Remove pos.capture_or_promotion()

This patch replaces `pos.capture_or_promotion()` with `pos.capture()`
and comes after a few attempts with elo-gaining bounds, two of which
failed yellow at LTC
(https://tests.stockfishchess.org/tests/view/622f8f0cc9e950cbfc237024
and
https://tests.stockfishchess.org/tests/view/62319a8bb3b498ba71a6b2dc).

Passed non-regression STC:
https://tests.stockfishchess.org/tests/view/623aff7eea447151c74828d3
LLR: 2.94 (-2.94,2.94) <-2.25,0.25>
Total: 246864 W: 65462 L: 65618 D: 115784
Ptnml(0-2): 1201, 28116, 65001, 27866, 1248

Passed non-regression LTC:
https://tests.stockfishchess.org/tests/view/623c1fdcea447151c7484fb0
LLR: 2.94 (-2.94,2.94) <-2.25,0.25>
Total: 30120 W: 8125 L: 7978 D: 14017
Ptnml(0-2): 22, 2993, 8881, 3144, 20

closes https://github.com/official-stockfish/Stockfish/pull/3968

Bench: 6847732

src/position.h

@@ -352,11 +352,6 @@ inline bool Position::is_chess960() const {
   return chess960;
 }
 
-inline bool Position::capture_or_promotion(Move m) const {
-  assert(is_ok(m));
-  return type_of(m) != NORMAL ? type_of(m) != CASTLING : !empty(to_sq(m));
-}
-
 inline bool Position::capture(Move m) const {
   assert(is_ok(m));
   // Castling is encoded as "king captures rook"

src/search.cpp

@@ -554,7 +554,7 @@ namespace {
     Depth extension, newDepth;
     Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
     bool givesCheck, improving, didLMR, priorCapture;
-    bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture;
+    bool capture, doFullDepthSearch, moveCountPruning, ttCapture;
     Piece movedPiece;
     int moveCount, captureCount, quietCount, bestMoveCount, improvement, complexity;
 
@@ -624,7 +624,7 @@ namespace {
     ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
     ttMove =  rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
             : ss->ttHit    ? tte->move() : MOVE_NONE;
-    ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+    ttCapture = ttMove && pos.capture(ttMove);
     if (!excludedMove)
         ss->ttPv = PvNode || (ss->ttHit && tte->is_pv());
 
@@ -865,12 +865,13 @@ namespace {
 
         MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, depth - 3, &captureHistory);
         bool ttPv = ss->ttPv;
+        bool captureOrPromotion;
         ss->ttPv = false;
 
         while ((move = mp.next_move()) != MOVE_NONE)
             if (move != excludedMove && pos.legal(move))
             {
-                assert(pos.capture_or_promotion(move));
+                assert(pos.capture(move) || promotion_type(move) == QUEEN);
 
                 captureOrPromotion = true;
 
@@ -987,7 +988,7 @@ moves_loop: // When in check, search starts here
           (ss+1)->pv = nullptr;
 
       extension = 0;
-      captureOrPromotion = pos.capture_or_promotion(move);
+      capture = pos.capture(move);
       movedPiece = pos.moved_piece(move);
       givesCheck = pos.gives_check(move);
 
@@ -1007,7 +1008,7 @@ moves_loop: // When in check, search starts here
           // Reduced depth of the next LMR search
           int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, delta, thisThread->rootDelta), 0);
 
-          if (   captureOrPromotion
+          if (   capture
               || givesCheck)
           {
               // Futility pruning for captures (~0 Elo)
@@ -1122,7 +1123,7 @@ moves_loop: // When in check, search starts here
       // Update the current move (this must be done after singular extension search)
       ss->currentMove = move;
       ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
-                                                                [captureOrPromotion]
+                                                                [capture]
                                                                 [movedPiece]
                                                                 [to_sq(move)];
 
@@ -1138,7 +1139,7 @@ moves_loop: // When in check, search starts here
       if (    depth >= 2
           &&  moveCount > 1 + (PvNode && ss->ply <= 1)
           && (   !ss->ttPv
-              || !captureOrPromotion
+              || !capture
               || (cutNode && (ss-1)->moveCount > 1)))
       {
           Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta);
@@ -1215,7 +1216,7 @@ moves_loop: // When in check, search starts here
               int bonus = value > alpha ?  stat_bonus(newDepth)
                                         : -stat_bonus(newDepth);
 
-              if (captureOrPromotion)
+              if (capture)
                   bonus /= 6;
 
               update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
@@ -1306,10 +1307,10 @@ moves_loop: // When in check, search starts here
       // If the move is worse than some previously searched move, remember it to update its stats later
       if (move != bestMove)
       {
-          if (captureOrPromotion && captureCount < 32)
+          if (capture && captureCount < 32)
               capturesSearched[captureCount++] = move;
 
-          else if (!captureOrPromotion && quietCount < 64)
+          else if (!capture && quietCount < 64)
               quietsSearched[quietCount++] = move;
       }
     }
@@ -1394,7 +1395,7 @@ moves_loop: // When in check, search starts here
     Move ttMove, move, bestMove;
     Depth ttDepth;
     Value bestValue, value, ttValue, futilityValue, futilityBase;
-    bool pvHit, givesCheck, captureOrPromotion;
+    bool pvHit, givesCheck, capture;
     int moveCount;
 
     if (PvNode)
@@ -1503,7 +1504,7 @@ moves_loop: // When in check, search starts here
           continue;
 
       givesCheck = pos.gives_check(move);
-      captureOrPromotion = pos.capture_or_promotion(move);
+      capture = pos.capture(move);
 
       moveCount++;
 
@@ -1543,12 +1544,12 @@ moves_loop: // When in check, search starts here
 
       ss->currentMove = move;
       ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
-                                                                [captureOrPromotion]
+                                                                [capture]
                                                                 [pos.moved_piece(move)]
                                                                 [to_sq(move)];
 
       // Continuation history based pruning (~2 Elo)
-      if (  !captureOrPromotion
+      if (  !capture
           && bestValue > VALUE_TB_LOSS_IN_MAX_PLY
           && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold
           && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold)
@@ -1557,11 +1558,11 @@ moves_loop: // When in check, search starts here
       // movecount pruning for quiet check evasions
       if (  bestValue > VALUE_TB_LOSS_IN_MAX_PLY
           && quietCheckEvasions > 1
-          && !captureOrPromotion
+          && !capture
           && ss->inCheck)
           continue;
 
-      quietCheckEvasions += !captureOrPromotion && ss->inCheck;
+      quietCheckEvasions += !capture && ss->inCheck;
 
       // Make and search the move
       pos.do_move(move, st, givesCheck);
@@ -1680,7 +1681,7 @@ moves_loop: // When in check, search starts here
     bonus2 = bestValue > beta + PawnValueMg ? bonus1               // larger bonus
                                             : stat_bonus(depth);   // smaller bonus
 
-    if (!pos.capture_or_promotion(bestMove))
+    if (!pos.capture(bestMove))
     {
         // Increase stats for the best move in case it was a quiet move
         update_quiet_stats(pos, ss, bestMove, bonus2);