1 //===- llvm/Analysis/LoopInfo.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 file defines the LoopInfo class that is used to identify natural loops 11 // and determine the loop depth of various nodes of the CFG. A natural loop 12 // has exactly one entry-point, which is called the header. Note that natural 13 // loops may actually be several loops that share the same header node. 14 // 15 // This analysis calculates the nesting structure of loops in a function. For 16 // each natural loop identified, this analysis identifies natural loops 17 // contained entirely within the loop and the basic blocks the make up the loop. 18 // 19 // It can calculate on the fly various bits of information, for example: 20 // 21 // * whether there is a preheader for the loop 22 // * the number of back edges to the header 23 // * whether or not a particular block branches out of the loop 24 // * the successor blocks of the loop 25 // * the loop depth 26 // * etc... 27 // 28 //===----------------------------------------------------------------------===// 29 30 #ifndef LLVM_ANALYSIS_LOOP_INFO_H 31 #define LLVM_ANALYSIS_LOOP_INFO_H 32 33 #include "llvm/Pass.h" 34 #include "llvm/ADT/DenseMap.h" 35 #include "llvm/ADT/DenseSet.h" 36 #include "llvm/ADT/DepthFirstIterator.h" 37 #include "llvm/ADT/GraphTraits.h" 38 #include "llvm/ADT/SmallVector.h" 39 #include "llvm/ADT/STLExtras.h" 40 #include "llvm/Analysis/Dominators.h" 41 #include "llvm/Support/CFG.h" 42 #include "llvm/Support/raw_ostream.h" 43 #include <algorithm> 44 #include <map> 45 46 namespace llvm { 47 48 template<typename T> 49 static void RemoveFromVector(std::vector<T*> &V, T *N) { 50 typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N); 51 assert(I != V.end() && "N is not in this list!"); 52 V.erase(I); 53 } 54 55 class DominatorTree; 56 class LoopInfo; 57 class Loop; 58 class PHINode; 59 template<class N, class M> class LoopInfoBase; 60 template<class N, class M> class LoopBase; 61 62 //===----------------------------------------------------------------------===// 63 /// LoopBase class - Instances of this class are used to represent loops that 64 /// are detected in the flow graph 65 /// 66 template<class BlockT, class LoopT> 67 class LoopBase { 68 LoopT *ParentLoop; 69 // SubLoops - Loops contained entirely within this one. 70 std::vector<LoopT *> SubLoops; 71 72 // Blocks - The list of blocks in this loop. First entry is the header node. 73 std::vector<BlockT*> Blocks; 74 75 // DO NOT IMPLEMENT 76 LoopBase(const LoopBase<BlockT, LoopT> &); 77 // DO NOT IMPLEMENT 78 const LoopBase<BlockT, LoopT>&operator=(const LoopBase<BlockT, LoopT> &); 79 public: 80 /// Loop ctor - This creates an empty loop. 81 LoopBase() : ParentLoop(0) {} 82 ~LoopBase() { 83 for (size_t i = 0, e = SubLoops.size(); i != e; ++i) 84 delete SubLoops[i]; 85 } 86 87 /// getLoopDepth - Return the nesting level of this loop. An outer-most 88 /// loop has depth 1, for consistency with loop depth values used for basic 89 /// blocks, where depth 0 is used for blocks not inside any loops. 90 unsigned getLoopDepth() const { 91 unsigned D = 1; 92 for (const LoopT *CurLoop = ParentLoop; CurLoop; 93 CurLoop = CurLoop->ParentLoop) 94 ++D; 95 return D; 96 } 97 BlockT *getHeader() const { return Blocks.front(); } 98 LoopT *getParentLoop() const { return ParentLoop; } 99 100 /// contains - Return true if the specified loop is contained within in 101 /// this loop. 102 /// 103 bool contains(const LoopT *L) const { 104 if (L == this) return true; 105 if (L == 0) return false; 106 return contains(L->getParentLoop()); 107 } 108 109 /// contains - Return true if the specified basic block is in this loop. 110 /// 111 bool contains(const BlockT *BB) const { 112 return std::find(block_begin(), block_end(), BB) != block_end(); 113 } 114 115 /// contains - Return true if the specified instruction is in this loop. 116 /// 117 template<class InstT> 118 bool contains(const InstT *Inst) const { 119 return contains(Inst->getParent()); 120 } 121 122 /// iterator/begin/end - Return the loops contained entirely within this loop. 123 /// 124 const std::vector<LoopT *> &getSubLoops() const { return SubLoops; } 125 typedef typename std::vector<LoopT *>::const_iterator iterator; 126 iterator begin() const { return SubLoops.begin(); } 127 iterator end() const { return SubLoops.end(); } 128 bool empty() const { return SubLoops.empty(); } 129 130 /// getBlocks - Get a list of the basic blocks which make up this loop. 131 /// 132 const std::vector<BlockT*> &getBlocks() const { return Blocks; } 133 typedef typename std::vector<BlockT*>::const_iterator block_iterator; 134 block_iterator block_begin() const { return Blocks.begin(); } 135 block_iterator block_end() const { return Blocks.end(); } 136 137 /// getNumBlocks - Get the number of blocks in this loop in constant time. 138 unsigned getNumBlocks() const { 139 return Blocks.size(); 140 } 141 142 /// isLoopExiting - True if terminator in the block can branch to another 143 /// block that is outside of the current loop. 144 /// 145 bool isLoopExiting(const BlockT *BB) const { 146 typedef GraphTraits<BlockT*> BlockTraits; 147 for (typename BlockTraits::ChildIteratorType SI = 148 BlockTraits::child_begin(const_cast<BlockT*>(BB)), 149 SE = BlockTraits::child_end(const_cast<BlockT*>(BB)); SI != SE; ++SI) { 150 if (!contains(*SI)) 151 return true; 152 } 153 return false; 154 } 155 156 /// getNumBackEdges - Calculate the number of back edges to the loop header 157 /// 158 unsigned getNumBackEdges() const { 159 unsigned NumBackEdges = 0; 160 BlockT *H = getHeader(); 161 162 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 163 for (typename InvBlockTraits::ChildIteratorType I = 164 InvBlockTraits::child_begin(const_cast<BlockT*>(H)), 165 E = InvBlockTraits::child_end(const_cast<BlockT*>(H)); I != E; ++I) 166 if (contains(*I)) 167 ++NumBackEdges; 168 169 return NumBackEdges; 170 } 171 172 //===--------------------------------------------------------------------===// 173 // APIs for simple analysis of the loop. 174 // 175 // Note that all of these methods can fail on general loops (ie, there may not 176 // be a preheader, etc). For best success, the loop simplification and 177 // induction variable canonicalization pass should be used to normalize loops 178 // for easy analysis. These methods assume canonical loops. 179 180 /// getExitingBlocks - Return all blocks inside the loop that have successors 181 /// outside of the loop. These are the blocks _inside of the current loop_ 182 /// which branch out. The returned list is always unique. 183 /// 184 void getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const { 185 // Sort the blocks vector so that we can use binary search to do quick 186 // lookups. 187 SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); 188 std::sort(LoopBBs.begin(), LoopBBs.end()); 189 190 typedef GraphTraits<BlockT*> BlockTraits; 191 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) 192 for (typename BlockTraits::ChildIteratorType I = 193 BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); 194 I != E; ++I) 195 if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) { 196 // Not in current loop? It must be an exit block. 197 ExitingBlocks.push_back(*BI); 198 break; 199 } 200 } 201 202 /// getExitingBlock - If getExitingBlocks would return exactly one block, 203 /// return that block. Otherwise return null. 204 BlockT *getExitingBlock() const { 205 SmallVector<BlockT*, 8> ExitingBlocks; 206 getExitingBlocks(ExitingBlocks); 207 if (ExitingBlocks.size() == 1) 208 return ExitingBlocks[0]; 209 return 0; 210 } 211 212 /// getExitBlocks - Return all of the successor blocks of this loop. These 213 /// are the blocks _outside of the current loop_ which are branched to. 214 /// 215 void getExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const { 216 // Sort the blocks vector so that we can use binary search to do quick 217 // lookups. 218 SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); 219 std::sort(LoopBBs.begin(), LoopBBs.end()); 220 221 typedef GraphTraits<BlockT*> BlockTraits; 222 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) 223 for (typename BlockTraits::ChildIteratorType I = 224 BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); 225 I != E; ++I) 226 if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) 227 // Not in current loop? It must be an exit block. 228 ExitBlocks.push_back(*I); 229 } 230 231 /// getExitBlock - If getExitBlocks would return exactly one block, 232 /// return that block. Otherwise return null. 233 BlockT *getExitBlock() const { 234 SmallVector<BlockT*, 8> ExitBlocks; 235 getExitBlocks(ExitBlocks); 236 if (ExitBlocks.size() == 1) 237 return ExitBlocks[0]; 238 return 0; 239 } 240 241 /// Edge type. 242 typedef std::pair<BlockT*, BlockT*> Edge; 243 244 /// getExitEdges - Return all pairs of (_inside_block_,_outside_block_). 245 template <typename EdgeT> 246 void getExitEdges(SmallVectorImpl<EdgeT> &ExitEdges) const { 247 // Sort the blocks vector so that we can use binary search to do quick 248 // lookups. 249 SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); 250 array_pod_sort(LoopBBs.begin(), LoopBBs.end()); 251 252 typedef GraphTraits<BlockT*> BlockTraits; 253 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) 254 for (typename BlockTraits::ChildIteratorType I = 255 BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); 256 I != E; ++I) 257 if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) 258 // Not in current loop? It must be an exit block. 259 ExitEdges.push_back(EdgeT(*BI, *I)); 260 } 261 262 /// getLoopPreheader - If there is a preheader for this loop, return it. A 263 /// loop has a preheader if there is only one edge to the header of the loop 264 /// from outside of the loop. If this is the case, the block branching to the 265 /// header of the loop is the preheader node. 266 /// 267 /// This method returns null if there is no preheader for the loop. 268 /// 269 BlockT *getLoopPreheader() const { 270 // Keep track of nodes outside the loop branching to the header... 271 BlockT *Out = getLoopPredecessor(); 272 if (!Out) return 0; 273 274 // Make sure there is only one exit out of the preheader. 275 typedef GraphTraits<BlockT*> BlockTraits; 276 typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out); 277 ++SI; 278 if (SI != BlockTraits::child_end(Out)) 279 return 0; // Multiple exits from the block, must not be a preheader. 280 281 // The predecessor has exactly one successor, so it is a preheader. 282 return Out; 283 } 284 285 /// getLoopPredecessor - If the given loop's header has exactly one unique 286 /// predecessor outside the loop, return it. Otherwise return null. 287 /// This is less strict that the loop "preheader" concept, which requires 288 /// the predecessor to have exactly one successor. 289 /// 290 BlockT *getLoopPredecessor() const { 291 // Keep track of nodes outside the loop branching to the header... 292 BlockT *Out = 0; 293 294 // Loop over the predecessors of the header node... 295 BlockT *Header = getHeader(); 296 typedef GraphTraits<BlockT*> BlockTraits; 297 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 298 for (typename InvBlockTraits::ChildIteratorType PI = 299 InvBlockTraits::child_begin(Header), 300 PE = InvBlockTraits::child_end(Header); PI != PE; ++PI) { 301 typename InvBlockTraits::NodeType *N = *PI; 302 if (!contains(N)) { // If the block is not in the loop... 303 if (Out && Out != N) 304 return 0; // Multiple predecessors outside the loop 305 Out = N; 306 } 307 } 308 309 // Make sure there is only one exit out of the preheader. 310 assert(Out && "Header of loop has no predecessors from outside loop?"); 311 return Out; 312 } 313 314 /// getLoopLatch - If there is a single latch block for this loop, return it. 315 /// A latch block is a block that contains a branch back to the header. 316 BlockT *getLoopLatch() const { 317 BlockT *Header = getHeader(); 318 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 319 typename InvBlockTraits::ChildIteratorType PI = 320 InvBlockTraits::child_begin(Header); 321 typename InvBlockTraits::ChildIteratorType PE = 322 InvBlockTraits::child_end(Header); 323 BlockT *Latch = 0; 324 for (; PI != PE; ++PI) { 325 typename InvBlockTraits::NodeType *N = *PI; 326 if (contains(N)) { 327 if (Latch) return 0; 328 Latch = N; 329 } 330 } 331 332 return Latch; 333 } 334 335 //===--------------------------------------------------------------------===// 336 // APIs for updating loop information after changing the CFG 337 // 338 339 /// addBasicBlockToLoop - This method is used by other analyses to update loop 340 /// information. NewBB is set to be a new member of the current loop. 341 /// Because of this, it is added as a member of all parent loops, and is added 342 /// to the specified LoopInfo object as being in the current basic block. It 343 /// is not valid to replace the loop header with this method. 344 /// 345 void addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LI); 346 347 /// replaceChildLoopWith - This is used when splitting loops up. It replaces 348 /// the OldChild entry in our children list with NewChild, and updates the 349 /// parent pointer of OldChild to be null and the NewChild to be this loop. 350 /// This updates the loop depth of the new child. 351 void replaceChildLoopWith(LoopT *OldChild, 352 LoopT *NewChild) { 353 assert(OldChild->ParentLoop == this && "This loop is already broken!"); 354 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!"); 355 typename std::vector<LoopT *>::iterator I = 356 std::find(SubLoops.begin(), SubLoops.end(), OldChild); 357 assert(I != SubLoops.end() && "OldChild not in loop!"); 358 *I = NewChild; 359 OldChild->ParentLoop = 0; 360 NewChild->ParentLoop = static_cast<LoopT *>(this); 361 } 362 363 /// addChildLoop - Add the specified loop to be a child of this loop. This 364 /// updates the loop depth of the new child. 365 /// 366 void addChildLoop(LoopT *NewChild) { 367 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!"); 368 NewChild->ParentLoop = static_cast<LoopT *>(this); 369 SubLoops.push_back(NewChild); 370 } 371 372 /// removeChildLoop - This removes the specified child from being a subloop of 373 /// this loop. The loop is not deleted, as it will presumably be inserted 374 /// into another loop. 375 LoopT *removeChildLoop(iterator I) { 376 assert(I != SubLoops.end() && "Cannot remove end iterator!"); 377 LoopT *Child = *I; 378 assert(Child->ParentLoop == this && "Child is not a child of this loop!"); 379 SubLoops.erase(SubLoops.begin()+(I-begin())); 380 Child->ParentLoop = 0; 381 return Child; 382 } 383 384 /// addBlockEntry - This adds a basic block directly to the basic block list. 385 /// This should only be used by transformations that create new loops. Other 386 /// transformations should use addBasicBlockToLoop. 387 void addBlockEntry(BlockT *BB) { 388 Blocks.push_back(BB); 389 } 390 391 /// moveToHeader - This method is used to move BB (which must be part of this 392 /// loop) to be the loop header of the loop (the block that dominates all 393 /// others). 394 void moveToHeader(BlockT *BB) { 395 if (Blocks[0] == BB) return; 396 for (unsigned i = 0; ; ++i) { 397 assert(i != Blocks.size() && "Loop does not contain BB!"); 398 if (Blocks[i] == BB) { 399 Blocks[i] = Blocks[0]; 400 Blocks[0] = BB; 401 return; 402 } 403 } 404 } 405 406 /// removeBlockFromLoop - This removes the specified basic block from the 407 /// current loop, updating the Blocks as appropriate. This does not update 408 /// the mapping in the LoopInfo class. 409 void removeBlockFromLoop(BlockT *BB) { 410 RemoveFromVector(Blocks, BB); 411 } 412 413 /// verifyLoop - Verify loop structure 414 void verifyLoop() const { 415 #ifndef NDEBUG 416 assert(!Blocks.empty() && "Loop header is missing"); 417 418 // Setup for using a depth-first iterator to visit every block in the loop. 419 SmallVector<BlockT*, 8> ExitBBs; 420 getExitBlocks(ExitBBs); 421 llvm::SmallPtrSet<BlockT*, 8> VisitSet; 422 VisitSet.insert(ExitBBs.begin(), ExitBBs.end()); 423 df_ext_iterator<BlockT*, llvm::SmallPtrSet<BlockT*, 8> > 424 BI = df_ext_begin(getHeader(), VisitSet), 425 BE = df_ext_end(getHeader(), VisitSet); 426 427 // Keep track of the number of BBs visited. 428 unsigned NumVisited = 0; 429 430 // Sort the blocks vector so that we can use binary search to do quick 431 // lookups. 432 SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); 433 std::sort(LoopBBs.begin(), LoopBBs.end()); 434 435 // Check the individual blocks. 436 for ( ; BI != BE; ++BI) { 437 BlockT *BB = *BI; 438 bool HasInsideLoopSuccs = false; 439 bool HasInsideLoopPreds = false; 440 SmallVector<BlockT *, 2> OutsideLoopPreds; 441 442 typedef GraphTraits<BlockT*> BlockTraits; 443 for (typename BlockTraits::ChildIteratorType SI = 444 BlockTraits::child_begin(BB), SE = BlockTraits::child_end(BB); 445 SI != SE; ++SI) 446 if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *SI)) { 447 HasInsideLoopSuccs = true; 448 break; 449 } 450 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 451 for (typename InvBlockTraits::ChildIteratorType PI = 452 InvBlockTraits::child_begin(BB), PE = InvBlockTraits::child_end(BB); 453 PI != PE; ++PI) { 454 BlockT *N = *PI; 455 if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), N)) 456 HasInsideLoopPreds = true; 457 else 458 OutsideLoopPreds.push_back(N); 459 } 460 461 if (BB == getHeader()) { 462 assert(!OutsideLoopPreds.empty() && "Loop is unreachable!"); 463 } else if (!OutsideLoopPreds.empty()) { 464 // A non-header loop shouldn't be reachable from outside the loop, 465 // though it is permitted if the predecessor is not itself actually 466 // reachable. 467 BlockT *EntryBB = BB->getParent()->begin(); 468 for (df_iterator<BlockT *> NI = df_begin(EntryBB), 469 NE = df_end(EntryBB); NI != NE; ++NI) 470 for (unsigned i = 0, e = OutsideLoopPreds.size(); i != e; ++i) 471 assert(*NI != OutsideLoopPreds[i] && 472 "Loop has multiple entry points!"); 473 } 474 assert(HasInsideLoopPreds && "Loop block has no in-loop predecessors!"); 475 assert(HasInsideLoopSuccs && "Loop block has no in-loop successors!"); 476 assert(BB != getHeader()->getParent()->begin() && 477 "Loop contains function entry block!"); 478 479 NumVisited++; 480 } 481 482 assert(NumVisited == getNumBlocks() && "Unreachable block in loop"); 483 484 // Check the subloops. 485 for (iterator I = begin(), E = end(); I != E; ++I) 486 // Each block in each subloop should be contained within this loop. 487 for (block_iterator BI = (*I)->block_begin(), BE = (*I)->block_end(); 488 BI != BE; ++BI) { 489 assert(std::binary_search(LoopBBs.begin(), LoopBBs.end(), *BI) && 490 "Loop does not contain all the blocks of a subloop!"); 491 } 492 493 // Check the parent loop pointer. 494 if (ParentLoop) { 495 assert(std::find(ParentLoop->begin(), ParentLoop->end(), this) != 496 ParentLoop->end() && 497 "Loop is not a subloop of its parent!"); 498 } 499 #endif 500 } 501 502 /// verifyLoop - Verify loop structure of this loop and all nested loops. 503 void verifyLoopNest(DenseSet<const LoopT*> *Loops) const { 504 Loops->insert(static_cast<const LoopT *>(this)); 505 // Verify this loop. 506 verifyLoop(); 507 // Verify the subloops. 508 for (iterator I = begin(), E = end(); I != E; ++I) 509 (*I)->verifyLoopNest(Loops); 510 } 511 512 void print(raw_ostream &OS, unsigned Depth = 0) const { 513 OS.indent(Depth*2) << "Loop at depth " << getLoopDepth() 514 << " containing: "; 515 516 for (unsigned i = 0; i < getBlocks().size(); ++i) { 517 if (i) OS << ","; 518 BlockT *BB = getBlocks()[i]; 519 WriteAsOperand(OS, BB, false); 520 if (BB == getHeader()) OS << "<header>"; 521 if (BB == getLoopLatch()) OS << "<latch>"; 522 if (isLoopExiting(BB)) OS << "<exiting>"; 523 } 524 OS << "\n"; 525 526 for (iterator I = begin(), E = end(); I != E; ++I) 527 (*I)->print(OS, Depth+2); 528 } 529 530 protected: 531 friend class LoopInfoBase<BlockT, LoopT>; 532 explicit LoopBase(BlockT *BB) : ParentLoop(0) { 533 Blocks.push_back(BB); 534 } 535 }; 536 537 template<class BlockT, class LoopT> 538 raw_ostream& operator<<(raw_ostream &OS, const LoopBase<BlockT, LoopT> &Loop) { 539 Loop.print(OS); 540 return OS; 541 } 542 543 class Loop : public LoopBase<BasicBlock, Loop> { 544 public: 545 Loop() {} 546 547 /// isLoopInvariant - Return true if the specified value is loop invariant 548 /// 549 bool isLoopInvariant(Value *V) const; 550 551 /// hasLoopInvariantOperands - Return true if all the operands of the 552 /// specified instruction are loop invariant. 553 bool hasLoopInvariantOperands(Instruction *I) const; 554 555 /// makeLoopInvariant - If the given value is an instruction inside of the 556 /// loop and it can be hoisted, do so to make it trivially loop-invariant. 557 /// Return true if the value after any hoisting is loop invariant. This 558 /// function can be used as a slightly more aggressive replacement for 559 /// isLoopInvariant. 560 /// 561 /// If InsertPt is specified, it is the point to hoist instructions to. 562 /// If null, the terminator of the loop preheader is used. 563 /// 564 bool makeLoopInvariant(Value *V, bool &Changed, 565 Instruction *InsertPt = 0) const; 566 567 /// makeLoopInvariant - If the given instruction is inside of the 568 /// loop and it can be hoisted, do so to make it trivially loop-invariant. 569 /// Return true if the instruction after any hoisting is loop invariant. This 570 /// function can be used as a slightly more aggressive replacement for 571 /// isLoopInvariant. 572 /// 573 /// If InsertPt is specified, it is the point to hoist instructions to. 574 /// If null, the terminator of the loop preheader is used. 575 /// 576 bool makeLoopInvariant(Instruction *I, bool &Changed, 577 Instruction *InsertPt = 0) const; 578 579 /// getCanonicalInductionVariable - Check to see if the loop has a canonical 580 /// induction variable: an integer recurrence that starts at 0 and increments 581 /// by one each time through the loop. If so, return the phi node that 582 /// corresponds to it. 583 /// 584 /// The IndVarSimplify pass transforms loops to have a canonical induction 585 /// variable. 586 /// 587 PHINode *getCanonicalInductionVariable() const; 588 589 /// isLCSSAForm - Return true if the Loop is in LCSSA form 590 bool isLCSSAForm(DominatorTree &DT) const; 591 592 /// isLoopSimplifyForm - Return true if the Loop is in the form that 593 /// the LoopSimplify form transforms loops to, which is sometimes called 594 /// normal form. 595 bool isLoopSimplifyForm() const; 596 597 /// isSafeToClone - Return true if the loop body is safe to clone in practice. 598 bool isSafeToClone() const; 599 600 /// hasDedicatedExits - Return true if no exit block for the loop 601 /// has a predecessor that is outside the loop. 602 bool hasDedicatedExits() const; 603 604 /// getUniqueExitBlocks - Return all unique successor blocks of this loop. 605 /// These are the blocks _outside of the current loop_ which are branched to. 606 /// This assumes that loop exits are in canonical form. 607 /// 608 void getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const; 609 610 /// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one 611 /// block, return that block. Otherwise return null. 612 BasicBlock *getUniqueExitBlock() const; 613 614 void dump() const; 615 616 private: 617 friend class LoopInfoBase<BasicBlock, Loop>; 618 explicit Loop(BasicBlock *BB) : LoopBase<BasicBlock, Loop>(BB) {} 619 }; 620 621 //===----------------------------------------------------------------------===// 622 /// LoopInfo - This class builds and contains all of the top level loop 623 /// structures in the specified function. 624 /// 625 626 template<class BlockT, class LoopT> 627 class LoopInfoBase { 628 // BBMap - Mapping of basic blocks to the inner most loop they occur in 629 DenseMap<BlockT *, LoopT *> BBMap; 630 std::vector<LoopT *> TopLevelLoops; 631 friend class LoopBase<BlockT, LoopT>; 632 friend class LoopInfo; 633 634 void operator=(const LoopInfoBase &); // do not implement 635 LoopInfoBase(const LoopInfo &); // do not implement 636 public: 637 LoopInfoBase() { } 638 ~LoopInfoBase() { releaseMemory(); } 639 640 void releaseMemory() { 641 for (typename std::vector<LoopT *>::iterator I = 642 TopLevelLoops.begin(), E = TopLevelLoops.end(); I != E; ++I) 643 delete *I; // Delete all of the loops... 644 645 BBMap.clear(); // Reset internal state of analysis 646 TopLevelLoops.clear(); 647 } 648 649 /// iterator/begin/end - The interface to the top-level loops in the current 650 /// function. 651 /// 652 typedef typename std::vector<LoopT *>::const_iterator iterator; 653 iterator begin() const { return TopLevelLoops.begin(); } 654 iterator end() const { return TopLevelLoops.end(); } 655 bool empty() const { return TopLevelLoops.empty(); } 656 657 /// getLoopFor - Return the inner most loop that BB lives in. If a basic 658 /// block is in no loop (for example the entry node), null is returned. 659 /// 660 LoopT *getLoopFor(const BlockT *BB) const { 661 return BBMap.lookup(const_cast<BlockT*>(BB)); 662 } 663 664 /// operator[] - same as getLoopFor... 665 /// 666 const LoopT *operator[](const BlockT *BB) const { 667 return getLoopFor(BB); 668 } 669 670 /// getLoopDepth - Return the loop nesting level of the specified block. A 671 /// depth of 0 means the block is not inside any loop. 672 /// 673 unsigned getLoopDepth(const BlockT *BB) const { 674 const LoopT *L = getLoopFor(BB); 675 return L ? L->getLoopDepth() : 0; 676 } 677 678 // isLoopHeader - True if the block is a loop header node 679 bool isLoopHeader(BlockT *BB) const { 680 const LoopT *L = getLoopFor(BB); 681 return L && L->getHeader() == BB; 682 } 683 684 /// removeLoop - This removes the specified top-level loop from this loop info 685 /// object. The loop is not deleted, as it will presumably be inserted into 686 /// another loop. 687 LoopT *removeLoop(iterator I) { 688 assert(I != end() && "Cannot remove end iterator!"); 689 LoopT *L = *I; 690 assert(L->getParentLoop() == 0 && "Not a top-level loop!"); 691 TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin())); 692 return L; 693 } 694 695 /// changeLoopFor - Change the top-level loop that contains BB to the 696 /// specified loop. This should be used by transformations that restructure 697 /// the loop hierarchy tree. 698 void changeLoopFor(BlockT *BB, LoopT *L) { 699 if (!L) { 700 BBMap.erase(BB); 701 return; 702 } 703 BBMap[BB] = L; 704 } 705 706 /// changeTopLevelLoop - Replace the specified loop in the top-level loops 707 /// list with the indicated loop. 708 void changeTopLevelLoop(LoopT *OldLoop, 709 LoopT *NewLoop) { 710 typename std::vector<LoopT *>::iterator I = 711 std::find(TopLevelLoops.begin(), TopLevelLoops.end(), OldLoop); 712 assert(I != TopLevelLoops.end() && "Old loop not at top level!"); 713 *I = NewLoop; 714 assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 && 715 "Loops already embedded into a subloop!"); 716 } 717 718 /// addTopLevelLoop - This adds the specified loop to the collection of 719 /// top-level loops. 720 void addTopLevelLoop(LoopT *New) { 721 assert(New->getParentLoop() == 0 && "Loop already in subloop!"); 722 TopLevelLoops.push_back(New); 723 } 724 725 /// removeBlock - This method completely removes BB from all data structures, 726 /// including all of the Loop objects it is nested in and our mapping from 727 /// BasicBlocks to loops. 728 void removeBlock(BlockT *BB) { 729 typename DenseMap<BlockT *, LoopT *>::iterator I = BBMap.find(BB); 730 if (I != BBMap.end()) { 731 for (LoopT *L = I->second; L; L = L->getParentLoop()) 732 L->removeBlockFromLoop(BB); 733 734 BBMap.erase(I); 735 } 736 } 737 738 // Internals 739 740 static bool isNotAlreadyContainedIn(const LoopT *SubLoop, 741 const LoopT *ParentLoop) { 742 if (SubLoop == 0) return true; 743 if (SubLoop == ParentLoop) return false; 744 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop); 745 } 746 747 void Calculate(DominatorTreeBase<BlockT> &DT) { 748 BlockT *RootNode = DT.getRootNode()->getBlock(); 749 750 for (df_iterator<BlockT*> NI = df_begin(RootNode), 751 NE = df_end(RootNode); NI != NE; ++NI) 752 if (LoopT *L = ConsiderForLoop(*NI, DT)) 753 TopLevelLoops.push_back(L); 754 } 755 756 LoopT *ConsiderForLoop(BlockT *BB, DominatorTreeBase<BlockT> &DT) { 757 if (BBMap.count(BB)) return 0; // Haven't processed this node? 758 759 std::vector<BlockT *> TodoStack; 760 761 // Scan the predecessors of BB, checking to see if BB dominates any of 762 // them. This identifies backedges which target this node... 763 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 764 for (typename InvBlockTraits::ChildIteratorType I = 765 InvBlockTraits::child_begin(BB), E = InvBlockTraits::child_end(BB); 766 I != E; ++I) { 767 typename InvBlockTraits::NodeType *N = *I; 768 // If BB dominates its predecessor... 769 if (DT.dominates(BB, N) && DT.isReachableFromEntry(N)) 770 TodoStack.push_back(N); 771 } 772 773 if (TodoStack.empty()) return 0; // No backedges to this block... 774 775 // Create a new loop to represent this basic block... 776 LoopT *L = new LoopT(BB); 777 BBMap[BB] = L; 778 779 while (!TodoStack.empty()) { // Process all the nodes in the loop 780 BlockT *X = TodoStack.back(); 781 TodoStack.pop_back(); 782 783 if (!L->contains(X) && // As of yet unprocessed?? 784 DT.isReachableFromEntry(X)) { 785 // Check to see if this block already belongs to a loop. If this occurs 786 // then we have a case where a loop that is supposed to be a child of 787 // the current loop was processed before the current loop. When this 788 // occurs, this child loop gets added to a part of the current loop, 789 // making it a sibling to the current loop. We have to reparent this 790 // loop. 791 if (LoopT *SubLoop = 792 const_cast<LoopT *>(getLoopFor(X))) 793 if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)){ 794 // Remove the subloop from its current parent... 795 assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L); 796 LoopT *SLP = SubLoop->ParentLoop; // SubLoopParent 797 typename std::vector<LoopT *>::iterator I = 798 std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop); 799 assert(I != SLP->SubLoops.end() &&"SubLoop not a child of parent?"); 800 SLP->SubLoops.erase(I); // Remove from parent... 801 802 // Add the subloop to THIS loop... 803 SubLoop->ParentLoop = L; 804 L->SubLoops.push_back(SubLoop); 805 } 806 807 // Normal case, add the block to our loop... 808 L->Blocks.push_back(X); 809 810 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 811 812 // Add all of the predecessors of X to the end of the work stack... 813 TodoStack.insert(TodoStack.end(), InvBlockTraits::child_begin(X), 814 InvBlockTraits::child_end(X)); 815 } 816 } 817 818 // If there are any loops nested within this loop, create them now! 819 for (typename std::vector<BlockT*>::iterator I = L->Blocks.begin(), 820 E = L->Blocks.end(); I != E; ++I) 821 if (LoopT *NewLoop = ConsiderForLoop(*I, DT)) { 822 L->SubLoops.push_back(NewLoop); 823 NewLoop->ParentLoop = L; 824 } 825 826 // Add the basic blocks that comprise this loop to the BBMap so that this 827 // loop can be found for them. 828 // 829 for (typename std::vector<BlockT*>::iterator I = L->Blocks.begin(), 830 E = L->Blocks.end(); I != E; ++I) 831 BBMap.insert(std::make_pair(*I, L)); 832 833 // Now that we have a list of all of the child loops of this loop, check to 834 // see if any of them should actually be nested inside of each other. We 835 // can accidentally pull loops our of their parents, so we must make sure to 836 // organize the loop nests correctly now. 837 { 838 std::map<BlockT *, LoopT *> ContainingLoops; 839 for (unsigned i = 0; i != L->SubLoops.size(); ++i) { 840 LoopT *Child = L->SubLoops[i]; 841 assert(Child->getParentLoop() == L && "Not proper child loop?"); 842 843 if (LoopT *ContainingLoop = ContainingLoops[Child->getHeader()]) { 844 // If there is already a loop which contains this loop, move this loop 845 // into the containing loop. 846 MoveSiblingLoopInto(Child, ContainingLoop); 847 --i; // The loop got removed from the SubLoops list. 848 } else { 849 // This is currently considered to be a top-level loop. Check to see 850 // if any of the contained blocks are loop headers for subloops we 851 // have already processed. 852 for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) { 853 LoopT *&BlockLoop = ContainingLoops[Child->Blocks[b]]; 854 if (BlockLoop == 0) { // Child block not processed yet... 855 BlockLoop = Child; 856 } else if (BlockLoop != Child) { 857 LoopT *SubLoop = BlockLoop; 858 // Reparent all of the blocks which used to belong to BlockLoops 859 for (unsigned j = 0, f = SubLoop->Blocks.size(); j != f; ++j) 860 ContainingLoops[SubLoop->Blocks[j]] = Child; 861 862 // There is already a loop which contains this block, that means 863 // that we should reparent the loop which the block is currently 864 // considered to belong to to be a child of this loop. 865 MoveSiblingLoopInto(SubLoop, Child); 866 --i; // We just shrunk the SubLoops list. 867 } 868 } 869 } 870 } 871 } 872 873 return L; 874 } 875 876 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside 877 /// of the NewParent Loop, instead of being a sibling of it. 878 void MoveSiblingLoopInto(LoopT *NewChild, 879 LoopT *NewParent) { 880 LoopT *OldParent = NewChild->getParentLoop(); 881 assert(OldParent && OldParent == NewParent->getParentLoop() && 882 NewChild != NewParent && "Not sibling loops!"); 883 884 // Remove NewChild from being a child of OldParent 885 typename std::vector<LoopT *>::iterator I = 886 std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), 887 NewChild); 888 assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??"); 889 OldParent->SubLoops.erase(I); // Remove from parent's subloops list 890 NewChild->ParentLoop = 0; 891 892 InsertLoopInto(NewChild, NewParent); 893 } 894 895 /// InsertLoopInto - This inserts loop L into the specified parent loop. If 896 /// the parent loop contains a loop which should contain L, the loop gets 897 /// inserted into L instead. 898 void InsertLoopInto(LoopT *L, LoopT *Parent) { 899 BlockT *LHeader = L->getHeader(); 900 assert(Parent->contains(LHeader) && 901 "This loop should not be inserted here!"); 902 903 // Check to see if it belongs in a child loop... 904 for (unsigned i = 0, e = static_cast<unsigned>(Parent->SubLoops.size()); 905 i != e; ++i) 906 if (Parent->SubLoops[i]->contains(LHeader)) { 907 InsertLoopInto(L, Parent->SubLoops[i]); 908 return; 909 } 910 911 // If not, insert it here! 912 Parent->SubLoops.push_back(L); 913 L->ParentLoop = Parent; 914 } 915 916 // Debugging 917 918 void print(raw_ostream &OS) const { 919 for (unsigned i = 0; i < TopLevelLoops.size(); ++i) 920 TopLevelLoops[i]->print(OS); 921 #if 0 922 for (DenseMap<BasicBlock*, LoopT*>::const_iterator I = BBMap.begin(), 923 E = BBMap.end(); I != E; ++I) 924 OS << "BB '" << I->first->getName() << "' level = " 925 << I->second->getLoopDepth() << "\n"; 926 #endif 927 } 928 }; 929 930 class LoopInfo : public FunctionPass { 931 LoopInfoBase<BasicBlock, Loop> LI; 932 friend class LoopBase<BasicBlock, Loop>; 933 934 void operator=(const LoopInfo &); // do not implement 935 LoopInfo(const LoopInfo &); // do not implement 936 public: 937 static char ID; // Pass identification, replacement for typeid 938 939 LoopInfo() : FunctionPass(ID) { 940 initializeLoopInfoPass(*PassRegistry::getPassRegistry()); 941 } 942 943 LoopInfoBase<BasicBlock, Loop>& getBase() { return LI; } 944 945 /// iterator/begin/end - The interface to the top-level loops in the current 946 /// function. 947 /// 948 typedef LoopInfoBase<BasicBlock, Loop>::iterator iterator; 949 inline iterator begin() const { return LI.begin(); } 950 inline iterator end() const { return LI.end(); } 951 bool empty() const { return LI.empty(); } 952 953 /// getLoopFor - Return the inner most loop that BB lives in. If a basic 954 /// block is in no loop (for example the entry node), null is returned. 955 /// 956 inline Loop *getLoopFor(const BasicBlock *BB) const { 957 return LI.getLoopFor(BB); 958 } 959 960 /// operator[] - same as getLoopFor... 961 /// 962 inline const Loop *operator[](const BasicBlock *BB) const { 963 return LI.getLoopFor(BB); 964 } 965 966 /// getLoopDepth - Return the loop nesting level of the specified block. A 967 /// depth of 0 means the block is not inside any loop. 968 /// 969 inline unsigned getLoopDepth(const BasicBlock *BB) const { 970 return LI.getLoopDepth(BB); 971 } 972 973 // isLoopHeader - True if the block is a loop header node 974 inline bool isLoopHeader(BasicBlock *BB) const { 975 return LI.isLoopHeader(BB); 976 } 977 978 /// runOnFunction - Calculate the natural loop information. 979 /// 980 virtual bool runOnFunction(Function &F); 981 982 virtual void verifyAnalysis() const; 983 984 virtual void releaseMemory() { LI.releaseMemory(); } 985 986 virtual void print(raw_ostream &O, const Module* M = 0) const; 987 988 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 989 990 /// removeLoop - This removes the specified top-level loop from this loop info 991 /// object. The loop is not deleted, as it will presumably be inserted into 992 /// another loop. 993 inline Loop *removeLoop(iterator I) { return LI.removeLoop(I); } 994 995 /// changeLoopFor - Change the top-level loop that contains BB to the 996 /// specified loop. This should be used by transformations that restructure 997 /// the loop hierarchy tree. 998 inline void changeLoopFor(BasicBlock *BB, Loop *L) { 999 LI.changeLoopFor(BB, L); 1000 } 1001 1002 /// changeTopLevelLoop - Replace the specified loop in the top-level loops 1003 /// list with the indicated loop. 1004 inline void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) { 1005 LI.changeTopLevelLoop(OldLoop, NewLoop); 1006 } 1007 1008 /// addTopLevelLoop - This adds the specified loop to the collection of 1009 /// top-level loops. 1010 inline void addTopLevelLoop(Loop *New) { 1011 LI.addTopLevelLoop(New); 1012 } 1013 1014 /// removeBlock - This method completely removes BB from all data structures, 1015 /// including all of the Loop objects it is nested in and our mapping from 1016 /// BasicBlocks to loops. 1017 void removeBlock(BasicBlock *BB) { 1018 LI.removeBlock(BB); 1019 } 1020 1021 /// updateUnloop - Update LoopInfo after removing the last backedge from a 1022 /// loop--now the "unloop". This updates the loop forest and parent loops for 1023 /// each block so that Unloop is no longer referenced, but the caller must 1024 /// actually delete the Unloop object. 1025 void updateUnloop(Loop *Unloop); 1026 1027 /// replacementPreservesLCSSAForm - Returns true if replacing From with To 1028 /// everywhere is guaranteed to preserve LCSSA form. 1029 bool replacementPreservesLCSSAForm(Instruction *From, Value *To) { 1030 // Preserving LCSSA form is only problematic if the replacing value is an 1031 // instruction. 1032 Instruction *I = dyn_cast<Instruction>(To); 1033 if (!I) return true; 1034 // If both instructions are defined in the same basic block then replacement 1035 // cannot break LCSSA form. 1036 if (I->getParent() == From->getParent()) 1037 return true; 1038 // If the instruction is not defined in a loop then it can safely replace 1039 // anything. 1040 Loop *ToLoop = getLoopFor(I->getParent()); 1041 if (!ToLoop) return true; 1042 // If the replacing instruction is defined in the same loop as the original 1043 // instruction, or in a loop that contains it as an inner loop, then using 1044 // it as a replacement will not break LCSSA form. 1045 return ToLoop->contains(getLoopFor(From->getParent())); 1046 } 1047 }; 1048 1049 1050 // Allow clients to walk the list of nested loops... 1051 template <> struct GraphTraits<const Loop*> { 1052 typedef const Loop NodeType; 1053 typedef LoopInfo::iterator ChildIteratorType; 1054 1055 static NodeType *getEntryNode(const Loop *L) { return L; } 1056 static inline ChildIteratorType child_begin(NodeType *N) { 1057 return N->begin(); 1058 } 1059 static inline ChildIteratorType child_end(NodeType *N) { 1060 return N->end(); 1061 } 1062 }; 1063 1064 template <> struct GraphTraits<Loop*> { 1065 typedef Loop NodeType; 1066 typedef LoopInfo::iterator ChildIteratorType; 1067 1068 static NodeType *getEntryNode(Loop *L) { return L; } 1069 static inline ChildIteratorType child_begin(NodeType *N) { 1070 return N->begin(); 1071 } 1072 static inline ChildIteratorType child_end(NodeType *N) { 1073 return N->end(); 1074 } 1075 }; 1076 1077 template<class BlockT, class LoopT> 1078 void 1079 LoopBase<BlockT, LoopT>::addBasicBlockToLoop(BlockT *NewBB, 1080 LoopInfoBase<BlockT, LoopT> &LIB) { 1081 assert((Blocks.empty() || LIB[getHeader()] == this) && 1082 "Incorrect LI specified for this loop!"); 1083 assert(NewBB && "Cannot add a null basic block to the loop!"); 1084 assert(LIB[NewBB] == 0 && "BasicBlock already in the loop!"); 1085 1086 LoopT *L = static_cast<LoopT *>(this); 1087 1088 // Add the loop mapping to the LoopInfo object... 1089 LIB.BBMap[NewBB] = L; 1090 1091 // Add the basic block to this loop and all parent loops... 1092 while (L) { 1093 L->Blocks.push_back(NewBB); 1094 L = L->getParentLoop(); 1095 } 1096 } 1097 1098 } // End llvm namespace 1099 1100 #endif 1101