[Bug tree-optimization/81028] GCC miscompiles placement new

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81028

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2017-06-09
          Component|c++                         |tree-optimization
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot 
gnu.org
     Ever confirmed|0                           |1
      Known to fail|                            |4.1.2, 4.3.6, 4.5.4, 4.8.5,
                   |                            |7.1.0

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  LIM applies store motion to ++*p.

non-C++11 testcase:

inline void* operator new(__SIZE_TYPE__, void* __p) { return __p; }

extern "C" void abort();

typedef int A;
typedef float B;

B *qq;

void __attribute__((noinline,noclone))
foo(A *p, A *q, long unk)
{
    for (long i = 0; i < unk; ++i) {
        ++*p;
        qq = new (static_cast<void *>(&q[i])) B(42);
    }
}

int main(void)
{
  union { A x; B f; } u = { 0 };
  foo(&u.x, &u.x, 1);
  if (*qq != 42) abort();
}