LLVM  3.7.0
GenericDomTreeConstruction.h
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1 //===- GenericDomTreeConstruction.h - Dominator Calculation ------*- 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 /// \file
10 ///
11 /// Generic dominator tree construction - This file provides routines to
12 /// construct immediate dominator information for a flow-graph based on the
13 /// algorithm described in this document:
14 ///
15 /// A Fast Algorithm for Finding Dominators in a Flowgraph
16 /// T. Lengauer & R. Tarjan, ACM TOPLAS July 1979, pgs 121-141.
17 ///
18 /// This implements the O(n*log(n)) versions of EVAL and LINK, because it turns
19 /// out that the theoretically slower O(n*log(n)) implementation is actually
20 /// faster than the almost-linear O(n*alpha(n)) version, even for large CFGs.
21 ///
22 //===----------------------------------------------------------------------===//
23 
24 
25 #ifndef LLVM_SUPPORT_GENERICDOMTREECONSTRUCTION_H
26 #define LLVM_SUPPORT_GENERICDOMTREECONSTRUCTION_H
27 
28 #include "llvm/ADT/SmallPtrSet.h"
30 
31 namespace llvm {
32 
33 template<class GraphT>
35  typename GraphT::NodeType* V, unsigned N) {
36  // This is more understandable as a recursive algorithm, but we can't use the
37  // recursive algorithm due to stack depth issues. Keep it here for
38  // documentation purposes.
39 #if 0
40  InfoRec &VInfo = DT.Info[DT.Roots[i]];
41  VInfo.DFSNum = VInfo.Semi = ++N;
42  VInfo.Label = V;
43 
44  Vertex.push_back(V); // Vertex[n] = V;
45 
46  for (succ_iterator SI = succ_begin(V), E = succ_end(V); SI != E; ++SI) {
47  InfoRec &SuccVInfo = DT.Info[*SI];
48  if (SuccVInfo.Semi == 0) {
49  SuccVInfo.Parent = V;
50  N = DTDFSPass(DT, *SI, N);
51  }
52  }
53 #else
54  bool IsChildOfArtificialExit = (N != 0);
55 
56  SmallVector<std::pair<typename GraphT::NodeType*,
57  typename GraphT::ChildIteratorType>, 32> Worklist;
58  Worklist.push_back(std::make_pair(V, GraphT::child_begin(V)));
59  while (!Worklist.empty()) {
60  typename GraphT::NodeType* BB = Worklist.back().first;
61  typename GraphT::ChildIteratorType NextSucc = Worklist.back().second;
62 
64  DT.Info[BB];
65 
66  // First time we visited this BB?
67  if (NextSucc == GraphT::child_begin(BB)) {
68  BBInfo.DFSNum = BBInfo.Semi = ++N;
69  BBInfo.Label = BB;
70 
71  DT.Vertex.push_back(BB); // Vertex[n] = V;
72 
73  if (IsChildOfArtificialExit)
74  BBInfo.Parent = 1;
75 
76  IsChildOfArtificialExit = false;
77  }
78 
79  // store the DFS number of the current BB - the reference to BBInfo might
80  // get invalidated when processing the successors.
81  unsigned BBDFSNum = BBInfo.DFSNum;
82 
83  // If we are done with this block, remove it from the worklist.
84  if (NextSucc == GraphT::child_end(BB)) {
85  Worklist.pop_back();
86  continue;
87  }
88 
89  // Increment the successor number for the next time we get to it.
90  ++Worklist.back().second;
91 
92  // Visit the successor next, if it isn't already visited.
93  typename GraphT::NodeType* Succ = *NextSucc;
94 
96  DT.Info[Succ];
97  if (SuccVInfo.Semi == 0) {
98  SuccVInfo.Parent = BBDFSNum;
99  Worklist.push_back(std::make_pair(Succ, GraphT::child_begin(Succ)));
100  }
101  }
102 #endif
103  return N;
104 }
105 
106 template<class GraphT>
107 typename GraphT::NodeType*
109  typename GraphT::NodeType *VIn, unsigned LastLinked) {
111  DT.Info[VIn];
112  if (VInInfo.DFSNum < LastLinked)
113  return VIn;
114 
117 
118  if (VInInfo.Parent >= LastLinked)
119  Work.push_back(VIn);
120 
121  while (!Work.empty()) {
122  typename GraphT::NodeType* V = Work.back();
124  DT.Info[V];
125  typename GraphT::NodeType* VAncestor = DT.Vertex[VInfo.Parent];
126 
127  // Process Ancestor first
128  if (Visited.insert(VAncestor).second && VInfo.Parent >= LastLinked) {
129  Work.push_back(VAncestor);
130  continue;
131  }
132  Work.pop_back();
133 
134  // Update VInfo based on Ancestor info
135  if (VInfo.Parent < LastLinked)
136  continue;
137 
139  DT.Info[VAncestor];
140  typename GraphT::NodeType* VAncestorLabel = VAInfo.Label;
141  typename GraphT::NodeType* VLabel = VInfo.Label;
142  if (DT.Info[VAncestorLabel].Semi < DT.Info[VLabel].Semi)
143  VInfo.Label = VAncestorLabel;
144  VInfo.Parent = VAInfo.Parent;
145  }
146 
147  return VInInfo.Label;
148 }
149 
150 template<class FuncT, class NodeT>
152  FuncT& F) {
153  typedef GraphTraits<NodeT> GraphT;
154 
155  unsigned N = 0;
156  bool MultipleRoots = (DT.Roots.size() > 1);
157  if (MultipleRoots) {
159  DT.Info[nullptr];
160  BBInfo.DFSNum = BBInfo.Semi = ++N;
161  BBInfo.Label = nullptr;
162 
163  DT.Vertex.push_back(nullptr); // Vertex[n] = V;
164  }
165 
166  // Step #1: Number blocks in depth-first order and initialize variables used
167  // in later stages of the algorithm.
168  for (unsigned i = 0, e = static_cast<unsigned>(DT.Roots.size());
169  i != e; ++i)
170  N = DFSPass<GraphT>(DT, DT.Roots[i], N);
171 
172  // it might be that some blocks did not get a DFS number (e.g., blocks of
173  // infinite loops). In these cases an artificial exit node is required.
174  MultipleRoots |= (DT.isPostDominator() && N != GraphTraits<FuncT*>::size(&F));
175 
176  // When naively implemented, the Lengauer-Tarjan algorithm requires a separate
177  // bucket for each vertex. However, this is unnecessary, because each vertex
178  // is only placed into a single bucket (that of its semidominator), and each
179  // vertex's bucket is processed before it is added to any bucket itself.
180  //
181  // Instead of using a bucket per vertex, we use a single array Buckets that
182  // has two purposes. Before the vertex V with preorder number i is processed,
183  // Buckets[i] stores the index of the first element in V's bucket. After V's
184  // bucket is processed, Buckets[i] stores the index of the next element in the
185  // bucket containing V, if any.
187  Buckets.resize(N + 1);
188  for (unsigned i = 1; i <= N; ++i)
189  Buckets[i] = i;
190 
191  for (unsigned i = N; i >= 2; --i) {
192  typename GraphT::NodeType* W = DT.Vertex[i];
194  DT.Info[W];
195 
196  // Step #2: Implicitly define the immediate dominator of vertices
197  for (unsigned j = i; Buckets[j] != i; j = Buckets[j]) {
198  typename GraphT::NodeType* V = DT.Vertex[Buckets[j]];
199  typename GraphT::NodeType* U = Eval<GraphT>(DT, V, i + 1);
200  DT.IDoms[V] = DT.Info[U].Semi < i ? U : W;
201  }
202 
203  // Step #3: Calculate the semidominators of all vertices
204 
205  // initialize the semi dominator to point to the parent node
206  WInfo.Semi = WInfo.Parent;
207  typedef GraphTraits<Inverse<NodeT> > InvTraits;
208  for (typename InvTraits::ChildIteratorType CI =
209  InvTraits::child_begin(W),
210  E = InvTraits::child_end(W); CI != E; ++CI) {
211  typename InvTraits::NodeType *N = *CI;
212  if (DT.Info.count(N)) { // Only if this predecessor is reachable!
213  unsigned SemiU = DT.Info[Eval<GraphT>(DT, N, i + 1)].Semi;
214  if (SemiU < WInfo.Semi)
215  WInfo.Semi = SemiU;
216  }
217  }
218 
219  // If V is a non-root vertex and sdom(V) = parent(V), then idom(V) is
220  // necessarily parent(V). In this case, set idom(V) here and avoid placing
221  // V into a bucket.
222  if (WInfo.Semi == WInfo.Parent) {
223  DT.IDoms[W] = DT.Vertex[WInfo.Parent];
224  } else {
225  Buckets[i] = Buckets[WInfo.Semi];
226  Buckets[WInfo.Semi] = i;
227  }
228  }
229 
230  if (N >= 1) {
231  typename GraphT::NodeType* Root = DT.Vertex[1];
232  for (unsigned j = 1; Buckets[j] != 1; j = Buckets[j]) {
233  typename GraphT::NodeType* V = DT.Vertex[Buckets[j]];
234  DT.IDoms[V] = Root;
235  }
236  }
237 
238  // Step #4: Explicitly define the immediate dominator of each vertex
239  for (unsigned i = 2; i <= N; ++i) {
240  typename GraphT::NodeType* W = DT.Vertex[i];
241  typename GraphT::NodeType*& WIDom = DT.IDoms[W];
242  if (WIDom != DT.Vertex[DT.Info[W].Semi])
243  WIDom = DT.IDoms[WIDom];
244  }
245 
246  if (DT.Roots.empty()) return;
247 
248  // Add a node for the root. This node might be the actual root, if there is
249  // one exit block, or it may be the virtual exit (denoted by (BasicBlock *)0)
250  // which postdominates all real exits if there are multiple exit blocks, or
251  // an infinite loop.
252  typename GraphT::NodeType* Root = !MultipleRoots ? DT.Roots[0] : nullptr;
253 
254  DT.RootNode =
255  (DT.DomTreeNodes[Root] =
256  llvm::make_unique<DomTreeNodeBase<typename GraphT::NodeType>>(
257  Root, nullptr)).get();
258 
259  // Loop over all of the reachable blocks in the function...
260  for (unsigned i = 2; i <= N; ++i) {
261  typename GraphT::NodeType* W = DT.Vertex[i];
262 
263  // Don't replace this with 'count', the insertion side effect is important
264  if (DT.DomTreeNodes[W])
265  continue; // Haven't calculated this node yet?
266 
267  typename GraphT::NodeType* ImmDom = DT.getIDom(W);
268 
269  assert(ImmDom || DT.DomTreeNodes[nullptr]);
270 
271  // Get or calculate the node for the immediate dominator
273  DT.getNodeForBlock(ImmDom);
274 
275  // Add a new tree node for this BasicBlock, and link it as a child of
276  // IDomNode
277  DT.DomTreeNodes[W] = IDomNode->addChild(
279  W, IDomNode));
280  }
281 
282  // Free temporary memory used to construct idom's
283  DT.IDoms.clear();
284  DT.Info.clear();
285  DT.Vertex.clear();
286  DT.Vertex.shrink_to_fit();
287 
288  DT.updateDFSNumbers();
289 }
290 
291 }
292 
293 #endif
std::vector< NodeT * > Roots
unsigned DFSPass(DominatorTreeBase< typename GraphT::NodeType > &DT, typename GraphT::NodeType *V, unsigned N)
DominatorTree GraphTraits specialization so the DominatorTree can be iterable by generic graph iterat...
Definition: GraphTraits.h:27
F(f)
NodeType
ISD::NodeType enum - This enum defines the target-independent operators for a SelectionDAG.
Definition: ISDOpcodes.h:39
Interval::succ_iterator succ_begin(Interval *I)
succ_begin/succ_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:104
bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const
Definition: SmallVector.h:57
Base class for the actual dominator tree node.
Interval::succ_iterator succ_end(Interval *I)
Definition: Interval.h:107
Core dominator tree base class.
Definition: LoopInfo.h:56
std::enable_if<!std::is_array< T >::value, std::unique_ptr< T > >::type make_unique(Args &&...args)
Constructs a new T() with the given args and returns a unique_ptr<T> which owns the object...
Definition: STLExtras.h:354
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:264
std::vector< NodeT * > Vertex
std::unique_ptr< DomTreeNodeBase< NodeT > > addChild(std::unique_ptr< DomTreeNodeBase< NodeT >> C)
DenseMap< NodeT *, InfoRec > Info
void Calculate(DominatorTreeBase< typename GraphTraits< N >::NodeType > &DT, FuncT &F)
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:299
GraphType::UnknownGraphTypeError NodeType
Definition: GraphTraits.h:60
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:861
#define N
GraphT::NodeType * Eval(DominatorTreeBase< typename GraphT::NodeType > &DT, typename GraphT::NodeType *VIn, unsigned LastLinked)
void size_t size
This file defines a set of templates that efficiently compute a dominator tree over a generic graph...
void resize(size_type N)
Definition: SmallVector.h:376