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

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

------- Comment #85 from rguenth at gcc dot gnu dot org  2007-05-18 14:46 -------
To avoid confusion about what testcase we speak, let's talk about the one
I replicated below.  I believe this one is valid as the storage is a union
instantiated in main() and a pointer to it is passed to foo().  It doesn't
matter the argument pointer type is double*, as we access the memory first
as int* (which is ok and starts lifetime of int typed memory) and then we
EOL that object and start lifetime of a long via placement new (alignment
is ok, as is size).

So, anyone disagrees that the below testcase is valid?


inline void* operator new(unsigned long, void* __p) throw() { return __p; }

void __attribute__((noinline)) bar() {};

long __attribute__((noinline)) foo(double *p, int n)
{
  long *f;
  for (int i=0; i<n; ++i)
  {
    int *l = (int *)p;
    *l = 0;
    f = new (p) long;
    *f = -1;
  }
  bar ();
  return *f;
}

extern "C" void abort(void);
int main()
{
  union {
    int i;
    long l;
  } u;
  if (foo((double *)&u, 1) != -1)
    abort ();
  return 0;
}


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