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/********************* */
/*! \file proof_node_algorithm.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 Implementation of proof node algorithm utilities
**/
#include "expr/proof_node_algorithm.h"
namespace CVC4 {
namespace expr {
void getFreeAssumptions(ProofNode* pn, std::vector<Node>& assump)
{
std::map<Node, std::vector<ProofNode*>> amap;
getFreeAssumptionsMap(pn, amap);
for (const std::pair<const Node, std::vector<ProofNode*>>& p : amap)
{
assump.push_back(p.first);
}
}
void getFreeAssumptionsMap(ProofNode* pn,
std::map<Node, std::vector<ProofNode*>>& amap)
{
// proof should not be cyclic
// visited set false after preorder traversal, true after postorder traversal
std::unordered_map<ProofNode*, bool> visited;
std::unordered_map<ProofNode*, bool>::iterator it;
std::vector<ProofNode*> visit;
// Maps a bound assumption to the number of bindings it is under
// e.g. in (SCOPE (SCOPE (ASSUME x) (x y)) (y)), y would be mapped to 2 at
// (ASSUME x), and x would be mapped to 1.
//
// This map is used to track which nodes are in scope while traversing the
// DAG. The in-scope assumptions are keys in the map. They're removed when
// their binding count drops to zero. Let's annotate the above example to
// serve as an illustration:
//
// (SCOPE0 (SCOPE1 (ASSUME x) (x y)) (y))
//
// This is how the map changes during the traversal:
// after previsiting SCOPE0: { y: 1 }
// after previsiting SCOPE1: { y: 2, x: 1 }
// at ASSUME: { y: 2, x: 1 } (so x is in scope!)
// after postvisiting SCOPE1: { y: 1 }
// after postvisiting SCOPE2: {}
//
std::unordered_map<Node, uint32_t, NodeHashFunction> scopeDepth;
ProofNode* cur;
visit.push_back(pn);
do
{
cur = visit.back();
visit.pop_back();
it = visited.find(cur);
const std::vector<Node>& cargs = cur->getArguments();
if (it == visited.end())
{
visited[cur] = true;
PfRule id = cur->getRule();
if (id == PfRule::ASSUME)
{
Assert(cargs.size() == 1);
Node f = cargs[0];
if (!scopeDepth.count(f))
{
amap[f].push_back(cur);
}
}
else
{
if (id == PfRule::SCOPE)
{
// mark that its arguments are bound in the current scope
for (const Node& a : cargs)
{
scopeDepth[a] += 1;
}
// will need to unbind the variables below
visited[cur] = false;
visit.push_back(cur);
}
// The following loop cannot be merged with the loop above because the
// same subproof
const std::vector<std::shared_ptr<ProofNode>>& cs = cur->getChildren();
for (const std::shared_ptr<ProofNode>& cp : cs)
{
visit.push_back(cp.get());
}
}
}
else if (!it->second)
{
visited[cur] = true;
Assert(cur->getRule() == PfRule::SCOPE);
// unbind its assumptions
for (const Node& a : cargs)
{
auto scopeCt = scopeDepth.find(a);
Assert(scopeCt != scopeDepth.end());
scopeCt->second -= 1;
if (scopeCt->second == 0)
{
scopeDepth.erase(scopeCt);
}
}
}
} while (!visit.empty());
}
} // namespace expr
} // namespace CVC4
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