> Some advice I've read is to only use unsigned integers if you want to explicitly opt-in to having overflow be defined behavior.
I read somewhere that the true reason for that advice is that it allows the compiler to silently store an "int" loop counter in a 64-bit register, without having to care about 32-bit overflow. If you use size_t for the loop counter, that's no longer an issue.
It commonly factors in loop analysis around unrolling and vectorization, e.g. the loop will run exactly 16*n times OR an integer will overflow and it'll run some other number of times.
Use of signed precludes the overflow and the exact bound enables efficient vectorization.
I read somewhere that the true reason for that advice is that it allows the compiler to silently store an "int" loop counter in a 64-bit register, without having to care about 32-bit overflow. If you use size_t for the loop counter, that's no longer an issue.