GCC optimized code

Last year i was taking part in a codegolf contest. Someone who "cheated" and was not eligible to win used a weird C/C++ code which i pressume it was an optimization made by the compiler. It was not assembly, it was C/C++ but it was using some weird functions. Even tho he had printf and cout in his original code with long strings to be printed, in that code (optimized one) he had no printf's and cout's and no strings.... instead of strings there were numbers. Could you tell me how can i do the same for any other code? I'd like to see how small it would look with this optimization made by compiler.