[quotemstr]

> Can assert() actually function this way? Can you use assert to tell the optimizer it can assume something is true?

Trivially.

  #ifdef NDEBUG
  # define assert_and_assume(cond) if(!(cond))     
    __builtin_unreachable((cond))
  #else
  # define assert_and_assume assert
  #endif

[haberman]

Interesting! This assert_and_assume() seems strictly better than vanilla assert() for any predicates that don't have side effects. But I guess you have to be sure that the compiler is able to deduce that there aren't side effects and feels comfortable optimizing away the predicate in release mode.