[Bug tree-optimization/83456] -Wrestrict false positive on a non-overlapping memcpy in an inline function

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83456

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
And another test case from bug 84095 comment #9, also due to the check in
gimple-fold.c.  This one seems closer to the first test case in comment #0. 

$ cat t.c && gcc -O2 -S -Wall t.c
extern void* memcpy (void*, const void*, __SIZE_TYPE__);

struct netdevice {
  void *priv;
};

struct ip_tunnel {
  struct netdevice *dev;
  int ip6rd[3];
};

struct sit_net {
  struct netdevice *fb_tunnel_dev;
};

void ipip6_tunnel_clone_6rd (struct netdevice *dev, struct sit_net *sitn)
{
  struct ip_tunnel *t = dev->priv;
  if (t->dev == sitn->fb_tunnel_dev)
    return;

  struct ip_tunnel *t0 = sitn->fb_tunnel_dev->priv;
  memcpy(&t->ip6rd, &t0->ip6rd, sizeof(t->ip6rd));
}

void sit_init_net (struct sit_net *sitn, struct netdevice *fb_tunnel_dev)
{
  sitn->fb_tunnel_dev = fb_tunnel_dev;
  ipip6_tunnel_clone_6rd (sitn->fb_tunnel_dev, sitn);
}
t.c: In function ‘sit_init_net’:
t.c:23:3: warning: ‘memcpy’ source argument is the same as destination
[-Wrestrict]
   memcpy(&t->ip6rd, &t0->ip6rd, sizeof(t->ip6rd));
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~