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Robert Nurnberg @ elitebookandDisservin
67a2c247d4
Ever since #5094 master only lets the main thread terminate `go mate` searches, reverting the earlier improvement #1215. This PR restores the old logic. So any thread that found a "mate in x" can now stop the search. To make this work robustly, we need to guard against inexact mate scores in the best thread selection. In addition, in contrast to time limits, the main thread may now not complete a d1 search for a mated-in position. In master an aborted d1 search may have a PV beginning with `Move::none()`, in which case no thread selection is performed. See #623. We fix this bug here by checking if `lastBestPV` is empty or not. For interrupted d1 searches we now label mated-in scores as inexact. While at it, we also simplify the logic for detecting if we can terminate a go mate x search, using the fact that threads.stop can only be false if we have a completed iteration with a valid score. The PR has no effect on game play, but should slightly improve general mate finding and speed up multi-threaded `go mate` searches. We also add a corresponding matecheck run to the CI. This only involves 61 mates up to mate-in-2. Test runs with the first 50 or 100 mates from `mates2000.epd` did at times not finish within 30 minutes on my fork or in local tests, possibly due to search explosions for some mate-in-3 positions. closes https://github.com/official-stockfish/Stockfish/pull/6668 No functional change