[Bug c/41630] [4.3/4.4 Regression] Optimization error on vectors of uint64_t

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2009-10-08 15:03 -------
What we can see after inlining is

<bb 2>:
  X[0][0] ={v} 12345;
  D.1614_1 = (long unsigned int *) &X[1];
  *D.1614_1 ={v} 67890;
  D.1614_2 = (long unsigned int *) &X[1];
  X.0_3 = (long unsigned int *) &X;
  D.1623_5 = *X.0_3;
  X[0][0] ={v} D.1623_5;
  D.1622_6 = *D.1614_2;
  X[1][0] ={v} D.1622_6;
  D.1623_7 = *X.0_3;
  if (D.1623_7 != 12345)
    goto <bb 4>;
...
<bb 6>:
  D.1625_10 = X[0][1];
  if (D.1625_10 != 67890)
    goto <bb 7>;
  else
    goto <bb 8>;

so the final check is reading from X[0][1] but we only ever store to X[1][0].

So the testcase can be simplified to

typedef unsigned long obj[1];
extern void abort (void);
static void test_level2(obj X[])
{
    if (*X[1] != 67890)
      abort ();
}
int main()
{
    obj X[2];
    X[1][0] = 67890;
    test_level2(X);
    return 0;
}

or even to

typedef unsigned long obj[1];
extern void abort (void);
int main()
{
    obj X[2];
    X[1][0] = 67890;
    if (X[0][1] != 67890)
      abort ();
    return 0;
}

which will also fail with 4.2.4 (but still not 4.5.0).  But that also
raises the question of the validity again.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41630