JuliaGPU / JuliaGPU/GPUArrays.jl
Vectorized getindex of wrapped array falls back to scalar indexing
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Description
I wasn't sure how much this issue overlaps with existing ones, so apologies if this is a duplicate.
I constantly get into the aforementioned scalar indexing issue when working with `transpose`.
I opened a new PR (https://github.com/JuliaLang/julia/pull/52626) on base Julia intended to fix the problem, so I wanted to raise awareness and get feedback from the experts here as well.
copying the MWE here to demonstrate the error (which is avoided after the PR changes):
```julia
julia> using LinearAlgebra, JLArrays
julia> JLArrays.allowscalar(false)
julia> x = rand(Float32, 2,2) |> jl ; y = transpose(x);
julia> y[:,1]
ERROR: Scalar indexing is disallowed.
Invocation of getindex resulted in scalar indexing of a GPU array.
This is typically caused by calling an iterating implementation of a method.
Such implementations *do not* execute on the GPU, but very slowly on the CPU,
and therefore should be avoided.
If you want to allow scalar iteration, use `allowscalar` or `@allowscalar`
to enable scalar iteration globally or for the operations in question.
Stacktrace:
[1] error(s::String)
@ Base ./error.jl:35
[2] errorscalar(op::String)
@ GPUArraysCore ~/.julia/packages/GPUArraysCore/GMsgk/src/GPUArraysCore.jl:155
[3] _assertscalar(op::String, behavior::GPUArraysCore.ScalarIndexing)
@ GPUArraysCore ~/.julia/packages/GPUArraysCore/GMsgk/src/GPUArraysCore.jl:128
[4] assertscalar(op::String)
@ GPUArraysCore ~/.julia/packages/GPUArraysCore/GMsgk/src/GPUArraysCore.jl:116
[5] getindex
@ ~/.julia/packages/GPUArrays/EoKy0/src/host/indexing.jl:48 [inlined]
[6] scalar_getindex
@ ~/.julia/packages/GPUArrays/EoKy0/src/host/indexing.jl:34 [inlined]
[7] _getindex
@ ~/.julia/packages/GPUArrays/EoKy0/src/host/indexing.jl:17 [inlined]
[8] getindex
@ ~/.julia/packages/GPUArrays/EoKy0/src/host/indexing.jl:15 [inlined]
[9] getindex
@ ~/julia/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/adjtrans.jl:334 [inlined]
[10] macro expansion
@ ./multidimensional.jl:921 [inlined]
[11] macro expansion
@ ./cartesian.jl:64 [inlined]
[12] _unsafe_getindex!
@ ./multidimensional.jl:916 [inlined]
[13] _unsafe_getindex(::IndexCartesian, ::Transpose{Float32, JLArray{Float32, 2}}, ::Base.Slice{Base.OneTo{Int64}}, ::Int64)
@ Base ./multidimensional.jl:907
[14] _getindex
@ Base ./multidimensional.jl:893 [inlined]
[15] getindex(::Transpose{Float32, JLArray{Float32, 2}}, ::Function, ::Int64)
@ Base ./abstractarray.jl:1314
[16] top-level scope
@ REPL[10]:1
```
In particular, I want to hear if there's something I'm missing like some memory contiguous requirements etc.
Cheers
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