ADT: Add DAGDeltaAlgorithm, which is a DAG minimization algorithm built on top of the standard 'delta debugging' algorithm.

- This can give substantial speedups in the delta process for inputs we can construct dependency information for.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105612 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/DAGDeltaAlgorithm.h

@@ -0,0 +1,73 @@
+//===--- DAGDeltaAlgorithm.h - A DAG Minimization Algorithm ----*- C++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_DAGDELTAALGORITHM_H
+#define LLVM_ADT_DAGDELTAALGORITHM_H
+
+#include <vector>
+#include <set>
+
+namespace llvm {
+
+/// DAGDeltaAlgorithm - Implements a "delta debugging" algorithm for minimizing
+/// directed acyclic graphs using a predicate function.
+///
+/// The result of the algorithm is a subset of the input change set which is
+/// guaranteed to satisfy the predicate, assuming that the input set did. For
+/// well formed predicates, the result set is guaranteed to be such that
+/// removing any single element not required by the dependencies on the other
+/// elements would falsify the predicate.
+///
+/// The DAG should be used to represent dependencies in the changes which are
+/// likely to hold across the predicate function. That is, for a particular
+/// changeset S and predicate P:
+///
+///   P(S) => P(S union pred(S))
+///
+/// The minization algorithm uses this dependency information to attempt to
+/// eagerly prune large subsets of changes. As with \see DeltaAlgorithm, the DAG
+/// is not required to satisfy this property, but the algorithm will run
+/// substantially fewer tests with appropriate dependencies. \see DeltaAlgorithm
+/// for more information on the properties which the predicate function itself
+/// should satisfy.
+class DAGDeltaAlgorithm {
+public:
+  typedef unsigned change_ty;
+  typedef std::pair<change_ty, change_ty> edge_ty;
+
+  // FIXME: Use a decent data structure.
+  typedef std::set<change_ty> changeset_ty;
+  typedef std::vector<changeset_ty> changesetlist_ty;
+
+public:
+  /// Run - Minimize the DAG formed by the \arg Changes vertices and the \arg
+  /// Dependencies edges by executing \see ExecuteOneTest() on subsets of
+  /// changes and returning the smallest set which still satisfies the test
+  /// predicate and the input \arg Dependencies.
+  ///
+  /// \param Changes The list of changes.
+  ///
+  /// \param Dependencies The list of dependencies amongst changes. For each
+  /// (x,y) in \arg Dependencies, both x and y must be in \arg Changes. The
+  /// minimization algorithm guarantees that for each tested changed set S, x
+  /// \in S implies y \in S. It is an error to have cyclic dependencies.
+  changeset_ty Run(const changeset_ty &Changes,
+                   const std::vector<edge_ty> &Dependencies);
+
+  /// UpdatedSearchState - Callback used when the search state changes.
+  virtual void UpdatedSearchState(const changeset_ty &Changes,
+                                  const changesetlist_ty &Sets,
+                                  const changeset_ty &Required) {}
+
+  /// ExecuteOneTest - Execute a single test predicate on the change set \arg S.
+  virtual bool ExecuteOneTest(const changeset_ty &S) = 0;
+};
+
+} // end namespace llvm
+
+#endif