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/ScalarEvolutionExpressions.h" 22 #include "llvm/Analysis/TargetLibraryInfo.h" 23 #include "llvm/Analysis/TargetTransformInfo.h" 24 #include "llvm/Analysis/ValueTracking.h" 25 #include "llvm/Analysis/VectorUtils.h" 26 #include "llvm/IR/IntrinsicInst.h" 27 #include "llvm/IR/PatternMatch.h" 28 #include "llvm/Transforms/Utils/SizeOpts.h" 29 #include "llvm/Transforms/Vectorize/LoopVectorize.h" 30 31 using namespace llvm; 32 using namespace PatternMatch; 33 34 #define LV_NAME "loop-vectorize" 35 #define DEBUG_TYPE LV_NAME 36 37 static cl::opt<bool> 38 EnableIfConversion("enable-if-conversion", cl::init(true), cl::Hidden, 39 cl::desc("Enable if-conversion during vectorization.")); 40 41 static cl::opt<bool> 42 AllowStridedPointerIVs("lv-strided-pointer-ivs", cl::init(false), cl::Hidden, 43 cl::desc("Enable recognition of non-constant strided " 44 "pointer induction variables.")); 45 46 namespace llvm { 47 cl::opt<bool> 48 HintsAllowReordering("hints-allow-reordering", cl::init(true), cl::Hidden, 49 cl::desc("Allow enabling loop hints to reorder " 50 "FP operations during vectorization.")); 51 } // namespace llvm 52 53 // TODO: Move size-based thresholds out of legality checking, make cost based 54 // decisions instead of hard thresholds. 55 static cl::opt<unsigned> VectorizeSCEVCheckThreshold( 56 "vectorize-scev-check-threshold", cl::init(16), cl::Hidden, 57 cl::desc("The maximum number of SCEV checks allowed.")); 58 59 static cl::opt<unsigned> PragmaVectorizeSCEVCheckThreshold( 60 "pragma-vectorize-scev-check-threshold", cl::init(128), cl::Hidden, 61 cl::desc("The maximum number of SCEV checks allowed with a " 62 "vectorize(enable) pragma")); 63 64 static cl::opt<LoopVectorizeHints::ScalableForceKind> 65 ForceScalableVectorization( 66 "scalable-vectorization", cl::init(LoopVectorizeHints::SK_Unspecified), 67 cl::Hidden, 68 cl::desc("Control whether the compiler can use scalable vectors to " 69 "vectorize a loop"), 70 cl::values( 71 clEnumValN(LoopVectorizeHints::SK_FixedWidthOnly, "off", 72 "Scalable vectorization is disabled."), 73 clEnumValN( 74 LoopVectorizeHints::SK_PreferScalable, "preferred", 75 "Scalable vectorization is available and favored when the " 76 "cost is inconclusive."), 77 clEnumValN( 78 LoopVectorizeHints::SK_PreferScalable, "on", 79 "Scalable vectorization is available and favored when the " 80 "cost is inconclusive."))); 81 82 /// Maximum vectorization interleave count. 83 static const unsigned MaxInterleaveFactor = 16; 84 85 namespace llvm { 86 87 bool LoopVectorizeHints::Hint::validate(unsigned Val) { 88 switch (Kind) { 89 case HK_WIDTH: 90 return isPowerOf2_32(Val) && Val <= VectorizerParams::MaxVectorWidth; 91 case HK_INTERLEAVE: 92 return isPowerOf2_32(Val) && Val <= MaxInterleaveFactor; 93 case HK_FORCE: 94 return (Val <= 1); 95 case HK_ISVECTORIZED: 96 case HK_PREDICATE: 97 case HK_SCALABLE: 98 return (Val == 0 || Val == 1); 99 } 100 return false; 101 } 102 103 LoopVectorizeHints::LoopVectorizeHints(const Loop *L, 104 bool InterleaveOnlyWhenForced, 105 OptimizationRemarkEmitter &ORE, 106 const TargetTransformInfo *TTI) 107 : Width("vectorize.width", VectorizerParams::VectorizationFactor, HK_WIDTH), 108 Interleave("interleave.count", InterleaveOnlyWhenForced, HK_INTERLEAVE), 109 Force("vectorize.enable", FK_Undefined, HK_FORCE), 110 IsVectorized("isvectorized", 0, HK_ISVECTORIZED), 111 Predicate("vectorize.predicate.enable", FK_Undefined, HK_PREDICATE), 112 Scalable("vectorize.scalable.enable", SK_Unspecified, HK_SCALABLE), 113 TheLoop(L), ORE(ORE) { 114 // Populate values with existing loop metadata. 115 getHintsFromMetadata(); 116 117 // force-vector-interleave overrides DisableInterleaving. 118 if (VectorizerParams::isInterleaveForced()) 119 Interleave.Value = VectorizerParams::VectorizationInterleave; 120 121 // If the metadata doesn't explicitly specify whether to enable scalable 122 // vectorization, then decide based on the following criteria (increasing 123 // level of priority): 124 // - Target default 125 // - Metadata width 126 // - Force option (always overrides) 127 if ((LoopVectorizeHints::ScalableForceKind)Scalable.Value == SK_Unspecified) { 128 if (TTI) 129 Scalable.Value = TTI->enableScalableVectorization() ? SK_PreferScalable 130 : SK_FixedWidthOnly; 131 132 if (Width.Value) 133 // If the width is set, but the metadata says nothing about the scalable 134 // property, then assume it concerns only a fixed-width UserVF. 135 // If width is not set, the flag takes precedence. 136 Scalable.Value = SK_FixedWidthOnly; 137 } 138 139 // If the flag is set to force any use of scalable vectors, override the loop 140 // hints. 141 if (ForceScalableVectorization.getValue() != 142 LoopVectorizeHints::SK_Unspecified) 143 Scalable.Value = ForceScalableVectorization.getValue(); 144 145 // Scalable vectorization is disabled if no preference is specified. 146 if ((LoopVectorizeHints::ScalableForceKind)Scalable.Value == SK_Unspecified) 147 Scalable.Value = SK_FixedWidthOnly; 148 149 if (IsVectorized.Value != 1) 150 // If the vectorization width and interleaving count are both 1 then 151 // consider the loop to have been already vectorized because there's 152 // nothing more that we can do. 153 IsVectorized.Value = 154 getWidth() == ElementCount::getFixed(1) && getInterleave() == 1; 155 LLVM_DEBUG(if (InterleaveOnlyWhenForced && getInterleave() == 1) dbgs() 156 << "LV: Interleaving disabled by the pass manager\n"); 157 } 158 159 void LoopVectorizeHints::setAlreadyVectorized() { 160 LLVMContext &Context = TheLoop->getHeader()->getContext(); 161 162 MDNode *IsVectorizedMD = MDNode::get( 163 Context, 164 {MDString::get(Context, "llvm.loop.isvectorized"), 165 ConstantAsMetadata::get(ConstantInt::get(Context, APInt(32, 1)))}); 166 MDNode *LoopID = TheLoop->getLoopID(); 167 MDNode *NewLoopID = 168 makePostTransformationMetadata(Context, LoopID, 169 {Twine(Prefix(), "vectorize.").str(), 170 Twine(Prefix(), "interleave.").str()}, 171 {IsVectorizedMD}); 172 TheLoop->setLoopID(NewLoopID); 173 174 // Update internal cache. 175 IsVectorized.Value = 1; 176 } 177 178 bool LoopVectorizeHints::allowVectorization( 179 Function *F, Loop *L, bool VectorizeOnlyWhenForced) const { 180 if (getForce() == LoopVectorizeHints::FK_Disabled) { 181 LLVM_DEBUG(dbgs() << "LV: Not vectorizing: #pragma vectorize disable.\n"); 182 emitRemarkWithHints(); 183 return false; 184 } 185 186 if (VectorizeOnlyWhenForced && getForce() != LoopVectorizeHints::FK_Enabled) { 187 LLVM_DEBUG(dbgs() << "LV: Not vectorizing: No #pragma vectorize enable.\n"); 188 emitRemarkWithHints(); 189 return false; 190 } 191 192 if (getIsVectorized() == 1) { 193 LLVM_DEBUG(dbgs() << "LV: Not vectorizing: Disabled/already vectorized.\n"); 194 // FIXME: Add interleave.disable metadata. This will allow 195 // vectorize.disable to be used without disabling the pass and errors 196 // to differentiate between disabled vectorization and a width of 1. 197 ORE.emit([&]() { 198 return OptimizationRemarkAnalysis(vectorizeAnalysisPassName(), 199 "AllDisabled", L->getStartLoc(), 200 L->getHeader()) 201 << "loop not vectorized: vectorization and interleaving are " 202 "explicitly disabled, or the loop has already been " 203 "vectorized"; 204 }); 205 return false; 206 } 207 208 return true; 209 } 210 211 void LoopVectorizeHints::emitRemarkWithHints() const { 212 using namespace ore; 213 214 ORE.emit([&]() { 215 if (Force.Value == LoopVectorizeHints::FK_Disabled) 216 return OptimizationRemarkMissed(LV_NAME, "MissedExplicitlyDisabled", 217 TheLoop->getStartLoc(), 218 TheLoop->getHeader()) 219 << "loop not vectorized: vectorization is explicitly disabled"; 220 221 OptimizationRemarkMissed R(LV_NAME, "MissedDetails", TheLoop->getStartLoc(), 222 TheLoop->getHeader()); 223 R << "loop not vectorized"; 224 if (Force.Value == LoopVectorizeHints::FK_Enabled) { 225 R << " (Force=" << NV("Force", true); 226 if (Width.Value != 0) 227 R << ", Vector Width=" << NV("VectorWidth", getWidth()); 228 if (getInterleave() != 0) 229 R << ", Interleave Count=" << NV("InterleaveCount", getInterleave()); 230 R << ")"; 231 } 232 return R; 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 (const MDOperand &MDO : llvm::drop_begin(LoopID->operands())) { 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>(MDO)) { 271 if (!MD || MD->getNumOperands() == 0) 272 continue; 273 S = dyn_cast<MDString>(MD->getOperand(0)); 274 for (unsigned Idx = 1; Idx < MD->getNumOperands(); ++Idx) 275 Args.push_back(MD->getOperand(Idx)); 276 } else { 277 S = dyn_cast<MDString>(MDO); 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 return SE->getSCEV(APtr) == SE->getSCEV(BPtr); 448 } 449 450 int LoopVectorizationLegality::isConsecutivePtr(Type *AccessTy, 451 Value *Ptr) const { 452 // FIXME: Currently, the set of symbolic strides is sometimes queried before 453 // it's collected. This happens from canVectorizeWithIfConvert, when the 454 // pointer is checked to reference consecutive elements suitable for a 455 // masked access. 456 const auto &Strides = 457 LAI ? LAI->getSymbolicStrides() : DenseMap<Value *, const SCEV *>(); 458 459 Function *F = TheLoop->getHeader()->getParent(); 460 bool OptForSize = F->hasOptSize() || 461 llvm::shouldOptimizeForSize(TheLoop->getHeader(), PSI, BFI, 462 PGSOQueryType::IRPass); 463 bool CanAddPredicate = !OptForSize; 464 int Stride = getPtrStride(PSE, AccessTy, Ptr, TheLoop, Strides, 465 CanAddPredicate, false).value_or(0); 466 if (Stride == 1 || Stride == -1) 467 return Stride; 468 return 0; 469 } 470 471 bool LoopVectorizationLegality::isInvariant(Value *V) const { 472 return LAI->isInvariant(V); 473 } 474 475 namespace { 476 /// A rewriter to build the SCEVs for each of the VF lanes in the expected 477 /// vectorized loop, which can then be compared to detect their uniformity. This 478 /// is done by replacing the AddRec SCEVs of the original scalar loop (TheLoop) 479 /// with new AddRecs where the step is multiplied by StepMultiplier and Offset * 480 /// Step is added. Also checks if all sub-expressions are analyzable w.r.t. 481 /// uniformity. 482 class SCEVAddRecForUniformityRewriter 483 : public SCEVRewriteVisitor<SCEVAddRecForUniformityRewriter> { 484 /// Multiplier to be applied to the step of AddRecs in TheLoop. 485 unsigned StepMultiplier; 486 487 /// Offset to be added to the AddRecs in TheLoop. 488 unsigned Offset; 489 490 /// Loop for which to rewrite AddRecsFor. 491 Loop *TheLoop; 492 493 /// Is any sub-expressions not analyzable w.r.t. uniformity? 494 bool CannotAnalyze = false; 495 496 bool canAnalyze() const { return !CannotAnalyze; } 497 498 public: 499 SCEVAddRecForUniformityRewriter(ScalarEvolution &SE, unsigned StepMultiplier, 500 unsigned Offset, Loop *TheLoop) 501 : SCEVRewriteVisitor(SE), StepMultiplier(StepMultiplier), Offset(Offset), 502 TheLoop(TheLoop) {} 503 504 const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) { 505 assert(Expr->getLoop() == TheLoop && 506 "addrec outside of TheLoop must be invariant and should have been " 507 "handled earlier"); 508 // Build a new AddRec by multiplying the step by StepMultiplier and 509 // incrementing the start by Offset * step. 510 Type *Ty = Expr->getType(); 511 const SCEV *Step = Expr->getStepRecurrence(SE); 512 if (!SE.isLoopInvariant(Step, TheLoop)) { 513 CannotAnalyze = true; 514 return Expr; 515 } 516 const SCEV *NewStep = 517 SE.getMulExpr(Step, SE.getConstant(Ty, StepMultiplier)); 518 const SCEV *ScaledOffset = SE.getMulExpr(Step, SE.getConstant(Ty, Offset)); 519 const SCEV *NewStart = SE.getAddExpr(Expr->getStart(), ScaledOffset); 520 return SE.getAddRecExpr(NewStart, NewStep, TheLoop, SCEV::FlagAnyWrap); 521 } 522 523 const SCEV *visit(const SCEV *S) { 524 if (CannotAnalyze || SE.isLoopInvariant(S, TheLoop)) 525 return S; 526 return SCEVRewriteVisitor<SCEVAddRecForUniformityRewriter>::visit(S); 527 } 528 529 const SCEV *visitUnknown(const SCEVUnknown *S) { 530 if (SE.isLoopInvariant(S, TheLoop)) 531 return S; 532 // The value could vary across iterations. 533 CannotAnalyze = true; 534 return S; 535 } 536 537 const SCEV *visitCouldNotCompute(const SCEVCouldNotCompute *S) { 538 // Could not analyze the expression. 539 CannotAnalyze = true; 540 return S; 541 } 542 543 static const SCEV *rewrite(const SCEV *S, ScalarEvolution &SE, 544 unsigned StepMultiplier, unsigned Offset, 545 Loop *TheLoop) { 546 /// Bail out if the expression does not contain an UDiv expression. 547 /// Uniform values which are not loop invariant require operations to strip 548 /// out the lowest bits. For now just look for UDivs and use it to avoid 549 /// re-writing UDIV-free expressions for other lanes to limit compile time. 550 if (!SCEVExprContains(S, 551 [](const SCEV *S) { return isa<SCEVUDivExpr>(S); })) 552 return SE.getCouldNotCompute(); 553 554 SCEVAddRecForUniformityRewriter Rewriter(SE, StepMultiplier, Offset, 555 TheLoop); 556 const SCEV *Result = Rewriter.visit(S); 557 558 if (Rewriter.canAnalyze()) 559 return Result; 560 return SE.getCouldNotCompute(); 561 } 562 }; 563 564 } // namespace 565 566 bool LoopVectorizationLegality::isUniform(Value *V, ElementCount VF) const { 567 if (isInvariant(V)) 568 return true; 569 if (VF.isScalable()) 570 return false; 571 if (VF.isScalar()) 572 return true; 573 574 // Since we rely on SCEV for uniformity, if the type is not SCEVable, it is 575 // never considered uniform. 576 auto *SE = PSE.getSE(); 577 if (!SE->isSCEVable(V->getType())) 578 return false; 579 const SCEV *S = SE->getSCEV(V); 580 581 // Rewrite AddRecs in TheLoop to step by VF and check if the expression for 582 // lane 0 matches the expressions for all other lanes. 583 unsigned FixedVF = VF.getKnownMinValue(); 584 const SCEV *FirstLaneExpr = 585 SCEVAddRecForUniformityRewriter::rewrite(S, *SE, FixedVF, 0, TheLoop); 586 if (isa<SCEVCouldNotCompute>(FirstLaneExpr)) 587 return false; 588 589 // Make sure the expressions for lanes FixedVF-1..1 match the expression for 590 // lane 0. We check lanes in reverse order for compile-time, as frequently 591 // checking the last lane is sufficient to rule out uniformity. 592 return all_of(reverse(seq<unsigned>(1, FixedVF)), [&](unsigned I) { 593 const SCEV *IthLaneExpr = 594 SCEVAddRecForUniformityRewriter::rewrite(S, *SE, FixedVF, I, TheLoop); 595 return FirstLaneExpr == IthLaneExpr; 596 }); 597 } 598 599 bool LoopVectorizationLegality::isUniformMemOp(Instruction &I, 600 ElementCount VF) const { 601 Value *Ptr = getLoadStorePointerOperand(&I); 602 if (!Ptr) 603 return false; 604 // Note: There's nothing inherent which prevents predicated loads and 605 // stores from being uniform. The current lowering simply doesn't handle 606 // it; in particular, the cost model distinguishes scatter/gather from 607 // scalar w/predication, and we currently rely on the scalar path. 608 return isUniform(Ptr, VF) && !blockNeedsPredication(I.getParent()); 609 } 610 611 bool LoopVectorizationLegality::canVectorizeOuterLoop() { 612 assert(!TheLoop->isInnermost() && "We are not vectorizing an outer loop."); 613 // Store the result and return it at the end instead of exiting early, in case 614 // allowExtraAnalysis is used to report multiple reasons for not vectorizing. 615 bool Result = true; 616 bool DoExtraAnalysis = ORE->allowExtraAnalysis(DEBUG_TYPE); 617 618 for (BasicBlock *BB : TheLoop->blocks()) { 619 // Check whether the BB terminator is a BranchInst. Any other terminator is 620 // not supported yet. 621 auto *Br = dyn_cast<BranchInst>(BB->getTerminator()); 622 if (!Br) { 623 reportVectorizationFailure("Unsupported basic block terminator", 624 "loop control flow is not understood by vectorizer", 625 "CFGNotUnderstood", ORE, TheLoop); 626 if (DoExtraAnalysis) 627 Result = false; 628 else 629 return false; 630 } 631 632 // Check whether the BranchInst is a supported one. Only unconditional 633 // branches, conditional branches with an outer loop invariant condition or 634 // backedges are supported. 635 // FIXME: We skip these checks when VPlan predication is enabled as we 636 // want to allow divergent branches. This whole check will be removed 637 // once VPlan predication is on by default. 638 if (Br && Br->isConditional() && 639 !TheLoop->isLoopInvariant(Br->getCondition()) && 640 !LI->isLoopHeader(Br->getSuccessor(0)) && 641 !LI->isLoopHeader(Br->getSuccessor(1))) { 642 reportVectorizationFailure("Unsupported conditional branch", 643 "loop control flow is not understood by vectorizer", 644 "CFGNotUnderstood", ORE, TheLoop); 645 if (DoExtraAnalysis) 646 Result = false; 647 else 648 return false; 649 } 650 } 651 652 // Check whether inner loops are uniform. At this point, we only support 653 // simple outer loops scenarios with uniform nested loops. 654 if (!isUniformLoopNest(TheLoop /*loop nest*/, 655 TheLoop /*context outer loop*/)) { 656 reportVectorizationFailure("Outer loop contains divergent loops", 657 "loop control flow is not understood by vectorizer", 658 "CFGNotUnderstood", ORE, TheLoop); 659 if (DoExtraAnalysis) 660 Result = false; 661 else 662 return false; 663 } 664 665 // Check whether we are able to set up outer loop induction. 666 if (!setupOuterLoopInductions()) { 667 reportVectorizationFailure("Unsupported outer loop Phi(s)", 668 "Unsupported outer loop Phi(s)", 669 "UnsupportedPhi", ORE, TheLoop); 670 if (DoExtraAnalysis) 671 Result = false; 672 else 673 return false; 674 } 675 676 return Result; 677 } 678 679 void LoopVectorizationLegality::addInductionPhi( 680 PHINode *Phi, const InductionDescriptor &ID, 681 SmallPtrSetImpl<Value *> &AllowedExit) { 682 Inductions[Phi] = ID; 683 684 // In case this induction also comes with casts that we know we can ignore 685 // in the vectorized loop body, record them here. All casts could be recorded 686 // here for ignoring, but suffices to record only the first (as it is the 687 // only one that may bw used outside the cast sequence). 688 const SmallVectorImpl<Instruction *> &Casts = ID.getCastInsts(); 689 if (!Casts.empty()) 690 InductionCastsToIgnore.insert(*Casts.begin()); 691 692 Type *PhiTy = Phi->getType(); 693 const DataLayout &DL = Phi->getDataLayout(); 694 695 // Get the widest type. 696 if (!PhiTy->isFloatingPointTy()) { 697 if (!WidestIndTy) 698 WidestIndTy = convertPointerToIntegerType(DL, PhiTy); 699 else 700 WidestIndTy = getWiderType(DL, PhiTy, WidestIndTy); 701 } 702 703 // Int inductions are special because we only allow one IV. 704 if (ID.getKind() == InductionDescriptor::IK_IntInduction && 705 ID.getConstIntStepValue() && ID.getConstIntStepValue()->isOne() && 706 isa<Constant>(ID.getStartValue()) && 707 cast<Constant>(ID.getStartValue())->isNullValue()) { 708 709 // Use the phi node with the widest type as induction. Use the last 710 // one if there are multiple (no good reason for doing this other 711 // than it is expedient). We've checked that it begins at zero and 712 // steps by one, so this is a canonical induction variable. 713 if (!PrimaryInduction || PhiTy == WidestIndTy) 714 PrimaryInduction = Phi; 715 } 716 717 // Both the PHI node itself, and the "post-increment" value feeding 718 // back into the PHI node may have external users. 719 // We can allow those uses, except if the SCEVs we have for them rely 720 // on predicates that only hold within the loop, since allowing the exit 721 // currently means re-using this SCEV outside the loop (see PR33706 for more 722 // details). 723 if (PSE.getPredicate().isAlwaysTrue()) { 724 AllowedExit.insert(Phi); 725 AllowedExit.insert(Phi->getIncomingValueForBlock(TheLoop->getLoopLatch())); 726 } 727 728 LLVM_DEBUG(dbgs() << "LV: Found an induction variable.\n"); 729 } 730 731 bool LoopVectorizationLegality::setupOuterLoopInductions() { 732 BasicBlock *Header = TheLoop->getHeader(); 733 734 // Returns true if a given Phi is a supported induction. 735 auto IsSupportedPhi = [&](PHINode &Phi) -> bool { 736 InductionDescriptor ID; 737 if (InductionDescriptor::isInductionPHI(&Phi, TheLoop, PSE, ID) && 738 ID.getKind() == InductionDescriptor::IK_IntInduction) { 739 addInductionPhi(&Phi, ID, AllowedExit); 740 return true; 741 } 742 // Bail out for any Phi in the outer loop header that is not a supported 743 // induction. 744 LLVM_DEBUG( 745 dbgs() << "LV: Found unsupported PHI for outer loop vectorization.\n"); 746 return false; 747 }; 748 749 return llvm::all_of(Header->phis(), IsSupportedPhi); 750 } 751 752 /// Checks if a function is scalarizable according to the TLI, in 753 /// the sense that it should be vectorized and then expanded in 754 /// multiple scalar calls. This is represented in the 755 /// TLI via mappings that do not specify a vector name, as in the 756 /// following example: 757 /// 758 /// const VecDesc VecIntrinsics[] = { 759 /// {"llvm.phx.abs.i32", "", 4} 760 /// }; 761 static bool isTLIScalarize(const TargetLibraryInfo &TLI, const CallInst &CI) { 762 const StringRef ScalarName = CI.getCalledFunction()->getName(); 763 bool Scalarize = TLI.isFunctionVectorizable(ScalarName); 764 // Check that all known VFs are not associated to a vector 765 // function, i.e. the vector name is emty. 766 if (Scalarize) { 767 ElementCount WidestFixedVF, WidestScalableVF; 768 TLI.getWidestVF(ScalarName, WidestFixedVF, WidestScalableVF); 769 for (ElementCount VF = ElementCount::getFixed(2); 770 ElementCount::isKnownLE(VF, WidestFixedVF); VF *= 2) 771 Scalarize &= !TLI.isFunctionVectorizable(ScalarName, VF); 772 for (ElementCount VF = ElementCount::getScalable(1); 773 ElementCount::isKnownLE(VF, WidestScalableVF); VF *= 2) 774 Scalarize &= !TLI.isFunctionVectorizable(ScalarName, VF); 775 assert((WidestScalableVF.isZero() || !Scalarize) && 776 "Caller may decide to scalarize a variant using a scalable VF"); 777 } 778 return Scalarize; 779 } 780 781 bool LoopVectorizationLegality::canVectorizeInstrs() { 782 BasicBlock *Header = TheLoop->getHeader(); 783 784 // For each block in the loop. 785 for (BasicBlock *BB : TheLoop->blocks()) { 786 // Scan the instructions in the block and look for hazards. 787 for (Instruction &I : *BB) { 788 if (auto *Phi = dyn_cast<PHINode>(&I)) { 789 Type *PhiTy = Phi->getType(); 790 // Check that this PHI type is allowed. 791 if (!PhiTy->isIntegerTy() && !PhiTy->isFloatingPointTy() && 792 !PhiTy->isPointerTy()) { 793 reportVectorizationFailure("Found a non-int non-pointer PHI", 794 "loop control flow is not understood by vectorizer", 795 "CFGNotUnderstood", ORE, TheLoop); 796 return false; 797 } 798 799 // If this PHINode is not in the header block, then we know that we 800 // can convert it to select during if-conversion. No need to check if 801 // the PHIs in this block are induction or reduction variables. 802 if (BB != Header) { 803 // Non-header phi nodes that have outside uses can be vectorized. Add 804 // them to the list of allowed exits. 805 // Unsafe cyclic dependencies with header phis are identified during 806 // legalization for reduction, induction and fixed order 807 // recurrences. 808 AllowedExit.insert(&I); 809 continue; 810 } 811 812 // We only allow if-converted PHIs with exactly two incoming values. 813 if (Phi->getNumIncomingValues() != 2) { 814 reportVectorizationFailure("Found an invalid PHI", 815 "loop control flow is not understood by vectorizer", 816 "CFGNotUnderstood", ORE, TheLoop, Phi); 817 return false; 818 } 819 820 RecurrenceDescriptor RedDes; 821 if (RecurrenceDescriptor::isReductionPHI(Phi, TheLoop, RedDes, DB, AC, 822 DT, PSE.getSE())) { 823 Requirements->addExactFPMathInst(RedDes.getExactFPMathInst()); 824 AllowedExit.insert(RedDes.getLoopExitInstr()); 825 Reductions[Phi] = RedDes; 826 continue; 827 } 828 829 // We prevent matching non-constant strided pointer IVS to preserve 830 // historical vectorizer behavior after a generalization of the 831 // IVDescriptor code. The intent is to remove this check, but we 832 // have to fix issues around code quality for such loops first. 833 auto IsDisallowedStridedPointerInduction = 834 [](const InductionDescriptor &ID) { 835 if (AllowStridedPointerIVs) 836 return false; 837 return ID.getKind() == InductionDescriptor::IK_PtrInduction && 838 ID.getConstIntStepValue() == nullptr; 839 }; 840 841 // TODO: Instead of recording the AllowedExit, it would be good to 842 // record the complementary set: NotAllowedExit. These include (but may 843 // not be limited to): 844 // 1. Reduction phis as they represent the one-before-last value, which 845 // is not available when vectorized 846 // 2. Induction phis and increment when SCEV predicates cannot be used 847 // outside the loop - see addInductionPhi 848 // 3. Non-Phis with outside uses when SCEV predicates cannot be used 849 // outside the loop - see call to hasOutsideLoopUser in the non-phi 850 // handling below 851 // 4. FixedOrderRecurrence phis that can possibly be handled by 852 // extraction. 853 // By recording these, we can then reason about ways to vectorize each 854 // of these NotAllowedExit. 855 InductionDescriptor ID; 856 if (InductionDescriptor::isInductionPHI(Phi, TheLoop, PSE, ID) && 857 !IsDisallowedStridedPointerInduction(ID)) { 858 addInductionPhi(Phi, ID, AllowedExit); 859 Requirements->addExactFPMathInst(ID.getExactFPMathInst()); 860 continue; 861 } 862 863 if (RecurrenceDescriptor::isFixedOrderRecurrence(Phi, TheLoop, DT)) { 864 AllowedExit.insert(Phi); 865 FixedOrderRecurrences.insert(Phi); 866 continue; 867 } 868 869 // As a last resort, coerce the PHI to a AddRec expression 870 // and re-try classifying it a an induction PHI. 871 if (InductionDescriptor::isInductionPHI(Phi, TheLoop, PSE, ID, true) && 872 !IsDisallowedStridedPointerInduction(ID)) { 873 addInductionPhi(Phi, ID, AllowedExit); 874 continue; 875 } 876 877 reportVectorizationFailure("Found an unidentified PHI", 878 "value that could not be identified as " 879 "reduction is used outside the loop", 880 "NonReductionValueUsedOutsideLoop", ORE, TheLoop, Phi); 881 return false; 882 } // end of PHI handling 883 884 // We handle calls that: 885 // * Are debug info intrinsics. 886 // * Have a mapping to an IR intrinsic. 887 // * Have a vector version available. 888 auto *CI = dyn_cast<CallInst>(&I); 889 890 if (CI && !getVectorIntrinsicIDForCall(CI, TLI) && 891 !isa<DbgInfoIntrinsic>(CI) && 892 !(CI->getCalledFunction() && TLI && 893 (!VFDatabase::getMappings(*CI).empty() || 894 isTLIScalarize(*TLI, *CI)))) { 895 // If the call is a recognized math libary call, it is likely that 896 // we can vectorize it given loosened floating-point constraints. 897 LibFunc Func; 898 bool IsMathLibCall = 899 TLI && CI->getCalledFunction() && 900 CI->getType()->isFloatingPointTy() && 901 TLI->getLibFunc(CI->getCalledFunction()->getName(), Func) && 902 TLI->hasOptimizedCodeGen(Func); 903 904 if (IsMathLibCall) { 905 // TODO: Ideally, we should not use clang-specific language here, 906 // but it's hard to provide meaningful yet generic advice. 907 // Also, should this be guarded by allowExtraAnalysis() and/or be part 908 // of the returned info from isFunctionVectorizable()? 909 reportVectorizationFailure( 910 "Found a non-intrinsic callsite", 911 "library call cannot be vectorized. " 912 "Try compiling with -fno-math-errno, -ffast-math, " 913 "or similar flags", 914 "CantVectorizeLibcall", ORE, TheLoop, CI); 915 } else { 916 reportVectorizationFailure("Found a non-intrinsic callsite", 917 "call instruction cannot be vectorized", 918 "CantVectorizeLibcall", ORE, TheLoop, CI); 919 } 920 return false; 921 } 922 923 // Some intrinsics have scalar arguments and should be same in order for 924 // them to be vectorized (i.e. loop invariant). 925 if (CI) { 926 auto *SE = PSE.getSE(); 927 Intrinsic::ID IntrinID = getVectorIntrinsicIDForCall(CI, TLI); 928 for (unsigned Idx = 0; Idx < CI->arg_size(); ++Idx) 929 if (isVectorIntrinsicWithScalarOpAtArg(IntrinID, Idx)) { 930 if (!SE->isLoopInvariant(PSE.getSCEV(CI->getOperand(Idx)), 931 TheLoop)) { 932 reportVectorizationFailure("Found unvectorizable intrinsic", 933 "intrinsic instruction cannot be vectorized", 934 "CantVectorizeIntrinsic", ORE, TheLoop, CI); 935 return false; 936 } 937 } 938 } 939 940 // If we found a vectorized variant of a function, note that so LV can 941 // make better decisions about maximum VF. 942 if (CI && !VFDatabase::getMappings(*CI).empty()) 943 VecCallVariantsFound = true; 944 945 // Check that the instruction return type is vectorizable. 946 // Also, we can't vectorize extractelement instructions. 947 if ((!VectorType::isValidElementType(I.getType()) && 948 !I.getType()->isVoidTy()) || 949 isa<ExtractElementInst>(I)) { 950 reportVectorizationFailure("Found unvectorizable type", 951 "instruction return type cannot be vectorized", 952 "CantVectorizeInstructionReturnType", ORE, TheLoop, &I); 953 return false; 954 } 955 956 // Check that the stored type is vectorizable. 957 if (auto *ST = dyn_cast<StoreInst>(&I)) { 958 Type *T = ST->getValueOperand()->getType(); 959 if (!VectorType::isValidElementType(T)) { 960 reportVectorizationFailure("Store instruction cannot be vectorized", 961 "store instruction cannot be vectorized", 962 "CantVectorizeStore", ORE, TheLoop, ST); 963 return false; 964 } 965 966 // For nontemporal stores, check that a nontemporal vector version is 967 // supported on the target. 968 if (ST->getMetadata(LLVMContext::MD_nontemporal)) { 969 // Arbitrarily try a vector of 2 elements. 970 auto *VecTy = FixedVectorType::get(T, /*NumElts=*/2); 971 assert(VecTy && "did not find vectorized version of stored type"); 972 if (!TTI->isLegalNTStore(VecTy, ST->getAlign())) { 973 reportVectorizationFailure( 974 "nontemporal store instruction cannot be vectorized", 975 "nontemporal store instruction cannot be vectorized", 976 "CantVectorizeNontemporalStore", ORE, TheLoop, ST); 977 return false; 978 } 979 } 980 981 } else if (auto *LD = dyn_cast<LoadInst>(&I)) { 982 if (LD->getMetadata(LLVMContext::MD_nontemporal)) { 983 // For nontemporal loads, check that a nontemporal vector version is 984 // supported on the target (arbitrarily try a vector of 2 elements). 985 auto *VecTy = FixedVectorType::get(I.getType(), /*NumElts=*/2); 986 assert(VecTy && "did not find vectorized version of load type"); 987 if (!TTI->isLegalNTLoad(VecTy, LD->getAlign())) { 988 reportVectorizationFailure( 989 "nontemporal load instruction cannot be vectorized", 990 "nontemporal load instruction cannot be vectorized", 991 "CantVectorizeNontemporalLoad", ORE, TheLoop, LD); 992 return false; 993 } 994 } 995 996 // FP instructions can allow unsafe algebra, thus vectorizable by 997 // non-IEEE-754 compliant SIMD units. 998 // This applies to floating-point math operations and calls, not memory 999 // operations, shuffles, or casts, as they don't change precision or 1000 // semantics. 1001 } else if (I.getType()->isFloatingPointTy() && (CI || I.isBinaryOp()) && 1002 !I.isFast()) { 1003 LLVM_DEBUG(dbgs() << "LV: Found FP op with unsafe algebra.\n"); 1004 Hints->setPotentiallyUnsafe(); 1005 } 1006 1007 // Reduction instructions are allowed to have exit users. 1008 // All other instructions must not have external users. 1009 if (hasOutsideLoopUser(TheLoop, &I, AllowedExit)) { 1010 // We can safely vectorize loops where instructions within the loop are 1011 // used outside the loop only if the SCEV predicates within the loop is 1012 // same as outside the loop. Allowing the exit means reusing the SCEV 1013 // outside the loop. 1014 if (PSE.getPredicate().isAlwaysTrue()) { 1015 AllowedExit.insert(&I); 1016 continue; 1017 } 1018 reportVectorizationFailure("Value cannot be used outside the loop", 1019 "value cannot be used outside the loop", 1020 "ValueUsedOutsideLoop", ORE, TheLoop, &I); 1021 return false; 1022 } 1023 } // next instr. 1024 } 1025 1026 if (!PrimaryInduction) { 1027 if (Inductions.empty()) { 1028 reportVectorizationFailure("Did not find one integer induction var", 1029 "loop induction variable could not be identified", 1030 "NoInductionVariable", ORE, TheLoop); 1031 return false; 1032 } 1033 if (!WidestIndTy) { 1034 reportVectorizationFailure("Did not find one integer induction var", 1035 "integer loop induction variable could not be identified", 1036 "NoIntegerInductionVariable", ORE, TheLoop); 1037 return false; 1038 } 1039 LLVM_DEBUG(dbgs() << "LV: Did not find one integer induction var.\n"); 1040 } 1041 1042 // Now we know the widest induction type, check if our found induction 1043 // is the same size. If it's not, unset it here and InnerLoopVectorizer 1044 // will create another. 1045 if (PrimaryInduction && WidestIndTy != PrimaryInduction->getType()) 1046 PrimaryInduction = nullptr; 1047 1048 return true; 1049 } 1050 1051 bool LoopVectorizationLegality::canVectorizeMemory() { 1052 LAI = &LAIs.getInfo(*TheLoop); 1053 const OptimizationRemarkAnalysis *LAR = LAI->getReport(); 1054 if (LAR) { 1055 ORE->emit([&]() { 1056 return OptimizationRemarkAnalysis(Hints->vectorizeAnalysisPassName(), 1057 "loop not vectorized: ", *LAR); 1058 }); 1059 } 1060 1061 if (!LAI->canVectorizeMemory()) 1062 return false; 1063 1064 if (LAI->hasLoadStoreDependenceInvolvingLoopInvariantAddress()) { 1065 reportVectorizationFailure("We don't allow storing to uniform addresses", 1066 "write to a loop invariant address could not " 1067 "be vectorized", 1068 "CantVectorizeStoreToLoopInvariantAddress", ORE, 1069 TheLoop); 1070 return false; 1071 } 1072 1073 // We can vectorize stores to invariant address when final reduction value is 1074 // guaranteed to be stored at the end of the loop. Also, if decision to 1075 // vectorize loop is made, runtime checks are added so as to make sure that 1076 // invariant address won't alias with any other objects. 1077 if (!LAI->getStoresToInvariantAddresses().empty()) { 1078 // For each invariant address, check if last stored value is unconditional 1079 // and the address is not calculated inside the loop. 1080 for (StoreInst *SI : LAI->getStoresToInvariantAddresses()) { 1081 if (!isInvariantStoreOfReduction(SI)) 1082 continue; 1083 1084 if (blockNeedsPredication(SI->getParent())) { 1085 reportVectorizationFailure( 1086 "We don't allow storing to uniform addresses", 1087 "write of conditional recurring variant value to a loop " 1088 "invariant address could not be vectorized", 1089 "CantVectorizeStoreToLoopInvariantAddress", ORE, TheLoop); 1090 return false; 1091 } 1092 1093 // Invariant address should be defined outside of loop. LICM pass usually 1094 // makes sure it happens, but in rare cases it does not, we do not want 1095 // to overcomplicate vectorization to support this case. 1096 if (Instruction *Ptr = dyn_cast<Instruction>(SI->getPointerOperand())) { 1097 if (TheLoop->contains(Ptr)) { 1098 reportVectorizationFailure( 1099 "Invariant address is calculated inside the loop", 1100 "write to a loop invariant address could not " 1101 "be vectorized", 1102 "CantVectorizeStoreToLoopInvariantAddress", ORE, TheLoop); 1103 return false; 1104 } 1105 } 1106 } 1107 1108 if (LAI->hasStoreStoreDependenceInvolvingLoopInvariantAddress()) { 1109 // For each invariant address, check its last stored value is the result 1110 // of one of our reductions. 1111 // 1112 // We do not check if dependence with loads exists because that is already 1113 // checked via hasLoadStoreDependenceInvolvingLoopInvariantAddress. 1114 ScalarEvolution *SE = PSE.getSE(); 1115 SmallVector<StoreInst *, 4> UnhandledStores; 1116 for (StoreInst *SI : LAI->getStoresToInvariantAddresses()) { 1117 if (isInvariantStoreOfReduction(SI)) { 1118 // Earlier stores to this address are effectively deadcode. 1119 // With opaque pointers it is possible for one pointer to be used with 1120 // different sizes of stored values: 1121 // store i32 0, ptr %x 1122 // store i8 0, ptr %x 1123 // The latest store doesn't complitely overwrite the first one in the 1124 // example. That is why we have to make sure that types of stored 1125 // values are same. 1126 // TODO: Check that bitwidth of unhandled store is smaller then the 1127 // one that overwrites it and add a test. 1128 erase_if(UnhandledStores, [SE, SI](StoreInst *I) { 1129 return storeToSameAddress(SE, SI, I) && 1130 I->getValueOperand()->getType() == 1131 SI->getValueOperand()->getType(); 1132 }); 1133 continue; 1134 } 1135 UnhandledStores.push_back(SI); 1136 } 1137 1138 bool IsOK = UnhandledStores.empty(); 1139 // TODO: we should also validate against InvariantMemSets. 1140 if (!IsOK) { 1141 reportVectorizationFailure( 1142 "We don't allow storing to uniform addresses", 1143 "write to a loop invariant address could not " 1144 "be vectorized", 1145 "CantVectorizeStoreToLoopInvariantAddress", ORE, TheLoop); 1146 return false; 1147 } 1148 } 1149 } 1150 1151 PSE.addPredicate(LAI->getPSE().getPredicate()); 1152 return true; 1153 } 1154 1155 bool LoopVectorizationLegality::canVectorizeFPMath( 1156 bool EnableStrictReductions) { 1157 1158 // First check if there is any ExactFP math or if we allow reassociations 1159 if (!Requirements->getExactFPInst() || Hints->allowReordering()) 1160 return true; 1161 1162 // If the above is false, we have ExactFPMath & do not allow reordering. 1163 // If the EnableStrictReductions flag is set, first check if we have any 1164 // Exact FP induction vars, which we cannot vectorize. 1165 if (!EnableStrictReductions || 1166 any_of(getInductionVars(), [&](auto &Induction) -> bool { 1167 InductionDescriptor IndDesc = Induction.second; 1168 return IndDesc.getExactFPMathInst(); 1169 })) 1170 return false; 1171 1172 // We can now only vectorize if all reductions with Exact FP math also 1173 // have the isOrdered flag set, which indicates that we can move the 1174 // reduction operations in-loop. 1175 return (all_of(getReductionVars(), [&](auto &Reduction) -> bool { 1176 const RecurrenceDescriptor &RdxDesc = Reduction.second; 1177 return !RdxDesc.hasExactFPMath() || RdxDesc.isOrdered(); 1178 })); 1179 } 1180 1181 bool LoopVectorizationLegality::isInvariantStoreOfReduction(StoreInst *SI) { 1182 return any_of(getReductionVars(), [&](auto &Reduction) -> bool { 1183 const RecurrenceDescriptor &RdxDesc = Reduction.second; 1184 return RdxDesc.IntermediateStore == SI; 1185 }); 1186 } 1187 1188 bool LoopVectorizationLegality::isInvariantAddressOfReduction(Value *V) { 1189 return any_of(getReductionVars(), [&](auto &Reduction) -> bool { 1190 const RecurrenceDescriptor &RdxDesc = Reduction.second; 1191 if (!RdxDesc.IntermediateStore) 1192 return false; 1193 1194 ScalarEvolution *SE = PSE.getSE(); 1195 Value *InvariantAddress = RdxDesc.IntermediateStore->getPointerOperand(); 1196 return V == InvariantAddress || 1197 SE->getSCEV(V) == SE->getSCEV(InvariantAddress); 1198 }); 1199 } 1200 1201 bool LoopVectorizationLegality::isInductionPhi(const Value *V) const { 1202 Value *In0 = const_cast<Value *>(V); 1203 PHINode *PN = dyn_cast_or_null<PHINode>(In0); 1204 if (!PN) 1205 return false; 1206 1207 return Inductions.count(PN); 1208 } 1209 1210 const InductionDescriptor * 1211 LoopVectorizationLegality::getIntOrFpInductionDescriptor(PHINode *Phi) const { 1212 if (!isInductionPhi(Phi)) 1213 return nullptr; 1214 auto &ID = getInductionVars().find(Phi)->second; 1215 if (ID.getKind() == InductionDescriptor::IK_IntInduction || 1216 ID.getKind() == InductionDescriptor::IK_FpInduction) 1217 return &ID; 1218 return nullptr; 1219 } 1220 1221 const InductionDescriptor * 1222 LoopVectorizationLegality::getPointerInductionDescriptor(PHINode *Phi) const { 1223 if (!isInductionPhi(Phi)) 1224 return nullptr; 1225 auto &ID = getInductionVars().find(Phi)->second; 1226 if (ID.getKind() == InductionDescriptor::IK_PtrInduction) 1227 return &ID; 1228 return nullptr; 1229 } 1230 1231 bool LoopVectorizationLegality::isCastedInductionVariable( 1232 const Value *V) const { 1233 auto *Inst = dyn_cast<Instruction>(V); 1234 return (Inst && InductionCastsToIgnore.count(Inst)); 1235 } 1236 1237 bool LoopVectorizationLegality::isInductionVariable(const Value *V) const { 1238 return isInductionPhi(V) || isCastedInductionVariable(V); 1239 } 1240 1241 bool LoopVectorizationLegality::isFixedOrderRecurrence( 1242 const PHINode *Phi) const { 1243 return FixedOrderRecurrences.count(Phi); 1244 } 1245 1246 bool LoopVectorizationLegality::blockNeedsPredication(BasicBlock *BB) const { 1247 return LoopAccessInfo::blockNeedsPredication(BB, TheLoop, DT); 1248 } 1249 1250 bool LoopVectorizationLegality::blockCanBePredicated( 1251 BasicBlock *BB, SmallPtrSetImpl<Value *> &SafePtrs, 1252 SmallPtrSetImpl<const Instruction *> &MaskedOp) const { 1253 for (Instruction &I : *BB) { 1254 // We can predicate blocks with calls to assume, as long as we drop them in 1255 // case we flatten the CFG via predication. 1256 if (match(&I, m_Intrinsic<Intrinsic::assume>())) { 1257 MaskedOp.insert(&I); 1258 continue; 1259 } 1260 1261 // Do not let llvm.experimental.noalias.scope.decl block the vectorization. 1262 // TODO: there might be cases that it should block the vectorization. Let's 1263 // ignore those for now. 1264 if (isa<NoAliasScopeDeclInst>(&I)) 1265 continue; 1266 1267 // We can allow masked calls if there's at least one vector variant, even 1268 // if we end up scalarizing due to the cost model calculations. 1269 // TODO: Allow other calls if they have appropriate attributes... readonly 1270 // and argmemonly? 1271 if (CallInst *CI = dyn_cast<CallInst>(&I)) 1272 if (VFDatabase::hasMaskedVariant(*CI)) { 1273 MaskedOp.insert(CI); 1274 continue; 1275 } 1276 1277 // Loads are handled via masking (or speculated if safe to do so.) 1278 if (auto *LI = dyn_cast<LoadInst>(&I)) { 1279 if (!SafePtrs.count(LI->getPointerOperand())) 1280 MaskedOp.insert(LI); 1281 continue; 1282 } 1283 1284 // Predicated store requires some form of masking: 1285 // 1) masked store HW instruction, 1286 // 2) emulation via load-blend-store (only if safe and legal to do so, 1287 // be aware on the race conditions), or 1288 // 3) element-by-element predicate check and scalar store. 1289 if (auto *SI = dyn_cast<StoreInst>(&I)) { 1290 MaskedOp.insert(SI); 1291 continue; 1292 } 1293 1294 if (I.mayReadFromMemory() || I.mayWriteToMemory() || I.mayThrow()) 1295 return false; 1296 } 1297 1298 return true; 1299 } 1300 1301 bool LoopVectorizationLegality::canVectorizeWithIfConvert() { 1302 if (!EnableIfConversion) { 1303 reportVectorizationFailure("If-conversion is disabled", 1304 "if-conversion is disabled", 1305 "IfConversionDisabled", 1306 ORE, TheLoop); 1307 return false; 1308 } 1309 1310 assert(TheLoop->getNumBlocks() > 1 && "Single block loops are vectorizable"); 1311 1312 // A list of pointers which are known to be dereferenceable within scope of 1313 // the loop body for each iteration of the loop which executes. That is, 1314 // the memory pointed to can be dereferenced (with the access size implied by 1315 // the value's type) unconditionally within the loop header without 1316 // introducing a new fault. 1317 SmallPtrSet<Value *, 8> SafePointers; 1318 1319 // Collect safe addresses. 1320 for (BasicBlock *BB : TheLoop->blocks()) { 1321 if (!blockNeedsPredication(BB)) { 1322 for (Instruction &I : *BB) 1323 if (auto *Ptr = getLoadStorePointerOperand(&I)) 1324 SafePointers.insert(Ptr); 1325 continue; 1326 } 1327 1328 // For a block which requires predication, a address may be safe to access 1329 // in the loop w/o predication if we can prove dereferenceability facts 1330 // sufficient to ensure it'll never fault within the loop. For the moment, 1331 // we restrict this to loads; stores are more complicated due to 1332 // concurrency restrictions. 1333 ScalarEvolution &SE = *PSE.getSE(); 1334 for (Instruction &I : *BB) { 1335 LoadInst *LI = dyn_cast<LoadInst>(&I); 1336 if (LI && !LI->getType()->isVectorTy() && !mustSuppressSpeculation(*LI) && 1337 isDereferenceableAndAlignedInLoop(LI, TheLoop, SE, *DT, AC)) 1338 SafePointers.insert(LI->getPointerOperand()); 1339 } 1340 } 1341 1342 // Collect the blocks that need predication. 1343 for (BasicBlock *BB : TheLoop->blocks()) { 1344 // We support only branches and switch statements as terminators inside the 1345 // loop. 1346 if (isa<SwitchInst>(BB->getTerminator())) { 1347 if (TheLoop->isLoopExiting(BB)) { 1348 reportVectorizationFailure("Loop contains an unsupported switch", 1349 "loop contains an unsupported switch", 1350 "LoopContainsUnsupportedSwitch", ORE, 1351 TheLoop, BB->getTerminator()); 1352 return false; 1353 } 1354 } else if (!isa<BranchInst>(BB->getTerminator())) { 1355 reportVectorizationFailure("Loop contains an unsupported terminator", 1356 "loop contains an unsupported terminator", 1357 "LoopContainsUnsupportedTerminator", ORE, 1358 TheLoop, BB->getTerminator()); 1359 return false; 1360 } 1361 1362 // We must be able to predicate all blocks that need to be predicated. 1363 if (blockNeedsPredication(BB) && 1364 !blockCanBePredicated(BB, SafePointers, MaskedOp)) { 1365 reportVectorizationFailure( 1366 "Control flow cannot be substituted for a select", 1367 "control flow cannot be substituted for a select", "NoCFGForSelect", 1368 ORE, TheLoop, BB->getTerminator()); 1369 return false; 1370 } 1371 } 1372 1373 // We can if-convert this loop. 1374 return true; 1375 } 1376 1377 // Helper function to canVectorizeLoopNestCFG. 1378 bool LoopVectorizationLegality::canVectorizeLoopCFG(Loop *Lp, 1379 bool UseVPlanNativePath) { 1380 assert((UseVPlanNativePath || Lp->isInnermost()) && 1381 "VPlan-native path is not enabled."); 1382 1383 // TODO: ORE should be improved to show more accurate information when an 1384 // outer loop can't be vectorized because a nested loop is not understood or 1385 // legal. Something like: "outer_loop_location: loop not vectorized: 1386 // (inner_loop_location) loop control flow is not understood by vectorizer". 1387 1388 // Store the result and return it at the end instead of exiting early, in case 1389 // allowExtraAnalysis is used to report multiple reasons for not vectorizing. 1390 bool Result = true; 1391 bool DoExtraAnalysis = ORE->allowExtraAnalysis(DEBUG_TYPE); 1392 1393 // We must have a loop in canonical form. Loops with indirectbr in them cannot 1394 // be canonicalized. 1395 if (!Lp->getLoopPreheader()) { 1396 reportVectorizationFailure("Loop doesn't have a legal pre-header", 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 // We must have a single backedge. 1406 if (Lp->getNumBackEdges() != 1) { 1407 reportVectorizationFailure("The loop must have a single backedge", 1408 "loop control flow is not understood by vectorizer", 1409 "CFGNotUnderstood", ORE, TheLoop); 1410 if (DoExtraAnalysis) 1411 Result = false; 1412 else 1413 return false; 1414 } 1415 1416 return Result; 1417 } 1418 1419 bool LoopVectorizationLegality::canVectorizeLoopNestCFG( 1420 Loop *Lp, bool UseVPlanNativePath) { 1421 // Store the result and return it at the end instead of exiting early, in case 1422 // allowExtraAnalysis is used to report multiple reasons for not vectorizing. 1423 bool Result = true; 1424 bool DoExtraAnalysis = ORE->allowExtraAnalysis(DEBUG_TYPE); 1425 if (!canVectorizeLoopCFG(Lp, UseVPlanNativePath)) { 1426 if (DoExtraAnalysis) 1427 Result = false; 1428 else 1429 return false; 1430 } 1431 1432 // Recursively check whether the loop control flow of nested loops is 1433 // understood. 1434 for (Loop *SubLp : *Lp) 1435 if (!canVectorizeLoopNestCFG(SubLp, UseVPlanNativePath)) { 1436 if (DoExtraAnalysis) 1437 Result = false; 1438 else 1439 return false; 1440 } 1441 1442 return Result; 1443 } 1444 1445 bool LoopVectorizationLegality::canVectorize(bool UseVPlanNativePath) { 1446 // Store the result and return it at the end instead of exiting early, in case 1447 // allowExtraAnalysis is used to report multiple reasons for not vectorizing. 1448 bool Result = true; 1449 1450 bool DoExtraAnalysis = ORE->allowExtraAnalysis(DEBUG_TYPE); 1451 // Check whether the loop-related control flow in the loop nest is expected by 1452 // vectorizer. 1453 if (!canVectorizeLoopNestCFG(TheLoop, UseVPlanNativePath)) { 1454 if (DoExtraAnalysis) { 1455 LLVM_DEBUG(dbgs() << "LV: legality check failed: loop nest"); 1456 Result = false; 1457 } else { 1458 return false; 1459 } 1460 } 1461 1462 // We need to have a loop header. 1463 LLVM_DEBUG(dbgs() << "LV: Found a loop: " << TheLoop->getHeader()->getName() 1464 << '\n'); 1465 1466 // Specific checks for outer loops. We skip the remaining legal checks at this 1467 // point because they don't support outer loops. 1468 if (!TheLoop->isInnermost()) { 1469 assert(UseVPlanNativePath && "VPlan-native path is not enabled."); 1470 1471 if (!canVectorizeOuterLoop()) { 1472 reportVectorizationFailure("Unsupported outer loop", 1473 "unsupported outer loop", 1474 "UnsupportedOuterLoop", 1475 ORE, TheLoop); 1476 // TODO: Implement DoExtraAnalysis when subsequent legal checks support 1477 // outer loops. 1478 return false; 1479 } 1480 1481 LLVM_DEBUG(dbgs() << "LV: We can vectorize this outer loop!\n"); 1482 return Result; 1483 } 1484 1485 assert(TheLoop->isInnermost() && "Inner loop expected."); 1486 // Check if we can if-convert non-single-bb loops. 1487 unsigned NumBlocks = TheLoop->getNumBlocks(); 1488 if (NumBlocks != 1 && !canVectorizeWithIfConvert()) { 1489 LLVM_DEBUG(dbgs() << "LV: Can't if-convert the loop.\n"); 1490 if (DoExtraAnalysis) 1491 Result = false; 1492 else 1493 return false; 1494 } 1495 1496 // Check if we can vectorize the instructions and CFG in this loop. 1497 if (!canVectorizeInstrs()) { 1498 LLVM_DEBUG(dbgs() << "LV: Can't vectorize the instructions or CFG\n"); 1499 if (DoExtraAnalysis) 1500 Result = false; 1501 else 1502 return false; 1503 } 1504 1505 // Go over each instruction and look at memory deps. 1506 if (!canVectorizeMemory()) { 1507 LLVM_DEBUG(dbgs() << "LV: Can't vectorize due to memory conflicts\n"); 1508 if (DoExtraAnalysis) 1509 Result = false; 1510 else 1511 return false; 1512 } 1513 1514 if (isa<SCEVCouldNotCompute>(PSE.getBackedgeTakenCount())) { 1515 reportVectorizationFailure("could not determine number of loop iterations", 1516 "could not determine number of loop iterations", 1517 "CantComputeNumberOfIterations", ORE, TheLoop); 1518 if (DoExtraAnalysis) 1519 Result = false; 1520 else 1521 return false; 1522 } 1523 1524 if (Result) { 1525 LLVM_DEBUG(dbgs() << "LV: We can vectorize this loop" 1526 << (LAI->getRuntimePointerChecking()->Need 1527 ? " (with a runtime bound check)" 1528 : "") 1529 << "!\n"); 1530 } 1531 1532 unsigned SCEVThreshold = VectorizeSCEVCheckThreshold; 1533 if (Hints->getForce() == LoopVectorizeHints::FK_Enabled) 1534 SCEVThreshold = PragmaVectorizeSCEVCheckThreshold; 1535 1536 if (PSE.getPredicate().getComplexity() > SCEVThreshold) { 1537 LLVM_DEBUG(dbgs() << "LV: Vectorization not profitable " 1538 "due to SCEVThreshold"); 1539 reportVectorizationFailure("Too many SCEV checks needed", 1540 "Too many SCEV assumptions need to be made and checked at runtime", 1541 "TooManySCEVRunTimeChecks", ORE, TheLoop); 1542 if (DoExtraAnalysis) 1543 Result = false; 1544 else 1545 return false; 1546 } 1547 1548 // Okay! We've done all the tests. If any have failed, return false. Otherwise 1549 // we can vectorize, and at this point we don't have any other mem analysis 1550 // which may limit our maximum vectorization factor, so just return true with 1551 // no restrictions. 1552 return Result; 1553 } 1554 1555 bool LoopVectorizationLegality::canFoldTailByMasking() const { 1556 1557 LLVM_DEBUG(dbgs() << "LV: checking if tail can be folded by masking.\n"); 1558 1559 SmallPtrSet<const Value *, 8> ReductionLiveOuts; 1560 1561 for (const auto &Reduction : getReductionVars()) 1562 ReductionLiveOuts.insert(Reduction.second.getLoopExitInstr()); 1563 1564 // TODO: handle non-reduction outside users when tail is folded by masking. 1565 for (auto *AE : AllowedExit) { 1566 // Check that all users of allowed exit values are inside the loop or 1567 // are the live-out of a reduction. 1568 if (ReductionLiveOuts.count(AE)) 1569 continue; 1570 for (User *U : AE->users()) { 1571 Instruction *UI = cast<Instruction>(U); 1572 if (TheLoop->contains(UI)) 1573 continue; 1574 LLVM_DEBUG( 1575 dbgs() 1576 << "LV: Cannot fold tail by masking, loop has an outside user for " 1577 << *UI << "\n"); 1578 return false; 1579 } 1580 } 1581 1582 for (const auto &Entry : getInductionVars()) { 1583 PHINode *OrigPhi = Entry.first; 1584 for (User *U : OrigPhi->users()) { 1585 auto *UI = cast<Instruction>(U); 1586 if (!TheLoop->contains(UI)) { 1587 LLVM_DEBUG(dbgs() << "LV: Cannot fold tail by masking, loop IV has an " 1588 "outside user for " 1589 << *UI << "\n"); 1590 return false; 1591 } 1592 } 1593 } 1594 1595 // The list of pointers that we can safely read and write to remains empty. 1596 SmallPtrSet<Value *, 8> SafePointers; 1597 1598 // Check all blocks for predication, including those that ordinarily do not 1599 // need predication such as the header block. 1600 SmallPtrSet<const Instruction *, 8> TmpMaskedOp; 1601 for (BasicBlock *BB : TheLoop->blocks()) { 1602 if (!blockCanBePredicated(BB, SafePointers, TmpMaskedOp)) { 1603 LLVM_DEBUG(dbgs() << "LV: Cannot fold tail by masking.\n"); 1604 return false; 1605 } 1606 } 1607 1608 LLVM_DEBUG(dbgs() << "LV: can fold tail by masking.\n"); 1609 1610 return true; 1611 } 1612 1613 void LoopVectorizationLegality::prepareToFoldTailByMasking() { 1614 // The list of pointers that we can safely read and write to remains empty. 1615 SmallPtrSet<Value *, 8> SafePointers; 1616 1617 // Mark all blocks for predication, including those that ordinarily do not 1618 // need predication such as the header block. 1619 for (BasicBlock *BB : TheLoop->blocks()) { 1620 [[maybe_unused]] bool R = blockCanBePredicated(BB, SafePointers, MaskedOp); 1621 assert(R && "Must be able to predicate block when tail-folding."); 1622 } 1623 } 1624 1625 } // namespace llvm 1626