Correctly reset bestMoveChanges

for searches not using time management (e.g. analysis, fixed node game play etc),
bestMoveChanges was not reset during search iterations. As LMR uses this quantity,
search was somewhat weaker.

Tested using fixed node playing games:
```
./c-chess-cli -each nodes=10000 option.Hash=16 -engine cmd=../Stockfish/src/fix -engine cmd=../Stockfish/src/master -concurrency 6 -openings file=../books/UHO_XXL_+0.90_+1.19.epd -games 10000
Score of Stockfish Fix vs Stockfish Master: 3187 - 3028 - 3785  [0.508] 10000

./c-chess-cli -each nodes=30000 option.Hash=16 -engine cmd=../Stockfish/src/fix -engine cmd=../Stockfish/src/master -concurrency 6 -openings file=../books/UHO_XXL_+0.90_+1.19.epd -games 10000
Score of Stockfish Fix vs Stockfish Master: 2946 - 2834 - 4220  [0.506] 10000
```

closes https://github.com/official-stockfish/Stockfish/pull/3818

bench: 5061979

diff --git a/src/search.cpp b/src/search.cpp
index 70dc4b2100cba60644fbe7ff58f76ec84b3c67bf..c926c1d20649d2c460f02c53d106b71b682a5cca 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -477,6 +477,13 @@ void Thread::search() {
       if (skill.enabled() && skill.time_to_pick(rootDepth))
           skill.pick_best(multiPV);
 
+      // Use part of the gained time from a previous stable move for the current move
+      for (Thread* th : Threads)
+      {
+          totBestMoveChanges += th->bestMoveChanges;
+          th->bestMoveChanges = 0;
+      }
+
       // Do we have time for the next iteration? Can we stop searching now?
       if (    Limits.use_time_management()
           && !Threads.stop
@@ -489,13 +496,6 @@ void Thread::search() {
           // If the bestMove is stable over several iterations, reduce time accordingly
           timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.92 : 0.95;
           double reduction = (1.47 + mainThread->previousTimeReduction) / (2.32 * timeReduction);
-
-          // Use part of the gained time from a previous stable move for the current move
-          for (Thread* th : Threads)
-          {
-              totBestMoveChanges += th->bestMoveChanges;
-              th->bestMoveChanges = 0;
-          }
           double bestMoveInstability = 1.073 + std::max(1.0, 2.25 - 9.9 / rootDepth)
                                               * totBestMoveChanges / Threads.size();
           double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability;