------- Additional Comments From dberlin at gcc dot gnu dot org 2004-12-03 13:47 ------- Actually, this is related to the aliasing stuff described in the non-bugs.
If you look, in the first instance, you are casting a structure to an unsigned short *, and treating it like an array. In fact, i get structa.c: In function `main': structa.c:46: warning: passing arg 1 of `in_chksum_tcp' from incompatible pointer type This is not legal code. The second invocation, where you pass p.a, is correct, and we give you correct code as a result. If you compile the file with -fno-strict-aliasing, you also get the result you want, since we ignore the fact that you are violating the aliasing rules. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18806
