This is a great question, but I think you’ve fallen victim to the compiler’s dependency analysis. The compiler only has to clear the high bits of eax once, and they remain clear for the second version. The second version would have to pay the price to xor eax, eax except that the compiler analysis proved … Read more
rep; nop is indeed the same as the pause instruction (opcode F390). It might be used for assemblers which don’t support the pause instruction yet. On previous processors, this simply did nothing, just like nop but in two bytes. On new processors which support hyperthreading, it is used as a hint to the processor that … Read more
The terms are indeed a bit confusing, because they are sometimes used inconsistently. Machine code: This is the most well-defined one. It is code that uses the byte-code instructions which your processor (the physical piece of metal that does the actual work) understands and executes directly. All other code must be translated or transformed into … Read more
Machine code is binary (1’s and 0’s) code that can be executed directly by the CPU. If you open a machine code file in a text editor you would see garbage, including unprintable characters (no, not those unprintable characters 😉 ). Object code is a portion of machine code not yet linked into a complete … Read more