https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93301
--- Comment #2 from Alexander Cherepanov <ch3root at openwall dot com> --- The problem is much more serious. It's not that C has some guarantees about two values of `y` while gcc doesn't provide them. It's that one part of gcc assumes there are some guarantees about two values of `y` while another part of gcc doesn't provide such guarantees. There were many discussions about "wobbly" values (DR 260, DR 451 etc.) and I don't expect gcc to give the same values for two `y`s at all. The second value is taken in the `else` branch, which we don't care about (at least while this branch doesn't invoke UB). Given that `b` is `1` we know that the `then` branch is taken. It's surely possible to make this testcase undefined. If I understand them correctly, llvm folks claim that "real compilers" (gcc included I assume) follow rules that are more like C++ than C (see the linked clang bug report). The C++ rules are much more strict and make `x == y` undefined if `y` is uninitialized. But my guess is that the C++ rules will not help. The problem is the internal inconsistency so everything will blow up independently of any external rules.
