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),
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
68 llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree, Function>(
69 DomTreeBuilder::BBDomTree &DT, Function &F);
71 llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree, Function>(
72 DomTreeBuilder::BBPostDomTree &DT, Function &F);
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 bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>(
85 const DomTreeBuilder::BBDomTree &DT);
86 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>(
87 const DomTreeBuilder::BBPostDomTree &DT);
89 bool DominatorTree::invalidate(Function &F, const PreservedAnalyses &PA,
90 FunctionAnalysisManager::Invalidator &) {
91 // Check whether the analysis, all analyses on functions, or the function's
92 // CFG have been preserved.
93 auto PAC = PA.getChecker<DominatorTreeAnalysis>();
94 return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
95 PAC.preservedSet<CFGAnalyses>());
98 // dominates - Return true if Def dominates a use in User. This performs
99 // the special checks necessary if Def and User are in the same basic block.
100 // Note that Def doesn't dominate a use in Def itself!
101 bool DominatorTree::dominates(const Instruction *Def,
102 const Instruction *User) const {
103 const BasicBlock *UseBB = User->getParent();
104 const BasicBlock *DefBB = Def->getParent();
106 // Any unreachable use is dominated, even if Def == User.
107 if (!isReachableFromEntry(UseBB))
110 // Unreachable definitions don't dominate anything.
111 if (!isReachableFromEntry(DefBB))
114 // An instruction doesn't dominate a use in itself.
118 // The value defined by an invoke dominates an instruction only if it
119 // dominates every instruction in UseBB.
120 // A PHI is dominated only if the instruction dominates every possible use in
122 if (isa<InvokeInst>(Def) || isa<PHINode>(User))
123 return dominates(Def, UseBB);
126 return dominates(DefBB, UseBB);
128 // Loop through the basic block until we find Def or User.
129 BasicBlock::const_iterator I = DefBB->begin();
130 for (; &*I != Def && &*I != User; ++I)
136 // true if Def would dominate a use in any instruction in UseBB.
137 // note that dominates(Def, Def->getParent()) is false.
138 bool DominatorTree::dominates(const Instruction *Def,
139 const BasicBlock *UseBB) const {
140 const BasicBlock *DefBB = Def->getParent();
142 // Any unreachable use is dominated, even if DefBB == UseBB.
143 if (!isReachableFromEntry(UseBB))
146 // Unreachable definitions don't dominate anything.
147 if (!isReachableFromEntry(DefBB))
153 // Invoke results are only usable in the normal destination, not in the
154 // exceptional destination.
155 if (const auto *II = dyn_cast<InvokeInst>(Def)) {
156 BasicBlock *NormalDest = II->getNormalDest();
157 BasicBlockEdge E(DefBB, NormalDest);
158 return dominates(E, UseBB);
161 return dominates(DefBB, UseBB);
164 bool DominatorTree::dominates(const BasicBlockEdge &BBE,
165 const BasicBlock *UseBB) const {
166 // If the BB the edge ends in doesn't dominate the use BB, then the
167 // edge also doesn't.
168 const BasicBlock *Start = BBE.getStart();
169 const BasicBlock *End = BBE.getEnd();
170 if (!dominates(End, UseBB))
173 // Simple case: if the end BB has a single predecessor, the fact that it
174 // dominates the use block implies that the edge also does.
175 if (End->getSinglePredecessor())
178 // The normal edge from the invoke is critical. Conceptually, what we would
179 // like to do is split it and check if the new block dominates the use.
180 // With X being the new block, the graph would look like:
193 // Given the definition of dominance, NormalDest is dominated by X iff X
194 // dominates all of NormalDest's predecessors (X, B, C in the example). X
195 // trivially dominates itself, so we only have to find if it dominates the
196 // other predecessors. Since the only way out of X is via NormalDest, X can
197 // only properly dominate a node if NormalDest dominates that node too.
198 int IsDuplicateEdge = 0;
199 for (const_pred_iterator PI = pred_begin(End), E = pred_end(End);
201 const BasicBlock *BB = *PI;
203 // If there are multiple edges between Start and End, by definition they
204 // can't dominate anything.
205 if (IsDuplicateEdge++)
210 if (!dominates(End, BB))
216 bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const {
217 Instruction *UserInst = cast<Instruction>(U.getUser());
218 // A PHI in the end of the edge is dominated by it.
219 PHINode *PN = dyn_cast<PHINode>(UserInst);
220 if (PN && PN->getParent() == BBE.getEnd() &&
221 PN->getIncomingBlock(U) == BBE.getStart())
224 // Otherwise use the edge-dominates-block query, which
225 // handles the crazy critical edge cases properly.
226 const BasicBlock *UseBB;
228 UseBB = PN->getIncomingBlock(U);
230 UseBB = UserInst->getParent();
231 return dominates(BBE, UseBB);
234 bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
235 Instruction *UserInst = cast<Instruction>(U.getUser());
236 const BasicBlock *DefBB = Def->getParent();
238 // Determine the block in which the use happens. PHI nodes use
239 // their operands on edges; simulate this by thinking of the use
240 // happening at the end of the predecessor block.
241 const BasicBlock *UseBB;
242 if (PHINode *PN = dyn_cast<PHINode>(UserInst))
243 UseBB = PN->getIncomingBlock(U);
245 UseBB = UserInst->getParent();
247 // Any unreachable use is dominated, even if Def == User.
248 if (!isReachableFromEntry(UseBB))
251 // Unreachable definitions don't dominate anything.
252 if (!isReachableFromEntry(DefBB))
255 // Invoke instructions define their return values on the edges to their normal
256 // successors, so we have to handle them specially.
257 // Among other things, this means they don't dominate anything in
258 // their own block, except possibly a phi, so we don't need to
259 // walk the block in any case.
260 if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) {
261 BasicBlock *NormalDest = II->getNormalDest();
262 BasicBlockEdge E(DefBB, NormalDest);
263 return dominates(E, U);
266 // If the def and use are in different blocks, do a simple CFG dominator
269 return dominates(DefBB, UseBB);
271 // Ok, def and use are in the same block. If the def is an invoke, it
272 // doesn't dominate anything in the block. If it's a PHI, it dominates
273 // everything in the block.
274 if (isa<PHINode>(UserInst))
277 // Otherwise, just loop through the basic block until we find Def or User.
278 BasicBlock::const_iterator I = DefBB->begin();
279 for (; &*I != Def && &*I != UserInst; ++I)
282 return &*I != UserInst;
285 bool DominatorTree::isReachableFromEntry(const Use &U) const {
286 Instruction *I = dyn_cast<Instruction>(U.getUser());
288 // ConstantExprs aren't really reachable from the entry block, but they
289 // don't need to be treated like unreachable code either.
292 // PHI nodes use their operands on their incoming edges.
293 if (PHINode *PN = dyn_cast<PHINode>(I))
294 return isReachableFromEntry(PN->getIncomingBlock(U));
296 // Everything else uses their operands in their own block.
297 return isReachableFromEntry(I->getParent());
300 void DominatorTree::verifyDomTree() const {
301 // Perform the expensive checks only when VerifyDomInfo is set.
302 if (VerifyDomInfo && !verify()) {
303 errs() << "\n~~~~~~~~~~~\n\t\tDomTree verification failed!\n~~~~~~~~~~~\n";
308 Function &F = *getRoot()->getParent();
310 DominatorTree OtherDT;
311 OtherDT.recalculate(F);
312 if (compare(OtherDT)) {
313 errs() << "DominatorTree is not up to date!\nComputed:\n";
315 errs() << "\nActual:\n";
316 OtherDT.print(errs());
321 //===----------------------------------------------------------------------===//
322 // DominatorTreeAnalysis and related pass implementations
323 //===----------------------------------------------------------------------===//
325 // This implements the DominatorTreeAnalysis which is used with the new pass
326 // manager. It also implements some methods from utility passes.
328 //===----------------------------------------------------------------------===//
330 DominatorTree DominatorTreeAnalysis::run(Function &F,
331 FunctionAnalysisManager &) {
337 AnalysisKey DominatorTreeAnalysis::Key;
339 DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {}
341 PreservedAnalyses DominatorTreePrinterPass::run(Function &F,
342 FunctionAnalysisManager &AM) {
343 OS << "DominatorTree for function: " << F.getName() << "\n";
344 AM.getResult<DominatorTreeAnalysis>(F).print(OS);
346 return PreservedAnalyses::all();
349 PreservedAnalyses DominatorTreeVerifierPass::run(Function &F,
350 FunctionAnalysisManager &AM) {
351 AM.getResult<DominatorTreeAnalysis>(F).verifyDomTree();
353 return PreservedAnalyses::all();
356 //===----------------------------------------------------------------------===//
357 // DominatorTreeWrapperPass Implementation
358 //===----------------------------------------------------------------------===//
360 // The implementation details of the wrapper pass that holds a DominatorTree
361 // suitable for use with the legacy pass manager.
363 //===----------------------------------------------------------------------===//
365 char DominatorTreeWrapperPass::ID = 0;
366 INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree",
367 "Dominator Tree Construction", true, true)
369 bool DominatorTreeWrapperPass::runOnFunction(Function &F) {
374 void DominatorTreeWrapperPass::verifyAnalysis() const {
379 void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const {