LoopInfo.h revision d0c6f3dafd7c3e9137d4e6415014c94137fcd3fc
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// * the trip count 27// * etc... 28// 29//===----------------------------------------------------------------------===// 30 31#ifndef LLVM_ANALYSIS_LOOP_INFO_H 32#define LLVM_ANALYSIS_LOOP_INFO_H 33 34#include "llvm/Pass.h" 35#include "llvm/ADT/DepthFirstIterator.h" 36#include "llvm/ADT/GraphTraits.h" 37#include "llvm/ADT/SmallVector.h" 38#include "llvm/ADT/STLExtras.h" 39#include "llvm/Analysis/Dominators.h" 40#include "llvm/Support/CFG.h" 41#include "llvm/Support/raw_ostream.h" 42#include <algorithm> 43 44namespace llvm { 45 46template<typename T> 47static void RemoveFromVector(std::vector<T*> &V, T *N) { 48 typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N); 49 assert(I != V.end() && "N is not in this list!"); 50 V.erase(I); 51} 52 53class DominatorTree; 54class LoopInfo; 55class Loop; 56template<class N, class M> class LoopInfoBase; 57template<class N, class M> class LoopBase; 58 59//===----------------------------------------------------------------------===// 60/// LoopBase class - Instances of this class are used to represent loops that 61/// are detected in the flow graph 62/// 63template<class BlockT, class LoopT> 64class LoopBase { 65 LoopT *ParentLoop; 66 // SubLoops - Loops contained entirely within this one. 67 std::vector<LoopT *> SubLoops; 68 69 // Blocks - The list of blocks in this loop. First entry is the header node. 70 std::vector<BlockT*> Blocks; 71 72 // DO NOT IMPLEMENT 73 LoopBase(const LoopBase<BlockT, LoopT> &); 74 // DO NOT IMPLEMENT 75 const LoopBase<BlockT, LoopT>&operator=(const LoopBase<BlockT, LoopT> &); 76public: 77 /// Loop ctor - This creates an empty loop. 78 LoopBase() : ParentLoop(0) {} 79 ~LoopBase() { 80 for (size_t i = 0, e = SubLoops.size(); i != e; ++i) 81 delete SubLoops[i]; 82 } 83 84 /// getLoopDepth - Return the nesting level of this loop. An outer-most 85 /// loop has depth 1, for consistency with loop depth values used for basic 86 /// blocks, where depth 0 is used for blocks not inside any loops. 87 unsigned getLoopDepth() const { 88 unsigned D = 1; 89 for (const LoopT *CurLoop = ParentLoop; CurLoop; 90 CurLoop = CurLoop->ParentLoop) 91 ++D; 92 return D; 93 } 94 BlockT *getHeader() const { return Blocks.front(); } 95 LoopT *getParentLoop() const { return ParentLoop; } 96 97 /// contains - Return true if the specified loop is contained within in 98 /// this loop. 99 /// 100 bool contains(const LoopT *L) const { 101 if (L == this) return true; 102 if (L == 0) return false; 103 return contains(L->getParentLoop()); 104 } 105 106 /// contains - Return true if the specified basic block is in this loop. 107 /// 108 bool contains(const BlockT *BB) const { 109 return std::find(block_begin(), block_end(), BB) != block_end(); 110 } 111 112 /// contains - Return true if the specified instruction is in this loop. 113 /// 114 template<class InstT> 115 bool contains(const InstT *Inst) const { 116 return contains(Inst->getParent()); 117 } 118 119 /// iterator/begin/end - Return the loops contained entirely within this loop. 120 /// 121 const std::vector<LoopT *> &getSubLoops() const { return SubLoops; } 122 typedef typename std::vector<LoopT *>::const_iterator iterator; 123 iterator begin() const { return SubLoops.begin(); } 124 iterator end() const { return SubLoops.end(); } 125 bool empty() const { return SubLoops.empty(); } 126 127 /// getBlocks - Get a list of the basic blocks which make up this loop. 128 /// 129 const std::vector<BlockT*> &getBlocks() const { return Blocks; } 130 typedef typename std::vector<BlockT*>::const_iterator block_iterator; 131 block_iterator block_begin() const { return Blocks.begin(); } 132 block_iterator block_end() const { return Blocks.end(); } 133 134 /// isLoopExiting - True if terminator in the block can branch to another 135 /// block that is outside of the current loop. 136 /// 137 bool isLoopExiting(const BlockT *BB) const { 138 typedef GraphTraits<BlockT*> BlockTraits; 139 for (typename BlockTraits::ChildIteratorType SI = 140 BlockTraits::child_begin(const_cast<BlockT*>(BB)), 141 SE = BlockTraits::child_end(const_cast<BlockT*>(BB)); SI != SE; ++SI) { 142 if (!contains(*SI)) 143 return true; 144 } 145 return false; 146 } 147 148 /// getNumBackEdges - Calculate the number of back edges to the loop header 149 /// 150 unsigned getNumBackEdges() const { 151 unsigned NumBackEdges = 0; 152 BlockT *H = getHeader(); 153 154 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 155 for (typename InvBlockTraits::ChildIteratorType I = 156 InvBlockTraits::child_begin(const_cast<BlockT*>(H)), 157 E = InvBlockTraits::child_end(const_cast<BlockT*>(H)); I != E; ++I) 158 if (contains(*I)) 159 ++NumBackEdges; 160 161 return NumBackEdges; 162 } 163 164 //===--------------------------------------------------------------------===// 165 // APIs for simple analysis of the loop. 166 // 167 // Note that all of these methods can fail on general loops (ie, there may not 168 // be a preheader, etc). For best success, the loop simplification and 169 // induction variable canonicalization pass should be used to normalize loops 170 // for easy analysis. These methods assume canonical loops. 171 172 /// getExitingBlocks - Return all blocks inside the loop that have successors 173 /// outside of the loop. These are the blocks _inside of the current loop_ 174 /// which branch out. The returned list is always unique. 175 /// 176 void getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const { 177 // Sort the blocks vector so that we can use binary search to do quick 178 // lookups. 179 SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); 180 std::sort(LoopBBs.begin(), LoopBBs.end()); 181 182 typedef GraphTraits<BlockT*> BlockTraits; 183 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) 184 for (typename BlockTraits::ChildIteratorType I = 185 BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); 186 I != E; ++I) 187 if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) { 188 // Not in current loop? It must be an exit block. 189 ExitingBlocks.push_back(*BI); 190 break; 191 } 192 } 193 194 /// getExitingBlock - If getExitingBlocks would return exactly one block, 195 /// return that block. Otherwise return null. 196 BlockT *getExitingBlock() const { 197 SmallVector<BlockT*, 8> ExitingBlocks; 198 getExitingBlocks(ExitingBlocks); 199 if (ExitingBlocks.size() == 1) 200 return ExitingBlocks[0]; 201 return 0; 202 } 203 204 /// getExitBlocks - Return all of the successor blocks of this loop. These 205 /// are the blocks _outside of the current loop_ which are branched to. 206 /// 207 void getExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const { 208 // Sort the blocks vector so that we can use binary search to do quick 209 // lookups. 210 SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); 211 std::sort(LoopBBs.begin(), LoopBBs.end()); 212 213 typedef GraphTraits<BlockT*> BlockTraits; 214 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) 215 for (typename BlockTraits::ChildIteratorType I = 216 BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); 217 I != E; ++I) 218 if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) 219 // Not in current loop? It must be an exit block. 220 ExitBlocks.push_back(*I); 221 } 222 223 /// getExitBlock - If getExitBlocks would return exactly one block, 224 /// return that block. Otherwise return null. 225 BlockT *getExitBlock() const { 226 SmallVector<BlockT*, 8> ExitBlocks; 227 getExitBlocks(ExitBlocks); 228 if (ExitBlocks.size() == 1) 229 return ExitBlocks[0]; 230 return 0; 231 } 232 233 /// Edge type. 234 typedef std::pair<BlockT*, BlockT*> Edge; 235 236 /// getExitEdges - Return all pairs of (_inside_block_,_outside_block_). 237 template <typename EdgeT> 238 void getExitEdges(SmallVectorImpl<EdgeT> &ExitEdges) const { 239 // Sort the blocks vector so that we can use binary search to do quick 240 // lookups. 241 SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); 242 array_pod_sort(LoopBBs.begin(), LoopBBs.end()); 243 244 typedef GraphTraits<BlockT*> BlockTraits; 245 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) 246 for (typename BlockTraits::ChildIteratorType I = 247 BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); 248 I != E; ++I) 249 if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) 250 // Not in current loop? It must be an exit block. 251 ExitEdges.push_back(EdgeT(*BI, *I)); 252 } 253 254 /// getLoopPreheader - If there is a preheader for this loop, return it. A 255 /// loop has a preheader if there is only one edge to the header of the loop 256 /// from outside of the loop. If this is the case, the block branching to the 257 /// header of the loop is the preheader node. 258 /// 259 /// This method returns null if there is no preheader for the loop. 260 /// 261 BlockT *getLoopPreheader() const { 262 // Keep track of nodes outside the loop branching to the header... 263 BlockT *Out = getLoopPredecessor(); 264 if (!Out) return 0; 265 266 // Make sure there is only one exit out of the preheader. 267 typedef GraphTraits<BlockT*> BlockTraits; 268 typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out); 269 ++SI; 270 if (SI != BlockTraits::child_end(Out)) 271 return 0; // Multiple exits from the block, must not be a preheader. 272 273 // The predecessor has exactly one successor, so it is a preheader. 274 return Out; 275 } 276 277 /// getLoopPredecessor - If the given loop's header has exactly one unique 278 /// predecessor outside the loop, return it. Otherwise return null. 279 /// This is less strict that the loop "preheader" concept, which requires 280 /// the predecessor to have exactly one successor. 281 /// 282 BlockT *getLoopPredecessor() const { 283 // Keep track of nodes outside the loop branching to the header... 284 BlockT *Out = 0; 285 286 // Loop over the predecessors of the header node... 287 BlockT *Header = getHeader(); 288 typedef GraphTraits<BlockT*> BlockTraits; 289 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 290 for (typename InvBlockTraits::ChildIteratorType PI = 291 InvBlockTraits::child_begin(Header), 292 PE = InvBlockTraits::child_end(Header); PI != PE; ++PI) { 293 typename InvBlockTraits::NodeType *N = *PI; 294 if (!contains(N)) { // If the block is not in the loop... 295 if (Out && Out != N) 296 return 0; // Multiple predecessors outside the loop 297 Out = N; 298 } 299 } 300 301 // Make sure there is only one exit out of the preheader. 302 assert(Out && "Header of loop has no predecessors from outside loop?"); 303 return Out; 304 } 305 306 /// getLoopLatch - If there is a single latch block for this loop, return it. 307 /// A latch block is a block that contains a branch back to the header. 308 BlockT *getLoopLatch() const { 309 BlockT *Header = getHeader(); 310 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 311 typename InvBlockTraits::ChildIteratorType PI = 312 InvBlockTraits::child_begin(Header); 313 typename InvBlockTraits::ChildIteratorType PE = 314 InvBlockTraits::child_end(Header); 315 BlockT *Latch = 0; 316 for (; PI != PE; ++PI) { 317 typename InvBlockTraits::NodeType *N = *PI; 318 if (contains(N)) { 319 if (Latch) return 0; 320 Latch = N; 321 } 322 } 323 324 return Latch; 325 } 326 327 //===--------------------------------------------------------------------===// 328 // APIs for updating loop information after changing the CFG 329 // 330 331 /// addBasicBlockToLoop - This method is used by other analyses to update loop 332 /// information. NewBB is set to be a new member of the current loop. 333 /// Because of this, it is added as a member of all parent loops, and is added 334 /// to the specified LoopInfo object as being in the current basic block. It 335 /// is not valid to replace the loop header with this method. 336 /// 337 void addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LI); 338 339 /// replaceChildLoopWith - This is used when splitting loops up. It replaces 340 /// the OldChild entry in our children list with NewChild, and updates the 341 /// parent pointer of OldChild to be null and the NewChild to be this loop. 342 /// This updates the loop depth of the new child. 343 void replaceChildLoopWith(LoopT *OldChild, 344 LoopT *NewChild) { 345 assert(OldChild->ParentLoop == this && "This loop is already broken!"); 346 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!"); 347 typename std::vector<LoopT *>::iterator I = 348 std::find(SubLoops.begin(), SubLoops.end(), OldChild); 349 assert(I != SubLoops.end() && "OldChild not in loop!"); 350 *I = NewChild; 351 OldChild->ParentLoop = 0; 352 NewChild->ParentLoop = static_cast<LoopT *>(this); 353 } 354 355 /// addChildLoop - Add the specified loop to be a child of this loop. This 356 /// updates the loop depth of the new child. 357 /// 358 void addChildLoop(LoopT *NewChild) { 359 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!"); 360 NewChild->ParentLoop = static_cast<LoopT *>(this); 361 SubLoops.push_back(NewChild); 362 } 363 364 /// removeChildLoop - This removes the specified child from being a subloop of 365 /// this loop. The loop is not deleted, as it will presumably be inserted 366 /// into another loop. 367 LoopT *removeChildLoop(iterator I) { 368 assert(I != SubLoops.end() && "Cannot remove end iterator!"); 369 LoopT *Child = *I; 370 assert(Child->ParentLoop == this && "Child is not a child of this loop!"); 371 SubLoops.erase(SubLoops.begin()+(I-begin())); 372 Child->ParentLoop = 0; 373 return Child; 374 } 375 376 /// addBlockEntry - This adds a basic block directly to the basic block list. 377 /// This should only be used by transformations that create new loops. Other 378 /// transformations should use addBasicBlockToLoop. 379 void addBlockEntry(BlockT *BB) { 380 Blocks.push_back(BB); 381 } 382 383 /// moveToHeader - This method is used to move BB (which must be part of this 384 /// loop) to be the loop header of the loop (the block that dominates all 385 /// others). 386 void moveToHeader(BlockT *BB) { 387 if (Blocks[0] == BB) return; 388 for (unsigned i = 0; ; ++i) { 389 assert(i != Blocks.size() && "Loop does not contain BB!"); 390 if (Blocks[i] == BB) { 391 Blocks[i] = Blocks[0]; 392 Blocks[0] = BB; 393 return; 394 } 395 } 396 } 397 398 /// removeBlockFromLoop - This removes the specified basic block from the 399 /// current loop, updating the Blocks as appropriate. This does not update 400 /// the mapping in the LoopInfo class. 401 void removeBlockFromLoop(BlockT *BB) { 402 RemoveFromVector(Blocks, BB); 403 } 404 405 /// verifyLoop - Verify loop structure 406 void verifyLoop() const { 407#ifndef NDEBUG 408 assert(!Blocks.empty() && "Loop header is missing"); 409 410 // Sort the blocks vector so that we can use binary search to do quick 411 // lookups. 412 SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); 413 std::sort(LoopBBs.begin(), LoopBBs.end()); 414 415 // Check the individual blocks. 416 for (block_iterator I = block_begin(), E = block_end(); I != E; ++I) { 417 BlockT *BB = *I; 418 bool HasInsideLoopSuccs = false; 419 bool HasInsideLoopPreds = false; 420 SmallVector<BlockT *, 2> OutsideLoopPreds; 421 422 typedef GraphTraits<BlockT*> BlockTraits; 423 for (typename BlockTraits::ChildIteratorType SI = 424 BlockTraits::child_begin(BB), SE = BlockTraits::child_end(BB); 425 SI != SE; ++SI) 426 if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *SI)) { 427 HasInsideLoopSuccs = true; 428 break; 429 } 430 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 431 for (typename InvBlockTraits::ChildIteratorType PI = 432 InvBlockTraits::child_begin(BB), PE = InvBlockTraits::child_end(BB); 433 PI != PE; ++PI) { 434 typename InvBlockTraits::NodeType *N = *PI; 435 if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), N)) 436 HasInsideLoopPreds = true; 437 else 438 OutsideLoopPreds.push_back(N); 439 } 440 441 if (BB == getHeader()) { 442 assert(!OutsideLoopPreds.empty() && "Loop is unreachable!"); 443 } else if (!OutsideLoopPreds.empty()) { 444 // A non-header loop shouldn't be reachable from outside the loop, 445 // though it is permitted if the predecessor is not itself actually 446 // reachable. 447 BlockT *EntryBB = BB->getParent()->begin(); 448 for (df_iterator<BlockT *> NI = df_begin(EntryBB), 449 NE = df_end(EntryBB); NI != NE; ++NI) 450 for (unsigned i = 0, e = OutsideLoopPreds.size(); i != e; ++i) 451 assert(*NI != OutsideLoopPreds[i] && 452 "Loop has multiple entry points!"); 453 } 454 assert(HasInsideLoopPreds && "Loop block has no in-loop predecessors!"); 455 assert(HasInsideLoopSuccs && "Loop block has no in-loop successors!"); 456 assert(BB != getHeader()->getParent()->begin() && 457 "Loop contains function entry block!"); 458 } 459 460 // Check the subloops. 461 for (iterator I = begin(), E = end(); I != E; ++I) 462 // Each block in each subloop should be contained within this loop. 463 for (block_iterator BI = (*I)->block_begin(), BE = (*I)->block_end(); 464 BI != BE; ++BI) { 465 assert(std::binary_search(LoopBBs.begin(), LoopBBs.end(), *BI) && 466 "Loop does not contain all the blocks of a subloop!"); 467 } 468 469 // Check the parent loop pointer. 470 if (ParentLoop) { 471 assert(std::find(ParentLoop->begin(), ParentLoop->end(), this) != 472 ParentLoop->end() && 473 "Loop is not a subloop of its parent!"); 474 } 475#endif 476 } 477 478 /// verifyLoop - Verify loop structure of this loop and all nested loops. 479 void verifyLoopNest() const { 480 // Verify this loop. 481 verifyLoop(); 482 // Verify the subloops. 483 for (iterator I = begin(), E = end(); I != E; ++I) 484 (*I)->verifyLoopNest(); 485 } 486 487 void print(raw_ostream &OS, unsigned Depth = 0) const { 488 OS.indent(Depth*2) << "Loop at depth " << getLoopDepth() 489 << " containing: "; 490 491 for (unsigned i = 0; i < getBlocks().size(); ++i) { 492 if (i) OS << ","; 493 BlockT *BB = getBlocks()[i]; 494 WriteAsOperand(OS, BB, false); 495 if (BB == getHeader()) OS << "<header>"; 496 if (BB == getLoopLatch()) OS << "<latch>"; 497 if (isLoopExiting(BB)) OS << "<exiting>"; 498 } 499 OS << "\n"; 500 501 for (iterator I = begin(), E = end(); I != E; ++I) 502 (*I)->print(OS, Depth+2); 503 } 504 505protected: 506 friend class LoopInfoBase<BlockT, LoopT>; 507 explicit LoopBase(BlockT *BB) : ParentLoop(0) { 508 Blocks.push_back(BB); 509 } 510}; 511 512template<class BlockT, class LoopT> 513raw_ostream& operator<<(raw_ostream &OS, const LoopBase<BlockT, LoopT> &Loop) { 514 Loop.print(OS); 515 return OS; 516} 517 518class Loop : public LoopBase<BasicBlock, Loop> { 519public: 520 Loop() {} 521 522 /// isLoopInvariant - Return true if the specified value is loop invariant 523 /// 524 bool isLoopInvariant(Value *V) const; 525 526 /// hasLoopInvariantOperands - Return true if all the operands of the 527 /// specified instruction are loop invariant. 528 bool hasLoopInvariantOperands(Instruction *I) const; 529 530 /// makeLoopInvariant - If the given value is an instruction inside of the 531 /// loop and it can be hoisted, do so to make it trivially loop-invariant. 532 /// Return true if the value after any hoisting is loop invariant. This 533 /// function can be used as a slightly more aggressive replacement for 534 /// isLoopInvariant. 535 /// 536 /// If InsertPt is specified, it is the point to hoist instructions to. 537 /// If null, the terminator of the loop preheader is used. 538 /// 539 bool makeLoopInvariant(Value *V, bool &Changed, 540 Instruction *InsertPt = 0) const; 541 542 /// makeLoopInvariant - If the given instruction is inside of the 543 /// loop and it can be hoisted, do so to make it trivially loop-invariant. 544 /// Return true if the instruction after any hoisting is loop invariant. This 545 /// function can be used as a slightly more aggressive replacement for 546 /// isLoopInvariant. 547 /// 548 /// If InsertPt is specified, it is the point to hoist instructions to. 549 /// If null, the terminator of the loop preheader is used. 550 /// 551 bool makeLoopInvariant(Instruction *I, bool &Changed, 552 Instruction *InsertPt = 0) const; 553 554 /// getCanonicalInductionVariable - Check to see if the loop has a canonical 555 /// induction variable: an integer recurrence that starts at 0 and increments 556 /// by one each time through the loop. If so, return the phi node that 557 /// corresponds to it. 558 /// 559 /// The IndVarSimplify pass transforms loops to have a canonical induction 560 /// variable. 561 /// 562 PHINode *getCanonicalInductionVariable() const; 563 564 /// getTripCount - Return a loop-invariant LLVM value indicating the number of 565 /// times the loop will be executed. Note that this means that the backedge 566 /// of the loop executes N-1 times. If the trip-count cannot be determined, 567 /// this returns null. 568 /// 569 /// The IndVarSimplify pass transforms loops to have a form that this 570 /// function easily understands. 571 /// 572 Value *getTripCount() const; 573 574 /// getSmallConstantTripCount - Returns the trip count of this loop as a 575 /// normal unsigned value, if possible. Returns 0 if the trip count is unknown 576 /// of not constant. Will also return 0 if the trip count is very large 577 /// (>= 2^32) 578 /// 579 /// The IndVarSimplify pass transforms loops to have a form that this 580 /// function easily understands. 581 /// 582 unsigned getSmallConstantTripCount() const; 583 584 /// getSmallConstantTripMultiple - Returns the largest constant divisor of the 585 /// trip count of this loop as a normal unsigned value, if possible. This 586 /// means that the actual trip count is always a multiple of the returned 587 /// value (don't forget the trip count could very well be zero as well!). 588 /// 589 /// Returns 1 if the trip count is unknown or not guaranteed to be the 590 /// multiple of a constant (which is also the case if the trip count is simply 591 /// constant, use getSmallConstantTripCount for that case), Will also return 1 592 /// if the trip count is very large (>= 2^32). 593 unsigned getSmallConstantTripMultiple() const; 594 595 /// isLCSSAForm - Return true if the Loop is in LCSSA form 596 bool isLCSSAForm(DominatorTree &DT) const; 597 598 /// isLoopSimplifyForm - Return true if the Loop is in the form that 599 /// the LoopSimplify form transforms loops to, which is sometimes called 600 /// normal form. 601 bool isLoopSimplifyForm() const; 602 603 /// hasDedicatedExits - Return true if no exit block for the loop 604 /// has a predecessor that is outside the loop. 605 bool hasDedicatedExits() const; 606 607 /// getUniqueExitBlocks - Return all unique successor blocks of this loop. 608 /// These are the blocks _outside of the current loop_ which are branched to. 609 /// This assumes that loop exits are in canonical form. 610 /// 611 void getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const; 612 613 /// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one 614 /// block, return that block. Otherwise return null. 615 BasicBlock *getUniqueExitBlock() const; 616 617 void dump() const; 618 619private: 620 friend class LoopInfoBase<BasicBlock, Loop>; 621 explicit Loop(BasicBlock *BB) : LoopBase<BasicBlock, Loop>(BB) {} 622}; 623 624//===----------------------------------------------------------------------===// 625/// LoopInfo - This class builds and contains all of the top level loop 626/// structures in the specified function. 627/// 628 629template<class BlockT, class LoopT> 630class LoopInfoBase { 631 // BBMap - Mapping of basic blocks to the inner most loop they occur in 632 std::map<BlockT *, LoopT *> BBMap; 633 std::vector<LoopT *> TopLevelLoops; 634 friend class LoopBase<BlockT, LoopT>; 635 636 void operator=(const LoopInfoBase &); // do not implement 637 LoopInfoBase(const LoopInfo &); // do not implement 638public: 639 LoopInfoBase() { } 640 ~LoopInfoBase() { releaseMemory(); } 641 642 void releaseMemory() { 643 for (typename std::vector<LoopT *>::iterator I = 644 TopLevelLoops.begin(), E = TopLevelLoops.end(); I != E; ++I) 645 delete *I; // Delete all of the loops... 646 647 BBMap.clear(); // Reset internal state of analysis 648 TopLevelLoops.clear(); 649 } 650 651 /// iterator/begin/end - The interface to the top-level loops in the current 652 /// function. 653 /// 654 typedef typename std::vector<LoopT *>::const_iterator iterator; 655 iterator begin() const { return TopLevelLoops.begin(); } 656 iterator end() const { return TopLevelLoops.end(); } 657 bool empty() const { return TopLevelLoops.empty(); } 658 659 /// getLoopFor - Return the inner most loop that BB lives in. If a basic 660 /// block is in no loop (for example the entry node), null is returned. 661 /// 662 LoopT *getLoopFor(const BlockT *BB) const { 663 typename std::map<BlockT *, LoopT *>::const_iterator I= 664 BBMap.find(const_cast<BlockT*>(BB)); 665 return I != BBMap.end() ? I->second : 0; 666 } 667 668 /// operator[] - same as getLoopFor... 669 /// 670 const LoopT *operator[](const BlockT *BB) const { 671 return getLoopFor(BB); 672 } 673 674 /// getLoopDepth - Return the loop nesting level of the specified block. A 675 /// depth of 0 means the block is not inside any loop. 676 /// 677 unsigned getLoopDepth(const BlockT *BB) const { 678 const LoopT *L = getLoopFor(BB); 679 return L ? L->getLoopDepth() : 0; 680 } 681 682 // isLoopHeader - True if the block is a loop header node 683 bool isLoopHeader(BlockT *BB) const { 684 const LoopT *L = getLoopFor(BB); 685 return L && L->getHeader() == BB; 686 } 687 688 /// removeLoop - This removes the specified top-level loop from this loop info 689 /// object. The loop is not deleted, as it will presumably be inserted into 690 /// another loop. 691 LoopT *removeLoop(iterator I) { 692 assert(I != end() && "Cannot remove end iterator!"); 693 LoopT *L = *I; 694 assert(L->getParentLoop() == 0 && "Not a top-level loop!"); 695 TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin())); 696 return L; 697 } 698 699 /// changeLoopFor - Change the top-level loop that contains BB to the 700 /// specified loop. This should be used by transformations that restructure 701 /// the loop hierarchy tree. 702 void changeLoopFor(BlockT *BB, LoopT *L) { 703 LoopT *&OldLoop = BBMap[BB]; 704 assert(OldLoop && "Block not in a loop yet!"); 705 OldLoop = L; 706 } 707 708 /// changeTopLevelLoop - Replace the specified loop in the top-level loops 709 /// list with the indicated loop. 710 void changeTopLevelLoop(LoopT *OldLoop, 711 LoopT *NewLoop) { 712 typename std::vector<LoopT *>::iterator I = 713 std::find(TopLevelLoops.begin(), TopLevelLoops.end(), OldLoop); 714 assert(I != TopLevelLoops.end() && "Old loop not at top level!"); 715 *I = NewLoop; 716 assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 && 717 "Loops already embedded into a subloop!"); 718 } 719 720 /// addTopLevelLoop - This adds the specified loop to the collection of 721 /// top-level loops. 722 void addTopLevelLoop(LoopT *New) { 723 assert(New->getParentLoop() == 0 && "Loop already in subloop!"); 724 TopLevelLoops.push_back(New); 725 } 726 727 /// removeBlock - This method completely removes BB from all data structures, 728 /// including all of the Loop objects it is nested in and our mapping from 729 /// BasicBlocks to loops. 730 void removeBlock(BlockT *BB) { 731 typename std::map<BlockT *, LoopT *>::iterator I = BBMap.find(BB); 732 if (I != BBMap.end()) { 733 for (LoopT *L = I->second; L; L = L->getParentLoop()) 734 L->removeBlockFromLoop(BB); 735 736 BBMap.erase(I); 737 } 738 } 739 740 // Internals 741 742 static bool isNotAlreadyContainedIn(const LoopT *SubLoop, 743 const LoopT *ParentLoop) { 744 if (SubLoop == 0) return true; 745 if (SubLoop == ParentLoop) return false; 746 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop); 747 } 748 749 void Calculate(DominatorTreeBase<BlockT> &DT) { 750 BlockT *RootNode = DT.getRootNode()->getBlock(); 751 752 for (df_iterator<BlockT*> NI = df_begin(RootNode), 753 NE = df_end(RootNode); NI != NE; ++NI) 754 if (LoopT *L = ConsiderForLoop(*NI, DT)) 755 TopLevelLoops.push_back(L); 756 } 757 758 LoopT *ConsiderForLoop(BlockT *BB, DominatorTreeBase<BlockT> &DT) { 759 if (BBMap.find(BB) != BBMap.end()) return 0;// Haven't processed this node? 760 761 std::vector<BlockT *> TodoStack; 762 763 // Scan the predecessors of BB, checking to see if BB dominates any of 764 // them. This identifies backedges which target this node... 765 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 766 for (typename InvBlockTraits::ChildIteratorType I = 767 InvBlockTraits::child_begin(BB), E = InvBlockTraits::child_end(BB); 768 I != E; ++I) { 769 typename InvBlockTraits::NodeType *N = *I; 770 if (DT.dominates(BB, N)) // If BB dominates its predecessor... 771 TodoStack.push_back(N); 772 } 773 774 if (TodoStack.empty()) return 0; // No backedges to this block... 775 776 // Create a new loop to represent this basic block... 777 LoopT *L = new LoopT(BB); 778 BBMap[BB] = L; 779 780 BlockT *EntryBlock = BB->getParent()->begin(); 781 782 while (!TodoStack.empty()) { // Process all the nodes in the loop 783 BlockT *X = TodoStack.back(); 784 TodoStack.pop_back(); 785 786 if (!L->contains(X) && // As of yet unprocessed?? 787 DT.dominates(EntryBlock, X)) { // X is reachable from entry block? 788 // Check to see if this block already belongs to a loop. If this occurs 789 // then we have a case where a loop that is supposed to be a child of 790 // the current loop was processed before the current loop. When this 791 // occurs, this child loop gets added to a part of the current loop, 792 // making it a sibling to the current loop. We have to reparent this 793 // loop. 794 if (LoopT *SubLoop = 795 const_cast<LoopT *>(getLoopFor(X))) 796 if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)){ 797 // Remove the subloop from its current parent... 798 assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L); 799 LoopT *SLP = SubLoop->ParentLoop; // SubLoopParent 800 typename std::vector<LoopT *>::iterator I = 801 std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop); 802 assert(I != SLP->SubLoops.end() &&"SubLoop not a child of parent?"); 803 SLP->SubLoops.erase(I); // Remove from parent... 804 805 // Add the subloop to THIS loop... 806 SubLoop->ParentLoop = L; 807 L->SubLoops.push_back(SubLoop); 808 } 809 810 // Normal case, add the block to our loop... 811 L->Blocks.push_back(X); 812 813 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 814 815 // Add all of the predecessors of X to the end of the work stack... 816 TodoStack.insert(TodoStack.end(), InvBlockTraits::child_begin(X), 817 InvBlockTraits::child_end(X)); 818 } 819 } 820 821 // If there are any loops nested within this loop, create them now! 822 for (typename std::vector<BlockT*>::iterator I = L->Blocks.begin(), 823 E = L->Blocks.end(); I != E; ++I) 824 if (LoopT *NewLoop = ConsiderForLoop(*I, DT)) { 825 L->SubLoops.push_back(NewLoop); 826 NewLoop->ParentLoop = L; 827 } 828 829 // Add the basic blocks that comprise this loop to the BBMap so that this 830 // loop can be found for them. 831 // 832 for (typename std::vector<BlockT*>::iterator I = L->Blocks.begin(), 833 E = L->Blocks.end(); I != E; ++I) 834 BBMap.insert(std::make_pair(*I, L)); 835 836 // Now that we have a list of all of the child loops of this loop, check to 837 // see if any of them should actually be nested inside of each other. We 838 // can accidentally pull loops our of their parents, so we must make sure to 839 // organize the loop nests correctly now. 840 { 841 std::map<BlockT *, LoopT *> ContainingLoops; 842 for (unsigned i = 0; i != L->SubLoops.size(); ++i) { 843 LoopT *Child = L->SubLoops[i]; 844 assert(Child->getParentLoop() == L && "Not proper child loop?"); 845 846 if (LoopT *ContainingLoop = ContainingLoops[Child->getHeader()]) { 847 // If there is already a loop which contains this loop, move this loop 848 // into the containing loop. 849 MoveSiblingLoopInto(Child, ContainingLoop); 850 --i; // The loop got removed from the SubLoops list. 851 } else { 852 // This is currently considered to be a top-level loop. Check to see 853 // if any of the contained blocks are loop headers for subloops we 854 // have already processed. 855 for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) { 856 LoopT *&BlockLoop = ContainingLoops[Child->Blocks[b]]; 857 if (BlockLoop == 0) { // Child block not processed yet... 858 BlockLoop = Child; 859 } else if (BlockLoop != Child) { 860 LoopT *SubLoop = BlockLoop; 861 // Reparent all of the blocks which used to belong to BlockLoops 862 for (unsigned j = 0, f = SubLoop->Blocks.size(); j != f; ++j) 863 ContainingLoops[SubLoop->Blocks[j]] = Child; 864 865 // There is already a loop which contains this block, that means 866 // that we should reparent the loop which the block is currently 867 // considered to belong to to be a child of this loop. 868 MoveSiblingLoopInto(SubLoop, Child); 869 --i; // We just shrunk the SubLoops list. 870 } 871 } 872 } 873 } 874 } 875 876 return L; 877 } 878 879 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside 880 /// of the NewParent Loop, instead of being a sibling of it. 881 void MoveSiblingLoopInto(LoopT *NewChild, 882 LoopT *NewParent) { 883 LoopT *OldParent = NewChild->getParentLoop(); 884 assert(OldParent && OldParent == NewParent->getParentLoop() && 885 NewChild != NewParent && "Not sibling loops!"); 886 887 // Remove NewChild from being a child of OldParent 888 typename std::vector<LoopT *>::iterator I = 889 std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), 890 NewChild); 891 assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??"); 892 OldParent->SubLoops.erase(I); // Remove from parent's subloops list 893 NewChild->ParentLoop = 0; 894 895 InsertLoopInto(NewChild, NewParent); 896 } 897 898 /// InsertLoopInto - This inserts loop L into the specified parent loop. If 899 /// the parent loop contains a loop which should contain L, the loop gets 900 /// inserted into L instead. 901 void InsertLoopInto(LoopT *L, LoopT *Parent) { 902 BlockT *LHeader = L->getHeader(); 903 assert(Parent->contains(LHeader) && 904 "This loop should not be inserted here!"); 905 906 // Check to see if it belongs in a child loop... 907 for (unsigned i = 0, e = static_cast<unsigned>(Parent->SubLoops.size()); 908 i != e; ++i) 909 if (Parent->SubLoops[i]->contains(LHeader)) { 910 InsertLoopInto(L, Parent->SubLoops[i]); 911 return; 912 } 913 914 // If not, insert it here! 915 Parent->SubLoops.push_back(L); 916 L->ParentLoop = Parent; 917 } 918 919 // Debugging 920 921 void print(raw_ostream &OS) const { 922 for (unsigned i = 0; i < TopLevelLoops.size(); ++i) 923 TopLevelLoops[i]->print(OS); 924 #if 0 925 for (std::map<BasicBlock*, LoopT*>::const_iterator I = BBMap.begin(), 926 E = BBMap.end(); I != E; ++I) 927 OS << "BB '" << I->first->getName() << "' level = " 928 << I->second->getLoopDepth() << "\n"; 929 #endif 930 } 931}; 932 933class LoopInfo : public FunctionPass { 934 LoopInfoBase<BasicBlock, Loop> LI; 935 friend class LoopBase<BasicBlock, Loop>; 936 937 void operator=(const LoopInfo &); // do not implement 938 LoopInfo(const LoopInfo &); // do not implement 939public: 940 static char ID; // Pass identification, replacement for typeid 941 942 LoopInfo() : FunctionPass(ID) { 943 initializeLoopInfoPass(*PassRegistry::getPassRegistry()); 944 } 945 946 LoopInfoBase<BasicBlock, Loop>& getBase() { return LI; } 947 948 /// iterator/begin/end - The interface to the top-level loops in the current 949 /// function. 950 /// 951 typedef LoopInfoBase<BasicBlock, Loop>::iterator iterator; 952 inline iterator begin() const { return LI.begin(); } 953 inline iterator end() const { return LI.end(); } 954 bool empty() const { return LI.empty(); } 955 956 /// getLoopFor - Return the inner most loop that BB lives in. If a basic 957 /// block is in no loop (for example the entry node), null is returned. 958 /// 959 inline Loop *getLoopFor(const BasicBlock *BB) const { 960 return LI.getLoopFor(BB); 961 } 962 963 /// operator[] - same as getLoopFor... 964 /// 965 inline const Loop *operator[](const BasicBlock *BB) const { 966 return LI.getLoopFor(BB); 967 } 968 969 /// getLoopDepth - Return the loop nesting level of the specified block. A 970 /// depth of 0 means the block is not inside any loop. 971 /// 972 inline unsigned getLoopDepth(const BasicBlock *BB) const { 973 return LI.getLoopDepth(BB); 974 } 975 976 // isLoopHeader - True if the block is a loop header node 977 inline bool isLoopHeader(BasicBlock *BB) const { 978 return LI.isLoopHeader(BB); 979 } 980 981 /// runOnFunction - Calculate the natural loop information. 982 /// 983 virtual bool runOnFunction(Function &F); 984 985 virtual void verifyAnalysis() const; 986 987 virtual void releaseMemory() { LI.releaseMemory(); } 988 989 virtual void print(raw_ostream &O, const Module* M = 0) const; 990 991 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 992 993 /// removeLoop - This removes the specified top-level loop from this loop info 994 /// object. The loop is not deleted, as it will presumably be inserted into 995 /// another loop. 996 inline Loop *removeLoop(iterator I) { return LI.removeLoop(I); } 997 998 /// changeLoopFor - Change the top-level loop that contains BB to the 999 /// specified loop. This should be used by transformations that restructure 1000 /// the loop hierarchy tree. 1001 inline void changeLoopFor(BasicBlock *BB, Loop *L) { 1002 LI.changeLoopFor(BB, L); 1003 } 1004 1005 /// changeTopLevelLoop - Replace the specified loop in the top-level loops 1006 /// list with the indicated loop. 1007 inline void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) { 1008 LI.changeTopLevelLoop(OldLoop, NewLoop); 1009 } 1010 1011 /// addTopLevelLoop - This adds the specified loop to the collection of 1012 /// top-level loops. 1013 inline void addTopLevelLoop(Loop *New) { 1014 LI.addTopLevelLoop(New); 1015 } 1016 1017 /// removeBlock - This method completely removes BB from all data structures, 1018 /// including all of the Loop objects it is nested in and our mapping from 1019 /// BasicBlocks to loops. 1020 void removeBlock(BasicBlock *BB) { 1021 LI.removeBlock(BB); 1022 } 1023 1024 /// replacementPreservesLCSSAForm - Returns true if replacing From with To 1025 /// everywhere is guaranteed to preserve LCSSA form. 1026 bool replacementPreservesLCSSAForm(Instruction *From, Value *To) { 1027 // Preserving LCSSA form is only problematic if the replacing value is an 1028 // instruction. 1029 Instruction *I = dyn_cast<Instruction>(To); 1030 if (!I) return true; 1031 // If the instruction is not defined in a loop then it can safely replace 1032 // anything. 1033 Loop *ToLoop = getLoopFor(I->getParent()); 1034 if (!ToLoop) return true; 1035 // If the replacing instruction is defined in the same loop as the original 1036 // instruction, or in a loop that contains it as an inner loop, then using 1037 // it as a replacement will not break LCSSA form. 1038 Loop *FromLoop = getLoopFor(From->getParent()); 1039 if (ToLoop->contains(FromLoop)) return true; 1040 return false; 1041 } 1042}; 1043 1044 1045// Allow clients to walk the list of nested loops... 1046template <> struct GraphTraits<const Loop*> { 1047 typedef const Loop NodeType; 1048 typedef LoopInfo::iterator ChildIteratorType; 1049 1050 static NodeType *getEntryNode(const Loop *L) { return L; } 1051 static inline ChildIteratorType child_begin(NodeType *N) { 1052 return N->begin(); 1053 } 1054 static inline ChildIteratorType child_end(NodeType *N) { 1055 return N->end(); 1056 } 1057}; 1058 1059template <> struct GraphTraits<Loop*> { 1060 typedef Loop NodeType; 1061 typedef LoopInfo::iterator ChildIteratorType; 1062 1063 static NodeType *getEntryNode(Loop *L) { return L; } 1064 static inline ChildIteratorType child_begin(NodeType *N) { 1065 return N->begin(); 1066 } 1067 static inline ChildIteratorType child_end(NodeType *N) { 1068 return N->end(); 1069 } 1070}; 1071 1072template<class BlockT, class LoopT> 1073void 1074LoopBase<BlockT, LoopT>::addBasicBlockToLoop(BlockT *NewBB, 1075 LoopInfoBase<BlockT, LoopT> &LIB) { 1076 assert((Blocks.empty() || LIB[getHeader()] == this) && 1077 "Incorrect LI specified for this loop!"); 1078 assert(NewBB && "Cannot add a null basic block to the loop!"); 1079 assert(LIB[NewBB] == 0 && "BasicBlock already in the loop!"); 1080 1081 LoopT *L = static_cast<LoopT *>(this); 1082 1083 // Add the loop mapping to the LoopInfo object... 1084 LIB.BBMap[NewBB] = L; 1085 1086 // Add the basic block to this loop and all parent loops... 1087 while (L) { 1088 L->Blocks.push_back(NewBB); 1089 L = L->getParentLoop(); 1090 } 1091} 1092 1093} // End llvm namespace 1094 1095#endif 1096