[FRONTEND] Improve error message for CPU tensors (#654)

Redo of #651 against master. Fixes #525 by catching CUDA error when we
check pytorch tensor size and rethrowing a more informative error that
says why we failed.

python/src/triton.cc

@@ -226,11 +226,16 @@ void parse_args(py::list& args, py::list do_not_specialize, const std::string& f
         // copy param
         std::memcpy(params_ptr, &value, 8);
         params_ptr += 8;
-        // udpate cache key
+        // update cache key
         cache_key += dtype_cache_key_part(arg.attr("dtype"));
         cache_key += "*";
         cache_key += "[multipleof(";
-        size_t range_size = get_pointer_range_size(value);
+        size_t range_size;
+        try {
+          range_size = get_pointer_range_size(value);
+        } catch (...) {
+          throw std::runtime_error("argument tensor #" + std::to_string(i) + " is not on cuda! " + std::string(py::str(arg)));
+        }
         cache_key += std::to_string(std::min(pow2_divisor(value), pow2_divisor(range_size)));
         cache_key += ")]";
         continue;