Thanks, though I'm not sure all compile time detectable undefined behaviours is exposed through warnings today. In the example in the article, why would somethi

Thanks, though I'm not sure all compile time detectable undefined behaviours is exposed through warnings today. In the example in the article, why would something like left shift of a -ve value require runtime detection, surely the fact a signed char was used with left shift is all the compiler needs. So perhaps a subset to UB that is detectable at compile time should be reported. In your example about the comparison of x + 1 vs x, I'm not sure that is a contraversial optimization. However this one, to me, is: http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html http://blog.llvm.org/2011/05/what-every-c-programmer-should-... Here a diligent programmer is trying to do a null pointer check, but because dereferencing null is UB, then the optimizer removes the null pointer check. This is compile time UB that should be flagged to users.