[Bug lto/106706] Enabling LTO causes incorrect calculation in in_csum()

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106706

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is an obvious C/C++ aliasing violation.

 ipv4_phdr_t ipv4_phdr;
...
in_csum(({ ( uint16_t *) (&ipv4_phdr); }), sizeof(ipv4_phdr), 0,
&vrrp->ipv4_csum);


inside in_csum:
uint16_t
in_csum(const uint16_t *addr, size_t len, uint32_t csum, uint32_t *acc)
....
 while (nleft > 1) {
  csum += *addr++;

You need to use either -fno-strict-aliasing or you need to mark the argument
addr in in_csum as may_alias.