https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72795
--- Comment #3 from Peter Cordes <peter at cordes dot ca> --- Based on further discussion (http://chat.stackoverflow.com/rooms/119045/discussion-between-a3f-and-peter-cordes), the only bug (or feature?) here is that asm("":::"memory") doesn't count as a reference for `y`. i.e. the reason that asm statement works as a barrier is that it might read `y`, but gcc will still optimize away `y` completely if the only explicit reference in the translation unit are the stores in g(). This leads to a link error for: static int y; int g() { y = 1; asm volatile("movl $5, y(%%rip)":::"memory"); y = 2; return y; } // int gety(){ return y; } // link error with this commented out, otherwise ok This can be seen as a feature: It's probably not desirable for any "memory" clobber to prevent optimizing away any static variables. If y does exist in the asm output at all, I think gcc's behaviour as far as making the y=1 and y=2 stores happen separately is correct. If y exists at all, its value in memory has to be up-to-date.