add more debug info.

test=develop

paddle/fluid/framework/ir/graph.cc

@@ -40,27 +40,32 @@ void CheckProgram(const ProgramDesc &program) {
         case _INT(OpRole::kForward):
           PADDLE_ENFORCE(
               visit.find(_INT(OpRole::kBackward)) == visit.end(),
-              "Cannot add forward operator before backward operator.");
+              "Cannot add backward operator before forward operator %s.",
+              op->Type());
           break;
         case _INT(OpRole::kBackward):
         case _INT(OpRole::kBackward) | _INT(OpRole::kLoss):
           PADDLE_ENFORCE(
               visit.find(_INT(OpRole::kOptimize)) == visit.end(),
-              "Cannot add backward operator before optimize operator.");
+              "Cannot add backward operator %s before optimize operator.",
+              op->Type());
           break;
         case _INT(OpRole::kForward) | _INT(OpRole::kLoss):
           PADDLE_ENFORCE(visit.find(_INT(OpRole::kBackward) |
                                     _INT(OpRole::kLoss)) == visit.end(),
                          "Cannot add backward|loss operator before "
-                         "forward|loss operator.");
+                         "forward|loss operator %s.",
+                         op->Type());
           PADDLE_ENFORCE(
               visit.find(_INT(OpRole::kOptimize)) == visit.end(),
-              "Cannot add backward operator before optimize operator.");
+              "Cannot add forward|loss operator %s after optimize operator.",
+              op->Type());
           break;
         case _INT(OpRole::kOptimize):
         case _INT(OpRole::kOptimize) | _INT(OpRole::kLRSched):
           PADDLE_ENFORCE(visit.find(_INT(OpRole::kBackward)) != visit.end(),
-                         "Optimize operators must follow backward operator.");
+                         "Optimize operators %s must follow backward operator.",
+                         op->Type());
           break;
         case _INT(OpRole::kLRSched):
         case _INT(OpRole::kDist):