Enzyme: Reversemode cudaconvert (#2476)

Author: wsmoses

ext/EnzymeCoreExt.jl

@@ -55,7 +55,7 @@ end
 function EnzymeCore.EnzymeRules.forward(ofn::Const{typeof(cudaconvert)},
                                         ::Type{RT}, x::IT) where {RT, IT}
     if RT <: Duplicated
-        RT(ofn.val(x.val), ofn.val(x.dval))
+        Duplicated(ofn.val(x.val), ofn.val(x.dval))
     elseif RT <: Const
         ofn.val(x.val)::eltype(RT)
     elseif RT <: DuplicatedNoNeed
@@ -73,6 +73,33 @@ function EnzymeCore.EnzymeRules.forward(ofn::Const{typeof(cudaconvert)},
     end
 end
 
+function EnzymeCore.EnzymeRules.augmented_primal(config, ofn::Const{typeof(cudaconvert)}, ::Type{RT}, x::IT) where {RT, IT}
+    primal = if EnzymeRules.needs_primal(config)
+        ofn.val(x.val)
+    else
+        nothing
+    end
+    
+    shadow = if EnzymeRules.needs_shadow(config)
+        if EnzymeRules.width(config) == 1
+            ofn.val(x.dval)
+        else
+          ntuple(Val(EnzymeRules.width(config))) do i
+              Base.@_inline_meta
+              ofn.val(x.dval[i])
+          end
+        end
+    else
+        nothing
+    end
+    return EnzymeRules.AugmentedReturn{(EnzymeRules.needs_primal(config) ? eltype(RT) : Nothing), (EnzymeRules.needs_shadow(config) ? (EnzymeRules.width(config) == 1 ? eltype(RT) : NTuple{EnzymeRules.width(config), eltype(RT)}) : Nothing), Nothing}(primal, shadow, nothing)
+end
+
+function EnzymeCore.EnzymeRules.reverse(config, ofn::Const{typeof(cudaconvert)}, ::Type{RT}, tape, x::IT) where {RT, IT}
+    (nothing,)
+end
+
+
 function EnzymeCore.EnzymeRules.forward(ofn::Const{Type{CT}},
         ::Type{RT}, uval::EnzymeCore.Annotation{UndefInitializer}, args...) where {CT <: CuArray, RT}
     primargs = ntuple(Val(length(args))) do i