Remove split reverse mode for mutating functions

DifferentiationInterface/docs/src/overview.md

@@ -124,7 +124,7 @@ This means the Hessian is obtained as the sparse Jacobian of the gradient.
 ### Split reverse mode
 
 Many reverse mode AD backends expose a "split" option, which runs only the forward sweep, and encapsulates the reverse sweep in a closure.
-We make this available for everyone with the following operators:
+We make this available for allocating functions only, with the following operators:
 
 | out-of-place                       | in-place (or not)                    |
 | ---------------------------------- | ------------------------------------ |

DifferentiationInterface/src/jacobian.jl

@@ -193,13 +193,14 @@ function value_and_jacobian_aux!!(
     x::AbstractArray,
     extras::PullbackJacobianExtras,
 )
-    y, pullbackfunc!! = value_and_pullback!!_split(
-        f!, y, backend, x, extras.pullback_extras
-    )
     for (k, i) in enumerate(CartesianIndices(y))
         dy_i = basis(backend, y, i)
         jac_row_i_old = reshape(view(jac, k, :), size(x))
-        jac_row_i_new = pullbackfunc!!(y, jac_row_i_old, dy_i)
+        jac_row_i_new = last(
+            value_and_pullback!!(
+                f!, y, jac_row_i_old, backend, x, dy_i, extras.pullback_extras
+            ),
+        )
         # this allocates
         copyto!(jac_row_i_old, jac_row_i_new)
     end

DifferentiationInterface/src/pullback.jl

@@ -158,26 +158,3 @@ function value_and_pullback!!_split(
     pullbackfunc!!(dx, dy) = pullback!!(f, dx, backend, x, dy, extras)
     return f(x), pullbackfunc!!
 end
-
-"""
-    value_and_pullback!!_split(f!, y, backend, x, [extras])
-
-Apply split reverse mode autodiff.
-
-Returns a tuple `(y, pullbackfunc!!)` where the second element is a function (closure) with the following signature:
-
-    pullbackfunc!!(y, dx, dy) -> dx
-"""
-function value_and_pullback!!_split(
-    f!,
-    y,
-    backend::AbstractADType,
-    x,
-    extras::PullbackExtras=prepare_pullback(f!, backend, y, x),
-)
-    function pullbackfunc!!(y, dx, dy)
-        return value_and_pullback!!(f!, y, dx, backend, x, dy, extras)[2]
-    end
-    f!(y, x)
-    return y, pullbackfunc!!
-end

DifferentiationInterfaceTest/src/tests/benchmark.jl

@@ -114,13 +114,10 @@ function run_benchmark!(
     (; f, x, y, dy) = deepcopy(scen)
     f! = f
     extras = prepare_pullback(f!, ba, y, x)
-    _, pullbackfunc!! = value_and_pullback!!_split(f!, y, ba, x, extras)
     bench1 = @be (mysimilar(y), mysimilar(x)) value_and_pullback!!(
         f!, _[1], _[2], ba, x, dy, extras
     )
-    bench2 = @be (mysimilar(y), mysimilar(x)) pullbackfunc!!(_[1], _[2], dy)
     record!(data, ba, value_and_pullback!!, scen, bench1)
-    record!(data, ba, pullbackfunc!!, scen, bench2)
     return nothing
 end
 

DifferentiationInterfaceTest/src/tests/correctness.jl

@@ -154,20 +154,13 @@ function test_correctness(
     y10 = mysimilar(y)
     y1, dx1 = value_and_pullback!!(f!, y10, mysimilar(x), ba, x, dy, extras)
 
-    y20 = mysimilar(y)
-    y2, pullbackfunc!! = value_and_pullback!!_split(f!, y20, ba, x, extras)
-    dx2 = pullbackfunc!!(y20, mysimilar(x), dy)
-
     let (≈)(x, y) = isapprox(x, y; atol, rtol)
         @testset "Primal value" begin
             @test y10 ≈ y
-            @test y20 ≈ y
             @test y1 ≈ y
-            @test y2 ≈ y
         end
         @testset "Cotangent value" begin
             @test dx1 ≈ dx_true
-            @test dx2 ≈ dx_true
         end
     end
     test_scen_intact(new_scen, scen)

DifferentiationInterfaceTest/src/tests/type_stability.jl

@@ -51,11 +51,8 @@ function test_jet(ba::AbstractADType, scen::PullbackScenario{true};)
     y_in = mysimilar(y)
     dx_in = mysimilar(x)
 
-    _, pullbackfunc!! = value_and_pullback!!_split(f!, y, ba, x, extras)
-
     if Bool(pullback_performance(ba))
         @test_opt value_and_pullback!!(f!, y_in, dx_in, ba, x, dy, extras)
-        @test_opt pullbackfunc!!(y_in, dx_in, dy)
     end
     return nothing
 end