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       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             : 
      16             : namespace 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.
      39             : class DAGDeltaAlgorithm {
      40             :   virtual void anchor();
      41             : 
      42             : public:
      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             : 
      50             : public:
      51           0 :   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          18 :   virtual void UpdatedSearchState(const changeset_ty &Changes,
      70             :                                   const changesetlist_ty &Sets,
      71          18 :                                   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