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/ScalarEvolutionExpander.h" 28#include "llvm/Analysis/ScalarEvolutionExpressions.h" 29#include "llvm/Analysis/TargetLibraryInfo.h" 30#include "llvm/Analysis/ValueTracking.h" 31#include "llvm/IR/BasicBlock.h" 32#include "llvm/IR/Constants.h" 33#include "llvm/IR/DataLayout.h" 34#include "llvm/IR/DerivedTypes.h" 35#include "llvm/IR/Dominators.h" 36#include "llvm/IR/IRBuilder.h" 37#include "llvm/IR/InstrTypes.h" 38#include "llvm/IR/Instruction.h" 39#include "llvm/IR/Instructions.h" 40#include "llvm/IR/IntrinsicInst.h" 41#include "llvm/IR/Intrinsics.h" 42#include "llvm/IR/Module.h" 43#include "llvm/IR/Type.h" 44#include "llvm/IR/Use.h" 45#include "llvm/IR/User.h" 46#include "llvm/IR/Value.h" 47#include "llvm/InitializePasses.h" 48#include "llvm/Pass.h" 49#include "llvm/Support/Casting.h" 50#include "llvm/Support/CommandLine.h" 51#include "llvm/Support/Debug.h" 52#include "llvm/Support/raw_ostream.h" 53#include "llvm/Transforms/Scalar.h" 54#include "llvm/Transforms/Utils.h" 55#include "llvm/Transforms/Utils/BasicBlockUtils.h" 56#include "llvm/Transforms/Utils/Local.h" 57#include "llvm/Transforms/Utils/LoopUtils.h" 58#include <cassert> 59#include <cstddef> 60#include <cstdint> 61#include <cstdlib> 62#include <iterator> 63#include <map> 64#include <utility> 65 66using namespace llvm; 67 68#define DEBUG_TYPE "loop-reroll" 69 70STATISTIC(NumRerolledLoops, "Number of rerolled loops"); 71 72static cl::opt<unsigned> 73NumToleratedFailedMatches("reroll-num-tolerated-failed-matches", cl::init(400), 74 cl::Hidden, 75 cl::desc("The maximum number of failures to tolerate" 76 " during fuzzy matching. (default: 400)")); 77 78// This loop re-rolling transformation aims to transform loops like this: 79// 80// int foo(int a); 81// void bar(int *x) { 82// for (int i = 0; i < 500; i += 3) { 83// foo(i); 84// foo(i+1); 85// foo(i+2); 86// } 87// } 88// 89// into a loop like this: 90// 91// void bar(int *x) { 92// for (int i = 0; i < 500; ++i) 93// foo(i); 94// } 95// 96// It does this by looking for loops that, besides the latch code, are composed 97// of isomorphic DAGs of instructions, with each DAG rooted at some increment 98// to the induction variable, and where each DAG is isomorphic to the DAG 99// rooted at the induction variable (excepting the sub-DAGs which root the 100// other induction-variable increments). In other words, we're looking for loop 101// bodies of the form: 102// 103// %iv = phi [ (preheader, ...), (body, %iv.next) ] 104// f(%iv) 105// %iv.1 = add %iv, 1 <-- a root increment 106// f(%iv.1) 107// %iv.2 = add %iv, 2 <-- a root increment 108// f(%iv.2) 109// %iv.scale_m_1 = add %iv, scale-1 <-- a root increment 110// f(%iv.scale_m_1) 111// ... 112// %iv.next = add %iv, scale 113// %cmp = icmp(%iv, ...) 114// br %cmp, header, exit 115// 116// where each f(i) is a set of instructions that, collectively, are a function 117// only of i (and other loop-invariant values). 118// 119// As a special case, we can also reroll loops like this: 120// 121// int foo(int); 122// void bar(int *x) { 123// for (int i = 0; i < 500; ++i) { 124// x[3*i] = foo(0); 125// x[3*i+1] = foo(0); 126// x[3*i+2] = foo(0); 127// } 128// } 129// 130// into this: 131// 132// void bar(int *x) { 133// for (int i = 0; i < 1500; ++i) 134// x[i] = foo(0); 135// } 136// 137// in which case, we're looking for inputs like this: 138// 139// %iv = phi [ (preheader, ...), (body, %iv.next) ] 140// %scaled.iv = mul %iv, scale 141// f(%scaled.iv) 142// %scaled.iv.1 = add %scaled.iv, 1 143// f(%scaled.iv.1) 144// %scaled.iv.2 = add %scaled.iv, 2 145// f(%scaled.iv.2) 146// %scaled.iv.scale_m_1 = add %scaled.iv, scale-1 147// f(%scaled.iv.scale_m_1) 148// ... 149// %iv.next = add %iv, 1 150// %cmp = icmp(%iv, ...) 151// br %cmp, header, exit 152 153namespace { 154 155 enum IterationLimits { 156 /// The maximum number of iterations that we'll try and reroll. 157 IL_MaxRerollIterations = 32, 158 /// The bitvector index used by loop induction variables and other 159 /// instructions that belong to all iterations. 160 IL_All, 161 IL_End 162 }; 163 164 class LoopReroll : public LoopPass { 165 public: 166 static char ID; // Pass ID, replacement for typeid 167 168 LoopReroll() : LoopPass(ID) { 169 initializeLoopRerollPass(*PassRegistry::getPassRegistry()); 170 } 171 172 bool runOnLoop(Loop *L, LPPassManager &LPM) override; 173 174 void getAnalysisUsage(AnalysisUsage &AU) const override { 175 AU.addRequired<TargetLibraryInfoWrapperPass>(); 176 getLoopAnalysisUsage(AU); 177 } 178 179 protected: 180 AliasAnalysis *AA; 181 LoopInfo *LI; 182 ScalarEvolution *SE; 183 TargetLibraryInfo *TLI; 184 DominatorTree *DT; 185 bool PreserveLCSSA; 186 187 using SmallInstructionVector = SmallVector<Instruction *, 16>; 188 using SmallInstructionSet = SmallPtrSet<Instruction *, 16>; 189 190 // Map between induction variable and its increment 191 DenseMap<Instruction *, int64_t> IVToIncMap; 192 193 // For loop with multiple induction variable, remember the one used only to 194 // control the loop. 195 Instruction *LoopControlIV; 196 197 // A chain of isomorphic instructions, identified by a single-use PHI 198 // representing a reduction. Only the last value may be used outside the 199 // loop. 200 struct SimpleLoopReduction { 201 SimpleLoopReduction(Instruction *P, Loop *L) : Instructions(1, P) { 202 assert(isa<PHINode>(P) && "First reduction instruction must be a PHI"); 203 add(L); 204 } 205 206 bool valid() const { 207 return Valid; 208 } 209 210 Instruction *getPHI() const { 211 assert(Valid && "Using invalid reduction"); 212 return Instructions.front(); 213 } 214 215 Instruction *getReducedValue() const { 216 assert(Valid && "Using invalid reduction"); 217 return Instructions.back(); 218 } 219 220 Instruction *get(size_t i) const { 221 assert(Valid && "Using invalid reduction"); 222 return Instructions[i+1]; 223 } 224 225 Instruction *operator [] (size_t i) const { return get(i); } 226 227 // The size, ignoring the initial PHI. 228 size_t size() const { 229 assert(Valid && "Using invalid reduction"); 230 return Instructions.size()-1; 231 } 232 233 using iterator = SmallInstructionVector::iterator; 234 using const_iterator = SmallInstructionVector::const_iterator; 235 236 iterator begin() { 237 assert(Valid && "Using invalid reduction"); 238 return std::next(Instructions.begin()); 239 } 240 241 const_iterator begin() const { 242 assert(Valid && "Using invalid reduction"); 243 return std::next(Instructions.begin()); 244 } 245 246 iterator end() { return Instructions.end(); } 247 const_iterator end() const { return Instructions.end(); } 248 249 protected: 250 bool Valid = false; 251 SmallInstructionVector Instructions; 252 253 void add(Loop *L); 254 }; 255 256 // The set of all reductions, and state tracking of possible reductions 257 // during loop instruction processing. 258 struct ReductionTracker { 259 using SmallReductionVector = SmallVector<SimpleLoopReduction, 16>; 260 261 // Add a new possible reduction. 262 void addSLR(SimpleLoopReduction &SLR) { PossibleReds.push_back(SLR); } 263 264 // Setup to track possible reductions corresponding to the provided 265 // rerolling scale. Only reductions with a number of non-PHI instructions 266 // that is divisible by the scale are considered. Three instructions sets 267 // are filled in: 268 // - A set of all possible instructions in eligible reductions. 269 // - A set of all PHIs in eligible reductions 270 // - A set of all reduced values (last instructions) in eligible 271 // reductions. 272 void restrictToScale(uint64_t Scale, 273 SmallInstructionSet &PossibleRedSet, 274 SmallInstructionSet &PossibleRedPHISet, 275 SmallInstructionSet &PossibleRedLastSet) { 276 PossibleRedIdx.clear(); 277 PossibleRedIter.clear(); 278 Reds.clear(); 279 280 for (unsigned i = 0, e = PossibleReds.size(); i != e; ++i) 281 if (PossibleReds[i].size() % Scale == 0) { 282 PossibleRedLastSet.insert(PossibleReds[i].getReducedValue()); 283 PossibleRedPHISet.insert(PossibleReds[i].getPHI()); 284 285 PossibleRedSet.insert(PossibleReds[i].getPHI()); 286 PossibleRedIdx[PossibleReds[i].getPHI()] = i; 287 for (Instruction *J : PossibleReds[i]) { 288 PossibleRedSet.insert(J); 289 PossibleRedIdx[J] = i; 290 } 291 } 292 } 293 294 // The functions below are used while processing the loop instructions. 295 296 // Are the two instructions both from reductions, and furthermore, from 297 // the same reduction? 298 bool isPairInSame(Instruction *J1, Instruction *J2) { 299 DenseMap<Instruction *, int>::iterator J1I = PossibleRedIdx.find(J1); 300 if (J1I != PossibleRedIdx.end()) { 301 DenseMap<Instruction *, int>::iterator J2I = PossibleRedIdx.find(J2); 302 if (J2I != PossibleRedIdx.end() && J1I->second == J2I->second) 303 return true; 304 } 305 306 return false; 307 } 308 309 // The two provided instructions, the first from the base iteration, and 310 // the second from iteration i, form a matched pair. If these are part of 311 // a reduction, record that fact. 312 void recordPair(Instruction *J1, Instruction *J2, unsigned i) { 313 if (PossibleRedIdx.count(J1)) { 314 assert(PossibleRedIdx.count(J2) && 315 "Recording reduction vs. non-reduction instruction?"); 316 317 PossibleRedIter[J1] = 0; 318 PossibleRedIter[J2] = i; 319 320 int Idx = PossibleRedIdx[J1]; 321 assert(Idx == PossibleRedIdx[J2] && 322 "Recording pair from different reductions?"); 323 Reds.insert(Idx); 324 } 325 } 326 327 // The functions below can be called after we've finished processing all 328 // instructions in the loop, and we know which reductions were selected. 329 330 bool validateSelected(); 331 void replaceSelected(); 332 333 protected: 334 // The vector of all possible reductions (for any scale). 335 SmallReductionVector PossibleReds; 336 337 DenseMap<Instruction *, int> PossibleRedIdx; 338 DenseMap<Instruction *, int> PossibleRedIter; 339 DenseSet<int> Reds; 340 }; 341 342 // A DAGRootSet models an induction variable being used in a rerollable 343 // loop. For example, 344 // 345 // x[i*3+0] = y1 346 // x[i*3+1] = y2 347 // x[i*3+2] = y3 348 // 349 // Base instruction -> i*3 350 // +---+----+ 351 // / | \ 352 // ST[y1] +1 +2 <-- Roots 353 // | | 354 // ST[y2] ST[y3] 355 // 356 // There may be multiple DAGRoots, for example: 357 // 358 // x[i*2+0] = ... (1) 359 // x[i*2+1] = ... (1) 360 // x[i*2+4] = ... (2) 361 // x[i*2+5] = ... (2) 362 // x[(i+1234)*2+5678] = ... (3) 363 // x[(i+1234)*2+5679] = ... (3) 364 // 365 // The loop will be rerolled by adding a new loop induction variable, 366 // one for the Base instruction in each DAGRootSet. 367 // 368 struct DAGRootSet { 369 Instruction *BaseInst; 370 SmallInstructionVector Roots; 371 372 // The instructions between IV and BaseInst (but not including BaseInst). 373 SmallInstructionSet SubsumedInsts; 374 }; 375 376 // The set of all DAG roots, and state tracking of all roots 377 // for a particular induction variable. 378 struct DAGRootTracker { 379 DAGRootTracker(LoopReroll *Parent, Loop *L, Instruction *IV, 380 ScalarEvolution *SE, AliasAnalysis *AA, 381 TargetLibraryInfo *TLI, DominatorTree *DT, LoopInfo *LI, 382 bool PreserveLCSSA, 383 DenseMap<Instruction *, int64_t> &IncrMap, 384 Instruction *LoopCtrlIV) 385 : Parent(Parent), L(L), SE(SE), AA(AA), TLI(TLI), DT(DT), LI(LI), 386 PreserveLCSSA(PreserveLCSSA), IV(IV), IVToIncMap(IncrMap), 387 LoopControlIV(LoopCtrlIV) {} 388 389 /// Stage 1: Find all the DAG roots for the induction variable. 390 bool findRoots(); 391 392 /// Stage 2: Validate if the found roots are valid. 393 bool validate(ReductionTracker &Reductions); 394 395 /// Stage 3: Assuming validate() returned true, perform the 396 /// replacement. 397 /// @param BackedgeTakenCount The backedge-taken count of L. 398 void replace(const SCEV *BackedgeTakenCount); 399 400 protected: 401 using UsesTy = MapVector<Instruction *, BitVector>; 402 403 void findRootsRecursive(Instruction *IVU, 404 SmallInstructionSet SubsumedInsts); 405 bool findRootsBase(Instruction *IVU, SmallInstructionSet SubsumedInsts); 406 bool collectPossibleRoots(Instruction *Base, 407 std::map<int64_t,Instruction*> &Roots); 408 bool validateRootSet(DAGRootSet &DRS); 409 410 bool collectUsedInstructions(SmallInstructionSet &PossibleRedSet); 411 void collectInLoopUserSet(const SmallInstructionVector &Roots, 412 const SmallInstructionSet &Exclude, 413 const SmallInstructionSet &Final, 414 DenseSet<Instruction *> &Users); 415 void collectInLoopUserSet(Instruction *Root, 416 const SmallInstructionSet &Exclude, 417 const SmallInstructionSet &Final, 418 DenseSet<Instruction *> &Users); 419 420 UsesTy::iterator nextInstr(int Val, UsesTy &In, 421 const SmallInstructionSet &Exclude, 422 UsesTy::iterator *StartI=nullptr); 423 bool isBaseInst(Instruction *I); 424 bool isRootInst(Instruction *I); 425 bool instrDependsOn(Instruction *I, 426 UsesTy::iterator Start, 427 UsesTy::iterator End); 428 void replaceIV(DAGRootSet &DRS, const SCEV *Start, const SCEV *IncrExpr); 429 430 LoopReroll *Parent; 431 432 // Members of Parent, replicated here for brevity. 433 Loop *L; 434 ScalarEvolution *SE; 435 AliasAnalysis *AA; 436 TargetLibraryInfo *TLI; 437 DominatorTree *DT; 438 LoopInfo *LI; 439 bool PreserveLCSSA; 440 441 // The loop induction variable. 442 Instruction *IV; 443 444 // Loop step amount. 445 int64_t Inc; 446 447 // Loop reroll count; if Inc == 1, this records the scaling applied 448 // to the indvar: a[i*2+0] = ...; a[i*2+1] = ... ; 449 // If Inc is not 1, Scale = Inc. 450 uint64_t Scale; 451 452 // The roots themselves. 453 SmallVector<DAGRootSet,16> RootSets; 454 455 // All increment instructions for IV. 456 SmallInstructionVector LoopIncs; 457 458 // Map of all instructions in the loop (in order) to the iterations 459 // they are used in (or specially, IL_All for instructions 460 // used in the loop increment mechanism). 461 UsesTy Uses; 462 463 // Map between induction variable and its increment 464 DenseMap<Instruction *, int64_t> &IVToIncMap; 465 466 Instruction *LoopControlIV; 467 }; 468 469 // Check if it is a compare-like instruction whose user is a branch 470 bool isCompareUsedByBranch(Instruction *I) { 471 auto *TI = I->getParent()->getTerminator(); 472 if (!isa<BranchInst>(TI) || !isa<CmpInst>(I)) 473 return false; 474 return I->hasOneUse() && TI->getOperand(0) == I; 475 }; 476 477 bool isLoopControlIV(Loop *L, Instruction *IV); 478 void collectPossibleIVs(Loop *L, SmallInstructionVector &PossibleIVs); 479 void collectPossibleReductions(Loop *L, 480 ReductionTracker &Reductions); 481 bool reroll(Instruction *IV, Loop *L, BasicBlock *Header, 482 const SCEV *BackedgeTakenCount, ReductionTracker &Reductions); 483 }; 484 485} // end anonymous namespace 486 487char LoopReroll::ID = 0; 488 489INITIALIZE_PASS_BEGIN(LoopReroll, "loop-reroll", "Reroll loops", false, false) 490INITIALIZE_PASS_DEPENDENCY(LoopPass) 491INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 492INITIALIZE_PASS_END(LoopReroll, "loop-reroll", "Reroll loops", false, false) 493 494Pass *llvm::createLoopRerollPass() { 495 return new LoopReroll; 496} 497 498// Returns true if the provided instruction is used outside the given loop. 499// This operates like Instruction::isUsedOutsideOfBlock, but considers PHIs in 500// non-loop blocks to be outside the loop. 501static bool hasUsesOutsideLoop(Instruction *I, Loop *L) { 502 for (User *U : I->users()) { 503 if (!L->contains(cast<Instruction>(U))) 504 return true; 505 } 506 return false; 507} 508 509// Check if an IV is only used to control the loop. There are two cases: 510// 1. It only has one use which is loop increment, and the increment is only 511// used by comparison and the PHI (could has sext with nsw in between), and the 512// comparison is only used by branch. 513// 2. It is used by loop increment and the comparison, the loop increment is 514// only used by the PHI, and the comparison is used only by the branch. 515bool LoopReroll::isLoopControlIV(Loop *L, Instruction *IV) { 516 unsigned IVUses = IV->getNumUses(); 517 if (IVUses != 2 && IVUses != 1) 518 return false; 519 520 for (auto *User : IV->users()) { 521 int32_t IncOrCmpUses = User->getNumUses(); 522 bool IsCompInst = isCompareUsedByBranch(cast<Instruction>(User)); 523 524 // User can only have one or two uses. 525 if (IncOrCmpUses != 2 && IncOrCmpUses != 1) 526 return false; 527 528 // Case 1 529 if (IVUses == 1) { 530 // The only user must be the loop increment. 531 // The loop increment must have two uses. 532 if (IsCompInst || IncOrCmpUses != 2) 533 return false; 534 } 535 536 // Case 2 537 if (IVUses == 2 && IncOrCmpUses != 1) 538 return false; 539 540 // The users of the IV must be a binary operation or a comparison 541 if (auto *BO = dyn_cast<BinaryOperator>(User)) { 542 if (BO->getOpcode() == Instruction::Add) { 543 // Loop Increment 544 // User of Loop Increment should be either PHI or CMP 545 for (auto *UU : User->users()) { 546 if (PHINode *PN = dyn_cast<PHINode>(UU)) { 547 if (PN != IV) 548 return false; 549 } 550 // Must be a CMP or an ext (of a value with nsw) then CMP 551 else { 552 Instruction *UUser = dyn_cast<Instruction>(UU); 553 // Skip SExt if we are extending an nsw value 554 // TODO: Allow ZExt too 555 if (BO->hasNoSignedWrap() && UUser && UUser->hasOneUse() && 556 isa<SExtInst>(UUser)) 557 UUser = dyn_cast<Instruction>(*(UUser->user_begin())); 558 if (!isCompareUsedByBranch(UUser)) 559 return false; 560 } 561 } 562 } else 563 return false; 564 // Compare : can only have one use, and must be branch 565 } else if (!IsCompInst) 566 return false; 567 } 568 return true; 569} 570 571// Collect the list of loop induction variables with respect to which it might 572// be possible to reroll the loop. 573void LoopReroll::collectPossibleIVs(Loop *L, 574 SmallInstructionVector &PossibleIVs) { 575 BasicBlock *Header = L->getHeader(); 576 for (BasicBlock::iterator I = Header->begin(), 577 IE = Header->getFirstInsertionPt(); I != IE; ++I) { 578 if (!isa<PHINode>(I)) 579 continue; 580 if (!I->getType()->isIntegerTy() && !I->getType()->isPointerTy()) 581 continue; 582 583 if (const SCEVAddRecExpr *PHISCEV = 584 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(&*I))) { 585 if (PHISCEV->getLoop() != L) 586 continue; 587 if (!PHISCEV->isAffine()) 588 continue; 589 auto IncSCEV = dyn_cast<SCEVConstant>(PHISCEV->getStepRecurrence(*SE)); 590 if (IncSCEV) { 591 IVToIncMap[&*I] = IncSCEV->getValue()->getSExtValue(); 592 LLVM_DEBUG(dbgs() << "LRR: Possible IV: " << *I << " = " << *PHISCEV 593 << "\n"); 594 595 if (isLoopControlIV(L, &*I)) { 596 assert(!LoopControlIV && "Found two loop control only IV"); 597 LoopControlIV = &(*I); 598 LLVM_DEBUG(dbgs() << "LRR: Possible loop control only IV: " << *I 599 << " = " << *PHISCEV << "\n"); 600 } else 601 PossibleIVs.push_back(&*I); 602 } 603 } 604 } 605} 606 607// Add the remainder of the reduction-variable chain to the instruction vector 608// (the initial PHINode has already been added). If successful, the object is 609// marked as valid. 610void LoopReroll::SimpleLoopReduction::add(Loop *L) { 611 assert(!Valid && "Cannot add to an already-valid chain"); 612 613 // The reduction variable must be a chain of single-use instructions 614 // (including the PHI), except for the last value (which is used by the PHI 615 // and also outside the loop). 616 Instruction *C = Instructions.front(); 617 if (C->user_empty()) 618 return; 619 620 do { 621 C = cast<Instruction>(*C->user_begin()); 622 if (C->hasOneUse()) { 623 if (!C->isBinaryOp()) 624 return; 625 626 if (!(isa<PHINode>(Instructions.back()) || 627 C->isSameOperationAs(Instructions.back()))) 628 return; 629 630 Instructions.push_back(C); 631 } 632 } while (C->hasOneUse()); 633 634 if (Instructions.size() < 2 || 635 !C->isSameOperationAs(Instructions.back()) || 636 C->use_empty()) 637 return; 638 639 // C is now the (potential) last instruction in the reduction chain. 640 for (User *U : C->users()) { 641 // The only in-loop user can be the initial PHI. 642 if (L->contains(cast<Instruction>(U))) 643 if (cast<Instruction>(U) != Instructions.front()) 644 return; 645 } 646 647 Instructions.push_back(C); 648 Valid = true; 649} 650 651// Collect the vector of possible reduction variables. 652void LoopReroll::collectPossibleReductions(Loop *L, 653 ReductionTracker &Reductions) { 654 BasicBlock *Header = L->getHeader(); 655 for (BasicBlock::iterator I = Header->begin(), 656 IE = Header->getFirstInsertionPt(); I != IE; ++I) { 657 if (!isa<PHINode>(I)) 658 continue; 659 if (!I->getType()->isSingleValueType()) 660 continue; 661 662 SimpleLoopReduction SLR(&*I, L); 663 if (!SLR.valid()) 664 continue; 665 666 LLVM_DEBUG(dbgs() << "LRR: Possible reduction: " << *I << " (with " 667 << SLR.size() << " chained instructions)\n"); 668 Reductions.addSLR(SLR); 669 } 670} 671 672// Collect the set of all users of the provided root instruction. This set of 673// users contains not only the direct users of the root instruction, but also 674// all users of those users, and so on. There are two exceptions: 675// 676// 1. Instructions in the set of excluded instructions are never added to the 677// use set (even if they are users). This is used, for example, to exclude 678// including root increments in the use set of the primary IV. 679// 680// 2. Instructions in the set of final instructions are added to the use set 681// if they are users, but their users are not added. This is used, for 682// example, to prevent a reduction update from forcing all later reduction 683// updates into the use set. 684void LoopReroll::DAGRootTracker::collectInLoopUserSet( 685 Instruction *Root, const SmallInstructionSet &Exclude, 686 const SmallInstructionSet &Final, 687 DenseSet<Instruction *> &Users) { 688 SmallInstructionVector Queue(1, Root); 689 while (!Queue.empty()) { 690 Instruction *I = Queue.pop_back_val(); 691 if (!Users.insert(I).second) 692 continue; 693 694 if (!Final.count(I)) 695 for (Use &U : I->uses()) { 696 Instruction *User = cast<Instruction>(U.getUser()); 697 if (PHINode *PN = dyn_cast<PHINode>(User)) { 698 // Ignore "wrap-around" uses to PHIs of this loop's header. 699 if (PN->getIncomingBlock(U) == L->getHeader()) 700 continue; 701 } 702 703 if (L->contains(User) && !Exclude.count(User)) { 704 Queue.push_back(User); 705 } 706 } 707 708 // We also want to collect single-user "feeder" values. 709 for (User::op_iterator OI = I->op_begin(), 710 OIE = I->op_end(); OI != OIE; ++OI) { 711 if (Instruction *Op = dyn_cast<Instruction>(*OI)) 712 if (Op->hasOneUse() && L->contains(Op) && !Exclude.count(Op) && 713 !Final.count(Op)) 714 Queue.push_back(Op); 715 } 716 } 717} 718 719// Collect all of the users of all of the provided root instructions (combined 720// into a single set). 721void LoopReroll::DAGRootTracker::collectInLoopUserSet( 722 const SmallInstructionVector &Roots, 723 const SmallInstructionSet &Exclude, 724 const SmallInstructionSet &Final, 725 DenseSet<Instruction *> &Users) { 726 for (Instruction *Root : Roots) 727 collectInLoopUserSet(Root, Exclude, Final, Users); 728} 729 730static bool isUnorderedLoadStore(Instruction *I) { 731 if (LoadInst *LI = dyn_cast<LoadInst>(I)) 732 return LI->isUnordered(); 733 if (StoreInst *SI = dyn_cast<StoreInst>(I)) 734 return SI->isUnordered(); 735 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) 736 return !MI->isVolatile(); 737 return false; 738} 739 740/// Return true if IVU is a "simple" arithmetic operation. 741/// This is used for narrowing the search space for DAGRoots; only arithmetic 742/// and GEPs can be part of a DAGRoot. 743static bool isSimpleArithmeticOp(User *IVU) { 744 if (Instruction *I = dyn_cast<Instruction>(IVU)) { 745 switch (I->getOpcode()) { 746 default: return false; 747 case Instruction::Add: 748 case Instruction::Sub: 749 case Instruction::Mul: 750 case Instruction::Shl: 751 case Instruction::AShr: 752 case Instruction::LShr: 753 case Instruction::GetElementPtr: 754 case Instruction::Trunc: 755 case Instruction::ZExt: 756 case Instruction::SExt: 757 return true; 758 } 759 } 760 return false; 761} 762 763static bool isLoopIncrement(User *U, Instruction *IV) { 764 BinaryOperator *BO = dyn_cast<BinaryOperator>(U); 765 766 if ((BO && BO->getOpcode() != Instruction::Add) || 767 (!BO && !isa<GetElementPtrInst>(U))) 768 return false; 769 770 for (auto *UU : U->users()) { 771 PHINode *PN = dyn_cast<PHINode>(UU); 772 if (PN && PN == IV) 773 return true; 774 } 775 return false; 776} 777 778bool LoopReroll::DAGRootTracker:: 779collectPossibleRoots(Instruction *Base, std::map<int64_t,Instruction*> &Roots) { 780 SmallInstructionVector BaseUsers; 781 782 for (auto *I : Base->users()) { 783 ConstantInt *CI = nullptr; 784 785 if (isLoopIncrement(I, IV)) { 786 LoopIncs.push_back(cast<Instruction>(I)); 787 continue; 788 } 789 790 // The root nodes must be either GEPs, ORs or ADDs. 791 if (auto *BO = dyn_cast<BinaryOperator>(I)) { 792 if (BO->getOpcode() == Instruction::Add || 793 BO->getOpcode() == Instruction::Or) 794 CI = dyn_cast<ConstantInt>(BO->getOperand(1)); 795 } else if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) { 796 Value *LastOperand = GEP->getOperand(GEP->getNumOperands()-1); 797 CI = dyn_cast<ConstantInt>(LastOperand); 798 } 799 800 if (!CI) { 801 if (Instruction *II = dyn_cast<Instruction>(I)) { 802 BaseUsers.push_back(II); 803 continue; 804 } else { 805 LLVM_DEBUG(dbgs() << "LRR: Aborting due to non-instruction: " << *I 806 << "\n"); 807 return false; 808 } 809 } 810 811 int64_t V = std::abs(CI->getValue().getSExtValue()); 812 if (Roots.find(V) != Roots.end()) 813 // No duplicates, please. 814 return false; 815 816 Roots[V] = cast<Instruction>(I); 817 } 818 819 // Make sure we have at least two roots. 820 if (Roots.empty() || (Roots.size() == 1 && BaseUsers.empty())) 821 return false; 822 823 // If we found non-loop-inc, non-root users of Base, assume they are 824 // for the zeroth root index. This is because "add %a, 0" gets optimized 825 // away. 826 if (BaseUsers.size()) { 827 if (Roots.find(0) != Roots.end()) { 828 LLVM_DEBUG(dbgs() << "LRR: Multiple roots found for base - aborting!\n"); 829 return false; 830 } 831 Roots[0] = Base; 832 } 833 834 // Calculate the number of users of the base, or lowest indexed, iteration. 835 unsigned NumBaseUses = BaseUsers.size(); 836 if (NumBaseUses == 0) 837 NumBaseUses = Roots.begin()->second->getNumUses(); 838 839 // Check that every node has the same number of users. 840 for (auto &KV : Roots) { 841 if (KV.first == 0) 842 continue; 843 if (!KV.second->hasNUses(NumBaseUses)) { 844 LLVM_DEBUG(dbgs() << "LRR: Aborting - Root and Base #users not the same: " 845 << "#Base=" << NumBaseUses 846 << ", #Root=" << KV.second->getNumUses() << "\n"); 847 return false; 848 } 849 } 850 851 return true; 852} 853 854void LoopReroll::DAGRootTracker:: 855findRootsRecursive(Instruction *I, SmallInstructionSet SubsumedInsts) { 856 // Does the user look like it could be part of a root set? 857 // All its users must be simple arithmetic ops. 858 if (I->hasNUsesOrMore(IL_MaxRerollIterations + 1)) 859 return; 860 861 if (I != IV && findRootsBase(I, SubsumedInsts)) 862 return; 863 864 SubsumedInsts.insert(I); 865 866 for (User *V : I->users()) { 867 Instruction *I = cast<Instruction>(V); 868 if (is_contained(LoopIncs, I)) 869 continue; 870 871 if (!isSimpleArithmeticOp(I)) 872 continue; 873 874 // The recursive call makes a copy of SubsumedInsts. 875 findRootsRecursive(I, SubsumedInsts); 876 } 877} 878 879bool LoopReroll::DAGRootTracker::validateRootSet(DAGRootSet &DRS) { 880 if (DRS.Roots.empty()) 881 return false; 882 883 // Consider a DAGRootSet with N-1 roots (so N different values including 884 // BaseInst). 885 // Define d = Roots[0] - BaseInst, which should be the same as 886 // Roots[I] - Roots[I-1] for all I in [1..N). 887 // Define D = BaseInst@J - BaseInst@J-1, where "@J" means the value at the 888 // loop iteration J. 889 // 890 // Now, For the loop iterations to be consecutive: 891 // D = d * N 892 const auto *ADR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(DRS.BaseInst)); 893 if (!ADR) 894 return false; 895 896 // Check that the first root is evenly spaced. 897 unsigned N = DRS.Roots.size() + 1; 898 const SCEV *StepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[0]), ADR); 899 const SCEV *ScaleSCEV = SE->getConstant(StepSCEV->getType(), N); 900 if (ADR->getStepRecurrence(*SE) != SE->getMulExpr(StepSCEV, ScaleSCEV)) 901 return false; 902 903 // Check that the remainling roots are evenly spaced. 904 for (unsigned i = 1; i < N - 1; ++i) { 905 const SCEV *NewStepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[i]), 906 SE->getSCEV(DRS.Roots[i-1])); 907 if (NewStepSCEV != StepSCEV) 908 return false; 909 } 910 911 return true; 912} 913 914bool LoopReroll::DAGRootTracker:: 915findRootsBase(Instruction *IVU, SmallInstructionSet SubsumedInsts) { 916 // The base of a RootSet must be an AddRec, so it can be erased. 917 const auto *IVU_ADR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IVU)); 918 if (!IVU_ADR || IVU_ADR->getLoop() != L) 919 return false; 920 921 std::map<int64_t, Instruction*> V; 922 if (!collectPossibleRoots(IVU, V)) 923 return false; 924 925 // If we didn't get a root for index zero, then IVU must be 926 // subsumed. 927 if (V.find(0) == V.end()) 928 SubsumedInsts.insert(IVU); 929 930 // Partition the vector into monotonically increasing indexes. 931 DAGRootSet DRS; 932 DRS.BaseInst = nullptr; 933 934 SmallVector<DAGRootSet, 16> PotentialRootSets; 935 936 for (auto &KV : V) { 937 if (!DRS.BaseInst) { 938 DRS.BaseInst = KV.second; 939 DRS.SubsumedInsts = SubsumedInsts; 940 } else if (DRS.Roots.empty()) { 941 DRS.Roots.push_back(KV.second); 942 } else if (V.find(KV.first - 1) != V.end()) { 943 DRS.Roots.push_back(KV.second); 944 } else { 945 // Linear sequence terminated. 946 if (!validateRootSet(DRS)) 947 return false; 948 949 // Construct a new DAGRootSet with the next sequence. 950 PotentialRootSets.push_back(DRS); 951 DRS.BaseInst = KV.second; 952 DRS.Roots.clear(); 953 } 954 } 955 956 if (!validateRootSet(DRS)) 957 return false; 958 959 PotentialRootSets.push_back(DRS); 960 961 RootSets.append(PotentialRootSets.begin(), PotentialRootSets.end()); 962 963 return true; 964} 965 966bool LoopReroll::DAGRootTracker::findRoots() { 967 Inc = IVToIncMap[IV]; 968 969 assert(RootSets.empty() && "Unclean state!"); 970 if (std::abs(Inc) == 1) { 971 for (auto *IVU : IV->users()) { 972 if (isLoopIncrement(IVU, IV)) 973 LoopIncs.push_back(cast<Instruction>(IVU)); 974 } 975 findRootsRecursive(IV, SmallInstructionSet()); 976 LoopIncs.push_back(IV); 977 } else { 978 if (!findRootsBase(IV, SmallInstructionSet())) 979 return false; 980 } 981 982 // Ensure all sets have the same size. 983 if (RootSets.empty()) { 984 LLVM_DEBUG(dbgs() << "LRR: Aborting because no root sets found!\n"); 985 return false; 986 } 987 for (auto &V : RootSets) { 988 if (V.Roots.empty() || V.Roots.size() != RootSets[0].Roots.size()) { 989 LLVM_DEBUG( 990 dbgs() 991 << "LRR: Aborting because not all root sets have the same size\n"); 992 return false; 993 } 994 } 995 996 Scale = RootSets[0].Roots.size() + 1; 997 998 if (Scale > IL_MaxRerollIterations) { 999 LLVM_DEBUG(dbgs() << "LRR: Aborting - too many iterations found. " 1000 << "#Found=" << Scale 1001 << ", #Max=" << IL_MaxRerollIterations << "\n"); 1002 return false; 1003 } 1004 1005 LLVM_DEBUG(dbgs() << "LRR: Successfully found roots: Scale=" << Scale 1006 << "\n"); 1007 1008 return true; 1009} 1010 1011bool LoopReroll::DAGRootTracker::collectUsedInstructions(SmallInstructionSet &PossibleRedSet) { 1012 // Populate the MapVector with all instructions in the block, in order first, 1013 // so we can iterate over the contents later in perfect order. 1014 for (auto &I : *L->getHeader()) { 1015 Uses[&I].resize(IL_End); 1016 } 1017 1018 SmallInstructionSet Exclude; 1019 for (auto &DRS : RootSets) { 1020 Exclude.insert(DRS.Roots.begin(), DRS.Roots.end()); 1021 Exclude.insert(DRS.SubsumedInsts.begin(), DRS.SubsumedInsts.end()); 1022 Exclude.insert(DRS.BaseInst); 1023 } 1024 Exclude.insert(LoopIncs.begin(), LoopIncs.end()); 1025 1026 for (auto &DRS : RootSets) { 1027 DenseSet<Instruction*> VBase; 1028 collectInLoopUserSet(DRS.BaseInst, Exclude, PossibleRedSet, VBase); 1029 for (auto *I : VBase) { 1030 Uses[I].set(0); 1031 } 1032 1033 unsigned Idx = 1; 1034 for (auto *Root : DRS.Roots) { 1035 DenseSet<Instruction*> V; 1036 collectInLoopUserSet(Root, Exclude, PossibleRedSet, V); 1037 1038 // While we're here, check the use sets are the same size. 1039 if (V.size() != VBase.size()) { 1040 LLVM_DEBUG(dbgs() << "LRR: Aborting - use sets are different sizes\n"); 1041 return false; 1042 } 1043 1044 for (auto *I : V) { 1045 Uses[I].set(Idx); 1046 } 1047 ++Idx; 1048 } 1049 1050 // Make sure our subsumed instructions are remembered too. 1051 for (auto *I : DRS.SubsumedInsts) { 1052 Uses[I].set(IL_All); 1053 } 1054 } 1055 1056 // Make sure the loop increments are also accounted for. 1057 1058 Exclude.clear(); 1059 for (auto &DRS : RootSets) { 1060 Exclude.insert(DRS.Roots.begin(), DRS.Roots.end()); 1061 Exclude.insert(DRS.SubsumedInsts.begin(), DRS.SubsumedInsts.end()); 1062 Exclude.insert(DRS.BaseInst); 1063 } 1064 1065 DenseSet<Instruction*> V; 1066 collectInLoopUserSet(LoopIncs, Exclude, PossibleRedSet, V); 1067 for (auto *I : V) { 1068 Uses[I].set(IL_All); 1069 } 1070 1071 return true; 1072} 1073 1074/// Get the next instruction in "In" that is a member of set Val. 1075/// Start searching from StartI, and do not return anything in Exclude. 1076/// If StartI is not given, start from In.begin(). 1077LoopReroll::DAGRootTracker::UsesTy::iterator 1078LoopReroll::DAGRootTracker::nextInstr(int Val, UsesTy &In, 1079 const SmallInstructionSet &Exclude, 1080 UsesTy::iterator *StartI) { 1081 UsesTy::iterator I = StartI ? *StartI : In.begin(); 1082 while (I != In.end() && (I->second.test(Val) == 0 || 1083 Exclude.count(I->first) != 0)) 1084 ++I; 1085 return I; 1086} 1087 1088bool LoopReroll::DAGRootTracker::isBaseInst(Instruction *I) { 1089 for (auto &DRS : RootSets) { 1090 if (DRS.BaseInst == I) 1091 return true; 1092 } 1093 return false; 1094} 1095 1096bool LoopReroll::DAGRootTracker::isRootInst(Instruction *I) { 1097 for (auto &DRS : RootSets) { 1098 if (is_contained(DRS.Roots, I)) 1099 return true; 1100 } 1101 return false; 1102} 1103 1104/// Return true if instruction I depends on any instruction between 1105/// Start and End. 1106bool LoopReroll::DAGRootTracker::instrDependsOn(Instruction *I, 1107 UsesTy::iterator Start, 1108 UsesTy::iterator End) { 1109 for (auto *U : I->users()) { 1110 for (auto It = Start; It != End; ++It) 1111 if (U == It->first) 1112 return true; 1113 } 1114 return false; 1115} 1116 1117static bool isIgnorableInst(const Instruction *I) { 1118 if (isa<DbgInfoIntrinsic>(I)) 1119 return true; 1120 const IntrinsicInst* II = dyn_cast<IntrinsicInst>(I); 1121 if (!II) 1122 return false; 1123 switch (II->getIntrinsicID()) { 1124 default: 1125 return false; 1126 case Intrinsic::annotation: 1127 case Intrinsic::ptr_annotation: 1128 case Intrinsic::var_annotation: 1129 // TODO: the following intrinsics may also be whitelisted: 1130 // lifetime_start, lifetime_end, invariant_start, invariant_end 1131 return true; 1132 } 1133 return false; 1134} 1135 1136bool LoopReroll::DAGRootTracker::validate(ReductionTracker &Reductions) { 1137 // We now need to check for equivalence of the use graph of each root with 1138 // that of the primary induction variable (excluding the roots). Our goal 1139 // here is not to solve the full graph isomorphism problem, but rather to 1140 // catch common cases without a lot of work. As a result, we will assume 1141 // that the relative order of the instructions in each unrolled iteration 1142 // is the same (although we will not make an assumption about how the 1143 // different iterations are intermixed). Note that while the order must be 1144 // the same, the instructions may not be in the same basic block. 1145 1146 // An array of just the possible reductions for this scale factor. When we 1147 // collect the set of all users of some root instructions, these reduction 1148 // instructions are treated as 'final' (their uses are not considered). 1149 // This is important because we don't want the root use set to search down 1150 // the reduction chain. 1151 SmallInstructionSet PossibleRedSet; 1152 SmallInstructionSet PossibleRedLastSet; 1153 SmallInstructionSet PossibleRedPHISet; 1154 Reductions.restrictToScale(Scale, PossibleRedSet, 1155 PossibleRedPHISet, PossibleRedLastSet); 1156 1157 // Populate "Uses" with where each instruction is used. 1158 if (!collectUsedInstructions(PossibleRedSet)) 1159 return false; 1160 1161 // Make sure we mark the reduction PHIs as used in all iterations. 1162 for (auto *I : PossibleRedPHISet) { 1163 Uses[I].set(IL_All); 1164 } 1165 1166 // Make sure we mark loop-control-only PHIs as used in all iterations. See 1167 // comment above LoopReroll::isLoopControlIV for more information. 1168 BasicBlock *Header = L->getHeader(); 1169 if (LoopControlIV && LoopControlIV != IV) { 1170 for (auto *U : LoopControlIV->users()) { 1171 Instruction *IVUser = dyn_cast<Instruction>(U); 1172 // IVUser could be loop increment or compare 1173 Uses[IVUser].set(IL_All); 1174 for (auto *UU : IVUser->users()) { 1175 Instruction *UUser = dyn_cast<Instruction>(UU); 1176 // UUser could be compare, PHI or branch 1177 Uses[UUser].set(IL_All); 1178 // Skip SExt 1179 if (isa<SExtInst>(UUser)) { 1180 UUser = dyn_cast<Instruction>(*(UUser->user_begin())); 1181 Uses[UUser].set(IL_All); 1182 } 1183 // Is UUser a compare instruction? 1184 if (UU->hasOneUse()) { 1185 Instruction *BI = dyn_cast<BranchInst>(*UUser->user_begin()); 1186 if (BI == cast<BranchInst>(Header->getTerminator())) 1187 Uses[BI].set(IL_All); 1188 } 1189 } 1190 } 1191 } 1192 1193 // Make sure all instructions in the loop are in one and only one 1194 // set. 1195 for (auto &KV : Uses) { 1196 if (KV.second.count() != 1 && !isIgnorableInst(KV.first)) { 1197 LLVM_DEBUG( 1198 dbgs() << "LRR: Aborting - instruction is not used in 1 iteration: " 1199 << *KV.first << " (#uses=" << KV.second.count() << ")\n"); 1200 return false; 1201 } 1202 } 1203 1204 LLVM_DEBUG(for (auto &KV 1205 : Uses) { 1206 dbgs() << "LRR: " << KV.second.find_first() << "\t" << *KV.first << "\n"; 1207 }); 1208 1209 for (unsigned Iter = 1; Iter < Scale; ++Iter) { 1210 // In addition to regular aliasing information, we need to look for 1211 // instructions from later (future) iterations that have side effects 1212 // preventing us from reordering them past other instructions with side 1213 // effects. 1214 bool FutureSideEffects = false; 1215 AliasSetTracker AST(*AA); 1216 // The map between instructions in f(%iv.(i+1)) and f(%iv). 1217 DenseMap<Value *, Value *> BaseMap; 1218 1219 // Compare iteration Iter to the base. 1220 SmallInstructionSet Visited; 1221 auto BaseIt = nextInstr(0, Uses, Visited); 1222 auto RootIt = nextInstr(Iter, Uses, Visited); 1223 auto LastRootIt = Uses.begin(); 1224 1225 while (BaseIt != Uses.end() && RootIt != Uses.end()) { 1226 Instruction *BaseInst = BaseIt->first; 1227 Instruction *RootInst = RootIt->first; 1228 1229 // Skip over the IV or root instructions; only match their users. 1230 bool Continue = false; 1231 if (isBaseInst(BaseInst)) { 1232 Visited.insert(BaseInst); 1233 BaseIt = nextInstr(0, Uses, Visited); 1234 Continue = true; 1235 } 1236 if (isRootInst(RootInst)) { 1237 LastRootIt = RootIt; 1238 Visited.insert(RootInst); 1239 RootIt = nextInstr(Iter, Uses, Visited); 1240 Continue = true; 1241 } 1242 if (Continue) continue; 1243 1244 if (!BaseInst->isSameOperationAs(RootInst)) { 1245 // Last chance saloon. We don't try and solve the full isomorphism 1246 // problem, but try and at least catch the case where two instructions 1247 // *of different types* are round the wrong way. We won't be able to 1248 // efficiently tell, given two ADD instructions, which way around we 1249 // should match them, but given an ADD and a SUB, we can at least infer 1250 // which one is which. 1251 // 1252 // This should allow us to deal with a greater subset of the isomorphism 1253 // problem. It does however change a linear algorithm into a quadratic 1254 // one, so limit the number of probes we do. 1255 auto TryIt = RootIt; 1256 unsigned N = NumToleratedFailedMatches; 1257 while (TryIt != Uses.end() && 1258 !BaseInst->isSameOperationAs(TryIt->first) && 1259 N--) { 1260 ++TryIt; 1261 TryIt = nextInstr(Iter, Uses, Visited, &TryIt); 1262 } 1263 1264 if (TryIt == Uses.end() || TryIt == RootIt || 1265 instrDependsOn(TryIt->first, RootIt, TryIt)) { 1266 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " 1267 << *BaseInst << " vs. " << *RootInst << "\n"); 1268 return false; 1269 } 1270 1271 RootIt = TryIt; 1272 RootInst = TryIt->first; 1273 } 1274 1275 // All instructions between the last root and this root 1276 // may belong to some other iteration. If they belong to a 1277 // future iteration, then they're dangerous to alias with. 1278 // 1279 // Note that because we allow a limited amount of flexibility in the order 1280 // that we visit nodes, LastRootIt might be *before* RootIt, in which 1281 // case we've already checked this set of instructions so we shouldn't 1282 // do anything. 1283 for (; LastRootIt < RootIt; ++LastRootIt) { 1284 Instruction *I = LastRootIt->first; 1285 if (LastRootIt->second.find_first() < (int)Iter) 1286 continue; 1287 if (I->mayWriteToMemory()) 1288 AST.add(I); 1289 // Note: This is specifically guarded by a check on isa<PHINode>, 1290 // which while a valid (somewhat arbitrary) micro-optimization, is 1291 // needed because otherwise isSafeToSpeculativelyExecute returns 1292 // false on PHI nodes. 1293 if (!isa<PHINode>(I) && !isUnorderedLoadStore(I) && 1294 !isSafeToSpeculativelyExecute(I)) 1295 // Intervening instructions cause side effects. 1296 FutureSideEffects = true; 1297 } 1298 1299 // Make sure that this instruction, which is in the use set of this 1300 // root instruction, does not also belong to the base set or the set of 1301 // some other root instruction. 1302 if (RootIt->second.count() > 1) { 1303 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst 1304 << " vs. " << *RootInst << " (prev. case overlap)\n"); 1305 return false; 1306 } 1307 1308 // Make sure that we don't alias with any instruction in the alias set 1309 // tracker. If we do, then we depend on a future iteration, and we 1310 // can't reroll. 1311 if (RootInst->mayReadFromMemory()) 1312 for (auto &K : AST) { 1313 if (K.aliasesUnknownInst(RootInst, *AA)) { 1314 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " 1315 << *BaseInst << " vs. " << *RootInst 1316 << " (depends on future store)\n"); 1317 return false; 1318 } 1319 } 1320 1321 // If we've past an instruction from a future iteration that may have 1322 // side effects, and this instruction might also, then we can't reorder 1323 // them, and this matching fails. As an exception, we allow the alias 1324 // set tracker to handle regular (unordered) load/store dependencies. 1325 if (FutureSideEffects && ((!isUnorderedLoadStore(BaseInst) && 1326 !isSafeToSpeculativelyExecute(BaseInst)) || 1327 (!isUnorderedLoadStore(RootInst) && 1328 !isSafeToSpeculativelyExecute(RootInst)))) { 1329 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst 1330 << " vs. " << *RootInst 1331 << " (side effects prevent reordering)\n"); 1332 return false; 1333 } 1334 1335 // For instructions that are part of a reduction, if the operation is 1336 // associative, then don't bother matching the operands (because we 1337 // already know that the instructions are isomorphic, and the order 1338 // within the iteration does not matter). For non-associative reductions, 1339 // we do need to match the operands, because we need to reject 1340 // out-of-order instructions within an iteration! 1341 // For example (assume floating-point addition), we need to reject this: 1342 // x += a[i]; x += b[i]; 1343 // x += a[i+1]; x += b[i+1]; 1344 // x += b[i+2]; x += a[i+2]; 1345 bool InReduction = Reductions.isPairInSame(BaseInst, RootInst); 1346 1347 if (!(InReduction && BaseInst->isAssociative())) { 1348 bool Swapped = false, SomeOpMatched = false; 1349 for (unsigned j = 0; j < BaseInst->getNumOperands(); ++j) { 1350 Value *Op2 = RootInst->getOperand(j); 1351 1352 // If this is part of a reduction (and the operation is not 1353 // associatve), then we match all operands, but not those that are 1354 // part of the reduction. 1355 if (InReduction) 1356 if (Instruction *Op2I = dyn_cast<Instruction>(Op2)) 1357 if (Reductions.isPairInSame(RootInst, Op2I)) 1358 continue; 1359 1360 DenseMap<Value *, Value *>::iterator BMI = BaseMap.find(Op2); 1361 if (BMI != BaseMap.end()) { 1362 Op2 = BMI->second; 1363 } else { 1364 for (auto &DRS : RootSets) { 1365 if (DRS.Roots[Iter-1] == (Instruction*) Op2) { 1366 Op2 = DRS.BaseInst; 1367 break; 1368 } 1369 } 1370 } 1371 1372 if (BaseInst->getOperand(Swapped ? unsigned(!j) : j) != Op2) { 1373 // If we've not already decided to swap the matched operands, and 1374 // we've not already matched our first operand (note that we could 1375 // have skipped matching the first operand because it is part of a 1376 // reduction above), and the instruction is commutative, then try 1377 // the swapped match. 1378 if (!Swapped && BaseInst->isCommutative() && !SomeOpMatched && 1379 BaseInst->getOperand(!j) == Op2) { 1380 Swapped = true; 1381 } else { 1382 LLVM_DEBUG(dbgs() 1383 << "LRR: iteration root match failed at " << *BaseInst 1384 << " vs. " << *RootInst << " (operand " << j << ")\n"); 1385 return false; 1386 } 1387 } 1388 1389 SomeOpMatched = true; 1390 } 1391 } 1392 1393 if ((!PossibleRedLastSet.count(BaseInst) && 1394 hasUsesOutsideLoop(BaseInst, L)) || 1395 (!PossibleRedLastSet.count(RootInst) && 1396 hasUsesOutsideLoop(RootInst, L))) { 1397 LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst 1398 << " vs. " << *RootInst << " (uses outside loop)\n"); 1399 return false; 1400 } 1401 1402 Reductions.recordPair(BaseInst, RootInst, Iter); 1403 BaseMap.insert(std::make_pair(RootInst, BaseInst)); 1404 1405 LastRootIt = RootIt; 1406 Visited.insert(BaseInst); 1407 Visited.insert(RootInst); 1408 BaseIt = nextInstr(0, Uses, Visited); 1409 RootIt = nextInstr(Iter, Uses, Visited); 1410 } 1411 assert(BaseIt == Uses.end() && RootIt == Uses.end() && 1412 "Mismatched set sizes!"); 1413 } 1414 1415 LLVM_DEBUG(dbgs() << "LRR: Matched all iteration increments for " << *IV 1416 << "\n"); 1417 1418 return true; 1419} 1420 1421void LoopReroll::DAGRootTracker::replace(const SCEV *BackedgeTakenCount) { 1422 BasicBlock *Header = L->getHeader(); 1423 1424 // Compute the start and increment for each BaseInst before we start erasing 1425 // instructions. 1426 SmallVector<const SCEV *, 8> StartExprs; 1427 SmallVector<const SCEV *, 8> IncrExprs; 1428 for (auto &DRS : RootSets) { 1429 const SCEVAddRecExpr *IVSCEV = 1430 cast<SCEVAddRecExpr>(SE->getSCEV(DRS.BaseInst)); 1431 StartExprs.push_back(IVSCEV->getStart()); 1432 IncrExprs.push_back(SE->getMinusSCEV(SE->getSCEV(DRS.Roots[0]), IVSCEV)); 1433 } 1434 1435 // Remove instructions associated with non-base iterations. 1436 for (BasicBlock::reverse_iterator J = Header->rbegin(), JE = Header->rend(); 1437 J != JE;) { 1438 unsigned I = Uses[&*J].find_first(); 1439 if (I > 0 && I < IL_All) { 1440 LLVM_DEBUG(dbgs() << "LRR: removing: " << *J << "\n"); 1441 J++->eraseFromParent(); 1442 continue; 1443 } 1444 1445 ++J; 1446 } 1447 1448 // Rewrite each BaseInst using SCEV. 1449 for (size_t i = 0, e = RootSets.size(); i != e; ++i) 1450 // Insert the new induction variable. 1451 replaceIV(RootSets[i], StartExprs[i], IncrExprs[i]); 1452 1453 { // Limit the lifetime of SCEVExpander. 1454 BranchInst *BI = cast<BranchInst>(Header->getTerminator()); 1455 const DataLayout &DL = Header->getModule()->getDataLayout(); 1456 SCEVExpander Expander(*SE, DL, "reroll"); 1457 auto Zero = SE->getZero(BackedgeTakenCount->getType()); 1458 auto One = SE->getOne(BackedgeTakenCount->getType()); 1459 auto NewIVSCEV = SE->getAddRecExpr(Zero, One, L, SCEV::FlagAnyWrap); 1460 Value *NewIV = 1461 Expander.expandCodeFor(NewIVSCEV, BackedgeTakenCount->getType(), 1462 Header->getFirstNonPHIOrDbg()); 1463 // FIXME: This arithmetic can overflow. 1464 auto TripCount = SE->getAddExpr(BackedgeTakenCount, One); 1465 auto ScaledTripCount = SE->getMulExpr( 1466 TripCount, SE->getConstant(BackedgeTakenCount->getType(), Scale)); 1467 auto ScaledBECount = SE->getMinusSCEV(ScaledTripCount, One); 1468 Value *TakenCount = 1469 Expander.expandCodeFor(ScaledBECount, BackedgeTakenCount->getType(), 1470 Header->getFirstNonPHIOrDbg()); 1471 Value *Cond = 1472 new ICmpInst(BI, CmpInst::ICMP_EQ, NewIV, TakenCount, "exitcond"); 1473 BI->setCondition(Cond); 1474 1475 if (BI->getSuccessor(1) != Header) 1476 BI->swapSuccessors(); 1477 } 1478 1479 SimplifyInstructionsInBlock(Header, TLI); 1480 DeleteDeadPHIs(Header, TLI); 1481} 1482 1483void LoopReroll::DAGRootTracker::replaceIV(DAGRootSet &DRS, 1484 const SCEV *Start, 1485 const SCEV *IncrExpr) { 1486 BasicBlock *Header = L->getHeader(); 1487 Instruction *Inst = DRS.BaseInst; 1488 1489 const SCEV *NewIVSCEV = 1490 SE->getAddRecExpr(Start, IncrExpr, L, SCEV::FlagAnyWrap); 1491 1492 { // Limit the lifetime of SCEVExpander. 1493 const DataLayout &DL = Header->getModule()->getDataLayout(); 1494 SCEVExpander Expander(*SE, DL, "reroll"); 1495 Value *NewIV = Expander.expandCodeFor(NewIVSCEV, Inst->getType(), 1496 Header->getFirstNonPHIOrDbg()); 1497 1498 for (auto &KV : Uses) 1499 if (KV.second.find_first() == 0) 1500 KV.first->replaceUsesOfWith(Inst, NewIV); 1501 } 1502} 1503 1504// Validate the selected reductions. All iterations must have an isomorphic 1505// part of the reduction chain and, for non-associative reductions, the chain 1506// entries must appear in order. 1507bool LoopReroll::ReductionTracker::validateSelected() { 1508 // For a non-associative reduction, the chain entries must appear in order. 1509 for (int i : Reds) { 1510 int PrevIter = 0, BaseCount = 0, Count = 0; 1511 for (Instruction *J : PossibleReds[i]) { 1512 // Note that all instructions in the chain must have been found because 1513 // all instructions in the function must have been assigned to some 1514 // iteration. 1515 int Iter = PossibleRedIter[J]; 1516 if (Iter != PrevIter && Iter != PrevIter + 1 && 1517 !PossibleReds[i].getReducedValue()->isAssociative()) { 1518 LLVM_DEBUG(dbgs() << "LRR: Out-of-order non-associative reduction: " 1519 << J << "\n"); 1520 return false; 1521 } 1522 1523 if (Iter != PrevIter) { 1524 if (Count != BaseCount) { 1525 LLVM_DEBUG(dbgs() 1526 << "LRR: Iteration " << PrevIter << " reduction use count " 1527 << Count << " is not equal to the base use count " 1528 << BaseCount << "\n"); 1529 return false; 1530 } 1531 1532 Count = 0; 1533 } 1534 1535 ++Count; 1536 if (Iter == 0) 1537 ++BaseCount; 1538 1539 PrevIter = Iter; 1540 } 1541 } 1542 1543 return true; 1544} 1545 1546// For all selected reductions, remove all parts except those in the first 1547// iteration (and the PHI). Replace outside uses of the reduced value with uses 1548// of the first-iteration reduced value (in other words, reroll the selected 1549// reductions). 1550void LoopReroll::ReductionTracker::replaceSelected() { 1551 // Fixup reductions to refer to the last instruction associated with the 1552 // first iteration (not the last). 1553 for (int i : Reds) { 1554 int j = 0; 1555 for (int e = PossibleReds[i].size(); j != e; ++j) 1556 if (PossibleRedIter[PossibleReds[i][j]] != 0) { 1557 --j; 1558 break; 1559 } 1560 1561 // Replace users with the new end-of-chain value. 1562 SmallInstructionVector Users; 1563 for (User *U : PossibleReds[i].getReducedValue()->users()) { 1564 Users.push_back(cast<Instruction>(U)); 1565 } 1566 1567 for (Instruction *User : Users) 1568 User->replaceUsesOfWith(PossibleReds[i].getReducedValue(), 1569 PossibleReds[i][j]); 1570 } 1571} 1572 1573// Reroll the provided loop with respect to the provided induction variable. 1574// Generally, we're looking for a loop like this: 1575// 1576// %iv = phi [ (preheader, ...), (body, %iv.next) ] 1577// f(%iv) 1578// %iv.1 = add %iv, 1 <-- a root increment 1579// f(%iv.1) 1580// %iv.2 = add %iv, 2 <-- a root increment 1581// f(%iv.2) 1582// %iv.scale_m_1 = add %iv, scale-1 <-- a root increment 1583// f(%iv.scale_m_1) 1584// ... 1585// %iv.next = add %iv, scale 1586// %cmp = icmp(%iv, ...) 1587// br %cmp, header, exit 1588// 1589// Notably, we do not require that f(%iv), f(%iv.1), etc. be isolated groups of 1590// instructions. In other words, the instructions in f(%iv), f(%iv.1), etc. can 1591// be intermixed with eachother. The restriction imposed by this algorithm is 1592// that the relative order of the isomorphic instructions in f(%iv), f(%iv.1), 1593// etc. be the same. 1594// 1595// First, we collect the use set of %iv, excluding the other increment roots. 1596// This gives us f(%iv). Then we iterate over the loop instructions (scale-1) 1597// times, having collected the use set of f(%iv.(i+1)), during which we: 1598// - Ensure that the next unmatched instruction in f(%iv) is isomorphic to 1599// the next unmatched instruction in f(%iv.(i+1)). 1600// - Ensure that both matched instructions don't have any external users 1601// (with the exception of last-in-chain reduction instructions). 1602// - Track the (aliasing) write set, and other side effects, of all 1603// instructions that belong to future iterations that come before the matched 1604// instructions. If the matched instructions read from that write set, then 1605// f(%iv) or f(%iv.(i+1)) has some dependency on instructions in 1606// f(%iv.(j+1)) for some j > i, and we cannot reroll the loop. Similarly, 1607// if any of these future instructions had side effects (could not be 1608// speculatively executed), and so do the matched instructions, when we 1609// cannot reorder those side-effect-producing instructions, and rerolling 1610// fails. 1611// 1612// Finally, we make sure that all loop instructions are either loop increment 1613// roots, belong to simple latch code, parts of validated reductions, part of 1614// f(%iv) or part of some f(%iv.i). If all of that is true (and all reductions 1615// have been validated), then we reroll the loop. 1616bool LoopReroll::reroll(Instruction *IV, Loop *L, BasicBlock *Header, 1617 const SCEV *BackedgeTakenCount, 1618 ReductionTracker &Reductions) { 1619 DAGRootTracker DAGRoots(this, L, IV, SE, AA, TLI, DT, LI, PreserveLCSSA, 1620 IVToIncMap, LoopControlIV); 1621 1622 if (!DAGRoots.findRoots()) 1623 return false; 1624 LLVM_DEBUG(dbgs() << "LRR: Found all root induction increments for: " << *IV 1625 << "\n"); 1626 1627 if (!DAGRoots.validate(Reductions)) 1628 return false; 1629 if (!Reductions.validateSelected()) 1630 return false; 1631 // At this point, we've validated the rerolling, and we're committed to 1632 // making changes! 1633 1634 Reductions.replaceSelected(); 1635 DAGRoots.replace(BackedgeTakenCount); 1636 1637 ++NumRerolledLoops; 1638 return true; 1639} 1640 1641bool LoopReroll::runOnLoop(Loop *L, LPPassManager &LPM) { 1642 if (skipLoop(L)) 1643 return false; 1644 1645 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults(); 1646 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); 1647 SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); 1648 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI( 1649 *L->getHeader()->getParent()); 1650 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 1651 PreserveLCSSA = mustPreserveAnalysisID(LCSSAID); 1652 1653 BasicBlock *Header = L->getHeader(); 1654 LLVM_DEBUG(dbgs() << "LRR: F[" << Header->getParent()->getName() << "] Loop %" 1655 << Header->getName() << " (" << L->getNumBlocks() 1656 << " block(s))\n"); 1657 1658 // For now, we'll handle only single BB loops. 1659 if (L->getNumBlocks() > 1) 1660 return false; 1661 1662 if (!SE->hasLoopInvariantBackedgeTakenCount(L)) 1663 return false; 1664 1665 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 1666 LLVM_DEBUG(dbgs() << "\n Before Reroll:\n" << *(L->getHeader()) << "\n"); 1667 LLVM_DEBUG(dbgs() << "LRR: backedge-taken count = " << *BackedgeTakenCount 1668 << "\n"); 1669 1670 // First, we need to find the induction variable with respect to which we can 1671 // reroll (there may be several possible options). 1672 SmallInstructionVector PossibleIVs; 1673 IVToIncMap.clear(); 1674 LoopControlIV = nullptr; 1675 collectPossibleIVs(L, PossibleIVs); 1676 1677 if (PossibleIVs.empty()) { 1678 LLVM_DEBUG(dbgs() << "LRR: No possible IVs found\n"); 1679 return false; 1680 } 1681 1682 ReductionTracker Reductions; 1683 collectPossibleReductions(L, Reductions); 1684 bool Changed = false; 1685 1686 // For each possible IV, collect the associated possible set of 'root' nodes 1687 // (i+1, i+2, etc.). 1688 for (Instruction *PossibleIV : PossibleIVs) 1689 if (reroll(PossibleIV, L, Header, BackedgeTakenCount, Reductions)) { 1690 Changed = true; 1691 break; 1692 } 1693 LLVM_DEBUG(dbgs() << "\n After Reroll:\n" << *(L->getHeader()) << "\n"); 1694 1695 // Trip count of L has changed so SE must be re-evaluated. 1696 if (Changed) 1697 SE->forgetLoop(L); 1698 1699 return Changed; 1700} 1701