Micro optimize pawn moves generation

It is very rare we have pawns on 7(2) rank, so we
can skip the promotion handling stuff in most cases.

With this patch pawn moves generation is almost 20% faster.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

diff --git a/src/movegen.cpp b/src/movegen.cpp
index ff8f6c6e16f6f2f186e27dad9972f43b8cf9bb1f..d4024b1145a36de890f7f9040decf0819124bdcc 100644 (file)
--- a/src/movegen.cpp
+++ b/src/movegen.cpp
@@ -61,7 +61,7 @@ namespace {
   MoveStack* generate_pawn_captures(const Position& pos, MoveStack* mlist);
 
   template<Color Us, SquareDelta Diagonal>
-  MoveStack* generate_pawn_captures_diagonal(MoveStack* mlist, Bitboard pawns, Bitboard enemyPieces);
+  MoveStack* generate_pawn_captures_diagonal(MoveStack* mlist, Bitboard pawns, Bitboard enemyPieces, bool promotion);
 
   template<Color Us>
   MoveStack* generate_pawn_noncaptures(const Position& pos, MoveStack* mlist);
@@ -611,7 +611,7 @@ namespace {
   }
 
   template<Color Us, SquareDelta Diagonal>
-  MoveStack* generate_pawn_captures_diagonal(MoveStack* mlist, Bitboard pawns, Bitboard enemyPieces) {
+  MoveStack* generate_pawn_captures_diagonal(MoveStack* mlist, Bitboard pawns, Bitboard enemyPieces, bool promotion) {
 
     // Calculate our parametrized parameters at compile time
     const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
@@ -626,18 +626,21 @@ namespace {
     Bitboard b1 = move_pawns<Us, Diagonal>(pawns) & ~TFileABB & enemyPieces;
 
     // Capturing promotions
-    Bitboard b2 = b1 & TRank8BB;
-    while (b2)
+    if (promotion)
     {
-        to = pop_1st_bit(&b2);
-        (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, QUEEN);
+        Bitboard b2 = b1 & TRank8BB;
+        b1 &= ~TRank8BB;
+        while (b2)
+        {
+            to = pop_1st_bit(&b2);
+            (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, QUEEN);
+        }
     }
 
     // Capturing non-promotions
-    b2 = b1 & ~TRank8BB;
-    while (b2)
+    while (b1)
     {
-        to = pop_1st_bit(&b2);
+        to = pop_1st_bit(&b1);
         (*mlist++).move = make_move(to - TTDELTA_NE, to);
     }
     return mlist;
@@ -649,22 +652,27 @@ namespace {
     // Calculate our parametrized parameters at compile time
     const Color Them = (Us == WHITE ? BLACK : WHITE);
     const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
+    const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
     const SquareDelta TDELTA_N = (Us == WHITE ? DELTA_N : DELTA_S);
 
     Square to;
     Bitboard pawns = pos.pawns(Us);
     Bitboard enemyPieces = pos.pieces_of_color(opposite_color(Us));
+    bool possiblePromotion = (pawns & TRank7BB);
 
     // Standard captures and capturing promotions in both directions
-    mlist = generate_pawn_captures_diagonal<Us, DELTA_NE>(mlist, pawns, enemyPieces);
-    mlist = generate_pawn_captures_diagonal<Us, DELTA_NW>(mlist, pawns, enemyPieces);
+    mlist = generate_pawn_captures_diagonal<Us, DELTA_NE>(mlist, pawns, enemyPieces, possiblePromotion);
+    mlist = generate_pawn_captures_diagonal<Us, DELTA_NW>(mlist, pawns, enemyPieces, possiblePromotion);
 
     // Non-capturing promotions
-    Bitboard b1 = move_pawns<Us, DELTA_N>(pawns) & pos.empty_squares() & TRank8BB;
-    while (b1)
+    if (possiblePromotion)
     {
-        to = pop_1st_bit(&b1);
-        (*mlist++).move = make_promotion_move(to - TDELTA_N, to, QUEEN);
+        Bitboard b1 = move_pawns<Us, DELTA_N>(pawns) & pos.empty_squares() & TRank8BB;
+        while (b1)
+        {
+            to = pop_1st_bit(&b1);
+            (*mlist++).move = make_promotion_move(to - TDELTA_N, to, QUEEN);
+        }
     }
 
     // En passant captures
@@ -673,7 +681,7 @@ namespace {
         assert(Us != WHITE || square_rank(pos.ep_square()) == RANK_6);
         assert(Us != BLACK || square_rank(pos.ep_square()) == RANK_3);
 
-        b1 = pawns & pos.pawn_attacks(Them, pos.ep_square());
+        Bitboard b1 = pawns & pos.pawn_attacks(Them, pos.ep_square());
         assert(b1 != EmptyBoardBB);
 
         while (b1)
@@ -690,6 +698,7 @@ namespace {
 
     // Calculate our parametrized parameters at compile time
     const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
+    const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
     const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
     const SquareDelta TDELTA_NE = (Us == WHITE ? DELTA_NE : DELTA_SE);
     const SquareDelta TDELTA_NW = (Us == WHITE ? DELTA_NW : DELTA_SW);
@@ -698,40 +707,45 @@ namespace {
     Bitboard b1, b2;
     Square to;
     Bitboard pawns = pos.pawns(Us);
-    Bitboard enemyPieces = pos.pieces_of_color(opposite_color(Us));
     Bitboard emptySquares = pos.empty_squares();
 
-    // Underpromotion captures in the a1-h8 (a8-h1 for black) direction
-    b1 = move_pawns<Us, DELTA_NE>(pawns) & ~FileABB & enemyPieces & TRank8BB;
-    while (b1)
+    if (pawns & TRank7BB) // There is some promotion candidate ?
     {
-        to = pop_1st_bit(&b1);
-        (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, ROOK);
-        (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, BISHOP);
-        (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, KNIGHT);
-    }
+         Bitboard enemyPieces = pos.pieces_of_color(opposite_color(Us));
 
-    // Underpromotion captures in the h1-a8 (h8-a1 for black) direction
-    b1 = move_pawns<Us, DELTA_NW>(pawns) & ~FileHBB & enemyPieces & TRank8BB;
-    while (b1)
-    {
-        to = pop_1st_bit(&b1);
-        (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, ROOK);
-        (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, BISHOP);
-        (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, KNIGHT);
+        // Underpromotion captures in the a1-h8 (a8-h1 for black) direction
+        b1 = move_pawns<Us, DELTA_NE>(pawns) & ~FileABB & enemyPieces & TRank8BB;
+        while (b1)
+        {
+            to = pop_1st_bit(&b1);
+            (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, ROOK);
+            (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, BISHOP);
+            (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, KNIGHT);
+        }
+
+        // Underpromotion captures in the h1-a8 (h8-a1 for black) direction
+        b1 = move_pawns<Us, DELTA_NW>(pawns) & ~FileHBB & enemyPieces & TRank8BB;
+        while (b1)
+        {
+            to = pop_1st_bit(&b1);
+            (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, ROOK);
+            (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, BISHOP);
+            (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, KNIGHT);
+        }
+
+        // Underpromotion pawn pushes
+        b1 = move_pawns<Us, DELTA_N>(pawns) & emptySquares & TRank8BB;
+        while (b1)
+        {
+            to = pop_1st_bit(&b1);
+            (*mlist++).move = make_promotion_move(to - TDELTA_N, to, ROOK);
+            (*mlist++).move = make_promotion_move(to - TDELTA_N, to, BISHOP);
+            (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
+        }
     }
 
     // Single pawn pushes
-    b1 = move_pawns<Us, DELTA_N>(pawns) & emptySquares;
-    b2 = b1 & TRank8BB;
-    while (b2)
-    {
-        to = pop_1st_bit(&b2);
-        (*mlist++).move = make_promotion_move(to - TDELTA_N, to, ROOK);
-        (*mlist++).move = make_promotion_move(to - TDELTA_N, to, BISHOP);
-        (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
-    }
-    b2 = b1 & ~TRank8BB;
+    b2 = b1 = move_pawns<Us, DELTA_N>(pawns) & emptySquares & ~TRank8BB;
     while (b2)
     {
         to = pop_1st_bit(&b2);