adaptive_avgpool2d_backward: Propagate memory format correctly (#668)

In inductor usage, generated Triton kernel assumes specific memory
layout after compile. The fallback operator in the graph need propagate
memory format correctly.

src/ATen/native/xpu/AdaptiveAveragePooling2d.cpp

@@ -69,14 +69,23 @@ Tensor sum_backward(
 
 Tensor mean_backward(
     const Tensor& grad,
+    const Tensor& input,
     c10::SymIntArrayRef shape,
     OptionalIntArrayRef opt_dim,
     c10::SymInt numel,
     bool keepdim) {
   bool is_all_reduce = !opt_dim.has_value() || opt_dim.value().empty();
   auto n =
       is_all_reduce ? std::move(numel) : _safe_size(shape, opt_dim.value());
-  return sum_backward(grad, shape, opt_dim, keepdim) / std::move(n);
+
+  Tensor grad_input =
+      sum_backward(grad, shape, opt_dim, keepdim) / std::move(n);
+
+  if (input.suggest_memory_format() == at::MemoryFormat::ChannelsLast) {
+    grad_input = grad_input.contiguous(input.suggest_memory_format());
+  }
+
+  return grad_input;
 }
 } // namespace
 
@@ -98,6 +107,7 @@ Tensor XPUNativeFunctions::_adaptive_avg_pool2d_backward(
   if (grad_output.size(-1) == 1 && grad_output.size(-2) == 1) {
     return mean_backward(
         grad_output,
+        input,
         input.sym_sizes().vec(),
         {-1, -2},
         input.sym_numel(),