Dominators.cpp revision 344779
15992SN/A//===- Dominators.cpp - Dominator Calculation -----------------------------===// 25992SN/A// 35992SN/A// The LLVM Compiler Infrastructure 45992SN/A// 55992SN/A// This file is distributed under the University of Illinois Open Source 65992SN/A// License. See LICENSE.TXT for details. 75992SN/A// 85992SN/A//===----------------------------------------------------------------------===// 95992SN/A// 105992SN/A// This file implements simple dominator construction algorithms for finding 115992SN/A// forward dominators. Postdominators are available in libanalysis, but are not 125992SN/A// included in libvmcore, because it's not needed. Forward dominators are 135992SN/A// needed to support the Verifier pass. 145992SN/A// 155992SN/A//===----------------------------------------------------------------------===// 165992SN/A 175992SN/A#include "llvm/IR/Dominators.h" 185992SN/A#include "llvm/ADT/DepthFirstIterator.h" 195992SN/A#include "llvm/ADT/SmallPtrSet.h" 205992SN/A#include "llvm/Config/llvm-config.h" 215992SN/A#include "llvm/IR/CFG.h" 225992SN/A#include "llvm/IR/Constants.h" 235992SN/A#include "llvm/IR/Instructions.h" 245992SN/A#include "llvm/IR/PassManager.h" 255992SN/A#include "llvm/Support/CommandLine.h" 265992SN/A#include "llvm/Support/Debug.h" 275992SN/A#include "llvm/Support/GenericDomTreeConstruction.h" 285992SN/A#include "llvm/Support/raw_ostream.h" 295992SN/A#include <algorithm> 305992SN/Ausing namespace llvm; 315992SN/A 325992SN/Abool llvm::VerifyDomInfo = false; 335992SN/Astatic cl::opt<bool, true> 345992SN/A VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), cl::Hidden, 355992SN/A cl::desc("Verify dominator info (time consuming)")); 365992SN/A 375992SN/A#ifdef EXPENSIVE_CHECKS 385992SN/Astatic constexpr bool ExpensiveChecksEnabled = true; 395992SN/A#else 405992SN/Astatic constexpr bool ExpensiveChecksEnabled = false; 415992SN/A#endif 425992SN/A 435992SN/Abool BasicBlockEdge::isSingleEdge() const { 445992SN/A const Instruction *TI = Start->getTerminator(); 455992SN/A unsigned NumEdgesToEnd = 0; 465992SN/A for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) { 475992SN/A if (TI->getSuccessor(i) == End) 485992SN/A ++NumEdgesToEnd; 495992SN/A if (NumEdgesToEnd >= 2) 505992SN/A return false; 515992SN/A } 525992SN/A assert(NumEdgesToEnd == 1); 535992SN/A return true; 545992SN/A} 555992SN/A 565992SN/A//===----------------------------------------------------------------------===// 575992SN/A// DominatorTree Implementation 585992SN/A//===----------------------------------------------------------------------===// 595992SN/A// 605992SN/A// Provide public access to DominatorTree information. Implementation details 615992SN/A// can be found in Dominators.h, GenericDomTree.h, and 625992SN/A// GenericDomTreeConstruction.h. 635992SN/A// 645992SN/A//===----------------------------------------------------------------------===// 655992SN/A 665992SN/Atemplate class llvm::DomTreeNodeBase<BasicBlock>; 675992SN/Atemplate class llvm::DominatorTreeBase<BasicBlock, false>; // DomTreeBase 685992SN/Atemplate class llvm::DominatorTreeBase<BasicBlock, true>; // PostDomTreeBase 695992SN/A 705992SN/Atemplate class llvm::cfg::Update<BasicBlock *>; 715992SN/A 725992SN/Atemplate void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree>( 735992SN/A DomTreeBuilder::BBDomTree &DT); 745992SN/Atemplate void 757084SN/Allvm::DomTreeBuilder::CalculateWithUpdates<DomTreeBuilder::BBDomTree>( 767084SN/A DomTreeBuilder::BBDomTree &DT, BBUpdates U); 777084SN/A 787084SN/Atemplate void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>( 795992SN/A DomTreeBuilder::BBPostDomTree &DT); 805992SN/A// No CalculateWithUpdates<PostDomTree> instantiation, unless a usecase arises. 815992SN/A 825992SN/Atemplate void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>( 835992SN/A DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To); 845992SN/Atemplate void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBPostDomTree>( 855992SN/A DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To); 865992SN/A 87template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBDomTree>( 88 DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To); 89template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBPostDomTree>( 90 DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To); 91 92template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBDomTree>( 93 DomTreeBuilder::BBDomTree &DT, DomTreeBuilder::BBUpdates); 94template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>( 95 DomTreeBuilder::BBPostDomTree &DT, DomTreeBuilder::BBUpdates); 96 97template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>( 98 const DomTreeBuilder::BBDomTree &DT, 99 DomTreeBuilder::BBDomTree::VerificationLevel VL); 100template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>( 101 const DomTreeBuilder::BBPostDomTree &DT, 102 DomTreeBuilder::BBPostDomTree::VerificationLevel VL); 103 104bool DominatorTree::invalidate(Function &F, const PreservedAnalyses &PA, 105 FunctionAnalysisManager::Invalidator &) { 106 // Check whether the analysis, all analyses on functions, or the function's 107 // CFG have been preserved. 108 auto PAC = PA.getChecker<DominatorTreeAnalysis>(); 109 return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() || 110 PAC.preservedSet<CFGAnalyses>()); 111} 112 113// dominates - Return true if Def dominates a use in User. This performs 114// the special checks necessary if Def and User are in the same basic block. 115// Note that Def doesn't dominate a use in Def itself! 116bool DominatorTree::dominates(const Instruction *Def, 117 const Instruction *User) const { 118 const BasicBlock *UseBB = User->getParent(); 119 const BasicBlock *DefBB = Def->getParent(); 120 121 // Any unreachable use is dominated, even if Def == User. 122 if (!isReachableFromEntry(UseBB)) 123 return true; 124 125 // Unreachable definitions don't dominate anything. 126 if (!isReachableFromEntry(DefBB)) 127 return false; 128 129 // An instruction doesn't dominate a use in itself. 130 if (Def == User) 131 return false; 132 133 // The value defined by an invoke dominates an instruction only if it 134 // dominates every instruction in UseBB. 135 // A PHI is dominated only if the instruction dominates every possible use in 136 // the UseBB. 137 if (isa<InvokeInst>(Def) || isa<PHINode>(User)) 138 return dominates(Def, UseBB); 139 140 if (DefBB != UseBB) 141 return dominates(DefBB, UseBB); 142 143 // Loop through the basic block until we find Def or User. 144 BasicBlock::const_iterator I = DefBB->begin(); 145 for (; &*I != Def && &*I != User; ++I) 146 /*empty*/; 147 148 return &*I == Def; 149} 150 151// true if Def would dominate a use in any instruction in UseBB. 152// note that dominates(Def, Def->getParent()) is false. 153bool DominatorTree::dominates(const Instruction *Def, 154 const BasicBlock *UseBB) const { 155 const BasicBlock *DefBB = Def->getParent(); 156 157 // Any unreachable use is dominated, even if DefBB == UseBB. 158 if (!isReachableFromEntry(UseBB)) 159 return true; 160 161 // Unreachable definitions don't dominate anything. 162 if (!isReachableFromEntry(DefBB)) 163 return false; 164 165 if (DefBB == UseBB) 166 return false; 167 168 // Invoke results are only usable in the normal destination, not in the 169 // exceptional destination. 170 if (const auto *II = dyn_cast<InvokeInst>(Def)) { 171 BasicBlock *NormalDest = II->getNormalDest(); 172 BasicBlockEdge E(DefBB, NormalDest); 173 return dominates(E, UseBB); 174 } 175 176 return dominates(DefBB, UseBB); 177} 178 179bool DominatorTree::dominates(const BasicBlockEdge &BBE, 180 const BasicBlock *UseBB) const { 181 // If the BB the edge ends in doesn't dominate the use BB, then the 182 // edge also doesn't. 183 const BasicBlock *Start = BBE.getStart(); 184 const BasicBlock *End = BBE.getEnd(); 185 if (!dominates(End, UseBB)) 186 return false; 187 188 // Simple case: if the end BB has a single predecessor, the fact that it 189 // dominates the use block implies that the edge also does. 190 if (End->getSinglePredecessor()) 191 return true; 192 193 // The normal edge from the invoke is critical. Conceptually, what we would 194 // like to do is split it and check if the new block dominates the use. 195 // With X being the new block, the graph would look like: 196 // 197 // DefBB 198 // /\ . . 199 // / \ . . 200 // / \ . . 201 // / \ | | 202 // A X B C 203 // | \ | / 204 // . \|/ 205 // . NormalDest 206 // . 207 // 208 // Given the definition of dominance, NormalDest is dominated by X iff X 209 // dominates all of NormalDest's predecessors (X, B, C in the example). X 210 // trivially dominates itself, so we only have to find if it dominates the 211 // other predecessors. Since the only way out of X is via NormalDest, X can 212 // only properly dominate a node if NormalDest dominates that node too. 213 int IsDuplicateEdge = 0; 214 for (const_pred_iterator PI = pred_begin(End), E = pred_end(End); 215 PI != E; ++PI) { 216 const BasicBlock *BB = *PI; 217 if (BB == Start) { 218 // If there are multiple edges between Start and End, by definition they 219 // can't dominate anything. 220 if (IsDuplicateEdge++) 221 return false; 222 continue; 223 } 224 225 if (!dominates(End, BB)) 226 return false; 227 } 228 return true; 229} 230 231bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const { 232 Instruction *UserInst = cast<Instruction>(U.getUser()); 233 // A PHI in the end of the edge is dominated by it. 234 PHINode *PN = dyn_cast<PHINode>(UserInst); 235 if (PN && PN->getParent() == BBE.getEnd() && 236 PN->getIncomingBlock(U) == BBE.getStart()) 237 return true; 238 239 // Otherwise use the edge-dominates-block query, which 240 // handles the crazy critical edge cases properly. 241 const BasicBlock *UseBB; 242 if (PN) 243 UseBB = PN->getIncomingBlock(U); 244 else 245 UseBB = UserInst->getParent(); 246 return dominates(BBE, UseBB); 247} 248 249bool DominatorTree::dominates(const Instruction *Def, const Use &U) const { 250 Instruction *UserInst = cast<Instruction>(U.getUser()); 251 const BasicBlock *DefBB = Def->getParent(); 252 253 // Determine the block in which the use happens. PHI nodes use 254 // their operands on edges; simulate this by thinking of the use 255 // happening at the end of the predecessor block. 256 const BasicBlock *UseBB; 257 if (PHINode *PN = dyn_cast<PHINode>(UserInst)) 258 UseBB = PN->getIncomingBlock(U); 259 else 260 UseBB = UserInst->getParent(); 261 262 // Any unreachable use is dominated, even if Def == User. 263 if (!isReachableFromEntry(UseBB)) 264 return true; 265 266 // Unreachable definitions don't dominate anything. 267 if (!isReachableFromEntry(DefBB)) 268 return false; 269 270 // Invoke instructions define their return values on the edges to their normal 271 // successors, so we have to handle them specially. 272 // Among other things, this means they don't dominate anything in 273 // their own block, except possibly a phi, so we don't need to 274 // walk the block in any case. 275 if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) { 276 BasicBlock *NormalDest = II->getNormalDest(); 277 BasicBlockEdge E(DefBB, NormalDest); 278 return dominates(E, U); 279 } 280 281 // If the def and use are in different blocks, do a simple CFG dominator 282 // tree query. 283 if (DefBB != UseBB) 284 return dominates(DefBB, UseBB); 285 286 // Ok, def and use are in the same block. If the def is an invoke, it 287 // doesn't dominate anything in the block. If it's a PHI, it dominates 288 // everything in the block. 289 if (isa<PHINode>(UserInst)) 290 return true; 291 292 // Otherwise, just loop through the basic block until we find Def or User. 293 BasicBlock::const_iterator I = DefBB->begin(); 294 for (; &*I != Def && &*I != UserInst; ++I) 295 /*empty*/; 296 297 return &*I != UserInst; 298} 299 300bool DominatorTree::isReachableFromEntry(const Use &U) const { 301 Instruction *I = dyn_cast<Instruction>(U.getUser()); 302 303 // ConstantExprs aren't really reachable from the entry block, but they 304 // don't need to be treated like unreachable code either. 305 if (!I) return true; 306 307 // PHI nodes use their operands on their incoming edges. 308 if (PHINode *PN = dyn_cast<PHINode>(I)) 309 return isReachableFromEntry(PN->getIncomingBlock(U)); 310 311 // Everything else uses their operands in their own block. 312 return isReachableFromEntry(I->getParent()); 313} 314 315//===----------------------------------------------------------------------===// 316// DominatorTreeAnalysis and related pass implementations 317//===----------------------------------------------------------------------===// 318// 319// This implements the DominatorTreeAnalysis which is used with the new pass 320// manager. It also implements some methods from utility passes. 321// 322//===----------------------------------------------------------------------===// 323 324DominatorTree DominatorTreeAnalysis::run(Function &F, 325 FunctionAnalysisManager &) { 326 DominatorTree DT; 327 DT.recalculate(F); 328 return DT; 329} 330 331AnalysisKey DominatorTreeAnalysis::Key; 332 333DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {} 334 335PreservedAnalyses DominatorTreePrinterPass::run(Function &F, 336 FunctionAnalysisManager &AM) { 337 OS << "DominatorTree for function: " << F.getName() << "\n"; 338 AM.getResult<DominatorTreeAnalysis>(F).print(OS); 339 340 return PreservedAnalyses::all(); 341} 342 343PreservedAnalyses DominatorTreeVerifierPass::run(Function &F, 344 FunctionAnalysisManager &AM) { 345 auto &DT = AM.getResult<DominatorTreeAnalysis>(F); 346 assert(DT.verify()); 347 (void)DT; 348 return PreservedAnalyses::all(); 349} 350 351//===----------------------------------------------------------------------===// 352// DominatorTreeWrapperPass Implementation 353//===----------------------------------------------------------------------===// 354// 355// The implementation details of the wrapper pass that holds a DominatorTree 356// suitable for use with the legacy pass manager. 357// 358//===----------------------------------------------------------------------===// 359 360char DominatorTreeWrapperPass::ID = 0; 361INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree", 362 "Dominator Tree Construction", true, true) 363 364bool DominatorTreeWrapperPass::runOnFunction(Function &F) { 365 DT.recalculate(F); 366 return false; 367} 368 369void DominatorTreeWrapperPass::verifyAnalysis() const { 370 if (VerifyDomInfo) 371 assert(DT.verify(DominatorTree::VerificationLevel::Full)); 372 else if (ExpensiveChecksEnabled) 373 assert(DT.verify(DominatorTree::VerificationLevel::Basic)); 374} 375 376void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const { 377 DT.print(OS); 378} 379 380