Merge pull request #15111 from jacquesqiao/fix-adam-tmp-var

Fix adam tmp var on cpu

paddle/fluid/operators/optimizers/adam_op.h

@@ -424,16 +424,23 @@ class AdamOpKernel : public framework::OpKernel<T> {
         }
       }
 
+      framework::SelectedRows cpu_grad_merge;
       const framework::SelectedRows* grad_merge_ptr;
       if (is_strict_sorted) {
         grad_merge_ptr = &grad;
       } else {
         // merge duplicated rows if any.
         // The rows of grad_merge have been sorted inside MergeAdd functor
+        framework::SelectedRows* grad_merge_var;
         scatter::MergeAdd<DeviceContext, T> merge_func;
-        auto* grad_merge_var = const_cast<framework::Scope&>(ctx.scope())
+        if (platform::is_cpu_place(ctx.GetPlace())) {
+          grad_merge_var = &cpu_grad_merge;
+        } else {
+          // FIXME(qiao): GPU also need to fix this
+          grad_merge_var = const_cast<framework::Scope&>(ctx.scope())
                                .Var()
                                ->GetMutable<framework::SelectedRows>();
+        }
         merge_func(ctx.template device_context<DeviceContext>(), grad,
                    grad_merge_var, true);
         grad_merge_ptr = grad_merge_var;