Adjust usage of LMR for 2nd move in move ordering

Current master prohibits usage of LMR for 2nd move at rootNode. This patch also disables LMR for 2nd move not only at rootNode but also at first PvNode that is a reply to rootNode.

passed STC:
https://tests.stockfishchess.org/tests/view/620e8c9026f5b17ec885143a
LLR: 2.94 (-2.94,2.94) <0.00,2.50>
Total: 54096 W: 14305 L: 13996 D: 25795
Ptnml(0-2): 209, 6075, 14192, 6342, 230

passed LTC:
https://tests.stockfishchess.org/tests/view/620eb327b1792e8985f81fb8
LLR: 2.94 (-2.94,2.94) <0.50,3.00>
Total: 110864 W: 29602 L: 29156 D: 52106
Ptnml(0-2): 112, 11147, 32455, 11619, 99

closes https://github.com/official-stockfish/Stockfish/pull/3940

bench 6820724

diff --git a/src/search.cpp b/src/search.cpp
index e64209317052b8af733e0187d7033c657555fc70..6785ba4c6b44d2bb3db6fc42bde736971fcd6d09 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1136,7 +1136,7 @@ moves_loop: // When in check, search starts here
       // 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 >= 2
-          &&  moveCount > 1 + rootNode
+          &&  moveCount > 1 + (PvNode && ss->ply <= 1)
           && (   !ss->ttPv
               || !captureOrPromotion
               || (cutNode && (ss-1)->moveCount > 1)))