add more comments in CMakelists.txt of operator

paddle/framework/op_registry.h

@@ -37,8 +37,8 @@ class Registrar {
  public:
   // In our design, various kinds of classes, e.g., operators and kernels,
   // have their corresponding registry and registrar. The action of
-  // registration is in the constructor of a global registrar variable, which,
-  // however, are not used in the code that calls package framework, and would
+  // registration is in the constructor of a global registrar variable, which
+  // are not used in the code that calls package framework, and would
   // be removed from the generated binary file by the linker. To avoid such
   // removal, we add Touch to all registrar classes and make USE_OP macros to
   // call this method. So, as long as the callee code calls USE_OP, the global

paddle/operators/CMakeLists.txt

@@ -68,9 +68,10 @@ function(op_library TARGET)
         endif()
     endforeach()
 
+    # The registration of USE_OP, please refer to paddle/framework/op_registry.h.
+    # Note that it's enough to just adding one operator to pybind in a *_op.cc file.
+    # And for detail pybind information, please see generated paddle/pybind/pybind.h.
     file(READ ${TARGET}.cc TARGET_CONTENT)
-    # It's enough to just adding one operator to pybind.
-    # And for detail pybind information, please see paddle/pybind/pybind.h.
     string(REGEX MATCH "REGISTER_OP\\(.*REGISTER_OP\\(" multi_register "${TARGET_CONTENT}")
     string(REGEX MATCH "REGISTER_OP\\([a-z0-9_]*," one_register "${multi_register}")
     if (one_register STREQUAL "")