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 SmallVector<BasicBlock*, 8> PredBlocks;
131 for (pred_iterator PI = pred_begin(NewBB), PE = pred_end(NewBB);
133 PredBlocks.push_back(*PI);
135 if (PredBlocks.empty())
136 // If NewBB does not have any predecessors then it is a entry block.
137 // In this case, NewBB and its successor NewBBSucc dominates all
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 if (DT.dominates(NewBB, NewBBSucc)) {
151 DominanceFrontier::iterator DFI = find(NewBBSucc);
153 DominanceFrontier::DomSetType Set = DFI->second;
154 // Filter out stuff in Set that we do not dominate a predecessor of.
155 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
156 E = Set.end(); SetI != E;) {
157 bool DominatesPred = false;
158 for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
160 if (DT.dominates(NewBB, *PI)) {
161 DominatesPred = true;
170 if (NewBBI != end()) {
171 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
172 E = Set.end(); SetI != E; ++SetI) {
173 BasicBlock *SB = *SetI;
174 addToFrontier(NewBBI, SB);
177 addBasicBlock(NewBB, Set);
181 // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
182 // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
183 // NewBBSucc)). NewBBSucc is the single successor of NewBB.
184 DominanceFrontier::DomSetType NewDFSet;
185 NewDFSet.insert(NewBBSucc);
186 addBasicBlock(NewBB, NewDFSet);
189 // Now we must loop over all of the dominance frontiers in the function,
190 // replacing occurrences of NewBBSucc with NewBB in some cases. All
191 // blocks that dominate a block in PredBlocks and contained NewBBSucc in
192 // their dominance frontier must be updated to contain NewBB instead.
194 for (Function::iterator FI = NewBB->getParent()->begin(),
195 FE = NewBB->getParent()->end(); FI != FE; ++FI) {
196 DominanceFrontier::iterator DFI = find(FI);
197 if (DFI == end()) continue; // unreachable block.
199 // Only consider nodes that have NewBBSucc in their dominator frontier.
200 if (!DFI->second.count(NewBBSucc)) continue;
202 // Verify whether this block dominates a block in predblocks. If not, do
204 bool BlockDominatesAny = false;
205 for (SmallVectorImpl<BasicBlock*>::const_iterator BI = PredBlocks.begin(),
206 BE = PredBlocks.end(); BI != BE; ++BI) {
207 if (DT.dominates(FI, *BI)) {
208 BlockDominatesAny = true;
213 // If NewBBSucc should not stay in our dominator frontier, remove it.
214 // We remove it unless there is a predecessor of NewBBSucc that we
215 // dominate, but we don't strictly dominate NewBBSucc.
216 bool ShouldRemove = true;
217 if ((BasicBlock*)FI == NewBBSucc || !DT.dominates(FI, NewBBSucc)) {
218 // Okay, we know that PredDom does not strictly dominate NewBBSucc.
219 // Check to see if it dominates any predecessors of NewBBSucc.
220 for (pred_iterator PI = pred_begin(NewBBSucc),
221 E = pred_end(NewBBSucc); PI != E; ++PI)
222 if (DT.dominates(FI, *PI)) {
223 ShouldRemove = false;
229 removeFromFrontier(DFI, NewBBSucc);
230 if (BlockDominatesAny && (&*FI == NewBB || !DT.dominates(FI, NewBB)))
231 addToFrontier(DFI, NewBB);
236 class DFCalculateWorkObject {
238 DFCalculateWorkObject(BasicBlock *B, BasicBlock *P,
239 const DomTreeNode *N,
240 const DomTreeNode *PN)
241 : currentBB(B), parentBB(P), Node(N), parentNode(PN) {}
242 BasicBlock *currentBB;
243 BasicBlock *parentBB;
244 const DomTreeNode *Node;
245 const DomTreeNode *parentNode;
249 const DominanceFrontier::DomSetType &
250 DominanceFrontier::calculate(const DominatorTree &DT,
251 const DomTreeNode *Node) {
252 BasicBlock *BB = Node->getBlock();
253 DomSetType *Result = NULL;
255 std::vector<DFCalculateWorkObject> workList;
256 SmallPtrSet<BasicBlock *, 32> visited;
258 workList.push_back(DFCalculateWorkObject(BB, NULL, Node, NULL));
260 DFCalculateWorkObject *currentW = &workList.back();
261 assert (currentW && "Missing work object.");
263 BasicBlock *currentBB = currentW->currentBB;
264 BasicBlock *parentBB = currentW->parentBB;
265 const DomTreeNode *currentNode = currentW->Node;
266 const DomTreeNode *parentNode = currentW->parentNode;
267 assert (currentBB && "Invalid work object. Missing current Basic Block");
268 assert (currentNode && "Invalid work object. Missing current Node");
269 DomSetType &S = Frontiers[currentBB];
271 // Visit each block only once.
272 if (visited.count(currentBB) == 0) {
273 visited.insert(currentBB);
275 // Loop over CFG successors to calculate DFlocal[currentNode]
276 for (succ_iterator SI = succ_begin(currentBB), SE = succ_end(currentBB);
278 // Does Node immediately dominate this successor?
279 if (DT[*SI]->getIDom() != currentNode)
284 // At this point, S is DFlocal. Now we union in DFup's of our children...
285 // Loop through and visit the nodes that Node immediately dominates (Node's
286 // children in the IDomTree)
287 bool visitChild = false;
288 for (DomTreeNode::const_iterator NI = currentNode->begin(),
289 NE = currentNode->end(); NI != NE; ++NI) {
290 DomTreeNode *IDominee = *NI;
291 BasicBlock *childBB = IDominee->getBlock();
292 if (visited.count(childBB) == 0) {
293 workList.push_back(DFCalculateWorkObject(childBB, currentBB,
294 IDominee, currentNode));
299 // If all children are visited or there is any child then pop this block
300 // from the workList.
308 DomSetType::const_iterator CDFI = S.begin(), CDFE = S.end();
309 DomSetType &parentSet = Frontiers[parentBB];
310 for (; CDFI != CDFE; ++CDFI) {
311 if (!DT.properlyDominates(parentNode, DT[*CDFI]))
312 parentSet.insert(*CDFI);
317 } while (!workList.empty());
322 void DominanceFrontierBase::print(raw_ostream &OS, const Module* ) const {
323 for (const_iterator I = begin(), E = end(); I != E; ++I) {
324 OS << " DomFrontier for BB ";
326 WriteAsOperand(OS, I->first, false);
328 OS << " <<exit node>>";
331 const std::set<BasicBlock*> &BBs = I->second;
333 for (std::set<BasicBlock*>::const_iterator I = BBs.begin(), E = BBs.end();
337 WriteAsOperand(OS, *I, false);
339 OS << "<<exit node>>";
345 void DominanceFrontierBase::dump() const {