LLVM  4.0.0
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 #ifndef LLVM_SUPPORT_GENERICDOMTREECONSTRUCTION_H
25 #define LLVM_SUPPORT_GENERICDOMTREECONSTRUCTION_H
26 
27 #include "llvm/ADT/SmallPtrSet.h"
29 
30 namespace llvm {
31 
32 template <class GraphT>
34  typename GraphT::NodeRef V, unsigned N) {
35  // This is more understandable as a recursive algorithm, but we can't use the
36  // recursive algorithm due to stack depth issues. Keep it here for
37  // documentation purposes.
38 #if 0
39  InfoRec &VInfo = DT.Info[DT.Roots[i]];
40  VInfo.DFSNum = VInfo.Semi = ++N;
41  VInfo.Label = V;
42 
43  Vertex.push_back(V); // Vertex[n] = V;
44 
45  for (succ_iterator SI = succ_begin(V), E = succ_end(V); SI != E; ++SI) {
46  InfoRec &SuccVInfo = DT.Info[*SI];
47  if (SuccVInfo.Semi == 0) {
48  SuccVInfo.Parent = V;
49  N = DTDFSPass(DT, *SI, N);
50  }
51  }
52 #else
53  bool IsChildOfArtificialExit = (N != 0);
54 
56  std::pair<typename GraphT::NodeRef, typename GraphT::ChildIteratorType>,
57  32>
58  Worklist;
59  Worklist.push_back(std::make_pair(V, GraphT::child_begin(V)));
60  while (!Worklist.empty()) {
61  typename GraphT::NodeRef BB = Worklist.back().first;
62  typename GraphT::ChildIteratorType NextSucc = Worklist.back().second;
63 
64  auto &BBInfo = 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::NodeRef Succ = *NextSucc;
94 
95  auto &SuccVInfo = DT.Info[Succ];
96  if (SuccVInfo.Semi == 0) {
97  SuccVInfo.Parent = BBDFSNum;
98  Worklist.push_back(std::make_pair(Succ, GraphT::child_begin(Succ)));
99  }
100  }
101 #endif
102  return N;
103 }
104 
105 template <class GraphT>
106 typename GraphT::NodeRef Eval(DominatorTreeBaseByGraphTraits<GraphT> &DT,
107  typename GraphT::NodeRef VIn,
108  unsigned LastLinked) {
109  auto &VInInfo = DT.Info[VIn];
110  if (VInInfo.DFSNum < LastLinked)
111  return VIn;
112 
115 
116  if (VInInfo.Parent >= LastLinked)
117  Work.push_back(VIn);
118 
119  while (!Work.empty()) {
120  typename GraphT::NodeRef V = Work.back();
121  auto &VInfo = DT.Info[V];
122  typename GraphT::NodeRef VAncestor = DT.Vertex[VInfo.Parent];
123 
124  // Process Ancestor first
125  if (Visited.insert(VAncestor).second && VInfo.Parent >= LastLinked) {
126  Work.push_back(VAncestor);
127  continue;
128  }
129  Work.pop_back();
130 
131  // Update VInfo based on Ancestor info
132  if (VInfo.Parent < LastLinked)
133  continue;
134 
135  auto &VAInfo = DT.Info[VAncestor];
136  typename GraphT::NodeRef VAncestorLabel = VAInfo.Label;
137  typename GraphT::NodeRef VLabel = VInfo.Label;
138  if (DT.Info[VAncestorLabel].Semi < DT.Info[VLabel].Semi)
139  VInfo.Label = VAncestorLabel;
140  VInfo.Parent = VAInfo.Parent;
141  }
142 
143  return VInInfo.Label;
144 }
145 
146 template <class FuncT, class NodeT>
148  FuncT &F) {
149  typedef GraphTraits<NodeT> GraphT;
150  static_assert(std::is_pointer<typename GraphT::NodeRef>::value,
151  "NodeRef should be pointer type");
152  typedef typename std::remove_pointer<typename GraphT::NodeRef>::type NodeType;
153 
154  unsigned N = 0;
155  bool MultipleRoots = (DT.Roots.size() > 1);
156  if (MultipleRoots) {
157  auto &BBInfo = DT.Info[nullptr];
158  BBInfo.DFSNum = BBInfo.Semi = ++N;
159  BBInfo.Label = nullptr;
160 
161  DT.Vertex.push_back(nullptr); // Vertex[n] = V;
162  }
163 
164  // Step #1: Number blocks in depth-first order and initialize variables used
165  // in later stages of the algorithm.
166  for (unsigned i = 0, e = static_cast<unsigned>(DT.Roots.size());
167  i != e; ++i)
168  N = DFSPass<GraphT>(DT, DT.Roots[i], N);
169 
170  // it might be that some blocks did not get a DFS number (e.g., blocks of
171  // infinite loops). In these cases an artificial exit node is required.
172  MultipleRoots |= (DT.isPostDominator() && N != GraphTraits<FuncT*>::size(&F));
173 
174  // When naively implemented, the Lengauer-Tarjan algorithm requires a separate
175  // bucket for each vertex. However, this is unnecessary, because each vertex
176  // is only placed into a single bucket (that of its semidominator), and each
177  // vertex's bucket is processed before it is added to any bucket itself.
178  //
179  // Instead of using a bucket per vertex, we use a single array Buckets that
180  // has two purposes. Before the vertex V with preorder number i is processed,
181  // Buckets[i] stores the index of the first element in V's bucket. After V's
182  // bucket is processed, Buckets[i] stores the index of the next element in the
183  // bucket containing V, if any.
185  Buckets.resize(N + 1);
186  for (unsigned i = 1; i <= N; ++i)
187  Buckets[i] = i;
188 
189  for (unsigned i = N; i >= 2; --i) {
190  typename GraphT::NodeRef W = DT.Vertex[i];
191  auto &WInfo = DT.Info[W];
192 
193  // Step #2: Implicitly define the immediate dominator of vertices
194  for (unsigned j = i; Buckets[j] != i; j = Buckets[j]) {
195  typename GraphT::NodeRef V = DT.Vertex[Buckets[j]];
196  typename GraphT::NodeRef U = Eval<GraphT>(DT, V, i + 1);
197  DT.IDoms[V] = DT.Info[U].Semi < i ? U : W;
198  }
199 
200  // Step #3: Calculate the semidominators of all vertices
201 
202  // initialize the semi dominator to point to the parent node
203  WInfo.Semi = WInfo.Parent;
204  typedef GraphTraits<Inverse<NodeT> > InvTraits;
205  for (typename InvTraits::ChildIteratorType CI =
206  InvTraits::child_begin(W),
207  E = InvTraits::child_end(W); CI != E; ++CI) {
208  typename InvTraits::NodeRef N = *CI;
209  if (DT.Info.count(N)) { // Only if this predecessor is reachable!
210  unsigned SemiU = DT.Info[Eval<GraphT>(DT, N, i + 1)].Semi;
211  if (SemiU < WInfo.Semi)
212  WInfo.Semi = SemiU;
213  }
214  }
215 
216  // If V is a non-root vertex and sdom(V) = parent(V), then idom(V) is
217  // necessarily parent(V). In this case, set idom(V) here and avoid placing
218  // V into a bucket.
219  if (WInfo.Semi == WInfo.Parent) {
220  DT.IDoms[W] = DT.Vertex[WInfo.Parent];
221  } else {
222  Buckets[i] = Buckets[WInfo.Semi];
223  Buckets[WInfo.Semi] = i;
224  }
225  }
226 
227  if (N >= 1) {
228  typename GraphT::NodeRef Root = DT.Vertex[1];
229  for (unsigned j = 1; Buckets[j] != 1; j = Buckets[j]) {
230  typename GraphT::NodeRef V = DT.Vertex[Buckets[j]];
231  DT.IDoms[V] = Root;
232  }
233  }
234 
235  // Step #4: Explicitly define the immediate dominator of each vertex
236  for (unsigned i = 2; i <= N; ++i) {
237  typename GraphT::NodeRef W = DT.Vertex[i];
238  typename GraphT::NodeRef &WIDom = DT.IDoms[W];
239  if (WIDom != DT.Vertex[DT.Info[W].Semi])
240  WIDom = DT.IDoms[WIDom];
241  }
242 
243  if (DT.Roots.empty()) return;
244 
245  // Add a node for the root. This node might be the actual root, if there is
246  // one exit block, or it may be the virtual exit (denoted by (BasicBlock *)0)
247  // which postdominates all real exits if there are multiple exit blocks, or
248  // an infinite loop.
249  typename GraphT::NodeRef Root = !MultipleRoots ? DT.Roots[0] : nullptr;
250 
251  DT.RootNode =
252  (DT.DomTreeNodes[Root] =
253  llvm::make_unique<DomTreeNodeBase<NodeType>>(Root, nullptr))
254  .get();
255 
256  // Loop over all of the reachable blocks in the function...
257  for (unsigned i = 2; i <= N; ++i) {
258  typename GraphT::NodeRef W = DT.Vertex[i];
259 
260  // Don't replace this with 'count', the insertion side effect is important
261  if (DT.DomTreeNodes[W])
262  continue; // Haven't calculated this node yet?
263 
264  typename GraphT::NodeRef ImmDom = DT.getIDom(W);
265 
266  assert(ImmDom || DT.DomTreeNodes[nullptr]);
267 
268  // Get or calculate the node for the immediate dominator
269  DomTreeNodeBase<NodeType> *IDomNode = DT.getNodeForBlock(ImmDom);
270 
271  // Add a new tree node for this BasicBlock, and link it as a child of
272  // IDomNode
273  DT.DomTreeNodes[W] = IDomNode->addChild(
275  }
276 
277  // Free temporary memory used to construct idom's
278  DT.IDoms.clear();
279  DT.Info.clear();
280  DT.Vertex.clear();
281  DT.Vertex.shrink_to_fit();
282 
283  DT.updateDFSNumbers();
284 }
285 }
286 
287 #endif
void push_back(const T &Elt)
Definition: SmallVector.h:211
std::unique_ptr< DomTreeNodeBase< NodeT > > addChild(std::unique_ptr< DomTreeNodeBase< NodeT >> C)
size_t i
void Calculate(DominatorTreeBaseByGraphTraits< GraphTraits< N >> &DT, FuncT &F)
NodeType
ISD::NodeType enum - This enum defines the target-independent operators for a SelectionDAG.
Definition: ISDOpcodes.h:39
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:60
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:106
#define F(x, y, z)
Definition: MD5.cpp:51
GraphT::NodeRef Eval(DominatorTreeBaseByGraphTraits< GraphT > &DT, typename GraphT::NodeRef VIn, unsigned LastLinked)
Base class for the actual dominator tree node.
static GCRegistry::Add< CoreCLRGC > E("coreclr","CoreCLR-compatible GC")
Interval::succ_iterator succ_end(Interval *I)
Definition: Interval.h:109
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:845
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:368
unsigned DFSPass(DominatorTreeBaseByGraphTraits< GraphT > &DT, typename GraphT::NodeRef V, unsigned N)
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:425
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:843
#define N
typename detail::DominatorTreeBaseTraits< GT >::type DominatorTreeBaseByGraphTraits
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
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:352