1 //===- PostDominators.cpp - Post-Dominator Calculation --------------------===//
3 // This file implements the post-dominator construction algorithms.
5 //===----------------------------------------------------------------------===//
7 #include "llvm/Analysis/PostDominators.h"
8 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
9 #include "llvm/Support/CFG.h"
10 #include "Support/DepthFirstIterator.h"
11 #include "Support/SetOperations.h"
13 //===----------------------------------------------------------------------===//
14 // PostDominatorSet Implementation
15 //===----------------------------------------------------------------------===//
17 static RegisterAnalysis<PostDominatorSet>
18 B("postdomset", "Post-Dominator Set Construction", true);
20 // Postdominator set construction. This converts the specified function to only
21 // have a single exit node (return stmt), then calculates the post dominance
22 // sets for the function.
24 bool PostDominatorSet::runOnFunction(Function &F) {
25 Doms.clear(); // Reset from the last time we were run...
26 // Since we require that the unify all exit nodes pass has been run, we know
27 // that there can be at most one return instruction in the function left.
30 Root = getAnalysis<UnifyFunctionExitNodes>().getExitNode();
32 if (Root == 0) { // No exit node for the function? Postdomsets are all empty
33 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
34 Doms[FI] = DomSetType();
42 std::set<const BasicBlock*> Visited;
43 DomSetType WorkingSet;
44 idf_iterator<BasicBlock*> It = idf_begin(Root), End = idf_end(Root);
45 for ( ; It != End; ++It) {
47 succ_iterator PI = succ_begin(BB), PEnd = succ_end(BB);
48 if (PI != PEnd) { // Is there SOME predecessor?
49 // Loop until we get to a successor that has had it's dom set filled
50 // in at least once. We are guaranteed to have this because we are
51 // traversing the graph in DFO and have handled start nodes specially.
53 while (Doms[*PI].size() == 0) ++PI;
54 WorkingSet = Doms[*PI];
56 for (++PI; PI != PEnd; ++PI) { // Intersect all of the successor sets
57 DomSetType &PredSet = Doms[*PI];
59 set_intersect(WorkingSet, PredSet);
61 } else if (BB != Root) {
62 // If this isn't the root basic block and it has no successors, it must
63 // be an non-returning block. Fib a bit by saying that the root node
64 // postdominates this unreachable node. This isn't exactly true,
65 // because there is no path from this node to the root node, but it is
66 // sorta true because any paths to the exit node would have to go
69 // This allows for postdominator properties to be built for code that
70 // doesn't return in a reasonable manner.
72 WorkingSet = Doms[Root];
75 WorkingSet.insert(BB); // A block always dominates itself
76 DomSetType &BBSet = Doms[BB];
77 if (BBSet != WorkingSet) {
78 BBSet.swap(WorkingSet); // Constant time operation!
79 Changed = true; // The sets changed.
81 WorkingSet.clear(); // Clear out the set for next iteration
87 // getAnalysisUsage - This obviously provides a post-dominator set, but it also
88 // requires the UnifyFunctionExitNodes pass.
90 void PostDominatorSet::getAnalysisUsage(AnalysisUsage &AU) const {
92 AU.addRequired<UnifyFunctionExitNodes>();
95 //===----------------------------------------------------------------------===//
96 // ImmediatePostDominators Implementation
97 //===----------------------------------------------------------------------===//
99 static RegisterAnalysis<ImmediatePostDominators>
100 D("postidom", "Immediate Post-Dominators Construction", true);
102 //===----------------------------------------------------------------------===//
103 // PostDominatorTree Implementation
104 //===----------------------------------------------------------------------===//
106 static RegisterAnalysis<PostDominatorTree>
107 F("postdomtree", "Post-Dominator Tree Construction", true);
109 void PostDominatorTree::calculate(const PostDominatorSet &DS) {
110 Nodes[Root] = new Node(Root, 0); // Add a node for the root...
113 // Iterate over all nodes in depth first order...
114 for (idf_iterator<BasicBlock*> I = idf_begin(Root), E = idf_end(Root);
117 const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
118 unsigned DomSetSize = Dominators.size();
119 if (DomSetSize == 1) continue; // Root node... IDom = null
121 // Loop over all dominators of this node. This corresponds to looping
122 // over nodes in the dominator chain, looking for a node whose dominator
123 // set is equal to the current nodes, except that the current node does
124 // not exist in it. This means that it is one level higher in the dom
125 // chain than the current node, and it is our idom! We know that we have
126 // already added a DominatorTree node for our idom, because the idom must
127 // be a predecessor in the depth first order that we are iterating through
130 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
131 DominatorSet::DomSetType::const_iterator End = Dominators.end();
132 for (; I != End; ++I) { // Iterate over dominators...
133 // All of our dominators should form a chain, where the number
134 // of elements in the dominator set indicates what level the
135 // node is at in the chain. We want the node immediately
136 // above us, so it will have an identical dominator set,
137 // 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) {
141 // We know that the immediate dominator should already have a node,
142 // because we are traversing the CFG in depth first order!
144 Node *IDomNode = Nodes[*I];
145 assert(IDomNode && "No node for IDOM?");
147 // Add a new tree node for this BasicBlock, and link it as a child of
149 Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
157 //===----------------------------------------------------------------------===//
158 // PostDominanceFrontier Implementation
159 //===----------------------------------------------------------------------===//
161 static RegisterAnalysis<PostDominanceFrontier>
162 H("postdomfrontier", "Post-Dominance Frontier Construction", true);
164 const DominanceFrontier::DomSetType &
165 PostDominanceFrontier::calculate(const PostDominatorTree &DT,
166 const DominatorTree::Node *Node) {
167 // Loop over CFG successors to calculate DFlocal[Node]
168 BasicBlock *BB = Node->getNode();
169 DomSetType &S = Frontiers[BB]; // The new set to fill in...
172 for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB);
174 // Does Node immediately dominate this predeccessor?
175 if (DT[*SI]->getIDom() != Node)
179 // At this point, S is DFlocal. Now we union in DFup's of our children...
180 // Loop through and visit the nodes that Node immediately dominates (Node's
181 // children in the IDomTree)
183 for (PostDominatorTree::Node::const_iterator
184 NI = Node->begin(), NE = Node->end(); NI != NE; ++NI) {
185 DominatorTree::Node *IDominee = *NI;
186 const DomSetType &ChildDF = calculate(DT, IDominee);
188 DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
189 for (; CDFI != CDFE; ++CDFI) {
190 if (!Node->dominates(DT[*CDFI]))
198 // stub - a dummy function to make linking work ok.
199 void PostDominanceFrontier::stub() {