Clean up comments for movepicker

Remove references to checks in MovePicker comments. Follow-up for
https://github.com/official-stockfish/Stockfish/pull/5498

closes https://github.com/official-stockfish/Stockfish/pull/5516

No functional change

src/movepick.cpp

@@ -74,12 +74,10 @@ void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {
 
 
 // Constructors of the MovePicker class. As arguments, we pass information
-// to help it return the (presumably) good moves first, to decide which
+// to decide which class of moves to emit, to help sorting the (presumably)
-// moves to return (in the quiescence search, for instance, we only want to
+// good moves first, and how important move ordering is at the current node.
-// search captures, promotions, and some checks) and how important a good
-// move ordering is at the current node.
 
-// MovePicker constructor for the main search
+// MovePicker constructor for the main search and for the quiescence search
 MovePicker::MovePicker(const Position&              p,
                        Move                         ttm,
                        Depth                        d,
@@ -102,8 +100,8 @@ MovePicker::MovePicker(const Position&              p,
         stage = (depth > 0 ? MAIN_TT : QSEARCH_TT) + !(ttm && pos.pseudo_legal(ttm));
 }
 
-// Constructor for ProbCut: we generate captures with SEE greater than or equal
+// MovePicker constructor for ProbCut: we generate captures with Static Exchange
-// to the given threshold.
+// Evaluation (SEE) greater than or equal to the given threshold.
 MovePicker::MovePicker(const Position& p, Move ttm, int th, const CapturePieceToHistory* cph) :
     pos(p),
     captureHistory(cph),
@@ -115,9 +113,9 @@ MovePicker::MovePicker(const Position& p, Move ttm, int th, const CapturePieceTo
           + !(ttm && pos.capture_stage(ttm) && pos.pseudo_legal(ttm) && pos.see_ge(ttm, threshold));
 }
 
-// Assigns a numerical value to each move in a list, used
+// Assigns a numerical value to each move in a list, used for sorting.
-// for sorting. Captures are ordered by Most Valuable Victim (MVV), preferring
+// Captures are ordered by Most Valuable Victim (MVV), preferring captures
-// captures with a good history. Quiets moves are ordered using the history tables.
+// with a good history. Quiets moves are ordered using the history tables.
 template<GenType Type>
 void MovePicker::score() {
 
@@ -191,7 +189,7 @@ void MovePicker::score() {
 }
 
 // Returns the next move satisfying a predicate function.
-// It never returns the TT move.
+// This never returns the TT move, as it was emitted before.
 template<MovePicker::PickType T, typename Pred>
 Move MovePicker::select(Pred filter) {
 
@@ -208,9 +206,9 @@ Move MovePicker::select(Pred filter) {
     return Move::none();
 }
 
-// Most important method of the MovePicker class. It
+// This is the most important method of the MovePicker class. We emit one
-// returns a new pseudo-legal move every time it is called until there are no more
+// new pseudo-legal move on every call until there are no more moves left,
-// moves left, picking the move with the highest score from a list of generated moves.
+// picking the move with the highest score from a list of generated moves.
 Move MovePicker::next_move(bool skipQuiets) {
 
     auto quiet_threshold = [](Depth d) { return -3560 * d; };

src/movepick.h

@@ -137,12 +137,12 @@ using PawnHistory = Stats<int16_t, 8192, PAWN_HISTORY_SIZE, PIECE_NB, SQUARE_NB>
 using CorrectionHistory =
   Stats<int16_t, CORRECTION_HISTORY_LIMIT, COLOR_NB, CORRECTION_HISTORY_SIZE>;
 
-// MovePicker class is used to pick one pseudo-legal move at a time from the
+// The MovePicker class is used to pick one pseudo-legal move at a time from the
-// current position. The most important method is next_move(), which returns a
+// current position. The most important method is next_move(), which emits one
-// new pseudo-legal move each time it is called, until there are no moves left,
+// new pseudo-legal move on every call, until there are no moves left, when
-// when Move::none() is returned. In order to improve the efficiency of the
+// Move::none() is returned. In order to improve the efficiency of the alpha-beta
-// alpha-beta algorithm, MovePicker attempts to return the moves which are most
+// algorithm, MovePicker attempts to return the moves which are most likely to get
-// likely to get a cut-off first.
+// a cut-off first.
 class MovePicker {
 
     enum PickType {

src/search.cpp

@@ -20,18 +20,18 @@
 
 #include <algorithm>
 #include <array>
-#include <list>
 #include <atomic>
 #include <cassert>
+#include <chrono>
 #include <cmath>
 #include <cstdint>
 #include <cstdlib>
 #include <initializer_list>
+#include <iostream>
+#include <list>
+#include <ratio>
 #include <string>
 #include <utility>
-#include <chrono>
-#include <iostream>
-#include <ratio>
 
 #include "evaluate.h"
 #include "misc.h"
@@ -1520,11 +1520,11 @@ Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta)
     const PieceToHistory* contHist[] = {(ss - 1)->continuationHistory,
                                         (ss - 2)->continuationHistory};
 
+    Square prevSq = ((ss - 1)->currentMove).is_ok() ? ((ss - 1)->currentMove).to_sq() : SQ_NONE;
+
     // Initialize a MovePicker object for the current position, and prepare to search
     // the moves. We presently use two stages of move generator in quiescence search:
-    // first captures+checks, then captures only (but when in check, we simply search
+    // captures, or evasions only when in check.
-    // all evasions).
-    Square     prevSq = ((ss - 1)->currentMove).is_ok() ? ((ss - 1)->currentMove).to_sq() : SQ_NONE;
     MovePicker mp(pos, ttData.move, DEPTH_QS, &thisThread->mainHistory, &thisThread->captureHistory,
                   contHist, &thisThread->pawnHistory);