1 //===- DominatorSet.cpp - Dominator Set Calculation --------------*- C++ -*--=//
3 // This file provides a simple class to calculate the dominator set of a method.
5 //===----------------------------------------------------------------------===//
7 #include "llvm/Analysis/Dominators.h"
8 #include "llvm/Analysis/SimplifyCFG.h" // To get cfg::UnifyAllExitNodes
9 #include "llvm/Support/DepthFirstIterator.h"
10 #include "llvm/Support/STLExtras.h"
11 #include "llvm/Method.h"
14 //===----------------------------------------------------------------------===//
16 //===----------------------------------------------------------------------===//
18 // set_intersect - Identical to set_intersection, except that it works on
19 // set<>'s and is nicer to use. Functionally, this iterates through S1,
20 // removing elements that are not contained in S2.
22 template <class Ty, class Ty2>
23 void set_intersect(set<Ty> &S1, const set<Ty2> &S2) {
24 for (typename set<Ty>::iterator I = S1.begin(); I != S1.end();) {
27 if (!S2.count(E)) S1.erase(E); // Erase element if not in S2
31 //===----------------------------------------------------------------------===//
32 // DominatorBase Implementation
33 //===----------------------------------------------------------------------===//
35 bool cfg::DominatorBase::isPostDominator() const {
36 // Root can be null if there is no exit node from the CFG and is postdom set
37 return Root == 0 || Root != Root->getParent()->front();
41 //===----------------------------------------------------------------------===//
42 // DominatorSet Implementation
43 //===----------------------------------------------------------------------===//
45 // DominatorSet ctor - Build either the dominator set or the post-dominator
46 // set for a method...
48 cfg::DominatorSet::DominatorSet(const Method *M) : DominatorBase(M->front()) {
49 calcForwardDominatorSet(M);
52 // calcForwardDominatorSet - This method calculates the forward dominator sets
53 // for the specified method.
55 void cfg::DominatorSet::calcForwardDominatorSet(const Method *M) {
56 assert(Root && M && "Can't build dominator set of null method!");
57 assert(Root->pred_begin() == Root->pred_end() &&
58 "Root node has predecessors in method!");
64 DomSetType WorkingSet;
65 df_iterator<const Method*> It = df_begin(M), End = df_end(M);
66 for ( ; It != End; ++It) {
67 const BasicBlock *BB = *It;
68 BasicBlock::pred_const_iterator PI = BB->pred_begin(),
69 PEnd = BB->pred_end();
70 if (PI != PEnd) { // Is there SOME predecessor?
71 // Loop until we get to a predecessor that has had it's dom set filled
72 // in at least once. We are guaranteed to have this because we are
73 // traversing the graph in DFO and have handled start nodes specially.
75 while (Doms[*PI].size() == 0) ++PI;
76 WorkingSet = Doms[*PI];
78 for (++PI; PI != PEnd; ++PI) { // Intersect all of the predecessor sets
79 DomSetType &PredSet = Doms[*PI];
81 set_intersect(WorkingSet, PredSet);
85 WorkingSet.insert(BB); // A block always dominates itself
86 DomSetType &BBSet = Doms[BB];
87 if (BBSet != WorkingSet) {
88 BBSet.swap(WorkingSet); // Constant time operation!
89 Changed = true; // The sets changed.
91 WorkingSet.clear(); // Clear out the set for next iteration
96 // Postdominator set constructor. This ctor converts the specified method to
97 // only have a single exit node (return stmt), then calculates the post
98 // dominance sets for the method.
100 cfg::DominatorSet::DominatorSet(Method *M, bool PostDomSet)
101 : DominatorBase(M->front()) {
102 if (!PostDomSet) { calcForwardDominatorSet(M); return; }
104 Root = cfg::UnifyAllExitNodes(M);
105 if (Root == 0) { // No exit node for the method? Postdomsets are all empty
106 for (Method::iterator MI = M->begin(), ME = M->end(); MI != ME; ++MI)
107 Doms[*MI] = DomSetType();
115 set<const BasicBlock*> Visited;
116 DomSetType WorkingSet;
117 idf_iterator<const BasicBlock*> It = idf_begin(Root), End = idf_end(Root);
118 for ( ; It != End; ++It) {
119 const BasicBlock *BB = *It;
120 BasicBlock::succ_const_iterator PI = BB->succ_begin(),
121 PEnd = BB->succ_end();
122 if (PI != PEnd) { // Is there SOME predecessor?
123 // Loop until we get to a successor that has had it's dom set filled
124 // in at least once. We are guaranteed to have this because we are
125 // traversing the graph in DFO and have handled start nodes specially.
127 while (Doms[*PI].size() == 0) ++PI;
128 WorkingSet = Doms[*PI];
130 for (++PI; PI != PEnd; ++PI) { // Intersect all of the successor sets
131 DomSetType &PredSet = Doms[*PI];
133 set_intersect(WorkingSet, PredSet);
137 WorkingSet.insert(BB); // A block always dominates itself
138 DomSetType &BBSet = Doms[BB];
139 if (BBSet != WorkingSet) {
140 BBSet.swap(WorkingSet); // Constant time operation!
141 Changed = true; // The sets changed.
143 WorkingSet.clear(); // Clear out the set for next iteration
149 //===----------------------------------------------------------------------===//
150 // ImmediateDominators Implementation
151 //===----------------------------------------------------------------------===//
153 // calcIDoms - Calculate the immediate dominator mapping, given a set of
154 // dominators for every basic block.
155 void cfg::ImmediateDominators::calcIDoms(const DominatorSet &DS) {
156 // Loop over all of the nodes that have dominators... figuring out the IDOM
159 for (DominatorSet::const_iterator DI = DS.begin(), DEnd = DS.end();
161 const BasicBlock *BB = DI->first;
162 const DominatorSet::DomSetType &Dominators = DI->second;
163 unsigned DomSetSize = Dominators.size();
164 if (DomSetSize == 1) continue; // Root node... IDom = null
166 // Loop over all dominators of this node. This corresponds to looping over
167 // nodes in the dominator chain, looking for a node whose dominator set is
168 // equal to the current nodes, except that the current node does not exist
169 // in it. This means that it is one level higher in the dom chain than the
170 // current node, and it is our idom!
172 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
173 DominatorSet::DomSetType::const_iterator End = Dominators.end();
174 for (; I != End; ++I) { // Iterate over dominators...
175 // All of our dominators should form a chain, where the number of elements
176 // in the dominator set indicates what level the node is at in the chain.
177 // We want the node immediately above us, so it will have an identical
178 // dominator set, except that BB will not dominate it... therefore it's
179 // dominator set size will be one less than BB's...
181 if (DS.getDominators(*I).size() == DomSetSize - 1) {
190 //===----------------------------------------------------------------------===//
191 // DominatorTree Implementation
192 //===----------------------------------------------------------------------===//
194 // DominatorTree dtor - Free all of the tree node memory.
196 cfg::DominatorTree::~DominatorTree() {
197 for (NodeMapType::iterator I = Nodes.begin(), E = Nodes.end(); I != E; ++I)
202 cfg::DominatorTree::DominatorTree(const ImmediateDominators &IDoms)
203 : DominatorBase(IDoms.getRoot()) {
204 const Method *M = Root->getParent();
206 Nodes[Root] = new Node(Root, 0); // Add a node for the root...
208 // Iterate over all nodes in depth first order...
209 for (df_iterator<const Method*> I = df_begin(M), E = df_end(M); I != E; ++I) {
210 const BasicBlock *BB = *I, *IDom = IDoms[*I];
212 if (IDom != 0) { // Ignore the root node and other nasty nodes
213 // We know that the immediate dominator should already have a node,
214 // because we are traversing the CFG in depth first order!
216 assert(Nodes[IDom] && "No node for IDOM?");
217 Node *IDomNode = Nodes[IDom];
219 // Add a new tree node for this BasicBlock, and link it as a child of
221 Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
226 void cfg::DominatorTree::calculate(const DominatorSet &DS) {
227 Nodes[Root] = new Node(Root, 0); // Add a node for the root...
229 if (!isPostDominator()) {
230 // Iterate over all nodes in depth first order...
231 for (df_iterator<const BasicBlock*> I = df_begin(Root), E = df_end(Root);
233 const BasicBlock *BB = *I;
234 const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
235 unsigned DomSetSize = Dominators.size();
236 if (DomSetSize == 1) continue; // Root node... IDom = null
238 // Loop over all dominators of this node. This corresponds to looping over
239 // nodes in the dominator chain, looking for a node whose dominator set is
240 // equal to the current nodes, except that the current node does not exist
241 // in it. This means that it is one level higher in the dom chain than the
242 // current node, and it is our idom! We know that we have already added
243 // a DominatorTree node for our idom, because the idom must be a
244 // predecessor in the depth first order that we are iterating through the
247 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
248 DominatorSet::DomSetType::const_iterator End = Dominators.end();
249 for (; I != End; ++I) { // Iterate over dominators...
250 // All of our dominators should form a chain, where the number of
251 // elements in the dominator set indicates what level the node is at in
252 // the chain. We want the node immediately above us, so it will have
253 // an identical dominator set, except that BB will not dominate it...
254 // therefore it's dominator set size will be one less than BB's...
256 if (DS.getDominators(*I).size() == DomSetSize - 1) {
257 // We know that the immediate dominator should already have a node,
258 // because we are traversing the CFG in depth first order!
260 Node *IDomNode = Nodes[*I];
261 assert(IDomNode && "No node for IDOM?");
263 // Add a new tree node for this BasicBlock, and link it as a child of
265 Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
271 // Iterate over all nodes in depth first order...
272 for (idf_iterator<const BasicBlock*> I = idf_begin(Root), E = idf_end(Root);
274 const BasicBlock *BB = *I;
275 const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
276 unsigned DomSetSize = Dominators.size();
277 if (DomSetSize == 1) continue; // Root node... IDom = null
279 // Loop over all dominators of this node. This corresponds to looping
280 // over nodes in the dominator chain, looking for a node whose dominator
281 // set is equal to the current nodes, except that the current node does
282 // not exist in it. This means that it is one level higher in the dom
283 // chain than the current node, and it is our idom! We know that we have
284 // already added a DominatorTree node for our idom, because the idom must
285 // be a predecessor in the depth first order that we are iterating through
288 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
289 DominatorSet::DomSetType::const_iterator End = Dominators.end();
290 for (; I != End; ++I) { // Iterate over dominators...
291 // All of our dominators should form a chain, where the number of elements
292 // in the dominator set indicates what level the node is at in the chain.
293 // We want the node immediately above us, so it will have an identical
294 // dominator set, except that BB will not dominate it... therefore it's
295 // dominator set size will be one less than BB's...
297 if (DS.getDominators(*I).size() == DomSetSize - 1) {
298 // We know that the immediate dominator should already have a node,
299 // because we are traversing the CFG in depth first order!
301 Node *IDomNode = Nodes[*I];
302 assert(IDomNode && "No node for IDOM?");
304 // Add a new tree node for this BasicBlock, and link it as a child of
306 Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
316 //===----------------------------------------------------------------------===//
317 // DominanceFrontier Implementation
318 //===----------------------------------------------------------------------===//
320 const cfg::DominanceFrontier::DomSetType &
321 cfg::DominanceFrontier::calcDomFrontier(const DominatorTree &DT,
322 const DominatorTree::Node *Node) {
323 // Loop over CFG successors to calculate DFlocal[Node]
324 const BasicBlock *BB = Node->getNode();
325 DomSetType &S = Frontiers[BB]; // The new set to fill in...
327 for (BasicBlock::succ_const_iterator SI = BB->succ_begin(),
328 SE = BB->succ_end(); SI != SE; ++SI) {
329 // Does Node immediately dominate this successor?
330 if (DT[*SI]->getIDom() != Node)
334 // At this point, S is DFlocal. Now we union in DFup's of our children...
335 // Loop through and visit the nodes that Node immediately dominates (Node's
336 // children in the IDomTree)
338 for (DominatorTree::Node::const_iterator NI = Node->begin(), NE = Node->end();
340 DominatorTree::Node *IDominee = *NI;
341 const DomSetType &ChildDF = calcDomFrontier(DT, IDominee);
343 DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
344 for (; CDFI != CDFE; ++CDFI) {
345 if (!Node->dominates(DT[*CDFI]))
353 const cfg::DominanceFrontier::DomSetType &
354 cfg::DominanceFrontier::calcPostDomFrontier(const DominatorTree &DT,
355 const DominatorTree::Node *Node) {
356 // Loop over CFG successors to calculate DFlocal[Node]
357 const BasicBlock *BB = Node->getNode();
358 DomSetType &S = Frontiers[BB]; // The new set to fill in...
361 for (BasicBlock::pred_const_iterator SI = BB->pred_begin(),
362 SE = BB->pred_end(); SI != SE; ++SI) {
363 // Does Node immediately dominate this predeccessor?
364 if (DT[*SI]->getIDom() != Node)
368 // At this point, S is DFlocal. Now we union in DFup's of our children...
369 // Loop through and visit the nodes that Node immediately dominates (Node's
370 // children in the IDomTree)
372 for (DominatorTree::Node::const_iterator NI = Node->begin(), NE = Node->end();
374 DominatorTree::Node *IDominee = *NI;
375 const DomSetType &ChildDF = calcPostDomFrontier(DT, IDominee);
377 DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
378 for (; CDFI != CDFE; ++CDFI) {
379 if (!Node->dominates(DT[*CDFI]))