1//===--- DeltaAlgorithm.cpp - A Set 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#include "llvm/ADT/DeltaAlgorithm.h"
10#include <algorithm>
11#include <iterator>
12using namespace llvm;
13
14DeltaAlgorithm::~DeltaAlgorithm() {
15}
16
17bool DeltaAlgorithm::GetTestResult(const changeset_ty &Changes) {
18  if (FailedTestsCache.count(Changes))
19    return false;
20
21  bool Result = ExecuteOneTest(Changes);
22  if (!Result)
23    FailedTestsCache.insert(Changes);
24
25  return Result;
26}
27
28void DeltaAlgorithm::Split(const changeset_ty &S, changesetlist_ty &Res) {
29  // FIXME: Allow clients to provide heuristics for improved splitting.
30
31  // FIXME: This is really slow.
32  changeset_ty LHS, RHS;
33  unsigned idx = 0, N = S.size() / 2;
34  for (changeset_ty::const_iterator it = S.begin(),
35         ie = S.end(); it != ie; ++it, ++idx)
36    ((idx < N) ? LHS : RHS).insert(*it);
37  if (!LHS.empty())
38    Res.push_back(LHS);
39  if (!RHS.empty())
40    Res.push_back(RHS);
41}
42
43DeltaAlgorithm::changeset_ty
44DeltaAlgorithm::Delta(const changeset_ty &Changes,
45                      const changesetlist_ty &Sets) {
46  // Invariant: union(Res) == Changes
47  UpdatedSearchState(Changes, Sets);
48
49  // If there is nothing left we can remove, we are done.
50  if (Sets.size() <= 1)
51    return Changes;
52
53  // Look for a passing subset.
54  changeset_ty Res;
55  if (Search(Changes, Sets, Res))
56    return Res;
57
58  // Otherwise, partition the sets if possible; if not we are done.
59  changesetlist_ty SplitSets;
60  for (changesetlist_ty::const_iterator it = Sets.begin(),
61         ie = Sets.end(); it != ie; ++it)
62    Split(*it, SplitSets);
63  if (SplitSets.size() == Sets.size())
64    return Changes;
65
66  return Delta(Changes, SplitSets);
67}
68
69bool DeltaAlgorithm::Search(const changeset_ty &Changes,
70                            const changesetlist_ty &Sets,
71                            changeset_ty &Res) {
72  // FIXME: Parallelize.
73  for (changesetlist_ty::const_iterator it = Sets.begin(),
74         ie = Sets.end(); it != ie; ++it) {
75    // If the test passes on this subset alone, recurse.
76    if (GetTestResult(*it)) {
77      changesetlist_ty Sets;
78      Split(*it, Sets);
79      Res = Delta(*it, Sets);
80      return true;
81    }
82
83    // Otherwise, if we have more than two sets, see if test passes on the
84    // complement.
85    if (Sets.size() > 2) {
86      // FIXME: This is really slow.
87      changeset_ty Complement;
88      std::set_difference(
89        Changes.begin(), Changes.end(), it->begin(), it->end(),
90        std::insert_iterator<changeset_ty>(Complement, Complement.begin()));
91      if (GetTestResult(Complement)) {
92        changesetlist_ty ComplementSets;
93        ComplementSets.insert(ComplementSets.end(), Sets.begin(), it);
94        ComplementSets.insert(ComplementSets.end(), it + 1, Sets.end());
95        Res = Delta(Complement, ComplementSets);
96        return true;
97      }
98    }
99  }
100
101  return false;
102}
103
104DeltaAlgorithm::changeset_ty DeltaAlgorithm::Run(const changeset_ty &Changes) {
105  // Check empty set first to quickly find poor test functions.
106  if (GetTestResult(changeset_ty()))
107    return changeset_ty();
108
109  // Otherwise run the real delta algorithm.
110  changesetlist_ty Sets;
111  Split(Changes, Sets);
112
113  return Delta(Changes, Sets);
114}
115