# Random numbers in KernelAbstractions

**URL:** <https://discourse.julialang.org/t/random-numbers-in-kernelabstractions/76476>\
**Category:** GPU\
**Tags:** question, kernelabstractions\
**Created:** [February 15, 2022, 8:41am UTC](https://discourse.julialang.org/t/random-numbers-in-kernelabstractions/76476 "2022-02-15T08:41:13Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![lawless-m](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lawless-m/32/30869_2.png) [@lawless-m](https://discourse.julialang.org/u/lawless-m)\
**Post date:** [February 15, 2022, 8:41am UTC](https://discourse.julialang.org/t/random-numbers-in-kernelabstractions/76476/1 "2022-02-15T08:41:13Z")

</div>

Cuda has random numbers CUDA.rand(2) but I can’t see how/if I can create them _inside_ a @kernel.

I need x,y pairs in a specific range and x^2 + y^ \<= 1

I used just plain `rand()` and got

```julia
... resulted in invalid LLVM IR
Reason: unsupported call to an unknown function (call to julia.get_pgcstack)

```

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<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:** [February 15, 2022, 9:22am UTC](https://discourse.julialang.org/t/random-numbers-in-kernelabstractions/76476/2 "2022-02-15T09:22:08Z")

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`rand()` is supported in CUDA kernels. You seem to be using Julia 1.7, make sure you’re also using the latest version of GPUCompiler.jl, which should handle the `get_pgcstack` intrinsic correctly.

---

<div class="post-metadata">

**Author:** ![lawless-m](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lawless-m/32/30869_2.png) [@lawless-m](https://discourse.julialang.org/u/lawless-m)\
**Post date:** [February 15, 2022, 9:44am UTC](https://discourse.julialang.org/t/random-numbers-in-kernelabstractions/76476/3 "2022-02-15T09:44:11Z")

</div>

Here’s an MWE in a new environment, with a square! function to show CUDA is working.

```julia
julia> versioninfo()
Julia Version 1.7.2
Commit bf53498635 (2022-02-06 15:21 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Xeon(R) CPU E5-2660 v3 @ 2.60GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-12.0.1 (ORCJIT, haswell)
Environment:
  JULIA_CPU_THREADS = 40
  JULIA_NUM_THREADS = 40

```

```julia
$ mkdir gpurand && cd gpurand && julia --project=. -q
julia> using GPUCompiler
...
  [61eb1bfa] + GPUCompiler v0.13.11
julia> using CUDA
...
  [052768ef] + CUDA v3.8.0
julia> using KernelAbstractions
...
 [63c18a36] + KernelAbstractions v0.7.2
julia> using CUDAKernels
...
  [72cfdca4] + CUDAKernels v0.3.3

julia> s = CUDA.rand(2)
2-element CuArray{Float32, 1, CUDA.Mem.DeviceBuffer}:
 0.049182236
 0.29649353

julia> @kernel function square!(S)
           I = @index(Global)
           @inbounds S[I] = S[I]^2
       end
square! (generic function with 5 methods)

julia> sq! = square!(CUDADevice(), 8)

julia> wait(sq!(s, ndrange=length(s))) ; s
2-element CuArray{Float32, 1, CUDA.Mem.DeviceBuffer}:
 0.0024188925
 0.08790842

julia> @kernel function rand!(R)
           I = @index(Global)
           @inbounds R[I] = rand()
       end
julia> r = CUDA.zeros(16)
16-element CuArray{Float32, 1, CUDA.Mem.DeviceBuffer}:
 0.0 
 ⋮
 0.0
julia> r! = rand!(CUDADevice(), 8)
KernelAbstractions.Kernel{CUDADevice, KernelAbstractions.NDIteration.StaticSize{(8,)}, KernelAbstractions.NDIteration.DynamicSize, typeof(gpu_rand!)}(gpu_rand!)

julia> wait(r!(r, ndrange=length(r)))
ERROR: InvalidIRError: compiling kernel gpu_rand!(Cassette.Context{nametype(CUDACtx), Nothing, Nothing, KernelAbstractions.var"##PassType#291", Nothing, Cassette.DisableHooks}, typeof(gpu_rand!), KernelAbstractions.CompilerMetadata{KernelAbstractions.NDIteration.DynamicSize, KernelAbstractions.NDIteration.DynamicCheck, Nothing, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}, KernelAbstractions.NDIteration.NDRange{1, KernelAbstractions.NDIteration.DynamicSize, KernelAbstractions.NDIteration.StaticSize{(8,)}, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}, Nothing}}, CuDeviceVector{Float32, 1}) resulted in invalid LLVM IR
Reason: unsupported call to an unknown function (call to julia.get_pgcstack)
```

---

<div class="post-metadata">

**Author:** ![vchuravy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/vchuravy/32/8_2.png) [@vchuravy](https://discourse.julialang.org/u/vchuravy)\
**Post date:** [February 15, 2022, 6:53pm UTC](https://discourse.julialang.org/t/random-numbers-in-kernelabstractions/76476/4 "2022-02-15T18:53:56Z")

</div>

I suspect this is Cassette.jl messing things up. This should hopefully be fixed by [https://github.com/JuliaGPU/KernelAbstractions.jl/pull/288](https://github.com/JuliaGPU/KernelAbstractions.jl/pull/288)

---

<div class="post-metadata">

**Author:** ![lawless-m](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lawless-m/32/30869_2.png) [@lawless-m](https://discourse.julialang.org/u/lawless-m)\
**Post date:** [February 15, 2022, 7:00pm UTC](https://discourse.julialang.org/t/random-numbers-in-kernelabstractions/76476/5 "2022-02-15T19:00:25Z")

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![image](https://global.discourse-cdn.com/julialang/original/3X/d/e/de0afccdf9df824a8bb941d2c419f63ee0742f3e.jpeg)