1 //===- LoopReroll.cpp - Loop rerolling pass -------------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This pass implements a simple loop reroller. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/ADT/APInt.h" 14 #include "llvm/ADT/BitVector.h" 15 #include "llvm/ADT/DenseMap.h" 16 #include "llvm/ADT/DenseSet.h" 17 #include "llvm/ADT/MapVector.h" 18 #include "llvm/ADT/STLExtras.h" 19 #include "llvm/ADT/SmallPtrSet.h" 20 #include "llvm/ADT/SmallVector.h" 21 #include "llvm/ADT/Statistic.h" 22 #include "llvm/Analysis/AliasAnalysis.h" 23 #include "llvm/Analysis/AliasSetTracker.h" 24 #include "llvm/Analysis/LoopInfo.h" 25 #include "llvm/Analysis/LoopPass.h" 26 #include "llvm/Analysis/ScalarEvolution.h" 27 #include "llvm/Analysis/ScalarEvolutionExpressions.h" 28 #include "llvm/Analysis/TargetLibraryInfo.h" 29 #include "llvm/Analysis/ValueTracking.h" 30 #include "llvm/IR/BasicBlock.h" 31 #include "llvm/IR/Constants.h" 32 #include "llvm/IR/Dominators.h" 33 #include "llvm/IR/InstrTypes.h" 34 #include "llvm/IR/Instruction.h" 35 #include "llvm/IR/Instructions.h" 36 #include "llvm/IR/IntrinsicInst.h" 37 #include "llvm/IR/Module.h" 38 #include "llvm/IR/Type.h" 39 #include "llvm/IR/Use.h" 40 #include "llvm/IR/User.h" 41 #include "llvm/IR/Value.h" 42 #include "llvm/Support/Casting.h" 43 #include "llvm/Support/CommandLine.h" 44 #include "llvm/Support/Debug.h" 45 #include "llvm/Support/raw_ostream.h" 46 #include "llvm/Transforms/Scalar/LoopReroll.h" 47 #include "llvm/Transforms/Utils.h" 48 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 49 #include "llvm/Transforms/Utils/Local.h" 50 #include "llvm/Transforms/Utils/LoopUtils.h" 51 #include "llvm/Transforms/Utils/ScalarEvolutionExpander.h" 52 #include <cassert> 53 #include <cstddef> 54 #include <cstdint> 55 #include <iterator> 56 #include <map> 57 #include <utility> 58 59 using namespace llvm; 60 61 #define DEBUG_TYPE "loop-reroll" 62 63 STATISTIC(NumRerolledLoops, "Number of rerolled loops"); 64 65 static cl::opt<unsigned> 66 NumToleratedFailedMatches("reroll-num-tolerated-failed-matches", cl::init(400), 67 cl::Hidden, 68 cl::desc("The maximum number of failures to tolerate" 69 " during fuzzy matching. (default: 400)")); 70 71 // This loop re-rolling transformation aims to transform loops like this: 72 // 73 // int foo(int a); 74 // void bar(int *x) { 75 // for (int i = 0; i < 500; i += 3) { 76 // foo(i); 77 // foo(i+1); 78 // foo(i+2); 79 // } 80 // } 81 // 82 // into a loop like this: 83 // 84 // void bar(int *x) { 85 // for (int i = 0; i < 500; ++i) 86 // foo(i); 87 // } 88 // 89 // It does this by looking for loops that, besides the latch code, are composed 90 // of isomorphic DAGs of instructions, with each DAG rooted at some increment 91 // to the induction variable, and where each DAG is isomorphic to the DAG 92 // rooted at the induction variable (excepting the sub-DAGs which root the 93 // other induction-variable increments). In other words, we're looking for loop 94 // bodies of the form: 95 // 96 // %iv = phi [ (preheader, ...), (body, %iv.next) ] 97 // f(%iv) 98 // %iv.1 = add %iv, 1 <-- a root increment 99 // f(%iv.1) 100 // %iv.2 = add %iv, 2 <-- a root increment 101 // f(%iv.2) 102 // %iv.scale_m_1 = add %iv, scale-1 <-- a root increment 103 // f(%iv.scale_m_1) 104 // ... 105 // %iv.next = add %iv, scale 106 // %cmp = icmp(%iv, ...) 107 // br %cmp, header, exit 108 // 109 // where each f(i) is a set of instructions that, collectively, are a function 110 // only of i (and other loop-invariant values). 111 // 112 // As a special case, we can also reroll loops like this: 113 // 114 // int foo(int); 115 // void bar(int *x) { 116 // for (int i = 0; i < 500; ++i) { 117 // x[3*i] = foo(0); 118 // x[3*i+1] = foo(0); 119 // x[3*i+2] = foo(0); 120 // } 121 // } 122 // 123 // into this: 124 // 125 // void bar(int *x) { 126 // for (int i = 0; i < 1500; ++i) 127 // x[i] = foo(0); 128 // } 129 // 130 // in which case, we're looking for inputs like this: 131 // 132 // %iv = phi [ (preheader, ...), (body, %iv.next) ] 133 // %scaled.iv = mul %iv, scale 134 // f(%scaled.iv) 135 // %scaled.iv.1 = add %scaled.iv, 1 136 // f(%scaled.iv.1) 137 // %scaled.iv.2 = add %scaled.iv, 2 138 // f(%scaled.iv.2) 139 // %scaled.iv.scale_m_1 = add %scaled.iv, scale-1 140 // f(%scaled.iv.scale_m_1) 141 // ... 142 // %iv.next = add %iv, 1 143 // %cmp = icmp(%iv, ...) 144 // br %cmp, header, exit 145 146 namespace { 147 148 enum IterationLimits { 149 /// The maximum number of iterations that we'll try and reroll. 150 IL_MaxRerollIterations = 32, 151 /// The bitvector index used by loop induction variables and other 152 /// instructions that belong to all iterations. 153 IL_All, 154 IL_End 155 }; 156 157 class LoopReroll { 158 public: 159 LoopReroll(AliasAnalysis *AA, LoopInfo *LI, ScalarEvolution *SE, 160 TargetLibraryInfo *TLI, DominatorTree *DT, bool PreserveLCSSA) 161 : AA(AA), LI(LI), SE(SE), TLI(TLI), DT(DT), 162 PreserveLCSSA(PreserveLCSSA) {} 163 bool runOnLoop(Loop *L); 164 165 protected: 166 AliasAnalysis *AA; 167 LoopInfo *LI; 168 ScalarEvolution *SE; 169 TargetLibraryInfo *TLI; 170 DominatorTree *DT; 171 bool PreserveLCSSA; 172 173 using SmallInstructionVector = SmallVector<Instruction *, 16>; 174 using SmallInstructionSet = SmallPtrSet<Instruction *, 16>; 175 using TinyInstructionVector = SmallVector<Instruction *, 1>; 176 177 // Map between induction variable and its increment 178 DenseMap<Instruction *, int64_t> IVToIncMap; 179 180 // For loop with multiple induction variables, remember the ones used only to 181 // control the loop. 182 TinyInstructionVector LoopControlIVs; 183 184 // A chain of isomorphic instructions, identified by a single-use PHI 185 // representing a reduction. Only the last value may be used outside the 186 // loop. 187 struct SimpleLoopReduction { 188 SimpleLoopReduction(Instruction *P, Loop *L) : Instructions(1, P) { 189 assert(isa<PHINode>(P) && "First reduction instruction must be a PHI"); 190 add(L); 191 } 192 193 bool valid() const { 194 return Valid; 195 } 196 197 Instruction *getPHI() const { 198 assert(Valid && "Using invalid reduction"); 199 return Instructions.front(); 200 } 201 202 Instruction *getReducedValue() const { 203 assert(Valid && "Using invalid reduction"); 204 return Instructions.back(); 205 } 206 207 Instruction *get(size_t i) const { 208 assert(Valid && "Using invalid reduction"); 209 return Instructions[i+1]; 210 } 211 212 Instruction *operator [] (size_t i) const { return get(i); } 213 214 // The size, ignoring the initial PHI. 215 size_t size() const { 216 assert(Valid && "Using invalid reduction"); 217 return Instructions.size()-1; 218 } 219 220 using iterator = SmallInstructionVector::iterator; 221 using const_iterator = SmallInstructionVector::const_iterator; 222 223 iterator begin() { 224 assert(Valid && "Using invalid reduction"); 225 return std::next(Instructions.begin()); 226 } 227 228 const_iterator begin() const { 229 assert(Valid && "Using invalid reduction"); 230 return std::next(Instructions.begin()); 231 } 232 233 iterator end() { return Instructions.end(); } 234 const_iterator end() const { return Instructions.end(); } 235 236 protected: 237 bool Valid = false; 238 SmallInstructionVector Instructions; 239 240 void add(Loop *L); 241 }; 242 243 // The set of all reductions, and state tracking of possible reductions 244 // during loop instruction processing. 245 struct ReductionTracker { 246 using SmallReductionVector = SmallVector<SimpleLoopReduction, 16>; 247 248 // Add a new possible reduction. 249 void addSLR(SimpleLoopReduction &SLR) { PossibleReds.push_back(SLR); } 250 251 // Setup to track possible reductions corresponding to the provided 252 // rerolling scale. Only reductions with a number of non-PHI instructions 253 // that is divisible by the scale are considered. Three instructions sets 254 // are filled in: 255 // - A set of all possible instructions in eligible reductions. 256 // - A set of all PHIs in eligible reductions 257 // - A set of all reduced values (last instructions) in eligible 258 // reductions. 259 void restrictToScale(uint64_t Scale, 260 SmallInstructionSet &PossibleRedSet, 261 SmallInstructionSet &PossibleRedPHISet, 262 SmallInstructionSet &PossibleRedLastSet) { 263 PossibleRedIdx.clear(); 264 PossibleRedIter.clear(); 265 Reds.clear(); 266 267 for (unsigned i = 0, e = PossibleReds.size(); i != e; ++i) 268 if (PossibleReds[i].size() % Scale == 0) { 269 PossibleRedLastSet.insert(PossibleReds[i].getReducedValue()); 270 PossibleRedPHISet.insert(PossibleReds[i].getPHI()); 271 272 PossibleRedSet.insert(PossibleReds[i].getPHI()); 273 PossibleRedIdx[PossibleReds[i].getPHI()] = i; 274 for (Instruction *J : PossibleReds[i]) { 275 PossibleRedSet.insert(J); 276 PossibleRedIdx[J] = i; 277 } 278 } 279 } 280 281 // The functions below are used while processing the loop instructions. 282 283 // Are the two instructions both from reductions, and furthermore, from 284 // the same reduction? 285 bool isPairInSame(Instruction *J1, Instruction *J2) { 286 DenseMap<Instruction *, int>::iterator J1I = PossibleRedIdx.find(J1); 287 if (J1I != PossibleRedIdx.end()) { 288 DenseMap<Instruction *, int>::iterator J2I = PossibleRedIdx.find(J2); 289 if (J2I != PossibleRedIdx.end() && J1I->second == J2I->second) 290 return true; 291 } 292 293 return false; 294 } 295 296 // The two provided instructions, the first from the base iteration, and 297 // the second from iteration i, form a matched pair. If these are part of 298 // a reduction, record that fact. 299 void recordPair(Instruction *J1, Instruction *J2, unsigned i) { 300 if (PossibleRedIdx.count(J1)) { 301 assert(PossibleRedIdx.count(J2) && 302 "Recording reduction vs. non-reduction instruction?"); 303 304 PossibleRedIter[J1] = 0; 305 PossibleRedIter[J2] = i; 306 307 int Idx = PossibleRedIdx[J1]; 308 assert(Idx == PossibleRedIdx[J2] && 309 "Recording pair from different reductions?"); 310 Reds.insert(Idx); 311 } 312 } 313 314 // The functions below can be called after we've finished processing all 315 // instructions in the loop, and we know which reductions were selected. 316 317 bool validateSelected(); 318 void replaceSelected(); 319 320 protected: 321 // The vector of all possible reductions (for any scale). 322 SmallReductionVector PossibleReds; 323 324 DenseMap<Instruction *, int> PossibleRedIdx; 325 DenseMap<Instruction *, int> PossibleRedIter; 326 DenseSet<int> Reds; 327 }; 328 329 // A DAGRootSet models an induction variable being used in a rerollable 330 // loop. For example, 331 // 332 // x[i*3+0] = y1 333 // x[i*3+1] = y2 334 // x[i*3+2] = y3 335 // 336 // Base instruction -> i*3 337 // +---+----+ 338 // / | \ 339 // ST[y1] +1 +2 <-- Roots 340 // | | 341 // ST[y2] ST[y3] 342 // 343 // There may be multiple DAGRoots, for example: 344 // 345 // x[i*2+0] = ... (1) 346 // x[i*2+1] = ... (1) 347 // x[i*2+4] = ... (2) 348 // x[i*2+5] = ... (2) 349 // x[(i+1234)*2+5678] = ... (3) 350 // x[(i+1234)*2+5679] = ... (3) 351 // 352 // The loop will be rerolled by adding a new loop induction variable, 353 // one for the Base instruction in each DAGRootSet. 354 // 355 struct DAGRootSet { 356 Instruction *BaseInst; 357 SmallInstructionVector Roots; 358 359 // The instructions between IV and BaseInst (but not including BaseInst). 360 SmallInstructionSet SubsumedInsts; 361 }; 362 363 // The set of all DAG roots, and state tracking of all roots 364 // for a particular induction variable. 365 struct DAGRootTracker { 366 DAGRootTracker(LoopReroll *Parent, Loop *L, Instruction *IV, 367 ScalarEvolution *SE, AliasAnalysis *AA, 368 TargetLibraryInfo *TLI, DominatorTree *DT, LoopInfo *LI, 369 bool PreserveLCSSA, 370 DenseMap<Instruction *, int64_t> &IncrMap, 371 TinyInstructionVector LoopCtrlIVs) 372 : Parent(Parent), L(L), SE(SE), AA(AA), TLI(TLI), DT(DT), LI(LI), 373 PreserveLCSSA(PreserveLCSSA), IV(IV), IVToIncMap(IncrMap), 374 LoopControlIVs(LoopCtrlIVs) {} 375 376 /// Stage 1: Find all the DAG roots for the induction variable. 377 bool findRoots(); 378 379 /// Stage 2: Validate if the found roots are valid. 380 bool validate(ReductionTracker &Reductions); 381 382 /// Stage 3: Assuming validate() returned true, perform the 383 /// replacement. 384 /// @param BackedgeTakenCount The backedge-taken count of L. 385 void replace(const SCEV *BackedgeTakenCount); 386 387 protected: 388 using UsesTy = MapVector<Instruction *, BitVector>; 389 390 void findRootsRecursive(Instruction *IVU, 391 SmallInstructionSet SubsumedInsts); 392 bool findRootsBase(Instruction *IVU, SmallInstructionSet SubsumedInsts); 393 bool collectPossibleRoots(Instruction *Base, 394 std::map<int64_t,Instruction*> &Roots); 395 bool validateRootSet(DAGRootSet &DRS); 396 397 bool collectUsedInstructions(SmallInstructionSet &PossibleRedSet); 398 void collectInLoopUserSet(const SmallInstructionVector &Roots, 399 const SmallInstructionSet &Exclude, 400 const SmallInstructionSet &Final, 401 DenseSet<Instruction *> &Users); 402 void collectInLoopUserSet(Instruction *Root, 403 const SmallInstructionSet &Exclude, 404 const SmallInstructionSet &Final, 405 DenseSet<Instruction *> &Users); 406 407 UsesTy::iterator nextInstr(int Val, UsesTy &In, 408 const SmallInstructionSet &Exclude, 409 UsesTy::iterator *StartI=nullptr); 410 bool isBaseInst(Instruction *I); 411 bool isRootInst(Instruction *I); 412 bool instrDependsOn(Instruction *I, 413 UsesTy::iterator Start, 414 UsesTy::iterator End); 415 void replaceIV(DAGRootSet &DRS, const SCEV *Start, const SCEV *IncrExpr); 416 417 LoopReroll *Parent; 418 419 // Members of Parent, replicated here for brevity. 420 Loop *L; 421 ScalarEvolution *SE; 422 AliasAnalysis *AA; 423 TargetLibraryInfo *TLI; 424 DominatorTree *DT; 425 LoopInfo *LI; 426 bool PreserveLCSSA; 427 428 // The loop induction variable. 429 Instruction *IV; 430 431 // Loop step amount. 432 int64_t Inc; 433 434 // Loop reroll count; if Inc == 1, this records the scaling applied 435 // to the indvar: a[i*2+0] = ...; a[i*2+1] = ... ; 436 // If Inc is not 1, Scale = Inc. 437 uint64_t Scale; 438 439 // The roots themselves. 440 SmallVector<DAGRootSet,16> RootSets; 441 442 // All increment instructions for IV. 443 SmallInstructionVector LoopIncs; 444 445 // Map of all instructions in the loop (in order) to the iterations 446 // they are used in (or specially, IL_All for instructions 447 // used in the loop increment mechanism). 448 UsesTy Uses; 449 450 // Map between induction variable and its increment 451 DenseMap<Instruction *, int64_t> &IVToIncMap; 452 453 TinyInstructionVector LoopControlIVs; 454 }; 455 456 // Check if it is a compare-like instruction whose user is a branch 457 bool isCompareUsedByBranch(Instruction *I) { 458 auto *TI = I->getParent()->getTerminator(); 459 if (!isa<BranchInst>(TI) || !isa<CmpInst>(I)) 460 return false; 461 return I->hasOneUse() && TI->getOperand(0) == I; 462 }; 463 464 bool isLoopControlIV(Loop *L, Instruction *IV); 465 void collectPossibleIVs(Loop *L, SmallInstructionVector &PossibleIVs); 466 void collectPossibleReductions(Loop *L, 467 ReductionTracker &Reductions); 468 bool reroll(Instruction *IV, Loop *L, BasicBlock *Header, 469 const SCEV *BackedgeTakenCount, ReductionTracker &Reductions); 470 }; 471 472 } // end anonymous namespace 473 474 // Returns true if the provided instruction is used outside the given loop. 475 // This operates like Instruction::isUsedOutsideOfBlock, but considers PHIs in 476 // non-loop blocks to be outside the loop. 477 static bool hasUsesOutsideLoop(Instruction *I, Loop *L) { 478 for (User *U : I->users()) { 479 if (!L->contains(cast<Instruction>(U))) 480 return true; 481 } 482 return false; 483 } 484 485 // Check if an IV is only used to control the loop. There are two cases: 486 // 1. It only has one use which is loop increment, and the increment is only 487 // used by comparison and the PHI (could has sext with nsw in between), and the 488 // comparison is only used by branch. 489 // 2. It is used by loop increment and the comparison, the loop increment is 490 // only used by the PHI, and the comparison is used only by the branch. 491 bool LoopReroll::isLoopControlIV(Loop *L, Instruction *IV) { 492 unsigned IVUses = IV->getNumUses(); 493 if (IVUses != 2 && IVUses != 1) 494 return false; 495 496 for (auto *User : IV->users()) { 497 int32_t IncOrCmpUses = User->getNumUses(); 498 bool IsCompInst = isCompareUsedByBranch(cast<Instruction>(User)); 499 500 // User can only have one or two uses. 501 if (IncOrCmpUses != 2 && IncOrCmpUses != 1) 502 return false; 503 504 // Case 1 505 if (IVUses == 1) { 506 // The only user must be the loop increment. 507 // The loop increment must have two uses. 508 if (IsCompInst || IncOrCmpUses != 2) 509 return false; 510 } 511 512 // Case 2 513 if (IVUses == 2 && IncOrCmpUses != 1) 514 return false; 515 516 // The users of the IV must be a binary operation or a comparison 517 if (auto *BO = dyn_cast<BinaryOperator>(User)) { 518 if (BO->getOpcode() == Instruction::Add) { 519 // Loop Increment 520 // User of Loop Increment should be either PHI or CMP 521 for (auto *UU : User->users()) { 522 if (PHINode *PN = dyn_cast<PHINode>(UU)) { 523 if (PN != IV) 524 return false; 525 } 526 // Must be a CMP or an ext (of a value with nsw) then CMP 527 else { 528 auto *UUser = cast<Instruction>(UU); 529 // Skip SExt if we are extending an nsw value 530 // TODO: Allow ZExt too 531 if (BO->hasNoSignedWrap() && UUser->hasOneUse() && 532 isa<SExtInst>(UUser)) 533 UUser = cast<Instruction>(*(UUser->user_begin())); 534 if (!isCompareUsedByBranch(UUser)) 535 return false; 536 } 537 } 538 } else 539 return false; 540 // Compare : can only have one use, and must be branch 541 } else if (!IsCompInst) 542 return false; 543 } 544 return true; 545 } 546 547 // Collect the list of loop induction variables with respect to which it might 548 // be possible to reroll the loop. 549 void LoopReroll::collectPossibleIVs(Loop *L, 550 SmallInstructionVector &PossibleIVs) { 551 for (Instruction &IV : L->getHeader()->phis()) { 552 if (!IV.getType()->isIntegerTy() && !IV.getType()->isPointerTy()) 553 continue; 554 555 if (const SCEVAddRecExpr *PHISCEV = 556 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(&IV))) { 557 if (PHISCEV->getLoop() != L) 558 continue; 559 if (!PHISCEV->isAffine()) 560 continue; 561 const auto *IncSCEV = dyn_cast<SCEVConstant>(PHISCEV->getStepRecurrence(*SE)); 562 if (IncSCEV) { 563 IVToIncMap[&IV] = IncSCEV->getValue()->getSExtValue(); 564 LLVM_DEBUG(dbgs() << "LRR: Possible IV: " << IV << " = " << *PHISCEV 565 << "\n"); 566 567 if (isLoopControlIV(L, &IV)) { 568 LoopControlIVs.push_back(&IV); 569 LLVM_DEBUG(dbgs() << "LRR: Loop control only IV: " << IV 570 << " = " << *PHISCEV << "\n"); 571 } else 572 PossibleIVs.push_back(&IV); 573 } 574 } 575 } 576 } 577 578 // Add the remainder of the reduction-variable chain to the instruction vector 579 // (the initial PHINode has already been added). If successful, the object is 580 // marked as valid. 581 void LoopReroll::SimpleLoopReduction::add(Loop *L) { 582 assert(!Valid && "Cannot add to an already-valid chain"); 583 584 // The reduction variable must be a chain of single-use instructions 585 // (including the PHI), except for the last value (which is used by the PHI 586 // and also outside the loop). 587 Instruction *C = Instructions.front(); 588 if (C->user_empty()) 589 return; 590 591 do { 592 C = cast<Instruction>(*C->user_begin()); 593 if (C->hasOneUse()) { 594 if (!C->isBinaryOp()) 595 return; 596 597 if (!(isa<PHINode>(Instructions.back()) || 598 C->isSameOperationAs(Instructions.back()))) 599 return; 600 601 Instructions.push_back(C); 602 } 603 } while (C->hasOneUse()); 604 605 if (Instructions.size() < 2 || 606 !C->isSameOperationAs(Instructions.back()) || 607 C->use_empty()) 608 return; 609 610 // C is now the (potential) last instruction in the reduction chain. 611 for (User *U : C->users()) { 612 // The only in-loop user can be the initial PHI. 613 if (L->contains(cast<Instruction>(U))) 614 if (cast<Instruction>(U) != Instructions.front()) 615 return; 616 } 617 618 Instructions.push_back(C); 619 Valid = true; 620 } 621 622 // Collect the vector of possible reduction variables. 623 void LoopReroll::collectPossibleReductions(Loop *L, 624 ReductionTracker &Reductions) { 625 BasicBlock *Header = L->getHeader(); 626 for (BasicBlock::iterator I = Header->begin(), 627 IE = Header->getFirstInsertionPt(); I != IE; ++I) { 628 if (!isa<PHINode>(I)) 629 continue; 630 if (!I->getType()->isSingleValueType()) 631 continue; 632 633 SimpleLoopReduction SLR(&*I, L); 634 if (!SLR.valid()) 635 continue; 636 637 LLVM_DEBUG(dbgs() << "LRR: Possible reduction: " << *I << " (with " 638 << SLR.size() << " chained instructions)\n"); 639 Reductions.addSLR(SLR); 640 } 641 } 642 643 // Collect the set of all users of the provided root instruction. This set of 644 // users contains not only the direct users of the root instruction, but also 645 // all users of those users, and so on. There are two exceptions: 646 // 647 // 1. Instructions in the set of excluded instructions are never added to the 648 // use set (even if they are users). This is used, for example, to exclude 649 // including root increments in the use set of the primary IV. 650 // 651 // 2. Instructions in the set of final instructions are added to the use set 652 // if they are users, but their users are not added. This is used, for 653 // example, to prevent a reduction update from forcing all later reduction 654 // updates into the use set. 655 void LoopReroll::DAGRootTracker::collectInLoopUserSet( 656 Instruction *Root, const SmallInstructionSet &Exclude, 657 const SmallInstructionSet &Final, 658 DenseSet<Instruction *> &Users) { 659 SmallInstructionVector Queue(1, Root); 660 while (!Queue.empty()) { 661 Instruction *I = Queue.pop_back_val(); 662 if (!Users.insert(I).second) 663 continue; 664 665 if (!Final.count(I)) 666 for (Use &U : I->uses()) { 667 Instruction *User = cast<Instruction>(U.getUser()); 668 if (PHINode *PN = dyn_cast<PHINode>(User)) { 669 // Ignore "wrap-around" uses to PHIs of this loop's header. 670 if (PN->getIncomingBlock(U) == L->getHeader()) 671 continue; 672 } 673 674 if (L->contains(User) && !Exclude.count(User)) { 675 Queue.push_back(User); 676 } 677 } 678 679 // We also want to collect single-user "feeder" values. 680 for (Use &U : I->operands()) { 681 if (Instruction *Op = dyn_cast<Instruction>(U)) 682 if (Op->hasOneUse() && L->contains(Op) && !Exclude.count(Op) && 683 !Final.count(Op)) 684 Queue.push_back(Op); 685 } 686 } 687 } 688 689 // Collect all of the users of all of the provided root instructions (combined 690 // into a single set). 691 void LoopReroll::DAGRootTracker::collectInLoopUserSet( 692 const SmallInstructionVector &Roots, 693 const SmallInstructionSet &Exclude, 694 const SmallInstructionSet &Final, 695 DenseSet<Instruction *> &Users) { 696 for (Instruction *Root : Roots) 697 collectInLoopUserSet(Root, Exclude, Final, Users); 698 } 699 700 static bool isUnorderedLoadStore(Instruction *I) { 701 if (LoadInst *LI = dyn_cast<LoadInst>(I)) 702 return LI->isUnordered(); 703 if (StoreInst *SI = dyn_cast<StoreInst>(I)) 704 return SI->isUnordered(); 705 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) 706 return !MI->isVolatile(); 707 return false; 708 } 709 710 /// Return true if IVU is a "simple" arithmetic operation. 711 /// This is used for narrowing the search space for DAGRoots; only arithmetic 712 /// and GEPs can be part of a DAGRoot. 713 static bool isSimpleArithmeticOp(User *IVU) { 714 if (Instruction *I = dyn_cast<Instruction>(IVU)) { 715 switch (I->getOpcode()) { 716 default: return false; 717 case Instruction::Add: 718 case Instruction::Sub: 719 case Instruction::Mul: 720 case Instruction::Shl: 721 case Instruction::AShr: 722 case Instruction::LShr: 723 case Instruction::GetElementPtr: 724 case Instruction::Trunc: 725 case Instruction::ZExt: 726 case Instruction::SExt: 727 return true; 728 } 729 } 730 return false; 731 } 732 733 static bool isLoopIncrement(User *U, Instruction *IV) { 734 BinaryOperator *BO = dyn_cast<BinaryOperator>(U); 735 736 if ((BO && BO->getOpcode() != Instruction::Add) || 737 (!BO && !isa<GetElementPtrInst>(U))) 738 return false; 739 740 for (auto *UU : U->users()) { 741 PHINode *PN = dyn_cast<PHINode>(UU); 742 if (PN && PN == IV) 743 return true; 744 } 745 return false; 746 } 747 748 bool LoopReroll::DAGRootTracker:: 749 collectPossibleRoots(Instruction *Base, std::map<int64_t,Instruction*> &Roots) { 750 SmallInstructionVector BaseUsers; 751 752 for (auto *I : Base->users()) { 753 ConstantInt *CI = nullptr; 754 755 if (isLoopIncrement(I, IV)) { 756 LoopIncs.push_back(cast<Instruction>(I)); 757 continue; 758 } 759 760 // The root nodes must be either GEPs, ORs or ADDs. 761 if (auto *BO = dyn_cast<BinaryOperator>(I)) { 762 if (BO->getOpcode() == Instruction::Add || 763 BO->getOpcode() == Instruction::Or) 764 CI = dyn_cast<ConstantInt>(BO->getOperand(1)); 765 } else if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) { 766 Value *LastOperand = GEP->getOperand(GEP->getNumOperands()-1); 767 CI = dyn_cast<ConstantInt>(LastOperand); 768 } 769 770 if (!CI) { 771 if (Instruction *II = dyn_cast<Instruction>(I)) { 772 BaseUsers.push_back(II); 773 continue; 774 } else { 775 LLVM_DEBUG(dbgs() << "LRR: Aborting due to non-instruction: " << *I 776 << "\n"); 777 return false; 778 } 779 } 780 781 int64_t V = std::abs(CI->getValue().getSExtValue()); 782 if (Roots.find(V) != Roots.end()) 783 // No duplicates, please. 784 return false; 785 786 Roots[V] = cast<Instruction>(I); 787 } 788 789 // Make sure we have at least two roots. 790 if (Roots.empty() || (Roots.size() == 1 && BaseUsers.empty())) 791 return false; 792 793 // If we found non-loop-inc, non-root users of Base, assume they are 794 // for the zeroth root index. This is because "add %a, 0" gets optimized 795 // away. 796 if (BaseUsers.size()) { 797 if (Roots.find(0) != Roots.end()) { 798 LLVM_DEBUG(dbgs() << "LRR: Multiple roots found for base - aborting!\n"); 799 return false; 800 } 801 Roots[0] = Base; 802 } 803 804 // Calculate the number of users of the base, or lowest indexed, iteration. 805 unsigned NumBaseUses = BaseUsers.size(); 806 if (NumBaseUses == 0) 807 NumBaseUses = Roots.begin()->second->getNumUses(); 808 809 // Check that every node has the same number of users. 810 for (auto &KV : Roots) { 811 if (KV.first == 0) 812 continue; 813 if (!KV.second->hasNUses(NumBaseUses)) { 814 LLVM_DEBUG(dbgs() << "LRR: Aborting - Root and Base #users not the same: " 815 << "#Base=" << NumBaseUses 816 << ", #Root=" << KV.second->getNumUses() << "\n"); 817 return false; 818 } 819 } 820 821 return true; 822 } 823 824 void LoopReroll::DAGRootTracker:: 825 findRootsRecursive(Instruction *I, SmallInstructionSet SubsumedInsts) { 826 // Does the user look like it could be part of a root set? 827 // All its users must be simple arithmetic ops. 828 if (I->hasNUsesOrMore(IL_MaxRerollIterations + 1)) 829 return; 830 831 if (I != IV && findRootsBase(I, SubsumedInsts)) 832 return; 833 834 SubsumedInsts.insert(I); 835 836 for (User *V : I->users()) { 837 Instruction *I = cast<Instruction>(V); 838 if (is_contained(LoopIncs, I)) 839 continue; 840 841 if (!isSimpleArithmeticOp(I)) 842 continue; 843 844 // The recursive call makes a copy of SubsumedInsts. 845 findRootsRecursive(I, SubsumedInsts); 846 } 847 } 848 849 bool LoopReroll::DAGRootTracker::validateRootSet(DAGRootSet &DRS) { 850 if (DRS.Roots.empty()) 851 return false; 852 853 // If the value of the base instruction is used outside the loop, we cannot 854 // reroll the loop. Check for other root instructions is unnecessary because 855 // they don't match any base instructions if their values are used outside. 856 if (hasUsesOutsideLoop(DRS.BaseInst, L)) 857 return false; 858 859 // Consider a DAGRootSet with N-1 roots (so N different values including 860 // BaseInst). 861 // Define d = Roots[0] - BaseInst, which should be the same as 862 // Roots[I] - Roots[I-1] for all I in [1..N). 863 // Define D = BaseInst@J - BaseInst@J-1, where "@J" means the value at the 864 // loop iteration J. 865 // 866 // Now, For the loop iterations to be consecutive: 867 // D = d * N 868 const auto *ADR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(DRS.BaseInst)); 869 if (!ADR) 870 return false; 871 872 // Check that the first root is evenly spaced. 873 unsigned N = DRS.Roots.size() + 1; 874 const SCEV *StepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[0]), ADR); 875 if (isa<SCEVCouldNotCompute>(StepSCEV) || StepSCEV->getType()->isPointerTy()) 876 return false; 877 const SCEV *ScaleSCEV = SE->getConstant(StepSCEV->getType(), N); 878 if (ADR->getStepRecurrence(*SE) != SE->getMulExpr(StepSCEV, ScaleSCEV)) 879 return false; 880 881 // Check that the remainling roots are evenly spaced. 882 for (unsigned i = 1; i < N - 1; ++i) { 883 const SCEV *NewStepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[i]), 884 SE->getSCEV(DRS.Roots[i-1])); 885 if (NewStepSCEV != StepSCEV) 886 return false; 887 } 888 889 return true; 890 } 891 892 bool LoopReroll::DAGRootTracker:: 893 findRootsBase(Instruction *IVU, SmallInstructionSet SubsumedInsts) { 894 // The base of a RootSet must be an AddRec, so it can be erased. 895 const auto *IVU_ADR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IVU)); 896 if (!IVU_ADR || IVU_ADR->getLoop() != L) 897 return false; 898 899 std::map<int64_t, Instruction*> V; 900 if (!collectPossibleRoots(IVU, V)) 901 return false; 902 903 // If we didn't get a root for index zero, then IVU must be 904 // subsumed. 905 if (V.find(0) == V.end()) 906 SubsumedInsts.insert(IVU); 907 908 // Partition the vector into monotonically increasing indexes. 909 DAGRootSet DRS; 910 DRS.BaseInst = nullptr; 911 912 SmallVector<DAGRootSet, 16> PotentialRootSets; 913 914 for (auto &KV : V) { 915 if (!DRS.BaseInst) { 916 DRS.BaseInst = KV.second; 917 DRS.SubsumedInsts = SubsumedInsts; 918 } else if (DRS.Roots.empty()) { 919 DRS.Roots.push_back(KV.second); 920 } else if (V.find(KV.first - 1) != V.end()) { 921 DRS.Roots.push_back(KV.second); 922 } else { 923 // Linear sequence terminated. 924 if (!validateRootSet(DRS)) 925 return false; 926 927 // Construct a new DAGRootSet with the next sequence. 928 PotentialRootSets.push_back(DRS); 929 DRS.BaseInst = KV.second; 930 DRS.Roots.clear(); 931 } 932 } 933 934 if (!validateRootSet(DRS)) 935 return false; 936 937 PotentialRootSets.push_back(DRS); 938 939 RootSets.append(PotentialRootSets.begin(), PotentialRootSets.end()); 940 941 return true; 942 } 943 944 bool LoopReroll::DAGRootTracker::findRoots() { 945 Inc = IVToIncMap[IV]; 946 947 assert(RootSets.empty() && "Unclean state!"); 948 if (std::abs(Inc) == 1) { 949 for (auto *IVU : IV->users()) { 950 if (isLoopIncrement(IVU, IV)) 951 LoopIncs.push_back(cast<Instruction>(IVU)); 952 } 953 findRootsRecursive(IV, SmallInstructionSet()); 954 LoopIncs.push_back(IV); 955 } else { 956 if (!findRootsBase(IV, SmallInstructionSet())) 957 return false; 958 } 959 960 // Ensure all sets have the same size. 961 if (RootSets.empty()) { 962 LLVM_DEBUG(dbgs() << "LRR: Aborting because no root sets found!\n"); 963 return false; 964 } 965 for (auto &V : RootSets) { 966 if (V.Roots.empty() || V.Roots.size() != RootSets[0].Roots.size()) { 967 LLVM_DEBUG( 968 dbgs() 969 << "LRR: Aborting because not all root sets have the same size\n"); 970 return false; 971 } 972 } 973 974 Scale = RootSets[0].Roots.size() + 1; 975 976 if (Scale > IL_MaxRerollIterations) { 977 LLVM_DEBUG(dbgs() << "LRR: Aborting - too many iterations found. " 978 << "#Found=" << Scale 979 << ", #Max=" << IL_MaxRerollIterations << "\n"); 980 return false; 981 } 982 983 LLVM_DEBUG(dbgs() << "LRR: Successfully found roots: Scale=" << Scale 984 << "\n"); 985 986 return true; 987 } 988 989 bool LoopReroll::DAGRootTracker::collectUsedInstructions(SmallInstructionSet &PossibleRedSet) { 990 // Populate the MapVector with all instructions in the block, in order first, 991 // so we can iterate over the contents later in perfect order. 992 for (auto &I : *L->getHeader()) { 993 Uses[&I].resize(IL_End); 994 } 995 996 SmallInstructionSet Exclude; 997 for (auto &DRS : RootSets) { 998 Exclude.insert(DRS.Roots.begin(), DRS.Roots.end()); 999 Exclude.insert(DRS.SubsumedInsts.begin(), DRS.SubsumedInsts.end()); 1000 Exclude.insert(DRS.BaseInst); 1001 } 1002 Exclude.insert(LoopIncs.begin(), LoopIncs.end()); 1003 1004 for (auto &DRS : RootSets) { 1005 DenseSet<Instruction*> VBase; 1006 collectInLoopUserSet(DRS.BaseInst, Exclude, PossibleRedSet, VBase); 1007 for (auto *I : VBase) { 1008 Uses[I].set(0); 1009 } 1010 1011 unsigned Idx = 1; 1012 for (auto *Root : DRS.Roots) { 1013 DenseSet<Instruction*> V; 1014 collectInLoopUserSet(Root, Exclude, PossibleRedSet, V); 1015 1016 // While we're here, check the use sets are the same size. 1017 if (V.size() != VBase.size()) { 1018 LLVM_DEBUG(dbgs() << "LRR: Aborting - use sets are different sizes\n"); 1019 return false; 1020 } 1021 1022 for (auto *I : V) { 1023 Uses[I].set(Idx); 1024 } 1025 ++Idx; 1026 } 1027 1028 // Make sure our subsumed instructions are remembered too. 1029 for (auto *I : DRS.SubsumedInsts) { 1030 Uses[I].set(IL_All); 1031 } 1032 } 1033 1034 // Make sure the loop increments are also accounted for. 1035 1036 Exclude.clear(); 1037 for (auto &DRS : RootSets) { 1038 Exclude.insert(DRS.Roots.begin(), DRS.Roots.end()); 1039 Exclude.insert(DRS.SubsumedInsts.begin(), DRS.SubsumedInsts.end()); 1040 Exclude.insert(DRS.BaseInst); 1041 } 1042 1043 DenseSet<Instruction*> V; 1044 collectInLoopUserSet(LoopIncs, Exclude, PossibleRedSet, V); 1045 for (auto *I : V) { 1046 if (I->mayHaveSideEffects()) { 1047 LLVM_DEBUG(dbgs() << "LRR: Aborting - " 1048 << "An instruction which does not belong to any root " 1049 << "sets must not have side effects: " << *I); 1050 return false; 1051 } 1052 Uses[I].set(IL_All); 1053 } 1054 1055 return true; 1056 } 1057 1058 /// Get the next instruction in "In" that is a member of set Val. 1059 /// Start searching from StartI, and do not return anything in Exclude. 1060 /// If StartI is not given, start from In.begin(). 1061 LoopReroll::DAGRootTracker::UsesTy::iterator 1062 LoopReroll::DAGRootTracker::nextInstr(int Val, UsesTy &In, 1063 const SmallInstructionSet &Exclude, 1064 UsesTy::iterator *StartI) { 1065 UsesTy::iterator I = StartI ? *StartI : In.begin(); 1066 while (I != In.end() && (I->second.test(Val) == 0 || 1067 Exclude.contains(I->first))) 1068 ++I; 1069 return I; 1070 } 1071 1072 bool LoopReroll::DAGRootTracker::isBaseInst(Instruction *I) { 1073 for (auto &DRS : RootSets) { 1074 if (DRS.BaseInst == I) 1075 return true; 1076 } 1077 return false; 1078 } 1079 1080 bool LoopReroll::DAGRootTracker::isRootInst(Instruction *I) { 1081 for (auto &DRS : RootSets) { 1082 if (is_contained(DRS.Roots, I)) 1083 return true; 1084 } 1085 return false; 1086 } 1087 1088 /// Return true if instruction I depends on any instruction between 1089 /// Start and End. 1090 bool LoopReroll::DAGRootTracker::instrDependsOn(Instruction *I, 1091 UsesTy::iterator Start, 1092 UsesTy::iterator End) { 1093 for (auto *U : I->users()) { 1094 for (auto It = Start; It != End; ++It) 1095 if (U == It->first) 1096 return true; 1097 } 1098 return false; 1099 } 1100 1101 static bool isIgnorableInst(const Instruction *I) { 1102 if (isa<DbgInfoIntrinsic>(I)) 1103 return true; 1104 const IntrinsicInst* II = dyn_cast<IntrinsicInst>(I); 1105 if (!II) 1106 return false; 1107 switch (II->getIntrinsicID()) { 1108 default: 1109 return false; 1110 case Intrinsic::annotation: 1111 case Intrinsic::ptr_annotation: 1112 case Intrinsic::var_annotation: 1113 // TODO: the following intrinsics may also be allowed: 1114 // lifetime_start, lifetime_end, invariant_start, invariant_end 1115 return true; 1116 } 1117 return false; 1118 } 1119 1120 bool LoopReroll::DAGRootTracker::validate(ReductionTracker &Reductions) { 1121 // We now need to check for equivalence of the use graph of each root with 1122 // that of the primary induction variable (excluding the roots). Our goal 1123 // here is not to solve the full graph isomorphism problem, but rather to 1124 // catch common cases without a lot of work. As a result, we will assume 1125 // that the relative order of the instructions in each unrolled iteration 1126 // is the same (although we will not make an assumption about how the 1127 // different iterations are intermixed). Note that while the order must be 1128 // the same, the instructions may not be in the same basic block. 1129 1130 // An array of just the possible reductions for this scale factor. When we 1131 // collect the set of all users of some root instructions, these reduction 1132 // instructions are treated as 'final' (their uses are not considered). 1133 // This is important because we don't want the root use set to search down 1134 // the reduction chain. 1135 SmallInstructionSet PossibleRedSet; 1136 SmallInstructionSet PossibleRedLastSet; 1137 SmallInstructionSet PossibleRedPHISet; 1138 Reductions.restrictToScale(Scale, PossibleRedSet, 1139 PossibleRedPHISet, PossibleRedLastSet); 1140 1141 // Populate "Uses" with where each instruction is used. 1142 if (!collectUsedInstructions(PossibleRedSet)) 1143 return false; 1144 1145 // Make sure we mark the reduction PHIs as used in all iterations. 1146 for (auto *I : PossibleRedPHISet) { 1147 Uses[I].set(IL_All); 1148 } 1149 1150 // Make sure we mark loop-control-only PHIs as used in all iterations. See 1151 // comment above LoopReroll::isLoopControlIV for more information. 1152 BasicBlock *Header = L->getHeader(); 1153 for (Instruction *LoopControlIV : LoopControlIVs) { 1154 for (auto *U : LoopControlIV->users()) { 1155 Instruction *IVUser = dyn_cast<Instruction>(U); 1156 // IVUser could be loop increment or compare 1157 Uses[IVUser].set(IL_All); 1158 for (auto *UU : IVUser->users()) { 1159 Instruction *UUser = dyn_cast<Instruction>(UU); 1160 // UUser could be compare, PHI or branch 1161 Uses[UUser].set(IL_All); 1162 // Skip SExt 1163 if (isa<SExtInst>(UUser)) { 1164 UUser = dyn_cast<Instruction>(*(UUser->user_begin())); 1165 Uses[UUser].set(IL_All); 1166 } 1167 // Is UUser a compare instruction? 1168 if (UU->hasOneUse()) { 1169 Instruction *BI = dyn_cast<BranchInst>(*UUser->user_begin()); 1170 if (BI == cast<BranchInst>(Header->getTerminator())) 1171 Uses[BI].set(IL_All); 1172 } 1173 } 1174 } 1175 } 1176 1177 // Make sure all instructions in the loop are in one and only one 1178 // set. 1179 for (auto &KV : Uses) { 1180 if (KV.second.count() != 1 && !isIgnorableInst(KV.first)) { 1181 LLVM_DEBUG( 1182 dbgs() << "LRR: Aborting - instruction is not used in 1 iteration: " 1183 << *KV.first << " (#uses=" << KV.second.count() << ")\n"); 1184 return false; 1185 } 1186 } 1187 1188 LLVM_DEBUG(for (auto &KV 1189 : Uses) { 1190 dbgs() << "LRR: " << KV.second.find_first() << "\t" << *KV.first << "\n"; 1191 }); 1192 1193 BatchAAResults BatchAA(*AA); 1194 for (unsigned Iter = 1; Iter < Scale; ++Iter) { 1195 // In addition to regular aliasing information, we need to look for 1196 // instructions from later (future) iterations that have side effects 1197 // preventing us from reordering them past other instructions with side 1198 // effects. 1199 bool FutureSideEffects = false; 1200 AliasSetTracker AST(BatchAA); 1201 // The map between instructions in f(%iv.(i+1)) and f(%iv). 1202 DenseMap<Value *, Value *> BaseMap; 1203 1204 // Compare iteration Iter to the base. 1205 SmallInstructionSet Visited; 1206 auto BaseIt = nextInstr(0, Uses, Visited); 1207 auto RootIt = nextInstr(Iter, Uses, Visited); 1208 auto LastRootIt = Uses.begin(); 1209 1210 while (BaseIt != Uses.end() && RootIt != Uses.end()) { 1211 Instruction *BaseInst = BaseIt->first; 1212 Instruction *RootInst = RootIt->first; 1213 1214 // Skip over the IV or root instructions; only match their users. 1215 bool Continue = false; 1216 if (isBaseInst(BaseInst)) { 1217 Visited.insert(BaseInst); 1218 BaseIt = nextInstr(0, Uses, Visited); 1219 Continue = true; 1220 } 1221 if (isRootInst(RootInst)) { 1222 LastRootIt = RootIt; 1223 Visited.insert(RootInst); 1224 RootIt = nextInstr(Iter, Uses, Visited); 1225 Continue = true; 1226 } 1227 if (Continue) continue; 1228 1229 if (!BaseInst->isSameOperationAs(RootInst)) { 1230 // Last chance saloon. We don't try and solve the full isomorphism 1231 // problem, but try and at least catch the case where two instructions 1232 // *of different types* are round the wrong way. We won't be able to 1233 // efficiently tell, given two ADD instructions, which way around we 1234 // should match them, but given an ADD and a SUB, we can at least infer 1235 // which one is which. 1236 // 1237 // This should allow us to deal with a greater subset of the isomorphism 1238 // problem. It does however change a linear algorithm into a quadratic 1239 // one, so limit the number of probes we do. 1240 auto TryIt = RootIt; 1241 unsigned N = NumToleratedFailedMatches; 1242 while (TryIt != Uses.end() && 1243 !BaseInst->isSameOperationAs(TryIt->first) && 1244 N--) { 1245 ++TryIt; 1246 TryIt = nextInstr(Iter, Uses, Visited, &TryIt); 1247 } 1248 1249 if (TryIt == Uses.end() || TryIt == RootIt || 1250 instrDependsOn(TryIt->first, RootIt, TryIt)) { 1251 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " 1252 << *BaseInst << " vs. " << *RootInst << "\n"); 1253 return false; 1254 } 1255 1256 RootIt = TryIt; 1257 RootInst = TryIt->first; 1258 } 1259 1260 // All instructions between the last root and this root 1261 // may belong to some other iteration. If they belong to a 1262 // future iteration, then they're dangerous to alias with. 1263 // 1264 // Note that because we allow a limited amount of flexibility in the order 1265 // that we visit nodes, LastRootIt might be *before* RootIt, in which 1266 // case we've already checked this set of instructions so we shouldn't 1267 // do anything. 1268 for (; LastRootIt < RootIt; ++LastRootIt) { 1269 Instruction *I = LastRootIt->first; 1270 if (LastRootIt->second.find_first() < (int)Iter) 1271 continue; 1272 if (I->mayWriteToMemory()) 1273 AST.add(I); 1274 // Note: This is specifically guarded by a check on isa<PHINode>, 1275 // which while a valid (somewhat arbitrary) micro-optimization, is 1276 // needed because otherwise isSafeToSpeculativelyExecute returns 1277 // false on PHI nodes. 1278 if (!isa<PHINode>(I) && !isUnorderedLoadStore(I) && 1279 !isSafeToSpeculativelyExecute(I)) 1280 // Intervening instructions cause side effects. 1281 FutureSideEffects = true; 1282 } 1283 1284 // Make sure that this instruction, which is in the use set of this 1285 // root instruction, does not also belong to the base set or the set of 1286 // some other root instruction. 1287 if (RootIt->second.count() > 1) { 1288 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst 1289 << " vs. " << *RootInst << " (prev. case overlap)\n"); 1290 return false; 1291 } 1292 1293 // Make sure that we don't alias with any instruction in the alias set 1294 // tracker. If we do, then we depend on a future iteration, and we 1295 // can't reroll. 1296 if (RootInst->mayReadFromMemory()) { 1297 for (auto &K : AST) { 1298 if (isModOrRefSet(K.aliasesUnknownInst(RootInst, BatchAA))) { 1299 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " 1300 << *BaseInst << " vs. " << *RootInst 1301 << " (depends on future store)\n"); 1302 return false; 1303 } 1304 } 1305 } 1306 1307 // If we've past an instruction from a future iteration that may have 1308 // side effects, and this instruction might also, then we can't reorder 1309 // them, and this matching fails. As an exception, we allow the alias 1310 // set tracker to handle regular (unordered) load/store dependencies. 1311 if (FutureSideEffects && ((!isUnorderedLoadStore(BaseInst) && 1312 !isSafeToSpeculativelyExecute(BaseInst)) || 1313 (!isUnorderedLoadStore(RootInst) && 1314 !isSafeToSpeculativelyExecute(RootInst)))) { 1315 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst 1316 << " vs. " << *RootInst 1317 << " (side effects prevent reordering)\n"); 1318 return false; 1319 } 1320 1321 // For instructions that are part of a reduction, if the operation is 1322 // associative, then don't bother matching the operands (because we 1323 // already know that the instructions are isomorphic, and the order 1324 // within the iteration does not matter). For non-associative reductions, 1325 // we do need to match the operands, because we need to reject 1326 // out-of-order instructions within an iteration! 1327 // For example (assume floating-point addition), we need to reject this: 1328 // x += a[i]; x += b[i]; 1329 // x += a[i+1]; x += b[i+1]; 1330 // x += b[i+2]; x += a[i+2]; 1331 bool InReduction = Reductions.isPairInSame(BaseInst, RootInst); 1332 1333 if (!(InReduction && BaseInst->isAssociative())) { 1334 bool Swapped = false, SomeOpMatched = false; 1335 for (unsigned j = 0; j < BaseInst->getNumOperands(); ++j) { 1336 Value *Op2 = RootInst->getOperand(j); 1337 1338 // If this is part of a reduction (and the operation is not 1339 // associatve), then we match all operands, but not those that are 1340 // part of the reduction. 1341 if (InReduction) 1342 if (Instruction *Op2I = dyn_cast<Instruction>(Op2)) 1343 if (Reductions.isPairInSame(RootInst, Op2I)) 1344 continue; 1345 1346 DenseMap<Value *, Value *>::iterator BMI = BaseMap.find(Op2); 1347 if (BMI != BaseMap.end()) { 1348 Op2 = BMI->second; 1349 } else { 1350 for (auto &DRS : RootSets) { 1351 if (DRS.Roots[Iter-1] == (Instruction*) Op2) { 1352 Op2 = DRS.BaseInst; 1353 break; 1354 } 1355 } 1356 } 1357 1358 if (BaseInst->getOperand(Swapped ? unsigned(!j) : j) != Op2) { 1359 // If we've not already decided to swap the matched operands, and 1360 // we've not already matched our first operand (note that we could 1361 // have skipped matching the first operand because it is part of a 1362 // reduction above), and the instruction is commutative, then try 1363 // the swapped match. 1364 if (!Swapped && BaseInst->isCommutative() && !SomeOpMatched && 1365 BaseInst->getOperand(!j) == Op2) { 1366 Swapped = true; 1367 } else { 1368 LLVM_DEBUG(dbgs() 1369 << "LRR: iteration root match failed at " << *BaseInst 1370 << " vs. " << *RootInst << " (operand " << j << ")\n"); 1371 return false; 1372 } 1373 } 1374 1375 SomeOpMatched = true; 1376 } 1377 } 1378 1379 if ((!PossibleRedLastSet.count(BaseInst) && 1380 hasUsesOutsideLoop(BaseInst, L)) || 1381 (!PossibleRedLastSet.count(RootInst) && 1382 hasUsesOutsideLoop(RootInst, L))) { 1383 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst 1384 << " vs. " << *RootInst << " (uses outside loop)\n"); 1385 return false; 1386 } 1387 1388 Reductions.recordPair(BaseInst, RootInst, Iter); 1389 BaseMap.insert(std::make_pair(RootInst, BaseInst)); 1390 1391 LastRootIt = RootIt; 1392 Visited.insert(BaseInst); 1393 Visited.insert(RootInst); 1394 BaseIt = nextInstr(0, Uses, Visited); 1395 RootIt = nextInstr(Iter, Uses, Visited); 1396 } 1397 assert(BaseIt == Uses.end() && RootIt == Uses.end() && 1398 "Mismatched set sizes!"); 1399 } 1400 1401 LLVM_DEBUG(dbgs() << "LRR: Matched all iteration increments for " << *IV 1402 << "\n"); 1403 1404 return true; 1405 } 1406 1407 void LoopReroll::DAGRootTracker::replace(const SCEV *BackedgeTakenCount) { 1408 BasicBlock *Header = L->getHeader(); 1409 1410 // Compute the start and increment for each BaseInst before we start erasing 1411 // instructions. 1412 SmallVector<const SCEV *, 8> StartExprs; 1413 SmallVector<const SCEV *, 8> IncrExprs; 1414 for (auto &DRS : RootSets) { 1415 const SCEVAddRecExpr *IVSCEV = 1416 cast<SCEVAddRecExpr>(SE->getSCEV(DRS.BaseInst)); 1417 StartExprs.push_back(IVSCEV->getStart()); 1418 IncrExprs.push_back(SE->getMinusSCEV(SE->getSCEV(DRS.Roots[0]), IVSCEV)); 1419 } 1420 1421 // Remove instructions associated with non-base iterations. 1422 for (Instruction &Inst : llvm::make_early_inc_range(llvm::reverse(*Header))) { 1423 unsigned I = Uses[&Inst].find_first(); 1424 if (I > 0 && I < IL_All) { 1425 LLVM_DEBUG(dbgs() << "LRR: removing: " << Inst << "\n"); 1426 Inst.eraseFromParent(); 1427 } 1428 } 1429 1430 // Rewrite each BaseInst using SCEV. 1431 for (size_t i = 0, e = RootSets.size(); i != e; ++i) 1432 // Insert the new induction variable. 1433 replaceIV(RootSets[i], StartExprs[i], IncrExprs[i]); 1434 1435 { // Limit the lifetime of SCEVExpander. 1436 BranchInst *BI = cast<BranchInst>(Header->getTerminator()); 1437 const DataLayout &DL = Header->getModule()->getDataLayout(); 1438 SCEVExpander Expander(*SE, DL, "reroll"); 1439 auto Zero = SE->getZero(BackedgeTakenCount->getType()); 1440 auto One = SE->getOne(BackedgeTakenCount->getType()); 1441 auto NewIVSCEV = SE->getAddRecExpr(Zero, One, L, SCEV::FlagAnyWrap); 1442 Value *NewIV = 1443 Expander.expandCodeFor(NewIVSCEV, BackedgeTakenCount->getType(), 1444 Header->getFirstNonPHIOrDbg()); 1445 // FIXME: This arithmetic can overflow. 1446 auto TripCount = SE->getAddExpr(BackedgeTakenCount, One); 1447 auto ScaledTripCount = SE->getMulExpr( 1448 TripCount, SE->getConstant(BackedgeTakenCount->getType(), Scale)); 1449 auto ScaledBECount = SE->getMinusSCEV(ScaledTripCount, One); 1450 Value *TakenCount = 1451 Expander.expandCodeFor(ScaledBECount, BackedgeTakenCount->getType(), 1452 Header->getFirstNonPHIOrDbg()); 1453 Value *Cond = 1454 new ICmpInst(BI, CmpInst::ICMP_EQ, NewIV, TakenCount, "exitcond"); 1455 BI->setCondition(Cond); 1456 1457 if (BI->getSuccessor(1) != Header) 1458 BI->swapSuccessors(); 1459 } 1460 1461 SimplifyInstructionsInBlock(Header, TLI); 1462 DeleteDeadPHIs(Header, TLI); 1463 } 1464 1465 void LoopReroll::DAGRootTracker::replaceIV(DAGRootSet &DRS, 1466 const SCEV *Start, 1467 const SCEV *IncrExpr) { 1468 BasicBlock *Header = L->getHeader(); 1469 Instruction *Inst = DRS.BaseInst; 1470 1471 const SCEV *NewIVSCEV = 1472 SE->getAddRecExpr(Start, IncrExpr, L, SCEV::FlagAnyWrap); 1473 1474 { // Limit the lifetime of SCEVExpander. 1475 const DataLayout &DL = Header->getModule()->getDataLayout(); 1476 SCEVExpander Expander(*SE, DL, "reroll"); 1477 Value *NewIV = Expander.expandCodeFor(NewIVSCEV, Inst->getType(), 1478 Header->getFirstNonPHIOrDbg()); 1479 1480 for (auto &KV : Uses) 1481 if (KV.second.find_first() == 0) 1482 KV.first->replaceUsesOfWith(Inst, NewIV); 1483 } 1484 } 1485 1486 // Validate the selected reductions. All iterations must have an isomorphic 1487 // part of the reduction chain and, for non-associative reductions, the chain 1488 // entries must appear in order. 1489 bool LoopReroll::ReductionTracker::validateSelected() { 1490 // For a non-associative reduction, the chain entries must appear in order. 1491 for (int i : Reds) { 1492 int PrevIter = 0, BaseCount = 0, Count = 0; 1493 for (Instruction *J : PossibleReds[i]) { 1494 // Note that all instructions in the chain must have been found because 1495 // all instructions in the function must have been assigned to some 1496 // iteration. 1497 int Iter = PossibleRedIter[J]; 1498 if (Iter != PrevIter && Iter != PrevIter + 1 && 1499 !PossibleReds[i].getReducedValue()->isAssociative()) { 1500 LLVM_DEBUG(dbgs() << "LRR: Out-of-order non-associative reduction: " 1501 << J << "\n"); 1502 return false; 1503 } 1504 1505 if (Iter != PrevIter) { 1506 if (Count != BaseCount) { 1507 LLVM_DEBUG(dbgs() 1508 << "LRR: Iteration " << PrevIter << " reduction use count " 1509 << Count << " is not equal to the base use count " 1510 << BaseCount << "\n"); 1511 return false; 1512 } 1513 1514 Count = 0; 1515 } 1516 1517 ++Count; 1518 if (Iter == 0) 1519 ++BaseCount; 1520 1521 PrevIter = Iter; 1522 } 1523 } 1524 1525 return true; 1526 } 1527 1528 // For all selected reductions, remove all parts except those in the first 1529 // iteration (and the PHI). Replace outside uses of the reduced value with uses 1530 // of the first-iteration reduced value (in other words, reroll the selected 1531 // reductions). 1532 void LoopReroll::ReductionTracker::replaceSelected() { 1533 // Fixup reductions to refer to the last instruction associated with the 1534 // first iteration (not the last). 1535 for (int i : Reds) { 1536 int j = 0; 1537 for (int e = PossibleReds[i].size(); j != e; ++j) 1538 if (PossibleRedIter[PossibleReds[i][j]] != 0) { 1539 --j; 1540 break; 1541 } 1542 1543 // Replace users with the new end-of-chain value. 1544 SmallInstructionVector Users; 1545 for (User *U : PossibleReds[i].getReducedValue()->users()) { 1546 Users.push_back(cast<Instruction>(U)); 1547 } 1548 1549 for (Instruction *User : Users) 1550 User->replaceUsesOfWith(PossibleReds[i].getReducedValue(), 1551 PossibleReds[i][j]); 1552 } 1553 } 1554 1555 // Reroll the provided loop with respect to the provided induction variable. 1556 // Generally, we're looking for a loop like this: 1557 // 1558 // %iv = phi [ (preheader, ...), (body, %iv.next) ] 1559 // f(%iv) 1560 // %iv.1 = add %iv, 1 <-- a root increment 1561 // f(%iv.1) 1562 // %iv.2 = add %iv, 2 <-- a root increment 1563 // f(%iv.2) 1564 // %iv.scale_m_1 = add %iv, scale-1 <-- a root increment 1565 // f(%iv.scale_m_1) 1566 // ... 1567 // %iv.next = add %iv, scale 1568 // %cmp = icmp(%iv, ...) 1569 // br %cmp, header, exit 1570 // 1571 // Notably, we do not require that f(%iv), f(%iv.1), etc. be isolated groups of 1572 // instructions. In other words, the instructions in f(%iv), f(%iv.1), etc. can 1573 // be intermixed with eachother. The restriction imposed by this algorithm is 1574 // that the relative order of the isomorphic instructions in f(%iv), f(%iv.1), 1575 // etc. be the same. 1576 // 1577 // First, we collect the use set of %iv, excluding the other increment roots. 1578 // This gives us f(%iv). Then we iterate over the loop instructions (scale-1) 1579 // times, having collected the use set of f(%iv.(i+1)), during which we: 1580 // - Ensure that the next unmatched instruction in f(%iv) is isomorphic to 1581 // the next unmatched instruction in f(%iv.(i+1)). 1582 // - Ensure that both matched instructions don't have any external users 1583 // (with the exception of last-in-chain reduction instructions). 1584 // - Track the (aliasing) write set, and other side effects, of all 1585 // instructions that belong to future iterations that come before the matched 1586 // instructions. If the matched instructions read from that write set, then 1587 // f(%iv) or f(%iv.(i+1)) has some dependency on instructions in 1588 // f(%iv.(j+1)) for some j > i, and we cannot reroll the loop. Similarly, 1589 // if any of these future instructions had side effects (could not be 1590 // speculatively executed), and so do the matched instructions, when we 1591 // cannot reorder those side-effect-producing instructions, and rerolling 1592 // fails. 1593 // 1594 // Finally, we make sure that all loop instructions are either loop increment 1595 // roots, belong to simple latch code, parts of validated reductions, part of 1596 // f(%iv) or part of some f(%iv.i). If all of that is true (and all reductions 1597 // have been validated), then we reroll the loop. 1598 bool LoopReroll::reroll(Instruction *IV, Loop *L, BasicBlock *Header, 1599 const SCEV *BackedgeTakenCount, 1600 ReductionTracker &Reductions) { 1601 DAGRootTracker DAGRoots(this, L, IV, SE, AA, TLI, DT, LI, PreserveLCSSA, 1602 IVToIncMap, LoopControlIVs); 1603 1604 if (!DAGRoots.findRoots()) 1605 return false; 1606 LLVM_DEBUG(dbgs() << "LRR: Found all root induction increments for: " << *IV 1607 << "\n"); 1608 1609 if (!DAGRoots.validate(Reductions)) 1610 return false; 1611 if (!Reductions.validateSelected()) 1612 return false; 1613 // At this point, we've validated the rerolling, and we're committed to 1614 // making changes! 1615 1616 Reductions.replaceSelected(); 1617 DAGRoots.replace(BackedgeTakenCount); 1618 1619 ++NumRerolledLoops; 1620 return true; 1621 } 1622 1623 bool LoopReroll::runOnLoop(Loop *L) { 1624 BasicBlock *Header = L->getHeader(); 1625 LLVM_DEBUG(dbgs() << "LRR: F[" << Header->getParent()->getName() << "] Loop %" 1626 << Header->getName() << " (" << L->getNumBlocks() 1627 << " block(s))\n"); 1628 1629 // For now, we'll handle only single BB loops. 1630 if (L->getNumBlocks() > 1) 1631 return false; 1632 1633 if (!SE->hasLoopInvariantBackedgeTakenCount(L)) 1634 return false; 1635 1636 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 1637 LLVM_DEBUG(dbgs() << "\n Before Reroll:\n" << *(L->getHeader()) << "\n"); 1638 LLVM_DEBUG(dbgs() << "LRR: backedge-taken count = " << *BackedgeTakenCount 1639 << "\n"); 1640 1641 // First, we need to find the induction variable with respect to which we can 1642 // reroll (there may be several possible options). 1643 SmallInstructionVector PossibleIVs; 1644 IVToIncMap.clear(); 1645 LoopControlIVs.clear(); 1646 collectPossibleIVs(L, PossibleIVs); 1647 1648 if (PossibleIVs.empty()) { 1649 LLVM_DEBUG(dbgs() << "LRR: No possible IVs found\n"); 1650 return false; 1651 } 1652 1653 ReductionTracker Reductions; 1654 collectPossibleReductions(L, Reductions); 1655 bool Changed = false; 1656 1657 // For each possible IV, collect the associated possible set of 'root' nodes 1658 // (i+1, i+2, etc.). 1659 for (Instruction *PossibleIV : PossibleIVs) 1660 if (reroll(PossibleIV, L, Header, BackedgeTakenCount, Reductions)) { 1661 Changed = true; 1662 break; 1663 } 1664 LLVM_DEBUG(dbgs() << "\n After Reroll:\n" << *(L->getHeader()) << "\n"); 1665 1666 // Trip count of L has changed so SE must be re-evaluated. 1667 if (Changed) 1668 SE->forgetLoop(L); 1669 1670 return Changed; 1671 } 1672 1673 PreservedAnalyses LoopRerollPass::run(Loop &L, LoopAnalysisManager &AM, 1674 LoopStandardAnalysisResults &AR, 1675 LPMUpdater &U) { 1676 return LoopReroll(&AR.AA, &AR.LI, &AR.SE, &AR.TLI, &AR.DT, true).runOnLoop(&L) 1677 ? getLoopPassPreservedAnalyses() 1678 : PreservedAnalyses::all(); 1679 } 1680