Revert "Use std::stable_sort() instead of std::sort()"

Unfortunatly std::stable_sort() implementation in gcc is
horrendously slow. We have a big performance regression on
Linux systems (-20% !)

So revert the commit and wait to fix the issue in a different
way, perhaps with an our home grown sorting, that should be
comparable in speed with std::sort()

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/move.h

@@ -62,7 +62,7 @@ struct MoveStack {
   int score;
 };
 
-// Note that operator< is set up such that std::stable_sort() will sort in descending order
+// Note that operator< is set up such that std::sort() will sort in descending order
 inline bool operator<(const MoveStack& f, const MoveStack& s) { return s.score < f.score; }
 
 

src/movepick.cpp

@@ -123,7 +123,7 @@ void MovePicker::go_next_phase() {
   case PH_GOOD_CAPTURES:
       lastMove = generate_captures(pos, moves);
       score_captures();
-      std::stable_sort(moves, lastMove);
+      std::sort(moves, lastMove);
       return;
 
   case PH_KILLERS:
@@ -134,7 +134,7 @@ void MovePicker::go_next_phase() {
   case PH_NONCAPTURES:
       lastMove = generate_noncaptures(pos, moves);
       score_noncaptures();
-      std::stable_sort(moves, lastMove);
+      std::sort(moves, lastMove);
       return;
 
   case PH_BAD_CAPTURES:
@@ -142,20 +142,20 @@ void MovePicker::go_next_phase() {
       // to get SEE move ordering.
       curMove = badCaptures;
       lastMove = lastBadCapture;
-      std::stable_sort(badCaptures, lastMove);
+      std::sort(badCaptures, lastMove);
       return;
 
   case PH_EVASIONS:
       assert(pos.is_check());
       lastMove = generate_evasions(pos, moves, pinned);
       score_evasions();
-      std::stable_sort(moves, lastMove);
+      std::sort(moves, lastMove);
       return;
 
   case PH_QCAPTURES:
       lastMove = generate_captures(pos, moves);
       score_captures();
-      std::stable_sort(moves, lastMove);
+      std::sort(moves, lastMove);
       return;
 
   case PH_QCHECKS:

src/ucioption.cpp

@@ -210,7 +210,7 @@ void print_uci_options() {
   for (Options::const_iterator it = options.begin(); it != options.end(); ++it)
       vec.push_back(it->second);
 
-  std::stable_sort(vec.begin(), vec.end());
+  std::sort(vec.begin(), vec.end());
 
   for (std::vector<Option>::const_iterator it = vec.begin(); it != vec.end(); ++it)
   {