Rework check/pawn-push/recapture extension gating on real SEE (GetMoveSee, generalized from GetCheckSee), restrict LMR to leftover moves only, and tighten recapture's window back to 1x after measuring a 6.8x node blowup from sharing the wider window.

Head-to-head match at 1170 games confirms parity with the prior head (score=0.510, LLR still between bounds) -- landing as a neutral-or-better baseline rather than a regression.

1 files changed, 23 insertions, 13 deletions

diff --git a/src/search.c b/src/search.c
index 4e89a2c..573f78c 100644
--- a/src/search.c
+++ b/src/search.c
@@ -189,7 +189,7 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
     ULONG uFutilityMargin = 0;
     FLAG fAnyMoveEFPPruned = FALSE;
     FLAG fThisMoveEFPPruned = FALSE;
-    SCORE iCheckSee;
+    SCORE iMoveSee;
 #ifdef DEBUG
     ASSERT(IS_VALID_SCORE(iAlpha));
     ASSERT(IS_VALID_SCORE(iBeta));
@@ -745,14 +745,22 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
 #endif
 
         // SEE must be computed on the PRE-move position -- see.c's
-        // exchange walk needs the piece still sitting on cFrom. Only
-        // needed for checking moves, where ComputeMoveExtension uses it
-        // to gate the check extension on soundness (Crafty-style: don't
-        // extend a checking move that's really just a losing sacrifice).
-        iCheckSee = 0;
-        if (IS_CHECKING_MOVE(mv))
+        // exchange walk needs the piece still sitting on cFrom.
+        // ComputeMoveExtension uses it for two soundness gates: the
+        // check extension (Crafty-style: don't extend a checking move
+        // that's really just a losing sacrifice) and the recapture
+        // extension (don't extend a "recapture" that actually loses
+        // material). uDepth <= THREE_PLY mirrors the recapture
+        // extension's own depth gate -- cheap to test here since
+        // uDepth is already loop-invariant, and it keeps this from
+        // computing a SEE on every single non-pawn capture at every
+        // depth. One call per move regardless of which gate(s) end up
+        // wanting it -- SEE is too hot a routine to pay for twice.
+        iMoveSee = 0;
+        if (IS_CHECKING_MOVE(mv) ||
+            (mv.pCaptured && !IS_PAWN(mv.pCaptured) && (uDepth <= THREE_PLY)))
         {
-            iCheckSee = GetCheckSee(ctx,
+            iMoveSee = GetMoveSee(ctx,
                                     mv,
                                     (uStage == TRY_GENERATED_MOVES) ?
                                         (x - 1) : (ULONG)-1);
@@ -773,7 +781,8 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
                                  (x - 1),     // Note: x==0 if doing mvHash
                                  iEval,
                                  uDepth,
-                                 iCheckSee,
+                                 iMoveSee,
+                                 fIsLeftoverMove,
                                  &iExtend);
 
             // Note: MAX_EXTEND_PER_LINE (a flat, non-depth-relative cap on
@@ -786,8 +795,9 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
             // Decide how much (if any) to reduce this move's depth --
             // graded LMR.
             if ((uDepth > TWO_PLY) &&
-                (NODE_PV != pi->eNodeType) &&
+                (pi->eNodeType != NODE_PV) &&
                 (uLegalMoves > 5) &&
+                (fIsLeftoverMove) &&
                 (0 == iExtend) &&
                 (!IS_ESCAPING_CHECK(mv)) &&
                 (!IS_CAPTURE_OR_PROMOTION(mv)) &&
@@ -1570,7 +1580,7 @@ _ShouldWeConsiderThisMove(IN SEARCHER_THREAD_CONTEXT *ctx,
         // a real (winning/even) iMoveValue gets the same value-plus-
         // flat-bonus treatment as any other capture; a move with no
         // usable value (SEE already called it losing) falls back to
-        // GetCheckSee's real tactical judgment, exactly like the
+        // GetMoveSee's real tactical judgment, exactly like the
         // quiet-check (VALUE_BISHOP) branch already does below.
         if (IS_CHECKING_MOVE(mv) && (TRUE == fGeneratedChecks))
         {
@@ -1590,7 +1600,7 @@ _ShouldWeConsiderThisMove(IN SEARCHER_THREAD_CONTEXT *ctx,
                 return(fConsider);
             }
             {
-                FLAG fConsider = (GetCheckSee(ctx, mv, uMoveNum) >= 0);
+                FLAG fConsider = (GetMoveSee(ctx, mv, uMoveNum) >= 0);
 #ifdef CALIBRATE_QSEARCH_FUTILITY
                 if (FALSE == fConsider)
                 {
@@ -1640,7 +1650,7 @@ _ShouldWeConsiderThisMove(IN SEARCHER_THREAD_CONTEXT *ctx,
             return(TRUE);
         }
         {
-            FLAG fConsider = (GetCheckSee(ctx, mv, uMoveNum) >= 0);
+            FLAG fConsider = (GetMoveSee(ctx, mv, uMoveNum) >= 0);
 #ifdef CALIBRATE_QSEARCH_FUTILITY
             if (FALSE == fConsider)
             {