include/llvm/ADT/DAGDeltaAlgorithm.h

   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
  15 namespace 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 minization 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.
  38 class DAGDeltaAlgorithm {
  39   virtual void anchor();
  40
  41 public:
  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
  49 public:
  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