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/IR/Dominators.h"
18 #include "llvm/ADT/DepthFirstIterator.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/IR/CFG.h"
21 #include "llvm/IR/Instructions.h"
22 #include "llvm/IR/PassManager.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/GenericDomTreeConstruction.h"
26 #include "llvm/Support/raw_ostream.h"
30 // Always verify dominfo if expensive checking is enabled.
31 #ifdef EXPENSIVE_CHECKS
32 bool llvm::VerifyDomInfo = true;
34 bool llvm::VerifyDomInfo = false;
36 static cl::opt<bool, true>
37 VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), cl::Hidden,
38 cl::desc("Verify dominator info (time consuming)"));
40 bool BasicBlockEdge::isSingleEdge() const {
41 const TerminatorInst *TI = Start->getTerminator();
42 unsigned NumEdgesToEnd = 0;
43 for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) {
44 if (TI->getSuccessor(i) == End)
46 if (NumEdgesToEnd >= 2)
49 assert(NumEdgesToEnd == 1);
53 //===----------------------------------------------------------------------===//
54 // DominatorTree Implementation
55 //===----------------------------------------------------------------------===//
57 // Provide public access to DominatorTree information. Implementation details
58 // can be found in Dominators.h, GenericDomTree.h, and
59 // GenericDomTreeConstruction.h.
61 //===----------------------------------------------------------------------===//
63 template class llvm::DomTreeNodeBase<BasicBlock>;
64 template class llvm::DominatorTreeBase<BasicBlock, false>; // DomTreeBase
65 template class llvm::DominatorTreeBase<BasicBlock, true>; // PostDomTreeBase
67 template struct llvm::DomTreeBuilder::Update<BasicBlock *>;
69 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree>(
70 DomTreeBuilder::BBDomTree &DT);
71 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>(
72 DomTreeBuilder::BBPostDomTree &DT);
74 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>(
75 DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
76 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBPostDomTree>(
77 DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
79 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBDomTree>(
80 DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
81 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBPostDomTree>(
82 DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
84 template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBDomTree>(
85 DomTreeBuilder::BBDomTree &DT, DomTreeBuilder::BBUpdates);
86 template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>(
87 DomTreeBuilder::BBPostDomTree &DT, DomTreeBuilder::BBUpdates);
89 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>(
90 const DomTreeBuilder::BBDomTree &DT);
91 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>(
92 const DomTreeBuilder::BBPostDomTree &DT);
94 bool DominatorTree::invalidate(Function &F, const PreservedAnalyses &PA,
95 FunctionAnalysisManager::Invalidator &) {
96 // Check whether the analysis, all analyses on functions, or the function's
97 // CFG have been preserved.
98 auto PAC = PA.getChecker<DominatorTreeAnalysis>();
99 return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
100 PAC.preservedSet<CFGAnalyses>());
103 // dominates - Return true if Def dominates a use in User. This performs
104 // the special checks necessary if Def and User are in the same basic block.
105 // Note that Def doesn't dominate a use in Def itself!
106 bool DominatorTree::dominates(const Instruction *Def,
107 const Instruction *User) const {
108 const BasicBlock *UseBB = User->getParent();
109 const BasicBlock *DefBB = Def->getParent();
111 // Any unreachable use is dominated, even if Def == User.
112 if (!isReachableFromEntry(UseBB))
115 // Unreachable definitions don't dominate anything.
116 if (!isReachableFromEntry(DefBB))
119 // An instruction doesn't dominate a use in itself.
123 // The value defined by an invoke dominates an instruction only if it
124 // dominates every instruction in UseBB.
125 // A PHI is dominated only if the instruction dominates every possible use in
127 if (isa<InvokeInst>(Def) || isa<PHINode>(User))
128 return dominates(Def, UseBB);
131 return dominates(DefBB, UseBB);
133 // Loop through the basic block until we find Def or User.
134 BasicBlock::const_iterator I = DefBB->begin();
135 for (; &*I != Def && &*I != User; ++I)
141 // true if Def would dominate a use in any instruction in UseBB.
142 // note that dominates(Def, Def->getParent()) is false.
143 bool DominatorTree::dominates(const Instruction *Def,
144 const BasicBlock *UseBB) const {
145 const BasicBlock *DefBB = Def->getParent();
147 // Any unreachable use is dominated, even if DefBB == UseBB.
148 if (!isReachableFromEntry(UseBB))
151 // Unreachable definitions don't dominate anything.
152 if (!isReachableFromEntry(DefBB))
158 // Invoke results are only usable in the normal destination, not in the
159 // exceptional destination.
160 if (const auto *II = dyn_cast<InvokeInst>(Def)) {
161 BasicBlock *NormalDest = II->getNormalDest();
162 BasicBlockEdge E(DefBB, NormalDest);
163 return dominates(E, UseBB);
166 return dominates(DefBB, UseBB);
169 bool DominatorTree::dominates(const BasicBlockEdge &BBE,
170 const BasicBlock *UseBB) const {
171 // If the BB the edge ends in doesn't dominate the use BB, then the
172 // edge also doesn't.
173 const BasicBlock *Start = BBE.getStart();
174 const BasicBlock *End = BBE.getEnd();
175 if (!dominates(End, UseBB))
178 // Simple case: if the end BB has a single predecessor, the fact that it
179 // dominates the use block implies that the edge also does.
180 if (End->getSinglePredecessor())
183 // The normal edge from the invoke is critical. Conceptually, what we would
184 // like to do is split it and check if the new block dominates the use.
185 // With X being the new block, the graph would look like:
198 // Given the definition of dominance, NormalDest is dominated by X iff X
199 // dominates all of NormalDest's predecessors (X, B, C in the example). X
200 // trivially dominates itself, so we only have to find if it dominates the
201 // other predecessors. Since the only way out of X is via NormalDest, X can
202 // only properly dominate a node if NormalDest dominates that node too.
203 int IsDuplicateEdge = 0;
204 for (const_pred_iterator PI = pred_begin(End), E = pred_end(End);
206 const BasicBlock *BB = *PI;
208 // If there are multiple edges between Start and End, by definition they
209 // can't dominate anything.
210 if (IsDuplicateEdge++)
215 if (!dominates(End, BB))
221 bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const {
222 Instruction *UserInst = cast<Instruction>(U.getUser());
223 // A PHI in the end of the edge is dominated by it.
224 PHINode *PN = dyn_cast<PHINode>(UserInst);
225 if (PN && PN->getParent() == BBE.getEnd() &&
226 PN->getIncomingBlock(U) == BBE.getStart())
229 // Otherwise use the edge-dominates-block query, which
230 // handles the crazy critical edge cases properly.
231 const BasicBlock *UseBB;
233 UseBB = PN->getIncomingBlock(U);
235 UseBB = UserInst->getParent();
236 return dominates(BBE, UseBB);
239 bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
240 Instruction *UserInst = cast<Instruction>(U.getUser());
241 const BasicBlock *DefBB = Def->getParent();
243 // Determine the block in which the use happens. PHI nodes use
244 // their operands on edges; simulate this by thinking of the use
245 // happening at the end of the predecessor block.
246 const BasicBlock *UseBB;
247 if (PHINode *PN = dyn_cast<PHINode>(UserInst))
248 UseBB = PN->getIncomingBlock(U);
250 UseBB = UserInst->getParent();
252 // Any unreachable use is dominated, even if Def == User.
253 if (!isReachableFromEntry(UseBB))
256 // Unreachable definitions don't dominate anything.
257 if (!isReachableFromEntry(DefBB))
260 // Invoke instructions define their return values on the edges to their normal
261 // successors, so we have to handle them specially.
262 // Among other things, this means they don't dominate anything in
263 // their own block, except possibly a phi, so we don't need to
264 // walk the block in any case.
265 if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) {
266 BasicBlock *NormalDest = II->getNormalDest();
267 BasicBlockEdge E(DefBB, NormalDest);
268 return dominates(E, U);
271 // If the def and use are in different blocks, do a simple CFG dominator
274 return dominates(DefBB, UseBB);
276 // Ok, def and use are in the same block. If the def is an invoke, it
277 // doesn't dominate anything in the block. If it's a PHI, it dominates
278 // everything in the block.
279 if (isa<PHINode>(UserInst))
282 // Otherwise, just loop through the basic block until we find Def or User.
283 BasicBlock::const_iterator I = DefBB->begin();
284 for (; &*I != Def && &*I != UserInst; ++I)
287 return &*I != UserInst;
290 bool DominatorTree::isReachableFromEntry(const Use &U) const {
291 Instruction *I = dyn_cast<Instruction>(U.getUser());
293 // ConstantExprs aren't really reachable from the entry block, but they
294 // don't need to be treated like unreachable code either.
297 // PHI nodes use their operands on their incoming edges.
298 if (PHINode *PN = dyn_cast<PHINode>(I))
299 return isReachableFromEntry(PN->getIncomingBlock(U));
301 // Everything else uses their operands in their own block.
302 return isReachableFromEntry(I->getParent());
305 void DominatorTree::verifyDomTree() const {
306 // Perform the expensive checks only when VerifyDomInfo is set.
307 if (VerifyDomInfo && !verify()) {
308 errs() << "\n~~~~~~~~~~~\n\t\tDomTree verification failed!\n~~~~~~~~~~~\n";
313 Function &F = *getRoot()->getParent();
315 DominatorTree OtherDT;
316 OtherDT.recalculate(F);
317 if (compare(OtherDT)) {
318 errs() << "DominatorTree for function " << F.getName()
319 << " is not up to date!\nComputed:\n";
321 errs() << "\nActual:\n";
322 OtherDT.print(errs());
323 errs() << "\nCFG:\n";
330 //===----------------------------------------------------------------------===//
331 // DominatorTreeAnalysis and related pass implementations
332 //===----------------------------------------------------------------------===//
334 // This implements the DominatorTreeAnalysis which is used with the new pass
335 // manager. It also implements some methods from utility passes.
337 //===----------------------------------------------------------------------===//
339 DominatorTree DominatorTreeAnalysis::run(Function &F,
340 FunctionAnalysisManager &) {
346 AnalysisKey DominatorTreeAnalysis::Key;
348 DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {}
350 PreservedAnalyses DominatorTreePrinterPass::run(Function &F,
351 FunctionAnalysisManager &AM) {
352 OS << "DominatorTree for function: " << F.getName() << "\n";
353 AM.getResult<DominatorTreeAnalysis>(F).print(OS);
355 return PreservedAnalyses::all();
358 PreservedAnalyses DominatorTreeVerifierPass::run(Function &F,
359 FunctionAnalysisManager &AM) {
360 AM.getResult<DominatorTreeAnalysis>(F).verifyDomTree();
362 return PreservedAnalyses::all();
365 //===----------------------------------------------------------------------===//
366 // DominatorTreeWrapperPass Implementation
367 //===----------------------------------------------------------------------===//
369 // The implementation details of the wrapper pass that holds a DominatorTree
370 // suitable for use with the legacy pass manager.
372 //===----------------------------------------------------------------------===//
374 char DominatorTreeWrapperPass::ID = 0;
375 INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree",
376 "Dominator Tree Construction", true, true)
378 bool DominatorTreeWrapperPass::runOnFunction(Function &F) {
383 void DominatorTreeWrapperPass::verifyAnalysis() const {
388 void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const {