From a1b23ace2517ad923dc4dc808ce01af0e802204e Mon Sep 17 00:00:00 2001
From: Tilps <Tilps@users.noreply.github.com>
Date: Tue, 31 Dec 2019 18:00:02 +1100
Subject: [PATCH] Don't discard games that are in positions that are already
 done. (#1048)

* Don't discard games that are in positions that are already done.

* Minor optimization.

* Minor tweak for consistency with surrounding code.
---
 src/selfplay/game.cc | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/selfplay/game.cc b/src/selfplay/game.cc
index aba8bce95e..95c948595b 100644
--- a/src/selfplay/game.cc
+++ b/src/selfplay/game.cc
@@ -206,9 +206,18 @@ void SelfPlayGame::Play(int white_threads, int black_threads, bool training,
                                          kMinimumAllowedVistsId.GetId())) {
         break;
       }
-      auto move_list_to_discard = GetMoves();
-      move_list_to_discard.push_back(move);
-      options_[idx].discarded_callback(move_list_to_discard);
+      PositionHistory history_copy = tree_[idx]->GetPositionHistory();
+      Move move_for_history = move;
+      if (tree_[idx]->IsBlackToMove()) {
+        move_for_history.Mirror();
+      }
+      history_copy.Append(move_for_history);
+      // Ensure not to discard games that are already decided.
+      if (history_copy.ComputeGameResult() == GameResult::UNDECIDED) {
+        auto move_list_to_discard = GetMoves();
+        move_list_to_discard.push_back(move);
+        options_[idx].discarded_callback(move_list_to_discard);
+      }
       search_->ResetBestMove();
     }
     // Add best move to the tree.