do more LMR extensions for PV nodes

LMR Pv and depth 6 Extension tweak:

LTC:
LLR: 2.93 (-2.94,2.94) <0.50,3.50>
Total: 52488 W: 1542 L: 1394 D: 49552
Ptnml(0-2): 18, 1253, 23552, 1405, 16
https://tests.stockfishchess.org/tests/view/611e49c34977aa1525c9caa7

STC:
LLR: 2.94 (-2.94,2.94) <-0.50,2.50>
Total: 76216 W: 6000 L: 5784 D: 64432
Ptnml(0-2): 204, 4745, 28006, 4937, 216
https://tests.stockfishchess.org/tests/view/611e0e254977aa1525c9ca89

closes https://github.com/official-stockfish/Stockfish/pull/3666

Bench: 5046381

diff --git a/src/search.cpp b/src/search.cpp
index 83ed2aebcd43eec239056671b373579ebb2fbf8e..a487ed1305b1ccdc8aabe5b42858ec71799b5895 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1173,8 +1173,8 @@ moves_loop: // When in check, search starts here
 
           // 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, unless ttMove was extended by 2.
-          Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && moveCount <= 5 && !doubleExtension));
+          // to be searched deeper than the first move in specific cases.
+          Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && (moveCount <= 5 || (depth > 6 && PvNode)) && !doubleExtension));
 
           value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);