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/iTerminators.h"
16 #include "llvm/Support/CFG.h"
17 #include "Support/DepthFirstIterator.h"
18 #include "Support/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 (isa<ReturnInst>(I->getTerminator()) ||
44 isa<UnwindInst>(I->getTerminator()))
48 // If there are no exit nodes for the function, postdomsets are all empty.
49 // This can happen if the function just contains an infinite loop, for
51 if (Roots.empty()) return false;
53 // If we have more than one root, we insert an artificial "null" exit, which
54 // has "virtual edges" to each of the real exit nodes.
62 std::set<BasicBlock*> Visited;
63 DomSetType WorkingSet;
65 for (unsigned i = 0, e = Roots.size(); i != e; ++i)
66 for (idf_ext_iterator<BasicBlock*> It = idf_ext_begin(Roots[i], Visited),
67 E = idf_ext_end(Roots[i], Visited); It != E; ++It) {
69 succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
70 if (SI != SE) { // Is there SOME successor?
71 // Loop until we get to a successor 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[*SI].size() == 0) ++SI;
76 WorkingSet = Doms[*SI];
78 for (++SI; SI != SE; ++SI) { // Intersect all of the successor sets
79 DomSetType &SuccSet = Doms[*SI];
81 set_intersect(WorkingSet, SuccSet);
84 // If this node has no successors, it must be one of the root nodes.
85 // We will already take care of the notion that the node
86 // post-dominates itself. The only thing we have to add is that if
87 // there are multiple root nodes, we want to insert a special "null"
88 // exit node which dominates the roots as well.
93 WorkingSet.insert(BB); // A block always dominates itself
94 DomSetType &BBSet = Doms[BB];
95 if (BBSet != WorkingSet) {
96 BBSet.swap(WorkingSet); // Constant time operation!
97 Changed = true; // The sets changed.
99 WorkingSet.clear(); // Clear out the set for next iteration
105 //===----------------------------------------------------------------------===//
106 // ImmediatePostDominators Implementation
107 //===----------------------------------------------------------------------===//
109 static RegisterAnalysis<ImmediatePostDominators>
110 D("postidom", "Immediate Post-Dominators Construction", true);
113 // calcIDoms - Calculate the immediate dominator mapping, given a set of
114 // dominators for every basic block.
115 void ImmediatePostDominators::calcIDoms(const DominatorSetBase &DS) {
116 // Loop over all of the nodes that have dominators... figuring out the IDOM
119 for (DominatorSet::const_iterator DI = DS.begin(), DEnd = DS.end();
121 BasicBlock *BB = DI->first;
122 const DominatorSet::DomSetType &Dominators = DI->second;
123 unsigned DomSetSize = Dominators.size();
124 if (DomSetSize == 1) continue; // Root node... IDom = null
126 // Loop over all dominators of this node. This corresponds to looping over
127 // nodes in the dominator chain, looking for a node whose dominator set is
128 // equal to the current nodes, except that the current node does not exist
129 // in it. This means that it is one level higher in the dom chain than the
130 // current node, and it is our idom!
132 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
133 DominatorSet::DomSetType::const_iterator End = Dominators.end();
134 for (; I != End; ++I) { // Iterate over dominators...
135 // All of our dominators should form a chain, where the number of elements
136 // in the dominator set indicates what level the node is at in the chain.
137 // We want the node immediately above us, so it will have an identical
138 // dominator set, except that BB will not dominate it... therefore it's
139 // dominator set size will be one less than BB's...
141 if (DS.getDominators(*I).size() == DomSetSize - 1) {
149 //===----------------------------------------------------------------------===//
150 // PostDominatorTree Implementation
151 //===----------------------------------------------------------------------===//
153 static RegisterAnalysis<PostDominatorTree>
154 F("postdomtree", "Post-Dominator Tree Construction", true);
156 void PostDominatorTree::calculate(const PostDominatorSet &DS) {
157 if (Roots.empty()) return;
158 BasicBlock *Root = Roots.size() == 1 ? Roots[0] : 0;
160 Nodes[Root] = RootNode = new Node(Root, 0); // Add a node for the root...
162 // Iterate over all nodes in depth first order...
163 for (unsigned i = 0, e = Roots.size(); i != e; ++i)
164 for (idf_iterator<BasicBlock*> I = idf_begin(Roots[i]),
165 E = idf_end(Roots[i]); I != E; ++I) {
167 const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
168 unsigned DomSetSize = Dominators.size();
169 if (DomSetSize == 1) continue; // Root node... IDom = null
171 // If we have already computed the immediate dominator for this node,
172 // don't revisit. This can happen due to nodes reachable from multiple
173 // roots, but which the idf_iterator doesn't know about.
174 if (Nodes.find(BB) != Nodes.end()) continue;
176 // Loop over all dominators of this node. This corresponds to looping
177 // over nodes in the dominator chain, looking for a node whose dominator
178 // set is equal to the current nodes, except that the current node does
179 // not exist in it. This means that it is one level higher in the dom
180 // chain than the current node, and it is our idom! We know that we have
181 // already added a DominatorTree node for our idom, because the idom must
182 // be a predecessor in the depth first order that we are iterating through
185 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
186 DominatorSet::DomSetType::const_iterator End = Dominators.end();
187 for (; I != End; ++I) { // Iterate over dominators...
188 // All of our dominators should form a chain, where the number
189 // of elements in the dominator set indicates what level the
190 // node is at in the chain. We want the node immediately
191 // above us, so it will have an identical dominator set,
192 // except that BB will not dominate it... therefore it's
193 // dominator set size will be one less than BB's...
195 if (DS.getDominators(*I).size() == DomSetSize - 1) {
196 // We know that the immediate dominator should already have a node,
197 // because we are traversing the CFG in depth first order!
199 Node *IDomNode = Nodes[*I];
200 assert(IDomNode && "No node for IDOM?");
202 // Add a new tree node for this BasicBlock, and link it as a child of
204 Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
211 //===----------------------------------------------------------------------===//
212 // PostDominanceFrontier Implementation
213 //===----------------------------------------------------------------------===//
215 static RegisterAnalysis<PostDominanceFrontier>
216 H("postdomfrontier", "Post-Dominance Frontier Construction", true);
218 const DominanceFrontier::DomSetType &
219 PostDominanceFrontier::calculate(const PostDominatorTree &DT,
220 const DominatorTree::Node *Node) {
221 // Loop over CFG successors to calculate DFlocal[Node]
222 BasicBlock *BB = Node->getBlock();
223 DomSetType &S = Frontiers[BB]; // The new set to fill in...
224 if (getRoots().empty()) return S;
227 for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB);
229 // Does Node immediately dominate this predecessor?
230 if (DT[*SI]->getIDom() != Node)
233 // At this point, S is DFlocal. Now we union in DFup's of our children...
234 // Loop through and visit the nodes that Node immediately dominates (Node's
235 // children in the IDomTree)
237 for (PostDominatorTree::Node::const_iterator
238 NI = Node->begin(), NE = Node->end(); NI != NE; ++NI) {
239 DominatorTree::Node *IDominee = *NI;
240 const DomSetType &ChildDF = calculate(DT, IDominee);
242 DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
243 for (; CDFI != CDFE; ++CDFI) {
244 if (!Node->dominates(DT[*CDFI]))
252 // stub - a dummy function to make linking work ok.
253 void PostDominanceFrontier::stub() {