Ian Lance Taylor <[EMAIL PROTECTED]> writes: > We could disable VRP's assumptions about signed overflow. I don't > know what else we could do to fix this case. I don't even know how we > could issue a useful warning. Perhaps there is a way.
It is a knotty problem. Thanks for thinking about it. I'm Handwaving with a capital H here, but one possibility is for plain -O2 to keep VRP, but disable its assumption about signed overflow when attempting to optimize away a comparison that comes directly from the user's code (as opposed to a comparison coming from subscript checking and the like). Here's another wild idea. Perhaps GCC could add an option "-fundefinedv" to request for aggressive optimizations assuming that the program will never have an signed integer overflow. I.e., if you want the optimization that is causing trouble here, you would specify "-O2 -fundefinedv"; but the default would be to disable this particular troublesome optimization.
