Retire pvMove in search()

Now we can directly replace it with
the definition resulting in simpler
and possibly faster code because
PvNode is evaluated at compile time.

No functional change.

src/search.cpp

@@ -407,7 +407,7 @@ namespace {
     Move ttMove, move, excludedMove, bestMove;
     Depth ext, newDepth, predictedDepth;
     Value bestValue, value, ttValue, eval, nullValue, futilityValue;
-    bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
+    bool inCheck, givesCheck, singularExtensionNode, improving;
     bool captureOrPromotion, dangerous, doFullDepthSearch;
     int moveCount, quietCount;
 
@@ -802,7 +802,6 @@ namespace {
           continue;
       }
 
-      pvMove = PvNode && moveCount == 1;
       ss->currentMove = move;
       if (!SpNode && !captureOrPromotion && quietCount < 64)
           quietsSearched[quietCount++] = move;
@@ -851,7 +850,7 @@ namespace {
           ss->reduction = DEPTH_ZERO;
       }
       else
-          doFullDepthSearch = !pvMove;
+          doFullDepthSearch = !PvNode || moveCount > 1;
 
       // Step 16. Full depth search, when LMR is skipped or fails high
       if (doFullDepthSearch)
@@ -868,7 +867,7 @@ namespace {
       // For PV nodes only, 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 fail low with value <= alpha and to try another move.
-      if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
+      if (PvNode && (moveCount == 1 || (value > alpha && (RootNode || value < beta))))
           value = newDepth <   ONE_PLY ?
                             givesCheck ? -qsearch<PV,  true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
                                        : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
@@ -897,15 +896,15 @@ namespace {
           RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
 
           // PV move or new best move ?
-          if (pvMove || value > alpha)
+          if (moveCount == 1 || value > alpha)
           {
               rm.score = value;
               rm.extract_pv_from_tt(pos);
 
               // 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 (!pvMove)
+              if (moveCount > 1)
                   ++BestMoveChanges;
           }
           else