1 //===- Dominators.cpp - Dominator Calculation -----------------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 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. 14 // 15 //===----------------------------------------------------------------------===// 16 17 #include "llvm/IR/Dominators.h" 18 #include "llvm/ADT/DepthFirstIterator.h" 19 #include "llvm/ADT/SmallPtrSet.h" 20 #include "llvm/ADT/SmallVector.h" 21 #include "llvm/IR/CFG.h" 22 #include "llvm/IR/Instructions.h" 23 #include "llvm/IR/PassManager.h" 24 #include "llvm/Support/CommandLine.h" 25 #include "llvm/Support/Compiler.h" 26 #include "llvm/Support/Debug.h" 27 #include "llvm/Support/GenericDomTreeConstruction.h" 28 #include "llvm/Support/raw_ostream.h" 29 #include <algorithm> 30 using namespace llvm; 31 32 // Always verify dominfo if expensive checking is enabled. 33 #ifdef XDEBUG 34 static bool VerifyDomInfo = true; 35 #else 36 static bool VerifyDomInfo = false; 37 #endif 38 static cl::opt<bool,true> 39 VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), 40 cl::desc("Verify dominator info (time consuming)")); 41 42 bool BasicBlockEdge::isSingleEdge() const { 43 const TerminatorInst *TI = Start->getTerminator(); 44 unsigned NumEdgesToEnd = 0; 45 for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) { 46 if (TI->getSuccessor(i) == End) 47 ++NumEdgesToEnd; 48 if (NumEdgesToEnd >= 2) 49 return false; 50 } 51 assert(NumEdgesToEnd == 1); 52 return true; 53 } 54 55 //===----------------------------------------------------------------------===// 56 // DominatorTree Implementation 57 //===----------------------------------------------------------------------===// 58 // 59 // Provide public access to DominatorTree information. Implementation details 60 // can be found in Dominators.h, GenericDomTree.h, and 61 // GenericDomTreeConstruction.h. 62 // 63 //===----------------------------------------------------------------------===// 64 65 TEMPLATE_INSTANTIATION(class llvm::DomTreeNodeBase<BasicBlock>); 66 TEMPLATE_INSTANTIATION(class llvm::DominatorTreeBase<BasicBlock>); 67 68 #define LLVM_COMMA , 69 TEMPLATE_INSTANTIATION(void llvm::Calculate<Function LLVM_COMMA BasicBlock *>( 70 DominatorTreeBase<GraphTraits<BasicBlock *>::NodeType> &DT LLVM_COMMA 71 Function &F)); 72 TEMPLATE_INSTANTIATION( 73 void llvm::Calculate<Function LLVM_COMMA Inverse<BasicBlock *> >( 74 DominatorTreeBase<GraphTraits<Inverse<BasicBlock *> >::NodeType> &DT 75 LLVM_COMMA Function &F)); 76 #undef LLVM_COMMA 77 78 // dominates - Return true if Def dominates a use in User. This performs 79 // the special checks necessary if Def and User are in the same basic block. 80 // Note that Def doesn't dominate a use in Def itself! 81 bool DominatorTree::dominates(const Instruction *Def, 82 const Instruction *User) const { 83 const BasicBlock *UseBB = User->getParent(); 84 const BasicBlock *DefBB = Def->getParent(); 85 86 // Any unreachable use is dominated, even if Def == User. 87 if (!isReachableFromEntry(UseBB)) 88 return true; 89 90 // Unreachable definitions don't dominate anything. 91 if (!isReachableFromEntry(DefBB)) 92 return false; 93 94 // An instruction doesn't dominate a use in itself. 95 if (Def == User) 96 return false; 97 98 // The value defined by an invoke dominates an instruction only if 99 // it dominates every instruction in UseBB. 100 // A PHI is dominated only if the instruction dominates every possible use 101 // in the UseBB. 102 if (isa<InvokeInst>(Def) || isa<PHINode>(User)) 103 return dominates(Def, UseBB); 104 105 if (DefBB != UseBB) 106 return dominates(DefBB, UseBB); 107 108 // Loop through the basic block until we find Def or User. 109 BasicBlock::const_iterator I = DefBB->begin(); 110 for (; &*I != Def && &*I != User; ++I) 111 /*empty*/; 112 113 return &*I == Def; 114 } 115 116 // true if Def would dominate a use in any instruction in UseBB. 117 // note that dominates(Def, Def->getParent()) is false. 118 bool DominatorTree::dominates(const Instruction *Def, 119 const BasicBlock *UseBB) const { 120 const BasicBlock *DefBB = Def->getParent(); 121 122 // Any unreachable use is dominated, even if DefBB == UseBB. 123 if (!isReachableFromEntry(UseBB)) 124 return true; 125 126 // Unreachable definitions don't dominate anything. 127 if (!isReachableFromEntry(DefBB)) 128 return false; 129 130 if (DefBB == UseBB) 131 return false; 132 133 const InvokeInst *II = dyn_cast<InvokeInst>(Def); 134 if (!II) 135 return dominates(DefBB, UseBB); 136 137 // Invoke results are only usable in the normal destination, not in the 138 // exceptional destination. 139 BasicBlock *NormalDest = II->getNormalDest(); 140 BasicBlockEdge E(DefBB, NormalDest); 141 return dominates(E, UseBB); 142 } 143 144 bool DominatorTree::dominates(const BasicBlockEdge &BBE, 145 const BasicBlock *UseBB) const { 146 // Assert that we have a single edge. We could handle them by simply 147 // returning false, but since isSingleEdge is linear on the number of 148 // edges, the callers can normally handle them more efficiently. 149 assert(BBE.isSingleEdge()); 150 151 // If the BB the edge ends in doesn't dominate the use BB, then the 152 // edge also doesn't. 153 const BasicBlock *Start = BBE.getStart(); 154 const BasicBlock *End = BBE.getEnd(); 155 if (!dominates(End, UseBB)) 156 return false; 157 158 // Simple case: if the end BB has a single predecessor, the fact that it 159 // dominates the use block implies that the edge also does. 160 if (End->getSinglePredecessor()) 161 return true; 162 163 // The normal edge from the invoke is critical. Conceptually, what we would 164 // like to do is split it and check if the new block dominates the use. 165 // With X being the new block, the graph would look like: 166 // 167 // DefBB 168 // /\ . . 169 // / \ . . 170 // / \ . . 171 // / \ | | 172 // A X B C 173 // | \ | / 174 // . \|/ 175 // . NormalDest 176 // . 177 // 178 // Given the definition of dominance, NormalDest is dominated by X iff X 179 // dominates all of NormalDest's predecessors (X, B, C in the example). X 180 // trivially dominates itself, so we only have to find if it dominates the 181 // other predecessors. Since the only way out of X is via NormalDest, X can 182 // only properly dominate a node if NormalDest dominates that node too. 183 for (const_pred_iterator PI = pred_begin(End), E = pred_end(End); 184 PI != E; ++PI) { 185 const BasicBlock *BB = *PI; 186 if (BB == Start) 187 continue; 188 189 if (!dominates(End, BB)) 190 return false; 191 } 192 return true; 193 } 194 195 bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const { 196 // Assert that we have a single edge. We could handle them by simply 197 // returning false, but since isSingleEdge is linear on the number of 198 // edges, the callers can normally handle them more efficiently. 199 assert(BBE.isSingleEdge()); 200 201 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()) 206 return true; 207 208 // Otherwise use the edge-dominates-block query, which 209 // handles the crazy critical edge cases properly. 210 const BasicBlock *UseBB; 211 if (PN) 212 UseBB = PN->getIncomingBlock(U); 213 else 214 UseBB = UserInst->getParent(); 215 return dominates(BBE, UseBB); 216 } 217 218 bool DominatorTree::dominates(const Instruction *Def, const Use &U) const { 219 Instruction *UserInst = cast<Instruction>(U.getUser()); 220 const BasicBlock *DefBB = Def->getParent(); 221 222 // 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); 228 else 229 UseBB = UserInst->getParent(); 230 231 // Any unreachable use is dominated, even if Def == User. 232 if (!isReachableFromEntry(UseBB)) 233 return true; 234 235 // Unreachable definitions don't dominate anything. 236 if (!isReachableFromEntry(DefBB)) 237 return false; 238 239 // Invoke instructions define their return values on the edges 240 // to their normal 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); 248 } 249 250 // If the def and use are in different blocks, do a simple CFG dominator 251 // tree query. 252 if (DefBB != UseBB) 253 return dominates(DefBB, UseBB); 254 255 // 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)) 259 return true; 260 261 // 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) 264 /*empty*/; 265 266 return &*I != UserInst; 267 } 268 269 bool DominatorTree::isReachableFromEntry(const Use &U) const { 270 Instruction *I = dyn_cast<Instruction>(U.getUser()); 271 272 // ConstantExprs aren't really reachable from the entry block, but they 273 // don't need to be treated like unreachable code either. 274 if (!I) return true; 275 276 // PHI nodes use their operands on their incoming edges. 277 if (PHINode *PN = dyn_cast<PHINode>(I)) 278 return isReachableFromEntry(PN->getIncomingBlock(U)); 279 280 // Everything else uses their operands in their own block. 281 return isReachableFromEntry(I->getParent()); 282 } 283 284 void DominatorTree::verifyDomTree() const { 285 if (!VerifyDomInfo) 286 return; 287 288 Function &F = *getRoot()->getParent(); 289 290 DominatorTree OtherDT; 291 OtherDT.recalculate(F); 292 if (compare(OtherDT)) { 293 errs() << "DominatorTree is not up to date!\nComputed:\n"; 294 print(errs()); 295 errs() << "\nActual:\n"; 296 OtherDT.print(errs()); 297 abort(); 298 } 299 } 300 301 //===----------------------------------------------------------------------===// 302 // DominatorTreeAnalysis and related pass implementations 303 //===----------------------------------------------------------------------===// 304 // 305 // This implements the DominatorTreeAnalysis which is used with the new pass 306 // manager. It also implements some methods from utility passes. 307 // 308 //===----------------------------------------------------------------------===// 309 310 DominatorTree DominatorTreeAnalysis::run(Function &F) { 311 DominatorTree DT; 312 DT.recalculate(F); 313 return DT; 314 } 315 316 char DominatorTreeAnalysis::PassID; 317 318 DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {} 319 320 PreservedAnalyses DominatorTreePrinterPass::run(Function &F, 321 FunctionAnalysisManager *AM) { 322 OS << "DominatorTree for function: " << F.getName() << "\n"; 323 AM->getResult<DominatorTreeAnalysis>(F).print(OS); 324 325 return PreservedAnalyses::all(); 326 } 327 328 PreservedAnalyses DominatorTreeVerifierPass::run(Function &F, 329 FunctionAnalysisManager *AM) { 330 AM->getResult<DominatorTreeAnalysis>(F).verifyDomTree(); 331 332 return PreservedAnalyses::all(); 333 } 334 335 //===----------------------------------------------------------------------===// 336 // DominatorTreeWrapperPass Implementation 337 //===----------------------------------------------------------------------===// 338 // 339 // The implementation details of the wrapper pass that holds a DominatorTree 340 // suitable for use with the legacy pass manager. 341 // 342 //===----------------------------------------------------------------------===// 343 344 char DominatorTreeWrapperPass::ID = 0; 345 INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree", 346 "Dominator Tree Construction", true, true) 347 348 bool DominatorTreeWrapperPass::runOnFunction(Function &F) { 349 DT.recalculate(F); 350 return false; 351 } 352 353 void DominatorTreeWrapperPass::verifyAnalysis() const { DT.verifyDomTree(); } 354 355 void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const { 356 DT.print(OS); 357 } 358 359