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Store distinct upper and lower bound scores

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This is more complex than what I'd like but I
was unable to split in small chunks.

Here we add 2 slots to TTEntry (valueUpper and depthUpper)
so that sizeof(TTEntry) returns to the original 16 bytes
and we can pack exactly 4 entries in a 64 bytes cache line.

Now we save an upper bound score alongside a lower (exact)
score. The idea is to increase TT cut-offs rates becuase
there is now an higher probability for a node to use TT info.

This patch is highly experimental and probably needs further
steps as is hinted by an unrealistic bench number:

bench: 2022385
This commit is contained in:
Marco Costalba
2012-12-09 13:15:50 +01:00
parent 23bdd06442
commit feeafb0a50
4 changed files with 94 additions and 42 deletions
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src/search.cpp
+52 -27
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@@ -482,7 +482,7 @@ namespace {
Key posKey;
Move ttMove, move, excludedMove, bestMove, threatMove;
Depth ext, newDepth;
Value bestValue, value, ttValue;
Value bestValue, value, ttValue, ttValueUpper;
Value eval, nullValue, futilityValue;
bool inCheck, givesCheck, pvMove, singularExtensionNode;
bool captureOrPromotion, dangerous, doFullDepthSearch;
@@ -544,31 +544,43 @@ namespace {
tte = TT.probe(posKey);
ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
ttValueUpper = tte ? value_from_tt(tte->value_upper(), ss->ply) : VALUE_NONE;
// At PV nodes we check for exact scores, while at non-PV nodes we check for
// a fail high/low. Biggest advantage at probing at PV nodes is to have a
// smooth experience in analysis mode. We don't probe at Root nodes otherwise
// we should also update RootMoveList to avoid bogus output.
if ( !RootNode
&& tte
&& tte->depth() >= depth
&& ttValue != VALUE_NONE // Only in case of TT access race
&& ( PvNode ? tte->type() == BOUND_EXACT
: ttValue >= beta ? (tte->type() & BOUND_LOWER)
: (tte->type() & BOUND_UPPER)))
if (!RootNode && tte)
{
TT.refresh(tte);
ss->currentMove = ttMove; // Can be MOVE_NONE
if ( ttValue >= beta
&& ttMove
&& !pos.is_capture_or_promotion(ttMove)
&& ttMove != ss->killers[0])
// Fail High
if ( (tte->type() & BOUND_LOWER)
&& ttValue >= beta
&& tte->depth() >= depth
&& ttValue != VALUE_NONE) // Only in case of TT access race
{
ss->killers[1] = ss->killers[0];
ss->killers[0] = ttMove;
// Update killers, we assume ttMove caused a cut-off
if ( ttMove
&& !pos.is_capture_or_promotion(ttMove)
&& ttMove != ss->killers[0])
{
ss->killers[1] = ss->killers[0];
ss->killers[0] = ttMove;
}
TT.refresh(tte);
ss->currentMove = ttMove; // Can be MOVE_NONE
return ttValue;
}
// Fail Low
if ( (tte->type() & BOUND_UPPER)
&& ttValueUpper < beta
&& tte->depth_upper() >= depth
&& ttValueUpper != VALUE_NONE) // Only in case of TT access race
{
TT.refresh(tte);
ss->currentMove = ttMove; // Can be MOVE_NONE
return ttValueUpper;
}
return ttValue;
}
// Step 5. Evaluate the position statically and update parent's gain statistics
@@ -1089,7 +1101,7 @@ split_point_start: // At split points actual search starts from here
const TTEntry* tte;
Key posKey;
Move ttMove, move, bestMove;
Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
Value bestValue, value, ttValue, ttValueUpper, futilityValue, futilityBase, oldAlpha;
bool givesCheck, enoughMaterial, evasionPrunable, fromNull;
Depth ttDepth;
@@ -1111,21 +1123,34 @@ split_point_start: // At split points actual search starts from here
tte = TT.probe(posKey);
ttMove = tte ? tte->move() : MOVE_NONE;
ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
ttValueUpper = tte ? value_from_tt(tte->value_upper(),ss->ply) : VALUE_NONE;
// Decide whether or not to include checks, this fixes also the type of
// TT entry depth that we are going to use. Note that in qsearch we use
// only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
: DEPTH_QS_NO_CHECKS;
if ( tte
&& tte->depth() >= ttDepth
&& ttValue != VALUE_NONE // Only in case of TT access race
&& ( PvNode ? tte->type() == BOUND_EXACT
: ttValue >= beta ? (tte->type() & BOUND_LOWER)
: (tte->type() & BOUND_UPPER)))
if (tte)
{
ss->currentMove = ttMove; // Can be MOVE_NONE
return ttValue;
// Fail High
if ( (tte->type() & BOUND_LOWER)
&& ttValue >= beta
&& tte->depth() >= ttDepth
&& ttValue != VALUE_NONE) // Only in case of TT access race
{
ss->currentMove = ttMove; // Can be MOVE_NONE
return ttValue;
}
// Fail Low
if ( (tte->type() & BOUND_UPPER)
&& ttValueUpper < beta
&& tte->depth_upper() >= ttDepth
&& ttValueUpper != VALUE_NONE) // Only in case of TT access race
{
ss->currentMove = ttMove; // Can be MOVE_NONE
return ttValueUpper;
}
}
// Evaluate the position statically