Andreas Lubensky wrote: > Hello, > i worked with g++ 4.3.1 (linux/586) and experienced some aliasing issues. > Basically, i have a base class and an derived class and i am doing downcasts > in a number of places using static_cast<derived*>(base_pointer) (no other > casting is involved, except implicit casting from derived* to base*). > To my understanding, this should not be a problem, since both types are > related. > Nevertheless, using -O2 or -O3 resulted in broken code. Apparently the order > of execution was mixed up in some places. Using -fno-strict-aliasing or > applying the may_alias attribute to these classes resolved the problem. > The whole issue is very hard to reproduce, so i could not boil it down to a > simple example (as the optimizer propably acts very unpredictable on > different code). > I did not have this problem using some GCC 4.1 and 4.2. I just upgraded to > 4.3.3 and the problem vanished again. > Nevertheless, i am worried the bug just *happens* to not show up, because the > optimizer may work a little different. > So: are there any aliasing issues that are known to be explicitly resolved by > 4.3.3? It's hard to know exactly what caused your problem, but yes, there are a number of aliasing changes on the 4.3 branch: I counted twelve patches. Andrew.
