Fix sum infershape issue

if dim is -1, compile time check fails.

test=develop
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

paddle/fluid/operators/sum_op.cc

@@ -65,7 +65,21 @@ class SumOp : public framework::OperatorWithKernel {
       if (framework::product(in_dim) == 0) {
         in_dim = x_dim;
       } else {
-        PADDLE_ENFORCE_EQ(in_dim, x_dim, "Input tensors must have same shape");
+        if (ctx->IsRuntime()) {
+          PADDLE_ENFORCE_EQ(in_dim, x_dim,
+                            "Input tensors must have same shape");
+        } else {
+          PADDLE_ENFORCE_EQ(in_dim.size(), x_dim.size(),
+                            "Input tensors must have same shape size");
+          // if in_dim or x_dim has -1, not check equal
+          for (int i = 0; i < x_dim.size(); ++i) {
+            if (x_dim[i] == -1 || in_dim[i] == -1) {
+              continue;
+            }
+            PADDLE_ENFORCE_EQ(in_dim[i], x_dim[i],
+                              "Input tensors must have same shape if not -1");
+          }
+        }
       }
     }
     ctx->SetOutputDim("Out", in_dim);