[Bug c++/34459] [4.1/4.3 Regression] incorrect code when compiled with optimization (-O1)

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2007-12-14 13:32 -------
Confirmed.  Reduced testcase:

extern "C" void abort(void);
extern "C" void *memset(void *s, int c, __SIZE_TYPE__ n);

struct ip_addr {
    void __attribute__((noinline)) verify() const
    {
        for (int i = 0; i < sizeof(addr_); ++i)
            if (addr_[i] != 0)
                abort ();
    }
    ip_addr() {
        memset(&addr_, 0, sizeof(addr_));
    }
    char addr_[25];
};

struct foo {
    foo(ip_addr const & a) : remote_(a) { remote_ = remote_; }
    ip_addr remote_;
};

int main()
{
    ip_addr a;
    a.verify();
    foo f(a);
    f.remote_.verify();
}


On trunk after inlining we end up with main() like the following:

<bb 2>:
  # a_6 = VDEF <a_4(D)>
  # f_7 = VDEF <f_5(D)>
  memset (&a.addr_, 0, 25);
  # a_8 = VDEF <a_6>
  # f_9 = VDEF <f_7>
  verify (&a);
  # VUSE <a_8>
  # f_10 = VDEF <f_9>
  f.remote_ = a;
  # f_11 = VDEF <f_10>
  f.remote_ = f.remote_;
  # a_12 = VDEF <a_8>
  # f_13 = VDEF <f_11>
  verify (&f.remote_);
  return 0;

and DSE chooses to remove the first store to f.remote.  Whoops.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |wrong-code
      Known to fail|                            |4.1.3 4.3.0
      Known to work|                            |4.2.2
   Last reconfirmed|0000-00-00 00:00:00         |2007-12-14 13:32:37
               date|                            |
            Summary|incorrect code when compiled|[4.1/4.3 Regression]
                   |with optimization (-O1)     |incorrect code when compiled
                   |                            |with optimization (-O1)
   Target Milestone|---                         |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34459