Refine ENFORCE in infer_shape of gru_op and lstm_unit_op.

test=develop

paddle/fluid/operators/gru_op.cc

@@ -47,8 +47,11 @@ class GRUOp : public framework::OperatorWithKernel {
     auto weight_dims = ctx->GetInputDim("Weight");
     int input_size = input_dims[1];
     int frame_size = weight_dims[0];
-    PADDLE_ENFORCE_EQ(input_size, frame_size * 3,
+    if (ctx->IsRuntime()) {
+      PADDLE_ENFORCE_EQ(
+          input_size, frame_size * 3,
           "The input_size must be 3 times of frame_size in GRUOp.");
+    }
     PADDLE_ENFORCE_EQ(
         weight_dims[1], frame_size * 3,
         "The shape of Weight matrix must be [frame_size, frame_size * 3].");

paddle/fluid/operators/lstm_unit_op.cc

@@ -34,10 +34,12 @@ class LstmUnitOp : public framework::OperatorWithKernel {
     auto c_prev_dims = ctx->GetInputDim("C_prev");
 
     PADDLE_ENFORCE_EQ(x_dims.size(), 2, "Input(X)'s rank must be 2.");
+    if (ctx->IsRuntime()) {
       PADDLE_ENFORCE_EQ(x_dims[0], c_prev_dims[0],
                         "Batch size of inputs and states must be equal");
       PADDLE_ENFORCE_EQ(x_dims[1], c_prev_dims[1] * 4,
                         "Dimension of FC should equal to prev state * 4");
+    }
 
     int b_size = c_prev_dims[0];  // batch size
     int s_dim = c_prev_dims[1];   // state dim