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 static bool VerifyDomInfo = true;
34 static bool 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>;
66 template void llvm::Calculate<Function, BasicBlock *>(
68 typename std::remove_pointer<GraphTraits<BasicBlock *>::NodeRef>::type>
71 template void llvm::Calculate<Function, Inverse<BasicBlock *>>(
72 DominatorTreeBase<typename std::remove_pointer<
73 GraphTraits<Inverse<BasicBlock *>>::NodeRef>::type> &DT,
76 // dominates - Return true if Def dominates a use in User. This performs
77 // the special checks necessary if Def and User are in the same basic block.
78 // Note that Def doesn't dominate a use in Def itself!
79 bool DominatorTree::dominates(const Instruction *Def,
80 const Instruction *User) const {
81 const BasicBlock *UseBB = User->getParent();
82 const BasicBlock *DefBB = Def->getParent();
84 // Any unreachable use is dominated, even if Def == User.
85 if (!isReachableFromEntry(UseBB))
88 // Unreachable definitions don't dominate anything.
89 if (!isReachableFromEntry(DefBB))
92 // An instruction doesn't dominate a use in itself.
96 // The value defined by an invoke dominates an instruction only if it
97 // dominates every instruction in UseBB.
98 // A PHI is dominated only if the instruction dominates every possible use in
100 if (isa<InvokeInst>(Def) || isa<PHINode>(User))
101 return dominates(Def, UseBB);
104 return dominates(DefBB, UseBB);
106 // Loop through the basic block until we find Def or User.
107 BasicBlock::const_iterator I = DefBB->begin();
108 for (; &*I != Def && &*I != User; ++I)
114 // true if Def would dominate a use in any instruction in UseBB.
115 // note that dominates(Def, Def->getParent()) is false.
116 bool DominatorTree::dominates(const Instruction *Def,
117 const BasicBlock *UseBB) const {
118 const BasicBlock *DefBB = Def->getParent();
120 // Any unreachable use is dominated, even if DefBB == UseBB.
121 if (!isReachableFromEntry(UseBB))
124 // Unreachable definitions don't dominate anything.
125 if (!isReachableFromEntry(DefBB))
131 // Invoke results are only usable in the normal destination, not in the
132 // exceptional destination.
133 if (const auto *II = dyn_cast<InvokeInst>(Def)) {
134 BasicBlock *NormalDest = II->getNormalDest();
135 BasicBlockEdge E(DefBB, NormalDest);
136 return dominates(E, UseBB);
139 return dominates(DefBB, UseBB);
142 bool DominatorTree::dominates(const BasicBlockEdge &BBE,
143 const BasicBlock *UseBB) const {
144 // Assert that we have a single edge. We could handle them by simply
145 // returning false, but since isSingleEdge is linear on the number of
146 // edges, the callers can normally handle them more efficiently.
147 assert(BBE.isSingleEdge() &&
148 "This function is not efficient in handling multiple edges");
150 // If the BB the edge ends in doesn't dominate the use BB, then the
151 // edge also doesn't.
152 const BasicBlock *Start = BBE.getStart();
153 const BasicBlock *End = BBE.getEnd();
154 if (!dominates(End, UseBB))
157 // Simple case: if the end BB has a single predecessor, the fact that it
158 // dominates the use block implies that the edge also does.
159 if (End->getSinglePredecessor())
162 // The normal edge from the invoke is critical. Conceptually, what we would
163 // like to do is split it and check if the new block dominates the use.
164 // With X being the new block, the graph would look like:
177 // Given the definition of dominance, NormalDest is dominated by X iff X
178 // dominates all of NormalDest's predecessors (X, B, C in the example). X
179 // trivially dominates itself, so we only have to find if it dominates the
180 // other predecessors. Since the only way out of X is via NormalDest, X can
181 // only properly dominate a node if NormalDest dominates that node too.
182 for (const_pred_iterator PI = pred_begin(End), E = pred_end(End);
184 const BasicBlock *BB = *PI;
188 if (!dominates(End, BB))
194 bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const {
195 // Assert that we have a single edge. We could handle them by simply
196 // returning false, but since isSingleEdge is linear on the number of
197 // edges, the callers can normally handle them more efficiently.
198 assert(BBE.isSingleEdge() &&
199 "This function is not efficient in handling multiple edges");
201 Instruction *UserInst = cast<Instruction>(U.getUser());
202 // A PHI in the end of the edge is dominated by it.
203 PHINode *PN = dyn_cast<PHINode>(UserInst);
204 if (PN && PN->getParent() == BBE.getEnd() &&
205 PN->getIncomingBlock(U) == BBE.getStart())
208 // Otherwise use the edge-dominates-block query, which
209 // handles the crazy critical edge cases properly.
210 const BasicBlock *UseBB;
212 UseBB = PN->getIncomingBlock(U);
214 UseBB = UserInst->getParent();
215 return dominates(BBE, UseBB);
218 bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
219 Instruction *UserInst = cast<Instruction>(U.getUser());
220 const BasicBlock *DefBB = Def->getParent();
222 // Determine the block in which the use happens. PHI nodes use
223 // their operands on edges; simulate this by thinking of the use
224 // happening at the end of the predecessor block.
225 const BasicBlock *UseBB;
226 if (PHINode *PN = dyn_cast<PHINode>(UserInst))
227 UseBB = PN->getIncomingBlock(U);
229 UseBB = UserInst->getParent();
231 // Any unreachable use is dominated, even if Def == User.
232 if (!isReachableFromEntry(UseBB))
235 // Unreachable definitions don't dominate anything.
236 if (!isReachableFromEntry(DefBB))
239 // Invoke instructions define their return values on the edges to their normal
240 // successors, so we have to handle them specially.
241 // Among other things, this means they don't dominate anything in
242 // their own block, except possibly a phi, so we don't need to
243 // walk the block in any case.
244 if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) {
245 BasicBlock *NormalDest = II->getNormalDest();
246 BasicBlockEdge E(DefBB, NormalDest);
247 return dominates(E, U);
250 // If the def and use are in different blocks, do a simple CFG dominator
253 return dominates(DefBB, UseBB);
255 // Ok, def and use are in the same block. If the def is an invoke, it
256 // doesn't dominate anything in the block. If it's a PHI, it dominates
257 // everything in the block.
258 if (isa<PHINode>(UserInst))
261 // Otherwise, just loop through the basic block until we find Def or User.
262 BasicBlock::const_iterator I = DefBB->begin();
263 for (; &*I != Def && &*I != UserInst; ++I)
266 return &*I != UserInst;
269 bool DominatorTree::isReachableFromEntry(const Use &U) const {
270 Instruction *I = dyn_cast<Instruction>(U.getUser());
272 // ConstantExprs aren't really reachable from the entry block, but they
273 // don't need to be treated like unreachable code either.
276 // PHI nodes use their operands on their incoming edges.
277 if (PHINode *PN = dyn_cast<PHINode>(I))
278 return isReachableFromEntry(PN->getIncomingBlock(U));
280 // Everything else uses their operands in their own block.
281 return isReachableFromEntry(I->getParent());
284 void DominatorTree::verifyDomTree() const {
285 Function &F = *getRoot()->getParent();
287 DominatorTree OtherDT;
288 OtherDT.recalculate(F);
289 if (compare(OtherDT)) {
290 errs() << "DominatorTree is not up to date!\nComputed:\n";
292 errs() << "\nActual:\n";
293 OtherDT.print(errs());
298 //===----------------------------------------------------------------------===//
299 // DominatorTreeAnalysis and related pass implementations
300 //===----------------------------------------------------------------------===//
302 // This implements the DominatorTreeAnalysis which is used with the new pass
303 // manager. It also implements some methods from utility passes.
305 //===----------------------------------------------------------------------===//
307 DominatorTree DominatorTreeAnalysis::run(Function &F,
308 FunctionAnalysisManager &) {
314 AnalysisKey DominatorTreeAnalysis::Key;
316 DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {}
318 PreservedAnalyses DominatorTreePrinterPass::run(Function &F,
319 FunctionAnalysisManager &AM) {
320 OS << "DominatorTree for function: " << F.getName() << "\n";
321 AM.getResult<DominatorTreeAnalysis>(F).print(OS);
323 return PreservedAnalyses::all();
326 PreservedAnalyses DominatorTreeVerifierPass::run(Function &F,
327 FunctionAnalysisManager &AM) {
328 AM.getResult<DominatorTreeAnalysis>(F).verifyDomTree();
330 return PreservedAnalyses::all();
333 //===----------------------------------------------------------------------===//
334 // DominatorTreeWrapperPass Implementation
335 //===----------------------------------------------------------------------===//
337 // The implementation details of the wrapper pass that holds a DominatorTree
338 // suitable for use with the legacy pass manager.
340 //===----------------------------------------------------------------------===//
342 char DominatorTreeWrapperPass::ID = 0;
343 INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree",
344 "Dominator Tree Construction", true, true)
346 bool DominatorTreeWrapperPass::runOnFunction(Function &F) {
351 void DominatorTreeWrapperPass::verifyAnalysis() const {
356 void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const {