--- Fix namespace qualification for cast functions in amp_utils.h
--- 
--- The code was using unqualified `sparse::cast_ad_func` and `cast_ad_func` which
--- don't exist. They should use the full namespace qualifier like the non-trace_backward
--- paths do: `paddle::experimental::sparse::cast` and `paddle::experimental::cast`.
---
--- This fixes compilation errors:
--- error: use of undeclared identifier 'sparse'
--- error: no member named 'cast_ad_func' in namespace 'paddle::experimental::sparse'
--- error: use of undeclared identifier 'cast_ad_func'

--- paddle/fluid/imperative/amp_utils.h.orig	2024-12-20 00:00:00 UTC
+++ paddle/fluid/imperative/amp_utils.h
@@ -229,14 +229,14 @@ static inline paddle::Tensor Cast(const paddle::Tenso
                                   const bool trace_backward = true) {
   if (input.is_sparse_coo_tensor() || input.is_sparse_csr_tensor()) {
     if (trace_backward) {
-      return sparse::cast_ad_func(input, phi::DataType::UNDEFINED, dst_dtype);
+      return paddle::experimental::sparse::cast(input, phi::DataType::UNDEFINED, dst_dtype);
     } else {
       return paddle::experimental::sparse::cast(
           input, phi::DataType::UNDEFINED, dst_dtype);
     }
   } else {
     if (trace_backward) {
-      return cast_ad_func(input, dst_dtype);
+      return paddle::experimental::cast(input, dst_dtype);
     } else {
       return paddle::experimental::cast(input, dst_dtype);
     }