1//===-- UnrollLoop.cpp - Loop unrolling utilities -------------------------===// 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 implements some loop unrolling utilities. It does not define any 11// actual pass or policy, but provides a single function to perform loop 12// unrolling. 13// 14// The process of unrolling can produce extraneous basic blocks linked with 15// unconditional branches. This will be corrected in the future. 16// 17//===----------------------------------------------------------------------===// 18 19#include "llvm/Transforms/Utils/UnrollLoop.h" 20#include "llvm/ADT/SmallPtrSet.h" 21#include "llvm/ADT/Statistic.h" 22#include "llvm/Analysis/AssumptionCache.h" 23#include "llvm/Analysis/InstructionSimplify.h" 24#include "llvm/Analysis/LoopIterator.h" 25#include "llvm/Analysis/LoopPass.h" 26#include "llvm/Analysis/ScalarEvolution.h" 27#include "llvm/IR/BasicBlock.h" 28#include "llvm/IR/DataLayout.h" 29#include "llvm/IR/DiagnosticInfo.h" 30#include "llvm/IR/Dominators.h" 31#include "llvm/IR/LLVMContext.h" 32#include "llvm/Support/Debug.h" 33#include "llvm/Support/raw_ostream.h" 34#include "llvm/Transforms/Utils/BasicBlockUtils.h" 35#include "llvm/Transforms/Utils/Cloning.h" 36#include "llvm/Transforms/Utils/Local.h" 37#include "llvm/Transforms/Utils/LoopUtils.h" 38#include "llvm/Transforms/Utils/SimplifyIndVar.h" 39using namespace llvm; 40 41#define DEBUG_TYPE "loop-unroll" 42 43// TODO: Should these be here or in LoopUnroll? 44STATISTIC(NumCompletelyUnrolled, "Number of loops completely unrolled"); 45STATISTIC(NumUnrolled, "Number of loops unrolled (completely or otherwise)"); 46 47/// RemapInstruction - Convert the instruction operands from referencing the 48/// current values into those specified by VMap. 49static inline void RemapInstruction(Instruction *I, 50 ValueToValueMapTy &VMap) { 51 for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { 52 Value *Op = I->getOperand(op); 53 ValueToValueMapTy::iterator It = VMap.find(Op); 54 if (It != VMap.end()) 55 I->setOperand(op, It->second); 56 } 57 58 if (PHINode *PN = dyn_cast<PHINode>(I)) { 59 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 60 ValueToValueMapTy::iterator It = VMap.find(PN->getIncomingBlock(i)); 61 if (It != VMap.end()) 62 PN->setIncomingBlock(i, cast<BasicBlock>(It->second)); 63 } 64 } 65} 66 67/// FoldBlockIntoPredecessor - Folds a basic block into its predecessor if it 68/// only has one predecessor, and that predecessor only has one successor. 69/// The LoopInfo Analysis that is passed will be kept consistent. If folding is 70/// successful references to the containing loop must be removed from 71/// ScalarEvolution by calling ScalarEvolution::forgetLoop because SE may have 72/// references to the eliminated BB. The argument ForgottenLoops contains a set 73/// of loops that have already been forgotten to prevent redundant, expensive 74/// calls to ScalarEvolution::forgetLoop. Returns the new combined block. 75static BasicBlock * 76FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI, LPPassManager *LPM, 77 SmallPtrSetImpl<Loop *> &ForgottenLoops) { 78 // Merge basic blocks into their predecessor if there is only one distinct 79 // pred, and if there is only one distinct successor of the predecessor, and 80 // if there are no PHI nodes. 81 BasicBlock *OnlyPred = BB->getSinglePredecessor(); 82 if (!OnlyPred) return nullptr; 83 84 if (OnlyPred->getTerminator()->getNumSuccessors() != 1) 85 return nullptr; 86 87 DEBUG(dbgs() << "Merging: " << *BB << "into: " << *OnlyPred); 88 89 // Resolve any PHI nodes at the start of the block. They are all 90 // guaranteed to have exactly one entry if they exist, unless there are 91 // multiple duplicate (but guaranteed to be equal) entries for the 92 // incoming edges. This occurs when there are multiple edges from 93 // OnlyPred to OnlySucc. 94 FoldSingleEntryPHINodes(BB); 95 96 // Delete the unconditional branch from the predecessor... 97 OnlyPred->getInstList().pop_back(); 98 99 // Make all PHI nodes that referred to BB now refer to Pred as their 100 // source... 101 BB->replaceAllUsesWith(OnlyPred); 102 103 // Move all definitions in the successor to the predecessor... 104 OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList()); 105 106 // OldName will be valid until erased. 107 StringRef OldName = BB->getName(); 108 109 // Erase basic block from the function... 110 111 // ScalarEvolution holds references to loop exit blocks. 112 if (LPM) { 113 if (ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>()) { 114 if (Loop *L = LI->getLoopFor(BB)) { 115 if (ForgottenLoops.insert(L).second) 116 SE->forgetLoop(L); 117 } 118 } 119 } 120 LI->removeBlock(BB); 121 122 // Inherit predecessor's name if it exists... 123 if (!OldName.empty() && !OnlyPred->hasName()) 124 OnlyPred->setName(OldName); 125 126 BB->eraseFromParent(); 127 128 return OnlyPred; 129} 130 131/// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true 132/// if unrolling was successful, or false if the loop was unmodified. Unrolling 133/// can only fail when the loop's latch block is not terminated by a conditional 134/// branch instruction. However, if the trip count (and multiple) are not known, 135/// loop unrolling will mostly produce more code that is no faster. 136/// 137/// TripCount is generally defined as the number of times the loop header 138/// executes. UnrollLoop relaxes the definition to permit early exits: here 139/// TripCount is the iteration on which control exits LatchBlock if no early 140/// exits were taken. Note that UnrollLoop assumes that the loop counter test 141/// terminates LatchBlock in order to remove unnecesssary instances of the 142/// test. In other words, control may exit the loop prior to TripCount 143/// iterations via an early branch, but control may not exit the loop from the 144/// LatchBlock's terminator prior to TripCount iterations. 145/// 146/// Similarly, TripMultiple divides the number of times that the LatchBlock may 147/// execute without exiting the loop. 148/// 149/// If AllowRuntime is true then UnrollLoop will consider unrolling loops that 150/// have a runtime (i.e. not compile time constant) trip count. Unrolling these 151/// loops require a unroll "prologue" that runs "RuntimeTripCount % Count" 152/// iterations before branching into the unrolled loop. UnrollLoop will not 153/// runtime-unroll the loop if computing RuntimeTripCount will be expensive and 154/// AllowExpensiveTripCount is false. 155/// 156/// The LoopInfo Analysis that is passed will be kept consistent. 157/// 158/// If a LoopPassManager is passed in, and the loop is fully removed, it will be 159/// removed from the LoopPassManager as well. LPM can also be NULL. 160/// 161/// This utility preserves LoopInfo. If DominatorTree or ScalarEvolution are 162/// available from the Pass it must also preserve those analyses. 163bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount, 164 bool AllowRuntime, bool AllowExpensiveTripCount, 165 unsigned TripMultiple, LoopInfo *LI, Pass *PP, 166 LPPassManager *LPM, AssumptionCache *AC) { 167 BasicBlock *Preheader = L->getLoopPreheader(); 168 if (!Preheader) { 169 DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n"); 170 return false; 171 } 172 173 BasicBlock *LatchBlock = L->getLoopLatch(); 174 if (!LatchBlock) { 175 DEBUG(dbgs() << " Can't unroll; loop exit-block-insertion failed.\n"); 176 return false; 177 } 178 179 // Loops with indirectbr cannot be cloned. 180 if (!L->isSafeToClone()) { 181 DEBUG(dbgs() << " Can't unroll; Loop body cannot be cloned.\n"); 182 return false; 183 } 184 185 BasicBlock *Header = L->getHeader(); 186 BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator()); 187 188 if (!BI || BI->isUnconditional()) { 189 // The loop-rotate pass can be helpful to avoid this in many cases. 190 DEBUG(dbgs() << 191 " Can't unroll; loop not terminated by a conditional branch.\n"); 192 return false; 193 } 194 195 if (Header->hasAddressTaken()) { 196 // The loop-rotate pass can be helpful to avoid this in many cases. 197 DEBUG(dbgs() << 198 " Won't unroll loop: address of header block is taken.\n"); 199 return false; 200 } 201 202 if (TripCount != 0) 203 DEBUG(dbgs() << " Trip Count = " << TripCount << "\n"); 204 if (TripMultiple != 1) 205 DEBUG(dbgs() << " Trip Multiple = " << TripMultiple << "\n"); 206 207 // Effectively "DCE" unrolled iterations that are beyond the tripcount 208 // and will never be executed. 209 if (TripCount != 0 && Count > TripCount) 210 Count = TripCount; 211 212 // Don't enter the unroll code if there is nothing to do. This way we don't 213 // need to support "partial unrolling by 1". 214 if (TripCount == 0 && Count < 2) 215 return false; 216 217 assert(Count > 0); 218 assert(TripMultiple > 0); 219 assert(TripCount == 0 || TripCount % TripMultiple == 0); 220 221 // Are we eliminating the loop control altogether? 222 bool CompletelyUnroll = Count == TripCount; 223 224 // We assume a run-time trip count if the compiler cannot 225 // figure out the loop trip count and the unroll-runtime 226 // flag is specified. 227 bool RuntimeTripCount = (TripCount == 0 && Count > 0 && AllowRuntime); 228 229 if (RuntimeTripCount && 230 !UnrollRuntimeLoopProlog(L, Count, AllowExpensiveTripCount, LI, LPM)) 231 return false; 232 233 // Notify ScalarEvolution that the loop will be substantially changed, 234 // if not outright eliminated. 235 ScalarEvolution *SE = 236 PP ? PP->getAnalysisIfAvailable<ScalarEvolution>() : nullptr; 237 if (SE) 238 SE->forgetLoop(L); 239 240 // If we know the trip count, we know the multiple... 241 unsigned BreakoutTrip = 0; 242 if (TripCount != 0) { 243 BreakoutTrip = TripCount % Count; 244 TripMultiple = 0; 245 } else { 246 // Figure out what multiple to use. 247 BreakoutTrip = TripMultiple = 248 (unsigned)GreatestCommonDivisor64(Count, TripMultiple); 249 } 250 251 // Report the unrolling decision. 252 DebugLoc LoopLoc = L->getStartLoc(); 253 Function *F = Header->getParent(); 254 LLVMContext &Ctx = F->getContext(); 255 256 if (CompletelyUnroll) { 257 DEBUG(dbgs() << "COMPLETELY UNROLLING loop %" << Header->getName() 258 << " with trip count " << TripCount << "!\n"); 259 emitOptimizationRemark(Ctx, DEBUG_TYPE, *F, LoopLoc, 260 Twine("completely unrolled loop with ") + 261 Twine(TripCount) + " iterations"); 262 } else { 263 auto EmitDiag = [&](const Twine &T) { 264 emitOptimizationRemark(Ctx, DEBUG_TYPE, *F, LoopLoc, 265 "unrolled loop by a factor of " + Twine(Count) + 266 T); 267 }; 268 269 DEBUG(dbgs() << "UNROLLING loop %" << Header->getName() 270 << " by " << Count); 271 if (TripMultiple == 0 || BreakoutTrip != TripMultiple) { 272 DEBUG(dbgs() << " with a breakout at trip " << BreakoutTrip); 273 EmitDiag(" with a breakout at trip " + Twine(BreakoutTrip)); 274 } else if (TripMultiple != 1) { 275 DEBUG(dbgs() << " with " << TripMultiple << " trips per branch"); 276 EmitDiag(" with " + Twine(TripMultiple) + " trips per branch"); 277 } else if (RuntimeTripCount) { 278 DEBUG(dbgs() << " with run-time trip count"); 279 EmitDiag(" with run-time trip count"); 280 } 281 DEBUG(dbgs() << "!\n"); 282 } 283 284 bool ContinueOnTrue = L->contains(BI->getSuccessor(0)); 285 BasicBlock *LoopExit = BI->getSuccessor(ContinueOnTrue); 286 287 // For the first iteration of the loop, we should use the precloned values for 288 // PHI nodes. Insert associations now. 289 ValueToValueMapTy LastValueMap; 290 std::vector<PHINode*> OrigPHINode; 291 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { 292 OrigPHINode.push_back(cast<PHINode>(I)); 293 } 294 295 std::vector<BasicBlock*> Headers; 296 std::vector<BasicBlock*> Latches; 297 Headers.push_back(Header); 298 Latches.push_back(LatchBlock); 299 300 // The current on-the-fly SSA update requires blocks to be processed in 301 // reverse postorder so that LastValueMap contains the correct value at each 302 // exit. 303 LoopBlocksDFS DFS(L); 304 DFS.perform(LI); 305 306 // Stash the DFS iterators before adding blocks to the loop. 307 LoopBlocksDFS::RPOIterator BlockBegin = DFS.beginRPO(); 308 LoopBlocksDFS::RPOIterator BlockEnd = DFS.endRPO(); 309 310 for (unsigned It = 1; It != Count; ++It) { 311 std::vector<BasicBlock*> NewBlocks; 312 SmallDenseMap<const Loop *, Loop *, 4> NewLoops; 313 NewLoops[L] = L; 314 315 for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) { 316 ValueToValueMapTy VMap; 317 BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It)); 318 Header->getParent()->getBasicBlockList().push_back(New); 319 320 // Tell LI about New. 321 if (*BB == Header) { 322 assert(LI->getLoopFor(*BB) == L && "Header should not be in a sub-loop"); 323 L->addBasicBlockToLoop(New, *LI); 324 } else { 325 // Figure out which loop New is in. 326 const Loop *OldLoop = LI->getLoopFor(*BB); 327 assert(OldLoop && "Should (at least) be in the loop being unrolled!"); 328 329 Loop *&NewLoop = NewLoops[OldLoop]; 330 if (!NewLoop) { 331 // Found a new sub-loop. 332 assert(*BB == OldLoop->getHeader() && 333 "Header should be first in RPO"); 334 335 Loop *NewLoopParent = NewLoops.lookup(OldLoop->getParentLoop()); 336 assert(NewLoopParent && 337 "Expected parent loop before sub-loop in RPO"); 338 NewLoop = new Loop; 339 NewLoopParent->addChildLoop(NewLoop); 340 341 // Forget the old loop, since its inputs may have changed. 342 if (SE) 343 SE->forgetLoop(OldLoop); 344 } 345 NewLoop->addBasicBlockToLoop(New, *LI); 346 } 347 348 if (*BB == Header) 349 // Loop over all of the PHI nodes in the block, changing them to use 350 // the incoming values from the previous block. 351 for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) { 352 PHINode *NewPHI = cast<PHINode>(VMap[OrigPHINode[i]]); 353 Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock); 354 if (Instruction *InValI = dyn_cast<Instruction>(InVal)) 355 if (It > 1 && L->contains(InValI)) 356 InVal = LastValueMap[InValI]; 357 VMap[OrigPHINode[i]] = InVal; 358 New->getInstList().erase(NewPHI); 359 } 360 361 // Update our running map of newest clones 362 LastValueMap[*BB] = New; 363 for (ValueToValueMapTy::iterator VI = VMap.begin(), VE = VMap.end(); 364 VI != VE; ++VI) 365 LastValueMap[VI->first] = VI->second; 366 367 // Add phi entries for newly created values to all exit blocks. 368 for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB); 369 SI != SE; ++SI) { 370 if (L->contains(*SI)) 371 continue; 372 for (BasicBlock::iterator BBI = (*SI)->begin(); 373 PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) { 374 Value *Incoming = phi->getIncomingValueForBlock(*BB); 375 ValueToValueMapTy::iterator It = LastValueMap.find(Incoming); 376 if (It != LastValueMap.end()) 377 Incoming = It->second; 378 phi->addIncoming(Incoming, New); 379 } 380 } 381 // Keep track of new headers and latches as we create them, so that 382 // we can insert the proper branches later. 383 if (*BB == Header) 384 Headers.push_back(New); 385 if (*BB == LatchBlock) 386 Latches.push_back(New); 387 388 NewBlocks.push_back(New); 389 } 390 391 // Remap all instructions in the most recent iteration 392 for (unsigned i = 0; i < NewBlocks.size(); ++i) 393 for (BasicBlock::iterator I = NewBlocks[i]->begin(), 394 E = NewBlocks[i]->end(); I != E; ++I) 395 ::RemapInstruction(I, LastValueMap); 396 } 397 398 // Loop over the PHI nodes in the original block, setting incoming values. 399 for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) { 400 PHINode *PN = OrigPHINode[i]; 401 if (CompletelyUnroll) { 402 PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader)); 403 Header->getInstList().erase(PN); 404 } 405 else if (Count > 1) { 406 Value *InVal = PN->removeIncomingValue(LatchBlock, false); 407 // If this value was defined in the loop, take the value defined by the 408 // last iteration of the loop. 409 if (Instruction *InValI = dyn_cast<Instruction>(InVal)) { 410 if (L->contains(InValI)) 411 InVal = LastValueMap[InVal]; 412 } 413 assert(Latches.back() == LastValueMap[LatchBlock] && "bad last latch"); 414 PN->addIncoming(InVal, Latches.back()); 415 } 416 } 417 418 // Now that all the basic blocks for the unrolled iterations are in place, 419 // set up the branches to connect them. 420 for (unsigned i = 0, e = Latches.size(); i != e; ++i) { 421 // The original branch was replicated in each unrolled iteration. 422 BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator()); 423 424 // The branch destination. 425 unsigned j = (i + 1) % e; 426 BasicBlock *Dest = Headers[j]; 427 bool NeedConditional = true; 428 429 if (RuntimeTripCount && j != 0) { 430 NeedConditional = false; 431 } 432 433 // For a complete unroll, make the last iteration end with a branch 434 // to the exit block. 435 if (CompletelyUnroll && j == 0) { 436 Dest = LoopExit; 437 NeedConditional = false; 438 } 439 440 // If we know the trip count or a multiple of it, we can safely use an 441 // unconditional branch for some iterations. 442 if (j != BreakoutTrip && (TripMultiple == 0 || j % TripMultiple != 0)) { 443 NeedConditional = false; 444 } 445 446 if (NeedConditional) { 447 // Update the conditional branch's successor for the following 448 // iteration. 449 Term->setSuccessor(!ContinueOnTrue, Dest); 450 } else { 451 // Remove phi operands at this loop exit 452 if (Dest != LoopExit) { 453 BasicBlock *BB = Latches[i]; 454 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); 455 SI != SE; ++SI) { 456 if (*SI == Headers[i]) 457 continue; 458 for (BasicBlock::iterator BBI = (*SI)->begin(); 459 PHINode *Phi = dyn_cast<PHINode>(BBI); ++BBI) { 460 Phi->removeIncomingValue(BB, false); 461 } 462 } 463 } 464 // Replace the conditional branch with an unconditional one. 465 BranchInst::Create(Dest, Term); 466 Term->eraseFromParent(); 467 } 468 } 469 470 // Merge adjacent basic blocks, if possible. 471 SmallPtrSet<Loop *, 4> ForgottenLoops; 472 for (unsigned i = 0, e = Latches.size(); i != e; ++i) { 473 BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator()); 474 if (Term->isUnconditional()) { 475 BasicBlock *Dest = Term->getSuccessor(0); 476 if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI, LPM, 477 ForgottenLoops)) 478 std::replace(Latches.begin(), Latches.end(), Dest, Fold); 479 } 480 } 481 482 // FIXME: We could register any cloned assumptions instead of clearing the 483 // whole function's cache. 484 AC->clear(); 485 486 DominatorTree *DT = nullptr; 487 if (PP) { 488 // FIXME: Reconstruct dom info, because it is not preserved properly. 489 // Incrementally updating domtree after loop unrolling would be easy. 490 if (DominatorTreeWrapperPass *DTWP = 491 PP->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) { 492 DT = &DTWP->getDomTree(); 493 DT->recalculate(*L->getHeader()->getParent()); 494 } 495 496 // Simplify any new induction variables in the partially unrolled loop. 497 if (SE && !CompletelyUnroll) { 498 SmallVector<WeakVH, 16> DeadInsts; 499 simplifyLoopIVs(L, SE, LPM, DeadInsts); 500 501 // Aggressively clean up dead instructions that simplifyLoopIVs already 502 // identified. Any remaining should be cleaned up below. 503 while (!DeadInsts.empty()) 504 if (Instruction *Inst = 505 dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val())) 506 RecursivelyDeleteTriviallyDeadInstructions(Inst); 507 } 508 } 509 // At this point, the code is well formed. We now do a quick sweep over the 510 // inserted code, doing constant propagation and dead code elimination as we 511 // go. 512 const DataLayout &DL = Header->getModule()->getDataLayout(); 513 const std::vector<BasicBlock*> &NewLoopBlocks = L->getBlocks(); 514 for (std::vector<BasicBlock*>::const_iterator BB = NewLoopBlocks.begin(), 515 BBE = NewLoopBlocks.end(); BB != BBE; ++BB) 516 for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ) { 517 Instruction *Inst = I++; 518 519 if (isInstructionTriviallyDead(Inst)) 520 (*BB)->getInstList().erase(Inst); 521 else if (Value *V = SimplifyInstruction(Inst, DL)) 522 if (LI->replacementPreservesLCSSAForm(Inst, V)) { 523 Inst->replaceAllUsesWith(V); 524 (*BB)->getInstList().erase(Inst); 525 } 526 } 527 528 NumCompletelyUnrolled += CompletelyUnroll; 529 ++NumUnrolled; 530 531 Loop *OuterL = L->getParentLoop(); 532 // Remove the loop from the LoopPassManager if it's completely removed. 533 if (CompletelyUnroll && LPM != nullptr) 534 LPM->deleteLoopFromQueue(L); 535 536 // If we have a pass and a DominatorTree we should re-simplify impacted loops 537 // to ensure subsequent analyses can rely on this form. We want to simplify 538 // at least one layer outside of the loop that was unrolled so that any 539 // changes to the parent loop exposed by the unrolling are considered. 540 if (PP && DT) { 541 if (!OuterL && !CompletelyUnroll) 542 OuterL = L; 543 if (OuterL) { 544 simplifyLoop(OuterL, DT, LI, PP, /*AliasAnalysis*/ nullptr, SE, AC); 545 546 // LCSSA must be performed on the outermost affected loop. The unrolled 547 // loop's last loop latch is guaranteed to be in the outermost loop after 548 // deleteLoopFromQueue updates LoopInfo. 549 Loop *LatchLoop = LI->getLoopFor(Latches.back()); 550 if (!OuterL->contains(LatchLoop)) 551 while (OuterL->getParentLoop() != LatchLoop) 552 OuterL = OuterL->getParentLoop(); 553 554 formLCSSARecursively(*OuterL, *DT, LI, SE); 555 } 556 } 557 558 return true; 559} 560 561/// Given an llvm.loop loop id metadata node, returns the loop hint metadata 562/// node with the given name (for example, "llvm.loop.unroll.count"). If no 563/// such metadata node exists, then nullptr is returned. 564MDNode *llvm::GetUnrollMetadata(MDNode *LoopID, StringRef Name) { 565 // First operand should refer to the loop id itself. 566 assert(LoopID->getNumOperands() > 0 && "requires at least one operand"); 567 assert(LoopID->getOperand(0) == LoopID && "invalid loop id"); 568 569 for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) { 570 MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i)); 571 if (!MD) 572 continue; 573 574 MDString *S = dyn_cast<MDString>(MD->getOperand(0)); 575 if (!S) 576 continue; 577 578 if (Name.equals(S->getString())) 579 return MD; 580 } 581 return nullptr; 582} 583