1 //===- LoopVectorizationLegality.cpp --------------------------------------===// 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 file provides loop vectorization legality analysis. Original code 10 // resided in LoopVectorize.cpp for a long time. 11 // 12 // At this point, it is implemented as a utility class, not as an analysis 13 // pass. It should be easy to create an analysis pass around it if there 14 // is a need (but D45420 needs to happen first). 15 // 16 17 #include "llvm/Transforms/Vectorize/LoopVectorizationLegality.h" 18 #include "llvm/Analysis/Loads.h" 19 #include "llvm/Analysis/LoopInfo.h" 20 #include "llvm/Analysis/OptimizationRemarkEmitter.h" 21 #include "llvm/Analysis/TargetLibraryInfo.h" 22 #include "llvm/Analysis/TargetTransformInfo.h" 23 #include "llvm/Analysis/ValueTracking.h" 24 #include "llvm/Analysis/VectorUtils.h" 25 #include "llvm/IR/IntrinsicInst.h" 26 #include "llvm/IR/PatternMatch.h" 27 #include "llvm/Transforms/Utils/SizeOpts.h" 28 #include "llvm/Transforms/Vectorize/LoopVectorize.h" 29 30 using namespace llvm; 31 using namespace PatternMatch; 32 33 #define LV_NAME "loop-vectorize" 34 #define DEBUG_TYPE LV_NAME 35 36 static cl::opt<bool> 37 EnableIfConversion("enable-if-conversion", cl::init(true), cl::Hidden, 38 cl::desc("Enable if-conversion during vectorization.")); 39 40 static cl::opt<bool> 41 AllowStridedPointerIVs("lv-strided-pointer-ivs", cl::init(false), cl::Hidden, 42 cl::desc("Enable recognition of non-constant strided " 43 "pointer induction variables.")); 44 45 namespace llvm { 46 cl::opt<bool> 47 HintsAllowReordering("hints-allow-reordering", cl::init(true), cl::Hidden, 48 cl::desc("Allow enabling loop hints to reorder " 49 "FP operations during vectorization.")); 50 } 51 52 // TODO: Move size-based thresholds out of legality checking, make cost based 53 // decisions instead of hard thresholds. 54 static cl::opt<unsigned> VectorizeSCEVCheckThreshold( 55 "vectorize-scev-check-threshold", cl::init(16), cl::Hidden, 56 cl::desc("The maximum number of SCEV checks allowed.")); 57 58 static cl::opt<unsigned> PragmaVectorizeSCEVCheckThreshold( 59 "pragma-vectorize-scev-check-threshold", cl::init(128), cl::Hidden, 60 cl::desc("The maximum number of SCEV checks allowed with a " 61 "vectorize(enable) pragma")); 62 63 static cl::opt<LoopVectorizeHints::ScalableForceKind> 64 ForceScalableVectorization( 65 "scalable-vectorization", cl::init(LoopVectorizeHints::SK_Unspecified), 66 cl::Hidden, 67 cl::desc("Control whether the compiler can use scalable vectors to " 68 "vectorize a loop"), 69 cl::values( 70 clEnumValN(LoopVectorizeHints::SK_FixedWidthOnly, "off", 71 "Scalable vectorization is disabled."), 72 clEnumValN( 73 LoopVectorizeHints::SK_PreferScalable, "preferred", 74 "Scalable vectorization is available and favored when the " 75 "cost is inconclusive."), 76 clEnumValN( 77 LoopVectorizeHints::SK_PreferScalable, "on", 78 "Scalable vectorization is available and favored when the " 79 "cost is inconclusive."))); 80 81 /// Maximum vectorization interleave count. 82 static const unsigned MaxInterleaveFactor = 16; 83 84 namespace llvm { 85 86 bool LoopVectorizeHints::Hint::validate(unsigned Val) { 87 switch (Kind) { 88 case HK_WIDTH: 89 return isPowerOf2_32(Val) && Val <= VectorizerParams::MaxVectorWidth; 90 case HK_INTERLEAVE: 91 return isPowerOf2_32(Val) && Val <= MaxInterleaveFactor; 92 case HK_FORCE: 93 return (Val <= 1); 94 case HK_ISVECTORIZED: 95 case HK_PREDICATE: 96 case HK_SCALABLE: 97 return (Val == 0 || Val == 1); 98 } 99 return false; 100 } 101 102 LoopVectorizeHints::LoopVectorizeHints(const Loop *L, 103 bool InterleaveOnlyWhenForced, 104 OptimizationRemarkEmitter &ORE, 105 const TargetTransformInfo *TTI) 106 : Width("vectorize.width", VectorizerParams::VectorizationFactor, HK_WIDTH), 107 Interleave("interleave.count", InterleaveOnlyWhenForced, HK_INTERLEAVE), 108 Force("vectorize.enable", FK_Undefined, HK_FORCE), 109 IsVectorized("isvectorized", 0, HK_ISVECTORIZED), 110 Predicate("vectorize.predicate.enable", FK_Undefined, HK_PREDICATE), 111 Scalable("vectorize.scalable.enable", SK_Unspecified, HK_SCALABLE), 112 TheLoop(L), ORE(ORE) { 113 // Populate values with existing loop metadata. 114 getHintsFromMetadata(); 115 116 // force-vector-interleave overrides DisableInterleaving. 117 if (VectorizerParams::isInterleaveForced()) 118 Interleave.Value = VectorizerParams::VectorizationInterleave; 119 120 // If the metadata doesn't explicitly specify whether to enable scalable 121 // vectorization, then decide based on the following criteria (increasing 122 // level of priority): 123 // - Target default 124 // - Metadata width 125 // - Force option (always overrides) 126 if ((LoopVectorizeHints::ScalableForceKind)Scalable.Value == SK_Unspecified) { 127 if (TTI) 128 Scalable.Value = TTI->enableScalableVectorization() ? SK_PreferScalable 129 : SK_FixedWidthOnly; 130 131 if (Width.Value) 132 // If the width is set, but the metadata says nothing about the scalable 133 // property, then assume it concerns only a fixed-width UserVF. 134 // If width is not set, the flag takes precedence. 135 Scalable.Value = SK_FixedWidthOnly; 136 } 137 138 // If the flag is set to force any use of scalable vectors, override the loop 139 // hints. 140 if (ForceScalableVectorization.getValue() != 141 LoopVectorizeHints::SK_Unspecified) 142 Scalable.Value = ForceScalableVectorization.getValue(); 143 144 // Scalable vectorization is disabled if no preference is specified. 145 if ((LoopVectorizeHints::ScalableForceKind)Scalable.Value == SK_Unspecified) 146 Scalable.Value = SK_FixedWidthOnly; 147 148 if (IsVectorized.Value != 1) 149 // If the vectorization width and interleaving count are both 1 then 150 // consider the loop to have been already vectorized because there's 151 // nothing more that we can do. 152 IsVectorized.Value = 153 getWidth() == ElementCount::getFixed(1) && getInterleave() == 1; 154 LLVM_DEBUG(if (InterleaveOnlyWhenForced && getInterleave() == 1) dbgs() 155 << "LV: Interleaving disabled by the pass manager\n"); 156 } 157 158 void LoopVectorizeHints::setAlreadyVectorized() { 159 LLVMContext &Context = TheLoop->getHeader()->getContext(); 160 161 MDNode *IsVectorizedMD = MDNode::get( 162 Context, 163 {MDString::get(Context, "llvm.loop.isvectorized"), 164 ConstantAsMetadata::get(ConstantInt::get(Context, APInt(32, 1)))}); 165 MDNode *LoopID = TheLoop->getLoopID(); 166 MDNode *NewLoopID = 167 makePostTransformationMetadata(Context, LoopID, 168 {Twine(Prefix(), "vectorize.").str(), 169 Twine(Prefix(), "interleave.").str()}, 170 {IsVectorizedMD}); 171 TheLoop->setLoopID(NewLoopID); 172 173 // Update internal cache. 174 IsVectorized.Value = 1; 175 } 176 177 bool LoopVectorizeHints::allowVectorization( 178 Function *F, Loop *L, bool VectorizeOnlyWhenForced) const { 179 if (getForce() == LoopVectorizeHints::FK_Disabled) { 180 LLVM_DEBUG(dbgs() << "LV: Not vectorizing: #pragma vectorize disable.\n"); 181 emitRemarkWithHints(); 182 return false; 183 } 184 185 if (VectorizeOnlyWhenForced && getForce() != LoopVectorizeHints::FK_Enabled) { 186 LLVM_DEBUG(dbgs() << "LV: Not vectorizing: No #pragma vectorize enable.\n"); 187 emitRemarkWithHints(); 188 return false; 189 } 190 191 if (getIsVectorized() == 1) { 192 LLVM_DEBUG(dbgs() << "LV: Not vectorizing: Disabled/already vectorized.\n"); 193 // FIXME: Add interleave.disable metadata. This will allow 194 // vectorize.disable to be used without disabling the pass and errors 195 // to differentiate between disabled vectorization and a width of 1. 196 ORE.emit([&]() { 197 return OptimizationRemarkAnalysis(vectorizeAnalysisPassName(), 198 "AllDisabled", L->getStartLoc(), 199 L->getHeader()) 200 << "loop not vectorized: vectorization and interleaving are " 201 "explicitly disabled, or the loop has already been " 202 "vectorized"; 203 }); 204 return false; 205 } 206 207 return true; 208 } 209 210 void LoopVectorizeHints::emitRemarkWithHints() const { 211 using namespace ore; 212 213 ORE.emit([&]() { 214 if (Force.Value == LoopVectorizeHints::FK_Disabled) 215 return OptimizationRemarkMissed(LV_NAME, "MissedExplicitlyDisabled", 216 TheLoop->getStartLoc(), 217 TheLoop->getHeader()) 218 << "loop not vectorized: vectorization is explicitly disabled"; 219 else { 220 OptimizationRemarkMissed R(LV_NAME, "MissedDetails", 221 TheLoop->getStartLoc(), TheLoop->getHeader()); 222 R << "loop not vectorized"; 223 if (Force.Value == LoopVectorizeHints::FK_Enabled) { 224 R << " (Force=" << NV("Force", true); 225 if (Width.Value != 0) 226 R << ", Vector Width=" << NV("VectorWidth", getWidth()); 227 if (getInterleave() != 0) 228 R << ", Interleave Count=" << NV("InterleaveCount", getInterleave()); 229 R << ")"; 230 } 231 return R; 232 } 233 }); 234 } 235 236 const char *LoopVectorizeHints::vectorizeAnalysisPassName() const { 237 if (getWidth() == ElementCount::getFixed(1)) 238 return LV_NAME; 239 if (getForce() == LoopVectorizeHints::FK_Disabled) 240 return LV_NAME; 241 if (getForce() == LoopVectorizeHints::FK_Undefined && getWidth().isZero()) 242 return LV_NAME; 243 return OptimizationRemarkAnalysis::AlwaysPrint; 244 } 245 246 bool LoopVectorizeHints::allowReordering() const { 247 // Allow the vectorizer to change the order of operations if enabling 248 // loop hints are provided 249 ElementCount EC = getWidth(); 250 return HintsAllowReordering && 251 (getForce() == LoopVectorizeHints::FK_Enabled || 252 EC.getKnownMinValue() > 1); 253 } 254 255 void LoopVectorizeHints::getHintsFromMetadata() { 256 MDNode *LoopID = TheLoop->getLoopID(); 257 if (!LoopID) 258 return; 259 260 // First operand should refer to the loop id itself. 261 assert(LoopID->getNumOperands() > 0 && "requires at least one operand"); 262 assert(LoopID->getOperand(0) == LoopID && "invalid loop id"); 263 264 for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) { 265 const MDString *S = nullptr; 266 SmallVector<Metadata *, 4> Args; 267 268 // The expected hint is either a MDString or a MDNode with the first 269 // operand a MDString. 270 if (const MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i))) { 271 if (!MD || MD->getNumOperands() == 0) 272 continue; 273 S = dyn_cast<MDString>(MD->getOperand(0)); 274 for (unsigned i = 1, ie = MD->getNumOperands(); i < ie; ++i) 275 Args.push_back(MD->getOperand(i)); 276 } else { 277 S = dyn_cast<MDString>(LoopID->getOperand(i)); 278 assert(Args.size() == 0 && "too many arguments for MDString"); 279 } 280 281 if (!S) 282 continue; 283 284 // Check if the hint starts with the loop metadata prefix. 285 StringRef Name = S->getString(); 286 if (Args.size() == 1) 287 setHint(Name, Args[0]); 288 } 289 } 290 291 void LoopVectorizeHints::setHint(StringRef Name, Metadata *Arg) { 292 if (!Name.starts_with(Prefix())) 293 return; 294 Name = Name.substr(Prefix().size(), StringRef::npos); 295 296 const ConstantInt *C = mdconst::dyn_extract<ConstantInt>(Arg); 297 if (!C) 298 return; 299 unsigned Val = C->getZExtValue(); 300 301 Hint *Hints[] = {&Width, &Interleave, &Force, 302 &IsVectorized, &Predicate, &Scalable}; 303 for (auto *H : Hints) { 304 if (Name == H->Name) { 305 if (H->validate(Val)) 306 H->Value = Val; 307 else 308 LLVM_DEBUG(dbgs() << "LV: ignoring invalid hint '" << Name << "'\n"); 309 break; 310 } 311 } 312 } 313 314 // Return true if the inner loop \p Lp is uniform with regard to the outer loop 315 // \p OuterLp (i.e., if the outer loop is vectorized, all the vector lanes 316 // executing the inner loop will execute the same iterations). This check is 317 // very constrained for now but it will be relaxed in the future. \p Lp is 318 // considered uniform if it meets all the following conditions: 319 // 1) it has a canonical IV (starting from 0 and with stride 1), 320 // 2) its latch terminator is a conditional branch and, 321 // 3) its latch condition is a compare instruction whose operands are the 322 // canonical IV and an OuterLp invariant. 323 // This check doesn't take into account the uniformity of other conditions not 324 // related to the loop latch because they don't affect the loop uniformity. 325 // 326 // NOTE: We decided to keep all these checks and its associated documentation 327 // together so that we can easily have a picture of the current supported loop 328 // nests. However, some of the current checks don't depend on \p OuterLp and 329 // would be redundantly executed for each \p Lp if we invoked this function for 330 // different candidate outer loops. This is not the case for now because we 331 // don't currently have the infrastructure to evaluate multiple candidate outer 332 // loops and \p OuterLp will be a fixed parameter while we only support explicit 333 // outer loop vectorization. It's also very likely that these checks go away 334 // before introducing the aforementioned infrastructure. However, if this is not 335 // the case, we should move the \p OuterLp independent checks to a separate 336 // function that is only executed once for each \p Lp. 337 static bool isUniformLoop(Loop *Lp, Loop *OuterLp) { 338 assert(Lp->getLoopLatch() && "Expected loop with a single latch."); 339 340 // If Lp is the outer loop, it's uniform by definition. 341 if (Lp == OuterLp) 342 return true; 343 assert(OuterLp->contains(Lp) && "OuterLp must contain Lp."); 344 345 // 1. 346 PHINode *IV = Lp->getCanonicalInductionVariable(); 347 if (!IV) { 348 LLVM_DEBUG(dbgs() << "LV: Canonical IV not found.\n"); 349 return false; 350 } 351 352 // 2. 353 BasicBlock *Latch = Lp->getLoopLatch(); 354 auto *LatchBr = dyn_cast<BranchInst>(Latch->getTerminator()); 355 if (!LatchBr || LatchBr->isUnconditional()) { 356 LLVM_DEBUG(dbgs() << "LV: Unsupported loop latch branch.\n"); 357 return false; 358 } 359 360 // 3. 361 auto *LatchCmp = dyn_cast<CmpInst>(LatchBr->getCondition()); 362 if (!LatchCmp) { 363 LLVM_DEBUG( 364 dbgs() << "LV: Loop latch condition is not a compare instruction.\n"); 365 return false; 366 } 367 368 Value *CondOp0 = LatchCmp->getOperand(0); 369 Value *CondOp1 = LatchCmp->getOperand(1); 370 Value *IVUpdate = IV->getIncomingValueForBlock(Latch); 371 if (!(CondOp0 == IVUpdate && OuterLp->isLoopInvariant(CondOp1)) && 372 !(CondOp1 == IVUpdate && OuterLp->isLoopInvariant(CondOp0))) { 373 LLVM_DEBUG(dbgs() << "LV: Loop latch condition is not uniform.\n"); 374 return false; 375 } 376 377 return true; 378 } 379 380 // Return true if \p Lp and all its nested loops are uniform with regard to \p 381 // OuterLp. 382 static bool isUniformLoopNest(Loop *Lp, Loop *OuterLp) { 383 if (!isUniformLoop(Lp, OuterLp)) 384 return false; 385 386 // Check if nested loops are uniform. 387 for (Loop *SubLp : *Lp) 388 if (!isUniformLoopNest(SubLp, OuterLp)) 389 return false; 390 391 return true; 392 } 393 394 static Type *convertPointerToIntegerType(const DataLayout &DL, Type *Ty) { 395 if (Ty->isPointerTy()) 396 return DL.getIntPtrType(Ty); 397 398 // It is possible that char's or short's overflow when we ask for the loop's 399 // trip count, work around this by changing the type size. 400 if (Ty->getScalarSizeInBits() < 32) 401 return Type::getInt32Ty(Ty->getContext()); 402 403 return Ty; 404 } 405 406 static Type *getWiderType(const DataLayout &DL, Type *Ty0, Type *Ty1) { 407 Ty0 = convertPointerToIntegerType(DL, Ty0); 408 Ty1 = convertPointerToIntegerType(DL, Ty1); 409 if (Ty0->getScalarSizeInBits() > Ty1->getScalarSizeInBits()) 410 return Ty0; 411 return Ty1; 412 } 413 414 /// Check that the instruction has outside loop users and is not an 415 /// identified reduction variable. 416 static bool hasOutsideLoopUser(const Loop *TheLoop, Instruction *Inst, 417 SmallPtrSetImpl<Value *> &AllowedExit) { 418 // Reductions, Inductions and non-header phis are allowed to have exit users. All 419 // other instructions must not have external users. 420 if (!AllowedExit.count(Inst)) 421 // Check that all of the users of the loop are inside the BB. 422 for (User *U : Inst->users()) { 423 Instruction *UI = cast<Instruction>(U); 424 // This user may be a reduction exit value. 425 if (!TheLoop->contains(UI)) { 426 LLVM_DEBUG(dbgs() << "LV: Found an outside user for : " << *UI << '\n'); 427 return true; 428 } 429 } 430 return false; 431 } 432 433 /// Returns true if A and B have same pointer operands or same SCEVs addresses 434 static bool storeToSameAddress(ScalarEvolution *SE, StoreInst *A, 435 StoreInst *B) { 436 // Compare store 437 if (A == B) 438 return true; 439 440 // Otherwise Compare pointers 441 Value *APtr = A->getPointerOperand(); 442 Value *BPtr = B->getPointerOperand(); 443 if (APtr == BPtr) 444 return true; 445 446 // Otherwise compare address SCEVs 447 if (SE->getSCEV(APtr) == SE->getSCEV(BPtr)) 448 return true; 449 450 return false; 451 } 452 453 int LoopVectorizationLegality::isConsecutivePtr(Type *AccessTy, 454 Value *Ptr) const { 455 // FIXME: Currently, the set of symbolic strides is sometimes queried before 456 // it's collected. This happens from canVectorizeWithIfConvert, when the 457 // pointer is checked to reference consecutive elements suitable for a 458 // masked access. 459 const auto &Strides = 460 LAI ? LAI->getSymbolicStrides() : DenseMap<Value *, const SCEV *>(); 461 462 Function *F = TheLoop->getHeader()->getParent(); 463 bool OptForSize = F->hasOptSize() || 464 llvm::shouldOptimizeForSize(TheLoop->getHeader(), PSI, BFI, 465 PGSOQueryType::IRPass); 466 bool CanAddPredicate = !OptForSize; 467 int Stride = getPtrStride(PSE, AccessTy, Ptr, TheLoop, Strides, 468 CanAddPredicate, false).value_or(0); 469 if (Stride == 1 || Stride == -1) 470 return Stride; 471 return 0; 472 } 473 474 bool LoopVectorizationLegality::isInvariant(Value *V) const { 475 return LAI->isInvariant(V); 476 } 477 478 namespace { 479 /// A rewriter to build the SCEVs for each of the VF lanes in the expected 480 /// vectorized loop, which can then be compared to detect their uniformity. This 481 /// is done by replacing the AddRec SCEVs of the original scalar loop (TheLoop) 482 /// with new AddRecs where the step is multiplied by StepMultiplier and Offset * 483 /// Step is added. Also checks if all sub-expressions are analyzable w.r.t. 484 /// uniformity. 485 class SCEVAddRecForUniformityRewriter 486 : public SCEVRewriteVisitor<SCEVAddRecForUniformityRewriter> { 487 /// Multiplier to be applied to the step of AddRecs in TheLoop. 488 unsigned StepMultiplier; 489 490 /// Offset to be added to the AddRecs in TheLoop. 491 unsigned Offset; 492 493 /// Loop for which to rewrite AddRecsFor. 494 Loop *TheLoop; 495 496 /// Is any sub-expressions not analyzable w.r.t. uniformity? 497 bool CannotAnalyze = false; 498 499 bool canAnalyze() const { return !CannotAnalyze; } 500 501 public: 502 SCEVAddRecForUniformityRewriter(ScalarEvolution &SE, unsigned StepMultiplier, 503 unsigned Offset, Loop *TheLoop) 504 : SCEVRewriteVisitor(SE), StepMultiplier(StepMultiplier), Offset(Offset), 505 TheLoop(TheLoop) {} 506 507 const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) { 508 assert(Expr->getLoop() == TheLoop && 509 "addrec outside of TheLoop must be invariant and should have been " 510 "handled earlier"); 511 // Build a new AddRec by multiplying the step by StepMultiplier and 512 // incrementing the start by Offset * step. 513 Type *Ty = Expr->getType(); 514 auto *Step = Expr->getStepRecurrence(SE); 515 if (!SE.isLoopInvariant(Step, TheLoop)) { 516 CannotAnalyze = true; 517 return Expr; 518 } 519 auto *NewStep = SE.getMulExpr(Step, SE.getConstant(Ty, StepMultiplier)); 520 auto *ScaledOffset = SE.getMulExpr(Step, SE.getConstant(Ty, Offset)); 521 auto *NewStart = SE.getAddExpr(Expr->getStart(), ScaledOffset); 522 return SE.getAddRecExpr(NewStart, NewStep, TheLoop, SCEV::FlagAnyWrap); 523 } 524 525 const SCEV *visit(const SCEV *S) { 526 if (CannotAnalyze || SE.isLoopInvariant(S, TheLoop)) 527 return S; 528 return SCEVRewriteVisitor<SCEVAddRecForUniformityRewriter>::visit(S); 529 } 530 531 const SCEV *visitUnknown(const SCEVUnknown *S) { 532 if (SE.isLoopInvariant(S, TheLoop)) 533 return S; 534 // The value could vary across iterations. 535 CannotAnalyze = true; 536 return S; 537 } 538 539 const SCEV *visitCouldNotCompute(const SCEVCouldNotCompute *S) { 540 // Could not analyze the expression. 541 CannotAnalyze = true; 542 return S; 543 } 544 545 static const SCEV *rewrite(const SCEV *S, ScalarEvolution &SE, 546 unsigned StepMultiplier, unsigned Offset, 547 Loop *TheLoop) { 548 /// Bail out if the expression does not contain an UDiv expression. 549 /// Uniform values which are not loop invariant require operations to strip 550 /// out the lowest bits. For now just look for UDivs and use it to avoid 551 /// re-writing UDIV-free expressions for other lanes to limit compile time. 552 if (!SCEVExprContains(S, 553 [](const SCEV *S) { return isa<SCEVUDivExpr>(S); })) 554 return SE.getCouldNotCompute(); 555 556 SCEVAddRecForUniformityRewriter Rewriter(SE, StepMultiplier, Offset, 557 TheLoop); 558 const SCEV *Result = Rewriter.visit(S); 559 560 if (Rewriter.canAnalyze()) 561 return Result; 562 return SE.getCouldNotCompute(); 563 } 564 }; 565 566 } // namespace 567 568 bool LoopVectorizationLegality::isUniform(Value *V, ElementCount VF) const { 569 if (isInvariant(V)) 570 return true; 571 if (VF.isScalable()) 572 return false; 573 if (VF.isScalar()) 574 return true; 575 576 // Since we rely on SCEV for uniformity, if the type is not SCEVable, it is 577 // never considered uniform. 578 auto *SE = PSE.getSE(); 579 if (!SE->isSCEVable(V->getType())) 580 return false; 581 const SCEV *S = SE->getSCEV(V); 582 583 // Rewrite AddRecs in TheLoop to step by VF and check if the expression for 584 // lane 0 matches the expressions for all other lanes. 585 unsigned FixedVF = VF.getKnownMinValue(); 586 const SCEV *FirstLaneExpr = 587 SCEVAddRecForUniformityRewriter::rewrite(S, *SE, FixedVF, 0, TheLoop); 588 if (isa<SCEVCouldNotCompute>(FirstLaneExpr)) 589 return false; 590 591 // Make sure the expressions for lanes FixedVF-1..1 match the expression for 592 // lane 0. We check lanes in reverse order for compile-time, as frequently 593 // checking the last lane is sufficient to rule out uniformity. 594 return all_of(reverse(seq<unsigned>(1, FixedVF)), [&](unsigned I) { 595 const SCEV *IthLaneExpr = 596 SCEVAddRecForUniformityRewriter::rewrite(S, *SE, FixedVF, I, TheLoop); 597 return FirstLaneExpr == IthLaneExpr; 598 }); 599 } 600 601 bool LoopVectorizationLegality::isUniformMemOp(Instruction &I, 602 ElementCount VF) const { 603 Value *Ptr = getLoadStorePointerOperand(&I); 604 if (!Ptr) 605 return false; 606 // Note: There's nothing inherent which prevents predicated loads and 607 // stores from being uniform. The current lowering simply doesn't handle 608 // it; in particular, the cost model distinguishes scatter/gather from 609 // scalar w/predication, and we currently rely on the scalar path. 610 return isUniform(Ptr, VF) && !blockNeedsPredication(I.getParent()); 611 } 612 613 bool LoopVectorizationLegality::canVectorizeOuterLoop() { 614 assert(!TheLoop->isInnermost() && "We are not vectorizing an outer loop."); 615 // Store the result and return it at the end instead of exiting early, in case 616 // allowExtraAnalysis is used to report multiple reasons for not vectorizing. 617 bool Result = true; 618 bool DoExtraAnalysis = ORE->allowExtraAnalysis(DEBUG_TYPE); 619 620 for (BasicBlock *BB : TheLoop->blocks()) { 621 // Check whether the BB terminator is a BranchInst. Any other terminator is 622 // not supported yet. 623 auto *Br = dyn_cast<BranchInst>(BB->getTerminator()); 624 if (!Br) { 625 reportVectorizationFailure("Unsupported basic block terminator", 626 "loop control flow is not understood by vectorizer", 627 "CFGNotUnderstood", ORE, TheLoop); 628 if (DoExtraAnalysis) 629 Result = false; 630 else 631 return false; 632 } 633 634 // Check whether the BranchInst is a supported one. Only unconditional 635 // branches, conditional branches with an outer loop invariant condition or 636 // backedges are supported. 637 // FIXME: We skip these checks when VPlan predication is enabled as we 638 // want to allow divergent branches. This whole check will be removed 639 // once VPlan predication is on by default. 640 if (Br && Br->isConditional() && 641 !TheLoop->isLoopInvariant(Br->getCondition()) && 642 !LI->isLoopHeader(Br->getSuccessor(0)) && 643 !LI->isLoopHeader(Br->getSuccessor(1))) { 644 reportVectorizationFailure("Unsupported conditional branch", 645 "loop control flow is not understood by vectorizer", 646 "CFGNotUnderstood", ORE, TheLoop); 647 if (DoExtraAnalysis) 648 Result = false; 649 else 650 return false; 651 } 652 } 653 654 // Check whether inner loops are uniform. At this point, we only support 655 // simple outer loops scenarios with uniform nested loops. 656 if (!isUniformLoopNest(TheLoop /*loop nest*/, 657 TheLoop /*context outer loop*/)) { 658 reportVectorizationFailure("Outer loop contains divergent loops", 659 "loop control flow is not understood by vectorizer", 660 "CFGNotUnderstood", ORE, TheLoop); 661 if (DoExtraAnalysis) 662 Result = false; 663 else 664 return false; 665 } 666 667 // Check whether we are able to set up outer loop induction. 668 if (!setupOuterLoopInductions()) { 669 reportVectorizationFailure("Unsupported outer loop Phi(s)", 670 "Unsupported outer loop Phi(s)", 671 "UnsupportedPhi", ORE, TheLoop); 672 if (DoExtraAnalysis) 673 Result = false; 674 else 675 return false; 676 } 677 678 return Result; 679 } 680 681 void LoopVectorizationLegality::addInductionPhi( 682 PHINode *Phi, const InductionDescriptor &ID, 683 SmallPtrSetImpl<Value *> &AllowedExit) { 684 Inductions[Phi] = ID; 685 686 // In case this induction also comes with casts that we know we can ignore 687 // in the vectorized loop body, record them here. All casts could be recorded 688 // here for ignoring, but suffices to record only the first (as it is the 689 // only one that may bw used outside the cast sequence). 690 const SmallVectorImpl<Instruction *> &Casts = ID.getCastInsts(); 691 if (!Casts.empty()) 692 InductionCastsToIgnore.insert(*Casts.begin()); 693 694 Type *PhiTy = Phi->getType(); 695 const DataLayout &DL = Phi->getModule()->getDataLayout(); 696 697 // Get the widest type. 698 if (!PhiTy->isFloatingPointTy()) { 699 if (!WidestIndTy) 700 WidestIndTy = convertPointerToIntegerType(DL, PhiTy); 701 else 702 WidestIndTy = getWiderType(DL, PhiTy, WidestIndTy); 703 } 704 705 // Int inductions are special because we only allow one IV. 706 if (ID.getKind() == InductionDescriptor::IK_IntInduction && 707 ID.getConstIntStepValue() && ID.getConstIntStepValue()->isOne() && 708 isa<Constant>(ID.getStartValue()) && 709 cast<Constant>(ID.getStartValue())->isNullValue()) { 710 711 // Use the phi node with the widest type as induction. Use the last 712 // one if there are multiple (no good reason for doing this other 713 // than it is expedient). We've checked that it begins at zero and 714 // steps by one, so this is a canonical induction variable. 715 if (!PrimaryInduction || PhiTy == WidestIndTy) 716 PrimaryInduction = Phi; 717 } 718 719 // Both the PHI node itself, and the "post-increment" value feeding 720 // back into the PHI node may have external users. 721 // We can allow those uses, except if the SCEVs we have for them rely 722 // on predicates that only hold within the loop, since allowing the exit 723 // currently means re-using this SCEV outside the loop (see PR33706 for more 724 // details). 725 if (PSE.getPredicate().isAlwaysTrue()) { 726 AllowedExit.insert(Phi); 727 AllowedExit.insert(Phi->getIncomingValueForBlock(TheLoop->getLoopLatch())); 728 } 729 730 LLVM_DEBUG(dbgs() << "LV: Found an induction variable.\n"); 731 } 732 733 bool LoopVectorizationLegality::setupOuterLoopInductions() { 734 BasicBlock *Header = TheLoop->getHeader(); 735 736 // Returns true if a given Phi is a supported induction. 737 auto isSupportedPhi = [&](PHINode &Phi) -> bool { 738 InductionDescriptor ID; 739 if (InductionDescriptor::isInductionPHI(&Phi, TheLoop, PSE, ID) && 740 ID.getKind() == InductionDescriptor::IK_IntInduction) { 741 addInductionPhi(&Phi, ID, AllowedExit); 742 return true; 743 } else { 744 // Bail out for any Phi in the outer loop header that is not a supported 745 // induction. 746 LLVM_DEBUG( 747 dbgs() 748 << "LV: Found unsupported PHI for outer loop vectorization.\n"); 749 return false; 750 } 751 }; 752 753 if (llvm::all_of(Header->phis(), isSupportedPhi)) 754 return true; 755 else 756 return false; 757 } 758 759 /// Checks if a function is scalarizable according to the TLI, in 760 /// the sense that it should be vectorized and then expanded in 761 /// multiple scalar calls. This is represented in the 762 /// TLI via mappings that do not specify a vector name, as in the 763 /// following example: 764 /// 765 /// const VecDesc VecIntrinsics[] = { 766 /// {"llvm.phx.abs.i32", "", 4} 767 /// }; 768 static bool isTLIScalarize(const TargetLibraryInfo &TLI, const CallInst &CI) { 769 const StringRef ScalarName = CI.getCalledFunction()->getName(); 770 bool Scalarize = TLI.isFunctionVectorizable(ScalarName); 771 // Check that all known VFs are not associated to a vector 772 // function, i.e. the vector name is emty. 773 if (Scalarize) { 774 ElementCount WidestFixedVF, WidestScalableVF; 775 TLI.getWidestVF(ScalarName, WidestFixedVF, WidestScalableVF); 776 for (ElementCount VF = ElementCount::getFixed(2); 777 ElementCount::isKnownLE(VF, WidestFixedVF); VF *= 2) 778 Scalarize &= !TLI.isFunctionVectorizable(ScalarName, VF); 779 for (ElementCount VF = ElementCount::getScalable(1); 780 ElementCount::isKnownLE(VF, WidestScalableVF); VF *= 2) 781 Scalarize &= !TLI.isFunctionVectorizable(ScalarName, VF); 782 assert((WidestScalableVF.isZero() || !Scalarize) && 783 "Caller may decide to scalarize a variant using a scalable VF"); 784 } 785 return Scalarize; 786 } 787 788 bool LoopVectorizationLegality::canVectorizeInstrs() { 789 BasicBlock *Header = TheLoop->getHeader(); 790 791 // For each block in the loop. 792 for (BasicBlock *BB : TheLoop->blocks()) { 793 // Scan the instructions in the block and look for hazards. 794 for (Instruction &I : *BB) { 795 if (auto *Phi = dyn_cast<PHINode>(&I)) { 796 Type *PhiTy = Phi->getType(); 797 // Check that this PHI type is allowed. 798 if (!PhiTy->isIntegerTy() && !PhiTy->isFloatingPointTy() && 799 !PhiTy->isPointerTy()) { 800 reportVectorizationFailure("Found a non-int non-pointer PHI", 801 "loop control flow is not understood by vectorizer", 802 "CFGNotUnderstood", ORE, TheLoop); 803 return false; 804 } 805 806 // If this PHINode is not in the header block, then we know that we 807 // can convert it to select during if-conversion. No need to check if 808 // the PHIs in this block are induction or reduction variables. 809 if (BB != Header) { 810 // Non-header phi nodes that have outside uses can be vectorized. Add 811 // them to the list of allowed exits. 812 // Unsafe cyclic dependencies with header phis are identified during 813 // legalization for reduction, induction and fixed order 814 // recurrences. 815 AllowedExit.insert(&I); 816 continue; 817 } 818 819 // We only allow if-converted PHIs with exactly two incoming values. 820 if (Phi->getNumIncomingValues() != 2) { 821 reportVectorizationFailure("Found an invalid PHI", 822 "loop control flow is not understood by vectorizer", 823 "CFGNotUnderstood", ORE, TheLoop, Phi); 824 return false; 825 } 826 827 RecurrenceDescriptor RedDes; 828 if (RecurrenceDescriptor::isReductionPHI(Phi, TheLoop, RedDes, DB, AC, 829 DT, PSE.getSE())) { 830 Requirements->addExactFPMathInst(RedDes.getExactFPMathInst()); 831 AllowedExit.insert(RedDes.getLoopExitInstr()); 832 Reductions[Phi] = RedDes; 833 continue; 834 } 835 836 // We prevent matching non-constant strided pointer IVS to preserve 837 // historical vectorizer behavior after a generalization of the 838 // IVDescriptor code. The intent is to remove this check, but we 839 // have to fix issues around code quality for such loops first. 840 auto isDisallowedStridedPointerInduction = 841 [](const InductionDescriptor &ID) { 842 if (AllowStridedPointerIVs) 843 return false; 844 return ID.getKind() == InductionDescriptor::IK_PtrInduction && 845 ID.getConstIntStepValue() == nullptr; 846 }; 847 848 // TODO: Instead of recording the AllowedExit, it would be good to 849 // record the complementary set: NotAllowedExit. These include (but may 850 // not be limited to): 851 // 1. Reduction phis as they represent the one-before-last value, which 852 // is not available when vectorized 853 // 2. Induction phis and increment when SCEV predicates cannot be used 854 // outside the loop - see addInductionPhi 855 // 3. Non-Phis with outside uses when SCEV predicates cannot be used 856 // outside the loop - see call to hasOutsideLoopUser in the non-phi 857 // handling below 858 // 4. FixedOrderRecurrence phis that can possibly be handled by 859 // extraction. 860 // By recording these, we can then reason about ways to vectorize each 861 // of these NotAllowedExit. 862 InductionDescriptor ID; 863 if (InductionDescriptor::isInductionPHI(Phi, TheLoop, PSE, ID) && 864 !isDisallowedStridedPointerInduction(ID)) { 865 addInductionPhi(Phi, ID, AllowedExit); 866 Requirements->addExactFPMathInst(ID.getExactFPMathInst()); 867 continue; 868 } 869 870 if (RecurrenceDescriptor::isFixedOrderRecurrence(Phi, TheLoop, DT)) { 871 AllowedExit.insert(Phi); 872 FixedOrderRecurrences.insert(Phi); 873 continue; 874 } 875 876 // As a last resort, coerce the PHI to a AddRec expression 877 // and re-try classifying it a an induction PHI. 878 if (InductionDescriptor::isInductionPHI(Phi, TheLoop, PSE, ID, true) && 879 !isDisallowedStridedPointerInduction(ID)) { 880 addInductionPhi(Phi, ID, AllowedExit); 881 continue; 882 } 883 884 reportVectorizationFailure("Found an unidentified PHI", 885 "value that could not be identified as " 886 "reduction is used outside the loop", 887 "NonReductionValueUsedOutsideLoop", ORE, TheLoop, Phi); 888 return false; 889 } // end of PHI handling 890 891 // We handle calls that: 892 // * Are debug info intrinsics. 893 // * Have a mapping to an IR intrinsic. 894 // * Have a vector version available. 895 auto *CI = dyn_cast<CallInst>(&I); 896 897 if (CI && !getVectorIntrinsicIDForCall(CI, TLI) && 898 !isa<DbgInfoIntrinsic>(CI) && 899 !(CI->getCalledFunction() && TLI && 900 (!VFDatabase::getMappings(*CI).empty() || 901 isTLIScalarize(*TLI, *CI)))) { 902 // If the call is a recognized math libary call, it is likely that 903 // we can vectorize it given loosened floating-point constraints. 904 LibFunc Func; 905 bool IsMathLibCall = 906 TLI && CI->getCalledFunction() && 907 CI->getType()->isFloatingPointTy() && 908 TLI->getLibFunc(CI->getCalledFunction()->getName(), Func) && 909 TLI->hasOptimizedCodeGen(Func); 910 911 if (IsMathLibCall) { 912 // TODO: Ideally, we should not use clang-specific language here, 913 // but it's hard to provide meaningful yet generic advice. 914 // Also, should this be guarded by allowExtraAnalysis() and/or be part 915 // of the returned info from isFunctionVectorizable()? 916 reportVectorizationFailure( 917 "Found a non-intrinsic callsite", 918 "library call cannot be vectorized. " 919 "Try compiling with -fno-math-errno, -ffast-math, " 920 "or similar flags", 921 "CantVectorizeLibcall", ORE, TheLoop, CI); 922 } else { 923 reportVectorizationFailure("Found a non-intrinsic callsite", 924 "call instruction cannot be vectorized", 925 "CantVectorizeLibcall", ORE, TheLoop, CI); 926 } 927 return false; 928 } 929 930 // Some intrinsics have scalar arguments and should be same in order for 931 // them to be vectorized (i.e. loop invariant). 932 if (CI) { 933 auto *SE = PSE.getSE(); 934 Intrinsic::ID IntrinID = getVectorIntrinsicIDForCall(CI, TLI); 935 for (unsigned i = 0, e = CI->arg_size(); i != e; ++i) 936 if (isVectorIntrinsicWithScalarOpAtArg(IntrinID, i)) { 937 if (!SE->isLoopInvariant(PSE.getSCEV(CI->getOperand(i)), TheLoop)) { 938 reportVectorizationFailure("Found unvectorizable intrinsic", 939 "intrinsic instruction cannot be vectorized", 940 "CantVectorizeIntrinsic", ORE, TheLoop, CI); 941 return false; 942 } 943 } 944 } 945 946 // If we found a vectorized variant of a function, note that so LV can 947 // make better decisions about maximum VF. 948 if (CI && !VFDatabase::getMappings(*CI).empty()) 949 VecCallVariantsFound = true; 950 951 // Check that the instruction return type is vectorizable. 952 // Also, we can't vectorize extractelement instructions. 953 if ((!VectorType::isValidElementType(I.getType()) && 954 !I.getType()->isVoidTy()) || 955 isa<ExtractElementInst>(I)) { 956 reportVectorizationFailure("Found unvectorizable type", 957 "instruction return type cannot be vectorized", 958 "CantVectorizeInstructionReturnType", ORE, TheLoop, &I); 959 return false; 960 } 961 962 // Check that the stored type is vectorizable. 963 if (auto *ST = dyn_cast<StoreInst>(&I)) { 964 Type *T = ST->getValueOperand()->getType(); 965 if (!VectorType::isValidElementType(T)) { 966 reportVectorizationFailure("Store instruction cannot be vectorized", 967 "store instruction cannot be vectorized", 968 "CantVectorizeStore", ORE, TheLoop, ST); 969 return false; 970 } 971 972 // For nontemporal stores, check that a nontemporal vector version is 973 // supported on the target. 974 if (ST->getMetadata(LLVMContext::MD_nontemporal)) { 975 // Arbitrarily try a vector of 2 elements. 976 auto *VecTy = FixedVectorType::get(T, /*NumElts=*/2); 977 assert(VecTy && "did not find vectorized version of stored type"); 978 if (!TTI->isLegalNTStore(VecTy, ST->getAlign())) { 979 reportVectorizationFailure( 980 "nontemporal store instruction cannot be vectorized", 981 "nontemporal store instruction cannot be vectorized", 982 "CantVectorizeNontemporalStore", ORE, TheLoop, ST); 983 return false; 984 } 985 } 986 987 } else if (auto *LD = dyn_cast<LoadInst>(&I)) { 988 if (LD->getMetadata(LLVMContext::MD_nontemporal)) { 989 // For nontemporal loads, check that a nontemporal vector version is 990 // supported on the target (arbitrarily try a vector of 2 elements). 991 auto *VecTy = FixedVectorType::get(I.getType(), /*NumElts=*/2); 992 assert(VecTy && "did not find vectorized version of load type"); 993 if (!TTI->isLegalNTLoad(VecTy, LD->getAlign())) { 994 reportVectorizationFailure( 995 "nontemporal load instruction cannot be vectorized", 996 "nontemporal load instruction cannot be vectorized", 997 "CantVectorizeNontemporalLoad", ORE, TheLoop, LD); 998 return false; 999 } 1000 } 1001 1002 // FP instructions can allow unsafe algebra, thus vectorizable by 1003 // non-IEEE-754 compliant SIMD units. 1004 // This applies to floating-point math operations and calls, not memory 1005 // operations, shuffles, or casts, as they don't change precision or 1006 // semantics. 1007 } else if (I.getType()->isFloatingPointTy() && (CI || I.isBinaryOp()) && 1008 !I.isFast()) { 1009 LLVM_DEBUG(dbgs() << "LV: Found FP op with unsafe algebra.\n"); 1010 Hints->setPotentiallyUnsafe(); 1011 } 1012 1013 // Reduction instructions are allowed to have exit users. 1014 // All other instructions must not have external users. 1015 if (hasOutsideLoopUser(TheLoop, &I, AllowedExit)) { 1016 // We can safely vectorize loops where instructions within the loop are 1017 // used outside the loop only if the SCEV predicates within the loop is 1018 // same as outside the loop. Allowing the exit means reusing the SCEV 1019 // outside the loop. 1020 if (PSE.getPredicate().isAlwaysTrue()) { 1021 AllowedExit.insert(&I); 1022 continue; 1023 } 1024 reportVectorizationFailure("Value cannot be used outside the loop", 1025 "value cannot be used outside the loop", 1026 "ValueUsedOutsideLoop", ORE, TheLoop, &I); 1027 return false; 1028 } 1029 } // next instr. 1030 } 1031 1032 if (!PrimaryInduction) { 1033 if (Inductions.empty()) { 1034 reportVectorizationFailure("Did not find one integer induction var", 1035 "loop induction variable could not be identified", 1036 "NoInductionVariable", ORE, TheLoop); 1037 return false; 1038 } else if (!WidestIndTy) { 1039 reportVectorizationFailure("Did not find one integer induction var", 1040 "integer loop induction variable could not be identified", 1041 "NoIntegerInductionVariable", ORE, TheLoop); 1042 return false; 1043 } else { 1044 LLVM_DEBUG(dbgs() << "LV: Did not find one integer induction var.\n"); 1045 } 1046 } 1047 1048 // Now we know the widest induction type, check if our found induction 1049 // is the same size. If it's not, unset it here and InnerLoopVectorizer 1050 // will create another. 1051 if (PrimaryInduction && WidestIndTy != PrimaryInduction->getType()) 1052 PrimaryInduction = nullptr; 1053 1054 return true; 1055 } 1056 1057 bool LoopVectorizationLegality::canVectorizeMemory() { 1058 LAI = &LAIs.getInfo(*TheLoop); 1059 const OptimizationRemarkAnalysis *LAR = LAI->getReport(); 1060 if (LAR) { 1061 ORE->emit([&]() { 1062 return OptimizationRemarkAnalysis(Hints->vectorizeAnalysisPassName(), 1063 "loop not vectorized: ", *LAR); 1064 }); 1065 } 1066 1067 if (!LAI->canVectorizeMemory()) 1068 return false; 1069 1070 // We can vectorize stores to invariant address when final reduction value is 1071 // guaranteed to be stored at the end of the loop. Also, if decision to 1072 // vectorize loop is made, runtime checks are added so as to make sure that 1073 // invariant address won't alias with any other objects. 1074 if (!LAI->getStoresToInvariantAddresses().empty()) { 1075 // For each invariant address, check if last stored value is unconditional 1076 // and the address is not calculated inside the loop. 1077 for (StoreInst *SI : LAI->getStoresToInvariantAddresses()) { 1078 if (!isInvariantStoreOfReduction(SI)) 1079 continue; 1080 1081 if (blockNeedsPredication(SI->getParent())) { 1082 reportVectorizationFailure( 1083 "We don't allow storing to uniform addresses", 1084 "write of conditional recurring variant value to a loop " 1085 "invariant address could not be vectorized", 1086 "CantVectorizeStoreToLoopInvariantAddress", ORE, TheLoop); 1087 return false; 1088 } 1089 1090 // Invariant address should be defined outside of loop. LICM pass usually 1091 // makes sure it happens, but in rare cases it does not, we do not want 1092 // to overcomplicate vectorization to support this case. 1093 if (Instruction *Ptr = dyn_cast<Instruction>(SI->getPointerOperand())) { 1094 if (TheLoop->contains(Ptr)) { 1095 reportVectorizationFailure( 1096 "Invariant address is calculated inside the loop", 1097 "write to a loop invariant address could not " 1098 "be vectorized", 1099 "CantVectorizeStoreToLoopInvariantAddress", ORE, TheLoop); 1100 return false; 1101 } 1102 } 1103 } 1104 1105 if (LAI->hasDependenceInvolvingLoopInvariantAddress()) { 1106 // For each invariant address, check its last stored value is the result 1107 // of one of our reductions. 1108 // 1109 // We do not check if dependence with loads exists because they are 1110 // currently rejected earlier in LoopAccessInfo::analyzeLoop. In case this 1111 // behaviour changes we have to modify this code. 1112 ScalarEvolution *SE = PSE.getSE(); 1113 SmallVector<StoreInst *, 4> UnhandledStores; 1114 for (StoreInst *SI : LAI->getStoresToInvariantAddresses()) { 1115 if (isInvariantStoreOfReduction(SI)) { 1116 // Earlier stores to this address are effectively deadcode. 1117 // With opaque pointers it is possible for one pointer to be used with 1118 // different sizes of stored values: 1119 // store i32 0, ptr %x 1120 // store i8 0, ptr %x 1121 // The latest store doesn't complitely overwrite the first one in the 1122 // example. That is why we have to make sure that types of stored 1123 // values are same. 1124 // TODO: Check that bitwidth of unhandled store is smaller then the 1125 // one that overwrites it and add a test. 1126 erase_if(UnhandledStores, [SE, SI](StoreInst *I) { 1127 return storeToSameAddress(SE, SI, I) && 1128 I->getValueOperand()->getType() == 1129 SI->getValueOperand()->getType(); 1130 }); 1131 continue; 1132 } 1133 UnhandledStores.push_back(SI); 1134 } 1135 1136 bool IsOK = UnhandledStores.empty(); 1137 // TODO: we should also validate against InvariantMemSets. 1138 if (!IsOK) { 1139 reportVectorizationFailure( 1140 "We don't allow storing to uniform addresses", 1141 "write to a loop invariant address could not " 1142 "be vectorized", 1143 "CantVectorizeStoreToLoopInvariantAddress", ORE, TheLoop); 1144 return false; 1145 } 1146 } 1147 } 1148 1149 PSE.addPredicate(LAI->getPSE().getPredicate()); 1150 return true; 1151 } 1152 1153 bool LoopVectorizationLegality::canVectorizeFPMath( 1154 bool EnableStrictReductions) { 1155 1156 // First check if there is any ExactFP math or if we allow reassociations 1157 if (!Requirements->getExactFPInst() || Hints->allowReordering()) 1158 return true; 1159 1160 // If the above is false, we have ExactFPMath & do not allow reordering. 1161 // If the EnableStrictReductions flag is set, first check if we have any 1162 // Exact FP induction vars, which we cannot vectorize. 1163 if (!EnableStrictReductions || 1164 any_of(getInductionVars(), [&](auto &Induction) -> bool { 1165 InductionDescriptor IndDesc = Induction.second; 1166 return IndDesc.getExactFPMathInst(); 1167 })) 1168 return false; 1169 1170 // We can now only vectorize if all reductions with Exact FP math also 1171 // have the isOrdered flag set, which indicates that we can move the 1172 // reduction operations in-loop. 1173 return (all_of(getReductionVars(), [&](auto &Reduction) -> bool { 1174 const RecurrenceDescriptor &RdxDesc = Reduction.second; 1175 return !RdxDesc.hasExactFPMath() || RdxDesc.isOrdered(); 1176 })); 1177 } 1178 1179 bool LoopVectorizationLegality::isInvariantStoreOfReduction(StoreInst *SI) { 1180 return any_of(getReductionVars(), [&](auto &Reduction) -> bool { 1181 const RecurrenceDescriptor &RdxDesc = Reduction.second; 1182 return RdxDesc.IntermediateStore == SI; 1183 }); 1184 } 1185 1186 bool LoopVectorizationLegality::isInvariantAddressOfReduction(Value *V) { 1187 return any_of(getReductionVars(), [&](auto &Reduction) -> bool { 1188 const RecurrenceDescriptor &RdxDesc = Reduction.second; 1189 if (!RdxDesc.IntermediateStore) 1190 return false; 1191 1192 ScalarEvolution *SE = PSE.getSE(); 1193 Value *InvariantAddress = RdxDesc.IntermediateStore->getPointerOperand(); 1194 return V == InvariantAddress || 1195 SE->getSCEV(V) == SE->getSCEV(InvariantAddress); 1196 }); 1197 } 1198 1199 bool LoopVectorizationLegality::isInductionPhi(const Value *V) const { 1200 Value *In0 = const_cast<Value *>(V); 1201 PHINode *PN = dyn_cast_or_null<PHINode>(In0); 1202 if (!PN) 1203 return false; 1204 1205 return Inductions.count(PN); 1206 } 1207 1208 const InductionDescriptor * 1209 LoopVectorizationLegality::getIntOrFpInductionDescriptor(PHINode *Phi) const { 1210 if (!isInductionPhi(Phi)) 1211 return nullptr; 1212 auto &ID = getInductionVars().find(Phi)->second; 1213 if (ID.getKind() == InductionDescriptor::IK_IntInduction || 1214 ID.getKind() == InductionDescriptor::IK_FpInduction) 1215 return &ID; 1216 return nullptr; 1217 } 1218 1219 const InductionDescriptor * 1220 LoopVectorizationLegality::getPointerInductionDescriptor(PHINode *Phi) const { 1221 if (!isInductionPhi(Phi)) 1222 return nullptr; 1223 auto &ID = getInductionVars().find(Phi)->second; 1224 if (ID.getKind() == InductionDescriptor::IK_PtrInduction) 1225 return &ID; 1226 return nullptr; 1227 } 1228 1229 bool LoopVectorizationLegality::isCastedInductionVariable( 1230 const Value *V) const { 1231 auto *Inst = dyn_cast<Instruction>(V); 1232 return (Inst && InductionCastsToIgnore.count(Inst)); 1233 } 1234 1235 bool LoopVectorizationLegality::isInductionVariable(const Value *V) const { 1236 return isInductionPhi(V) || isCastedInductionVariable(V); 1237 } 1238 1239 bool LoopVectorizationLegality::isFixedOrderRecurrence( 1240 const PHINode *Phi) const { 1241 return FixedOrderRecurrences.count(Phi); 1242 } 1243 1244 bool LoopVectorizationLegality::blockNeedsPredication(BasicBlock *BB) const { 1245 return LoopAccessInfo::blockNeedsPredication(BB, TheLoop, DT); 1246 } 1247 1248 bool LoopVectorizationLegality::blockCanBePredicated( 1249 BasicBlock *BB, SmallPtrSetImpl<Value *> &SafePtrs, 1250 SmallPtrSetImpl<const Instruction *> &MaskedOp) const { 1251 for (Instruction &I : *BB) { 1252 // We can predicate blocks with calls to assume, as long as we drop them in 1253 // case we flatten the CFG via predication. 1254 if (match(&I, m_Intrinsic<Intrinsic::assume>())) { 1255 MaskedOp.insert(&I); 1256 continue; 1257 } 1258 1259 // Do not let llvm.experimental.noalias.scope.decl block the vectorization. 1260 // TODO: there might be cases that it should block the vectorization. Let's 1261 // ignore those for now. 1262 if (isa<NoAliasScopeDeclInst>(&I)) 1263 continue; 1264 1265 // We can allow masked calls if there's at least one vector variant, even 1266 // if we end up scalarizing due to the cost model calculations. 1267 // TODO: Allow other calls if they have appropriate attributes... readonly 1268 // and argmemonly? 1269 if (CallInst *CI = dyn_cast<CallInst>(&I)) 1270 if (VFDatabase::hasMaskedVariant(*CI)) { 1271 MaskedOp.insert(CI); 1272 continue; 1273 } 1274 1275 // Loads are handled via masking (or speculated if safe to do so.) 1276 if (auto *LI = dyn_cast<LoadInst>(&I)) { 1277 if (!SafePtrs.count(LI->getPointerOperand())) 1278 MaskedOp.insert(LI); 1279 continue; 1280 } 1281 1282 // Predicated store requires some form of masking: 1283 // 1) masked store HW instruction, 1284 // 2) emulation via load-blend-store (only if safe and legal to do so, 1285 // be aware on the race conditions), or 1286 // 3) element-by-element predicate check and scalar store. 1287 if (auto *SI = dyn_cast<StoreInst>(&I)) { 1288 MaskedOp.insert(SI); 1289 continue; 1290 } 1291 1292 if (I.mayReadFromMemory() || I.mayWriteToMemory() || I.mayThrow()) 1293 return false; 1294 } 1295 1296 return true; 1297 } 1298 1299 bool LoopVectorizationLegality::canVectorizeWithIfConvert() { 1300 if (!EnableIfConversion) { 1301 reportVectorizationFailure("If-conversion is disabled", 1302 "if-conversion is disabled", 1303 "IfConversionDisabled", 1304 ORE, TheLoop); 1305 return false; 1306 } 1307 1308 assert(TheLoop->getNumBlocks() > 1 && "Single block loops are vectorizable"); 1309 1310 // A list of pointers which are known to be dereferenceable within scope of 1311 // the loop body for each iteration of the loop which executes. That is, 1312 // the memory pointed to can be dereferenced (with the access size implied by 1313 // the value's type) unconditionally within the loop header without 1314 // introducing a new fault. 1315 SmallPtrSet<Value *, 8> SafePointers; 1316 1317 // Collect safe addresses. 1318 for (BasicBlock *BB : TheLoop->blocks()) { 1319 if (!blockNeedsPredication(BB)) { 1320 for (Instruction &I : *BB) 1321 if (auto *Ptr = getLoadStorePointerOperand(&I)) 1322 SafePointers.insert(Ptr); 1323 continue; 1324 } 1325 1326 // For a block which requires predication, a address may be safe to access 1327 // in the loop w/o predication if we can prove dereferenceability facts 1328 // sufficient to ensure it'll never fault within the loop. For the moment, 1329 // we restrict this to loads; stores are more complicated due to 1330 // concurrency restrictions. 1331 ScalarEvolution &SE = *PSE.getSE(); 1332 for (Instruction &I : *BB) { 1333 LoadInst *LI = dyn_cast<LoadInst>(&I); 1334 if (LI && !LI->getType()->isVectorTy() && !mustSuppressSpeculation(*LI) && 1335 isDereferenceableAndAlignedInLoop(LI, TheLoop, SE, *DT, AC)) 1336 SafePointers.insert(LI->getPointerOperand()); 1337 } 1338 } 1339 1340 // Collect the blocks that need predication. 1341 for (BasicBlock *BB : TheLoop->blocks()) { 1342 // We don't support switch statements inside loops. 1343 if (!isa<BranchInst>(BB->getTerminator())) { 1344 reportVectorizationFailure("Loop contains a switch statement", 1345 "loop contains a switch statement", 1346 "LoopContainsSwitch", ORE, TheLoop, 1347 BB->getTerminator()); 1348 return false; 1349 } 1350 1351 // We must be able to predicate all blocks that need to be predicated. 1352 if (blockNeedsPredication(BB) && 1353 !blockCanBePredicated(BB, SafePointers, MaskedOp)) { 1354 reportVectorizationFailure( 1355 "Control flow cannot be substituted for a select", 1356 "control flow cannot be substituted for a select", "NoCFGForSelect", 1357 ORE, TheLoop, BB->getTerminator()); 1358 return false; 1359 } 1360 } 1361 1362 // We can if-convert this loop. 1363 return true; 1364 } 1365 1366 // Helper function to canVectorizeLoopNestCFG. 1367 bool LoopVectorizationLegality::canVectorizeLoopCFG(Loop *Lp, 1368 bool UseVPlanNativePath) { 1369 assert((UseVPlanNativePath || Lp->isInnermost()) && 1370 "VPlan-native path is not enabled."); 1371 1372 // TODO: ORE should be improved to show more accurate information when an 1373 // outer loop can't be vectorized because a nested loop is not understood or 1374 // legal. Something like: "outer_loop_location: loop not vectorized: 1375 // (inner_loop_location) loop control flow is not understood by vectorizer". 1376 1377 // Store the result and return it at the end instead of exiting early, in case 1378 // allowExtraAnalysis is used to report multiple reasons for not vectorizing. 1379 bool Result = true; 1380 bool DoExtraAnalysis = ORE->allowExtraAnalysis(DEBUG_TYPE); 1381 1382 // We must have a loop in canonical form. Loops with indirectbr in them cannot 1383 // be canonicalized. 1384 if (!Lp->getLoopPreheader()) { 1385 reportVectorizationFailure("Loop doesn't have a legal pre-header", 1386 "loop control flow is not understood by vectorizer", 1387 "CFGNotUnderstood", ORE, TheLoop); 1388 if (DoExtraAnalysis) 1389 Result = false; 1390 else 1391 return false; 1392 } 1393 1394 // We must have a single backedge. 1395 if (Lp->getNumBackEdges() != 1) { 1396 reportVectorizationFailure("The loop must have a single backedge", 1397 "loop control flow is not understood by vectorizer", 1398 "CFGNotUnderstood", ORE, TheLoop); 1399 if (DoExtraAnalysis) 1400 Result = false; 1401 else 1402 return false; 1403 } 1404 1405 return Result; 1406 } 1407 1408 bool LoopVectorizationLegality::canVectorizeLoopNestCFG( 1409 Loop *Lp, bool UseVPlanNativePath) { 1410 // Store the result and return it at the end instead of exiting early, in case 1411 // allowExtraAnalysis is used to report multiple reasons for not vectorizing. 1412 bool Result = true; 1413 bool DoExtraAnalysis = ORE->allowExtraAnalysis(DEBUG_TYPE); 1414 if (!canVectorizeLoopCFG(Lp, UseVPlanNativePath)) { 1415 if (DoExtraAnalysis) 1416 Result = false; 1417 else 1418 return false; 1419 } 1420 1421 // Recursively check whether the loop control flow of nested loops is 1422 // understood. 1423 for (Loop *SubLp : *Lp) 1424 if (!canVectorizeLoopNestCFG(SubLp, UseVPlanNativePath)) { 1425 if (DoExtraAnalysis) 1426 Result = false; 1427 else 1428 return false; 1429 } 1430 1431 return Result; 1432 } 1433 1434 bool LoopVectorizationLegality::canVectorize(bool UseVPlanNativePath) { 1435 // Store the result and return it at the end instead of exiting early, in case 1436 // allowExtraAnalysis is used to report multiple reasons for not vectorizing. 1437 bool Result = true; 1438 1439 bool DoExtraAnalysis = ORE->allowExtraAnalysis(DEBUG_TYPE); 1440 // Check whether the loop-related control flow in the loop nest is expected by 1441 // vectorizer. 1442 if (!canVectorizeLoopNestCFG(TheLoop, UseVPlanNativePath)) { 1443 if (DoExtraAnalysis) 1444 Result = false; 1445 else 1446 return false; 1447 } 1448 1449 // We need to have a loop header. 1450 LLVM_DEBUG(dbgs() << "LV: Found a loop: " << TheLoop->getHeader()->getName() 1451 << '\n'); 1452 1453 // Specific checks for outer loops. We skip the remaining legal checks at this 1454 // point because they don't support outer loops. 1455 if (!TheLoop->isInnermost()) { 1456 assert(UseVPlanNativePath && "VPlan-native path is not enabled."); 1457 1458 if (!canVectorizeOuterLoop()) { 1459 reportVectorizationFailure("Unsupported outer loop", 1460 "unsupported outer loop", 1461 "UnsupportedOuterLoop", 1462 ORE, TheLoop); 1463 // TODO: Implement DoExtraAnalysis when subsequent legal checks support 1464 // outer loops. 1465 return false; 1466 } 1467 1468 LLVM_DEBUG(dbgs() << "LV: We can vectorize this outer loop!\n"); 1469 return Result; 1470 } 1471 1472 assert(TheLoop->isInnermost() && "Inner loop expected."); 1473 // Check if we can if-convert non-single-bb loops. 1474 unsigned NumBlocks = TheLoop->getNumBlocks(); 1475 if (NumBlocks != 1 && !canVectorizeWithIfConvert()) { 1476 LLVM_DEBUG(dbgs() << "LV: Can't if-convert the loop.\n"); 1477 if (DoExtraAnalysis) 1478 Result = false; 1479 else 1480 return false; 1481 } 1482 1483 // Check if we can vectorize the instructions and CFG in this loop. 1484 if (!canVectorizeInstrs()) { 1485 LLVM_DEBUG(dbgs() << "LV: Can't vectorize the instructions or CFG\n"); 1486 if (DoExtraAnalysis) 1487 Result = false; 1488 else 1489 return false; 1490 } 1491 1492 // Go over each instruction and look at memory deps. 1493 if (!canVectorizeMemory()) { 1494 LLVM_DEBUG(dbgs() << "LV: Can't vectorize due to memory conflicts\n"); 1495 if (DoExtraAnalysis) 1496 Result = false; 1497 else 1498 return false; 1499 } 1500 1501 LLVM_DEBUG(dbgs() << "LV: We can vectorize this loop" 1502 << (LAI->getRuntimePointerChecking()->Need 1503 ? " (with a runtime bound check)" 1504 : "") 1505 << "!\n"); 1506 1507 unsigned SCEVThreshold = VectorizeSCEVCheckThreshold; 1508 if (Hints->getForce() == LoopVectorizeHints::FK_Enabled) 1509 SCEVThreshold = PragmaVectorizeSCEVCheckThreshold; 1510 1511 if (PSE.getPredicate().getComplexity() > SCEVThreshold) { 1512 reportVectorizationFailure("Too many SCEV checks needed", 1513 "Too many SCEV assumptions need to be made and checked at runtime", 1514 "TooManySCEVRunTimeChecks", ORE, TheLoop); 1515 if (DoExtraAnalysis) 1516 Result = false; 1517 else 1518 return false; 1519 } 1520 1521 // Okay! We've done all the tests. If any have failed, return false. Otherwise 1522 // we can vectorize, and at this point we don't have any other mem analysis 1523 // which may limit our maximum vectorization factor, so just return true with 1524 // no restrictions. 1525 return Result; 1526 } 1527 1528 bool LoopVectorizationLegality::prepareToFoldTailByMasking() { 1529 1530 LLVM_DEBUG(dbgs() << "LV: checking if tail can be folded by masking.\n"); 1531 1532 SmallPtrSet<const Value *, 8> ReductionLiveOuts; 1533 1534 for (const auto &Reduction : getReductionVars()) 1535 ReductionLiveOuts.insert(Reduction.second.getLoopExitInstr()); 1536 1537 // TODO: handle non-reduction outside users when tail is folded by masking. 1538 for (auto *AE : AllowedExit) { 1539 // Check that all users of allowed exit values are inside the loop or 1540 // are the live-out of a reduction. 1541 if (ReductionLiveOuts.count(AE)) 1542 continue; 1543 for (User *U : AE->users()) { 1544 Instruction *UI = cast<Instruction>(U); 1545 if (TheLoop->contains(UI)) 1546 continue; 1547 LLVM_DEBUG( 1548 dbgs() 1549 << "LV: Cannot fold tail by masking, loop has an outside user for " 1550 << *UI << "\n"); 1551 return false; 1552 } 1553 } 1554 1555 // The list of pointers that we can safely read and write to remains empty. 1556 SmallPtrSet<Value *, 8> SafePointers; 1557 1558 // Collect masked ops in temporary set first to avoid partially populating 1559 // MaskedOp if a block cannot be predicated. 1560 SmallPtrSet<const Instruction *, 8> TmpMaskedOp; 1561 1562 // Check and mark all blocks for predication, including those that ordinarily 1563 // do not need predication such as the header block. 1564 for (BasicBlock *BB : TheLoop->blocks()) { 1565 if (!blockCanBePredicated(BB, SafePointers, TmpMaskedOp)) { 1566 LLVM_DEBUG(dbgs() << "LV: Cannot fold tail by masking as requested.\n"); 1567 return false; 1568 } 1569 } 1570 1571 LLVM_DEBUG(dbgs() << "LV: can fold tail by masking.\n"); 1572 1573 MaskedOp.insert(TmpMaskedOp.begin(), TmpMaskedOp.end()); 1574 return true; 1575 } 1576 1577 } // namespace llvm 1578