Use quiescence search for Probcut

Perform qsearch for the preliminary search in Probcut

Passed STC with sprt[-3..1] bounds:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 31090 W: 6386 L: 6283 D: 18421
http://tests.stockfishchess.org/tests/view/5aa598ed0ebc59029780ff9f

Passed LTC with sprt[0..4] bounds:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 104056 W: 15990 L: 15531 D: 72535
http://tests.stockfishchess.org/tests/view/5aa5b0f30ebc59029780ffa9

Closes https://github.com/official-stockfish/Stockfish/pull/1483

Bench: 5404567

diff --git a/src/search.cpp b/src/search.cpp
index adb6a22a846de879a9627fb26e8549ff4c4e0c83..8639393c16567ed03f2db3c3b74da90e583953b1 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -778,15 +778,11 @@ namespace {
 
                 pos.do_move(move, st);
 
 
                 pos.do_move(move, st);
 

-                // Perform a preliminary search at depth 1 to verify that the move holds.
-                // We will only do this search if the depth is not 5, thus avoiding two
-                // searches at depth 1 in a row.
-                if (depth != 5 * ONE_PLY)
-                    value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, ONE_PLY, !cutNode, true);
-
-                // If the first search was skipped or was performed and held, perform
-                // the regular search.
-                if (depth == 5 * ONE_PLY || value >= rbeta)
+                // Perform a preliminary qsearch to verify that the move holds
+                value = -qsearch<NonPV>(pos, ss+1, -rbeta, -rbeta+1);
+
+                // If the qsearch held perform the regular search
+                if (value >= rbeta)

                     value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
 
                 pos.undo_move(move);
                     value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
 
                 pos.undo_move(move);