# FoldsCUDA not working with simple reduction

**URL:** <https://discourse.julialang.org/t/foldscuda-not-working-with-simple-reduction/101917>\
**Category:** GPU\
**Tags:** question, gpu, floops\
**Created:** [July 22, 2023, 5:30am UTC](https://discourse.julialang.org/t/foldscuda-not-working-with-simple-reduction/101917 "2023-07-22T05:30:25Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![RobertGregg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/robertgregg/32/22105_2.png) [@RobertGregg](https://discourse.julialang.org/u/RobertGregg)\
**Post date:** [July 22, 2023, 5:30am UTC](https://discourse.julialang.org/t/foldscuda-not-working-with-simple-reduction/101917/1 "2023-07-22T05:30:25Z")

</div>

I was trying to find the largest error between two matrix columns and I wanted to try parallelizing it on the GPU:

```plaintext
using FLoops
using CUDA
using FoldsCUDA

#To loop through all column pairs
allpairs(v) = ((i,j) for j in v for i in v if i > j)

function maxScore(data::CuArray{T}) where T

    @floop CUDAEx() for (i,j) in allpairs(axes(data,2))

        X = view(data,:,i)
        Y = view(data,:,j)
        currentScore = sum(abs2,X-Y)

        @reduce() do (bestScore = zero(T); currentScore)
            if bestScore < currentScore
                bestScore = currentScore
            end
        end
    end

    return bestScore
end

```

When I run this function I get some odd errors about `InvalidIRError` and `unsupported dynamic function invocation (call to print_to_string(xs...)` which doesn’t make sense to me. Does anyone see the problem I’m missing? The data I was using as input was just `data = CUDA.rand(100,100)`

---

<div class="post-metadata">

**Author:** ![maleadt](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/maleadt/32/10097_2.png) [@maleadt](https://discourse.julialang.org/u/maleadt)\
**Post date:** [July 22, 2023, 7:58am UTC](https://discourse.julialang.org/t/foldscuda-not-working-with-simple-reduction/101917/2 "2023-07-22T07:58:52Z")

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> [@RobertGregg](#):
>
> When I run this function I get some odd errors about `InvalidIRError` and `unsupported dynamic function invocation (call to print_to_string(xs...)` which doesn’t make sense to me.

That probably means some error code is being compiled, which often does I/O to a buffer because of string interpolation. Inspect the backtrace and try to avoid the code path leading to it. Worst case, this may need additional “quirks” ([https://github.com/JuliaGPU/CUDA.jl/blob/master/src/device/quirks.jl](https://github.com/JuliaGPU/CUDA.jl/blob/master/src/device/quirks.jl)) that disable the offending string interpolation.