[Bug c++/54770] sibling call optimization is not applied where it ought to be

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54770

Steven Bosscher <steven at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW

--- Comment #2 from Steven Bosscher <steven at gcc dot gnu.org> 2012-10-02 11:44:41 UTC ---
Confirmed, complete test case:

---------------------- 8< ----------------------
typedef long unsigned int size_t;

namespace std
{
    using ::size_t;

  class exception
    {
  public:
    exception() throw() { }
    virtual ~exception() throw();
    };

  class bad_alloc : public exception
    {
  public:
    bad_alloc() throw() { }
    virtual ~bad_alloc() throw();
    };

  struct nothrow_t { };
  extern const nothrow_t nothrow;
}

inline void* operator new(std::size_t, void* __p) throw() { return __p; }
inline void operator delete (void*, void*) throw() { }

template<typename T> struct Intrusive
{
  Intrusive(T * p = 0) : px(p) { if(px) incref(px); }
  ~Intrusive() { if(px) decref(px); }
  T * operator->() const { return px; }
  T * px;
};
struct Node;
typedef Intrusive<Node> NodePtr;
struct Node
{
  Node() : refcnt(0) {}
  virtual ~Node() {}
  virtual void H() {}
  unsigned short refcnt;
  friend void incref(Node * node) { ++node->refcnt; }
  friend void decref(Node * node) { if(--node->refcnt == 0) delete node; }
};
struct MainNode : Node
{
  MainNode(NodePtr const & arg_) : Node(), arg(arg_) {}
  virtual ~MainNode() {}
  NodePtr arg;
  virtual void H()
    {
        {
          NodePtr tmp(arg);
          this->~Node();
          new(this) MainNode(tmp);
        }
      this->H();
    }
};
int main()
{
  NodePtr arg = NodePtr();
  NodePtr root(new MainNode(arg));
  root->H();
  return 0;
}
---------------------- 8< ----------------------

At trunk r191835, compiling with:
"./xgcc -B. -S -O3 -fdump-tree-optimized-lineno t.C"

Gives the call at line 58:

<L6>:
  tmp ={v} {CLOBBER};
  [t.C : 58:15] _13 = MEM[(int (*__vtbl_ptr_type) () *)prephitmp_29+16B];
  [t.C : 58:16] OBJ_TYPE_REF(_13;this_3(D)->2) (this_3(D));
  [t.C : 59:5] return;