getting very close

ext/LinearSolveEnzymeExt.jl

@@ -83,13 +83,12 @@ function EnzymeCore.EnzymeRules.augmented_primal(config, func::Const{typeof(Line
         (dr.u for dr in dres)
     end
 
-    cache = (res, resvals)
+    cache = (res, resvals, deepcopy(linsolve.val))
     return EnzymeCore.EnzymeRules.AugmentedReturn(res, dres, cache)
 end
 
 function EnzymeCore.EnzymeRules.reverse(config, func::Const{typeof(LinearSolve.solve!)}, ::Type{RT}, cache, linsolve::EnzymeCore.Annotation{LP}; kwargs...) where {RT, LP <: LinearSolve.LinearCache}
-    y, dys = cache
-    _linsolve = linsolve.val
+    y, dys, _linsolve = cache
 
     @assert !(typeof(linsolve) <: Const)
     @assert !(typeof(linsolve) <: Active)
@@ -113,9 +112,9 @@ function EnzymeCore.EnzymeRules.reverse(config, func::Const{typeof(LinearSolve.s
     for (dA, db, dy) in zip(dAs, dbs, dys)
         z = if _linsolve.cacheval isa Factorization
             _linsolve.cacheval' \ dy
-        elseif linsolve.cacheval isa Tuple && linsolve.cacheval[1] isa Factorization
+        elseif _linsolve.cacheval isa Tuple && _linsolve.cacheval[1] isa Factorization
             _linsolve.cacheval[1]' \ dy
-        elseif linsolve.alg isa AbstractKrylovSubspaceMethod
+        elseif _linsolve.alg isa AbstractKrylovSubspaceMethod
             # Doesn't modify `A`, so it's safe to just reuse it
             invprob = LinearSolve.LinearProblem(transpose(_linsolve.A), dy)
             solve(invprob;

test/enzyme.jl

@@ -1,4 +1,4 @@
-using Enzyme, FiniteDiff
+using Enzyme, ForwardDiff
 using LinearSolve, LinearAlgebra, Test
 
 n = 4
@@ -20,8 +20,8 @@ f(A, b1) # Uses BLAS
 
 Enzyme.autodiff(Reverse, f, Duplicated(copy(A), dA), Duplicated(copy(b1), db1))
 
-dA2 = FiniteDiff.finite_difference_gradient(x->f(x,b1), copy(A))
-db12 = FiniteDiff.finite_difference_gradient(x->f(A,x), copy(b1))
+dA2 = ForwardDiff.gradient(x->f(x,eltype(x).(b1)), copy(A))
+db12 = ForwardDiff.gradient(x->f(eltype(x).(A),x), copy(b1))
 
 @test dA ≈ dA2
 @test db1 ≈ db12
@@ -35,8 +35,8 @@ db12 = zeros(n);
 
 @test_broken Enzyme.autodiff(Reverse, f, BatchDuplicated(copy(A), (dA, dA2)), BatchDuplicated(copy(b1), (db1, db12)))
 
-dA_2 = FiniteDiff.finite_difference_gradient(x->f(x,b1), copy(A))
-db1_2 = FiniteDiff.finite_difference_gradient(x->f(A,x), copy(b1))
+dA2 = ForwardDiff.gradient(x->f(x,eltype(x).(b1)), copy(A))
+db12 = ForwardDiff.gradient(x->f(eltype(x).(A),x), copy(b1))
 
 @test_broken dA ≈ dA_2
 @test_broken dA2 ≈ dA_2
@@ -45,9 +45,8 @@ db1_2 = FiniteDiff.finite_difference_gradient(x->f(A,x), copy(b1))
 
 function f(A, b1, b2; alg = LUFactorization())
     prob = LinearProblem(A, b1)
-
     cache = init(prob, alg)
-    s1 = solve!(cache).u
+    s1 = copy(solve!(cache).u)
     cache.b = b2
     s2 = solve!(cache).u
     norm(s1 + s2)
@@ -60,11 +59,46 @@ db1 = zeros(n);
 b2 = rand(n);
 db2 = zeros(n);
 
+f(A, b1, b2)
 Enzyme.autodiff(Reverse, f, Duplicated(copy(A), dA), Duplicated(copy(b1), db1), Duplicated(copy(b2), db2))
 
-dA2 = FiniteDiff.finite_difference_gradient(x->f(x,b1,b2), copy(A))
-db12 = FiniteDiff.finite_difference_gradient(x->f(A,x,b2), copy(b1))
-db22 = FiniteDiff.finite_difference_gradient(x->f(A,b1,x), copy(b2))
+dA2 = ForwardDiff.gradient(x->f(x,eltype(x).(b1),eltype(x).(b2)), copy(A))
+db12 = ForwardDiff.gradient(x->f(eltype(x).(A),x,eltype(x).(b2)), copy(b1))
+db22 = ForwardDiff.gradient(x->f(eltype(x).(A),eltype(x).(b1),x), copy(b2))
+
+@test dA ≈ dA2
+@test db1 ≈ db12
+@test db2 ≈ db22
+
+function f2(A, b1, b2; alg = RFLUFactorization())
+    prob = LinearProblem(A, b1)
+    cache = init(prob, alg)
+    s1 = copy(solve!(cache).u)
+    cache.b = b2
+    s2 = solve!(cache).u
+    norm(s1 + s2)
+end
+
+f2(A, b1, b2)
+dA = zeros(n, n);
+db1 = zeros(n);
+db2 = zeros(n);
+Enzyme.autodiff(Reverse, f2, Duplicated(copy(A), dA), Duplicated(copy(b1), db1), Duplicated(copy(b2), db2))
+
+@test dA ≈ dA2
+@test db1 ≈ db12
+@test db2 ≈ db22
+
+function f3(A, b1, b2; alg = KrylovJL_GMRES())
+    prob = LinearProblem(A, b1)
+    cache = init(prob, alg)
+    s1 = solve!(cache).u
+    cache.b = b2
+    s2 = solve!(cache).u
+    norm(s1 + s2)
+end
+
+Enzyme.autodiff(Reverse, f3, Duplicated(copy(A), dA), Duplicated(copy(b1), db1), Duplicated(copy(b2), db2))
 
 @test dA ≈ dA2 atol=5e-5
 @test db1 ≈ db12