From cef551092c7d4ca4d9a2d6402f412332b1f3e88a Mon Sep 17 00:00:00 2001
From: aronpetkovski <aronpetko@gmail.com>
Date: Sun, 27 Jul 2025 22:39:12 +0200
Subject: [PATCH] Only do IIR in minimally reduced nodes

Passed STC
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 164256 W: 42799 L: 42299 D: 79158
Ptnml(0-2): 451, 19305, 42087, 19863, 422
https://tests.stockfishchess.org/tests/view/68868e9b7b562f5f7b731615

Passed LTC
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 279396 W: 71871 L: 71062 D: 136463
Ptnml(0-2): 126, 30117, 78404, 30924, 127
https://tests.stockfishchess.org/tests/view/6886a4977b562f5f7b731663

closes https://github.com/official-stockfish/Stockfish/pull/6196

Bench: 3490609
---
 src/search.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index e3044bf6a..9775e46b1 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -813,7 +813,8 @@ Value Search::Worker::search(
     {
         int bonus = std::clamp(-10 * int((ss - 1)->staticEval + ss->staticEval), -1979, 1561) + 630;
         mainHistory[~us][((ss - 1)->currentMove).from_to()] << bonus * 935 / 1024;
-        if (!ttHit && type_of(pos.piece_on(prevSq)) != PAWN && ((ss - 1)->currentMove).type_of() != PROMOTION)
+        if (!ttHit && type_of(pos.piece_on(prevSq)) != PAWN
+            && ((ss - 1)->currentMove).type_of() != PROMOTION)
             pawnHistory[pawn_structure_index(pos)][pos.piece_on(prevSq)][prevSq]
               << bonus * 1428 / 1024;
     }
@@ -900,7 +901,7 @@ Value Search::Worker::search(
     // Step 10. Internal iterative reductions
     // At sufficient depth, reduce depth for PV/Cut nodes without a TTMove.
     // (*Scaler) Especially if they make IIR less aggressive.
-    if (!allNode && depth >= 6 && !ttData.move)
+    if (!allNode && depth >= 6 && !ttData.move && priorReduction <= 3)
         depth--;
 
     // Step 11. ProbCut