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Prune before extension

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Switch execution order in search: do move pruning before extension detection.

STC:
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 5762 W: 1307 L: 1181 D: 3274
http://tests.stockfishchess.org/tests/view/5dcc56e90ebc59025bcbb833

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 72956 W: 11959 L: 11585 D: 49412
http://tests.stockfishchess.org/tests/view/5dcc62840ebc59025bcbb96f

Closes https://github.com/official-stockfish/Stockfish/pull/2413

Bench: 4532366
This commit is contained in:
Stefan Geschwentner 2019-11-12 18:36:12 +01:00 • committed by Stéphane Nicolet
parent a131975170
commit a00a336946
2 changed files with 42 additions and 40 deletions
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80
src/search.cpp
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@ -955,7 +955,45 @@ moves_loop: // When in check, search starts from here
movedPiece = pos.moved_piece(move);
givesCheck = pos.gives_check(move);
// Step 13. Extensions (~70 Elo)
// Calculate new depth for this move
newDepth = depth - 1;
// Step 13. Pruning at shallow depth (~170 Elo)
if ( !rootNode
&& pos.non_pawn_material(us)
&& bestValue > VALUE_MATED_IN_MAX_PLY)
{
// Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
moveCountPruning = moveCount >= futility_move_count(improving, depth);
if ( !captureOrPromotion
&& !givesCheck
&& (!PvNode || !pos.advanced_pawn_push(move) || pos.non_pawn_material(~us) > BishopValueMg))
{
// Reduced depth of the next LMR search
int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
// Countermoves based pruning (~20 Elo)
if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
&& (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
&& (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
continue;
// Futility pruning: parent node (~2 Elo)
if ( lmrDepth < 6
&& !inCheck
&& ss->staticEval + 250 + 211 * lmrDepth <= alpha)
continue;
// Prune moves with negative SEE (~10 Elo)
if (!pos.see_ge(move, Value(-(31 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
continue;
}
else if (!pos.see_ge(move, Value(-199) * depth)) // (~20 Elo)
continue;
}
// Step 14. Extensions (~70 Elo)
// Singular extension search (~60 Elo). If all moves but one fail low on a
// search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
@ -1009,44 +1047,8 @@ moves_loop: // When in check, search starts from here
if (type_of(move) == CASTLING)
extension = 1;
// Calculate new depth for this move
newDepth = depth - 1 + extension;
// Step 14. Pruning at shallow depth (~170 Elo)
if ( !rootNode
&& pos.non_pawn_material(us)
&& bestValue > VALUE_MATED_IN_MAX_PLY)
{
// Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
moveCountPruning = moveCount >= futility_move_count(improving, depth);
if ( !captureOrPromotion
&& !givesCheck
&& (!PvNode || !pos.advanced_pawn_push(move) || pos.non_pawn_material(~us) > BishopValueMg))
{
// Reduced depth of the next LMR search
int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
// Countermoves based pruning (~20 Elo)
if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
&& (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
&& (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
continue;
// Futility pruning: parent node (~2 Elo)
if ( lmrDepth < 6
&& !inCheck
&& ss->staticEval + 250 + 211 * lmrDepth <= alpha)
continue;
// Prune moves with negative SEE (~10 Elo)
if (!pos.see_ge(move, Value(-(31 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
continue;
}
else if ( !(givesCheck && extension)
&& !pos.see_ge(move, Value(-199) * depth)) // (~20 Elo)
continue;
}
// Add extension to new depth
newDepth += extension;
// Speculative prefetch as early as possible
prefetch(TT.first_entry(pos.key_after(move)));