-- 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	2026-09-09 02:40:49 UTC
+++ paddle/fluid/imperative/amp_utils.h
@@ -227,14 +227,15 @@ static inline paddle::Tensor Cast(const paddle::Tensor
                                   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, DataType::UNDEFINED, dst_dtype);
+      return paddle::experimental::sparse::cast(
+          input, DataType::UNDEFINED, dst_dtype);
     } else {
       return paddle::experimental::sparse::cast(
           input, 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);
     }