make extract_gradient[_chunk]! GPU compatible

Author: marius311

Diff for: Project.toml

@@ -32,8 +32,9 @@ julia = "1.6"
 Calculus = "49dc2e85-a5d0-5ad3-a950-438e2897f1b9"
 DiffTests = "de460e47-3fe3-5279-bb4a-814414816d5d"
 InteractiveUtils = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
+JLArrays = "27aeb0d3-9eb9-45fb-866b-73c2ecf80fcb"
 SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Calculus", "DiffTests", "SparseArrays", "Test", "InteractiveUtils"]
+test = ["Calculus", "DiffTests", "SparseArrays", "Test", "InteractiveUtils", "JLArrays"]

Diff for: src/gradient.jl

@@ -80,12 +80,12 @@ function extract_gradient!(::Type{T}, result::DiffResult, dual::Dual) where {T}
 end
 
 extract_gradient!(::Type{T}, result::AbstractArray, y::Real) where {T} = fill!(result, zero(y))
-extract_gradient!(::Type{T}, result::AbstractArray, dual::Dual) where {T}= copyto!(result, partials(T, dual))
+extract_gradient!(::Type{T}, result::AbstractArray, dual::Dual) where {T} =
+    extract_gradient_chunk!(T, result, dual, 1, npartials(dual))
 
 function extract_gradient_chunk!(::Type{T}, result, dual, index, chunksize) where {T}
-    offset = index - 1
-    for i in 1:chunksize
-        result[i + offset] = partials(T, dual, i)
+    map!(view(Base.ReshapedArray(result, (length(result),), ()), index:index+chunksize-1), 1:chunksize) do i
+        @inbounds partials(T, dual, i)
     end
     return result
 end

Diff for: test/AllocationsTest.jl

@@ -37,4 +37,26 @@ convert_test_574() = convert(ForwardDiff.Dual{Nothing,ForwardDiff.Dual{Nothing,F
 
 end
 
+@testset "Test extract_gradient! allocations" begin
+    T = Float64
+    @testset "vector-mode size(result)=$size" for size in [(4,), (2,2)]
+        dual = ForwardDiff.Dual(0, (rand(T, size...)...,))
+        y = Array{T}(undef, size)
+        alloc = @allocated ForwardDiff.extract_gradient!(Nothing, y, dual)
+        alloc = @allocated ForwardDiff.extract_gradient!(Nothing, y, dual)
+        @test alloc == 0
+    end
+    @testset "chunk-mode size(result)=$size" for size in [(DEFAULT_CHUNK_THRESHOLD+1,), (DEFAULT_CHUNK_THRESHOLD+1, DEFAULT_CHUNK_THRESHOLD+1)]
+        Npartials = DEFAULT_CHUNK_THRESHOLD÷2
+        dual = ForwardDiff.Dual(0, (rand(T, Npartials...)...,))
+        y = Array{T}(undef, size)
+        alloc = @allocated ForwardDiff.extract_gradient_chunk!(Nothing, y, dual, 2, Npartials)
+        alloc = @allocated ForwardDiff.extract_gradient_chunk!(Nothing, y, dual, 2, Npartials)
+        @test alloc == 0
+        alloc = @allocated ForwardDiff.extract_gradient_chunk!(Nothing, y, dual, 2, Npartials-1)
+        alloc = @allocated ForwardDiff.extract_gradient_chunk!(Nothing, y, dual, 2, Npartials-1)
+        @test alloc == 0
+    end
+end
+
 end

Diff for: test/GradientTest.jl

@@ -8,6 +8,8 @@ using ForwardDiff
 using ForwardDiff: Dual, Tag
 using StaticArrays
 using DiffTests
+using JLArrays
+JLArrays.allowscalar(false)
 
 include(joinpath(dirname(@__FILE__), "utils.jl"))
 
@@ -149,6 +151,26 @@ end
     @test isequal(ForwardDiff.gradient(t -> t[1]^t[2], [0.0,  1.5]), [0.0, 0.0])
 end
 
+
+##############################################
+# test GPUArray compatibility (via JLArrays) #
+##############################################
+
+println("  ...testing GPUArray compatibility (via JLArrays)")
+
+@testset "size = $(size(x))" for x in JLArray.([
+    rand(1), 
+    rand(DEFAULT_CHUNK_THRESHOLD+1), 
+    rand(1,1), 
+    rand(DEFAULT_CHUNK_THRESHOLD+1,DEFAULT_CHUNK_THRESHOLD+1), 
+    rand(1,1,1)
+])
+    
+    @test ForwardDiff.gradient(prod, x) isa typeof(x)
+
+end
+
+
 #############
 # bug fixes #
 #############