Remove reduction for moving threatened piece

Simplify away "Decrease reduction if we move a threatened piece".

Running a dbg_hit_on() shows that this line is only called ~0.12% of the time.

Simplification STC: https://tests.stockfishchess.org/tests/view/641ec2dcdb43ab2ba6f88103
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 146128 W: 39168 L: 39070 D: 67890
Ptnml(0-2): 466, 16117, 39830, 16155, 496

Simplification LTC: https://tests.stockfishchess.org/tests/view/64200689db43ab2ba6f8bca8
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 248016 W: 66703 L: 66714 D: 114599
Ptnml(0-2): 105, 24202, 75406, 24189, 106

closes https://github.com/official-stockfish/Stockfish/pull/4471

Bench: 4961236

diff --git a/src/search.cpp b/src/search.cpp
index 5f95a1bd718a4256d06aaa5e37b020334cf5817d..2fcbc7df2a524d1e33617814f45bbc75696c957b 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1181,11 +1181,6 @@ moves_loop: // When in check, search starts here
       if (singularQuietLMR)
           r--;
 
-      // Decrease reduction if we move a threatened piece (~1 Elo)
-      if (   depth > 9
-          && (mp.threatenedPieces & from_sq(move)))
-          r--;
-
       // Increase reduction if next ply has a lot of fail high (~5 Elo)
       if ((ss+1)->cutoffCnt > 3)
           r++;