if these are ttMoves and played in positions with a high value of the rule50 counter. The unusual extension of 2 is safe in this context as awarding it will reset the rule50 counter, making sure it is awarded very rarely in a search path.
This patch partially addresses https://github.com/official-stockfish/Stockfish/issues/2620 as it should make it less likely to play a move that resets the counter, but that is worse than alternative moves after a slightly deeper search.
passed STC:
LLR: 2.96 (-2.94,2.94) {-0.50,1.50}
Total: 71658 W: 13840 L: 13560 D: 44258
Ptnml(0-2): 1058, 7921, 17643, 8097, 1110
https://tests.stockfishchess.org/tests/view/
5e90d0f6754c3424c4cf9f41
passed LTC:
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 85082 W: 11069 L: 10680 D: 63333
Ptnml(0-2): 459, 6982, 27259, 7393, 448
https://tests.stockfishchess.org/tests/view/
5e917470af0a0143109dc341
closes https://github.com/official-stockfish/Stockfish/pull/2623
Bench:
4432822
if (type_of(move) == CASTLING)
extension = 1;
+ // Late irreversible move extension
+ if ( move == ttMove
+ && pos.rule50_count() > 80
+ && (captureOrPromotion || type_of(movedPiece) == PAWN))
+ extension = 2;
+
// Add extension to new depth
newDepth += extension;