Remove RescoreMovesViaSearch's dead same-ply recursive pre-call.

Before searching its own move list, RescoreMovesViaSearch called itself
recursively at an even shallower depth, at the *same* ctx->uPly, on the
theory that the extra rescore's side effects (hash/killer/history table
population) would help the real loop's own -Search() calls find cutoffs
faster. But the recursive call's own iValue writes were always fully
overwritten by this same call's loop immediately after it (same ply,
same move-stack range), so the only way it could possibly help was via
those side effects.

Measured directly: disabling it produced a bit-identical result across
all three test suites (ecm_ringers.ep_, ecm_confident_quick.ep_,
ecm_hard_quick.ep_ at sn=5M) -- no change whatsoever, not even a single
position. It was pure wasted search effort. Removed.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YGSMkwjqiCk4XhbfN7ugD2

1 files changed, 12 insertions, 5 deletions

diff --git a/src/searchsup.c b/src/searchsup.c
index efdde67..8bc74ef 100644
--- a/src/searchsup.c
+++ b/src/searchsup.c
@@ -626,13 +626,20 @@ Return value:
     ASSERT(uDepth >= (IID_R_FACTOR + ONE_PLY));
 
     //
-    // Compute next depth, possibly recurse
+    // Compute next depth.
     //
+    // This used to recurse here first (call itself at this same
+    // ctx->uPly, before the loop below), on the theory that an even
+    // shallower rescore's *side effects* -- hash/killer/history table
+    // population -- would help the loop below's own -Search() calls
+    // find cutoffs faster. Measured (see lmr_testing/RESULTS.md): removing
+    // it entirely produced a bit-identical result on all three test
+    // suites (ecm_ringers/confident_quick/hard_quick). Its own writes to
+    // iValue were always fully overwritten by this same call's loop
+    // right after it (same ctx->uPly, same move-stack range), so it had
+    // no way to help other than those side effects, and empirically it
+    // wasn't -- just wasted nodes. Removed.
     uDepth -= (IID_R_FACTOR + ONE_PLY);
-    if (uDepth >= (IID_R_FACTOR + ONE_PLY))
-    {
-        (void)RescoreMovesViaSearch(ctx, uDepth, iAlpha, iBeta);
-    }
     ASSERT(uDepth < MAX_DEPTH_PER_SEARCH);
 
     //