# Out-of-bounds error when calling map!

**URL:** <https://discourse.julialang.org/t/out-of-bounds-error-when-calling-map/69053>\
**Category:** GPU\
**Tags:** cuda\
**Created:** [October 1, 2021, 3:16pm UTC](https://discourse.julialang.org/t/out-of-bounds-error-when-calling-map/69053 "2021-10-01T15:16:48Z")\
**Posts on this page:** 1\
**Showing post:** 13

<div class="post-metadata">

**Author:** ![JAgho](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jagho/32/33240_2.png) [@JAgho](https://discourse.julialang.org/u/JAgho)\
**Post date:** [October 4, 2021, 12:03pm UTC](https://discourse.julialang.org/t/out-of-bounds-error-when-calling-map/69053/13 "2021-10-04T12:03:43Z")

</div>

My shortest MWE was:

```julia
using CUDA

function test1(u, X)
    X1 = similar(X)
    X1 .= rem.(X, u)
    return X1
end

function test2(u, X)
    
    X2 = similar(X)
    map!(x->rem(x, u), X2, X)
    return X2
end

function main()
    t = 0
    for i in 1:10000
        X = CUDA.rand(Float32, Int(1e6)) .- 0.5
        a= test1(0.1, X)
        b = test2(0.1, X)
        t += sum(a .!== b)
    end
    return t
end

main()

```

Which produced the error:

```julia
ERROR: LoadError: Failed to compile PTX code (ptxas exited with code 1)
Error in get_form_value default
If you think this is a bug, please file an issue and attach C:\Users\James\AppData\Local\Temp\jl_3S0cNQ349S.ptx
Stacktrace:
  [1] error(s::String)
    @ Base .\error.jl:33
  [2] cufunction_compile(job::GPUCompiler.CompilerJob)
    @ CUDA C:\Users\James\.julia\packages\CUDA\O0mym\src\compiler\execution.jl:399
  [3] cached_compilation(cache::Dict{UInt64, Any}, job::GPUCompiler.CompilerJob, compiler::typeof(CUDA.cufunction_compile), linker::typeof(CUDA.cufunction_link))
    @ GPUCompiler C:\Users\James\.julia\packages\GPUCompiler\7APUC\src\cache.jl:89
  [4] cufunction(f::GPUArrays.var"#map_kernel#18"{Int64}, tt::Type{Tuple{CUDA.CuKernelContext, CuDeviceVector{Float64, 1}, Base.Broadcast.Broadcasted{CUDA.CuArrayStyle{1}, Tuple{Base.OneTo{Int64}}, var"#1#2"{Float64}, 
Tuple{Base.Broadcast.Extruded{CuDeviceVector{Float64, 1}, Tuple{Bool}, Tuple{Int64}}}}, Int64}}; name::Nothing, kwargs::Base.Iterators.Pairs{Union{}, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ CUDA C:\Users\James\.julia\packages\CUDA\O0mym\src\compiler\execution.jl:297
  [5] cufunction
    @ C:\Users\James\.julia\packages\CUDA\O0mym\src\compiler\execution.jl:291 [inlined]
  [6] macro expansion
    @ C:\Users\James\.julia\packages\CUDA\O0mym\src\compiler\execution.jl:102 [inlined]
  [7] #launch_heuristic#234
    @ C:\Users\James\.julia\packages\CUDA\O0mym\src\gpuarrays.jl:17 [inlined]
  [8] map!(f::Function, dest::CuArray{Float64, 1, CUDA.Mem.DeviceBuffer}, xs::CuArray{Float64, 1, CUDA.Mem.DeviceBuffer})
    @ GPUArrays C:\Users\James\.julia\packages\GPUArrays\0vqbc\src\host\broadcast.jl:130
  [9] test2(u::Float64, X::CuArray{Float64, 1, CUDA.Mem.DeviceBuffer})
    @ Main C:\Users\James\.julia\dev\DiffusionSimulator\test\modrem.jl:13
 [10] main()
    @ Main C:\Users\James\.julia\dev\DiffusionSimulator\test\modrem.jl:22
 [11] top-level scope
    @ C:\Users\James\.julia\dev\DiffusionSimulator\test\modrem.jl:28
 [12] include(fname::String)
    @ Base.MainInclude .\client.jl:444
 [13] top-level scope
    @ REPL[7]:1
 [14] top-level scope
    @ C:\Users\James\.julia\packages\CUDA\O0mym\src\initialization.jl:52
in expression starting at C:\Users\James\.julia\dev\DiffusionSimulator\test\modrem.jl:28

```

The offending line doesn’t always trigger an error, so the outer loop helps to force this.

I’m running this from the REPL in debug l2, no `check-bounds` etc, or `Pkg.test`, unmodified Julia 1.6.2 on both devices, totally standard `add CUDA` installs.

---

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