Move expand definitions to its own file (#5528)

We are changing our policy on how expand definitions is handled during preprocessing.

This will require some additions to expand definitions handling. This PR makes a standalone module for expanding definitions.

1 files changed, 278 insertions, 0 deletions

diff --git a/src/smt/expand_definitions.cpp b/src/smt/expand_definitions.cpp
new file mode 100644
index 000000000..20c4f8ef6
--- /dev/null
+++ b/src/smt/expand_definitions.cpp
@@ -0,0 +1,278 @@
+/*********************                                                        */
+/*! \file expand_definitions.cpp
+ ** \verbatim
+ ** Top contributors (to current version):
+ **   Andrew Reynolds, Tim King, Haniel Barbosa
+ ** 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 Implementation of expand definitions for an SMT engine.
+ **/
+
+#include "smt/expand_definitions.h"
+
+#include <stack>
+#include <utility>
+
+#include "expr/node_manager_attributes.h"
+#include "smt/defined_function.h"
+#include "smt/smt_engine.h"
+#include "theory/theory_engine.h"
+
+using namespace CVC4::preprocessing;
+using namespace CVC4::theory;
+using namespace CVC4::kind;
+
+namespace CVC4 {
+namespace smt {
+
+ExpandDefs::ExpandDefs(SmtEngine& smt,
+                       ResourceManager& rm,
+                       SmtEngineStatistics& stats)
+    : d_smt(smt), d_resourceManager(rm), d_smtStats(stats)
+{
+}
+
+ExpandDefs::~ExpandDefs() {}
+
+Node ExpandDefs::expandDefinitions(
+    TNode n,
+    std::unordered_map<Node, Node, NodeHashFunction>& cache,
+    bool expandOnly)
+{
+  NodeManager* nm = d_smt.getNodeManager();
+  std::stack<std::tuple<Node, Node, bool>> worklist;
+  std::stack<Node> result;
+  worklist.push(std::make_tuple(Node(n), Node(n), false));
+  // The worklist is made of triples, each is input / original node then the
+  // output / rewritten node and finally a flag tracking whether the children
+  // have been explored (i.e. if this is a downward or upward pass).
+
+  do
+  {
+    d_resourceManager.spendResource(ResourceManager::Resource::PreprocessStep);
+
+    // n is the input / original
+    // node is the output / result
+    Node node;
+    bool childrenPushed;
+    std::tie(n, node, childrenPushed) = worklist.top();
+    worklist.pop();
+
+    // Working downwards
+    if (!childrenPushed)
+    {
+      Kind k = n.getKind();
+
+      // we can short circuit (variable) leaves
+      if (n.isVar())
+      {
+        SmtEngine::DefinedFunctionMap* dfuns = d_smt.getDefinedFunctionMap();
+        SmtEngine::DefinedFunctionMap::const_iterator i = dfuns->find(n);
+        if (i != dfuns->end())
+        {
+          Node f = (*i).second.getFormula();
+          // must expand its definition
+          Node fe = expandDefinitions(f, cache, expandOnly);
+          // replacement must be closed
+          if ((*i).second.getFormals().size() > 0)
+          {
+            result.push(
+                nm->mkNode(LAMBDA,
+                           nm->mkNode(BOUND_VAR_LIST, (*i).second.getFormals()),
+                           fe));
+            continue;
+          }
+          // don't bother putting in the cache
+          result.push(fe);
+          continue;
+        }
+        // don't bother putting in the cache
+        result.push(n);
+        continue;
+      }
+
+      // maybe it's in the cache
+      std::unordered_map<Node, Node, NodeHashFunction>::iterator cacheHit =
+          cache.find(n);
+      if (cacheHit != cache.end())
+      {
+        TNode ret = (*cacheHit).second;
+        result.push(ret.isNull() ? n : ret);
+        continue;
+      }
+
+      // otherwise expand it
+      bool doExpand = false;
+      if (k == APPLY_UF)
+      {
+        // Always do beta-reduction here. The reason is that there may be
+        // operators such as INTS_MODULUS in the body of the lambda that would
+        // otherwise be introduced by beta-reduction via the rewriter, but are
+        // not expanded here since the traversal in this function does not
+        // traverse the operators of nodes. Hence, we beta-reduce here to
+        // ensure terms in the body of the lambda are expanded during this
+        // call.
+        if (n.getOperator().getKind() == LAMBDA)
+        {
+          doExpand = true;
+        }
+        else
+        {
+          // We always check if this operator corresponds to a defined function.
+          doExpand = d_smt.isDefinedFunction(n.getOperator().toExpr());
+        }
+      }
+      if (doExpand)
+      {
+        std::vector<Node> formals;
+        TNode fm;
+        if (n.getOperator().getKind() == LAMBDA)
+        {
+          TNode op = n.getOperator();
+          // lambda
+          for (unsigned i = 0; i < op[0].getNumChildren(); i++)
+          {
+            formals.push_back(op[0][i]);
+          }
+          fm = op[1];
+        }
+        else
+        {
+          // application of a user-defined symbol
+          TNode func = n.getOperator();
+          SmtEngine::DefinedFunctionMap* dfuns = d_smt.getDefinedFunctionMap();
+          SmtEngine::DefinedFunctionMap::const_iterator i = dfuns->find(func);
+          if (i == dfuns->end())
+          {
+            throw TypeCheckingException(
+                n.toExpr(),
+                std::string("Undefined function: `") + func.toString() + "'");
+          }
+          DefinedFunction def = (*i).second;
+          formals = def.getFormals();
+
+          if (Debug.isOn("expand"))
+          {
+            Debug("expand") << "found: " << n << std::endl;
+            Debug("expand") << " func: " << func << std::endl;
+            std::string name = func.getAttribute(expr::VarNameAttr());
+            Debug("expand") << "     : \"" << name << "\"" << std::endl;
+          }
+          if (Debug.isOn("expand"))
+          {
+            Debug("expand") << " defn: " << def.getFunction() << std::endl
+                            << "       [";
+            if (formals.size() > 0)
+            {
+              copy(formals.begin(),
+                   formals.end() - 1,
+                   std::ostream_iterator<Node>(Debug("expand"), ", "));
+              Debug("expand") << formals.back();
+            }
+            Debug("expand")
+                << "]" << std::endl
+                << "       " << def.getFunction().getType() << std::endl
+                << "       " << def.getFormula() << std::endl;
+          }
+
+          fm = def.getFormula();
+        }
+
+        Node instance = fm.substitute(formals.begin(),
+                                      formals.end(),
+                                      n.begin(),
+                                      n.begin() + formals.size());
+        Debug("expand") << "made : " << instance << std::endl;
+
+        Node expanded = expandDefinitions(instance, cache, expandOnly);
+        cache[n] = (n == expanded ? Node::null() : expanded);
+        result.push(expanded);
+        continue;
+      }
+      else if (!expandOnly)
+      {
+        // do not do any theory stuff if expandOnly is true
+
+        theory::Theory* t = d_smt.getTheoryEngine()->theoryOf(node);
+
+        Assert(t != NULL);
+        TrustNode trn = t->expandDefinition(n);
+        node = trn.isNull() ? Node(n) : trn.getNode();
+      }
+
+      // the partial functions can fall through, in which case we still
+      // consider their children
+      worklist.push(std::make_tuple(
+          Node(n), node, true));  // Original and rewritten result
+
+      for (size_t i = 0; i < node.getNumChildren(); ++i)
+      {
+        worklist.push(
+            std::make_tuple(node[i],
+                            node[i],
+                            false));  // Rewrite the children of the result only
+      }
+    }
+    else
+    {
+      // Working upwards
+      // Reconstruct the node from it's (now rewritten) children on the stack
+
+      Debug("expand") << "cons : " << node << std::endl;
+      if (node.getNumChildren() > 0)
+      {
+        // cout << "cons : " << node << std::endl;
+        NodeBuilder<> nb(node.getKind());
+        if (node.getMetaKind() == metakind::PARAMETERIZED)
+        {
+          Debug("expand") << "op   : " << node.getOperator() << std::endl;
+          // cout << "op   : " << node.getOperator() << std::endl;
+          nb << node.getOperator();
+        }
+        for (size_t i = 0, nchild = node.getNumChildren(); i < nchild; ++i)
+        {
+          Assert(!result.empty());
+          Node expanded = result.top();
+          result.pop();
+          // cout << "exchld : " << expanded << std::endl;
+          Debug("expand") << "exchld : " << expanded << std::endl;
+          nb << expanded;
+        }
+        node = nb;
+      }
+      // Only cache once all subterms are expanded
+      cache[n] = n == node ? Node::null() : node;
+      result.push(node);
+    }
+  } while (!worklist.empty());
+
+  AlwaysAssert(result.size() == 1);
+
+  return result.top();
+}
+
+void ExpandDefs::expandAssertions(AssertionPipeline& assertions,
+                                  bool expandOnly)
+{
+  Chat() << "expanding definitions in assertions..." << std::endl;
+  Trace("simplify") << "ExpandDefs::simplify(): expanding definitions"
+                    << std::endl;
+  TimerStat::CodeTimer codeTimer(d_smtStats.d_definitionExpansionTime);
+  std::unordered_map<Node, Node, NodeHashFunction> cache;
+  for (size_t i = 0, nasserts = assertions.size(); i < nasserts; ++i)
+  {
+    Node assert = assertions[i];
+    Node expd = expandDefinitions(assert, cache, expandOnly);
+    if (expd != assert)
+    {
+      assertions.replace(i, expd);
+    }
+  }
+}
+
+}  // namespace smt
+}  // namespace CVC4