1//===- DAGDeltaAlgorithm.h - A DAG Minimization Algorithm ------*- C++ -*--===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//===----------------------------------------------------------------------===//
8
9#ifndef LLVM_ADT_DAGDELTAALGORITHM_H
10#define LLVM_ADT_DAGDELTAALGORITHM_H
11
12#include <set>
13#include <utility>
14#include <vector>
15
16namespace llvm {
17
18/// DAGDeltaAlgorithm - Implements a "delta debugging" algorithm for minimizing
19/// directed acyclic graphs using a predicate function.
20///
21/// The result of the algorithm is a subset of the input change set which is
22/// guaranteed to satisfy the predicate, assuming that the input set did. For
23/// well formed predicates, the result set is guaranteed to be such that
24/// removing any single element not required by the dependencies on the other
25/// elements would falsify the predicate.
26///
27/// The DAG should be used to represent dependencies in the changes which are
28/// likely to hold across the predicate function. That is, for a particular
29/// changeset S and predicate P:
30///
31///   P(S) => P(S union pred(S))
32///
33/// The minization algorithm uses this dependency information to attempt to
34/// eagerly prune large subsets of changes. As with \see DeltaAlgorithm, the DAG
35/// is not required to satisfy this property, but the algorithm will run
36/// substantially fewer tests with appropriate dependencies. \see DeltaAlgorithm
37/// for more information on the properties which the predicate function itself
38/// should satisfy.
39class DAGDeltaAlgorithm {
40  virtual void anchor();
41
42public:
43  using change_ty = unsigned;
44  using edge_ty = std::pair<change_ty, change_ty>;
45
46  // FIXME: Use a decent data structure.
47  using changeset_ty = std::set<change_ty>;
48  using changesetlist_ty = std::vector<changeset_ty>;
49
50public:
51  virtual ~DAGDeltaAlgorithm() = default;
52
53  /// Run - Minimize the DAG formed by the \p Changes vertices and the
54  /// \p Dependencies edges by executing \see ExecuteOneTest() on subsets of
55  /// changes and returning the smallest set which still satisfies the test
56  /// predicate and the input \p Dependencies.
57  ///
58  /// \param Changes The list of changes.
59  ///
60  /// \param Dependencies The list of dependencies amongst changes. For each
61  /// (x,y) in \p Dependencies, both x and y must be in \p Changes. The
62  /// minimization algorithm guarantees that for each tested changed set S,
63  /// \f$ x \in S \f$ implies \f$ y \in S \f$. It is an error to have cyclic
64  /// dependencies.
65  changeset_ty Run(const changeset_ty &Changes,
66                   const std::vector<edge_ty> &Dependencies);
67
68  /// UpdatedSearchState - Callback used when the search state changes.
69  virtual void UpdatedSearchState(const changeset_ty &Changes,
70                                  const changesetlist_ty &Sets,
71                                  const changeset_ty &Required) {}
72
73  /// ExecuteOneTest - Execute a single test predicate on the change set \p S.
74  virtual bool ExecuteOneTest(const changeset_ty &S) = 0;
75};
76
77} // end namespace llvm
78
79#endif // LLVM_ADT_DAGDELTAALGORITHM_H
80