Use byte-range overlap for dense JLArray alias detection

lib/JLArrays/src/array.jl

@@ -44,6 +44,21 @@ mutable struct JLArray{T, N} <: AbstractGPUArray{T, N}
 end
 
 GPUArrays.storage(a::JLArray) = a.data
+
+## alias detection
+
+# Byte-range overlap follows CUDA's Base.mightalias(::CuArray, ::CuArray):
+# https://github.com/JuliaGPU/CUDA.jl/blob/main/CUDACore/src/array.jl#L113-L116
+# Keep shared-allocation dataids for conservative alias detection involving wrappers.
+function Base.mightalias(A::JLArray, B::JLArray)
+    nA, nB = sizeof(A), sizeof(B)
+    (iszero(nA) || iszero(nB)) && return false
+    GC.@preserve A B begin
+        pA, pB = UInt(pointer(A)), UInt(pointer(B))
+        return pA <= pB < pA + nA || pB <= pA < pB + nB
+    end
+end
+
 GPUArrays.dense_array_type(a::JLArray{T, N}) where {T, N} = JLArray{T, N}
 GPUArrays.dense_array_type(::Type{JLArray{T, N}}) where {T, N} = JLArray{T, N}
 GPUArrays.dense_vector_type(a::JLArray{T, N}) where {T, N} = JLArray{T, 1}

test/testsuite.jl

@@ -125,6 +125,7 @@ end
 include("testsuite/construction.jl")
 include("testsuite/indexing.jl")
 include("testsuite/base.jl")
+include("testsuite/aliasing.jl")
 include("testsuite/vector.jl")
 include("testsuite/reductions.jl")
 include("testsuite/sorting.jl")

test/testsuite/aliasing.jl

@@ -0,0 +1,18 @@
+@testsuite "aliasing" (AT, eltypes)->begin
+    T = Float32 in eltypes ? Float32 : first(eltypes)
+    buffer = AT{T}(undef, 32)
+    left = view(buffer, 1:16)
+    right = view(buffer, 17:32)
+    overlap = view(buffer, 9:24)
+    @test Base.mightalias(left, left)
+    @test !Base.mightalias(left, right)
+    @test !Base.mightalias(right, left)
+    @test Base.mightalias(left, overlap)
+    @test Base.mightalias(overlap, left)
+    @test !Base.mightalias(left, copy(left))
+    # The last element still overlaps after reinterpreting to a different element size.
+    @test Base.mightalias(reinterpret(UInt8, left), view(buffer, 16:16))
+    empty = view(buffer, 9:8)
+    @test !Base.mightalias(empty, left)
+    @test !Base.mightalias(left, empty)
+end