[Bug tree-optimization/39100] [4.4 Regression] -fstrict-aliasing miscompilation

["rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #5 from rguenth at gcc dot gnu dot org  2009-02-04 20:59 -------
On the alias-improvements branch the testcase also fails with
-O -fdelete-null-pointer-checks, so this is definitely a PTA bug.
PTA thinks the points-to set for na_5 is

na_5, is dereferenced, points-to NULL, points-to vars: { nl }

which would definitely enable deleting the store, as nl is a local variable.

The constraints that should make na_5 point to NONLOCAL as well are

h = &NONLOCAL
x = &NONLOCAL
x_1 = x
*na_5 = x_1
D.1262_20 = *na_5
na_21 = D.1262_20 + 32
na_4 = na_21
na_5 = na_4

relevant unifications are

Unifying x to h
Unifying na_4 to na_5


The PTA bug can be seen with the following simplified testcase:

typedef struct E
{
  struct E *n;
} *EP;

void __attribute__((noinline))
foo (EP x)
{
  EP nl = 0, *na = &nl;
  EP n;

  while (x)
    {
      n = x->n;
      *na = x;
      na = &((*na)->n);
      x = n;
    }
  *na = 0;
}


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dberlin at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39100