Remove ttPv tree shrinking.

locutus2 · vondele · commit e31f97e3baa5 · 2022-03-19T13:40:35.000+01:00
Via the ttPv flag an implicit tree of current and former PV nodes is maintained. In addition this tree is grown or shrinked at the leafs dependant on the search results. But now the shrinking step has been removed. As the frequency of ttPv nodes decreases with depth the shown scaling behavior (STC barely passed but LTC scales well) of the tests was expected. STC: LLR: 2.93 (-2.94,2.94) <-2.25,0.25> Total: 270408 W: 71593 L: 71785 D: 127030 Ptnml(0-2): 1339, 31024, 70630, 30912, 1299 https://tests.stockfishchess.org/tests/view/622fbf9dc9e950cbfc2376d6 LTC: LLR: 2.96 (-2.94,2.94) <-2.25,0.25> Total: 34368 W: 9135 L: 8992 D: 16241 Ptnml(0-2): 28, 3423, 10135, 3574, 24 https://tests.stockfishchess.org/tests/view/62305257c9e950cbfc238964 closes #3963 Bench: 7044203
diff --git a/src/search.cpp b/src/search.cpp
@@ -1359,10 +1359,6 @@ namespace {
     // opponent move is probably good and the new position is added to the search tree.
     if (bestValue <= alpha)
         ss->ttPv = ss->ttPv || ((ss-1)->ttPv && depth > 3);
-    // Otherwise, a counter move has been found and if the position is the last leaf
-    // in the search tree, remove the position from the search tree.
-    else if (depth > 3)
-        ss->ttPv = ss->ttPv && (ss+1)->ttPv;
 
     // Write gathered information in transposition table
     if (!excludedMove && !(rootNode && thisThread->pvIdx))
