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/DominanceFrontier.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/Assembly/Writer.h"
27 #include "llvm/Instructions.h"
28 #include "llvm/Support/raw_ostream.h"
29 #include "llvm/Support/CommandLine.h"
33 // Always verify dominfo if expensive checking is enabled.
35 static bool VerifyDomInfo = true;
37 static bool VerifyDomInfo = false;
39 static cl::opt<bool,true>
40 VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo),
41 cl::desc("Verify dominator info (time consuming)"));
43 //===----------------------------------------------------------------------===//
44 // DominatorTree Implementation
45 //===----------------------------------------------------------------------===//
47 // Provide public access to DominatorTree information. Implementation details
48 // can be found in DominatorCalculation.h.
50 //===----------------------------------------------------------------------===//
52 TEMPLATE_INSTANTIATION(class llvm::DomTreeNodeBase<BasicBlock>);
53 TEMPLATE_INSTANTIATION(class llvm::DominatorTreeBase<BasicBlock>);
55 char DominatorTree::ID = 0;
56 INITIALIZE_PASS(DominatorTree, "domtree",
57 "Dominator Tree Construction", true, true)
59 bool DominatorTree::runOnFunction(Function &F) {
64 void DominatorTree::verifyAnalysis() const {
65 if (!VerifyDomInfo) return;
67 Function &F = *getRoot()->getParent();
69 DominatorTree OtherDT;
70 OtherDT.getBase().recalculate(F);
71 if (compare(OtherDT)) {
72 errs() << "DominatorTree is not up to date! Computed:\n";
75 errs() << "\nActual:\n";
76 OtherDT.print(errs());
81 void DominatorTree::print(raw_ostream &OS, const Module *) const {
85 // dominates - Return true if A dominates a use in B. This performs the
86 // special checks necessary if A and B are in the same basic block.
87 bool DominatorTree::dominates(const Instruction *A, const Instruction *B) const{
88 const BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
90 // If A is an invoke instruction, its value is only available in this normal
92 if (const InvokeInst *II = dyn_cast<InvokeInst>(A))
93 BBA = II->getNormalDest();
95 if (BBA != BBB) return dominates(BBA, BBB);
97 // It is not possible to determine dominance between two PHI nodes
98 // based on their ordering.
99 if (isa<PHINode>(A) && isa<PHINode>(B))
102 // Loop through the basic block until we find A or B.
103 BasicBlock::const_iterator I = BBA->begin();
104 for (; &*I != A && &*I != B; ++I)
112 //===----------------------------------------------------------------------===//
113 // DominanceFrontier Implementation
114 //===----------------------------------------------------------------------===//
116 char DominanceFrontier::ID = 0;
117 INITIALIZE_PASS_BEGIN(DominanceFrontier, "domfrontier",
118 "Dominance Frontier Construction", true, true)
119 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
120 INITIALIZE_PASS_END(DominanceFrontier, "domfrontier",
121 "Dominance Frontier Construction", true, true)
123 void DominanceFrontier::verifyAnalysis() const {
124 if (!VerifyDomInfo) return;
126 DominatorTree &DT = getAnalysis<DominatorTree>();
128 DominanceFrontier OtherDF;
129 const std::vector<BasicBlock*> &DTRoots = DT.getRoots();
130 OtherDF.calculate(DT, DT.getNode(DTRoots[0]));
131 assert(!compare(OtherDF) && "Invalid DominanceFrontier info!");
134 // NewBB is split and now it has one successor. Update dominance frontier to
135 // reflect this change.
136 void DominanceFrontier::splitBlock(BasicBlock *NewBB) {
137 assert(NewBB->getTerminator()->getNumSuccessors() == 1 &&
138 "NewBB should have a single successor!");
139 BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);
141 // NewBBSucc inherits original NewBB frontier.
142 DominanceFrontier::iterator NewBBI = find(NewBB);
144 addBasicBlock(NewBBSucc, NewBBI->second);
146 // If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
147 // DF(NewBBSucc) without the stuff that the new block does not dominate
149 DominatorTree &DT = getAnalysis<DominatorTree>();
150 DomTreeNode *NewBBNode = DT.getNode(NewBB);
151 DomTreeNode *NewBBSuccNode = DT.getNode(NewBBSucc);
152 if (DT.dominates(NewBBNode, NewBBSuccNode)) {
153 DominanceFrontier::iterator DFI = find(NewBBSucc);
155 DominanceFrontier::DomSetType Set = DFI->second;
156 // Filter out stuff in Set that we do not dominate a predecessor of.
157 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
158 E = Set.end(); SetI != E;) {
159 bool DominatesPred = false;
160 for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
162 if (DT.dominates(NewBBNode, DT.getNode(*PI))) {
163 DominatesPred = true;
172 if (NewBBI != end()) {
173 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
174 E = Set.end(); SetI != E; ++SetI) {
175 BasicBlock *SB = *SetI;
176 addToFrontier(NewBBI, SB);
179 addBasicBlock(NewBB, Set);
183 // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
184 // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
185 // NewBBSucc)). NewBBSucc is the single successor of NewBB.
186 DominanceFrontier::DomSetType NewDFSet;
187 NewDFSet.insert(NewBBSucc);
188 addBasicBlock(NewBB, NewDFSet);
191 // Now update dominance frontiers which either used to contain NewBBSucc
192 // or which now need to include NewBB.
194 // Collect the set of blocks which dominate a predecessor of NewBB or
195 // NewSuccBB and which don't dominate both. This is an initial
196 // approximation of the blocks whose dominance frontiers will need updates.
197 SmallVector<DomTreeNode *, 16> AllPredDoms;
199 // Compute the block which dominates both NewBBSucc and NewBB. This is
200 // the immediate dominator of NewBBSucc unless NewBB dominates NewBBSucc.
201 // The code below which climbs dominator trees will stop at this point,
202 // because from this point up, dominance frontiers are unaffected.
203 DomTreeNode *DominatesBoth = 0;
205 DominatesBoth = NewBBSuccNode->getIDom();
206 if (DominatesBoth == NewBBNode)
207 DominatesBoth = NewBBNode->getIDom();
210 // Collect the set of all blocks which dominate a predecessor of NewBB.
211 SmallPtrSet<DomTreeNode *, 8> NewBBPredDoms;
212 for (pred_iterator PI = pred_begin(NewBB), E = pred_end(NewBB); PI != E; ++PI)
213 for (DomTreeNode *DTN = DT.getNode(*PI); DTN; DTN = DTN->getIDom()) {
214 if (DTN == DominatesBoth)
216 if (!NewBBPredDoms.insert(DTN))
218 AllPredDoms.push_back(DTN);
221 // Collect the set of all blocks which dominate a predecessor of NewSuccBB.
222 SmallPtrSet<DomTreeNode *, 8> NewBBSuccPredDoms;
223 for (pred_iterator PI = pred_begin(NewBBSucc),
224 E = pred_end(NewBBSucc); PI != E; ++PI)
225 for (DomTreeNode *DTN = DT.getNode(*PI); DTN; DTN = DTN->getIDom()) {
226 if (DTN == DominatesBoth)
228 if (!NewBBSuccPredDoms.insert(DTN))
230 if (!NewBBPredDoms.count(DTN))
231 AllPredDoms.push_back(DTN);
234 // Visit all relevant dominance frontiers and make any needed updates.
235 for (SmallVectorImpl<DomTreeNode *>::const_iterator I = AllPredDoms.begin(),
236 E = AllPredDoms.end(); I != E; ++I) {
237 DomTreeNode *DTN = *I;
238 iterator DFI = find((*I)->getBlock());
240 // Only consider nodes that have NewBBSucc in their dominator frontier.
241 if (DFI == end() || !DFI->second.count(NewBBSucc)) continue;
243 // If the block dominates a predecessor of NewBB but does not properly
244 // dominate NewBB itself, add NewBB to its dominance frontier.
245 if (NewBBPredDoms.count(DTN) &&
246 !DT.properlyDominates(DTN, NewBBNode))
247 addToFrontier(DFI, NewBB);
249 // If the block does not dominate a predecessor of NewBBSucc or
250 // properly dominates NewBBSucc itself, remove NewBBSucc from its
251 // dominance frontier.
252 if (!NewBBSuccPredDoms.count(DTN) ||
253 DT.properlyDominates(DTN, NewBBSuccNode))
254 removeFromFrontier(DFI, NewBBSucc);
259 class DFCalculateWorkObject {
261 DFCalculateWorkObject(BasicBlock *B, BasicBlock *P,
262 const DomTreeNode *N,
263 const DomTreeNode *PN)
264 : currentBB(B), parentBB(P), Node(N), parentNode(PN) {}
265 BasicBlock *currentBB;
266 BasicBlock *parentBB;
267 const DomTreeNode *Node;
268 const DomTreeNode *parentNode;
272 const DominanceFrontier::DomSetType &
273 DominanceFrontier::calculate(const DominatorTree &DT,
274 const DomTreeNode *Node) {
275 BasicBlock *BB = Node->getBlock();
276 DomSetType *Result = NULL;
278 std::vector<DFCalculateWorkObject> workList;
279 SmallPtrSet<BasicBlock *, 32> visited;
281 workList.push_back(DFCalculateWorkObject(BB, NULL, Node, NULL));
283 DFCalculateWorkObject *currentW = &workList.back();
284 assert (currentW && "Missing work object.");
286 BasicBlock *currentBB = currentW->currentBB;
287 BasicBlock *parentBB = currentW->parentBB;
288 const DomTreeNode *currentNode = currentW->Node;
289 const DomTreeNode *parentNode = currentW->parentNode;
290 assert (currentBB && "Invalid work object. Missing current Basic Block");
291 assert (currentNode && "Invalid work object. Missing current Node");
292 DomSetType &S = Frontiers[currentBB];
294 // Visit each block only once.
295 if (visited.count(currentBB) == 0) {
296 visited.insert(currentBB);
298 // Loop over CFG successors to calculate DFlocal[currentNode]
299 for (succ_iterator SI = succ_begin(currentBB), SE = succ_end(currentBB);
301 // Does Node immediately dominate this successor?
302 if (DT[*SI]->getIDom() != currentNode)
307 // At this point, S is DFlocal. Now we union in DFup's of our children...
308 // Loop through and visit the nodes that Node immediately dominates (Node's
309 // children in the IDomTree)
310 bool visitChild = false;
311 for (DomTreeNode::const_iterator NI = currentNode->begin(),
312 NE = currentNode->end(); NI != NE; ++NI) {
313 DomTreeNode *IDominee = *NI;
314 BasicBlock *childBB = IDominee->getBlock();
315 if (visited.count(childBB) == 0) {
316 workList.push_back(DFCalculateWorkObject(childBB, currentBB,
317 IDominee, currentNode));
322 // If all children are visited or there is any child then pop this block
323 // from the workList.
331 DomSetType::const_iterator CDFI = S.begin(), CDFE = S.end();
332 DomSetType &parentSet = Frontiers[parentBB];
333 for (; CDFI != CDFE; ++CDFI) {
334 if (!DT.properlyDominates(parentNode, DT[*CDFI]))
335 parentSet.insert(*CDFI);
340 } while (!workList.empty());
345 void DominanceFrontierBase::print(raw_ostream &OS, const Module* ) const {
346 for (const_iterator I = begin(), E = end(); I != E; ++I) {
347 OS << " DomFrontier for BB ";
349 WriteAsOperand(OS, I->first, false);
351 OS << " <<exit node>>";
354 const std::set<BasicBlock*> &BBs = I->second;
356 for (std::set<BasicBlock*>::const_iterator I = BBs.begin(), E = BBs.end();
360 WriteAsOperand(OS, *I, false);
362 OS << "<<exit node>>";
368 void DominanceFrontierBase::dump() const {