Remove skipEarlyPruning argument to search()

Remove nine boolean arguments and the corresponding skipEarlyPruning variable.
Instead, skip early pruning only when there is an excluded move, and try null
move pruning only if the previous move was not itself a null move.

passed STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 33623 W: 6853 L: 6755 D: 20015
http://tests.stockfishchess.org/tests/view/5aef462a0ebc5902a409a10e

passed LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 39474 W: 5882 L: 5789 D: 27803
http://tests.stockfishchess.org/tests/view/5aefd4b80ebc5902a409a164

Closes https://github.com/official-stockfish/Stockfish/pull/1585

Bench: 4953556

diff --git a/src/search.cpp b/src/search.cpp
index 8a6105711aae2720c112371c7f6ca3b2cf9a9532..2072c4bc241d7590d8dca47ba04e3e2c6985146b 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -107,7 +107,7 @@ namespace {
   };
 
   template <NodeType NT>
   };
 
   template <NodeType NT>

-  Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
+  Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);

 
   template <NodeType NT>
   Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
 
   template <NodeType NT>
   Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);


@@ -390,7 +390,7 @@ void Thread::search() {
           // high/low anymore.
           while (true)
           {
           // high/low anymore.
           while (true)
           {

-              bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false, false);
+              bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false);

 
               // Bring the best move to the front. It is critical that sorting
               // is done with a stable algorithm because all the values but the
 
               // Bring the best move to the front. It is critical that sorting
               // is done with a stable algorithm because all the values but the


@@ -517,7 +517,7 @@ namespace {
   // search<>() is the main search function for both PV and non-PV nodes
 
   template <NodeType NT>
   // search<>() is the main search function for both PV and non-PV nodes
 
   template <NodeType NT>

-  Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) {
+  Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {

 
     // Use quiescence search when needed
     if (depth < ONE_PLY)
 
     // Use quiescence search when needed
     if (depth < ONE_PLY)


@@ -713,7 +713,7 @@ namespace {
     improving =   ss->staticEval >= (ss-2)->staticEval
                ||(ss-2)->staticEval == VALUE_NONE;
 
     improving =   ss->staticEval >= (ss-2)->staticEval
                ||(ss-2)->staticEval == VALUE_NONE;
 

-    if (skipEarlyPruning || !pos.non_pawn_material(pos.side_to_move()))
+    if (ss->excludedMove || !pos.non_pawn_material(pos.side_to_move()))

         goto moves_loop;
 
     // Step 7. Razoring (skipped when in check, ~2 Elo)
         goto moves_loop;
 
     // Step 7. Razoring (skipped when in check, ~2 Elo)


@@ -736,6 +736,7 @@ namespace {
 
     // Step 9. Null move search with verification search (~40 Elo)
     if (   !PvNode
 
     // Step 9. Null move search with verification search (~40 Elo)
     if (   !PvNode

+        && (ss-1)->currentMove != MOVE_NULL

         &&  eval >= beta
         &&  ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
         && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd))
         &&  eval >= beta
         &&  ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
         && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd))


@@ -750,7 +751,7 @@ namespace {
 
         pos.do_null_move(st);
 
 
         pos.do_null_move(st);
 

-        Value nullValue = -search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true);
+        Value nullValue = -search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);

 
         pos.undo_null_move();
 
 
         pos.undo_null_move();
 


@@ -768,7 +769,7 @@ namespace {
             thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4;
             thisThread->nmp_odd = ss->ply % 2;
 
             thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4;
             thisThread->nmp_odd = ss->ply % 2;
 

-            Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
+            Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false);

 
             thisThread->nmp_odd = thisThread->nmp_ply = 0;
 
 
             thisThread->nmp_odd = thisThread->nmp_ply = 0;
 


@@ -784,8 +785,6 @@ namespace {
         &&  depth >= 5 * ONE_PLY
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY)
     {
         &&  depth >= 5 * ONE_PLY
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY)
     {

-        assert(is_ok((ss-1)->currentMove));
-

         Value rbeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE);
         MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory);
         int probCutCount = 0;
         Value rbeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE);
         MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory);
         int probCutCount = 0;


@@ -808,7 +807,7 @@ namespace {
 
                 // If the qsearch held perform the regular search
                 if (value >= rbeta)
 
                 // If the qsearch held perform the regular search
                 if (value >= rbeta)

-                    value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
+                    value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode);

 
                 pos.undo_move(move);
 
 
                 pos.undo_move(move);
 


@@ -822,7 +821,7 @@ namespace {
         && !ttMove)
     {
         Depth d = 3 * depth / 4 - 2 * ONE_PLY;
         && !ttMove)
     {
         Depth d = 3 * depth / 4 - 2 * ONE_PLY;

-        search<NT>(pos, ss, alpha, beta, d, cutNode, true);
+        search<NT>(pos, ss, alpha, beta, d, cutNode);

 
         tte = TT.probe(posKey, ttHit);
         ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
 
         tte = TT.probe(posKey, ttHit);
         ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;


@@ -897,7 +896,7 @@ moves_loop: // When in check, search starts from here
       {
           Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
           ss->excludedMove = move;
       {
           Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
           ss->excludedMove = move;

-          value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode, true);
+          value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);

           ss->excludedMove = MOVE_NONE;
 
           if (value < rBeta)
           ss->excludedMove = MOVE_NONE;
 
           if (value < rBeta)


@@ -1027,7 +1026,7 @@ moves_loop: // When in check, search starts from here
 
           Depth d = std::max(newDepth - r, ONE_PLY);
 
 
           Depth d = std::max(newDepth - r, ONE_PLY);
 

-          value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
+          value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);

 
           doFullDepthSearch = (value > alpha && d != newDepth);
       }
 
           doFullDepthSearch = (value > alpha && d != newDepth);
       }


@@ -1036,7 +1035,7 @@ moves_loop: // When in check, search starts from here
 
       // Step 17. Full depth search when LMR is skipped or fails high
       if (doFullDepthSearch)
 
       // Step 17. Full depth search when LMR is skipped or fails high
       if (doFullDepthSearch)

-          value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
+          value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);

 
       // 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
 
       // 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


@@ -1046,7 +1045,7 @@ moves_loop: // When in check, search starts from here
           (ss+1)->pv = pv;
           (ss+1)->pv[0] = MOVE_NONE;
 
           (ss+1)->pv = pv;
           (ss+1)->pv[0] = MOVE_NONE;
 

-          value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, false);
+          value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);

       }
 
       // Step 18. Undo move
       }
 
       // Step 18. Undo move