More bonus for bestMoves on past PV nodes

It looks like it is important to keep past PV (ttPv) nodes as close as possible to current PV nodes.
Credits to Mark Tenzer (31m059) & Stefan Geschwentner who first tried ideas on ttPv nodes.

STC:
https://tests.stockfishchess.org/tests/view/5e2ff5efab2d69d58394fd52
LLR: 2.95 (-2.94,2.94) {-1.00,3.00}
Total: 13302 W: 2647 L: 2507 D: 8148
Ptnml(0-2): 237, 1540, 2956, 1632, 260

LTC:
https://tests.stockfishchess.org/tests/view/5e2fff38ab2d69d58394fd55
LLR: 2.95 (-2.94,2.94) {0.00,2.00}
Total: 15797 W: 2137 L: 1960 D: 11700
Ptnml(0-2): 96, 1443, 4628, 1547, 130

closes #2529

bench: 5545845

src/search.cpp

@@ -158,7 +158,7 @@ namespace {
   void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
   void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus);
   void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq,
-                        Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth);
+                        Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth, bool pastPV);
 
   // perft() is our utility to verify move generation. All the leaf nodes up
   // to the given depth are generated and counted, and the sum is returned.
@@ -713,7 +713,7 @@ namespace {
             if (ttValue >= beta)
             {
                 if (!pos.capture_or_promotion(ttMove))
-                    update_quiet_stats(pos, ss, ttMove, stat_bonus(depth));
+                    update_quiet_stats(pos, ss, ttMove, stat_bonus(depth + (!PvNode && ttPv)));
 
                 // Extra penalty for early quiet moves of the previous ply
                 if ((ss-1)->moveCount <= 2 && !priorCapture)
@@ -722,7 +722,7 @@ namespace {
             // Penalty for a quiet ttMove that fails low
             else if (!pos.capture_or_promotion(ttMove))
             {
-                int penalty = -stat_bonus(depth);
+                int penalty = -stat_bonus(depth + (!PvNode && ttPv));
                 thisThread->mainHistory[us][from_to(ttMove)] << penalty;
                 update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
             }
@@ -1326,7 +1326,7 @@ namespace {
 
     else if (bestMove)
         update_all_stats(pos, ss, bestMove, bestValue, beta, prevSq,
-                         quietsSearched, quietCount, capturesSearched, captureCount, depth);
+                         quietsSearched, quietCount, capturesSearched, captureCount, depth, (!PvNode && ttPv));
 
     // Bonus for prior countermove that caused the fail low
     else if (   (depth >= 3 || PvNode)
@@ -1602,7 +1602,7 @@ namespace {
   // update_all_stats() updates stats at the end of search() when a bestMove is found
 
   void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq,
-                        Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth) {
+                        Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth, bool pastPV) {
 
     int bonus1, bonus2;
     Color us = pos.side_to_move();
@@ -1612,8 +1612,8 @@ namespace {
     PieceType captured = type_of(pos.piece_on(to_sq(bestMove)));
 
     bonus1 = stat_bonus(depth + 1);
-    bonus2 = bestValue > beta + PawnValueMg ? bonus1               // larger bonus
-                                            : stat_bonus(depth);   // smaller bonus
+    bonus2 = pastPV || bestValue > beta + PawnValueMg ? bonus1               // larger bonus
+                                                      : stat_bonus(depth);   // smaller bonus
 
     if (!pos.capture_or_promotion(bestMove))
     {