Simplify statScore initialization

This patch simplifies initialization of statScore to "always set it up to 0" instead of setting it up to 0 two plies deeper.
Reason for why it was done in previous way partially was because of LMR usage of previous statScore which was simplified long time ago so it makes sense to make in more simple there.

Passed STC:
https://tests.stockfishchess.org/tests/view/641a86d1db43ab2ba6f7b31d
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 115648 W: 30895 L: 30764 D: 53989
Ptnml(0-2): 368, 12741, 31473, 12876, 366

Passed LTC:
https://tests.stockfishchess.org/tests/view/641b1c31db43ab2ba6f7d17a
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 175576 W: 47122 L: 47062 D: 81392
Ptnml(0-2): 91, 17077, 53390, 17141, 89

closes https://github.com/official-stockfish/Stockfish/pull/4460

bench 5081969

diff --git a/src/search.cpp b/src/search.cpp
index b2983f6647ae860093d9d92d9587cd7faa23437e..d2358ea2e1c2d9ccf1507947d87d9d85192e5e33 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -607,14 +607,7 @@ namespace {
     (ss+2)->cutoffCnt    = 0;
     ss->doubleExtensions = (ss-1)->doubleExtensions;
     Square prevSq        = is_ok((ss-1)->currentMove) ? to_sq((ss-1)->currentMove) : SQ_NONE;
-
-    // Initialize statScore to zero for the grandchildren of the current position.
-    // So statScore is shared between all grandchildren and only the first grandchild
-    // starts with statScore = 0. Later grandchildren start with the last calculated
-    // statScore of the previous grandchild. This influences the reduction rules in
-    // LMR which are based on the statScore of parent position.
-    if (!rootNode)
-        (ss+2)->statScore = 0;
+    ss->statScore        = 0;
 
     // Step 4. Transposition table lookup.
     excludedMove = ss->excludedMove;