Simplify stats assignment for Pv nodes

This patch is a simplification of my recent elo gainer.
Logically the Elo gainer didn't make much sense and this patch simplifies it into smth more logical.
Instead of assigning negative bonuses to all non-first moves that enter PV nodes
we assign positive bonuses in full depth search after LMR only for moves that
will result in a fail high - thus not assigning positive bonuses
for moves that will go to pv search - so doing "almost" the same as we do in master now for them.
Logic differs for some other moves, though, but this removes some lines of code.

Passed STC:
https://tests.stockfishchess.org/tests/view/642cf5cf77ff3301150dc5ec
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 409320 W: 109124 L: 109308 D: 190888
Ptnml(0-2): 1149, 45385, 111751, 45251, 1124

Passed LTC:
https://tests.stockfishchess.org/tests/view/642fe75d20eb941419bde200
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 260336 W: 70280 L: 70303 D: 119753
Ptnml(0-2): 99, 25236, 79528, 25199, 106

closes https://github.com/official-stockfish/Stockfish/pull/4522

Bench:  4286815

diff --git a/src/search.cpp b/src/search.cpp
index 411befdedfb460459902ffd8d9fc62fede6cc0d4..390c6b1c72fb37eb87940d71105d7fdf7f3ad80e 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1229,8 +1229,9 @@ moves_loop: // When in check, search starts here
               if (newDepth > d)
                   value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
 
-              int bonus = value > alpha ?  stat_bonus(newDepth)
-                                        : -stat_bonus(newDepth);
+              int bonus = value <= alpha ? -stat_bonus(newDepth)
+                        : value >= beta  ?  stat_bonus(newDepth)
+                                         :  0;
 
               update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
           }
@@ -1255,9 +1256,6 @@ moves_loop: // When in check, search starts here
           (ss+1)->pv[0] = MOVE_NONE;
 
           value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
-
-          if (moveCount > 1 && newDepth >= depth && !capture)
-              update_continuation_histories(ss, movedPiece, to_sq(move), -stat_bonus(newDepth));
       }
 
       // Step 19. Undo move