[Bug middle-end/39460] strange aliasing warnings compiling pymol under gcc 4.4

["howarth at nitro dot med dot uc dot edu" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #5 from howarth at nitro dot med dot uc dot edu  2009-03-14 06:25 -------
Well, these two offending inlined routines do have the comments...

/* Only works with aligned 4-byte quantities, will cause a bus error */
/* on some platforms if used on unaligned data.                      */
static void swap4_aligned(void *v, long ndata) {
  int *data = (int *) v;
  long i;
  int *N;
  for (i=0; i<ndata; i++) {
    N = data + i;
    *N=(((*N>>24)&0xff) | ((*N&0xff)<<24) |
        ((*N>>8)&0xff00) | ((*N&0xff00)<<8));
  }
}


/* Only works with aligned 8-byte quantities, will cause a bus error */
/* on some platforms if used on unaligned data.                      */
static void swap8_aligned(void *v, long ndata) {
  /* Use int* internally to prevent bugs caused by some compilers */
  /* and hardware that would potentially load data into an FP reg */
  /* and hose everything, such as the old "jmemcpy()" bug in NAMD */
  int *data = (int *) v;
  long i;
  int *N;
  int t0, t1;

  for (i=0; i<ndata; i++) {
    N = data + (i<<1);
    t0 = N[0];
    t0=(((t0>>24)&0xff) | ((t0&0xff)<<24) |
        ((t0>>8)&0xff00) | ((t0&0xff00)<<8));

    t1 = N[1];
    t1=(((t1>>24)&0xff) | ((t1&0xff)<<24) |
        ((t1>>8)&0xff00) | ((t1&0xff00)<<8));

    N[0] = t1;
    N[1] = t0;
  }
}

Any idea how hard this one is to work around? It unclear if this could be fixed
with a union in any easy manner.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39460