Better check evasion move sorting

Use in addition the counter move history table for sorting quiet
check evasion moves in main and quiecence search. Also rename
"contHistory" to "continuationHistory" while there.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 73284 W: 16433 L: 15938 D: 40913
http://tests.stockfishchess.org/tests/view/5b4f526e0ebc5902bdb7a401

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 12135 W: 2171 L: 1997 D: 7967
http://tests.stockfishchess.org/tests/view/5b4fc0ef0ebc5902bdb7ae0e

Closes https://github.com/official-stockfish/Stockfish/pull/1685

Bench 4817583

src/movepick.cpp

@@ -61,7 +61,7 @@ namespace {
 /// MovePicker constructor for the main search
 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
                        const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers)
-           : pos(p), mainHistory(mh), captureHistory(cph), contHistory(ch),
+           : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch),
              refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d) {
 
   assert(d > DEPTH_ZERO);
@@ -73,8 +73,8 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHist
 
 /// MovePicker constructor for quiescence search
 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
-                       const CapturePieceToHistory* cph, Square rs)
-           : pos(p), mainHistory(mh), captureHistory(cph), recaptureSquare(rs), depth(d) {
+                       const CapturePieceToHistory* cph, const PieceToHistory** ch, Square rs)
+           : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), recaptureSquare(rs), depth(d) {
 
   assert(d <= DEPTH_ZERO);
 
@@ -115,9 +115,9 @@ void MovePicker::score() {
 
       else if (Type == QUIETS)
           m.value =  (*mainHistory)[pos.side_to_move()][from_to(m)]
-                   + (*contHistory[0])[pos.moved_piece(m)][to_sq(m)]
-                   + (*contHistory[1])[pos.moved_piece(m)][to_sq(m)]
-                   + (*contHistory[3])[pos.moved_piece(m)][to_sq(m)];
+                   + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
+                   + (*continuationHistory[1])[pos.moved_piece(m)][to_sq(m)]
+                   + (*continuationHistory[3])[pos.moved_piece(m)][to_sq(m)];
 
       else // Type == EVASIONS
       {
@@ -125,7 +125,9 @@ void MovePicker::score() {
               m.value =  PieceValue[MG][pos.piece_on(to_sq(m))]
                        - Value(type_of(pos.moved_piece(m)));
           else
-              m.value = (*mainHistory)[pos.side_to_move()][from_to(m)] - (1 << 28);
+              m.value =  (*mainHistory)[pos.side_to_move()][from_to(m)]
+                       + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
+                       - (1 << 28);
       }
 }
 

src/movepick.h

@@ -119,6 +119,7 @@ public:
   MovePicker(const Position&, Move, Value, const CapturePieceToHistory*);
   MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
                                            const CapturePieceToHistory*,
+                                           const PieceToHistory**,
                                            Square);
   MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
                                            const CapturePieceToHistory*,
@@ -136,7 +137,7 @@ private:
   const Position& pos;
   const ButterflyHistory* mainHistory;
   const CapturePieceToHistory* captureHistory;
-  const PieceToHistory** contHistory;
+  const PieceToHistory** continuationHistory;
   Move ttMove;
   ExtMove refutations[3], *cur, *endMoves, *endBadCaptures;
   int stage;

src/search.cpp

@@ -290,7 +290,7 @@ void Thread::search() {
 
   std::memset(ss-4, 0, 7 * sizeof(Stack));
   for (int i = 4; i > 0; i--)
-     (ss-i)->contHistory = this->contHistory[NO_PIECE][0].get(); // Use as sentinel
+     (ss-i)->continuationHistory = this->continuationHistory[NO_PIECE][0].get(); // Use as sentinel
 
   bestValue = delta = alpha = -VALUE_INFINITE;
   beta = VALUE_INFINITE;
@@ -587,7 +587,7 @@ namespace {
 
     (ss+1)->ply = ss->ply + 1;
     ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
-    ss->contHistory = thisThread->contHistory[NO_PIECE][0].get();
+    ss->continuationHistory = thisThread->continuationHistory[NO_PIECE][0].get();
     (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
     Square prevSq = to_sq((ss-1)->currentMove);
 
@@ -751,7 +751,7 @@ namespace {
         Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
 
         ss->currentMove = MOVE_NULL;
-        ss->contHistory = thisThread->contHistory[NO_PIECE][0].get();
+        ss->continuationHistory = thisThread->continuationHistory[NO_PIECE][0].get();
 
         pos.do_null_move(st);
 
@@ -802,7 +802,7 @@ namespace {
                 probCutCount++;
 
                 ss->currentMove = move;
-                ss->contHistory = thisThread->contHistory[pos.moved_piece(move)][to_sq(move)].get();
+                ss->continuationHistory = thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)].get();
 
                 assert(depth >= 5 * ONE_PLY);
 
@@ -835,7 +835,7 @@ namespace {
 
 moves_loop: // When in check, search starts from here
 
-    const PieceToHistory* contHist[] = { (ss-1)->contHistory, (ss-2)->contHistory, nullptr, (ss-4)->contHistory };
+    const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory };
     Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
 
     MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
@@ -970,7 +970,7 @@ moves_loop: // When in check, search starts from here
 
       // Update the current move (this must be done after singular extension search)
       ss->currentMove = move;
-      ss->contHistory = thisThread->contHistory[movedPiece][to_sq(move)].get();
+      ss->continuationHistory = thisThread->continuationHistory[movedPiece][to_sq(move)].get();
 
       // Step 15. Make the move
       pos.do_move(move, st, givesCheck);
@@ -1212,8 +1212,10 @@ moves_loop: // When in check, search starts from here
         ss->pv[0] = MOVE_NONE;
     }
 
+    Thread* thisThread = pos.this_thread();
     (ss+1)->ply = ss->ply + 1;
     ss->currentMove = bestMove = MOVE_NONE;
+    ss->continuationHistory = thisThread->continuationHistory[NO_PIECE][0].get();
     inCheck = pos.checkers();
     moveCount = 0;
 
@@ -1283,12 +1285,15 @@ moves_loop: // When in check, search starts from here
         futilityBase = bestValue + 128;
     }
 
+    const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory };
+
     // 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 >= DEPTH_QS_CHECKS) will
     // be generated.
-    MovePicker mp(pos, ttMove, depth, &pos.this_thread()->mainHistory,
-                                      &pos.this_thread()->captureHistory,
+    MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
+                                      &thisThread->captureHistory,
+                                      contHist,
                                       to_sq((ss-1)->currentMove));
 
     // Loop through the moves until no moves remain or a beta cutoff occurs
@@ -1345,6 +1350,7 @@ moves_loop: // When in check, search starts from here
       }
 
       ss->currentMove = move;
+      ss->continuationHistory = thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)].get();
 
       // Make and search the move
       pos.do_move(move, st, givesCheck);
@@ -1436,7 +1442,7 @@ moves_loop: // When in check, search starts from here
 
     for (int i : {1, 2, 4})
         if (is_ok((ss-i)->currentMove))
-            (*(ss-i)->contHistory)[pc][to] << bonus;
+            (*(ss-i)->continuationHistory)[pc][to] << bonus;
   }
 
 

src/search.h

@@ -41,7 +41,7 @@ constexpr int CounterMovePruneThreshold = 0;
 
 struct Stack {
   Move* pv;
-  PieceToHistory* contHistory;
+  PieceToHistory* continuationHistory;
   int ply;
   Move currentMove;
   Move excludedMove;

src/thread.cpp

@@ -61,11 +61,11 @@ void Thread::clear() {
   mainHistory.fill(0);
   captureHistory.fill(0);
 
-  for (auto& to : contHistory)
+  for (auto& to : continuationHistory)
       for (auto& h : to)
           h.get()->fill(0);
 
-  contHistory[NO_PIECE][0].get()->fill(Search::CounterMovePruneThreshold - 1);
+  continuationHistory[NO_PIECE][0].get()->fill(Search::CounterMovePruneThreshold - 1);
 }
 
 /// Thread::start_searching() wakes up the thread that will start the search

src/thread.h

@@ -71,7 +71,7 @@ public:
   CounterMoveHistory counterMoves;
   ButterflyHistory mainHistory;
   CapturePieceToHistory captureHistory;
-  ContinuationHistory contHistory;
+  ContinuationHistory continuationHistory;
   Score contempt;
 };