speed up update_piece_threats after SFNNv12

with the removal of all king-related threats in SFNNv12 we can avoid some work in update_piece_threats

STC for anematode's swan:
https://tests.stockfishchess.org/tests/view/6986b920b0f3ca5200aaf80a
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 262880 W: 68379 L: 67747 D: 126754
Ptnml(0-2): 808, 29001, 71223, 29567, 841

STC of further speedups on top of swan:
https://tests.stockfishchess.org/tests/view/698d7f8362a8f472da3a8a35
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 65920 W: 17126 L: 16781 D: 32013
Ptnml(0-2): 186, 7084, 18105, 7369, 216

closes https://github.com/official-stockfish/Stockfish/pull/6614

No functional change

Co-Authored-By: Timothy Herchen <timothy.herchen@gmail.com>

src/position.cpp

@@ -1072,7 +1072,7 @@ void write_multiple_dirties(const Position& p,
 
     const __m512i dirties =
       _mm512_ternarylogic_epi32(template_v, threat_squares, threat_pieces, 254 /* A | B | C */);
-    _mm512_storeu_si512(reinterpret_cast<__m512i*>(write), dirties);
+    _mm512_storeu_si512(write, dirties);
 }
 #endif
 
@@ -1084,16 +1084,48 @@ void Position::update_piece_threats(Piece                     pc,
     const Bitboard occupied     = pieces();
     const Bitboard rookQueens   = pieces(ROOK, QUEEN);
     const Bitboard bishopQueens = pieces(BISHOP, QUEEN);
-    const Bitboard knights      = pieces(KNIGHT);
+    const Bitboard rAttacks     = attacks_bb<ROOK>(s, occupied);
+    const Bitboard bAttacks     = attacks_bb<BISHOP>(s, occupied);
     const Bitboard kings        = pieces(KING);
-    const Bitboard whitePawns   = pieces(WHITE, PAWN);
+    Bitboard       occupiedNoK  = occupied ^ kings;
-    const Bitboard blackPawns   = pieces(BLACK, PAWN);
 
-    const Bitboard rAttacks = attacks_bb<ROOK>(s, occupied);
+    Bitboard sliders         = (rookQueens & rAttacks) | (bishopQueens & bAttacks);
-    const Bitboard bAttacks = attacks_bb<BISHOP>(s, occupied);
+    auto     process_sliders = [&](bool addDirectAttacks) {
+        while (sliders)
+        {
+            Square sliderSq = pop_lsb(sliders);
+            Piece  slider   = piece_on(sliderSq);
 
-    Bitboard threatened = attacks_bb(pc, s, occupied) & occupied;
+            const Bitboard ray        = RayPassBB[sliderSq][s];
-    Bitboard sliders    = (rookQueens & rAttacks) | (bishopQueens & bAttacks);
+            const Bitboard discovered = ray & (rAttacks | bAttacks) & occupiedNoK;
+
+            assert(!more_than_one(discovered));
+            if (discovered && (RayPassBB[sliderSq][s] & noRaysContaining) != noRaysContaining)
+            {
+                const Square threatenedSq = lsb(discovered);
+                const Piece  threatenedPc = piece_on(threatenedSq);
+                add_dirty_threat<!PutPiece>(dts, slider, threatenedPc, sliderSq, threatenedSq);
+            }
+
+            if (addDirectAttacks)
+                add_dirty_threat<PutPiece>(dts, slider, pc, sliderSq, s);
+        }
+    };
+
+    if (type_of(pc) == KING)
+    {
+        if constexpr (ComputeRay)
+            process_sliders(false);
+        return;
+    }
+
+
+    const Bitboard knights    = pieces(KNIGHT);
+    const Bitboard whitePawns = pieces(WHITE, PAWN);
+    const Bitboard blackPawns = pieces(BLACK, PAWN);
+
+
+    Bitboard threatened = attacks_bb(pc, s, occupied) & occupiedNoK;
     Bitboard incoming_threats =
       (PseudoAttacks[KNIGHT][s] & knights) | (attacks_bb<PAWN>(s, WHITE) & blackPawns)
       | (attacks_bb<PAWN>(s, BLACK) & whitePawns) | (PseudoAttacks[KING][s] & kings);
@@ -1135,26 +1167,11 @@ void Position::update_piece_threats(Piece                     pc,
 
     if constexpr (ComputeRay)
     {
-        while (sliders)
+#ifndef USE_AVX512ICL
-        {
+        process_sliders(true);
-            Square sliderSq = pop_lsb(sliders);
+#else  // for ICL, direct threats were processed earlier (all_attackers)
-            Piece  slider   = piece_on(sliderSq);
+        process_sliders(false);
-
-            const Bitboard ray        = RayPassBB[sliderSq][s] & ~BetweenBB[sliderSq][s];
-            const Bitboard discovered = ray & (rAttacks | bAttacks) & occupied;
-
-            assert(!more_than_one(discovered));
-            if (discovered && (RayPassBB[sliderSq][s] & noRaysContaining) != noRaysContaining)
-            {
-                const Square threatenedSq = lsb(discovered);
-                const Piece  threatenedPc = piece_on(threatenedSq);
-                add_dirty_threat<!PutPiece>(dts, slider, threatenedPc, sliderSq, threatenedSq);
-            }
-
-#ifndef USE_AVX512ICL  // for ICL, direct threats were processed earlier (all_attackers)
-            add_dirty_threat<PutPiece>(dts, slider, pc, sliderSq, s);
 #endif
-        }
     }
     else
     {