------- Comment #9 from guillaume dot melquiond at ens-lyon dot fr 2006-04-12 05:28 ------- > This is undefined only if b is known to be negative otherwise it is defined.
What is undefined? The value of "b" does not matter here. As soon as "a" is INT_MAX, the computed value with the optimization will be the exact opposite of the computed value without the optimization, whatever the sign of "b". So the result is always wrong. As far as I understand it, the compiler should be allowed to add a unary minus only if it can prove (VRP?) that INT_MIN is outside the range of the expression. However, for compilations with -fno-wrapv, a range excluding INT_MIN should be added after any unary minus written by the user. As a consequence of these two points, when nothing is known about "a" and -fno-wrapv is in effect, the compiler would be allowed to optimize (-a)/(-b) (PR 23669) but would be forbidden to optimize (-1-a)/(-b). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27116
