From 985b9fd7b05d1d81be7a1ac90862a5790ee56176 Mon Sep 17 00:00:00 2001
From: Shawn Xu <xu107288696@gmail.com>
Date: Sat, 20 Jul 2024 12:40:16 -0700
Subject: [PATCH] Remove Killer Heuristic In Move Ordering

Passed Non-regression STC:
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 80480 W: 20979 L: 20802 D: 38699
Ptnml(0-2): 279, 9610, 20337, 9683, 331
https://tests.stockfishchess.org/tests/view/669c12c14ff211be9d4ec69b

Passed Non-regression LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 77988 W: 19788 L: 19624 D: 38576
Ptnml(0-2): 66, 8605, 21481, 8783, 59
https://tests.stockfishchess.org/tests/view/669d628a4ff211be9d4ec7a8

closes https://github.com/official-stockfish/Stockfish/pull/5511

bench 1367740
---
 src/movepick.cpp | 6 +-----
 src/movepick.h   | 5 ++---
 src/search.cpp   | 2 +-
 3 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/src/movepick.cpp b/src/movepick.cpp
index 81384328..7bd0252c 100644
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -86,15 +86,13 @@ MovePicker::MovePicker(const Position&              p,
                        const ButterflyHistory*      mh,
                        const CapturePieceToHistory* cph,
                        const PieceToHistory**       ch,
-                       const PawnHistory*           ph,
-                       Move                         km) :
+                       const PawnHistory*           ph) :
     pos(p),
     mainHistory(mh),
     captureHistory(cph),
     continuationHistory(ch),
     pawnHistory(ph),
     ttMove(ttm),
-    killer(km),
     depth(d) {
 
     if (pos.checkers())
@@ -164,8 +162,6 @@ void MovePicker::score() {
             m.value += (*continuationHistory[3])[pc][to];
             m.value += (*continuationHistory[5])[pc][to];
 
-            m.value += (m == killer) * 65536;
-
             // bonus for checks
             m.value += bool(pos.check_squares(pt) & to) * 16384;
 
diff --git a/src/movepick.h b/src/movepick.h
index 92e11de2..671cbb9c 100644
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -159,8 +159,7 @@ class MovePicker {
                const ButterflyHistory*,
                const CapturePieceToHistory*,
                const PieceToHistory**,
-               const PawnHistory*,
-               Move killer = Move::none());
+               const PawnHistory*);
     MovePicker(const Position&, Move, int, const CapturePieceToHistory*);
     Move next_move(bool skipQuiets = false);
 
@@ -177,7 +176,7 @@ class MovePicker {
     const CapturePieceToHistory* captureHistory;
     const PieceToHistory**       continuationHistory;
     const PawnHistory*           pawnHistory;
-    Move                         ttMove, killer;
+    Move                         ttMove;
     ExtMove *                    cur, *endMoves, *endBadCaptures, *beginBadQuiets, *endBadQuiets;
     int                          stage;
     int                          threshold;
diff --git a/src/search.cpp b/src/search.cpp
index ca346502..233dc4f7 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -907,7 +907,7 @@ moves_loop:  // When in check, search starts here
 
 
     MovePicker mp(pos, ttData.move, depth, &thisThread->mainHistory, &thisThread->captureHistory,
-                  contHist, &thisThread->pawnHistory, ss->killer);
+                  contHist, &thisThread->pawnHistory);
 
     value = bestValue;