[Bug middle-end/68470] [4.9/5/6 Regression] Internal Compiler Error observed by g++-4.9.2 and a few other versions (reported to Debian)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68470

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code
      Known to work|                            |4.8.4
            Summary|Internal Compiler Error     |[4.9/5/6 Regression]
                   |observed by g++-4.9.2 and a |Internal Compiler Error
                   |few other versions          |observed by g++-4.9.2 and a
                   |(reported to Debian)        |few other versions
                   |                            |(reported to Debian)

--- Comment #2 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
It is the same issue, but the testcase came out a bit smaller:

trippels@CFARM-IUT-TLSE3 ~ % cat cc.ii
template <typename...> using _Require = int;
template <typename _Alloc> struct A {
  typedef decltype(0) pointer;
  template <typename _Tp> static _Require<> _S_destroy(_Alloc, _Tp *__p) {
    __p->~_Tp();
  }
  static void deallocate(_Alloc, pointer, int);
  template <class _Tp> static void destroy(_Alloc __a, _Tp __p) {
    _S_destroy(__a, __p);
  }
};
template <typename _Tp> struct B { typedef _Tp *pointer; };
template <typename _Alloc> struct _Vector_base {
  typedef _Alloc _Tp_alloc_type;
  typedef typename _Tp_alloc_type::pointer pointer;
  struct G : _Tp_alloc_type {
    pointer _M_finish;
  };
  ~_Vector_base() {
    if (_M_deallocate___p)
      A<_Tp_alloc_type>::deallocate(_M_impl, 0, _M_deallocate___n);
  }
  G _M_impl;
  pointer _M_deallocate___p;
  int _M_deallocate___n;
};
template <typename _Tp, typename _Alloc = B<_Tp>>
struct H : _Vector_base<_Alloc> {
  int size();
  void back();
  void pop_back() {
    A<_Alloc>::destroy(this->_M_impl, this->_M_impl._M_finish);
  }
};
struct C {
  virtual void PopClip();
};
struct I : C {
  void PopClip();
  H<int> mTiles;
  H<H<unsigned>> mClippedOutTilesStack;
};
void abort() __attribute__((__noreturn__));
struct D {
  C *mRawPtr;
  C *operator->() {
    if (__builtin_expect(mRawPtr != 0, 0))
      abort();
  }
};
struct {
  D mDrawTarget;
} a;
void I::PopClip() {
  for (; mTiles.size();)
    a.mDrawTarget->PopClip();
  mClippedOutTilesStack.back();
  mClippedOutTilesStack.pop_back();
}

trippels@CFARM-IUT-TLSE3 ~ % g++ -O2 -c cc.ii
cc.ii: In member function âvirtual void I::PopClip()â:
cc.ii:59:1: error: statement uses released SSA name:
 }
 ^

# .MEM_31 = VDEF <.MEM>
MEM[(struct  &)_19] ={v} {CLOBBER};
The use of _19 should have been replaced
cc.ii:59:1: internal compiler error: cannot update SSA form