Always remember the ttMove

In master, if the received ttMove meets the prescribed conditions in the various MovePicker constructors, it is returned as the first move, otherwise we set it to MOVE_NONE. If set to MOVE_NONE, we no longer track what the ttMove was, and it will might be returned later in a list of generated moves. This may be a waste. With this patch, if the ttMove fails to meet the prescribed conditions, we simply skip the TT stages, but still store the move and make sure it's never returned.

STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 66424 W: 12903 L: 12806 D: 40715
Ptnml(0-2): 1195, 7730, 15230, 7897, 1160

LTC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 45682 W: 5989 L: 5926 D: 33767
Ptnml(0-2): 329, 4361, 13443, 4334, 374

closes https://github.com/official-stockfish/Stockfish/pull/2616

Bench 4928928

diff --git a/src/movepick.cpp b/src/movepick.cpp
index 580c6d7..b1e1058 100644 (file)
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -59,42 +59,36 @@ namespace {
 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh, const LowPlyHistory* lp,
                        const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers, int pl)
            : pos(p), mainHistory(mh), lowPlyHistory(lp), captureHistory(cph), continuationHistory(ch),
-             refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d), ply(pl) {
+             ttMove(ttm), refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d), ply(pl) {
 
   assert(d > 0);
 
-  stage = pos.checkers() ? EVASION_TT : MAIN_TT;
-  ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
-  stage += (ttMove == MOVE_NONE);
+  stage = (pos.checkers() ? EVASION_TT : MAIN_TT) +
+          !(ttm && pos.pseudo_legal(ttm));
 }
 
 /// MovePicker constructor for quiescence search
 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
                        const CapturePieceToHistory* cph, const PieceToHistory** ch, Square rs)
-           : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), recaptureSquare(rs), depth(d) {
+           : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), ttMove(ttm), recaptureSquare(rs), depth(d) {
 
   assert(d <= 0);
 
-  stage = pos.checkers() ? EVASION_TT : QSEARCH_TT;
-  ttMove =   ttm
-          && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare)
-          && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
-  stage += (ttMove == MOVE_NONE);
+  stage = (pos.checkers() ? EVASION_TT : QSEARCH_TT) +
+           !(ttm && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare)
+                 && pos.pseudo_legal(ttm));
 }
 
 /// MovePicker constructor for ProbCut: we generate captures with SEE greater
 /// than or equal to the given threshold.
 MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)
-           : pos(p), captureHistory(cph), threshold(th) {
+           : pos(p), captureHistory(cph), ttMove(ttm), threshold(th) {
 
   assert(!pos.checkers());
 
-  stage = PROBCUT_TT;
-  ttMove =   ttm
-          && pos.capture(ttm)
-          && pos.pseudo_legal(ttm)
-          && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;
-  stage += (ttMove == MOVE_NONE);
+  stage = PROBCUT_TT + !(ttm && pos.capture(ttm)
+                             && pos.pseudo_legal(ttm)
+                             && pos.see_ge(ttm, threshold));
 }
 
 /// MovePicker::score() assigns a numerical value to each move in a list, used