Chao Hieu, I don't know if this is possible for your target environment, but if possible, try running valgrind or similar memory-debugging tool. If not, examine your code carefully for possible access of uninitialized memory, etc. I have found that very often (but not always), what at first seems to us to be compiler generating incorrect code is, in fact, our own bad code. Code that produces behavior that differs between optimization options is often the result of access of uninitialized memory. Otherwise, as others have suggested, look at the assembly, but this is likely only helpful if your program is small or you can narrow the problem down to a particular small portion of the code. Good luck, -- David Favro
