Use Base method for scalar indexing.

src/host/indexing.jl

@@ -9,8 +9,8 @@ vectorized_indices(Is::Union{Integer,CartesianIndex}...) = Val{false}()
 vectorized_indices(Is...) = Val{true}()
 
 # TODO: re-use Base functionality for the conversion of indices to a linear index,
-#       by only implementing `getindex(A, ::Int)` etc. this is difficult if we want
-#       to also want to match the case where we take any vectorized index...
+#       by only implementing `getindex(A, ::Int)` etc. this is difficult due to
+#       ambiguities with the vectorized method that can take any index type.
 
 Base.@propagate_inbounds Base.getindex(A::AbstractGPUArray, Is...) =
     _getindex(vectorized_indices(Is...), A, to_indices(A, Is)...)
@@ -29,20 +29,33 @@ Base.@propagate_inbounds _setindex!(::Val{true}, A::AbstractGPUArray, v, Is...)
 ## scalar indexing
 
 function scalar_getindex(A::AbstractGPUArray{T}, Is...) where T
-    assertscalar("getindex")
     @boundscheck checkbounds(A, Is...)
-    i = Base._to_linear_index(A, Is...)
+    I = Base._to_linear_index(A, Is...)
+    getindex(A, I)
+end
+
+function scalar_setindex!(A::AbstractGPUArray{T}, v, Is...) where T
+    @boundscheck checkbounds(A, Is...)
+    I = Base._to_linear_index(A, Is...)
+    setindex!(A, v, I)
+end
+
+# we still dispatch to `Base.getindex(a, ::Int)` etc so that there's a single method to
+# override when a back-end (e.g. with unified memory) wants to allow scalar indexing.
+
+function Base.getindex(A::AbstractGPUArray{T}, I::Int) where T
+    @boundscheck checkbounds(A, I)
+    assertscalar("getindex")
     x = Array{T}(undef, 1)
-    copyto!(x, 1, A, i, 1)
+    copyto!(x, 1, A, I, 1)
     return x[1]
 end
 
-function scalar_setindex!(A::AbstractGPUArray{T}, v, Is...) where T
+function Base.setindex!(A::AbstractGPUArray{T}, v, I::Int) where T
+    @boundscheck checkbounds(A, I)
     assertscalar("setindex!")
-    @boundscheck checkbounds(A, Is...)
-    i = Base._to_linear_index(A, Is...)
     x = T[v]
-    copyto!(A, i, x, 1, 1)
+    copyto!(A, I, x, 1, 1)
     return A
 end