[AutoDiff] Handle materializing adjoints with non-differentiable fields

Fixes #66522

Author: jkshtj

lib/SILOptimizer/Differentiation/AdjointValue.cpp

@@ -1,5 +1,4 @@
-//===--- AdjointValue.cpp - Helper class for differentiation ----*- C++
-//-*---===//
+//===--- AdjointValue.h - Helper class for differentiation ----*- C++ -*---===//
 //
 // This source file is part of the Swift.org open source project
 //
@@ -68,4 +67,4 @@ void swift::autodiff::AdjointValue::print(llvm::raw_ostream &s) const {
     s << "]";
     break;
   }
-}
+}

lib/SILOptimizer/Differentiation/PullbackCloner.cpp

@@ -430,6 +430,8 @@ class PullbackCloner::Implementation final
     }
     case AdjointValueKind::AddElement: {
       auto baseAdjoint = val;
+      assert(baseAdjoint.getType().is<TupleType>() ||
+             baseAdjoint.getType().getStructOrBoundGenericStruct() != nullptr);
 
       // Current adjoint may be made up of layers of `AddElement` adjoints.
       // We can iteratively gather the list of elements to add instead of making