[Bug ipa/59948] Optimize std::function

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59948

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-01-29
                 CC|                            |hubicka at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Honza will know the correct condition ...

As for optimization the issue is that

  <bb 2>:
  MEM[(struct _Function_base *)&h]._M_manager = 0B;
  MEM[(int (*<T5869>) (int) *)&h] = f;
  h._M_invoker = _M_invoke;
  h.D.26161._M_manager = _M_manager;
  _4 = std::function<int(int)>::operator() (&h, 1);

  <bb 3>:
  _5 = _4;
  _11 = MEM[(struct _Function_base *)&h]._M_manager;
  if (_11 != 0B)
    goto <bb 4>;
  else
    goto <bb 5>;

  <bb 4>:
  _11 (&MEM[(struct _Function_base *)&h]._M_functor, &MEM[(struct
_Function_base *)&h]._M_functor, 3);

the call to std::function<int(int)>::operator() (&h, 1) may clobber h and
thus the _M_manager field.  This function is not early-inlined at -O[23]
and thus the call is not made direct before IPA inlining (or earlier).

Considering inline candidate _Res std::function<_Res(_ArgTypes
...)>::operator()(_ArgTypes ...) const [with _Res = int; _ArgTypes = {int}].
   Estimating body: _Res std::function<_Res(_ArgTypes
...)>::operator()(_ArgTypes ...) const [with _Res = int; _ArgTypes = {int}]/360
   Known to be false: not inlined
   size:10 time:21
   Estimating body: _Res std::function<_Res(_ArgTypes
...)>::operator()(_ArgTypes ...) const [with _Res = int; _ArgTypes = {int}]/360
   Known to be false: not inlined
   size:10 time:21
  will not early inline: int m()/273->_Res std::function<_Res(_ArgTypes
...)>::operator()(_ArgTypes ...) const [with _Res = int; _ArgTypes =
{int}]/360, growth 6 exceeds --param early-inlining-insns divided by number of
calls

forcing that with --param early-inlining-insns=100 arrives at

  <bb 2>:
  MEM[(struct _Function_base *)&h]._M_manager = 0B;
  MEM[(int (*<T5869>) (int) *)&h] = f;
  h._M_invoker = _M_invoke;
  h.D.26161._M_manager = _M_manager;
  _14 = std::_Function_handler<int(int), int (*)(int)>::_M_invoke
(&h.D.26161._M_functor, 1);

  <bb 3>:
  _15 = MEM[(struct _Function_base *)&h]._M_manager;

which has the same problem - just with another function call which the
early inliner doesn't see.