1 //===- llvm/Analysis/ET-Forest.h - ET-Forest implementation -----*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file was written by Daniel Berlin from code written by Pavel Nejedy, and
6 // is distributed under the University of Illinois Open Source License. See
7 // LICENSE.TXT for details.
9 //===----------------------------------------------------------------------===//
11 // This file defines the following classes:
12 // 1. ETNode: A node in the ET forest.
13 // 2. ETOccurrence: An occurrence of the node in the splay tree
14 // storing the DFS path information.
16 // The ET-forest structure is described in:
17 // D. D. Sleator and R. E. Tarjan. A data structure for dynamic trees.
18 // J. G'omput. System Sci., 26(3):362 381, 1983.
20 // Basically, the ET-Forest is storing the dominator tree (ETNode),
21 // and a splay tree containing the depth first path information for
22 // those nodes (ETOccurrence). This enables us to answer queries
23 // about domination (DominatedBySlow), and ancestry (NCA) in
24 // logarithmic time, and perform updates to the information in
27 //===----------------------------------------------------------------------===//
29 #ifndef LLVM_ANALYSIS_ETFOREST_H
30 #define LLVM_ANALYSIS_ETFOREST_H
38 /// ETOccurrence - An occurrence for a node in the et tree
40 /// The et occurrence tree is really storing the sequences you get from
41 /// doing a DFS over the ETNode's. It is stored as a modified splay
43 /// ET occurrences can occur at multiple places in the ordering depending
44 /// on how many ET nodes have it as their father. To handle
45 /// this, they are separate from the nodes.
49 ETOccurrence(ETNode *n): OccFor(n), Parent(NULL), Left(NULL), Right(NULL),
50 Depth(0), Min(0), MinOccurrence(this) {};
52 void setParent(ETOccurrence *n) {
53 assert(n != this && "Trying to set parent to ourselves");
57 // Add D to our current depth
58 void setDepthAdd(int d) {
63 // Reset our depth to D
64 void setDepth(int d) {
70 void setLeft(ETOccurrence *n) {
71 assert(n != this && "Trying to set our left to ourselves");
78 void setRight(ETOccurrence *n) {
79 assert(n != this && "Trying to set our right to ourselves");
85 // Splay us to the root of the tree
88 // Recompute the minimum occurrence for this occurrence.
89 void recomputeMin(void) {
90 ETOccurrence *themin = Left;
92 // The min may be our Right, too.
93 if (!themin || (Right && themin->Min > Right->Min))
96 if (themin && themin->Min < 0) {
97 Min = themin->Min + Depth;
98 MinOccurrence = themin->MinOccurrence;
101 MinOccurrence = this;
110 // Parent in the splay tree
111 ETOccurrence *Parent;
113 // Left Son in the splay tree
116 // Right Son in the splay tree
119 // Depth of the node is the sum of the depth on the path to the
123 // Subtree occurrence's minimum depth
126 // Subtree occurrence with minimum depth
127 ETOccurrence *MinOccurrence;
133 ETNode(void *d) : data(d), DFSNumIn(-1), DFSNumOut(-1),
134 Father(NULL), Left(NULL),
135 Right(NULL), Son(NULL), ParentOcc(NULL) {
136 RightmostOcc = new ETOccurrence(this);
139 // This does *not* maintain the tree structure.
140 // If you want to remove a node from the forest structure, use
141 // removeFromForest()
147 void removeFromForest() {
148 // Split us away from all our sons.
152 // And then split us away from our father.
157 // Split us away from our parents and children, so that we can be
158 // reparented. NB: setFather WILL NOT DO WHAT YOU WANT IF YOU DO NOT
162 // Set our parent node to the passed in node
163 void setFather(ETNode *);
165 // Nearest Common Ancestor of two et nodes.
166 ETNode *NCA(ETNode *);
168 // Return true if we are below the passed in node in the forest.
169 bool Below(ETNode *);
171 Given a dominator tree, we can determine whether one thing
172 dominates another in constant time by using two DFS numbers:
174 1. The number for when we visit a node on the way down the tree
175 2. The number for when we visit a node on the way back up the tree
177 You can view these as bounds for the range of dfs numbers the
178 nodes in the subtree of the dominator tree rooted at that node
181 The dominator tree is always a simple acyclic tree, so there are
182 only three possible relations two nodes in the dominator tree have
185 1. Node A is above Node B (and thus, Node A dominates node B)
194 In the above case, DFS_Number_In of A will be <= DFS_Number_In of
195 B, and DFS_Number_Out of A will be >= DFS_Number_Out of B. This is
196 because we must hit A in the dominator tree *before* B on the walk
197 down, and we will hit A *after* B on the walk back up
199 2. Node A is below node B (and thus, node B dominates node B)
207 In the above case, DFS_Number_In of A will be >= DFS_Number_In of
208 B, and DFS_Number_Out of A will be <= DFS_Number_Out of B.
210 This is because we must hit A in the dominator tree *after* B on
211 the walk down, and we will hit A *before* B on the walk back up
213 3. Node A and B are siblings (and thus, neither dominates the other)
221 In the above case, DFS_Number_In of A will *always* be <=
222 DFS_Number_In of B, and DFS_Number_Out of A will *always* be <=
223 DFS_Number_Out of B. This is because we will always finish the dfs
224 walk of one of the subtrees before the other, and thus, the dfs
225 numbers for one subtree can't intersect with the range of dfs
226 numbers for the other subtree. If you swap A and B's position in
227 the dominator tree, the comparison changes direction, but the point
228 is that both comparisons will always go the same way if there is no
229 dominance relationship.
231 Thus, it is sufficient to write
233 A_Dominates_B(node A, node B) {
234 return DFS_Number_In(A) <= DFS_Number_In(B) &&
235 DFS_Number_Out(A) >= DFS_Number_Out(B);
238 A_Dominated_by_B(node A, node B) {
239 return DFS_Number_In(A) >= DFS_Number_In(A) &&
240 DFS_Number_Out(A) <= DFS_Number_Out(B);
243 bool DominatedBy(ETNode *other) const {
244 return this->DFSNumIn >= other->DFSNumIn &&
245 this->DFSNumOut <= other->DFSNumOut;
248 // This method is slower, but doesn't require the DFS numbers to
250 bool DominatedBySlow(ETNode *other) {
251 return this->Below(other);
254 void assignDFSNumber (int);
256 bool hasFather() const {
257 return Father != NULL;
260 // Do not let people play around with fathers.
261 const ETNode *getFather() const {
265 template <typename T>
267 return static_cast<T*>(data);
270 unsigned getDFSNumIn() const {
274 unsigned getDFSNumOut() const {
278 const ETNode *getSon() const {
282 const ETNode *getBrother() const {
287 // Data represented by the node
291 int DFSNumIn, DFSNumOut;
296 // Brothers. Node, this ends up being a circularly linked list.
297 // Thus, if you want to get all the brothers, you need to stop when
298 // you hit node == this again.
299 ETNode *Left, *Right;
304 // Rightmost occurrence for this node
305 ETOccurrence *RightmostOcc;
307 // Parent occurrence for this node
308 ETOccurrence *ParentOcc;
310 } // end llvm namespace