On 29/10/20 23:12, David Laight wrote: >> https://godbolt.org/z/4dzPbM >> >> With -fno-strict-aliasing, the compiler reloads the pointer if you write >> to the start of what it points to, but not if you write to later >> elements. > I guess it assumes that global data doesn't overlap. Yeah, setting p = (struct s *) ((char *)&p) - 8; invokes undefined behavior _for a different reason than strict aliasing_ (it's a pointer that is based on "p" but points before its start or after one byte past its end). So the compiler assumes that only the first few bytes of a global can overlap it. If you change the size of the fields from long to char in the compiler explorer link above, every field forces a reload of the global. Paolo
