Revert array wrapper union changes

[maleadt]

Too costly, latency wise.

[GiggleLiu]

Thanks! Using CuArrays only definitely makes the design simpler.
Wondering what is the motivation of the previous change? Does it make the performance in some practical applications better?

[maleadt]

Using CuArray is of course simpler, but puts a lot of burden on the GPU package, requiring us to implement and maintain functionality that's already available in Base. For example, to decide if a view is contiguous, to compute the dimensions of a reshape, etc. I really don't want to do that, but sadly the cost in load time is too great.

[GiggleLiu]

I see. Hope the load time can be optimized later. Just add an example to the issue in #494

julia> reshape(zeros(4,4), 2, 8) |> typeof
Array{Float64,2}

julia> reshape(CUDA.zeros(4,4), 2, 8) |> typeof
Base.ReshapedArray{Float32,2,CuArray{Float32,2},Tuple{}}

In a tensor package, reshaping happens quite often. It will be easier to handle if the array type is not changed.

[maleadt]

Just add an example to the issue in #494

Right, but is that an issue? Your package should probably handle ReshapedArray, or you're only compatible with Array and its specific optimizations. You can't expect other array types to copy that behavior, since it involves a fair bit of complexity (not only duplicating the reshape implementation, but also refcounting the underlying storage, or whatever). That doesn't solve the instability though, but you get that with other wrappers anyway:

julia> reinterpret(Float64, zeros(4,4)) |> typeof
Base.ReinterpretArray{Float64,2,Float64,Array{Float64,2}}

[GiggleLiu]

Hmm, you are right. It is more likely a matter of fixing legacy code.

[codecov]

Codecov Report

Merging #498 into master will increase coverage by 0.09%.
The diff coverage is 91.89%.

@@            Coverage Diff             @@
##           master     #498      +/-   ##
==========================================
+ Coverage   80.45%   80.54%   +0.09%     
==========================================
  Files         166      166              
  Lines        8822     8879      +57     
==========================================
+ Hits         7098     7152      +54     
- Misses       1724     1727       +3     

Impacted Files	Coverage Δ
test/array.jl	0.00% <ø> (ø)
src/array.jl	88.29% <91.66%> (+0.44%)	⬆️
src/pool.jl	72.91% <92.85%> (+0.62%)	⬆️
lib/nvml/error.jl	71.42% <0.00%> (+21.42%)	⬆️

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