http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58270
--- Comment #16 from Krzysztof Strasburger <strasbur at chkw386 dot ch.pwr.wroc.pl> --- Dear Dominique, I cannot agree with you. You are interpreting the code that may access the array beyond declared bounds as invalid, which is simply not true. As you pointed it out before, unnamed common block may be declared larger elsewhere, so writing the dmem array beyond its first element may be a design decision and therefore may be perfectly legal. The compiler has no clue about real size of unnamed common while compiling buggy.f and bounds checking is optional. I would also like to point it out that interpreting things this way you do, you exclude some older FORTRAN77 software (for example: quantum chemistry GAMESS), in which the lack of dynamic memory allocation was overcome using the trick we are discussing here (mixing with C was needed). BTW, change the size of dmem to 2 in buggy.f and things start to work correctly, although "out of bounds" memory accesses still do happen. The problem occurs only if dmem is of size 1. Of course you (developers) may decide to ignore this problem anyway, so if you do so, feel free to close this bug. I'm not going to reopen it again, because I'm out of arguments. I'm also not competent enough to tamper with the compiler.