Avoid using EmptySearchStack global

This reduces contention in SMP case and also
cleanups the code a bit.

No functional change

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

src/movepick.cpp

@@ -63,13 +63,18 @@ namespace {
 /// search captures, promotions and some checks) and about how important good
 /// move ordering is at the current node.
 
-MovePicker::MovePicker(const Position& p, bool pv, Move ttm,
-                       const SearchStack& ss, Depth d) : pos(p) {
+MovePicker::MovePicker(const Position& p, bool pv, Move ttm, Depth d, SearchStack* ss) : pos(p) {
+
   pvNode = pv;
   ttMove = ttm;
-  mateKiller = (ss.mateKiller == ttm)? MOVE_NONE : ss.mateKiller;
-  killer1 = ss.killers[0];
-  killer2 = ss.killers[1];
+  if (ss)
+  {
+      mateKiller = (ss->mateKiller == ttm)? MOVE_NONE : ss->mateKiller;
+      killer1 = ss->killers[0];
+      killer2 = ss->killers[1];
+  } else
+      mateKiller = killer1 = killer2 = MOVE_NONE;
+
   depth = d;
   movesPicked = 0;
   numOfMoves = 0;

src/movepick.h

@@ -37,8 +37,6 @@
 struct EvalInfo;
 struct SearchStack;
 
-extern SearchStack EmptySearchStack;
-
 /// MovePicker is a class which is used to pick one legal move at a time from
 /// the current position. It is initialized with a Position object and a few
 /// moves we have reason to believe are good. The most important method is
@@ -66,7 +64,7 @@ public:
     PH_STOP
   };
 
-  MovePicker(const Position& p, bool pvnode, Move ttm, const SearchStack& ss, Depth d);
+  MovePicker(const Position& p, bool pvnode, Move ttm, Depth d, SearchStack* ss = NULL);
   Move get_next_move();
   Move get_next_move(Lock& lock);
   int number_of_moves() const;

src/san.cpp

@@ -143,7 +143,7 @@ Move move_from_san(const Position& pos, const string& movestr) {
 
   assert(pos.is_ok());
 
-  MovePicker mp = MovePicker(pos, false, MOVE_NONE, EmptySearchStack, OnePly);
+  MovePicker mp = MovePicker(pos, false, MOVE_NONE, OnePly);
 
   // Castling moves
   if (movestr == "O-O-O" || movestr == "O-O-O+")
@@ -367,7 +367,7 @@ namespace {
     if (type_of_piece(pc) == KING)
         return AMBIGUITY_NONE;
 
-    MovePicker mp = MovePicker(pos, false, MOVE_NONE, EmptySearchStack, OnePly);
+    MovePicker mp = MovePicker(pos, false, MOVE_NONE, OnePly);
     Move mv, moveList[8];
 
     int n = 0;

src/search.cpp

@@ -332,9 +332,6 @@ Lock IOLock;
 
 History H;  // Should be made local?
 
-// The empty search stack
-SearchStack EmptySearchStack;
-
 
 // SearchStack::init() initializes a search stack. Used at the beginning of a
 // new search from the root.
@@ -597,10 +594,6 @@ void init_threads() {
       // Wait until the thread has finished launching:
       while (!Threads[i].running);
   }
-
-  // Init also the empty search stack
-  EmptySearchStack.init(0);
-  EmptySearchStack.initKillers();
 }
 
 
@@ -1063,7 +1056,7 @@ namespace {
 
     // Initialize a MovePicker object for the current position, and prepare
     // to search all moves
-    MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
+    MovePicker mp = MovePicker(pos, true, ttMove, depth, &ss[ply]);
 
     Move move, movesSearched[256];
     int moveCount = 0;
@@ -1324,7 +1317,7 @@ namespace {
 
     // Initialize a MovePicker object for the current position, and prepare
     // to search all moves:
-    MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
+    MovePicker mp = MovePicker(pos, false, ttMove, depth, &ss[ply]);
 
     Move move, movesSearched[256];
     int moveCount = 0;
@@ -1545,7 +1538,7 @@ namespace {
     // Initialize a MovePicker object for the current position, and prepare
     // to search the moves.  Because the depth is <= 0 here, only captures,
     // queen promotions and checks (only if depth == 0) will be generated.
-    MovePicker mp = MovePicker(pos, pvNode, ttMove, EmptySearchStack, depth);
+    MovePicker mp = MovePicker(pos, pvNode, ttMove, depth);
     Move move;
     int moveCount = 0;
     Bitboard dcCandidates = mp.discovered_check_candidates();

src/search.h

@@ -69,7 +69,6 @@ struct SearchStack {
 //// Global variables
 ////
 
-extern SearchStack EmptySearchStack;
 extern TranspositionTable TT;
 extern int ActiveThreads;
 extern Lock SMPLock;