1 //===- Dominators.cpp - Dominator Calculation -----------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements simple dominator construction algorithms for finding
11 // forward dominators. Postdominators are available in libanalysis, but are not
12 // included in libvmcore, because it's not needed. Forward dominators are
13 // needed to support the Verifier pass.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Analysis/Dominators.h"
18 #include "llvm/Support/CFG.h"
19 #include "llvm/Support/Compiler.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/ADT/DepthFirstIterator.h"
22 #include "llvm/ADT/SetOperations.h"
23 #include "llvm/ADT/SmallPtrSet.h"
24 #include "llvm/ADT/SmallVector.h"
25 #include "llvm/Analysis/DominatorInternals.h"
26 #include "llvm/Instructions.h"
27 #include "llvm/Support/raw_ostream.h"
28 #include "llvm/Support/CommandLine.h"
32 // Always verify dominfo if expensive checking is enabled.
34 static bool VerifyDomInfo = true;
36 static bool VerifyDomInfo = false;
38 static cl::opt<bool,true>
39 VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo),
40 cl::desc("Verify dominator info (time consuming)"));
42 //===----------------------------------------------------------------------===//
43 // DominatorTree Implementation
44 //===----------------------------------------------------------------------===//
46 // Provide public access to DominatorTree information. Implementation details
47 // can be found in DominatorCalculation.h.
49 //===----------------------------------------------------------------------===//
51 TEMPLATE_INSTANTIATION(class llvm::DomTreeNodeBase<BasicBlock>);
52 TEMPLATE_INSTANTIATION(class llvm::DominatorTreeBase<BasicBlock>);
54 char DominatorTree::ID = 0;
55 INITIALIZE_PASS(DominatorTree, "domtree",
56 "Dominator Tree Construction", true, true)
58 bool DominatorTree::runOnFunction(Function &F) {
63 void DominatorTree::verifyAnalysis() const {
64 if (!VerifyDomInfo) return;
66 Function &F = *getRoot()->getParent();
68 DominatorTree OtherDT;
69 OtherDT.getBase().recalculate(F);
70 assert(!compare(OtherDT) && "Invalid DominatorTree info!");
73 void DominatorTree::print(raw_ostream &OS, const Module *) const {
77 // dominates - Return true if A dominates a use in B. This performs the
78 // special checks necessary if A and B are in the same basic block.
79 bool DominatorTree::dominates(const Instruction *A, const Instruction *B) const{
80 const BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
82 // If A is an invoke instruction, its value is only available in this normal
84 if (const InvokeInst *II = dyn_cast<InvokeInst>(A))
85 BBA = II->getNormalDest();
87 if (BBA != BBB) return dominates(BBA, BBB);
89 // It is not possible to determine dominance between two PHI nodes
90 // based on their ordering.
91 if (isa<PHINode>(A) && isa<PHINode>(B))
94 // Loop through the basic block until we find A or B.
95 BasicBlock::const_iterator I = BBA->begin();
96 for (; &*I != A && &*I != B; ++I)
104 //===----------------------------------------------------------------------===//
105 // DominanceFrontier Implementation
106 //===----------------------------------------------------------------------===//
108 char DominanceFrontier::ID = 0;
109 INITIALIZE_PASS(DominanceFrontier, "domfrontier",
110 "Dominance Frontier Construction", true, true)
112 void DominanceFrontier::verifyAnalysis() const {
113 if (!VerifyDomInfo) return;
115 DominatorTree &DT = getAnalysis<DominatorTree>();
117 DominanceFrontier OtherDF;
118 const std::vector<BasicBlock*> &DTRoots = DT.getRoots();
119 OtherDF.calculate(DT, DT.getNode(DTRoots[0]));
120 assert(!compare(OtherDF) && "Invalid DominanceFrontier info!");
123 // NewBB is split and now it has one successor. Update dominance frontier to
124 // reflect this change.
125 void DominanceFrontier::splitBlock(BasicBlock *NewBB) {
126 assert(NewBB->getTerminator()->getNumSuccessors() == 1 &&
127 "NewBB should have a single successor!");
128 BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);
130 // NewBBSucc inherits original NewBB frontier.
131 DominanceFrontier::iterator NewBBI = find(NewBB);
133 addBasicBlock(NewBBSucc, NewBBI->second);
135 // If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
136 // DF(NewBBSucc) without the stuff that the new block does not dominate
138 DominatorTree &DT = getAnalysis<DominatorTree>();
139 DomTreeNode *NewBBNode = DT.getNode(NewBB);
140 DomTreeNode *NewBBSuccNode = DT.getNode(NewBBSucc);
141 if (DT.dominates(NewBBNode, NewBBSuccNode)) {
142 DominanceFrontier::iterator DFI = find(NewBBSucc);
144 DominanceFrontier::DomSetType Set = DFI->second;
145 // Filter out stuff in Set that we do not dominate a predecessor of.
146 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
147 E = Set.end(); SetI != E;) {
148 bool DominatesPred = false;
149 for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
151 if (DT.dominates(NewBBNode, DT.getNode(*PI))) {
152 DominatesPred = true;
161 if (NewBBI != end()) {
162 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
163 E = Set.end(); SetI != E; ++SetI) {
164 BasicBlock *SB = *SetI;
165 addToFrontier(NewBBI, SB);
168 addBasicBlock(NewBB, Set);
172 // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
173 // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
174 // NewBBSucc)). NewBBSucc is the single successor of NewBB.
175 DominanceFrontier::DomSetType NewDFSet;
176 NewDFSet.insert(NewBBSucc);
177 addBasicBlock(NewBB, NewDFSet);
180 // Now update dominance frontiers which either used to contain NewBBSucc
181 // or which now need to include NewBB.
183 // Collect the set of blocks which dominate a predecessor of NewBB or
184 // NewSuccBB and which don't dominate both. This is an initial
185 // approximation of the blocks whose dominance frontiers will need updates.
186 SmallVector<DomTreeNode *, 16> AllPredDoms;
188 // Compute the block which dominates both NewBBSucc and NewBB. This is
189 // the immediate dominator of NewBBSucc unless NewBB dominates NewBBSucc.
190 // The code below which climbs dominator trees will stop at this point,
191 // because from this point up, dominance frontiers are unaffected.
192 DomTreeNode *DominatesBoth = 0;
194 DominatesBoth = NewBBSuccNode->getIDom();
195 if (DominatesBoth == NewBBNode)
196 DominatesBoth = NewBBNode->getIDom();
199 // Collect the set of all blocks which dominate a predecessor of NewBB.
200 SmallPtrSet<DomTreeNode *, 8> NewBBPredDoms;
201 for (pred_iterator PI = pred_begin(NewBB), E = pred_end(NewBB); PI != E; ++PI)
202 for (DomTreeNode *DTN = DT.getNode(*PI); DTN; DTN = DTN->getIDom()) {
203 if (DTN == DominatesBoth)
205 if (!NewBBPredDoms.insert(DTN))
207 AllPredDoms.push_back(DTN);
210 // Collect the set of all blocks which dominate a predecessor of NewSuccBB.
211 SmallPtrSet<DomTreeNode *, 8> NewBBSuccPredDoms;
212 for (pred_iterator PI = pred_begin(NewBBSucc),
213 E = pred_end(NewBBSucc); PI != E; ++PI)
214 for (DomTreeNode *DTN = DT.getNode(*PI); DTN; DTN = DTN->getIDom()) {
215 if (DTN == DominatesBoth)
217 if (!NewBBSuccPredDoms.insert(DTN))
219 if (!NewBBPredDoms.count(DTN))
220 AllPredDoms.push_back(DTN);
223 // Visit all relevant dominance frontiers and make any needed updates.
224 for (SmallVectorImpl<DomTreeNode *>::const_iterator I = AllPredDoms.begin(),
225 E = AllPredDoms.end(); I != E; ++I) {
226 DomTreeNode *DTN = *I;
227 iterator DFI = find((*I)->getBlock());
229 // Only consider nodes that have NewBBSucc in their dominator frontier.
230 if (DFI == end() || !DFI->second.count(NewBBSucc)) continue;
232 // If the block dominates a predecessor of NewBB but does not properly
233 // dominate NewBB itself, add NewBB to its dominance frontier.
234 if (NewBBPredDoms.count(DTN) &&
235 !DT.properlyDominates(DTN, NewBBNode))
236 addToFrontier(DFI, NewBB);
238 // If the block does not dominate a predecessor of NewBBSucc or
239 // properly dominates NewBBSucc itself, remove NewBBSucc from its
240 // dominance frontier.
241 if (!NewBBSuccPredDoms.count(DTN) ||
242 DT.properlyDominates(DTN, NewBBSuccNode))
243 removeFromFrontier(DFI, NewBBSucc);
248 class DFCalculateWorkObject {
250 DFCalculateWorkObject(BasicBlock *B, BasicBlock *P,
251 const DomTreeNode *N,
252 const DomTreeNode *PN)
253 : currentBB(B), parentBB(P), Node(N), parentNode(PN) {}
254 BasicBlock *currentBB;
255 BasicBlock *parentBB;
256 const DomTreeNode *Node;
257 const DomTreeNode *parentNode;
261 const DominanceFrontier::DomSetType &
262 DominanceFrontier::calculate(const DominatorTree &DT,
263 const DomTreeNode *Node) {
264 BasicBlock *BB = Node->getBlock();
265 DomSetType *Result = NULL;
267 std::vector<DFCalculateWorkObject> workList;
268 SmallPtrSet<BasicBlock *, 32> visited;
270 workList.push_back(DFCalculateWorkObject(BB, NULL, Node, NULL));
272 DFCalculateWorkObject *currentW = &workList.back();
273 assert (currentW && "Missing work object.");
275 BasicBlock *currentBB = currentW->currentBB;
276 BasicBlock *parentBB = currentW->parentBB;
277 const DomTreeNode *currentNode = currentW->Node;
278 const DomTreeNode *parentNode = currentW->parentNode;
279 assert (currentBB && "Invalid work object. Missing current Basic Block");
280 assert (currentNode && "Invalid work object. Missing current Node");
281 DomSetType &S = Frontiers[currentBB];
283 // Visit each block only once.
284 if (visited.count(currentBB) == 0) {
285 visited.insert(currentBB);
287 // Loop over CFG successors to calculate DFlocal[currentNode]
288 for (succ_iterator SI = succ_begin(currentBB), SE = succ_end(currentBB);
290 // Does Node immediately dominate this successor?
291 if (DT[*SI]->getIDom() != currentNode)
296 // At this point, S is DFlocal. Now we union in DFup's of our children...
297 // Loop through and visit the nodes that Node immediately dominates (Node's
298 // children in the IDomTree)
299 bool visitChild = false;
300 for (DomTreeNode::const_iterator NI = currentNode->begin(),
301 NE = currentNode->end(); NI != NE; ++NI) {
302 DomTreeNode *IDominee = *NI;
303 BasicBlock *childBB = IDominee->getBlock();
304 if (visited.count(childBB) == 0) {
305 workList.push_back(DFCalculateWorkObject(childBB, currentBB,
306 IDominee, currentNode));
311 // If all children are visited or there is any child then pop this block
312 // from the workList.
320 DomSetType::const_iterator CDFI = S.begin(), CDFE = S.end();
321 DomSetType &parentSet = Frontiers[parentBB];
322 for (; CDFI != CDFE; ++CDFI) {
323 if (!DT.properlyDominates(parentNode, DT[*CDFI]))
324 parentSet.insert(*CDFI);
329 } while (!workList.empty());
334 void DominanceFrontierBase::print(raw_ostream &OS, const Module* ) const {
335 for (const_iterator I = begin(), E = end(); I != E; ++I) {
336 OS << " DomFrontier for BB ";
338 WriteAsOperand(OS, I->first, false);
340 OS << " <<exit node>>";
343 const std::set<BasicBlock*> &BBs = I->second;
345 for (std::set<BasicBlock*>::const_iterator I = BBs.begin(), E = BBs.end();
349 WriteAsOperand(OS, *I, false);
351 OS << "<<exit node>>";
357 void DominanceFrontierBase::dump() const {