If you create two ImageParams with the same name, you can only call .trace_loads() on the first one. The second one will silently do nothing. That's because of this section of code in Tracing.cpp:

        } else if (op->call_type == Call::Image) {
            trace_it = trace_all_loads;
            // If there is a Function in the env named "name_im", assume that
            // this image is an ImageParam, so sniff that Function to see
            // if we want to trace loads on it. (This allows us to trace
            // loads on inputs without having to enable them globally.)
            auto it = env.find(op->name + "_im");

...only that name gets rendered as something like input_im$1 when input is duplicated. It would need to be called input$1_im for this logic to work.

This PR fixes that issue by allowing ImageParams to be marked for tracing directly. Params initially appear in the trace before any func, so the order was changed in one of the tests.