1//===- DAGDeltaAlgorithm.h - A DAG Minimization Algorithm ------*- C++ -*--===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//===----------------------------------------------------------------------===//
7
8#ifndef LLVM_ADT_DAGDELTAALGORITHM_H
9#define LLVM_ADT_DAGDELTAALGORITHM_H
10
11#include <set>
12#include <utility>
13#include <vector>
14
15namespace llvm {
16
17/// DAGDeltaAlgorithm - Implements a "delta debugging" algorithm for minimizing
18/// directed acyclic graphs using a predicate function.
19///
20/// The result of the algorithm is a subset of the input change set which is
21/// guaranteed to satisfy the predicate, assuming that the input set did. For
22/// well formed predicates, the result set is guaranteed to be such that
23/// removing any single element not required by the dependencies on the other
24/// elements would falsify the predicate.
25///
26/// The DAG should be used to represent dependencies in the changes which are
27/// likely to hold across the predicate function. That is, for a particular
28/// changeset S and predicate P:
29///
30///   P(S) => P(S union pred(S))
31///
32/// The minimization algorithm uses this dependency information to attempt to
33/// eagerly prune large subsets of changes. As with \see DeltaAlgorithm, the DAG
34/// is not required to satisfy this property, but the algorithm will run
35/// substantially fewer tests with appropriate dependencies. \see DeltaAlgorithm
36/// for more information on the properties which the predicate function itself
37/// should satisfy.
38class DAGDeltaAlgorithm {
39  virtual void anchor();
40
41public:
42  using change_ty = unsigned;
43  using edge_ty = std::pair<change_ty, change_ty>;
44
45  // FIXME: Use a decent data structure.
46  using changeset_ty = std::set<change_ty>;
47  using changesetlist_ty = std::vector<changeset_ty>;
48
49public:
50  virtual ~DAGDeltaAlgorithm() = default;
51
52  /// Run - Minimize the DAG formed by the \p Changes vertices and the
53  /// \p Dependencies edges by executing \see ExecuteOneTest() on subsets of
54  /// changes and returning the smallest set which still satisfies the test
55  /// predicate and the input \p Dependencies.
56  ///
57  /// \param Changes The list of changes.
58  ///
59  /// \param Dependencies The list of dependencies amongst changes. For each
60  /// (x,y) in \p Dependencies, both x and y must be in \p Changes. The
61  /// minimization algorithm guarantees that for each tested changed set S,
62  /// \f$ x \in S \f$ implies \f$ y \in S \f$. It is an error to have cyclic
63  /// dependencies.
64  changeset_ty Run(const changeset_ty &Changes,
65                   const std::vector<edge_ty> &Dependencies);
66
67  /// UpdatedSearchState - Callback used when the search state changes.
68  virtual void UpdatedSearchState(const changeset_ty &Changes,
69                                  const changesetlist_ty &Sets,
70                                  const changeset_ty &Required) {}
71
72  /// ExecuteOneTest - Execute a single test predicate on the change set \p S.
73  virtual bool ExecuteOneTest(const changeset_ty &S) = 0;
74};
75
76} // end namespace llvm
77
78#endif // LLVM_ADT_DAGDELTAALGORITHM_H
79