1 //===-- LoopUnroll.cpp - Loop unroller pass -------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass implements a simple loop unroller. It works best when loops have
11 // been canonicalized by the -indvars pass, allowing it to determine the trip
12 // counts of loops easily.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Scalar.h"
16 #include "llvm/Analysis/AssumptionCache.h"
17 #include "llvm/Analysis/CodeMetrics.h"
18 #include "llvm/Analysis/LoopPass.h"
19 #include "llvm/Analysis/ScalarEvolution.h"
20 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
21 #include "llvm/Analysis/TargetTransformInfo.h"
22 #include "llvm/IR/DataLayout.h"
23 #include "llvm/IR/DiagnosticInfo.h"
24 #include "llvm/IR/Dominators.h"
25 #include "llvm/IR/IntrinsicInst.h"
26 #include "llvm/IR/Metadata.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/Transforms/Utils/UnrollLoop.h"
31 #include "llvm/IR/InstVisitor.h"
32 #include "llvm/Analysis/InstructionSimplify.h"
37 #define DEBUG_TYPE "loop-unroll"
39 static cl::opt<unsigned>
40 UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden,
41 cl::desc("The cut-off point for automatic loop unrolling"));
43 static cl::opt<unsigned> UnrollMaxIterationsCountToAnalyze(
44 "unroll-max-iteration-count-to-analyze", cl::init(1000), cl::Hidden,
45 cl::desc("Don't allow loop unrolling to simulate more than this number of"
46 "iterations when checking full unroll profitability"));
48 static cl::opt<unsigned>
49 UnrollCount("unroll-count", cl::init(0), cl::Hidden,
50 cl::desc("Use this unroll count for all loops including those with "
51 "unroll_count pragma values, for testing purposes"));
54 UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden,
55 cl::desc("Allows loops to be partially unrolled until "
56 "-unroll-threshold loop size is reached."));
59 UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden,
60 cl::desc("Unroll loops with run-time trip counts"));
62 static cl::opt<unsigned>
63 PragmaUnrollThreshold("pragma-unroll-threshold", cl::init(16 * 1024), cl::Hidden,
64 cl::desc("Unrolled size limit for loops with an unroll(full) or "
65 "unroll_count pragma."));
68 class LoopUnroll : public LoopPass {
70 static char ID; // Pass ID, replacement for typeid
71 LoopUnroll(int T = -1, int C = -1, int P = -1, int R = -1) : LoopPass(ID) {
72 CurrentThreshold = (T == -1) ? UnrollThreshold : unsigned(T);
73 CurrentCount = (C == -1) ? UnrollCount : unsigned(C);
74 CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P;
75 CurrentRuntime = (R == -1) ? UnrollRuntime : (bool)R;
77 UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0);
78 UserAllowPartial = (P != -1) ||
79 (UnrollAllowPartial.getNumOccurrences() > 0);
80 UserRuntime = (R != -1) || (UnrollRuntime.getNumOccurrences() > 0);
81 UserCount = (C != -1) || (UnrollCount.getNumOccurrences() > 0);
83 initializeLoopUnrollPass(*PassRegistry::getPassRegistry());
86 /// A magic value for use with the Threshold parameter to indicate
87 /// that the loop unroll should be performed regardless of how much
88 /// code expansion would result.
89 static const unsigned NoThreshold = UINT_MAX;
91 // Threshold to use when optsize is specified (and there is no
92 // explicit -unroll-threshold).
93 static const unsigned OptSizeUnrollThreshold = 50;
95 // Default unroll count for loops with run-time trip count if
96 // -unroll-count is not set
97 static const unsigned UnrollRuntimeCount = 8;
99 unsigned CurrentCount;
100 unsigned CurrentThreshold;
101 bool CurrentAllowPartial;
103 bool UserCount; // CurrentCount is user-specified.
104 bool UserThreshold; // CurrentThreshold is user-specified.
105 bool UserAllowPartial; // CurrentAllowPartial is user-specified.
106 bool UserRuntime; // CurrentRuntime is user-specified.
108 bool runOnLoop(Loop *L, LPPassManager &LPM) override;
110 /// This transformation requires natural loop information & requires that
111 /// loop preheaders be inserted into the CFG...
113 void getAnalysisUsage(AnalysisUsage &AU) const override {
114 AU.addRequired<AssumptionCacheTracker>();
115 AU.addRequired<LoopInfoWrapperPass>();
116 AU.addPreserved<LoopInfoWrapperPass>();
117 AU.addRequiredID(LoopSimplifyID);
118 AU.addPreservedID(LoopSimplifyID);
119 AU.addRequiredID(LCSSAID);
120 AU.addPreservedID(LCSSAID);
121 AU.addRequired<ScalarEvolution>();
122 AU.addPreserved<ScalarEvolution>();
123 AU.addRequired<TargetTransformInfoWrapperPass>();
124 // FIXME: Loop unroll requires LCSSA. And LCSSA requires dom info.
125 // If loop unroll does not preserve dom info then LCSSA pass on next
126 // loop will receive invalid dom info.
127 // For now, recreate dom info, if loop is unrolled.
128 AU.addPreserved<DominatorTreeWrapperPass>();
131 // Fill in the UnrollingPreferences parameter with values from the
132 // TargetTransformationInfo.
133 void getUnrollingPreferences(Loop *L, const TargetTransformInfo &TTI,
134 TargetTransformInfo::UnrollingPreferences &UP) {
135 UP.Threshold = CurrentThreshold;
136 UP.OptSizeThreshold = OptSizeUnrollThreshold;
137 UP.PartialThreshold = CurrentThreshold;
138 UP.PartialOptSizeThreshold = OptSizeUnrollThreshold;
139 UP.Count = CurrentCount;
140 UP.MaxCount = UINT_MAX;
141 UP.Partial = CurrentAllowPartial;
142 UP.Runtime = CurrentRuntime;
143 TTI.getUnrollingPreferences(L, UP);
146 // Select and return an unroll count based on parameters from
147 // user, unroll preferences, unroll pragmas, or a heuristic.
148 // SetExplicitly is set to true if the unroll count is is set by
149 // the user or a pragma rather than selected heuristically.
151 selectUnrollCount(const Loop *L, unsigned TripCount, bool PragmaFullUnroll,
152 unsigned PragmaCount,
153 const TargetTransformInfo::UnrollingPreferences &UP,
154 bool &SetExplicitly);
156 // Select threshold values used to limit unrolling based on a
157 // total unrolled size. Parameters Threshold and PartialThreshold
158 // are set to the maximum unrolled size for fully and partially
159 // unrolled loops respectively.
160 void selectThresholds(const Loop *L, bool HasPragma,
161 const TargetTransformInfo::UnrollingPreferences &UP,
162 unsigned &Threshold, unsigned &PartialThreshold,
163 unsigned NumberOfSimplifiedInstructions) {
164 // Determine the current unrolling threshold. While this is
165 // normally set from UnrollThreshold, it is overridden to a
166 // smaller value if the current function is marked as
167 // optimize-for-size, and the unroll threshold was not user
169 Threshold = UserThreshold ? CurrentThreshold : UP.Threshold;
170 PartialThreshold = UserThreshold ? CurrentThreshold : UP.PartialThreshold;
171 if (!UserThreshold &&
172 L->getHeader()->getParent()->getAttributes().
173 hasAttribute(AttributeSet::FunctionIndex,
174 Attribute::OptimizeForSize)) {
175 Threshold = UP.OptSizeThreshold;
176 PartialThreshold = UP.PartialOptSizeThreshold;
179 // If the loop has an unrolling pragma, we want to be more
180 // aggressive with unrolling limits. Set thresholds to at
181 // least the PragmaTheshold value which is larger than the
183 if (Threshold != NoThreshold)
184 Threshold = std::max<unsigned>(Threshold, PragmaUnrollThreshold);
185 if (PartialThreshold != NoThreshold)
187 std::max<unsigned>(PartialThreshold, PragmaUnrollThreshold);
189 Threshold += NumberOfSimplifiedInstructions;
194 char LoopUnroll::ID = 0;
195 INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
196 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
197 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
198 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
199 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
200 INITIALIZE_PASS_DEPENDENCY(LCSSA)
201 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
202 INITIALIZE_PASS_END(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
204 Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial,
206 return new LoopUnroll(Threshold, Count, AllowPartial, Runtime);
209 Pass *llvm::createSimpleLoopUnrollPass() {
210 return llvm::createLoopUnrollPass(-1, -1, 0, 0);
213 static bool IsLoadFromConstantInitializer(Value *V) {
214 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
215 if (GV->isConstant() && GV->hasDefinitiveInitializer())
216 return GV->getInitializer();
220 struct FindConstantPointers {
221 bool LoadCanBeConstantFolded;
222 bool IndexIsConstant;
228 FindConstantPointers(const Loop *loop, ScalarEvolution &SE)
229 : LoadCanBeConstantFolded(true), IndexIsConstant(true), L(loop), SE(SE) {}
231 bool follow(const SCEV *S) {
232 if (const SCEVUnknown *SC = dyn_cast<SCEVUnknown>(S)) {
233 // We've reached the leaf node of SCEV, it's most probably just a
234 // variable. Now it's time to see if it corresponds to a global constant
235 // global (in which case we can eliminate the load), or not.
236 BaseAddress = SC->getValue();
237 LoadCanBeConstantFolded =
238 IndexIsConstant && IsLoadFromConstantInitializer(BaseAddress);
241 if (isa<SCEVConstant>(S))
243 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
244 // If the current SCEV expression is AddRec, and its loop isn't the loop
245 // we are about to unroll, then we won't get a constant address after
246 // unrolling, and thus, won't be able to eliminate the load.
247 if (AR->getLoop() != L)
248 return IndexIsConstant = false;
249 // If the step isn't constant, we won't get constant addresses in unrolled
250 // version. Bail out.
251 if (const SCEVConstant *StepSE =
252 dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
253 Step = StepSE->getValue()->getValue();
255 return IndexIsConstant = false;
257 return IndexIsConstant;
259 // If Result is true, continue traversal.
260 // Otherwise, we have found something that prevents us from (possible) load
262 return IndexIsConstant;
264 bool isDone() const { return !IndexIsConstant; }
267 // This class is used to get an estimate of the optimization effects that we
268 // could get from complete loop unrolling. It comes from the fact that some
269 // loads might be replaced with concrete constant values and that could trigger
270 // a chain of instruction simplifications.
272 // E.g. we might have:
273 // int a[] = {0, 1, 0};
275 // for (i = 0; i < 3; i ++)
277 // If we completely unroll the loop, we would get:
278 // v = b[0]*a[0] + b[1]*a[1] + b[2]*a[2]
279 // Which then will be simplified to:
280 // v = b[0]* 0 + b[1]* 1 + b[2]* 0
283 class UnrollAnalyzer : public InstVisitor<UnrollAnalyzer, bool> {
284 typedef InstVisitor<UnrollAnalyzer, bool> Base;
285 friend class InstVisitor<UnrollAnalyzer, bool>;
290 const TargetTransformInfo &TTI;
291 unsigned NumberOfOptimizedInstructions;
293 DenseMap<Value *, Constant *> SimplifiedValues;
294 DenseMap<LoadInst *, Value *> LoadBaseAddresses;
295 SmallPtrSet<Instruction *, 32> CountedInsns;
297 // Provide base case for our instruction visit.
298 bool visitInstruction(Instruction &I) { return false; };
299 // TODO: We should also visit ICmp, FCmp, GetElementPtr, Trunc, ZExt, SExt,
300 // FPTrunc, FPExt, FPToUI, FPToSI, UIToFP, SIToFP, BitCast, Select,
301 // ExtractElement, InsertElement, ShuffleVector, ExtractValue, InsertValue.
303 // Probaly it's worth to hoist the code for estimating the simplifications
304 // effects to a separate class, since we have a very similar code in
305 // InlineCost already.
306 bool visitBinaryOperator(BinaryOperator &I) {
307 Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
308 if (!isa<Constant>(LHS))
309 if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS))
311 if (!isa<Constant>(RHS))
312 if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS))
314 Value *SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS);
316 if (SimpleV && CountedInsns.insert(&I).second)
317 NumberOfOptimizedInstructions += TTI.getUserCost(&I);
319 if (Constant *C = dyn_cast_or_null<Constant>(SimpleV)) {
320 SimplifiedValues[&I] = C;
326 Constant *computeLoadValue(LoadInst *LI, unsigned Iteration) {
329 Value *BaseAddr = LoadBaseAddresses[LI];
333 auto GV = dyn_cast<GlobalVariable>(BaseAddr);
337 ConstantDataSequential *CDS =
338 dyn_cast<ConstantDataSequential>(GV->getInitializer());
342 const SCEV *BaseAddrSE = SE.getSCEV(BaseAddr);
343 const SCEV *S = SE.getSCEV(LI->getPointerOperand());
344 const SCEV *OffSE = SE.getMinusSCEV(S, BaseAddrSE);
347 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(OffSE);
351 if (const SCEVConstant *StepSE =
352 dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
353 StepC = StepSE->getValue()->getValue();
357 if (const SCEVConstant *StartSE = dyn_cast<SCEVConstant>(AR->getStart()))
358 StartC = StartSE->getValue()->getValue();
362 unsigned ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U;
363 unsigned Start = StartC.getLimitedValue();
364 unsigned Step = StepC.getLimitedValue();
366 unsigned Index = (Start + Step * Iteration) / ElemSize;
367 if (Index >= CDS->getNumElements())
370 Constant *CV = CDS->getElementAsConstant(Index);
376 UnrollAnalyzer(const Loop *L, unsigned TripCount, ScalarEvolution &SE,
377 const TargetTransformInfo &TTI)
378 : L(L), TripCount(TripCount), SE(SE), TTI(TTI),
379 NumberOfOptimizedInstructions(0) {}
381 // Visit all loads the loop L, and for those that, after complete loop
382 // unrolling, would have a constant address and it will point to a known
383 // constant initializer, record its base address for future use. It is used
384 // when we estimate number of potentially simplified instructions.
385 void FindConstFoldableLoads() {
386 for (auto BB : L->getBlocks()) {
387 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
388 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
391 Value *AddrOp = LI->getPointerOperand();
392 const SCEV *S = SE.getSCEV(AddrOp);
393 FindConstantPointers Visitor(L, SE);
394 SCEVTraversal<FindConstantPointers> T(Visitor);
396 if (Visitor.IndexIsConstant && Visitor.LoadCanBeConstantFolded) {
397 LoadBaseAddresses[LI] = Visitor.BaseAddress;
404 // Given a list of loads that could be constant-folded (LoadBaseAddresses),
405 // estimate number of optimized instructions after substituting the concrete
406 // values for the given Iteration.
407 // Fill in SimplifiedInsns map for future use in DCE-estimation.
408 unsigned EstimateNumberOfSimplifiedInsns(unsigned Iteration) {
409 SmallVector<Instruction *, 8> Worklist;
410 SimplifiedValues.clear();
411 CountedInsns.clear();
413 NumberOfOptimizedInstructions = 0;
414 // We start by adding all loads to the worklist.
415 for (auto LoadDescr : LoadBaseAddresses) {
416 LoadInst *LI = LoadDescr.first;
417 SimplifiedValues[LI] = computeLoadValue(LI, Iteration);
418 if (CountedInsns.insert(LI).second)
419 NumberOfOptimizedInstructions += TTI.getUserCost(LI);
421 for (auto U : LI->users()) {
422 Instruction *UI = dyn_cast<Instruction>(U);
425 if (!L->contains(UI))
427 Worklist.push_back(UI);
431 // And then we try to simplify every user of every instruction from the
432 // worklist. If we do simplify a user, add it to the worklist to process
433 // its users as well.
434 while (!Worklist.empty()) {
435 Instruction *I = Worklist.pop_back_val();
438 for (auto U : I->users()) {
439 Instruction *UI = dyn_cast<Instruction>(U);
442 if (!L->contains(UI))
444 Worklist.push_back(UI);
447 return NumberOfOptimizedInstructions;
450 // Given a list of potentially simplifed instructions, estimate number of
451 // instructions that would become dead if we do perform the simplification.
452 unsigned EstimateNumberOfDeadInsns() {
453 NumberOfOptimizedInstructions = 0;
454 SmallVector<Instruction *, 8> Worklist;
455 DenseMap<Instruction *, bool> DeadInstructions;
456 // Start by initializing worklist with simplified instructions.
457 for (auto Folded : SimplifiedValues) {
458 if (auto FoldedInsn = dyn_cast<Instruction>(Folded.first)) {
459 Worklist.push_back(FoldedInsn);
460 DeadInstructions[FoldedInsn] = true;
463 // If a definition of an insn is only used by simplified or dead
464 // instructions, it's also dead. Check defs of all instructions from the
466 while (!Worklist.empty()) {
467 Instruction *FoldedInsn = Worklist.pop_back_val();
468 for (Value *Op : FoldedInsn->operands()) {
469 if (auto I = dyn_cast<Instruction>(Op)) {
472 if (SimplifiedValues[I])
473 continue; // This insn has been counted already.
474 if (I->getNumUses() == 0)
476 bool AllUsersFolded = true;
477 for (auto U : I->users()) {
478 Instruction *UI = dyn_cast<Instruction>(U);
479 if (!SimplifiedValues[UI] && !DeadInstructions[UI]) {
480 AllUsersFolded = false;
484 if (AllUsersFolded) {
485 NumberOfOptimizedInstructions += TTI.getUserCost(I);
486 Worklist.push_back(I);
487 DeadInstructions[I] = true;
492 return NumberOfOptimizedInstructions;
496 // Complete loop unrolling can make some loads constant, and we need to know if
497 // that would expose any further optimization opportunities.
498 // This routine estimates this optimization effect and returns the number of
499 // instructions, that potentially might be optimized away.
501 ApproximateNumberOfOptimizedInstructions(const Loop *L, ScalarEvolution &SE,
503 const TargetTransformInfo &TTI) {
507 UnrollAnalyzer UA(L, TripCount, SE, TTI);
508 UA.FindConstFoldableLoads();
510 // Estimate number of instructions, that could be simplified if we replace a
511 // load with the corresponding constant. Since the same load will take
512 // different values on different iterations, we have to go through all loop's
513 // iterations here. To limit ourselves here, we check only first N
514 // iterations, and then scale the found number, if necessary.
515 unsigned IterationsNumberForEstimate =
516 std::min<unsigned>(UnrollMaxIterationsCountToAnalyze, TripCount);
517 unsigned NumberOfOptimizedInstructions = 0;
518 for (unsigned i = 0; i < IterationsNumberForEstimate; ++i) {
519 NumberOfOptimizedInstructions += UA.EstimateNumberOfSimplifiedInsns(i);
520 NumberOfOptimizedInstructions += UA.EstimateNumberOfDeadInsns();
522 NumberOfOptimizedInstructions *= TripCount / IterationsNumberForEstimate;
524 return NumberOfOptimizedInstructions;
527 /// ApproximateLoopSize - Approximate the size of the loop.
528 static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls,
529 bool &NotDuplicatable,
530 const TargetTransformInfo &TTI,
531 AssumptionCache *AC) {
532 SmallPtrSet<const Value *, 32> EphValues;
533 CodeMetrics::collectEphemeralValues(L, AC, EphValues);
536 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
538 Metrics.analyzeBasicBlock(*I, TTI, EphValues);
539 NumCalls = Metrics.NumInlineCandidates;
540 NotDuplicatable = Metrics.notDuplicatable;
542 unsigned LoopSize = Metrics.NumInsts;
544 // Don't allow an estimate of size zero. This would allows unrolling of loops
545 // with huge iteration counts, which is a compile time problem even if it's
546 // not a problem for code quality. Also, the code using this size may assume
547 // that each loop has at least three instructions (likely a conditional
548 // branch, a comparison feeding that branch, and some kind of loop increment
549 // feeding that comparison instruction).
550 LoopSize = std::max(LoopSize, 3u);
555 // Returns the loop hint metadata node with the given name (for example,
556 // "llvm.loop.unroll.count"). If no such metadata node exists, then nullptr is
558 static MDNode *GetUnrollMetadataForLoop(const Loop *L, StringRef Name) {
559 if (MDNode *LoopID = L->getLoopID())
560 return GetUnrollMetadata(LoopID, Name);
564 // Returns true if the loop has an unroll(full) pragma.
565 static bool HasUnrollFullPragma(const Loop *L) {
566 return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.full");
569 // Returns true if the loop has an unroll(disable) pragma.
570 static bool HasUnrollDisablePragma(const Loop *L) {
571 return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.disable");
574 // If loop has an unroll_count pragma return the (necessarily
575 // positive) value from the pragma. Otherwise return 0.
576 static unsigned UnrollCountPragmaValue(const Loop *L) {
577 MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll.count");
579 assert(MD->getNumOperands() == 2 &&
580 "Unroll count hint metadata should have two operands.");
582 mdconst::extract<ConstantInt>(MD->getOperand(1))->getZExtValue();
583 assert(Count >= 1 && "Unroll count must be positive.");
589 // Remove existing unroll metadata and add unroll disable metadata to
590 // indicate the loop has already been unrolled. This prevents a loop
591 // from being unrolled more than is directed by a pragma if the loop
592 // unrolling pass is run more than once (which it generally is).
593 static void SetLoopAlreadyUnrolled(Loop *L) {
594 MDNode *LoopID = L->getLoopID();
597 // First remove any existing loop unrolling metadata.
598 SmallVector<Metadata *, 4> MDs;
599 // Reserve first location for self reference to the LoopID metadata node.
600 MDs.push_back(nullptr);
601 for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
602 bool IsUnrollMetadata = false;
603 MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
605 const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
606 IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll.");
608 if (!IsUnrollMetadata)
609 MDs.push_back(LoopID->getOperand(i));
612 // Add unroll(disable) metadata to disable future unrolling.
613 LLVMContext &Context = L->getHeader()->getContext();
614 SmallVector<Metadata *, 1> DisableOperands;
615 DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable"));
616 MDNode *DisableNode = MDNode::get(Context, DisableOperands);
617 MDs.push_back(DisableNode);
619 MDNode *NewLoopID = MDNode::get(Context, MDs);
620 // Set operand 0 to refer to the loop id itself.
621 NewLoopID->replaceOperandWith(0, NewLoopID);
622 L->setLoopID(NewLoopID);
625 unsigned LoopUnroll::selectUnrollCount(
626 const Loop *L, unsigned TripCount, bool PragmaFullUnroll,
627 unsigned PragmaCount, const TargetTransformInfo::UnrollingPreferences &UP,
628 bool &SetExplicitly) {
629 SetExplicitly = true;
631 // User-specified count (either as a command-line option or
632 // constructor parameter) has highest precedence.
633 unsigned Count = UserCount ? CurrentCount : 0;
635 // If there is no user-specified count, unroll pragmas have the next
636 // highest precendence.
640 } else if (PragmaFullUnroll) {
649 SetExplicitly = false;
651 // Runtime trip count.
652 Count = UnrollRuntimeCount;
654 // Conservative heuristic: if we know the trip count, see if we can
655 // completely unroll (subject to the threshold, checked below); otherwise
656 // try to find greatest modulo of the trip count which is still under
660 if (TripCount && Count > TripCount)
665 bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
666 if (skipOptnoneFunction(L))
669 Function &F = *L->getHeader()->getParent();
671 LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
672 ScalarEvolution *SE = &getAnalysis<ScalarEvolution>();
673 const TargetTransformInfo &TTI =
674 getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
675 auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
677 BasicBlock *Header = L->getHeader();
678 DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName()
679 << "] Loop %" << Header->getName() << "\n");
681 if (HasUnrollDisablePragma(L)) {
684 bool PragmaFullUnroll = HasUnrollFullPragma(L);
685 unsigned PragmaCount = UnrollCountPragmaValue(L);
686 bool HasPragma = PragmaFullUnroll || PragmaCount > 0;
688 TargetTransformInfo::UnrollingPreferences UP;
689 getUnrollingPreferences(L, TTI, UP);
691 // Find trip count and trip multiple if count is not available
692 unsigned TripCount = 0;
693 unsigned TripMultiple = 1;
694 // If there are multiple exiting blocks but one of them is the latch, use the
695 // latch for the trip count estimation. Otherwise insist on a single exiting
696 // block for the trip count estimation.
697 BasicBlock *ExitingBlock = L->getLoopLatch();
698 if (!ExitingBlock || !L->isLoopExiting(ExitingBlock))
699 ExitingBlock = L->getExitingBlock();
701 TripCount = SE->getSmallConstantTripCount(L, ExitingBlock);
702 TripMultiple = SE->getSmallConstantTripMultiple(L, ExitingBlock);
705 // Select an initial unroll count. This may be reduced later based
706 // on size thresholds.
707 bool CountSetExplicitly;
708 unsigned Count = selectUnrollCount(L, TripCount, PragmaFullUnroll,
709 PragmaCount, UP, CountSetExplicitly);
711 unsigned NumInlineCandidates;
712 bool notDuplicatable;
714 ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI, &AC);
715 DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n");
717 // When computing the unrolled size, note that the conditional branch on the
718 // backedge and the comparison feeding it are not replicated like the rest of
719 // the loop body (which is why 2 is subtracted).
720 uint64_t UnrolledSize = (uint64_t)(LoopSize-2) * Count + 2;
721 if (notDuplicatable) {
722 DEBUG(dbgs() << " Not unrolling loop which contains non-duplicatable"
723 << " instructions.\n");
726 if (NumInlineCandidates != 0) {
727 DEBUG(dbgs() << " Not unrolling loop with inlinable calls.\n");
731 unsigned NumberOfOptimizedInstructions =
732 ApproximateNumberOfOptimizedInstructions(L, *SE, TripCount, TTI);
733 DEBUG(dbgs() << " Complete unrolling could save: "
734 << NumberOfOptimizedInstructions << "\n");
736 unsigned Threshold, PartialThreshold;
737 selectThresholds(L, HasPragma, UP, Threshold, PartialThreshold,
738 NumberOfOptimizedInstructions);
740 // Given Count, TripCount and thresholds determine the type of
741 // unrolling which is to be performed.
742 enum { Full = 0, Partial = 1, Runtime = 2 };
744 if (TripCount && Count == TripCount) {
745 if (Threshold != NoThreshold && UnrolledSize > Threshold) {
746 DEBUG(dbgs() << " Too large to fully unroll with count: " << Count
747 << " because size: " << UnrolledSize << ">" << Threshold
753 } else if (TripCount && Count < TripCount) {
759 // Reduce count based on the type of unrolling and the threshold values.
760 unsigned OriginalCount = Count;
761 bool AllowRuntime = UserRuntime ? CurrentRuntime : UP.Runtime;
762 if (Unrolling == Partial) {
763 bool AllowPartial = UserAllowPartial ? CurrentAllowPartial : UP.Partial;
764 if (!AllowPartial && !CountSetExplicitly) {
765 DEBUG(dbgs() << " will not try to unroll partially because "
766 << "-unroll-allow-partial not given\n");
769 if (PartialThreshold != NoThreshold && UnrolledSize > PartialThreshold) {
770 // Reduce unroll count to be modulo of TripCount for partial unrolling.
771 Count = (std::max(PartialThreshold, 3u)-2) / (LoopSize-2);
772 while (Count != 0 && TripCount % Count != 0)
775 } else if (Unrolling == Runtime) {
776 if (!AllowRuntime && !CountSetExplicitly) {
777 DEBUG(dbgs() << " will not try to unroll loop with runtime trip count "
778 << "-unroll-runtime not given\n");
781 // Reduce unroll count to be the largest power-of-two factor of
782 // the original count which satisfies the threshold limit.
783 while (Count != 0 && UnrolledSize > PartialThreshold) {
785 UnrolledSize = (LoopSize-2) * Count + 2;
787 if (Count > UP.MaxCount)
789 DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n");
793 if (PragmaCount != 0)
794 // If loop has an unroll count pragma mark loop as unrolled to prevent
795 // unrolling beyond that requested by the pragma.
796 SetLoopAlreadyUnrolled(L);
798 // Emit optimization remarks if we are unable to unroll the loop
799 // as directed by a pragma.
800 DebugLoc LoopLoc = L->getStartLoc();
801 Function *F = Header->getParent();
802 LLVMContext &Ctx = F->getContext();
803 if (PragmaFullUnroll && PragmaCount == 0) {
804 if (TripCount && Count != TripCount) {
805 emitOptimizationRemarkMissed(
806 Ctx, DEBUG_TYPE, *F, LoopLoc,
807 "Unable to fully unroll loop as directed by unroll(full) pragma "
808 "because unrolled size is too large.");
809 } else if (!TripCount) {
810 emitOptimizationRemarkMissed(
811 Ctx, DEBUG_TYPE, *F, LoopLoc,
812 "Unable to fully unroll loop as directed by unroll(full) pragma "
813 "because loop has a runtime trip count.");
815 } else if (PragmaCount > 0 && Count != OriginalCount) {
816 emitOptimizationRemarkMissed(
817 Ctx, DEBUG_TYPE, *F, LoopLoc,
818 "Unable to unroll loop the number of times directed by "
819 "unroll_count pragma because unrolled size is too large.");
823 if (Unrolling != Full && Count < 2) {
824 // Partial unrolling by 1 is a nop. For full unrolling, a factor
825 // of 1 makes sense because loop control can be eliminated.
830 if (!UnrollLoop(L, Count, TripCount, AllowRuntime, TripMultiple, LI, this,