Retire cPawns/cNonPawns piece-location lists in favor of bbPawns/bbPieces/cKingSq, and hoist two redundant TotalNonPawnCount POPCNT calls out of per-node hot loops.

POSITION no longer stores cPawns[2][8], cNonPawns[2][16], uPawnCount[2],
uNonPawnCount[2][8], or uWhiteSqBishopCount[2] -- every reader now goes
through PawnMaterial/TotalNonPawnCount/WhiteSqBishopCount/KingPosition
(chess.h), computed from the already-incrementally-maintained bbPawns/
bbPieces/cKingSq bitboards via a single -mpopcnt POPCNT instead of a
stored counter. move.c's make/unmake loses the list-swap-on-removal
bookkeeping entirely. GNUmakefile now passes -mpopcnt so the popcount
builtins actually compile to one instruction instead of clang's ~15-op
SWAR fallback.

Measured a small but real nps regression from the naive swap (search.c's
QSearch move-filter and eval.c's _EvalKing were each recomputing the same
TotalNonPawnCount sum on every candidate move / twice per node); hoisted
both to a single call per node instead. Net result across a same-code
self-play match: ~1541.5 knps candidate vs ~1505.7 knps head_reference.

A third hoist (FindEnprisePiece out of SelectBestWithHistory) was tried
and reverted -- its cache isn't actually loop-invariant within a node
(populated from inside Eval(), which doesn't run before every selection
call), caught by a DEBUG-build ASSERT before it landed.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/see.c b/src/see.c
index 893a9bb..47efd30 100644
--- a/src/see.c
+++ b/src/see.c
@@ -112,9 +112,9 @@ Return value:
     ULONG u;
 
     bbAttackers = g_KnightAttacksBB[cSquare] & pos->bbPieces[uSide][KNIGHT];
-    if (DISTANCE(cSquare, pos->cNonPawns[uSide][0]) == 1)
+    if (DISTANCE(cSquare, KingPosition(pos, uSide)) == 1)
     {
-        bbAttackers |= COOR_TO_BB(pos->cNonPawns[uSide][0]);
+        bbAttackers |= COOR_TO_BB(KingPosition(pos, uSide));
     }
 
     // Measured slower: deriving the needed direction(s) directly from
@@ -703,7 +703,7 @@ Return value:
             // would exposes his king to check, skip it and try the
             // next least valuable.
             //
-            cKing = pos->cNonPawns[uColor][0];
+            cKing = KingPosition(pos, uColor);
             c = ExposesCheck(pos, pList->data[x].cLoc, cKing);
 
             //
@@ -795,7 +795,7 @@ Return value:
             // would exposes his king to check, skip it and try the
             // next least valuable.
             //
-            cKing = pos->cNonPawns[uColor][0];
+            cKing = KingPosition(pos, uColor);
             c = ExposesCheck(pos, pList->data[x].cLoc, cKing);
 
             //