Qsearch simplification. (#1828)

Don't do an extra TT update in case of a fail-high,
but simply break off the moves loop and let the TT update
at the end of qsearch do this job.
Same workflow/logic as in our main search function now.

Tested for no regression to be on the safe side.
STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 30237 W: 6665 L: 6560 D: 17012
http://tests.stockfishchess.org/tests/view/5bf928e80ebc5902bced3f3a

LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 51067 W: 8625 L: 8553 D: 33889
http://tests.stockfishchess.org/tests/view/5bf937180ebc5902bced3fdc

No functional change.

diff --git a/src/search.cpp b/src/search.cpp
index f4e1da977990f18d2b77e988cbbc4c1c0798370e..38d5683493a5b14df76a7196a340b49a8b429ebd 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1395,21 +1395,15 @@ moves_loop: // When in check, search starts from here
 
           if (value > alpha)
           {
+              bestMove = move;
+
               if (PvNode) // Update pv even in fail-high case
                   update_pv(ss->pv, move, (ss+1)->pv);
 
               if (PvNode && value < beta) // Update alpha here!
-              {
                   alpha = value;
-                  bestMove = move;
-              }
-              else // Fail high
-              {
-                  tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
-                            ttDepth, move, ss->staticEval);
-
-                  return value;
-              }
+              else
+                  break; // Fail high
           }
        }
     }
@@ -1420,7 +1414,8 @@ moves_loop: // When in check, search starts from here
         return mated_in(ss->ply); // Plies to mate from the root
 
     tte->save(posKey, value_to_tt(bestValue, ss->ply),
-              PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
+              bestValue >= beta ? BOUND_LOWER :
+              PvNode && bestValue > oldAlpha  ? BOUND_EXACT : BOUND_UPPER,
               ttDepth, bestMove, ss->staticEval);
 
     assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);