Remove lmrDepth restriction on quiet see pruning

And tweak the threshold value. With this threshold and the current piece
values, this permits see pruning on quiets to be done up to an lmrDepth
of 9 (beyond that the threshold is below -QueenValueMg and see_ge will
pass unconditionally).

STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 110316 W: 24612 L: 24667 D: 61037
http://tests.stockfishchess.org/tests/view/5b20aa760ebc5902ab9c9c1d

LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 17352 W: 2968 L: 2842 D: 11542
http://tests.stockfishchess.org/tests/view/5b20cf1e0ebc5902ab9c9fb6

Closes https://github.com/official-stockfish/Stockfish/pull/1651

Bench: 5069074

diff --git a/src/search.cpp b/src/search.cpp
index c678cd5340badeafdd3f9790511a9b908c9ca916..fb5dfd00776c4a549f196c2761f2452ffb1abd7b 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -947,8 +947,7 @@ moves_loop: // When in check, search starts from here
                   continue;
 
               // Prune moves with negative SEE (~10 Elo)
                   continue;
 
               // Prune moves with negative SEE (~10 Elo)

-              if (   lmrDepth < 8
-                  && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
+              if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth)))

                   continue;
           }
           else if (   !extension // (~20 Elo)
                   continue;
           }
           else if (   !extension // (~20 Elo)