fix, test=document_fix

Author: co63oc

paddle/fluid/framework/ir/graph_helper.cc

@@ -547,12 +547,12 @@ void ReplaceAllReduceOp(const Node &node,
   // ### v1 = op1(grad1)
   // It is converted to:
   // ### fused_grad = check_memory_continue(grad0, grad1, grad2, ...)
-  // ### fused_grad = c_sum_allreduce(fused_grad)
+  // ### fused_grad = all_reduce(fused_grad)
   // ### v0 = op0(grad0)
   // ### v1 = op1(grad1)
   // We should add the following dependency to ensure that op0 and op1 both run
-  // after c_sum_allreduce:
-  // ### grad0 =  depend(grad0, fused_grad)
+  // after all_reduce(sum):
+  // ### grad0 = depend(grad0, fused_grad)
   // ### grad1 = depend(grad1, fused_grad)
   if (is_fused) {
     for (const auto &in : in_var_handles) {