Retire ss->bestMove

And introduce SPlitPoint bestMove to pass back the
best move after a split point.

This allow to define as const the search stack passed
to split.

No functional change.

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

src/thread.h

@@ -34,9 +34,9 @@ const int MAX_SPLITPOINTS_PER_THREAD = 8;
 
 struct SplitPoint {
 
-  // Const data after splitPoint has been setup
-  SplitPoint* parent;
+  // Const data after split point has been setup
   const Position* pos;
+  const Search::Stack* ss;
   Depth depth;
   Value beta;
   int nodeType;
@@ -45,7 +45,8 @@ struct SplitPoint {
 
   // Const pointers to shared data
   MovePicker* mp;
-  Search::Stack* ss;
+  SplitPoint* parent;
+
 
   // Shared data
   Lock lock;
@@ -53,6 +54,7 @@ struct SplitPoint {
   volatile int64_t nodes;
   volatile Value alpha;
   volatile Value bestValue;
+  volatile Move bestMove;
   volatile int moveCount;
   volatile bool cutoff;
 };
@@ -116,7 +118,7 @@ public:
                       const std::set<Move>& = std::set<Move>(), bool async = false);
 
   template <bool Fake>
-  Value split(Position& pos, Search::Stack* ss, Value alpha, Value beta, Value bestValue,
+  Value split(Position& pos, Search::Stack* ss, Value alpha, Value beta, Value bestValue, Move* bestMove,
               Depth depth, Move threatMove, int moveCount, MovePicker* mp, int nodeType);
 private:
   friend struct Thread;