1 //===- PostDominators.cpp - Post-Dominator Calculation --------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the post-dominator construction algorithms.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Analysis/PostDominators.h"
15 #include "llvm/Instructions.h"
16 #include "llvm/Support/CFG.h"
17 #include "llvm/ADT/DepthFirstIterator.h"
18 #include "llvm/ADT/SetOperations.h"
21 //===----------------------------------------------------------------------===//
22 // PostDominatorSet Implementation
23 //===----------------------------------------------------------------------===//
25 static RegisterAnalysis<PostDominatorSet>
26 B("postdomset", "Post-Dominator Set Construction", true);
28 // Postdominator set construction. This converts the specified function to only
29 // have a single exit node (return stmt), then calculates the post dominance
30 // sets for the function.
32 bool PostDominatorSet::runOnFunction(Function &F) {
33 Doms.clear(); // Reset from the last time we were run...
35 // Scan the function looking for the root nodes of the post-dominance
36 // relationships. These blocks end with return and unwind instructions.
37 // While we are iterating over the function, we also initialize all of the
40 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
41 Doms[I]; // Initialize to empty
43 if (succ_begin(I) == succ_end(I))
47 // If there are no exit nodes for the function, postdomsets are all empty.
48 // This can happen if the function just contains an infinite loop, for
50 if (Roots.empty()) return false;
52 // If we have more than one root, we insert an artificial "null" exit, which
53 // has "virtual edges" to each of the real exit nodes.
61 std::set<BasicBlock*> Visited;
62 DomSetType WorkingSet;
64 for (unsigned i = 0, e = Roots.size(); i != e; ++i)
65 for (idf_ext_iterator<BasicBlock*> It = idf_ext_begin(Roots[i], Visited),
66 E = idf_ext_end(Roots[i], Visited); It != E; ++It) {
68 succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
69 if (SI != SE) { // Is there SOME successor?
70 // Loop until we get to a successor that has had it's dom set filled
71 // in at least once. We are guaranteed to have this because we are
72 // traversing the graph in DFO and have handled start nodes specially.
74 while (Doms[*SI].size() == 0) ++SI;
75 WorkingSet = Doms[*SI];
77 for (++SI; SI != SE; ++SI) { // Intersect all of the successor sets
78 DomSetType &SuccSet = Doms[*SI];
80 set_intersect(WorkingSet, SuccSet);
83 // If this node has no successors, it must be one of the root nodes.
84 // We will already take care of the notion that the node
85 // post-dominates itself. The only thing we have to add is that if
86 // there are multiple root nodes, we want to insert a special "null"
87 // exit node which dominates the roots as well.
92 WorkingSet.insert(BB); // A block always dominates itself
93 DomSetType &BBSet = Doms[BB];
94 if (BBSet != WorkingSet) {
95 BBSet.swap(WorkingSet); // Constant time operation!
96 Changed = true; // The sets changed.
98 WorkingSet.clear(); // Clear out the set for next iteration
104 //===----------------------------------------------------------------------===//
105 // ImmediatePostDominators Implementation
106 //===----------------------------------------------------------------------===//
108 static RegisterAnalysis<ImmediatePostDominators>
109 D("postidom", "Immediate Post-Dominators Construction", true);
112 // calcIDoms - Calculate the immediate dominator mapping, given a set of
113 // dominators for every basic block.
114 void ImmediatePostDominators::calcIDoms(const DominatorSetBase &DS) {
115 // Loop over all of the nodes that have dominators... figuring out the IDOM
118 for (DominatorSet::const_iterator DI = DS.begin(), DEnd = DS.end();
120 BasicBlock *BB = DI->first;
121 const DominatorSet::DomSetType &Dominators = DI->second;
122 unsigned DomSetSize = Dominators.size();
123 if (DomSetSize == 1) continue; // Root node... IDom = null
125 // Loop over all dominators of this node. This corresponds to looping over
126 // nodes in the dominator chain, looking for a node whose dominator set is
127 // equal to the current nodes, except that the current node does not exist
128 // in it. This means that it is one level higher in the dom chain than the
129 // current node, and it is our idom!
131 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
132 DominatorSet::DomSetType::const_iterator End = Dominators.end();
133 for (; I != End; ++I) { // Iterate over dominators...
134 // All of our dominators should form a chain, where the number of elements
135 // in the dominator set indicates what level the node is at in the chain.
136 // We want the node immediately above us, so it will have an identical
137 // dominator set, except that BB will not dominate it... therefore it's
138 // dominator set size will be one less than BB's...
140 if (DS.getDominators(*I).size() == DomSetSize - 1) {
148 //===----------------------------------------------------------------------===//
149 // PostDominatorTree Implementation
150 //===----------------------------------------------------------------------===//
152 static RegisterAnalysis<PostDominatorTree>
153 F("postdomtree", "Post-Dominator Tree Construction", true);
155 void PostDominatorTree::calculate(const PostDominatorSet &DS) {
156 if (Roots.empty()) return;
157 BasicBlock *Root = Roots.size() == 1 ? Roots[0] : 0;
159 Nodes[Root] = RootNode = new Node(Root, 0); // Add a node for the root...
161 // Iterate over all nodes in depth first order...
162 for (unsigned i = 0, e = Roots.size(); i != e; ++i)
163 for (idf_iterator<BasicBlock*> I = idf_begin(Roots[i]),
164 E = idf_end(Roots[i]); I != E; ++I) {
166 const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
167 unsigned DomSetSize = Dominators.size();
168 if (DomSetSize == 1) continue; // Root node... IDom = null
170 // If we have already computed the immediate dominator for this node,
171 // don't revisit. This can happen due to nodes reachable from multiple
172 // roots, but which the idf_iterator doesn't know about.
173 if (Nodes.find(BB) != Nodes.end()) continue;
175 // Loop over all dominators of this node. This corresponds to looping
176 // over nodes in the dominator chain, looking for a node whose dominator
177 // set is equal to the current nodes, except that the current node does
178 // not exist in it. This means that it is one level higher in the dom
179 // chain than the current node, and it is our idom! We know that we have
180 // already added a DominatorTree node for our idom, because the idom must
181 // be a predecessor in the depth first order that we are iterating through
184 for (DominatorSet::DomSetType::const_iterator I = Dominators.begin(),
185 E = Dominators.end(); I != E; ++I) { // Iterate over dominators.
186 // All of our dominators should form a chain, where the number
187 // of elements in the dominator set indicates what level the
188 // node is at in the chain. We want the node immediately
189 // above us, so it will have an identical dominator set,
190 // except that BB will not dominate it... therefore it's
191 // dominator set size will be one less than BB's...
193 if (DS.getDominators(*I).size() == DomSetSize - 1) {
194 // We know that the immediate dominator should already have a node,
195 // because we are traversing the CFG in depth first order!
197 Node *IDomNode = Nodes[*I];
198 assert(IDomNode && "No node for IDOM?");
200 // Add a new tree node for this BasicBlock, and link it as a child of
202 Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
208 //===----------------------------------------------------------------------===//
209 // PostETForest Implementation
210 //===----------------------------------------------------------------------===//
212 static RegisterAnalysis<PostETForest>
213 G("postetforest", "Post-ET-Forest Construction", true);
215 ETNode *PostETForest::getNodeForBlock(BasicBlock *BB) {
216 ETNode *&BBNode = Nodes[BB];
217 if (BBNode) return BBNode;
219 // Haven't calculated this node yet? Get or calculate the node for the
220 // immediate dominator.
221 BasicBlock *IDom = getAnalysis<ImmediatePostDominators>()[BB];
223 // If we are unreachable, we may not have an immediate dominator.
225 return BBNode = new ETNode(BB);
227 ETNode *IDomNode = getNodeForBlock(IDom);
229 // Add a new tree node for this BasicBlock, and link it as a child of
231 BBNode = new ETNode(BB);
232 BBNode->setFather(IDomNode);
237 void PostETForest::calculate(const ImmediatePostDominators &ID) {
238 for (unsigned i = 0, e = Roots.size(); i != e; ++i)
239 Nodes[Roots[i]] = new ETNode(Roots[i]); // Add a node for the root
241 // Iterate over all nodes in inverse depth first order.
242 for (unsigned i = 0, e = Roots.size(); i != e; ++i)
243 for (idf_iterator<BasicBlock*> I = idf_begin(Roots[i]),
244 E = idf_end(Roots[i]); I != E; ++I) {
246 ETNode *&BBNode = Nodes[BB];
248 ETNode *IDomNode = NULL;
251 IDomNode = getNodeForBlock(ID.get(BB));
253 // Add a new ETNode for this BasicBlock, and set it's parent
254 // to it's immediate dominator.
255 BBNode = new ETNode(BB);
257 BBNode->setFather(IDomNode);
262 // Iterate over all nodes in depth first order...
263 for (unsigned i = 0, e = Roots.size(); i != e; ++i)
264 for (idf_iterator<BasicBlock*> I = idf_begin(Roots[i]),
265 E = idf_end(Roots[i]); I != E; ++I) {
266 if (!getNodeForBlock(*I)->hasFather())
267 getNodeForBlock(*I)->assignDFSNumber(dfsnum);
272 //===----------------------------------------------------------------------===//
273 // PostDominanceFrontier Implementation
274 //===----------------------------------------------------------------------===//
276 static RegisterAnalysis<PostDominanceFrontier>
277 H("postdomfrontier", "Post-Dominance Frontier Construction", true);
279 const DominanceFrontier::DomSetType &
280 PostDominanceFrontier::calculate(const PostDominatorTree &DT,
281 const DominatorTree::Node *Node) {
282 // Loop over CFG successors to calculate DFlocal[Node]
283 BasicBlock *BB = Node->getBlock();
284 DomSetType &S = Frontiers[BB]; // The new set to fill in...
285 if (getRoots().empty()) return S;
288 for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB);
290 // Does Node immediately dominate this predecessor?
291 if (DT[*SI]->getIDom() != Node)
294 // At this point, S is DFlocal. Now we union in DFup's of our children...
295 // Loop through and visit the nodes that Node immediately dominates (Node's
296 // children in the IDomTree)
298 for (PostDominatorTree::Node::const_iterator
299 NI = Node->begin(), NE = Node->end(); NI != NE; ++NI) {
300 DominatorTree::Node *IDominee = *NI;
301 const DomSetType &ChildDF = calculate(DT, IDominee);
303 DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
304 for (; CDFI != CDFE; ++CDFI) {
305 if (!Node->properlyDominates(DT[*CDFI]))
313 // stub - a dummy function to make linking work ok.
314 void PostDominanceFrontier::stub() {