Faster path for onehotbatch(::CUArray{Int}, ::UnitRange)

[mcabbott]

Follow-up to #27, moves the inbounds check:

julia> inds100 = rand(1:100, 100); inds100cu = inds100 |> cu;

julia> @btime onehotbatch($inds100, 1:100);
  348.811 ns (1 allocation: 496 bytes)

julia> @btime onehotbatch($inds100cu, 1:100);  # with #27, minimum + maximum sync twice
  70.267 μs (86 allocations: 4.02 KiB)

julia> @btime unsafe_onehotbatch($inds100, 1:100);
  231.916 ns (1 allocation: 496 bytes)

julia> @btime unsafe_onehotbatch($inds100cu, 1:100);  # version with no checks
  8.889 μs (28 allocations: 1.11 KiB)

julia> function fused_onehotbatch(data::AbstractArray{<:Integer}, labels::AbstractUnitRange{<:Integer})
         offset = 1 - first(labels)
         indices = map(data) do datum
                    i = UInt32(datum + offset)
                    checkbounds(labels, i)  # like this PR
                    i
                  end
         return OneHotArray(indices, length(labels))
       end
fused_onehotbatch (generic function with 1 method)

julia> @btime fused_onehotbatch($inds100cu, 1:100);
  10.708 μs (31 allocations: 1.20 KiB)

julia> bad100 = copy(inds100); bad100[33] = 101; bad100cu = bad100 |> cu;

julia> fused_onehotbatch(bad100cu, 1:100)
ERROR: Out-of-bounds array access.
ERROR: a exception was thrown during kernel execution.
       Run Julia on debug level 2 for device stack traces.
ERROR: KernelException: exception thrown during kernel execution on device Tesla V100-PCIE-16GB
Stacktrace:
 [1] check_exceptions()
   @ CUDA ~/.julia/packages/CUDA/DfvRa/src/compiler/exceptions.jl:34
 [2] nonblocking_synchronize
   @ ~/.julia/packages/CUDA/DfvRa/lib/cudadrv/context.jl:331 [inlined]
 [3] device_synchronize()
   @ CUDA ~/.julia/packages/CUDA/DfvRa/lib/cudadrv/context.jl:319

julia> cu(ones(100))[bad100cu]  # getindex does much the same check, inside the kernel
ERROR: Out-of-bounds array access.
ERROR: a exception was thrown during kernel execution.
       Run Julia on debug level 2 for device stack traces.
ERROR: KernelException: exception thrown during kernel execution on device Tesla V100-PCIE-16GB
Stacktrace:
 [1] check_exceptions()
   @ CUDA ~/.julia/packages/CUDA/DfvRa/src/compiler/exceptions.jl:34
 [2] nonblocking_synchronize
   @ ~/.julia/packages/CUDA/DfvRa/lib/cudadrv/context.jl:331 [inlined]
 [3] device_synchronize()
   @ CUDA ~/.julia/packages/CUDA/DfvRa/lib/cudadrv/context.jl:319

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.68%. Comparing base (32e06c8) to head (49561f9).
⚠️ Report is 21 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #29      +/-   ##
==========================================
- Coverage   96.21%   95.68%   -0.53%     
==========================================
  Files           4        4              
  Lines         132      139       +7     
==========================================
+ Hits          127      133       +6     
- Misses          5        6       +1     

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