(proof-new) SMT Preprocess proof generator (#4708)

This adds the proof generator for storing proofs of preprocessing. It stores assertions added via preprocessing passes and their rewrites. This utility will eventually live in SmtEngine.

It also adds 2 new proof rules, and fixes an issue in ProofNodeUpdater.

2 files changed, 220 insertions, 0 deletions

diff --git a/src/smt/preprocess_proof_generator.cpp b/src/smt/preprocess_proof_generator.cpp
new file mode 100644
index 000000000..969ffa9bb
--- /dev/null
+++ b/src/smt/preprocess_proof_generator.cpp
@@ -0,0 +1,139 @@
+/*********************                                                        */
+/*! \file preprocess_proof_generator.cpp
+ ** \verbatim
+ ** Top contributors (to current version):
+ **   Andrew Reynolds
+ ** This file is part of the CVC4 project.
+ ** Copyright (c) 2009-2020 by the authors listed in the file AUTHORS
+ ** in the top-level source directory) and their institutional affiliations.
+ ** All rights reserved.  See the file COPYING in the top-level source
+ ** directory for licensing information.\endverbatim
+ **
+ ** \brief The implementation of the module for proofs for preprocessing in an
+ ** SMT engine.
+ **/
+
+#include "smt/preprocess_proof_generator.h"
+
+#include "expr/proof.h"
+#include "theory/rewriter.h"
+
+namespace CVC4 {
+namespace smt {
+
+PreprocessProofGenerator::PreprocessProofGenerator(ProofNodeManager* pnm)
+    : d_pnm(pnm)
+{
+}
+
+void PreprocessProofGenerator::notifyNewAssert(Node n, ProofGenerator* pg)
+{
+  Trace("smt-proof-pp-debug") << "- notifyNewAssert: " << n << std::endl;
+  d_src[n] = theory::TrustNode::mkTrustLemma(n, pg);
+}
+
+void PreprocessProofGenerator::notifyPreprocessed(Node n,
+                                                  Node np,
+                                                  ProofGenerator* pg)
+{
+  // only keep if indeed it rewrote
+  if (n != np)
+  {
+    Trace("smt-proof-pp-debug")
+        << "- notifyPreprocessed: " << n << "..." << np << std::endl;
+    d_src[np] = theory::TrustNode::mkTrustRewrite(n, np, pg);
+  }
+}
+
+std::shared_ptr<ProofNode> PreprocessProofGenerator::getProofFor(Node f)
+{
+  std::map<Node, theory::TrustNode>::iterator it = d_src.find(f);
+  if (it == d_src.end())
+  {
+    // could be an assumption, return nullptr
+    return nullptr;
+  }
+  // make CDProof to construct the proof below
+  CDProof cdp(d_pnm);
+
+  Node curr = f;
+  std::vector<Node> transChildren;
+  bool success;
+  do
+  {
+    success = false;
+    if (it != d_src.end())
+    {
+      Assert(it->second.getNode() == curr);
+      bool proofStepProcessed = false;
+      std::shared_ptr<ProofNode> pfr = it->second.toProofNode();
+      if (pfr != nullptr)
+      {
+        Assert(pfr->getResult() == it->second.getProven());
+        cdp.addProof(pfr);
+        proofStepProcessed = true;
+      }
+
+      if (it->second.getKind() == theory::TrustNodeKind::REWRITE)
+      {
+        Node eq = it->second.getProven();
+        Assert(eq.getKind() == kind::EQUAL);
+        if (!proofStepProcessed)
+        {
+          // maybe its just a simple rewrite?
+          if (eq[1] == theory::Rewriter::rewrite(eq[0]))
+          {
+            cdp.addStep(eq, PfRule::REWRITE, {}, {eq[0]});
+            proofStepProcessed = true;
+          }
+        }
+        transChildren.push_back(eq);
+        // continue with source
+        curr = eq[0];
+        success = true;
+        // find the next node
+        it = d_src.find(curr);
+      }
+      else
+      {
+        Assert(it->second.getKind() == theory::TrustNodeKind::LEMMA);
+      }
+
+      if (!proofStepProcessed)
+      {
+        // add trusted step
+        Node proven = it->second.getProven();
+        cdp.addStep(proven, PfRule::PREPROCESS, {}, {proven});
+      }
+    }
+  } while (success);
+
+  Assert(curr != f);
+  // prove ( curr == f )
+  Node fullRewrite = curr.eqNode(f);
+  if (transChildren.size() >= 2)
+  {
+    cdp.addStep(fullRewrite, PfRule::TRANS, transChildren, {});
+  }
+  // prove f
+  cdp.addStep(f, PfRule::EQ_RESOLVE, {curr, fullRewrite}, {});
+
+  // overall, proof is:
+  //        --------- from proof generator       ---------- from proof generator
+  //        F_1 = F_2          ...               F_{n-1} = F_n
+  // ---?   -------------------------------------------------- TRANS
+  // F_1    F_1 = F_n
+  // ---------------- EQ_RESOLVE
+  // F_n
+  // Note F_1 may have been given a proof if it was not an input assumption.
+
+  return cdp.getProofFor(f);
+}
+
+std::string PreprocessProofGenerator::identify() const
+{
+  return "PreprocessProofGenerator";
+}
+
+}  // namespace smt
+}  // namespace CVC4
diff --git a/src/smt/preprocess_proof_generator.h b/src/smt/preprocess_proof_generator.h
new file mode 100644
index 000000000..3b960b051
--- /dev/null
+++ b/src/smt/preprocess_proof_generator.h
@@ -0,0 +1,81 @@
+/*********************                                                        */
+/*! \file preprocess_proof_generator.h
+ ** \verbatim
+ ** Top contributors (to current version):
+ **   Andrew Reynolds
+ ** This file is part of the CVC4 project.
+ ** Copyright (c) 2009-2020 by the authors listed in the file AUTHORS
+ ** in the top-level source directory) and their institutional affiliations.
+ ** All rights reserved.  See the file COPYING in the top-level source
+ ** directory for licensing information.\endverbatim
+ **
+ ** \brief The module for proofs for preprocessing in an SMT engine.
+ **/
+
+#include "cvc4_private.h"
+
+#ifndef CVC4__SMT__PREPROCESS_PROOF_GENERATOR_H
+#define CVC4__SMT__PREPROCESS_PROOF_GENERATOR_H
+
+#include <map>
+
+#include "expr/proof_generator.h"
+#include "expr/proof_node_manager.h"
+#include "theory/trust_node.h"
+
+namespace CVC4 {
+namespace smt {
+
+/**
+ * A proof generator storing proofs of preprocessing. This has two main
+ * interfaces during solving:
+ * (1) notifyNewAssert, for assertions that are not part of the input and are
+ * added by preprocessing passes,
+ * (2) notifyPreprocessed, which is called when a preprocessing pass rewrites
+ * an assertion into another.
+ * Notice that input assertions do not need to be provided to this class.
+ *
+ * Its getProofFor method produces a proof for a preprocessed assertion
+ * whose free assumptions are intended to be input assertions, which are
+ * implictly all assertions that are not notified to this class.
+ */
+class PreprocessProofGenerator : public ProofGenerator
+{
+ public:
+  PreprocessProofGenerator(ProofNodeManager* pnm);
+  ~PreprocessProofGenerator() {}
+  /**
+   * Notify that n is a new assertion, where pg can provide a proof of n.
+   */
+  void notifyNewAssert(Node n, ProofGenerator* pg);
+  /**
+   * Notify that n was replaced by np due to preprocessing, where pg can
+   * provide a proof of the equality n=np.
+   */
+  void notifyPreprocessed(Node n, Node np, ProofGenerator* pg);
+  /**
+   * Get proof for f, which returns a proof based on proving an equality based
+   * on transitivity of preprocessing steps, and then using the original
+   * assertion with EQ_RESOLVE to obtain the proof of the ending assertion f.
+   */
+  std::shared_ptr<ProofNode> getProofFor(Node f) override;
+  /** Identify */
+  std::string identify() const override;
+
+ private:
+  /** The proof node manager */
+  ProofNodeManager* d_pnm;
+  /**
+   * The trust node that was the source of each node constructed during
+   * preprocessing. For each n, d_src[n] is a trust node whose node is n. This
+   * can either be:
+   * (1) A trust node REWRITE proving (n_src = n) for some n_src, or
+   * (2) A trust node LEMMA proving n.
+   */
+  std::map<Node, theory::TrustNode> d_src;
+};
+
+}  // namespace smt
+}  // namespace CVC4
+
+#endif