------- Comment #3 from rguenth at gcc dot gnu dot org 2009-11-26 11:25 ------- Correct. We can either produce possibly lots of false positives or not warn. Warning in the cases where we can prove your code is wrong would be pointless as in that case we'd better take measures to not miscompile it (and we then can do so as we were able to detect the situation). With 4.4 one alias warning machinery did exactly this (warn but then not miscompile - but then it didn't warn in cases where it _did_ miscompile).
It's generally impossible to please all folks here ;) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42179