1 //===- Dominators.cpp - Dominator Calculation -----------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file implements simple dominator construction algorithms for finding 10 // forward dominators. Postdominators are available in libanalysis, but are not 11 // included in libvmcore, because it's not needed. Forward dominators are 12 // needed to support the Verifier pass. 13 // 14 //===----------------------------------------------------------------------===// 15 16 #include "llvm/IR/Dominators.h" 17 #include "llvm/ADT/StringRef.h" 18 #include "llvm/Config/llvm-config.h" 19 #include "llvm/IR/CFG.h" 20 #include "llvm/IR/Function.h" 21 #include "llvm/IR/Instruction.h" 22 #include "llvm/IR/Instructions.h" 23 #include "llvm/IR/PassManager.h" 24 #include "llvm/InitializePasses.h" 25 #include "llvm/PassRegistry.h" 26 #include "llvm/Support/Casting.h" 27 #include "llvm/Support/CommandLine.h" 28 #include "llvm/Support/GenericDomTreeConstruction.h" 29 #include "llvm/Support/raw_ostream.h" 30 31 #include <cassert> 32 33 namespace llvm { 34 class Argument; 35 class Constant; 36 class Value; 37 } // namespace llvm 38 using namespace llvm; 39 40 bool llvm::VerifyDomInfo = false; 41 static cl::opt<bool, true> 42 VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), cl::Hidden, 43 cl::desc("Verify dominator info (time consuming)")); 44 45 #ifdef EXPENSIVE_CHECKS 46 static constexpr bool ExpensiveChecksEnabled = true; 47 #else 48 static constexpr bool ExpensiveChecksEnabled = false; 49 #endif 50 51 bool BasicBlockEdge::isSingleEdge() const { 52 const Instruction *TI = Start->getTerminator(); 53 unsigned NumEdgesToEnd = 0; 54 for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) { 55 if (TI->getSuccessor(i) == End) 56 ++NumEdgesToEnd; 57 if (NumEdgesToEnd >= 2) 58 return false; 59 } 60 assert(NumEdgesToEnd == 1); 61 return true; 62 } 63 64 //===----------------------------------------------------------------------===// 65 // DominatorTree Implementation 66 //===----------------------------------------------------------------------===// 67 // 68 // Provide public access to DominatorTree information. Implementation details 69 // can be found in Dominators.h, GenericDomTree.h, and 70 // GenericDomTreeConstruction.h. 71 // 72 //===----------------------------------------------------------------------===// 73 74 template class llvm::DomTreeNodeBase<BasicBlock>; 75 template class llvm::DominatorTreeBase<BasicBlock, false>; // DomTreeBase 76 template class llvm::DominatorTreeBase<BasicBlock, true>; // PostDomTreeBase 77 78 template class llvm::cfg::Update<BasicBlock *>; 79 80 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree>( 81 DomTreeBuilder::BBDomTree &DT); 82 template void 83 llvm::DomTreeBuilder::CalculateWithUpdates<DomTreeBuilder::BBDomTree>( 84 DomTreeBuilder::BBDomTree &DT, BBUpdates U); 85 86 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>( 87 DomTreeBuilder::BBPostDomTree &DT); 88 // No CalculateWithUpdates<PostDomTree> instantiation, unless a usecase arises. 89 90 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>( 91 DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To); 92 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBPostDomTree>( 93 DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To); 94 95 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBDomTree>( 96 DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To); 97 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBPostDomTree>( 98 DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To); 99 100 template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBDomTree>( 101 DomTreeBuilder::BBDomTree &DT, DomTreeBuilder::BBDomTreeGraphDiff &, 102 DomTreeBuilder::BBDomTreeGraphDiff *); 103 template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>( 104 DomTreeBuilder::BBPostDomTree &DT, DomTreeBuilder::BBPostDomTreeGraphDiff &, 105 DomTreeBuilder::BBPostDomTreeGraphDiff *); 106 107 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>( 108 const DomTreeBuilder::BBDomTree &DT, 109 DomTreeBuilder::BBDomTree::VerificationLevel VL); 110 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>( 111 const DomTreeBuilder::BBPostDomTree &DT, 112 DomTreeBuilder::BBPostDomTree::VerificationLevel VL); 113 114 bool DominatorTree::invalidate(Function &F, const PreservedAnalyses &PA, 115 FunctionAnalysisManager::Invalidator &) { 116 // Check whether the analysis, all analyses on functions, or the function's 117 // CFG have been preserved. 118 auto PAC = PA.getChecker<DominatorTreeAnalysis>(); 119 return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() || 120 PAC.preservedSet<CFGAnalyses>()); 121 } 122 123 bool DominatorTree::dominates(const BasicBlock *BB, const Use &U) const { 124 Instruction *UserInst = cast<Instruction>(U.getUser()); 125 if (auto *PN = dyn_cast<PHINode>(UserInst)) 126 // A phi use using a value from a block is dominated by the end of that 127 // block. Note that the phi's parent block may not be. 128 return dominates(BB, PN->getIncomingBlock(U)); 129 else 130 return properlyDominates(BB, UserInst->getParent()); 131 } 132 133 // dominates - Return true if Def dominates a use in User. This performs 134 // the special checks necessary if Def and User are in the same basic block. 135 // Note that Def doesn't dominate a use in Def itself! 136 bool DominatorTree::dominates(const Value *DefV, 137 const Instruction *User) const { 138 const Instruction *Def = dyn_cast<Instruction>(DefV); 139 if (!Def) { 140 assert((isa<Argument>(DefV) || isa<Constant>(DefV)) && 141 "Should be called with an instruction, argument or constant"); 142 return true; // Arguments and constants dominate everything. 143 } 144 145 const BasicBlock *UseBB = User->getParent(); 146 const BasicBlock *DefBB = Def->getParent(); 147 148 // Any unreachable use is dominated, even if Def == User. 149 if (!isReachableFromEntry(UseBB)) 150 return true; 151 152 // Unreachable definitions don't dominate anything. 153 if (!isReachableFromEntry(DefBB)) 154 return false; 155 156 // An instruction doesn't dominate a use in itself. 157 if (Def == User) 158 return false; 159 160 // The value defined by an invoke dominates an instruction only if it 161 // dominates every instruction in UseBB. 162 // A PHI is dominated only if the instruction dominates every possible use in 163 // the UseBB. 164 if (isa<InvokeInst>(Def) || isa<CallBrInst>(Def) || isa<PHINode>(User)) 165 return dominates(Def, UseBB); 166 167 if (DefBB != UseBB) 168 return dominates(DefBB, UseBB); 169 170 return Def->comesBefore(User); 171 } 172 173 // true if Def would dominate a use in any instruction in UseBB. 174 // note that dominates(Def, Def->getParent()) is false. 175 bool DominatorTree::dominates(const Instruction *Def, 176 const BasicBlock *UseBB) const { 177 const BasicBlock *DefBB = Def->getParent(); 178 179 // Any unreachable use is dominated, even if DefBB == UseBB. 180 if (!isReachableFromEntry(UseBB)) 181 return true; 182 183 // Unreachable definitions don't dominate anything. 184 if (!isReachableFromEntry(DefBB)) 185 return false; 186 187 if (DefBB == UseBB) 188 return false; 189 190 // Invoke results are only usable in the normal destination, not in the 191 // exceptional destination. 192 if (const auto *II = dyn_cast<InvokeInst>(Def)) { 193 BasicBlock *NormalDest = II->getNormalDest(); 194 BasicBlockEdge E(DefBB, NormalDest); 195 return dominates(E, UseBB); 196 } 197 198 return dominates(DefBB, UseBB); 199 } 200 201 bool DominatorTree::dominates(const BasicBlockEdge &BBE, 202 const BasicBlock *UseBB) const { 203 // If the BB the edge ends in doesn't dominate the use BB, then the 204 // edge also doesn't. 205 const BasicBlock *Start = BBE.getStart(); 206 const BasicBlock *End = BBE.getEnd(); 207 if (!dominates(End, UseBB)) 208 return false; 209 210 // Simple case: if the end BB has a single predecessor, the fact that it 211 // dominates the use block implies that the edge also does. 212 if (End->getSinglePredecessor()) 213 return true; 214 215 // The normal edge from the invoke is critical. Conceptually, what we would 216 // like to do is split it and check if the new block dominates the use. 217 // With X being the new block, the graph would look like: 218 // 219 // DefBB 220 // /\ . . 221 // / \ . . 222 // / \ . . 223 // / \ | | 224 // A X B C 225 // | \ | / 226 // . \|/ 227 // . NormalDest 228 // . 229 // 230 // Given the definition of dominance, NormalDest is dominated by X iff X 231 // dominates all of NormalDest's predecessors (X, B, C in the example). X 232 // trivially dominates itself, so we only have to find if it dominates the 233 // other predecessors. Since the only way out of X is via NormalDest, X can 234 // only properly dominate a node if NormalDest dominates that node too. 235 int IsDuplicateEdge = 0; 236 for (const BasicBlock *BB : predecessors(End)) { 237 if (BB == Start) { 238 // If there are multiple edges between Start and End, by definition they 239 // can't dominate anything. 240 if (IsDuplicateEdge++) 241 return false; 242 continue; 243 } 244 245 if (!dominates(End, BB)) 246 return false; 247 } 248 return true; 249 } 250 251 bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const { 252 Instruction *UserInst = cast<Instruction>(U.getUser()); 253 // A PHI in the end of the edge is dominated by it. 254 PHINode *PN = dyn_cast<PHINode>(UserInst); 255 if (PN && PN->getParent() == BBE.getEnd() && 256 PN->getIncomingBlock(U) == BBE.getStart()) 257 return true; 258 259 // Otherwise use the edge-dominates-block query, which 260 // handles the crazy critical edge cases properly. 261 const BasicBlock *UseBB; 262 if (PN) 263 UseBB = PN->getIncomingBlock(U); 264 else 265 UseBB = UserInst->getParent(); 266 return dominates(BBE, UseBB); 267 } 268 269 bool DominatorTree::dominates(const Value *DefV, const Use &U) const { 270 const Instruction *Def = dyn_cast<Instruction>(DefV); 271 if (!Def) { 272 assert((isa<Argument>(DefV) || isa<Constant>(DefV)) && 273 "Should be called with an instruction, argument or constant"); 274 return true; // Arguments and constants dominate everything. 275 } 276 277 Instruction *UserInst = cast<Instruction>(U.getUser()); 278 const BasicBlock *DefBB = Def->getParent(); 279 280 // Determine the block in which the use happens. PHI nodes use 281 // their operands on edges; simulate this by thinking of the use 282 // happening at the end of the predecessor block. 283 const BasicBlock *UseBB; 284 if (PHINode *PN = dyn_cast<PHINode>(UserInst)) 285 UseBB = PN->getIncomingBlock(U); 286 else 287 UseBB = UserInst->getParent(); 288 289 // Any unreachable use is dominated, even if Def == User. 290 if (!isReachableFromEntry(UseBB)) 291 return true; 292 293 // Unreachable definitions don't dominate anything. 294 if (!isReachableFromEntry(DefBB)) 295 return false; 296 297 // Invoke instructions define their return values on the edges to their normal 298 // successors, so we have to handle them specially. 299 // Among other things, this means they don't dominate anything in 300 // their own block, except possibly a phi, so we don't need to 301 // walk the block in any case. 302 if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) { 303 BasicBlock *NormalDest = II->getNormalDest(); 304 BasicBlockEdge E(DefBB, NormalDest); 305 return dominates(E, U); 306 } 307 308 // If the def and use are in different blocks, do a simple CFG dominator 309 // tree query. 310 if (DefBB != UseBB) 311 return dominates(DefBB, UseBB); 312 313 // Ok, def and use are in the same block. If the def is an invoke, it 314 // doesn't dominate anything in the block. If it's a PHI, it dominates 315 // everything in the block. 316 if (isa<PHINode>(UserInst)) 317 return true; 318 319 return Def->comesBefore(UserInst); 320 } 321 322 bool DominatorTree::isReachableFromEntry(const Use &U) const { 323 Instruction *I = dyn_cast<Instruction>(U.getUser()); 324 325 // ConstantExprs aren't really reachable from the entry block, but they 326 // don't need to be treated like unreachable code either. 327 if (!I) return true; 328 329 // PHI nodes use their operands on their incoming edges. 330 if (PHINode *PN = dyn_cast<PHINode>(I)) 331 return isReachableFromEntry(PN->getIncomingBlock(U)); 332 333 // Everything else uses their operands in their own block. 334 return isReachableFromEntry(I->getParent()); 335 } 336 337 // Edge BBE1 dominates edge BBE2 if they match or BBE1 dominates start of BBE2. 338 bool DominatorTree::dominates(const BasicBlockEdge &BBE1, 339 const BasicBlockEdge &BBE2) const { 340 if (BBE1.getStart() == BBE2.getStart() && BBE1.getEnd() == BBE2.getEnd()) 341 return true; 342 return dominates(BBE1, BBE2.getStart()); 343 } 344 345 Instruction *DominatorTree::findNearestCommonDominator(Instruction *I1, 346 Instruction *I2) const { 347 BasicBlock *BB1 = I1->getParent(); 348 BasicBlock *BB2 = I2->getParent(); 349 if (BB1 == BB2) 350 return I1->comesBefore(I2) ? I1 : I2; 351 if (!isReachableFromEntry(BB2)) 352 return I1; 353 if (!isReachableFromEntry(BB1)) 354 return I2; 355 BasicBlock *DomBB = findNearestCommonDominator(BB1, BB2); 356 if (BB1 == DomBB) 357 return I1; 358 if (BB2 == DomBB) 359 return I2; 360 return DomBB->getTerminator(); 361 } 362 363 //===----------------------------------------------------------------------===// 364 // DominatorTreeAnalysis and related pass implementations 365 //===----------------------------------------------------------------------===// 366 // 367 // This implements the DominatorTreeAnalysis which is used with the new pass 368 // manager. It also implements some methods from utility passes. 369 // 370 //===----------------------------------------------------------------------===// 371 372 DominatorTree DominatorTreeAnalysis::run(Function &F, 373 FunctionAnalysisManager &) { 374 DominatorTree DT; 375 DT.recalculate(F); 376 return DT; 377 } 378 379 AnalysisKey DominatorTreeAnalysis::Key; 380 381 DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {} 382 383 PreservedAnalyses DominatorTreePrinterPass::run(Function &F, 384 FunctionAnalysisManager &AM) { 385 OS << "DominatorTree for function: " << F.getName() << "\n"; 386 AM.getResult<DominatorTreeAnalysis>(F).print(OS); 387 388 return PreservedAnalyses::all(); 389 } 390 391 PreservedAnalyses DominatorTreeVerifierPass::run(Function &F, 392 FunctionAnalysisManager &AM) { 393 auto &DT = AM.getResult<DominatorTreeAnalysis>(F); 394 assert(DT.verify()); 395 (void)DT; 396 return PreservedAnalyses::all(); 397 } 398 399 //===----------------------------------------------------------------------===// 400 // DominatorTreeWrapperPass Implementation 401 //===----------------------------------------------------------------------===// 402 // 403 // The implementation details of the wrapper pass that holds a DominatorTree 404 // suitable for use with the legacy pass manager. 405 // 406 //===----------------------------------------------------------------------===// 407 408 char DominatorTreeWrapperPass::ID = 0; 409 410 DominatorTreeWrapperPass::DominatorTreeWrapperPass() : FunctionPass(ID) { 411 initializeDominatorTreeWrapperPassPass(*PassRegistry::getPassRegistry()); 412 } 413 414 INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree", 415 "Dominator Tree Construction", true, true) 416 417 bool DominatorTreeWrapperPass::runOnFunction(Function &F) { 418 DT.recalculate(F); 419 return false; 420 } 421 422 void DominatorTreeWrapperPass::verifyAnalysis() const { 423 if (VerifyDomInfo) 424 assert(DT.verify(DominatorTree::VerificationLevel::Full)); 425 else if (ExpensiveChecksEnabled) 426 assert(DT.verify(DominatorTree::VerificationLevel::Basic)); 427 } 428 429 void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const { 430 DT.print(OS); 431 } 432