Be careful: it's not just that the result of the multiplication won't be what you expect. The entire execution of the program becomes undefined. For example, if you had an unconditional `puts("hello");` between the multiplication and comparison lines, if the overflow happens, it would be allowed to print "goodbye" instead.
Yes, and in particular the compiler can assume that you stay within the defined behavior. That's what's enabling the optimization in removing the i < 0 check.
