I don't know enough about ASM. Are u saying the first one is more optimal because it is faster or because it uses less instructions? Would this reflect a real world use case? Do any other compilers (e.g. V8) optimize modulo's into something else?
The compiler didn't recognize that x % 2 == 0 && x % 3 == 0 is exactly the same as x % 6 == 0 for all C/C++ int values. In theory a compiler could detect that and generate identical code for both functions, but it isn't done because this case is "niche" despite being trivial. My point is not to over rely on optimizer for math expressions and algorithms.
