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Revert futility pruning patches 

reverts 09b6d28391 and
dbd7f602d3 that significantly impact mate
finding capabilities. For example on ChestUCI_23102018.epd, at 1M nodes,
the number of mates found is nearly reduced 2x without these depth conditions:

       sf6  2091
       sf7  2093
       sf8  2107
       sf9  2062
      sf10  2208
      sf11  2552
      sf12  2563
      sf13  2509
      sf14  2427
    master  1246
   patched  2467

(script for testing at https://github.com/official-stockfish/Stockfish/files/6936412/matecheck.zip)

closes https://github.com/official-stockfish/Stockfish/pull/3641

fixes https://github.com/official-stockfish/Stockfish/issues/3627

Bench: 5467570
pull/3580/head^2
Joost VandeVondele 2021-08-05 16:34:37 +02:00
parent a1a83f3869
commit dabaf2220f
1 changed files with 5 additions and 2 deletions
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7
src/search.cpp
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@ -779,8 +779,10 @@ namespace {
? ss->staticEval > (ss-4)->staticEval || (ss-4)->staticEval == VALUE_NONE
: ss->staticEval > (ss-2)->staticEval;
// Step 7. Futility pruning: child node (~50 Elo)
// Step 7. Futility pruning: child node (~50 Elo).
// The depth condition is important for mate finding.
if ( !PvNode
&& depth < 9
&& eval - futility_margin(depth, improving) >= beta
&& eval < VALUE_KNOWN_WIN) // Do not return unproven wins
return eval;
@ -989,7 +991,7 @@ moves_loop: // When in check, search starts here
// Calculate new depth for this move
newDepth = depth - 1;
// Step 13. Pruning at shallow depth (~200 Elo)
// Step 13. Pruning at shallow depth (~200 Elo). Depth conditions are important for mate finding.
if ( !rootNode
&& pos.non_pawn_material(us)
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
@ -1023,6 +1025,7 @@ moves_loop: // When in check, search starts here
// Futility pruning: parent node (~5 Elo)
if ( !ss->inCheck
&& lmrDepth < 7
&& ss->staticEval + 174 + 157 * lmrDepth <= alpha)
continue;