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, 7 insertions, 7 deletions

diff --git a/src/searchsup.c b/src/searchsup.c
index 7ab8695..2ec001f 100644
--- a/src/searchsup.c
+++ b/src/searchsup.c
@@ -614,7 +614,7 @@ Return value:
             *piExtend += HALF_PLY;
             if (!fIsLeftoverMove ||
                 ((g_KingAttacksBB[mv.cTo] &
-                  COOR_TO_BB(pos->cNonPawns[uPawnColor][0])) ||
+                  COOR_TO_BB(KingPosition(pos, uPawnColor))) ||
                  (_RookAttacksBB(mv.cTo, pos->bbOccupied) &
                   (pos->bbPieces[uPawnColor][ROOK] |
                    pos->bbPieces[uPawnColor][QUEEN])) ||
@@ -669,8 +669,8 @@ Return value:
     {
         // Endgame extension
         if ((ctx->sPlyInfo[1].uTotalNonPawns > 2) &&
-            ((pos->uNonPawnCount[BLACK][0] +
-              pos->uNonPawnCount[WHITE][0]) == 2))
+            ((TotalNonPawnCount(pos, BLACK) +
+              TotalNonPawnCount(pos, WHITE)) == 2))
         {
             if ((mv.pCaptured && !IS_PAWN(mv.pCaptured)) ||
                 (mvLast.pCaptured && !IS_PAWN(mvLast.pCaptured)))
@@ -1334,8 +1334,8 @@ SelectNullmoveRFactor(SEARCHER_THREAD_CONTEXT *ctx,
                       INT uDepth)
 {
     ULONG u = TWO_PLY;
-    ULONG uMaxPiecesPerSide = MAXU(ctx->sPosition.uNonPawnCount[WHITE][0],
-                                   ctx->sPosition.uNonPawnCount[BLACK][0]);
+    ULONG uMaxPiecesPerSide = MAXU(TotalNonPawnCount(&ctx->sPosition, WHITE),
+                                   TotalNonPawnCount(&ctx->sPosition, BLACK));
     ASSERT(uMaxPiecesPerSide <= 16);
 
     if ((uDepth > 8 * ONE_PLY) ||
@@ -1369,7 +1369,7 @@ FLAG WeShouldTryNullmovePruning(SEARCHER_THREAD_CONTEXT *ctx,
     ASSERT(uNullDepth < MAX_PLY_PER_SEARCH * ONE_PLY);
 
     if ((FALSE == pf->fAvoidNullmove) &&
-        (pos->uNonPawnCount[pos->uToMove][0] > 2) &&
+        (TotalNonPawnCount(pos, pos->uToMove) > 2) &&
         (FALSE == pi->fInCheck) &&
         (iBeta != +INFINITY) &&
         (NODE_PV != pi->eNodeType))
@@ -1440,7 +1440,7 @@ TryNullmovePruning(SEARCHER_THREAD_CONTEXT *ctx,
 
         // If there are very few pieces on the board, launch a
         // separate "verification search".
-        if ((pos->uNonPawnCount[pos->uToMove][0] < 4) &&
+        if ((TotalNonPawnCount(pos, pos->uToMove) < 4) &&
             (pf->fVerifyNullmove == TRUE))
         {
             ASSERT(pf->fAvoidNullmove == FALSE);