On main thread: reduce depth after fail high

pb00068 · snicolet · commit 081af9080542 · 2018-10-25T23:08:06.000+02:00
This helps resolving consecutive FH's during aspiration more efficiently STC: http://tests.stockfishchess.org/tests/view/5bc857920ebc592439f85765 LLR: 2.95 (-2.94,2.94) [0.00,5.00] Total: 4992 W: 1134 L: 980 D: 2878 Elo +10.72 LTC: http://tests.stockfishchess.org/tests/view/5bc868050ebc592439f857ef LLR: 2.95 (-2.94,2.94) [0.00,5.00] Total: 8123 W: 1363 L: 1210 D: 5550 Elo +6.54 No-Regression test with 8 threads, tc=15+0.15: http://tests.stockfishchess.org/tests/view/5bc874ca0ebc592439f85938 LLR: 2.94 (-2.94,2.94) [-3.00,1.00] Total: 24740 W: 3977 L: 3863 D: 16900 Elo +1.60 This was a cooperation between me and Michael Stembera: -me recognizing SF having problems with resolving FH's efficiently at high depths, thus starting some tests based on consecutive FH's. -mstembera picking up the idea with first success at STC & LTC (so full credits to him!) -me suggesting how to resolve the issues pinpointed by S.G on PR #1768 and finally restricting the logic to the main thread so that it don't regresses at multi-thread. bench: 3314347
diff --git a/src/search.cpp b/src/search.cpp
@@ -368,6 +368,7 @@ void Thread::search() {
 
       size_t pvFirst = 0;
       pvLast = 0;
+      Depth adjustedDepth = rootDepth;
 
       // MultiPV loop. We perform a full root search for each PV line
       for (pvIdx = 0; pvIdx < multiPV && !Threads.stop; ++pvIdx)
@@ -401,9 +402,11 @@ void Thread::search() {
           // Start with a small aspiration window and, in the case of a fail
           // high/low, re-search with a bigger window until we don't fail
           // high/low anymore.
+          int failedHighCnt = 0;
           while (true)
           {
-              bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false);
+        	  adjustedDepth = std::max(ONE_PLY, rootDepth - failedHighCnt * ONE_PLY);
+              bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, 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
@@ -425,7 +428,7 @@ void Thread::search() {
                   && multiPV == 1
                   && (bestValue <= alpha || bestValue >= beta)
                   && Time.elapsed() > 3000)
-                  sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
+                  sync_cout << UCI::pv(rootPos, adjustedDepth, alpha, beta) << sync_endl;
 
               // In case of failing low/high increase aspiration window and
               // re-search, otherwise exit the loop.
@@ -436,12 +439,17 @@ void Thread::search() {
 
                   if (mainThread)
                   {
+                      failedHighCnt = 0;
                       failedLow = true;
                       Threads.stopOnPonderhit = false;
                   }
               }
               else if (bestValue >= beta)
+              {
                   beta = std::min(bestValue + delta, VALUE_INFINITE);
+                  if (mainThread)
+                	  ++failedHighCnt;
+              }
               else
                   break;
 
@@ -455,15 +463,15 @@ void Thread::search() {
 
           if (    mainThread
               && (Threads.stop || pvIdx + 1 == multiPV || Time.elapsed() > 3000))
-              sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
+              sync_cout << UCI::pv(rootPos, adjustedDepth, alpha, beta) << sync_endl;
       }
 
       if (!Threads.stop)
-          completedDepth = rootDepth;
+          completedDepth = adjustedDepth;
 
       if (rootMoves[0].pv[0] != lastBestMove) {
          lastBestMove = rootMoves[0].pv[0];
-         lastBestMoveDepth = rootDepth;
+         lastBestMoveDepth = adjustedDepth;
       }
 
       // Have we found a "mate in x"?
