Revert "Move draw by material check"

Possible regression

bench: 4554579

Author: mcostalba

src/endgame.h

@@ -43,7 +43,7 @@ enum EndgameType {
   KQKP,  // KQ vs KP
   KQKR,  // KQ vs KR
   KBBKN, // KBB vs KN
-  KmmKm, // K and one or two minors vs K and zero or one minor
+  KmmKm, // K and two minors vs K and one or two minors
 
 
   // Scaling functions

src/material.cpp

@@ -173,18 +173,10 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
       return e;
   }
 
-  // Draw by insufficient material (trivial draws like KK, KBK and KNK)
-  if (   !pos.pieces(PAWN)
-      &&  pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) <= BishopValueMg)
-  {
-      e->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
-      return e;
-  }
-
-  // Minor piece endgame with at least one minor piece per side and
-  // no pawns. Note that the case KmmK is already handled by KXK.
   if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
   {
+      // Minor piece endgame with at least one minor piece per side and
+      // no pawns. Note that the case KmmK is already handled by KXK.
       assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP)));
       assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP)));
 
@@ -248,7 +240,8 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
       }
   }
 
-  // No pawns makes it difficult to win, even with a material advantage
+  // No pawns makes it difficult to win, even with a material advantage. This
+  // catches some trivial draws like KK, KBK and KNK
   if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
   {
       e->factor[WHITE] = (uint8_t)

src/position.cpp

@@ -1255,11 +1255,17 @@ Value Position::compute_non_pawn_material(Color c) const {
 }
 
 
-/// Position::is_draw() tests whether the position is drawn by 50 moves rule
-/// or by repetition. It does not detect stalemates.
-
+/// Position::is_draw() tests whether the position is drawn by material,
+/// repetition, or the 50 moves rule. It does not detect stalemates, this
+/// must be done by the search.
 bool Position::is_draw() const {
 
+  // Draw by material?
+  if (   !pieces(PAWN)
+      && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
+      return true;
+
+  // Draw by the 50 moves rule?
   if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
       return true;