 bytes)
2×2×2 HybridArray{Tuple{2, 2, StaticArraysCore.Dynamic()}, Float64, 3, 3, SubArray{Float64, 3, HybridArray{Tuple{2, 2, StaticArraysCore.Dynamic()}, Float64, 3, 3, Array{Float64, 3}}, Tuple{Base.Slice{SOneTo{2}}, Base.Slice{SOneTo{2}}, UnitRange{Int64}}, true}} with indices SOneTo(2)×SOneTo(2)×Base.OneTo(2):
[:, :, 1] =
  0.363275 -1.4971
 -0.380408 0.34421

[:, :, 2] =
 0.191441 0.681372
 0.667848 0.128238

```

`--track-allocation` returns results that don’t seem to make sense, Cthulhu/`@code_llvm`/`@code_native`/`@code_typed` either don’t report anything looking like an allocation or (in case of Cthulhu) give up on a generated function. They seem to not even completely agree what is inlined and what isn’t. Execution time profiling gives the strongest hint, pointing to this line: [HybridArrays.jl/indexing.jl at eb631401cfdf3aa048f5728b02a16a3b638c9cad · JuliaArrays/HybridArrays.jl · GitHub](https://github.com/JuliaArrays/HybridArrays.jl/blob/eb631401cfdf3aa048f5728b02a16a3b638c9cad/src/indexing.jl#L238) as the source of allocations but it doesn’t make any sense to me. It just invokes a `setindex!` on a subarray, a very straightforward function that shouldn’t allocate. Can someone give me an advice?

---

<div class="post-metadata">

**Author:** ![judober](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/judober/32/6676_2.png) [@judober](https://discourse.julialang.org/u/judober)\
**Post date:** [May 8, 2023, 2:04pm UTC](https://discourse.julialang.org/t/tracking-the-cause-of-allocation-in-the-presence-of-a-generated-function/98215/2 "2023-05-08T14:04:42Z")

</div>

I played a litte with this.  
For me it is similar with 1.8.5 and 1.9.0-rc3:  
`193.553 ns (16 allocations: 512 bytes)` and `199.266 ns (16 allocations: 512 bytes)` respectively.  
However, in 1.6.7 it is a little better with `130.306 ns (16 allocations: 256 bytes)`.  
So maybe it is a compiler-problem?