X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=f8f956fa9375241536e3a61eadc23eff83e1b467;hb=49c79aa15ce5a0de54fe0f4cef1037751af3d7d1;hp=d77ab691d62b34d68e678801c120ae4d607fbbf5;hpb=76daa88cf878b12a03755dc0550b3fa8e4d19cb1;p=stockfish diff --git a/src/search.cpp b/src/search.cpp index d77ab691..f8f956fa 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -35,6 +35,8 @@ #include "uci.h" #include "syzygy/tbprobe.h" +namespace Stockfish { + namespace Search { LimitsType Limits; @@ -64,7 +66,7 @@ namespace { // Futility margin Value futility_margin(Depth d, bool improving) { - return Value(234 * (d - improving)); + return Value(231 * (d - improving)); } // Reductions lookup table, initialized at startup @@ -100,49 +102,6 @@ namespace { Move best = MOVE_NONE; }; - // Breadcrumbs are used to mark nodes as being searched by a given thread - struct Breadcrumb { - std::atomic thread; - std::atomic key; - }; - std::array breadcrumbs; - - // ThreadHolding structure keeps track of which thread left breadcrumbs at the given - // node for potential reductions. A free node will be marked upon entering the moves - // loop by the constructor, and unmarked upon leaving that loop by the destructor. - struct ThreadHolding { - explicit ThreadHolding(Thread* thisThread, Key posKey, int ply) { - location = ply < 8 ? &breadcrumbs[posKey & (breadcrumbs.size() - 1)] : nullptr; - otherThread = false; - owning = false; - if (location) - { - // See if another already marked this location, if not, mark it ourselves - Thread* tmp = (*location).thread.load(std::memory_order_relaxed); - if (tmp == nullptr) - { - (*location).thread.store(thisThread, std::memory_order_relaxed); - (*location).key.store(posKey, std::memory_order_relaxed); - owning = true; - } - else if ( tmp != thisThread - && (*location).key.load(std::memory_order_relaxed) == posKey) - otherThread = true; - } - } - - ~ThreadHolding() { - if (owning) // Free the marked location - (*location).thread.store(nullptr, std::memory_order_relaxed); - } - - bool marked() { return otherThread; } - - private: - Breadcrumb* location; - bool otherThread, owning; - }; - template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode); @@ -163,7 +122,7 @@ namespace { uint64_t perft(Position& pos, Depth depth) { StateInfo st; - ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize); uint64_t cnt, nodes = 0; const bool leaf = (depth == 2); @@ -418,11 +377,11 @@ void Thread::search() { // Start with a small aspiration window and, in the case of a fail // high/low, re-search with a bigger window until we don't fail // high/low anymore. - failedHighCnt = 0; + int failedHighCnt = 0; while (true) { Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter); - bestValue = ::search(rootPos, ss, alpha, beta, adjustedDepth, false); + bestValue = Stockfish::search(rootPos, ss, alpha, beta, adjustedDepth, false); // Bring the best move to the front. It is critical that sorting // is done with a stable algorithm because all the values but the @@ -595,7 +554,7 @@ namespace { Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64]; StateInfo st; - ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize); TTEntry* tte; Key posKey; @@ -610,12 +569,12 @@ namespace { // Step 1. Initialize node Thread* thisThread = pos.this_thread(); - ss->inCheck = pos.checkers(); - priorCapture = pos.captured_piece(); - Color us = pos.side_to_move(); - moveCount = captureCount = quietCount = ss->moveCount = 0; - bestValue = -VALUE_INFINITE; - maxValue = VALUE_INFINITE; + ss->inCheck = pos.checkers(); + priorCapture = pos.captured_piece(); + Color us = pos.side_to_move(); + moveCount = captureCount = quietCount = ss->moveCount = 0; + bestValue = -VALUE_INFINITE; + maxValue = VALUE_INFINITE; // Check for the available remaining time if (thisThread == Threads.main()) @@ -808,7 +767,7 @@ namespace { if ((ss-1)->currentMove != MOVE_NULL) ss->staticEval = eval = evaluate(pos); else - ss->staticEval = eval = -(ss-1)->staticEval + 2 * Tempo; + ss->staticEval = eval = -(ss-1)->staticEval; // Save static evaluation into transposition table tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); @@ -817,7 +776,7 @@ namespace { // Use static evaluation difference to improve quiet move ordering if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture) { - int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval - 2 * Tempo), -1000, 1000); + int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval), -1000, 1000); thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; } @@ -839,10 +798,10 @@ namespace { // Step 8. Null move search with verification search (~40 Elo) if ( !PvNode && (ss-1)->currentMove != MOVE_NULL - && (ss-1)->statScore < 22661 + && (ss-1)->statScore < 24185 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 24 * depth - 34 * improving + 162 * ss->ttPv + 159 + && ss->staticEval >= beta - 22 * depth - 34 * improving + 162 * ss->ttPv + 159 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) @@ -888,7 +847,7 @@ namespace { probCutBeta = beta + 209 - 44 * improving; - // Step 9. ProbCut (~10 Elo) + // Step 9. ProbCut (~4 Elo) // If we have a good enough capture and a reduced search returns a value // much above beta, we can (almost) safely prune the previous move. if ( !PvNode @@ -903,17 +862,8 @@ namespace { && ttValue != VALUE_NONE && ttValue < probCutBeta)) { - // if ttMove is a capture and value from transposition table is good enough produce probCut - // cutoff without digging into actual probCut search - if ( ss->ttHit - && tte->depth() >= depth - 3 - && ttValue != VALUE_NONE - && ttValue >= probCutBeta - && ttMove - && pos.capture_or_promotion(ttMove)) - return probCutBeta; - assert(probCutBeta < VALUE_INFINITE); + MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory); int probCutCount = 0; bool ttPv = ss->ttPv; @@ -969,6 +919,23 @@ namespace { moves_loop: // When in check, search starts from here + ttCapture = ttMove && pos.capture_or_promotion(ttMove); + + // Step 11. A small Probcut idea, when we are in check + probCutBeta = beta + 400; + if ( ss->inCheck + && !PvNode + && depth >= 4 + && ttCapture + && (tte->bound() & BOUND_LOWER) + && tte->depth() >= depth - 3 + && ttValue >= probCutBeta + && abs(ttValue) <= VALUE_KNOWN_WIN + && abs(beta) <= VALUE_KNOWN_WIN + ) + return probCutBeta; + + const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr , (ss-4)->continuationHistory, nullptr , (ss-6)->continuationHistory }; @@ -985,12 +952,15 @@ moves_loop: // When in check, search starts from here value = bestValue; singularQuietLMR = moveCountPruning = false; - ttCapture = ttMove && pos.capture_or_promotion(ttMove); - // Mark this node as being searched - ThreadHolding th(thisThread, posKey, ss->ply); + // Indicate PvNodes that will probably fail low if the node was searched + // at a depth equal or greater than the current depth, and the result of this search was a fail low. + bool likelyFailLow = PvNode + && ttMove + && (tte->bound() & BOUND_UPPER) + && tte->depth() >= depth; - // Step 11. Loop through all pseudo-legal moves until no moves remain + // Step 12. Loop through all pseudo-legal moves until no moves remain // or a beta cutoff occurs. while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE) { @@ -1025,18 +995,10 @@ moves_loop: // When in check, search starts from here movedPiece = pos.moved_piece(move); givesCheck = pos.gives_check(move); - // Indicate PvNodes that will probably fail low if node was searched with non-PV search - // at depth equal or greater to current depth and result of this search was far below alpha - bool likelyFailLow = PvNode - && ttMove - && (tte->bound() & BOUND_UPPER) - && ttValue < alpha + 200 + 100 * depth - && tte->depth() >= depth; - // Calculate new depth for this move newDepth = depth - 1; - // Step 12. Pruning at shallow depth (~200 Elo) + // Step 13. Pruning at shallow depth (~200 Elo) if ( !rootNode && pos.non_pawn_material(us) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY) @@ -1062,8 +1024,8 @@ moves_loop: // When in check, search starts from here } else { - // Countermoves based pruning (~20 Elo) - if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1) + // Continuation history based pruning (~20 Elo) + if ( lmrDepth < 5 && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold) continue; @@ -1075,7 +1037,7 @@ moves_loop: // When in check, search starts from here && (*contHist[0])[movedPiece][to_sq(move)] + (*contHist[1])[movedPiece][to_sq(move)] + (*contHist[3])[movedPiece][to_sq(move)] - + (*contHist[5])[movedPiece][to_sq(move)] / 3 < 26237) + + (*contHist[5])[movedPiece][to_sq(move)] / 3 < 28255) continue; // Prune moves with negative SEE (~20 Elo) @@ -1084,7 +1046,7 @@ moves_loop: // When in check, search starts from here } } - // Step 13. Extensions (~75 Elo) + // Step 14. Extensions (~75 Elo) // Singular extension search (~70 Elo). If all moves but one fail low on a // search of (alpha-s, beta-s), and just one fails high on (alpha, beta), @@ -1102,6 +1064,7 @@ moves_loop: // When in check, search starts from here { Value singularBeta = ttValue - ((formerPv + 4) * depth) / 2; Depth singularDepth = (depth - 1 + 3 * formerPv) / 2; + ss->excludedMove = move; value = search(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode); ss->excludedMove = MOVE_NONE; @@ -1110,6 +1073,8 @@ moves_loop: // When in check, search starts from here { extension = 1; singularQuietLMR = !ttCapture; + if (!PvNode && value < singularBeta - 140) + extension = 2; } // Multi-cut pruning @@ -1133,16 +1098,6 @@ moves_loop: // When in check, search starts from here } } - // Check extension (~2 Elo) - else if ( givesCheck - && (pos.is_discovered_check_on_king(~us, move) || pos.see_ge(move))) - extension = 1; - - // Last captures extension - else if ( PieceValue[EG][pos.captured_piece()] > PawnValueEg - && pos.non_pawn_material() <= 2 * RookValueMg) - extension = 1; - // Add extension to new depth newDepth += extension; @@ -1156,117 +1111,85 @@ moves_loop: // When in check, search starts from here [movedPiece] [to_sq(move)]; - // Step 14. Make the move + // Step 15. Make the move pos.do_move(move, st, givesCheck); - // Step 15. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be - // re-searched at full depth. + // Step 16. Late moves reduction / extension (LMR, ~200 Elo) + // We use various heuristics for the sons of a node after the first son has + // been searched. In general we would like to reduce them, but there are many + // cases where we extend a son if it has good chances to be "interesting". if ( depth >= 3 && moveCount > 1 + 2 * rootNode && ( !captureOrPromotion - || moveCountPruning - || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha || cutNode - || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506) - || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024)) + || (!PvNode && !formerPv)) + && (!PvNode || ss->ply > 1 || thisThread->id() % 4 != 3)) { Depth r = reduction(improving, depth, moveCount); - // Decrease reduction if the ttHit running average is large + // Decrease reduction if the ttHit running average is large (~0 Elo) if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024) r--; - // Increase reduction if other threads are searching this position - if (th.marked()) - r++; - - // Decrease reduction if position is or has been on the PV - // and node is not likely to fail low (~10 Elo) - if (ss->ttPv && !likelyFailLow) + // Decrease reduction if position is or has been on the PV + // and node is not likely to fail low. (~3 Elo) + if ( ss->ttPv + && !likelyFailLow) r -= 2; // Increase reduction at root and non-PV nodes when the best move does not change frequently - if ((rootNode || !PvNode) && thisThread->rootDepth > 10 && thisThread->bestMoveChanges <= 2) + if ( (rootNode || !PvNode) + && thisThread->rootDepth > 10 + && thisThread->bestMoveChanges <= 2) r++; - // More reductions for late moves if position was not in previous PV - if (moveCountPruning && !formerPv) - r++; - - // Decrease reduction if opponent's move count is high (~5 Elo) + // Decrease reduction if opponent's move count is high (~1 Elo) if ((ss-1)->moveCount > 13) r--; - // Decrease reduction if ttMove has been singularly extended (~3 Elo) + // Decrease reduction if ttMove has been singularly extended (~1 Elo) if (singularQuietLMR) r--; - if (captureOrPromotion) + if (!captureOrPromotion) { - // Unless giving check, this capture is likely bad - if ( !givesCheck - && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha) - r++; - } - else - { - // Increase reduction if ttMove is a capture (~5 Elo) + // Increase reduction if ttMove is a capture (~3 Elo) if (ttCapture) r++; - // Increase reduction at root if failing high - r += rootNode ? thisThread->failedHighCnt * thisThread->failedHighCnt * moveCount / 512 : 0; - - // Increase reduction for cut nodes (~10 Elo) + // Increase reduction for cut nodes (~3 Elo) if (cutNode) r += 2; - // Decrease reduction for moves that escape a capture. Filter out - // castling moves, because they are coded as "king captures rook" and - // hence break make_move(). (~2 Elo) - else if ( type_of(move) == NORMAL - && !pos.see_ge(reverse_move(move))) - r -= 2 + ss->ttPv - (type_of(movedPiece) == PAWN); - ss->statScore = thisThread->mainHistory[us][from_to(move)] + (*contHist[0])[movedPiece][to_sq(move)] + (*contHist[1])[movedPiece][to_sq(move)] + (*contHist[3])[movedPiece][to_sq(move)] - - 5337; - - // Decrease/increase reduction by comparing opponent's stat score (~10 Elo) - if (ss->statScore >= -89 && (ss-1)->statScore < -116) - r--; - - else if ((ss-1)->statScore >= -112 && ss->statScore < -100) - r++; + - 4791; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - // If we are not in check use statScore, if we are in check - // use sum of main history and first continuation history with an offset - if (ss->inCheck) - r -= (thisThread->mainHistory[us][from_to(move)] - + (*contHist[0])[movedPiece][to_sq(move)] - 4341) / 16384; - else - r -= ss->statScore / 14382; + if (!ss->inCheck) + r -= ss->statScore / 14790; } - Depth d = std::clamp(newDepth - r, 1, newDepth); + // In general we want to cap the LMR depth search at newDepth. But if + // reductions are really negative and movecount is low, we allow this move + // to be searched deeper than the first move. + Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && moveCount <= 5)); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); - doFullDepthSearch = value > alpha && d != newDepth; - + // If the son is reduced and fails high it will be re-searched at full depth + doFullDepthSearch = value > alpha && d < newDepth; didLMR = true; } else { doFullDepthSearch = !PvNode || moveCount > 1; - didLMR = false; } - // Step 16. Full depth search when LMR is skipped or fails high + // Step 17. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) { value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); @@ -1293,12 +1216,12 @@ moves_loop: // When in check, search starts from here std::min(maxNextDepth, newDepth), false); } - // Step 17. Undo move + // Step 18. Undo move pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Step 18. Check for a new best move + // Step 19. Check for a new best move // Finished searching the move. If a stop occurred, the return value of // the search cannot be trusted, and we return immediately without // updating best move, PV and TT. @@ -1375,7 +1298,7 @@ moves_loop: // When in check, search starts from here return VALUE_DRAW; */ - // Step 19. Check for mate and stalemate + // Step 20. Check for mate and stalemate // All legal moves have been searched and if there are no legal moves, it // must be a mate or a stalemate. If we are in a singular extension search then // return a fail low score. @@ -1383,8 +1306,9 @@ moves_loop: // When in check, search starts from here assert(moveCount || !ss->inCheck || excludedMove || !MoveList(pos).size()); if (!moveCount) - bestValue = excludedMove ? alpha - : ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW; + bestValue = excludedMove ? alpha : + ss->inCheck ? mated_in(ss->ply) + : VALUE_DRAW; // If there is a move which produces search value greater than alpha we update stats of searched moves else if (bestMove) @@ -1434,7 +1358,7 @@ moves_loop: // When in check, search starts from here Move pv[MAX_PLY+1]; StateInfo st; - ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize); TTEntry* tte; Key posKey; @@ -1508,7 +1432,7 @@ moves_loop: // When in check, search starts from here // and addition of two tempos ss->staticEval = bestValue = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) - : -(ss-1)->staticEval + 2 * Tempo; + : -(ss-1)->staticEval; // Stand pat. Return immediately if static value is at least beta if (bestValue >= beta) @@ -1550,15 +1474,13 @@ moves_loop: // When in check, search starts from here moveCount++; - // Futility pruning + // Futility pruning and moveCount pruning if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY && !givesCheck && futilityBase > -VALUE_KNOWN_WIN - && !pos.advanced_pawn_push(move)) + && type_of(move) != PROMOTION) { - assert(type_of(move) != EN_PASSANT); // Due to !pos.advanced_pawn_push - // moveCount pruning if (moveCount > 2) continue; @@ -1598,7 +1520,7 @@ moves_loop: // When in check, search starts from here [pos.moved_piece(move)] [to_sq(move)]; - // CounterMove based pruning + // Continuation history based pruning if ( !captureOrPromotion && bestValue > VALUE_TB_LOSS_IN_MAX_PLY && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold @@ -1942,7 +1864,7 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { bool RootMove::extract_ponder_from_tt(Position& pos) { StateInfo st; - ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize); bool ttHit; @@ -2011,3 +1933,5 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) { m.tbRank = 0; } } + +} // namespace Stockfish