DRAT-Optimization (#2971)

This commit enables DRAT-optimization, which consists of two sub-processes:
1. removing unnecessary instructions from DRAT-proofs and
2. not proving clauses which are not needed by DRAT proofs.

These changes have the effect of dramatically shortening some some bit-vector proofs. Specifically,  proofs using lemmas in the ER, DRAT, and LRAT formats, since proofs in any of these formats are derived from a (now optimized!) DRAT proof produced by CryptoMiniSat. What follows is a description of the main parts of this PR:

## DRAT Optimization

The DRAT-optimization is done by `drat-trim`, which is bundled with `drat2er`. The (new) function `ClausalBitVectorProof::optimizeDratProof` is our interface to the optimization machinery, and most of the new logic in this PR is in that function.

## CNF Representation

The ability to not prove unused clauses requires a slight architectural change as well. In particular, we need to be able to describe **which** subset of the original clause set actually needs to be proved. To facilitate this, when the clause set for CryptoMiniSat is first formed it is represented as a (a) map from clause indices to clauses and (b) a list of indices. Then, when the CNF is optimized, we temporarily store a new list of the clauses in the optimized formula. This change in representation requires a number of small tweaks throughout the code.

## Small Fixes to Signatures

When we decided to check and accept two different kinds of DRAT, some of our DRAT-checking broke. In particular, when supporting one kind of DRAT, it is okay to `fail` (crash) when a proof fails to check. If you're supporting two kinds of DRAT, crashing in response to the first checker rejecting the proof denies the second checker an opportunity to check the proof. This PR tweaks the signatures slightly (and soundly!) to do something else instead of `fail`ing. 

1 files changed, 13 insertions, 8 deletions

diff --git a/src/proof/er/er_proof.h b/src/proof/er/er_proof.h
index f5af0783b..d6cbd9213 100644
--- a/src/proof/er/er_proof.h
+++ b/src/proof/er/er_proof.h
@@ -27,6 +27,7 @@
 #define CVC4__PROOF__ER__ER_PROOF_H
 
 #include <memory>
+#include <unordered_map>
 #include <vector>
 
 #include "proof/clause_id.h"
@@ -36,8 +37,6 @@ namespace CVC4 {
 namespace proof {
 namespace er {
 
-using ClauseUseRecord = std::vector<std::pair<ClauseId, prop::SatClause>>;
-
 /**
  * A definition of the form:
  *    newVar <-> p v (~x_1 ^ ~x_2 ^ ... ^ ~x_n)
@@ -116,11 +115,14 @@ class ErProof
   /**
    * Construct an ER proof from a DRAT proof, using drat2er
    *
-   * @param usedClauses The CNF formula that we're deriving bottom from.
-   * @param dratBinary  The DRAT proof from the SAT solver, as a binary stream.
+   * @param clauses A store of clauses that might be in our formula
+   * @param usedIds the ids of clauses that are actually in our formula
+   * @param dratBinary  The DRAT proof from the SAT solver, as a binary stream
    */
-  static ErProof fromBinaryDratProof(const ClauseUseRecord& usedClauses,
-                                     const std::string& dratBinary);
+  static ErProof fromBinaryDratProof(
+      const std::unordered_map<ClauseId, prop::SatClause>& clauses,
+      const std::vector<ClauseId>& usedIds,
+      const std::string& dratBinary);
 
   /**
    * Construct an ER proof from a TRACECHECK ER proof
@@ -128,10 +130,13 @@ class ErProof
    * This basically just identifies groups of lines which correspond to
    * definitions, and extracts them.
    *
-   * @param usedClauses The CNF formula that we're deriving bottom from.
+   * @param clauses A store of clauses that might be in our formula
+   * @param usedIds the ids of clauses that are actually in our formula
    * @param tracecheck  The TRACECHECK proof, as a stream.
    */
-  ErProof(const ClauseUseRecord& usedClauses, TraceCheckProof&& tracecheck);
+  ErProof(const std::unordered_map<ClauseId, prop::SatClause>& clauses,
+          const std::vector<ClauseId>& usedIds,
+          TraceCheckProof&& tracecheck);
 
   /**
    * Write the ER proof as an LFSC value of type (holds cln).