1//===- llvm/Analysis/LoopInfoImpl.h - Natural Loop Calculator ---*- C++ -*-===// 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 is the generic implementation of LoopInfo used for both Loops and 11// MachineLoops. 12// 13//===----------------------------------------------------------------------===// 14 15#ifndef LLVM_ANALYSIS_LOOPINFOIMPL_H 16#define LLVM_ANALYSIS_LOOPINFOIMPL_H 17 18#include "llvm/ADT/DepthFirstIterator.h" 19#include "llvm/ADT/PostOrderIterator.h" 20#include "llvm/ADT/STLExtras.h" 21#include "llvm/Analysis/LoopInfo.h" 22#include "llvm/IR/Dominators.h" 23 24namespace llvm { 25 26//===----------------------------------------------------------------------===// 27// APIs for simple analysis of the loop. See header notes. 28 29/// getExitingBlocks - Return all blocks inside the loop that have successors 30/// outside of the loop. These are the blocks _inside of the current loop_ 31/// which branch out. The returned list is always unique. 32/// 33template<class BlockT, class LoopT> 34void LoopBase<BlockT, LoopT>:: 35getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const { 36 typedef GraphTraits<BlockT*> BlockTraits; 37 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) 38 for (typename BlockTraits::ChildIteratorType I = 39 BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); 40 I != E; ++I) 41 if (!contains(*I)) { 42 // Not in current loop? It must be an exit block. 43 ExitingBlocks.push_back(*BI); 44 break; 45 } 46} 47 48/// getExitingBlock - If getExitingBlocks would return exactly one block, 49/// return that block. Otherwise return null. 50template<class BlockT, class LoopT> 51BlockT *LoopBase<BlockT, LoopT>::getExitingBlock() const { 52 SmallVector<BlockT*, 8> ExitingBlocks; 53 getExitingBlocks(ExitingBlocks); 54 if (ExitingBlocks.size() == 1) 55 return ExitingBlocks[0]; 56 return nullptr; 57} 58 59/// getExitBlocks - Return all of the successor blocks of this loop. These 60/// are the blocks _outside of the current loop_ which are branched to. 61/// 62template<class BlockT, class LoopT> 63void LoopBase<BlockT, LoopT>:: 64getExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const { 65 typedef GraphTraits<BlockT*> BlockTraits; 66 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) 67 for (typename BlockTraits::ChildIteratorType I = 68 BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); 69 I != E; ++I) 70 if (!contains(*I)) 71 // Not in current loop? It must be an exit block. 72 ExitBlocks.push_back(*I); 73} 74 75/// getExitBlock - If getExitBlocks would return exactly one block, 76/// return that block. Otherwise return null. 77template<class BlockT, class LoopT> 78BlockT *LoopBase<BlockT, LoopT>::getExitBlock() const { 79 SmallVector<BlockT*, 8> ExitBlocks; 80 getExitBlocks(ExitBlocks); 81 if (ExitBlocks.size() == 1) 82 return ExitBlocks[0]; 83 return nullptr; 84} 85 86/// getExitEdges - Return all pairs of (_inside_block_,_outside_block_). 87template<class BlockT, class LoopT> 88void LoopBase<BlockT, LoopT>:: 89getExitEdges(SmallVectorImpl<Edge> &ExitEdges) const { 90 typedef GraphTraits<BlockT*> BlockTraits; 91 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) 92 for (typename BlockTraits::ChildIteratorType I = 93 BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); 94 I != E; ++I) 95 if (!contains(*I)) 96 // Not in current loop? It must be an exit block. 97 ExitEdges.push_back(Edge(*BI, *I)); 98} 99 100/// getLoopPreheader - If there is a preheader for this loop, return it. A 101/// loop has a preheader if there is only one edge to the header of the loop 102/// from outside of the loop. If this is the case, the block branching to the 103/// header of the loop is the preheader node. 104/// 105/// This method returns null if there is no preheader for the loop. 106/// 107template<class BlockT, class LoopT> 108BlockT *LoopBase<BlockT, LoopT>::getLoopPreheader() const { 109 // Keep track of nodes outside the loop branching to the header... 110 BlockT *Out = getLoopPredecessor(); 111 if (!Out) return nullptr; 112 113 // Make sure there is only one exit out of the preheader. 114 typedef GraphTraits<BlockT*> BlockTraits; 115 typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out); 116 ++SI; 117 if (SI != BlockTraits::child_end(Out)) 118 return nullptr; // Multiple exits from the block, must not be a preheader. 119 120 // The predecessor has exactly one successor, so it is a preheader. 121 return Out; 122} 123 124/// getLoopPredecessor - If the given loop's header has exactly one unique 125/// predecessor outside the loop, return it. Otherwise return null. 126/// This is less strict that the loop "preheader" concept, which requires 127/// the predecessor to have exactly one successor. 128/// 129template<class BlockT, class LoopT> 130BlockT *LoopBase<BlockT, LoopT>::getLoopPredecessor() const { 131 // Keep track of nodes outside the loop branching to the header... 132 BlockT *Out = nullptr; 133 134 // Loop over the predecessors of the header node... 135 BlockT *Header = getHeader(); 136 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 137 for (typename InvBlockTraits::ChildIteratorType PI = 138 InvBlockTraits::child_begin(Header), 139 PE = InvBlockTraits::child_end(Header); PI != PE; ++PI) { 140 typename InvBlockTraits::NodeType *N = *PI; 141 if (!contains(N)) { // If the block is not in the loop... 142 if (Out && Out != N) 143 return nullptr; // Multiple predecessors outside the loop 144 Out = N; 145 } 146 } 147 148 // Make sure there is only one exit out of the preheader. 149 assert(Out && "Header of loop has no predecessors from outside loop?"); 150 return Out; 151} 152 153/// getLoopLatch - If there is a single latch block for this loop, return it. 154/// A latch block is a block that contains a branch back to the header. 155template<class BlockT, class LoopT> 156BlockT *LoopBase<BlockT, LoopT>::getLoopLatch() const { 157 BlockT *Header = getHeader(); 158 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 159 typename InvBlockTraits::ChildIteratorType PI = 160 InvBlockTraits::child_begin(Header); 161 typename InvBlockTraits::ChildIteratorType PE = 162 InvBlockTraits::child_end(Header); 163 BlockT *Latch = nullptr; 164 for (; PI != PE; ++PI) { 165 typename InvBlockTraits::NodeType *N = *PI; 166 if (contains(N)) { 167 if (Latch) return nullptr; 168 Latch = N; 169 } 170 } 171 172 return Latch; 173} 174 175//===----------------------------------------------------------------------===// 176// APIs for updating loop information after changing the CFG 177// 178 179/// addBasicBlockToLoop - This method is used by other analyses to update loop 180/// information. NewBB is set to be a new member of the current loop. 181/// Because of this, it is added as a member of all parent loops, and is added 182/// to the specified LoopInfo object as being in the current basic block. It 183/// is not valid to replace the loop header with this method. 184/// 185template<class BlockT, class LoopT> 186void LoopBase<BlockT, LoopT>:: 187addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LIB) { 188 assert((Blocks.empty() || LIB[getHeader()] == this) && 189 "Incorrect LI specified for this loop!"); 190 assert(NewBB && "Cannot add a null basic block to the loop!"); 191 assert(!LIB[NewBB] && "BasicBlock already in the loop!"); 192 193 LoopT *L = static_cast<LoopT *>(this); 194 195 // Add the loop mapping to the LoopInfo object... 196 LIB.BBMap[NewBB] = L; 197 198 // Add the basic block to this loop and all parent loops... 199 while (L) { 200 L->addBlockEntry(NewBB); 201 L = L->getParentLoop(); 202 } 203} 204 205/// replaceChildLoopWith - This is used when splitting loops up. It replaces 206/// the OldChild entry in our children list with NewChild, and updates the 207/// parent pointer of OldChild to be null and the NewChild to be this loop. 208/// This updates the loop depth of the new child. 209template<class BlockT, class LoopT> 210void LoopBase<BlockT, LoopT>:: 211replaceChildLoopWith(LoopT *OldChild, LoopT *NewChild) { 212 assert(OldChild->ParentLoop == this && "This loop is already broken!"); 213 assert(!NewChild->ParentLoop && "NewChild already has a parent!"); 214 typename std::vector<LoopT *>::iterator I = 215 std::find(SubLoops.begin(), SubLoops.end(), OldChild); 216 assert(I != SubLoops.end() && "OldChild not in loop!"); 217 *I = NewChild; 218 OldChild->ParentLoop = nullptr; 219 NewChild->ParentLoop = static_cast<LoopT *>(this); 220} 221 222/// verifyLoop - Verify loop structure 223template<class BlockT, class LoopT> 224void LoopBase<BlockT, LoopT>::verifyLoop() const { 225#ifndef NDEBUG 226 assert(!Blocks.empty() && "Loop header is missing"); 227 228 // Setup for using a depth-first iterator to visit every block in the loop. 229 SmallVector<BlockT*, 8> ExitBBs; 230 getExitBlocks(ExitBBs); 231 llvm::SmallPtrSet<BlockT*, 8> VisitSet; 232 VisitSet.insert(ExitBBs.begin(), ExitBBs.end()); 233 df_ext_iterator<BlockT*, llvm::SmallPtrSet<BlockT*, 8> > 234 BI = df_ext_begin(getHeader(), VisitSet), 235 BE = df_ext_end(getHeader(), VisitSet); 236 237 // Keep track of the number of BBs visited. 238 unsigned NumVisited = 0; 239 240 // Check the individual blocks. 241 for ( ; BI != BE; ++BI) { 242 BlockT *BB = *BI; 243 bool HasInsideLoopSuccs = false; 244 bool HasInsideLoopPreds = false; 245 SmallVector<BlockT *, 2> OutsideLoopPreds; 246 247 typedef GraphTraits<BlockT*> BlockTraits; 248 for (typename BlockTraits::ChildIteratorType SI = 249 BlockTraits::child_begin(BB), SE = BlockTraits::child_end(BB); 250 SI != SE; ++SI) 251 if (contains(*SI)) { 252 HasInsideLoopSuccs = true; 253 break; 254 } 255 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 256 for (typename InvBlockTraits::ChildIteratorType PI = 257 InvBlockTraits::child_begin(BB), PE = InvBlockTraits::child_end(BB); 258 PI != PE; ++PI) { 259 BlockT *N = *PI; 260 if (contains(N)) 261 HasInsideLoopPreds = true; 262 else 263 OutsideLoopPreds.push_back(N); 264 } 265 266 if (BB == getHeader()) { 267 assert(!OutsideLoopPreds.empty() && "Loop is unreachable!"); 268 } else if (!OutsideLoopPreds.empty()) { 269 // A non-header loop shouldn't be reachable from outside the loop, 270 // though it is permitted if the predecessor is not itself actually 271 // reachable. 272 BlockT *EntryBB = BB->getParent()->begin(); 273 for (BlockT *CB : depth_first(EntryBB)) 274 for (unsigned i = 0, e = OutsideLoopPreds.size(); i != e; ++i) 275 assert(CB != OutsideLoopPreds[i] && 276 "Loop has multiple entry points!"); 277 } 278 assert(HasInsideLoopPreds && "Loop block has no in-loop predecessors!"); 279 assert(HasInsideLoopSuccs && "Loop block has no in-loop successors!"); 280 assert(BB != getHeader()->getParent()->begin() && 281 "Loop contains function entry block!"); 282 283 NumVisited++; 284 } 285 286 assert(NumVisited == getNumBlocks() && "Unreachable block in loop"); 287 288 // Check the subloops. 289 for (iterator I = begin(), E = end(); I != E; ++I) 290 // Each block in each subloop should be contained within this loop. 291 for (block_iterator BI = (*I)->block_begin(), BE = (*I)->block_end(); 292 BI != BE; ++BI) { 293 assert(contains(*BI) && 294 "Loop does not contain all the blocks of a subloop!"); 295 } 296 297 // Check the parent loop pointer. 298 if (ParentLoop) { 299 assert(std::find(ParentLoop->begin(), ParentLoop->end(), this) != 300 ParentLoop->end() && 301 "Loop is not a subloop of its parent!"); 302 } 303#endif 304} 305 306/// verifyLoop - Verify loop structure of this loop and all nested loops. 307template<class BlockT, class LoopT> 308void LoopBase<BlockT, LoopT>::verifyLoopNest( 309 DenseSet<const LoopT*> *Loops) const { 310 Loops->insert(static_cast<const LoopT *>(this)); 311 // Verify this loop. 312 verifyLoop(); 313 // Verify the subloops. 314 for (iterator I = begin(), E = end(); I != E; ++I) 315 (*I)->verifyLoopNest(Loops); 316} 317 318template<class BlockT, class LoopT> 319void LoopBase<BlockT, LoopT>::print(raw_ostream &OS, unsigned Depth) const { 320 OS.indent(Depth*2) << "Loop at depth " << getLoopDepth() 321 << " containing: "; 322 323 for (unsigned i = 0; i < getBlocks().size(); ++i) { 324 if (i) OS << ","; 325 BlockT *BB = getBlocks()[i]; 326 BB->printAsOperand(OS, false); 327 if (BB == getHeader()) OS << "<header>"; 328 if (BB == getLoopLatch()) OS << "<latch>"; 329 if (isLoopExiting(BB)) OS << "<exiting>"; 330 } 331 OS << "\n"; 332 333 for (iterator I = begin(), E = end(); I != E; ++I) 334 (*I)->print(OS, Depth+2); 335} 336 337//===----------------------------------------------------------------------===// 338/// Stable LoopInfo Analysis - Build a loop tree using stable iterators so the 339/// result does / not depend on use list (block predecessor) order. 340/// 341 342/// Discover a subloop with the specified backedges such that: All blocks within 343/// this loop are mapped to this loop or a subloop. And all subloops within this 344/// loop have their parent loop set to this loop or a subloop. 345template<class BlockT, class LoopT> 346static void discoverAndMapSubloop(LoopT *L, ArrayRef<BlockT*> Backedges, 347 LoopInfoBase<BlockT, LoopT> *LI, 348 DominatorTreeBase<BlockT> &DomTree) { 349 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 350 351 unsigned NumBlocks = 0; 352 unsigned NumSubloops = 0; 353 354 // Perform a backward CFG traversal using a worklist. 355 std::vector<BlockT *> ReverseCFGWorklist(Backedges.begin(), Backedges.end()); 356 while (!ReverseCFGWorklist.empty()) { 357 BlockT *PredBB = ReverseCFGWorklist.back(); 358 ReverseCFGWorklist.pop_back(); 359 360 LoopT *Subloop = LI->getLoopFor(PredBB); 361 if (!Subloop) { 362 if (!DomTree.isReachableFromEntry(PredBB)) 363 continue; 364 365 // This is an undiscovered block. Map it to the current loop. 366 LI->changeLoopFor(PredBB, L); 367 ++NumBlocks; 368 if (PredBB == L->getHeader()) 369 continue; 370 // Push all block predecessors on the worklist. 371 ReverseCFGWorklist.insert(ReverseCFGWorklist.end(), 372 InvBlockTraits::child_begin(PredBB), 373 InvBlockTraits::child_end(PredBB)); 374 } 375 else { 376 // This is a discovered block. Find its outermost discovered loop. 377 while (LoopT *Parent = Subloop->getParentLoop()) 378 Subloop = Parent; 379 380 // If it is already discovered to be a subloop of this loop, continue. 381 if (Subloop == L) 382 continue; 383 384 // Discover a subloop of this loop. 385 Subloop->setParentLoop(L); 386 ++NumSubloops; 387 NumBlocks += Subloop->getBlocks().capacity(); 388 PredBB = Subloop->getHeader(); 389 // Continue traversal along predecessors that are not loop-back edges from 390 // within this subloop tree itself. Note that a predecessor may directly 391 // reach another subloop that is not yet discovered to be a subloop of 392 // this loop, which we must traverse. 393 for (typename InvBlockTraits::ChildIteratorType PI = 394 InvBlockTraits::child_begin(PredBB), 395 PE = InvBlockTraits::child_end(PredBB); PI != PE; ++PI) { 396 if (LI->getLoopFor(*PI) != Subloop) 397 ReverseCFGWorklist.push_back(*PI); 398 } 399 } 400 } 401 L->getSubLoopsVector().reserve(NumSubloops); 402 L->reserveBlocks(NumBlocks); 403} 404 405/// Populate all loop data in a stable order during a single forward DFS. 406template<class BlockT, class LoopT> 407class PopulateLoopsDFS { 408 typedef GraphTraits<BlockT*> BlockTraits; 409 typedef typename BlockTraits::ChildIteratorType SuccIterTy; 410 411 LoopInfoBase<BlockT, LoopT> *LI; 412public: 413 PopulateLoopsDFS(LoopInfoBase<BlockT, LoopT> *li): 414 LI(li) {} 415 416 void traverse(BlockT *EntryBlock); 417 418protected: 419 void insertIntoLoop(BlockT *Block); 420}; 421 422/// Top-level driver for the forward DFS within the loop. 423template<class BlockT, class LoopT> 424void PopulateLoopsDFS<BlockT, LoopT>::traverse(BlockT *EntryBlock) { 425 for (BlockT *BB : post_order(EntryBlock)) 426 insertIntoLoop(BB); 427} 428 429/// Add a single Block to its ancestor loops in PostOrder. If the block is a 430/// subloop header, add the subloop to its parent in PostOrder, then reverse the 431/// Block and Subloop vectors of the now complete subloop to achieve RPO. 432template<class BlockT, class LoopT> 433void PopulateLoopsDFS<BlockT, LoopT>::insertIntoLoop(BlockT *Block) { 434 LoopT *Subloop = LI->getLoopFor(Block); 435 if (Subloop && Block == Subloop->getHeader()) { 436 // We reach this point once per subloop after processing all the blocks in 437 // the subloop. 438 if (Subloop->getParentLoop()) 439 Subloop->getParentLoop()->getSubLoopsVector().push_back(Subloop); 440 else 441 LI->addTopLevelLoop(Subloop); 442 443 // For convenience, Blocks and Subloops are inserted in postorder. Reverse 444 // the lists, except for the loop header, which is always at the beginning. 445 Subloop->reverseBlock(1); 446 std::reverse(Subloop->getSubLoopsVector().begin(), 447 Subloop->getSubLoopsVector().end()); 448 449 Subloop = Subloop->getParentLoop(); 450 } 451 for (; Subloop; Subloop = Subloop->getParentLoop()) 452 Subloop->addBlockEntry(Block); 453} 454 455/// Analyze LoopInfo discovers loops during a postorder DominatorTree traversal 456/// interleaved with backward CFG traversals within each subloop 457/// (discoverAndMapSubloop). The backward traversal skips inner subloops, so 458/// this part of the algorithm is linear in the number of CFG edges. Subloop and 459/// Block vectors are then populated during a single forward CFG traversal 460/// (PopulateLoopDFS). 461/// 462/// During the two CFG traversals each block is seen three times: 463/// 1) Discovered and mapped by a reverse CFG traversal. 464/// 2) Visited during a forward DFS CFG traversal. 465/// 3) Reverse-inserted in the loop in postorder following forward DFS. 466/// 467/// The Block vectors are inclusive, so step 3 requires loop-depth number of 468/// insertions per block. 469template<class BlockT, class LoopT> 470void LoopInfoBase<BlockT, LoopT>:: 471Analyze(DominatorTreeBase<BlockT> &DomTree) { 472 473 // Postorder traversal of the dominator tree. 474 DomTreeNodeBase<BlockT>* DomRoot = DomTree.getRootNode(); 475 for (auto DomNode : post_order(DomRoot)) { 476 477 BlockT *Header = DomNode->getBlock(); 478 SmallVector<BlockT *, 4> Backedges; 479 480 // Check each predecessor of the potential loop header. 481 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 482 for (typename InvBlockTraits::ChildIteratorType PI = 483 InvBlockTraits::child_begin(Header), 484 PE = InvBlockTraits::child_end(Header); PI != PE; ++PI) { 485 486 BlockT *Backedge = *PI; 487 488 // If Header dominates predBB, this is a new loop. Collect the backedges. 489 if (DomTree.dominates(Header, Backedge) 490 && DomTree.isReachableFromEntry(Backedge)) { 491 Backedges.push_back(Backedge); 492 } 493 } 494 // Perform a backward CFG traversal to discover and map blocks in this loop. 495 if (!Backedges.empty()) { 496 LoopT *L = new LoopT(Header); 497 discoverAndMapSubloop(L, ArrayRef<BlockT*>(Backedges), this, DomTree); 498 } 499 } 500 // Perform a single forward CFG traversal to populate block and subloop 501 // vectors for all loops. 502 PopulateLoopsDFS<BlockT, LoopT> DFS(this); 503 DFS.traverse(DomRoot->getBlock()); 504} 505 506// Debugging 507template<class BlockT, class LoopT> 508void LoopInfoBase<BlockT, LoopT>::print(raw_ostream &OS) const { 509 for (unsigned i = 0; i < TopLevelLoops.size(); ++i) 510 TopLevelLoops[i]->print(OS); 511#if 0 512 for (DenseMap<BasicBlock*, LoopT*>::const_iterator I = BBMap.begin(), 513 E = BBMap.end(); I != E; ++I) 514 OS << "BB '" << I->first->getName() << "' level = " 515 << I->second->getLoopDepth() << "\n"; 516#endif 517} 518 519template<class BlockT, class LoopT> 520void LoopInfoBase<BlockT, LoopT>::verify() const { 521 DenseSet<const LoopT*> Loops; 522 for (iterator I = begin(), E = end(); I != E; ++I) { 523 assert(!(*I)->getParentLoop() && "Top-level loop has a parent!"); 524 (*I)->verifyLoopNest(&Loops); 525 } 526 527 // Verify that blocks are mapped to valid loops. 528#ifndef NDEBUG 529 for (auto &Entry : BBMap) { 530 BlockT *BB = Entry.first; 531 LoopT *L = Entry.second; 532 assert(Loops.count(L) && "orphaned loop"); 533 assert(L->contains(BB) && "orphaned block"); 534 } 535#endif 536} 537 538} // End llvm namespace 539 540#endif 541