user15223: As I understand it, engines use so-called "bitboards" to generate the current position & possible moves. I'm wondering if any engine uses the pawn bitboard to refine its search and eval.
To illustrate what I mean, suppose this is the current pawn structure:
[FEN "8/8/8/2p5/1pPp4/pP1P4/P7/B7 w - - 0 1"]

In this pawn structure, impose massive penalties for the Bishop on a1 because it's more or less permanently stuck.
[FEN "8/1pp4p/p2p4/3Pp1p1/2P1Pp2/5P2/PP4PP/8 w - - 0 1"]

In this pawn structure, as White, prioritize searching variations that include the moves b4-c5, and as Black, prioritize searching variations that include h5-g4.
I don't know how many possible pawn bitboards are there, but presumably not too many arise in serious play (a couple hundred perhaps) and one could have handwritten functions for all of them. Some bitboards could even be duplicated, e.g. in the second bitboard it doesn't matter if Black's pawn is on h7 or h6, general plans for both sides remain the same. If there are no special plans for the current pawn structure, one could also default to the current search/eval algorithms.
Question: Is this idea feasible? If so, are there any engines that use it? If not, why not?
EDIT: seems to me that traditional engines could really use something like this, e.g. in this game no less an engine than Stockfish falls into this trap, when in spite of having a firmly entombed bishop, it thought its position was superior.
[FEN "2r3k1/p2n1r2/4q3/2Pp2b1/PP4p1/B4pPp/2Q2P1P/R2R2KB w - - 1 30"]


user19281: Something very similar is doubtless encoded into AlphaZero and Leela's neural network evaluators, which are very positional.  Most conventional Minimax engines, by contrast, are stronger at tactics and can therefore search very deeply.
Pawn structure is indeed a factor in most of the top engines' evaluation.  This might take the relatively simple form of rewarding connected pawns and penalising isolated and doubled pawns.  The pawn bitboards are mainly a means of recognising when the pawn structure changes (which happens relatively infrequently once established) and recalculating that factor of the evaluation, thereby saving some calculation time.
However, the pawn structure does not directly lead to the bishop mobility analysis you note in your first example.  This would be deferred to threat and control maps, which would put any of the bishop's legal moves low on the priority list for further analysis, since they leave the bishop on a threatened square with no support.

15223: <p>As I understand it, engines use so-called "bitboards" to generate the current position &amp; possible moves. I'm wondering if any engine uses the pawn bitboard to refine its search and eval.</p>

<p>To illustrate what I mean, suppose this is the current pawn structure:</p>

<pre><code>[FEN "8/8/8/2p5/1pPp4/pP1P4/P7/B7 w - - 0 1"]
</code></pre>

<p>In this pawn structure, impose massive penalties for the Bishop on a1 because it's more or less permanently stuck.</p>

<pre><code>[FEN "8/1pp4p/p2p4/3Pp1p1/2P1Pp2/5P2/PP4PP/8 w - - 0 1"]
</code></pre>

<p>In this pawn structure, as White, prioritize searching variations that include the moves b4-c5, and as Black, prioritize searching variations that include h5-g4.</p>

<p>I don't know how many possible pawn bitboards are there, but presumably not too many arise in serious play (a couple hundred perhaps) and one could have handwritten functions for all of them. Some bitboards could even be duplicated, e.g. in the second bitboard it doesn't matter if Black's pawn is on h7 or h6, general plans for both sides remain the same. If there are no special plans for the current pawn structure, one could also default to the current search/eval algorithms.</p>

<p>Question: Is this idea feasible? If so, are there any engines that use it? If not, why not?</p>

<p><strong>EDIT</strong>: seems to me that traditional engines could really use something like this, e.g. in <a href="https://www.tcec-chess.com/archive.html?season=17&amp;div=cpul1redtest1&amp;game=29" rel="nofollow noreferrer">this game</a> no less an engine than Stockfish falls into this trap, when in spite of having a firmly entombed bishop, it thought its position was superior.</p>

<pre><code>[FEN "2r3k1/p2n1r2/4q3/2Pp2b1/PP4p1/B4pPp/2Q2P1P/R2R2KB w - - 1 30"]
</code></pre>
 19281: <p>Something very similar is doubtless encoded into AlphaZero and Leela's neural network evaluators, which are very positional.  Most conventional Minimax engines, by contrast, are stronger at tactics and can therefore search very deeply.</p>

<p>Pawn structure is indeed a factor in most of the top engines' evaluation.  This might take the relatively simple form of rewarding connected pawns and penalising isolated and doubled pawns.  The pawn bitboards are mainly a means of recognising when the pawn structure changes (which happens relatively infrequently once established) and recalculating that factor of the evaluation, thereby saving some calculation time.</p>

<p>However, the pawn structure does not directly lead to the bishop mobility analysis you note in your first example.  This would be deferred to threat and control maps, which would put any of the bishop's legal moves low on the priority list for further analysis, since they leave the bishop on a threatened square with no support.</p>
