Support for atomic `max` on `Float`

For feature-parity it'd be good to support atomic max on Float. Currently MWE below fails:

using AMDGPU
using ROCKernels
using KernelAbstractions
using KernelAbstractions: @atomic

@kernel function f(target, source, indices)
    i = @index(Global)
    idx = indices[i]
    v = source[i]
    @atomic max(target[idx], v)
end

function main()
    source = rand(Float32, 1024)
    indices = rand(1:32, 1024)
    target = zeros(Float32, 32)
    @assert length(unique(indices)) < length(indices)

    dsource, dindices, dtarget = ROCArray.((source, indices, target))

    for i in 1:1024
        idx = indices[i]
        target[idx] = max(target[idx], source[i])
    end

    wait(f(AMDGPU.default_device())(dtarget, dsource, dindices; ndrange=1024))
    @assert Array(dtarget) == target
end

Error

```julia ERROR: InvalidIRError: compiling kernel gpu_f(KernelAbstractions.CompilerMetadata{KernelAbstractions.NDIteration.DynamicSize, KernelAbstractions.NDIteration.DynamicCheck, Nothing, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}, KernelAbstractions.NDIteration.NDRange{1, KernelAbstractions.NDIteration.DynamicSize, KernelAbstractions.NDIteration.DynamicSize, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}}}, AMDGPU.Device.ROCDeviceVector{Float32, 1}, AMDGPU.Device.ROCDeviceVector{Float32, 1}, AMDGPU.Device.ROCDeviceVector{Int64, 1}) resulted in invalid LLVM IR Reason: unsupported call to an unknown function (call to ijl_get_nth_field_checked) Stacktrace: [1] indexed_iterate @ ./namedtuple.jl:140 [2] multiple call sites @ unknown:0 Reason: unsupported call to an unknown function (call to jl_f_tuple) Stacktrace: [1] indexed_iterate @ ./namedtuple.jl:140 [2] multiple call sites @ unknown:0 Reason: unsupported call to an unknown function (call to ijl_get_nth_field_checked) Stacktrace: [1] atomic_pointermodify @ ~/.julia/packages/LLVM/9gCXO/src/interop/atomics.jl:395 [2] modify! @ ~/.julia/packages/UnsafeAtomicsLLVM/i4GMj/src/internal.jl:18 [3] modify! @ ~/.julia/packages/Atomix/F9VIX/src/core.jl:33 [4] macro expansion @ ~/code/Nerf.jl/src/Nerf.jl:155 [5] gpu_f @ ~/.julia/packages/KernelAbstractions/C8flJ/src/macros.jl:81 [6] gpu_f @ ./none:0 Reason: unsupported dynamic function invocation (call to atomic_pointerreplace) Stacktrace: [1] atomic_pointermodify @ ~/.julia/packages/LLVM/9gCXO/src/interop/atomics.jl:395 [2] modify! @ ~/.julia/packages/UnsafeAtomicsLLVM/i4GMj/src/internal.jl:18 [3] modify! @ ~/.julia/packages/Atomix/F9VIX/src/core.jl:33 [4] macro expansion @ ~/code/Nerf.jl/src/Nerf.jl:155 [5] gpu_f @ ~/.julia/packages/KernelAbstractions/C8flJ/src/macros.jl:81 [6] gpu_f @ ./none:0 ```

As a temporary workaround, we can reinterpret Float32 as UInt32:

wait(f(DEVICE)(
    reinterpret(UInt32, dtarget),
    reinterpret(UInt32, dsource), dindices; ndrange=1024))

JuliaGPU / AMDGPU.jl

Support for atomic `max` on `Float` #339