[Bug libstdc++/29286] [4.0/4.1/4.2/4.3 Regression] placement new does not change the dynamic type as it should

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #161 from rguenther at suse dot de  2007-05-28 11:14 -------
Subject: Re:  [4.0/4.1/4.2/4.3 Regression] placement
 new does not change the dynamic type as it should

Btw, it could save us many bugs (or bug reports) if if PTA says must-alias
we'd trust it, instead of using TBAA to say "but it shouldn't".  Like for
the (invalid)

int foo(void *p)
{
  double *q = p;
  int *r = p;
  *q = 1.0;
  return *r;
}

where we correctly figure that

Points-to sets
q_2 = same as p
r_3 = same as p

but still we get (with -fstrict-aliasing)

<bb 2>:
  q_2 = (double *) p_1(D);
  r_3 = (int *) p_1(D);
  # SMT.4_7 = VDEF <SMT.4_6(D)>
  *q_2 = 1.0e+0;
  # VUSE <SMT.5_8(D)>
  D.1641_4 = *r_3;

which just for the point to make the invalid input produce unexpected
output is possibly creating many of the hard-to-fix issues like this one.

Danny, how easy is it to "fix" the above?  It looks like another 
attractive solution to this problem.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29286