what is the usage of value compare?

Hi all, I am confused about the usage of the value_compare struct in the image. There seems to have a example

using TensorInfo = std::map<Value, tensor_info_t, value_compare>;

in the code. what the meaning of it?

And could anyone tell me how to find the definition order of SSAs? I mean is there an API that shows 5% happens before 10%?