Please see the description of how a DO loop operated in 1960s CDC Fortran (page I.5.9, PDF page number 70). Not only is the at-least-one-trip DO feature described, but also another curious feature: the DO index variable became undefined after normal completion of the DO loop! Furthermore, the variables/expressions m1, m2, m3 in DO I = m1,m2,m3 were all required to be positive. There was provision for the “extended range” of the DO loop – a jump out of the loop, followed by execution of some statements, and then a jump back into the loop.
Some of these seemingly odd features may be related to the architecture of the CDC: data registers were 60 bit (integers and reals), index registers were only 18 bits. There were no separate instructions for integer arithmetic.