LoopInfo.h revision 306afdf443a0e2d5d89c1a3ece00cfe18be1c4c4
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/DenseMap.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 46namespace llvm { 47 48template<typename T> 49static 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 55class DominatorTree; 56class LoopInfo; 57class Loop; 58class PHINode; 59template<class N, class M> class LoopInfoBase; 60template<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/// 66template<class BlockT, class LoopT> 67class 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> &); 79public: 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 // Sort the blocks vector so that we can use binary search to do quick 419 // lookups. 420 SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); 421 std::sort(LoopBBs.begin(), LoopBBs.end()); 422 423 // Check the individual blocks. 424 for (block_iterator I = block_begin(), E = block_end(); I != E; ++I) { 425 BlockT *BB = *I; 426 bool HasInsideLoopSuccs = false; 427 bool HasInsideLoopPreds = false; 428 SmallVector<BlockT *, 2> OutsideLoopPreds; 429 430 typedef GraphTraits<BlockT*> BlockTraits; 431 for (typename BlockTraits::ChildIteratorType SI = 432 BlockTraits::child_begin(BB), SE = BlockTraits::child_end(BB); 433 SI != SE; ++SI) 434 if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *SI)) { 435 HasInsideLoopSuccs = true; 436 break; 437 } 438 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 439 for (typename InvBlockTraits::ChildIteratorType PI = 440 InvBlockTraits::child_begin(BB), PE = InvBlockTraits::child_end(BB); 441 PI != PE; ++PI) { 442 typename InvBlockTraits::NodeType *N = *PI; 443 if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), N)) 444 HasInsideLoopPreds = true; 445 else 446 OutsideLoopPreds.push_back(N); 447 } 448 449 if (BB == getHeader()) { 450 assert(!OutsideLoopPreds.empty() && "Loop is unreachable!"); 451 } else if (!OutsideLoopPreds.empty()) { 452 // A non-header loop shouldn't be reachable from outside the loop, 453 // though it is permitted if the predecessor is not itself actually 454 // reachable. 455 BlockT *EntryBB = BB->getParent()->begin(); 456 for (df_iterator<BlockT *> NI = df_begin(EntryBB), 457 NE = df_end(EntryBB); NI != NE; ++NI) 458 for (unsigned i = 0, e = OutsideLoopPreds.size(); i != e; ++i) 459 assert(*NI != OutsideLoopPreds[i] && 460 "Loop has multiple entry points!"); 461 } 462 assert(HasInsideLoopPreds && "Loop block has no in-loop predecessors!"); 463 assert(HasInsideLoopSuccs && "Loop block has no in-loop successors!"); 464 assert(BB != getHeader()->getParent()->begin() && 465 "Loop contains function entry block!"); 466 } 467 468 // Check the subloops. 469 for (iterator I = begin(), E = end(); I != E; ++I) 470 // Each block in each subloop should be contained within this loop. 471 for (block_iterator BI = (*I)->block_begin(), BE = (*I)->block_end(); 472 BI != BE; ++BI) { 473 assert(std::binary_search(LoopBBs.begin(), LoopBBs.end(), *BI) && 474 "Loop does not contain all the blocks of a subloop!"); 475 } 476 477 // Check the parent loop pointer. 478 if (ParentLoop) { 479 assert(std::find(ParentLoop->begin(), ParentLoop->end(), this) != 480 ParentLoop->end() && 481 "Loop is not a subloop of its parent!"); 482 } 483#endif 484 } 485 486 /// verifyLoop - Verify loop structure of this loop and all nested loops. 487 void verifyLoopNest() const { 488 // Verify this loop. 489 verifyLoop(); 490 // Verify the subloops. 491 for (iterator I = begin(), E = end(); I != E; ++I) 492 (*I)->verifyLoopNest(); 493 } 494 495 void print(raw_ostream &OS, unsigned Depth = 0) const { 496 OS.indent(Depth*2) << "Loop at depth " << getLoopDepth() 497 << " containing: "; 498 499 for (unsigned i = 0; i < getBlocks().size(); ++i) { 500 if (i) OS << ","; 501 BlockT *BB = getBlocks()[i]; 502 WriteAsOperand(OS, BB, false); 503 if (BB == getHeader()) OS << "<header>"; 504 if (BB == getLoopLatch()) OS << "<latch>"; 505 if (isLoopExiting(BB)) OS << "<exiting>"; 506 } 507 OS << "\n"; 508 509 for (iterator I = begin(), E = end(); I != E; ++I) 510 (*I)->print(OS, Depth+2); 511 } 512 513protected: 514 friend class LoopInfoBase<BlockT, LoopT>; 515 explicit LoopBase(BlockT *BB) : ParentLoop(0) { 516 Blocks.push_back(BB); 517 } 518}; 519 520template<class BlockT, class LoopT> 521raw_ostream& operator<<(raw_ostream &OS, const LoopBase<BlockT, LoopT> &Loop) { 522 Loop.print(OS); 523 return OS; 524} 525 526class Loop : public LoopBase<BasicBlock, Loop> { 527public: 528 Loop() {} 529 530 /// isLoopInvariant - Return true if the specified value is loop invariant 531 /// 532 bool isLoopInvariant(Value *V) const; 533 534 /// hasLoopInvariantOperands - Return true if all the operands of the 535 /// specified instruction are loop invariant. 536 bool hasLoopInvariantOperands(Instruction *I) const; 537 538 /// makeLoopInvariant - If the given value is an instruction inside of the 539 /// loop and it can be hoisted, do so to make it trivially loop-invariant. 540 /// Return true if the value after any hoisting is loop invariant. This 541 /// function can be used as a slightly more aggressive replacement for 542 /// isLoopInvariant. 543 /// 544 /// If InsertPt is specified, it is the point to hoist instructions to. 545 /// If null, the terminator of the loop preheader is used. 546 /// 547 bool makeLoopInvariant(Value *V, bool &Changed, 548 Instruction *InsertPt = 0) const; 549 550 /// makeLoopInvariant - If the given instruction is inside of the 551 /// loop and it can be hoisted, do so to make it trivially loop-invariant. 552 /// Return true if the instruction after any hoisting is loop invariant. This 553 /// function can be used as a slightly more aggressive replacement for 554 /// isLoopInvariant. 555 /// 556 /// If InsertPt is specified, it is the point to hoist instructions to. 557 /// If null, the terminator of the loop preheader is used. 558 /// 559 bool makeLoopInvariant(Instruction *I, bool &Changed, 560 Instruction *InsertPt = 0) const; 561 562 /// getCanonicalInductionVariable - Check to see if the loop has a canonical 563 /// induction variable: an integer recurrence that starts at 0 and increments 564 /// by one each time through the loop. If so, return the phi node that 565 /// corresponds to it. 566 /// 567 /// The IndVarSimplify pass transforms loops to have a canonical induction 568 /// variable. 569 /// 570 PHINode *getCanonicalInductionVariable() const; 571 572 /// getTripCount - Return a loop-invariant LLVM value indicating the number of 573 /// times the loop will be executed. Note that this means that the backedge 574 /// of the loop executes N-1 times. If the trip-count cannot be determined, 575 /// this returns null. 576 /// 577 /// The IndVarSimplify pass transforms loops to have a form that this 578 /// function easily understands. 579 /// 580 Value *getTripCount() const; 581 582 /// getSmallConstantTripCount - Returns the trip count of this loop as a 583 /// normal unsigned value, if possible. Returns 0 if the trip count is unknown 584 /// of not constant. Will also return 0 if the trip count is very large 585 /// (>= 2^32) 586 /// 587 /// The IndVarSimplify pass transforms loops to have a form that this 588 /// function easily understands. 589 /// 590 unsigned getSmallConstantTripCount() const; 591 592 /// getSmallConstantTripMultiple - Returns the largest constant divisor of the 593 /// trip count of this loop as a normal unsigned value, if possible. This 594 /// means that the actual trip count is always a multiple of the returned 595 /// value (don't forget the trip count could very well be zero as well!). 596 /// 597 /// Returns 1 if the trip count is unknown or not guaranteed to be the 598 /// multiple of a constant (which is also the case if the trip count is simply 599 /// constant, use getSmallConstantTripCount for that case), Will also return 1 600 /// if the trip count is very large (>= 2^32). 601 unsigned getSmallConstantTripMultiple() const; 602 603 /// isLCSSAForm - Return true if the Loop is in LCSSA form 604 bool isLCSSAForm(DominatorTree &DT) const; 605 606 /// isLoopSimplifyForm - Return true if the Loop is in the form that 607 /// the LoopSimplify form transforms loops to, which is sometimes called 608 /// normal form. 609 bool isLoopSimplifyForm() const; 610 611 /// hasDedicatedExits - Return true if no exit block for the loop 612 /// has a predecessor that is outside the loop. 613 bool hasDedicatedExits() const; 614 615 /// getUniqueExitBlocks - Return all unique successor blocks of this loop. 616 /// These are the blocks _outside of the current loop_ which are branched to. 617 /// This assumes that loop exits are in canonical form. 618 /// 619 void getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const; 620 621 /// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one 622 /// block, return that block. Otherwise return null. 623 BasicBlock *getUniqueExitBlock() const; 624 625 void dump() const; 626 627private: 628 friend class LoopInfoBase<BasicBlock, Loop>; 629 explicit Loop(BasicBlock *BB) : LoopBase<BasicBlock, Loop>(BB) {} 630}; 631 632//===----------------------------------------------------------------------===// 633/// LoopInfo - This class builds and contains all of the top level loop 634/// structures in the specified function. 635/// 636 637template<class BlockT, class LoopT> 638class LoopInfoBase { 639 // BBMap - Mapping of basic blocks to the inner most loop they occur in 640 DenseMap<BlockT *, LoopT *> BBMap; 641 std::vector<LoopT *> TopLevelLoops; 642 friend class LoopBase<BlockT, LoopT>; 643 644 void operator=(const LoopInfoBase &); // do not implement 645 LoopInfoBase(const LoopInfo &); // do not implement 646public: 647 LoopInfoBase() { } 648 ~LoopInfoBase() { releaseMemory(); } 649 650 void releaseMemory() { 651 for (typename std::vector<LoopT *>::iterator I = 652 TopLevelLoops.begin(), E = TopLevelLoops.end(); I != E; ++I) 653 delete *I; // Delete all of the loops... 654 655 BBMap.clear(); // Reset internal state of analysis 656 TopLevelLoops.clear(); 657 } 658 659 /// iterator/begin/end - The interface to the top-level loops in the current 660 /// function. 661 /// 662 typedef typename std::vector<LoopT *>::const_iterator iterator; 663 iterator begin() const { return TopLevelLoops.begin(); } 664 iterator end() const { return TopLevelLoops.end(); } 665 bool empty() const { return TopLevelLoops.empty(); } 666 667 /// getLoopFor - Return the inner most loop that BB lives in. If a basic 668 /// block is in no loop (for example the entry node), null is returned. 669 /// 670 LoopT *getLoopFor(const BlockT *BB) const { 671 typename DenseMap<BlockT *, LoopT *>::const_iterator I= 672 BBMap.find(const_cast<BlockT*>(BB)); 673 return I != BBMap.end() ? I->second : 0; 674 } 675 676 /// operator[] - same as getLoopFor... 677 /// 678 const LoopT *operator[](const BlockT *BB) const { 679 return getLoopFor(BB); 680 } 681 682 /// getLoopDepth - Return the loop nesting level of the specified block. A 683 /// depth of 0 means the block is not inside any loop. 684 /// 685 unsigned getLoopDepth(const BlockT *BB) const { 686 const LoopT *L = getLoopFor(BB); 687 return L ? L->getLoopDepth() : 0; 688 } 689 690 // isLoopHeader - True if the block is a loop header node 691 bool isLoopHeader(BlockT *BB) const { 692 const LoopT *L = getLoopFor(BB); 693 return L && L->getHeader() == BB; 694 } 695 696 /// removeLoop - This removes the specified top-level loop from this loop info 697 /// object. The loop is not deleted, as it will presumably be inserted into 698 /// another loop. 699 LoopT *removeLoop(iterator I) { 700 assert(I != end() && "Cannot remove end iterator!"); 701 LoopT *L = *I; 702 assert(L->getParentLoop() == 0 && "Not a top-level loop!"); 703 TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin())); 704 return L; 705 } 706 707 /// changeLoopFor - Change the top-level loop that contains BB to the 708 /// specified loop. This should be used by transformations that restructure 709 /// the loop hierarchy tree. 710 void changeLoopFor(BlockT *BB, LoopT *L) { 711 LoopT *&OldLoop = BBMap[BB]; 712 assert(OldLoop && "Block not in a loop yet!"); 713 OldLoop = L; 714 } 715 716 /// changeTopLevelLoop - Replace the specified loop in the top-level loops 717 /// list with the indicated loop. 718 void changeTopLevelLoop(LoopT *OldLoop, 719 LoopT *NewLoop) { 720 typename std::vector<LoopT *>::iterator I = 721 std::find(TopLevelLoops.begin(), TopLevelLoops.end(), OldLoop); 722 assert(I != TopLevelLoops.end() && "Old loop not at top level!"); 723 *I = NewLoop; 724 assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 && 725 "Loops already embedded into a subloop!"); 726 } 727 728 /// addTopLevelLoop - This adds the specified loop to the collection of 729 /// top-level loops. 730 void addTopLevelLoop(LoopT *New) { 731 assert(New->getParentLoop() == 0 && "Loop already in subloop!"); 732 TopLevelLoops.push_back(New); 733 } 734 735 /// removeBlock - This method completely removes BB from all data structures, 736 /// including all of the Loop objects it is nested in and our mapping from 737 /// BasicBlocks to loops. 738 void removeBlock(BlockT *BB) { 739 typename DenseMap<BlockT *, LoopT *>::iterator I = BBMap.find(BB); 740 if (I != BBMap.end()) { 741 for (LoopT *L = I->second; L; L = L->getParentLoop()) 742 L->removeBlockFromLoop(BB); 743 744 BBMap.erase(I); 745 } 746 } 747 748 // Internals 749 750 static bool isNotAlreadyContainedIn(const LoopT *SubLoop, 751 const LoopT *ParentLoop) { 752 if (SubLoop == 0) return true; 753 if (SubLoop == ParentLoop) return false; 754 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop); 755 } 756 757 void Calculate(DominatorTreeBase<BlockT> &DT) { 758 BlockT *RootNode = DT.getRootNode()->getBlock(); 759 760 for (df_iterator<BlockT*> NI = df_begin(RootNode), 761 NE = df_end(RootNode); NI != NE; ++NI) 762 if (LoopT *L = ConsiderForLoop(*NI, DT)) 763 TopLevelLoops.push_back(L); 764 } 765 766 LoopT *ConsiderForLoop(BlockT *BB, DominatorTreeBase<BlockT> &DT) { 767 if (BBMap.find(BB) != BBMap.end()) return 0;// Haven't processed this node? 768 769 std::vector<BlockT *> TodoStack; 770 771 // Scan the predecessors of BB, checking to see if BB dominates any of 772 // them. This identifies backedges which target this node... 773 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 774 for (typename InvBlockTraits::ChildIteratorType I = 775 InvBlockTraits::child_begin(BB), E = InvBlockTraits::child_end(BB); 776 I != E; ++I) { 777 typename InvBlockTraits::NodeType *N = *I; 778 if (DT.dominates(BB, N)) // If BB dominates its predecessor... 779 TodoStack.push_back(N); 780 } 781 782 if (TodoStack.empty()) return 0; // No backedges to this block... 783 784 // Create a new loop to represent this basic block... 785 LoopT *L = new LoopT(BB); 786 BBMap[BB] = L; 787 788 BlockT *EntryBlock = BB->getParent()->begin(); 789 790 while (!TodoStack.empty()) { // Process all the nodes in the loop 791 BlockT *X = TodoStack.back(); 792 TodoStack.pop_back(); 793 794 if (!L->contains(X) && // As of yet unprocessed?? 795 DT.dominates(EntryBlock, X)) { // X is reachable from entry block? 796 // Check to see if this block already belongs to a loop. If this occurs 797 // then we have a case where a loop that is supposed to be a child of 798 // the current loop was processed before the current loop. When this 799 // occurs, this child loop gets added to a part of the current loop, 800 // making it a sibling to the current loop. We have to reparent this 801 // loop. 802 if (LoopT *SubLoop = 803 const_cast<LoopT *>(getLoopFor(X))) 804 if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)){ 805 // Remove the subloop from its current parent... 806 assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L); 807 LoopT *SLP = SubLoop->ParentLoop; // SubLoopParent 808 typename std::vector<LoopT *>::iterator I = 809 std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop); 810 assert(I != SLP->SubLoops.end() &&"SubLoop not a child of parent?"); 811 SLP->SubLoops.erase(I); // Remove from parent... 812 813 // Add the subloop to THIS loop... 814 SubLoop->ParentLoop = L; 815 L->SubLoops.push_back(SubLoop); 816 } 817 818 // Normal case, add the block to our loop... 819 L->Blocks.push_back(X); 820 821 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; 822 823 // Add all of the predecessors of X to the end of the work stack... 824 TodoStack.insert(TodoStack.end(), InvBlockTraits::child_begin(X), 825 InvBlockTraits::child_end(X)); 826 } 827 } 828 829 // If there are any loops nested within this loop, create them now! 830 for (typename std::vector<BlockT*>::iterator I = L->Blocks.begin(), 831 E = L->Blocks.end(); I != E; ++I) 832 if (LoopT *NewLoop = ConsiderForLoop(*I, DT)) { 833 L->SubLoops.push_back(NewLoop); 834 NewLoop->ParentLoop = L; 835 } 836 837 // Add the basic blocks that comprise this loop to the BBMap so that this 838 // loop can be found for them. 839 // 840 for (typename std::vector<BlockT*>::iterator I = L->Blocks.begin(), 841 E = L->Blocks.end(); I != E; ++I) 842 BBMap.insert(std::make_pair(*I, L)); 843 844 // Now that we have a list of all of the child loops of this loop, check to 845 // see if any of them should actually be nested inside of each other. We 846 // can accidentally pull loops our of their parents, so we must make sure to 847 // organize the loop nests correctly now. 848 { 849 std::map<BlockT *, LoopT *> ContainingLoops; 850 for (unsigned i = 0; i != L->SubLoops.size(); ++i) { 851 LoopT *Child = L->SubLoops[i]; 852 assert(Child->getParentLoop() == L && "Not proper child loop?"); 853 854 if (LoopT *ContainingLoop = ContainingLoops[Child->getHeader()]) { 855 // If there is already a loop which contains this loop, move this loop 856 // into the containing loop. 857 MoveSiblingLoopInto(Child, ContainingLoop); 858 --i; // The loop got removed from the SubLoops list. 859 } else { 860 // This is currently considered to be a top-level loop. Check to see 861 // if any of the contained blocks are loop headers for subloops we 862 // have already processed. 863 for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) { 864 LoopT *&BlockLoop = ContainingLoops[Child->Blocks[b]]; 865 if (BlockLoop == 0) { // Child block not processed yet... 866 BlockLoop = Child; 867 } else if (BlockLoop != Child) { 868 LoopT *SubLoop = BlockLoop; 869 // Reparent all of the blocks which used to belong to BlockLoops 870 for (unsigned j = 0, f = SubLoop->Blocks.size(); j != f; ++j) 871 ContainingLoops[SubLoop->Blocks[j]] = Child; 872 873 // There is already a loop which contains this block, that means 874 // that we should reparent the loop which the block is currently 875 // considered to belong to to be a child of this loop. 876 MoveSiblingLoopInto(SubLoop, Child); 877 --i; // We just shrunk the SubLoops list. 878 } 879 } 880 } 881 } 882 } 883 884 return L; 885 } 886 887 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside 888 /// of the NewParent Loop, instead of being a sibling of it. 889 void MoveSiblingLoopInto(LoopT *NewChild, 890 LoopT *NewParent) { 891 LoopT *OldParent = NewChild->getParentLoop(); 892 assert(OldParent && OldParent == NewParent->getParentLoop() && 893 NewChild != NewParent && "Not sibling loops!"); 894 895 // Remove NewChild from being a child of OldParent 896 typename std::vector<LoopT *>::iterator I = 897 std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), 898 NewChild); 899 assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??"); 900 OldParent->SubLoops.erase(I); // Remove from parent's subloops list 901 NewChild->ParentLoop = 0; 902 903 InsertLoopInto(NewChild, NewParent); 904 } 905 906 /// InsertLoopInto - This inserts loop L into the specified parent loop. If 907 /// the parent loop contains a loop which should contain L, the loop gets 908 /// inserted into L instead. 909 void InsertLoopInto(LoopT *L, LoopT *Parent) { 910 BlockT *LHeader = L->getHeader(); 911 assert(Parent->contains(LHeader) && 912 "This loop should not be inserted here!"); 913 914 // Check to see if it belongs in a child loop... 915 for (unsigned i = 0, e = static_cast<unsigned>(Parent->SubLoops.size()); 916 i != e; ++i) 917 if (Parent->SubLoops[i]->contains(LHeader)) { 918 InsertLoopInto(L, Parent->SubLoops[i]); 919 return; 920 } 921 922 // If not, insert it here! 923 Parent->SubLoops.push_back(L); 924 L->ParentLoop = Parent; 925 } 926 927 // Debugging 928 929 void print(raw_ostream &OS) const { 930 for (unsigned i = 0; i < TopLevelLoops.size(); ++i) 931 TopLevelLoops[i]->print(OS); 932 #if 0 933 for (DenseMap<BasicBlock*, LoopT*>::const_iterator I = BBMap.begin(), 934 E = BBMap.end(); I != E; ++I) 935 OS << "BB '" << I->first->getName() << "' level = " 936 << I->second->getLoopDepth() << "\n"; 937 #endif 938 } 939}; 940 941class LoopInfo : public FunctionPass { 942 LoopInfoBase<BasicBlock, Loop> LI; 943 friend class LoopBase<BasicBlock, Loop>; 944 945 void operator=(const LoopInfo &); // do not implement 946 LoopInfo(const LoopInfo &); // do not implement 947public: 948 static char ID; // Pass identification, replacement for typeid 949 950 LoopInfo() : FunctionPass(ID) { 951 initializeLoopInfoPass(*PassRegistry::getPassRegistry()); 952 } 953 954 LoopInfoBase<BasicBlock, Loop>& getBase() { return LI; } 955 956 /// iterator/begin/end - The interface to the top-level loops in the current 957 /// function. 958 /// 959 typedef LoopInfoBase<BasicBlock, Loop>::iterator iterator; 960 inline iterator begin() const { return LI.begin(); } 961 inline iterator end() const { return LI.end(); } 962 bool empty() const { return LI.empty(); } 963 964 /// getLoopFor - Return the inner most loop that BB lives in. If a basic 965 /// block is in no loop (for example the entry node), null is returned. 966 /// 967 inline Loop *getLoopFor(const BasicBlock *BB) const { 968 return LI.getLoopFor(BB); 969 } 970 971 /// operator[] - same as getLoopFor... 972 /// 973 inline const Loop *operator[](const BasicBlock *BB) const { 974 return LI.getLoopFor(BB); 975 } 976 977 /// getLoopDepth - Return the loop nesting level of the specified block. A 978 /// depth of 0 means the block is not inside any loop. 979 /// 980 inline unsigned getLoopDepth(const BasicBlock *BB) const { 981 return LI.getLoopDepth(BB); 982 } 983 984 // isLoopHeader - True if the block is a loop header node 985 inline bool isLoopHeader(BasicBlock *BB) const { 986 return LI.isLoopHeader(BB); 987 } 988 989 /// runOnFunction - Calculate the natural loop information. 990 /// 991 virtual bool runOnFunction(Function &F); 992 993 virtual void verifyAnalysis() const; 994 995 virtual void releaseMemory() { LI.releaseMemory(); } 996 997 virtual void print(raw_ostream &O, const Module* M = 0) const; 998 999 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 1000 1001 /// removeLoop - This removes the specified top-level loop from this loop info 1002 /// object. The loop is not deleted, as it will presumably be inserted into 1003 /// another loop. 1004 inline Loop *removeLoop(iterator I) { return LI.removeLoop(I); } 1005 1006 /// changeLoopFor - Change the top-level loop that contains BB to the 1007 /// specified loop. This should be used by transformations that restructure 1008 /// the loop hierarchy tree. 1009 inline void changeLoopFor(BasicBlock *BB, Loop *L) { 1010 LI.changeLoopFor(BB, L); 1011 } 1012 1013 /// changeTopLevelLoop - Replace the specified loop in the top-level loops 1014 /// list with the indicated loop. 1015 inline void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) { 1016 LI.changeTopLevelLoop(OldLoop, NewLoop); 1017 } 1018 1019 /// addTopLevelLoop - This adds the specified loop to the collection of 1020 /// top-level loops. 1021 inline void addTopLevelLoop(Loop *New) { 1022 LI.addTopLevelLoop(New); 1023 } 1024 1025 /// removeBlock - This method completely removes BB from all data structures, 1026 /// including all of the Loop objects it is nested in and our mapping from 1027 /// BasicBlocks to loops. 1028 void removeBlock(BasicBlock *BB) { 1029 LI.removeBlock(BB); 1030 } 1031 1032 /// replacementPreservesLCSSAForm - Returns true if replacing From with To 1033 /// everywhere is guaranteed to preserve LCSSA form. 1034 bool replacementPreservesLCSSAForm(Instruction *From, Value *To) { 1035 // Preserving LCSSA form is only problematic if the replacing value is an 1036 // instruction. 1037 Instruction *I = dyn_cast<Instruction>(To); 1038 if (!I) return true; 1039 // If both instructions are defined in the same basic block then replacement 1040 // cannot break LCSSA form. 1041 if (I->getParent() == From->getParent()) 1042 return true; 1043 // If the instruction is not defined in a loop then it can safely replace 1044 // anything. 1045 Loop *ToLoop = getLoopFor(I->getParent()); 1046 if (!ToLoop) return true; 1047 // If the replacing instruction is defined in the same loop as the original 1048 // instruction, or in a loop that contains it as an inner loop, then using 1049 // it as a replacement will not break LCSSA form. 1050 return ToLoop->contains(getLoopFor(From->getParent())); 1051 } 1052}; 1053 1054 1055// Allow clients to walk the list of nested loops... 1056template <> struct GraphTraits<const Loop*> { 1057 typedef const Loop NodeType; 1058 typedef LoopInfo::iterator ChildIteratorType; 1059 1060 static NodeType *getEntryNode(const Loop *L) { return L; } 1061 static inline ChildIteratorType child_begin(NodeType *N) { 1062 return N->begin(); 1063 } 1064 static inline ChildIteratorType child_end(NodeType *N) { 1065 return N->end(); 1066 } 1067}; 1068 1069template <> struct GraphTraits<Loop*> { 1070 typedef Loop NodeType; 1071 typedef LoopInfo::iterator ChildIteratorType; 1072 1073 static NodeType *getEntryNode(Loop *L) { return L; } 1074 static inline ChildIteratorType child_begin(NodeType *N) { 1075 return N->begin(); 1076 } 1077 static inline ChildIteratorType child_end(NodeType *N) { 1078 return N->end(); 1079 } 1080}; 1081 1082template<class BlockT, class LoopT> 1083void 1084LoopBase<BlockT, LoopT>::addBasicBlockToLoop(BlockT *NewBB, 1085 LoopInfoBase<BlockT, LoopT> &LIB) { 1086 assert((Blocks.empty() || LIB[getHeader()] == this) && 1087 "Incorrect LI specified for this loop!"); 1088 assert(NewBB && "Cannot add a null basic block to the loop!"); 1089 assert(LIB[NewBB] == 0 && "BasicBlock already in the loop!"); 1090 1091 LoopT *L = static_cast<LoopT *>(this); 1092 1093 // Add the loop mapping to the LoopInfo object... 1094 LIB.BBMap[NewBB] = L; 1095 1096 // Add the basic block to this loop and all parent loops... 1097 while (L) { 1098 L->Blocks.push_back(NewBB); 1099 L = L->getParentLoop(); 1100 } 1101} 1102 1103} // End llvm namespace 1104 1105#endif 1106