From: Marco Costalba <mcostalba@gmail.com>
Date: Sat, 29 Sep 2012 15:41:53 +0000 (+0200)
Subject: Don't need to early check PV moves for legality
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=d53c928261a3a1b50304ec0a69312b6c2c338ccb

Don't need to early check PV moves for legality

As long as isPvMove (renamed to pvMove) is set after
legality check, we can postpone legality even in PV case.

Patch aligns the PV case with the common non-pv one.

No functional change.
---

diff --git a/src/search.cpp b/src/search.cpp
index 62948590..6cab3f6c 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -528,7 +528,7 @@ namespace {
     Bound bt;
     Value bestValue, value, oldAlpha, ttValue;
     Value refinedValue, nullValue, futilityBase, futilityValue;
-    bool isPvMove, inCheck, singularExtensionNode, givesCheck;
+    bool pvMove, inCheck, singularExtensionNode, givesCheck;
     bool captureOrPromotion, dangerous, doFullDepthSearch;
     int moveCount = 0, playedMoveCount = 0;
     Thread* thisThread = pos.this_thread();
@@ -818,12 +818,12 @@ split_point_start: // At split points actual search starts from here
       if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
           continue;
 
-      // At PV and SpNode nodes we want all moves to be legal since the beginning
-      if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
-          continue;
-
       if (SpNode)
       {
+          // Shared counter cannot be decremented later if move turns out to be illegal
+          if (!pos.pl_move_is_legal(move, ci.pinned))
+              continue;
+
           moveCount = ++sp->moveCount;
           sp->mutex.unlock();
       }
@@ -840,7 +840,6 @@ split_point_start: // At split points actual search starts from here
                         << " currmovenumber " << moveCount + PVIdx << sync_endl;
       }
 
-      isPvMove = (PvNode && moveCount <= 1);
       captureOrPromotion = pos.is_capture_or_promotion(move);
       givesCheck = pos.move_gives_check(move, ci);
       dangerous = givesCheck || is_dangerous(pos, move, captureOrPromotion);
@@ -929,6 +928,7 @@ split_point_start: // At split points actual search starts from here
           continue;
       }
 
+      pvMove = PvNode ? moveCount <= 1 : false;
       ss->currentMove = move;
       if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
           movesSearched[playedMoveCount++] = move;
@@ -939,7 +939,7 @@ split_point_start: // At split points actual search starts from here
       // Step 15. Reduced depth search (LMR). If the move fails high will be
       // re-searched at full depth.
       if (    depth > 3 * ONE_PLY
-          && !isPvMove
+          && !pvMove
           && !captureOrPromotion
           && !dangerous
           &&  ss->killers[0] != move
@@ -955,7 +955,7 @@ split_point_start: // At split points actual search starts from here
           ss->reduction = DEPTH_ZERO;
       }
       else
-          doFullDepthSearch = !isPvMove;
+          doFullDepthSearch = !pvMove;
 
       // Step 16. Full depth search, when LMR is skipped or fails high
       if (doFullDepthSearch)
@@ -968,7 +968,7 @@ split_point_start: // At split points actual search starts from here
       // Only for PV nodes do a full PV search on the first move or after a fail
       // high, in the latter case search only if value < beta, otherwise let the
       // parent node to fail low with value <= alpha and to try another move.
-      if (PvNode && (isPvMove || (value > alpha && (RootNode || value < beta))))
+      if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
           value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
                                      : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
 
@@ -994,7 +994,7 @@ split_point_start: // At split points actual search starts from here
           RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
 
           // PV move or new best move ?
-          if (isPvMove || value > alpha)
+          if (pvMove || value > alpha)
           {
               rm.score = value;
               rm.extract_pv_from_tt(pos);
@@ -1002,7 +1002,7 @@ split_point_start: // At split points actual search starts from here
               // We record how often the best move has been changed in each
               // iteration. This information is used for time management: When
               // the best move changes frequently, we allocate some more time.
-              if (!isPvMove && MultiPV == 1)
+              if (!pvMove && MultiPV == 1)
                   BestMoveChanges++;
           }
           else