Add support to using CuVector{Int} and CuVector{UnitRange} as indexes for another CuArray

As discussed in the forum, I'd like to use a vector of ranges as indices to apply an operation over segments of another array, but it seems this is not currently supported.

Something like this:

using CUDA
CUDA.allowscalar(false)

# example: sum only a part of an array
rangesum(x, r::UnitRange) = sum(x[r])

# broadcast over the ranges
rangesum(x, rr::AbstractVector{UnitRange}) = map(r -> rangesum(x, r), rr)

x = collect(1:100) |> cu
r = [1:10, 33:37, 50:80]

# this works fine if r is on cpu
rangesum(x, r) # results in a Vector{Int}

# but it fails if r in on the gpu
rangesum(x, cu(r))

The last line throws:

ERROR: InvalidIRError: compiling kernel broadcast_kernel(CUDA.CuKernelContext, CuDeviceVector{Int64, 1}, Base.Broadcast.Broadcasted{Nothing, Tuple{Base.OneTo{Int64}}, var"#1#2"{CuDeviceVector{Int64, 1}}, Tuple{Base.Broadcast.Extruded{CuDeviceVector{UnitRange{Int64}, 1}, Tuple{Bool}, Tuple{Int64}}}}, Int64) resulted in invalid LLVM IR
Reason: unsupported dynamic function invocation (call to print_to_string(xs...) in Base at strings/io.jl:124)
Stacktrace:
  [1] string
    @ ./strings/io.jl:174
  [2] throw_checksize_error
    @ ./multidimensional.jl:881
  [3] _unsafe_getindex
    @ ./multidimensional.jl:845
  [4] _getindex
    @ ./multidimensional.jl:832
  [5] getindex
    @ ./abstractarray.jl:1170
  [6] rangesum
    @ ./REPL[3]:2
  [7] #1
    @ ./REPL[4]:2
  [8] _broadcast_getindex_evalf
    @ ./broadcast.jl:648
  [9] _broadcast_getindex
    @ ./broadcast.jl:621
 [10] getindex
    @ ./broadcast.jl:575
 [11] broadcast_kernel
    @ ~/.julia/packages/GPUArrays/3sW6s/src/host/broadcast.jl:59
Reason: unsupported call through a literal pointer (call to )
Stacktrace:
  [1] Array
    @ ./boot.jl:448
  [2] Array
    @ ./boot.jl:457
  [3] similar
    @ ./abstractarray.jl:750
  [4] similar
    @ ./abstractarray.jl:740
  [5] _unsafe_getindex
    @ ./multidimensional.jl:844
  [6] _getindex
    @ ./multidimensional.jl:832
  [7] getindex
    @ ./abstractarray.jl:1170
  [8] rangesum
    @ ./REPL[3]:2
  [9] #1
    @ ./REPL[4]:2
 [10] _broadcast_getindex_evalf
    @ ./broadcast.jl:648
 [11] _broadcast_getindex
    @ ./broadcast.jl:621
 [12] getindex
    @ ./broadcast.jl:575
 [13] broadcast_kernel
    @ ~/.julia/packages/GPUArrays/3sW6s/src/host/broadcast.jl:59
Stacktrace:
  [1] check_ir(job::GPUCompiler.CompilerJob{GPUCompiler.PTXCompilerTarget, CUDA.CUDACompilerParams, GPUCompiler.FunctionSpec{GPUArrays.var"#broadcast_kernel#17", Tuple{CUDA.CuKernelContext, CuDeviceVector{Int64, 1}, Base.Broadcast.Broadcasted{Nothing, Tuple{Base.OneTo{Int64}}, var"#1#2"{CuDeviceVector{Int64, 1}}, Tuple{Base.Broadcast.Extruded{CuDeviceVector{UnitRange{Int64}, 1}, Tuple{Bool}, Tuple{Int64}}}}, Int64}}}, args::LLVM.Module)
    @ GPUCompiler ~/.julia/packages/GPUCompiler/9rK1I/src/validation.jl:111
  [2] macro expansion
    @ ~/.julia/packages/GPUCompiler/9rK1I/src/driver.jl:333 [inlined]
  [3] macro expansion
    @ ~/.julia/packages/TimerOutputs/SSeq1/src/TimerOutput.jl:252 [inlined]
  [4] macro expansion
    @ ~/.julia/packages/GPUCompiler/9rK1I/src/driver.jl:331 [inlined]
  [5] emit_asm(job::GPUCompiler.CompilerJob, ir::LLVM.Module; strip::Bool, validate::Bool, format::LLVM.API.LLVMCodeGenFileType)
    @ GPUCompiler ~/.julia/packages/GPUCompiler/9rK1I/src/utils.jl:62
  [6] cufunction_compile(job::GPUCompiler.CompilerJob)
    @ CUDA ~/.julia/packages/CUDA/Xt3hr/src/compiler/execution.jl:326
  [7] cached_compilation(cache::Dict{UInt64, Any}, job::GPUCompiler.CompilerJob, compiler::typeof(CUDA.cufunction_compile), linker::typeof(CUDA.cufunction_link))
    @ GPUCompiler ~/.julia/packages/GPUCompiler/9rK1I/src/cache.jl:89
  [8] cufunction(f::GPUArrays.var"#broadcast_kernel#17", tt::Type{Tuple{CUDA.CuKernelContext, CuDeviceVector{Int64, 1}, Base.Broadcast.Broadcasted{Nothing, Tuple{Base.OneTo{Int64}}, var"#1#2"{CuDeviceVector{Int64, 1}}, Tuple{Base.Broadcast.Extruded{CuDeviceVector{UnitRange{Int64}, 1}, Tuple{Bool}, Tuple{Int64}}}}, Int64}}; name::Nothing, kwargs::Base.Iterators.Pairs{Union{}, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ CUDA ~/.julia/packages/CUDA/Xt3hr/src/compiler/execution.jl:297
  [9] cufunction(f::GPUArrays.var"#broadcast_kernel#17", tt::Type{Tuple{CUDA.CuKernelContext, CuDeviceVector{Int64, 1}, Base.Broadcast.Broadcasted{Nothing, Tuple{Base.OneTo{Int64}}, var"#1#2"{CuDeviceVector{Int64, 1}}, Tuple{Base.Broadcast.Extruded{CuDeviceVector{UnitRange{Int64}, 1}, Tuple{Bool}, Tuple{Int64}}}}, Int64}})
    @ CUDA ~/.julia/packages/CUDA/Xt3hr/src/compiler/execution.jl:291
 [10] macro expansion
    @ ~/.julia/packages/CUDA/Xt3hr/src/compiler/execution.jl:102 [inlined]
 [11] #launch_heuristic#234
    @ ~/.julia/packages/CUDA/Xt3hr/src/gpuarrays.jl:17 [inlined]
 [12] copyto!
    @ ~/.julia/packages/GPUArrays/3sW6s/src/host/broadcast.jl:65 [inlined]
 [13] copyto!
    @ ./broadcast.jl:936 [inlined]
 [14] copy
    @ ~/.julia/packages/GPUArrays/3sW6s/src/host/broadcast.jl:47 [inlined]
 [15] materialize(bc::Base.Broadcast.Broadcasted{CUDA.CuArrayStyle{1}, Nothing, var"#1#2"{CuArray{Int64, 1, CUDA.Mem.DeviceBuffer}}, Tuple{CuArray{UnitRange{Int64}, 1, CUDA.Mem.DeviceBuffer}}})
    @ Base.Broadcast ./broadcast.jl:883
 [16] map(::Function, ::CuArray{UnitRange{Int64}, 1, CUDA.Mem.DeviceBuffer})
    @ GPUArrays ~/.julia/packages/GPUArrays/3sW6s/src/host/broadcast.jl:90
 [17] rangesum(x::CuArray{Int64, 1, CUDA.Mem.DeviceBuffer}, rr::CuArray{UnitRange{Int64}, 1, CUDA.Mem.DeviceBuffer})
    @ Main ./REPL[4]:2
 [18] top-level scope
    @ REPL[8]:2
 [19] top-level scope
    @ ~/.julia/packages/CUDA/Xt3hr/src/initialization.jl:52

I would like to do this entire operation GPU-wise as a part of a bigger computation.