From 9f42980dd2c6109aeb4a56b2f717c223e569e052 Mon Sep 17 00:00:00 2001
From: KazApps <kazuki_shogi@outlook.jp>
Date: Tue, 20 Jan 2026 11:23:49 +0900
Subject: [PATCH] refactor update_piece_threats to reduce branching

Passed STC Non-Regression:
https://tests.stockfishchess.org/tests/view/696f1a398b64097dacd231c3
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 122272 W: 31587 L: 31466 D: 59219
Ptnml(0-2): 301, 13358, 33750, 13373, 354

slight speedup as well:

1 thread bench:
sf_base =  2238429 +/-   1221 (95%)
sf_test =  2248298 +/-   1371 (95%)
diff    =     9869 +/-   1571 (95%)
speedup = 0.44090% +/- 0.070% (95%)

32 thread speedtest:
sf_base = 41016996 +/-  83654 (95%)
sf_test = 41185801 +/-  84269 (95%)
diff    =   168805 +/-  79986 (95%)
speedup = 0.41155% +/- 0.195% (95%)

closes https://github.com/official-stockfish/Stockfish/pull/6559

No functional change
---
 src/position.cpp | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/src/position.cpp b/src/position.cpp
index 3bbe60d6d..a8d3cc506 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -1069,8 +1069,8 @@ inline void add_dirty_threat(
   DirtyThreats* const dts, Piece pc, Piece threatened, Square s, Square threatenedSq) {
     if (PutPiece)
     {
-        dts->threatenedSqs |= square_bb(threatenedSq);
-        dts->threateningSqs |= square_bb(s);
+        dts->threatenedSqs |= threatenedSq;
+        dts->threateningSqs |= s;
     }
 
     dts->list.push_back({pc, threatened, s, threatenedSq, PutPiece});
@@ -1139,30 +1139,25 @@ void Position::update_piece_threats(Piece                     pc,
       | (attacks_bb<PAWN>(s, BLACK) & whitePawns) | (PseudoAttacks[KING][s] & kings);
 
 #ifdef USE_AVX512ICL
-    if (threatened)
+    if constexpr (PutPiece)
     {
-        if constexpr (PutPiece)
-        {
-            dts->threatenedSqs |= threatened;
-            dts->threateningSqs |= square_bb(s);
-        }
-
-        DirtyThreat dt_template{pc, NO_PIECE, s, Square(0), PutPiece};
-        write_multiple_dirties<DirtyThreat::ThreatenedSqOffset, DirtyThreat::ThreatenedPcOffset>(
-          *this, threatened, dt_template, dts);
+        dts->threatenedSqs |= threatened;
+        dts->threateningSqs |= s;
     }
 
+    DirtyThreat dt_template{pc, NO_PIECE, s, Square(0), PutPiece};
+    write_multiple_dirties<DirtyThreat::ThreatenedSqOffset, DirtyThreat::ThreatenedPcOffset>(
+      *this, threatened, dt_template, dts);
+
     Bitboard all_attackers = sliders | incoming_threats;
-    if (!all_attackers)
-        return;  // Square s is threatened iff there's at least one attacker
 
     if constexpr (PutPiece)
     {
-        dts->threatenedSqs |= square_bb(s);
+        dts->threatenedSqs |= s;
         dts->threateningSqs |= all_attackers;
     }
 
-    DirtyThreat dt_template{NO_PIECE, pc, Square(0), s, PutPiece};
+    dt_template = {NO_PIECE, pc, Square(0), s, PutPiece};
     write_multiple_dirties<DirtyThreat::PcSqOffset, DirtyThreat::PcOffset>(*this, all_attackers,
                                                                            dt_template, dts);
 #else