------- Comment #32 from veksler at il dot ibm dot com 2010-02-21 12:44 ------- (In reply to comment #31) > (In reply to comment #30) > > Wouldn't it be a violation of the one definition rule (ODR), > > when one translation unit is compiled with -fwrapv and another without? > > In that case this would be a regression. > > I don't know if this comes as a surprise to you, but in the library we have > *tons* of potential violations of this type, due to command line switches, not > just the big cases like debug-mode, but also rtti, exceptions, etc. That said, > if people prefer a false value, always, just tell me and let's close this PR > because I don't think the compiler is going to change any time soon to warrant > a true value irrespective of any command line option ...
If this hazard is so prevalent shouldn't it deserve a separate PR? If a method or function depend on a flag or macro then it can be handled by overloading and specialization without ODR violation. When this hazard is, like in this case, appears in a constant then things are more difficult. An unexpected behavior may be observed when is_modulo is passed by reference, and I don't see what can be done in this case, not in 100% of the scenarios. Even if GCC annotates the two different variants of is_modulo differently, such that there will be two different physical allocations of is_modulo, it will still be possible to get to some misbehavior in weird cases. Oh well... -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22200
