[josephcsible]

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.

[symmetricsaurus]

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.