From: Marco Costalba <mcostalba@gmail.com>
Date: Thu, 26 Nov 2009 12:44:48 +0000 (+0100)
Subject: Fix a possible crash in excluded search condition
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=5bec768d42fc8ce34b4dc0574ef9f4e61bfd8853

Fix a possible crash in excluded search condition

Due to IID we could have a ttMove and not a tte, or,
even if we have a tte they could belong to different
searches so that the depth and type of tte don't
have the same origin of the ttMove.

To fix this we always use tte entry in excluded search
condition and, after an IID, we reprobe the TT table.

No functional change. Apart from possible crash fix.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---

diff --git a/src/search.cpp b/src/search.cpp
index 0a53225a..7eb04308 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1137,6 +1137,11 @@ namespace {
     {
         search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
         ttMove = ss[ply].pv[ply];
+        tte = TT.retrieve(pos.get_key());
+
+        // Following assert could fail, for instance when we have
+        // moveCount == 0 we return without saving a TT entry.
+        /* assert(tte); */
     }
 
     // Initialize a MovePicker object for the current position, and prepare
@@ -1165,8 +1170,11 @@ namespace {
       // To verify this we do a reduced search on all the other moves but the ttMove,
       // if result is lower then TT value minus a margin then we assume ttMove is the
       // only one playable. It is a kind of relaxed single reply extension.
+      // Note that could be ttMove != tte->move() due to IID, so we always use tte->move()
+      // to avoid aliases when we probe tte->depth() and tte->type()
       if (   depth >= 8 * OnePly
-          && move == ttMove
+          && tte
+          && move == tte->move()
           && ext < OnePly
           && is_lower_bound(tte->type())
           && tte->depth() >= depth - 3 * OnePly)
@@ -1430,6 +1438,7 @@ namespace {
     {
         search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
         ttMove = ss[ply].pv[ply];
+        tte = TT.retrieve(pos.get_key());
     }
 
     // Initialize a MovePicker object for the current position, and prepare
@@ -1467,9 +1476,12 @@ namespace {
       // To verify this we do a reduced search on all the other moves but the ttMove,
       // if result is lower then TT value minus a margin then we assume ttMove is the
       // only one playable. It is a kind of relaxed single reply extension.
+      // Note that could be ttMove != tte->move() due to IID, so we always use tte->move()
+      // to avoid aliases when we probe tte->depth() and tte->type()
       if (   depth >= 8 * OnePly
-          && !excludedMove // do not allow recursive single-reply search
-          && move == ttMove
+          && tte
+          && move == tte->move()
+          && !excludedMove // Do not allow recursive single-reply search
           && ext < OnePly
           && is_lower_bound(tte->type())
           && tte->depth() >= depth - 3 * OnePly)