Question

I had an issue that a Win32 application has huge performance difference between debug and release build. It takes 20 sec for release, while 6 min for debug build to initialize the application. This is painful since when debugging, it always takes 6 min to proceed the initialization before starting doing anything. So I am looking for a way to tune the performance in debug build.

After running profiler, I found below code is the hot-spot.

class CellList {
    std::vector<CellPtr>* _cells;
    iterator begin() { return (*_cells).begin(); }
    iterator end()   { return (*_cells).end(); }
    reverse_iterator rbegin() { return (*_cells).rbegin(); }
    reverse_iterator rend()   { return (*_cells).rend(); }
    ...
}

CellList _cellList = ...;

for (CellList::iterator itr = _cellList.begin(), end = _cellList.end(); itr < end; ++itr) {
  Cell* cell = *itr;
  if (cell->getFoo()) cell->setBar(true);
  else cell->setBar(false);
}

for (CellList::iterator itr = _cellList.rbegin(), end = _cellList.rend(); itr < end; ++itr) {
  Cell* cell = *itr;
  if (cell->getFoo2()) cell->setBar2(true);
  else cell->setBar2(false);
}

And these are the hot-spot in the time-base profile result.

std::operator< <std::_Vector_iterator<Cell *,std::allocator<Cell *> >,std::_Vector_iterator<Cell *,std::allocator<Cell *> > >
std::_Vector_const_iterator<Cell *,std::allocator<Cell *> >::operator<
std::reverse_iterator<std::_Vector_iterator<Cell *,std::allocator<Cell *> > >::operator*
std::reverse_iterator<std::_Vector_const_iterator<Cell *,std::allocator<Cell *> > >::reverse_iterator<std::_Vector_const_iterator<Cell *,std::allocator<Cell *> > ><std::_Vector_iterator<Cell *,std::allocator<Cell *> > >

I guess it’s the iterator operation not being inlined and causes this huge difference. Is there any way to improve this? I can debug in release mode as long as it’s still possible to step line by line in the source code and check all the variable values.

Answer 1

The difference is normal. What’d I’d do is place

#pragma optimize("",off)

#pragma optimize("",on)

around the methods you want to check, and keep the rest of the build in release mode.