From 278a755fb552131b7e2a5da24256b6a4b13246fc Mon Sep 17 00:00:00 2001
From: Carlos Esparza <ca2010es@gmail.com>
Date: Wed, 10 Jun 2026 12:37:12 +0200
Subject: [PATCH] Reorder operations in do_move

Passed STC
 https://tests.stockfishchess.org/tests/view/6a2682ce351b79f679cc47c5
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 57248 W: 14730 L: 14399 D: 28119
Ptnml(0-2): 145, 6159, 15698, 6464, 158

Reordering operations in `do_move` allows us to effectively prefetch the TT entry earlier, since the piece moving helpers don't actually modify the position key.  I suspect that with threat inputs, `put_piece` and friends got a lot more expensive, and so this helps us a lot.

vondele's machine:

==== master ====
1 Nodes/second : 294311526
2 Nodes/second : 297068312
3 Nodes/second : 297418763
Average (over 3):  296266200
==== pfearly ====
1 Nodes/second : 303986449
2 Nodes/second : 304221719
3 Nodes/second : 305302969
Average (over 3):  304503712 (+2.78%)

Locally, `bench`:

Result of 200 runs
speedup         = +0.0158
P(speedup > 0) =  1.0000

As expected it helps even more in a large-hash, NUMA setting.

closes https://github.com/official-stockfish/Stockfish/pull/6891

No functional change
---
 src/position.cpp | 46 +++++++++++++++++++++++-----------------------
 1 file changed, 23 insertions(+), 23 deletions(-)

diff --git a/src/position.cpp b/src/position.cpp
index 4744d5102..e87091783 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -946,27 +946,6 @@ void Position::do_move(Move                      m,
     st->castlingRights &= ~(castlingRightsMask[from] | castlingRightsMask[to]);
     k ^= Zobrist::castling[st->castlingRights];
 
-    // Move the piece. The tricky Chess960 castling is handled earlier
-    if (m.type_of() != CASTLING)
-    {
-        Piece toPc = pc;
-        if (m.type_of() == PROMOTION)
-            toPc = make_piece(us, m.promotion_type());
-
-        if (captured && m.type_of() != EN_PASSANT)
-        {
-            remove_piece(from, &dts);
-            swap_piece(to, toPc, &dts);
-        }
-        else if (pc == toPc)
-            move_piece(from, to, &dts);
-        else
-        {
-            remove_piece(from, &dts);
-            put_piece(toPc, to, &dts);
-        }
-    }
-
     // If the moving piece is a pawn do some special extra work
     if (type_of(pc) == PAWN)
     {
@@ -1036,10 +1015,10 @@ void Position::do_move(Move                      m,
             st->minorPieceKey ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
     }
 
+    if (tt)
+        prefetch(tt->first_entry(adjust_key50(k)));
     // Update the key with the final value
     st->key = k;
-    if (tt)
-        prefetch(tt->first_entry(key()));
 
     if (history)
     {
@@ -1050,6 +1029,27 @@ void Position::do_move(Move                      m,
         prefetch(&history->nonpawn_correction_entry<BLACK>(*this));
     }
 
+    // Move the piece. The tricky Chess960 castling is handled earlier
+    if (m.type_of() != CASTLING)
+    {
+        Piece toPc = pc;
+        if (m.type_of() == PROMOTION)
+            toPc = make_piece(us, m.promotion_type());
+
+        if (captured && m.type_of() != EN_PASSANT)
+        {
+            remove_piece(from, &dts);
+            swap_piece(to, toPc, &dts);
+        }
+        else if (pc == toPc)
+            move_piece(from, to, &dts);
+        else
+        {
+            remove_piece(from, &dts);
+            put_piece(toPc, to, &dts);
+        }
+    }
+
     // Set capture piece
     st->capturedPiece = captured;