1 //===-- LoopUtils.cpp - Loop Utility functions -------------------------===//
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 file defines common loop utility functions.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Analysis/LoopInfo.h"
15 #include "llvm/IR/Instructions.h"
16 #include "llvm/IR/PatternMatch.h"
17 #include "llvm/IR/ValueHandle.h"
18 #include "llvm/Support/Debug.h"
19 #include "llvm/Analysis/ScalarEvolution.h"
20 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
21 #include "llvm/IR/Module.h"
22 #include "llvm/Transforms/Utils/LoopUtils.h"
25 using namespace llvm::PatternMatch;
27 #define DEBUG_TYPE "loop-utils"
29 bool ReductionDescriptor::areAllUsesIn(Instruction *I,
30 SmallPtrSetImpl<Instruction *> &Set) {
31 for (User::op_iterator Use = I->op_begin(), E = I->op_end(); Use != E; ++Use)
32 if (!Set.count(dyn_cast<Instruction>(*Use)))
37 bool ReductionDescriptor::AddReductionVar(PHINode *Phi, ReductionKind Kind,
38 Loop *TheLoop, bool HasFunNoNaNAttr,
39 ReductionDescriptor &RedDes) {
40 if (Phi->getNumIncomingValues() != 2)
43 // Reduction variables are only found in the loop header block.
44 if (Phi->getParent() != TheLoop->getHeader())
47 // Obtain the reduction start value from the value that comes from the loop
49 Value *RdxStart = Phi->getIncomingValueForBlock(TheLoop->getLoopPreheader());
51 // ExitInstruction is the single value which is used outside the loop.
52 // We only allow for a single reduction value to be used outside the loop.
53 // This includes users of the reduction, variables (which form a cycle
54 // which ends in the phi node).
55 Instruction *ExitInstruction = nullptr;
56 // Indicates that we found a reduction operation in our scan.
57 bool FoundReduxOp = false;
59 // We start with the PHI node and scan for all of the users of this
60 // instruction. All users must be instructions that can be used as reduction
61 // variables (such as ADD). We must have a single out-of-block user. The cycle
62 // must include the original PHI.
63 bool FoundStartPHI = false;
65 // To recognize min/max patterns formed by a icmp select sequence, we store
66 // the number of instruction we saw from the recognized min/max pattern,
67 // to make sure we only see exactly the two instructions.
68 unsigned NumCmpSelectPatternInst = 0;
69 ReductionInstDesc ReduxDesc(false, nullptr);
71 SmallPtrSet<Instruction *, 8> VisitedInsts;
72 SmallVector<Instruction *, 8> Worklist;
73 Worklist.push_back(Phi);
74 VisitedInsts.insert(Phi);
76 // A value in the reduction can be used:
77 // - By the reduction:
78 // - Reduction operation:
79 // - One use of reduction value (safe).
80 // - Multiple use of reduction value (not safe).
82 // - All uses of the PHI must be the reduction (safe).
83 // - Otherwise, not safe.
84 // - By one instruction outside of the loop (safe).
85 // - By further instructions outside of the loop (not safe).
86 // - By an instruction that is not part of the reduction (not safe).
88 // * An instruction type other than PHI or the reduction operation.
89 // * A PHI in the header other than the initial PHI.
90 while (!Worklist.empty()) {
91 Instruction *Cur = Worklist.back();
95 // If the instruction has no users then this is a broken chain and can't be
96 // a reduction variable.
100 bool IsAPhi = isa<PHINode>(Cur);
102 // A header PHI use other than the original PHI.
103 if (Cur != Phi && IsAPhi && Cur->getParent() == Phi->getParent())
106 // Reductions of instructions such as Div, and Sub is only possible if the
107 // LHS is the reduction variable.
108 if (!Cur->isCommutative() && !IsAPhi && !isa<SelectInst>(Cur) &&
109 !isa<ICmpInst>(Cur) && !isa<FCmpInst>(Cur) &&
110 !VisitedInsts.count(dyn_cast<Instruction>(Cur->getOperand(0))))
113 // Any reduction instruction must be of one of the allowed kinds.
114 ReduxDesc = isReductionInstr(Cur, Kind, ReduxDesc, HasFunNoNaNAttr);
115 if (!ReduxDesc.isReduction())
118 // A reduction operation must only have one use of the reduction value.
119 if (!IsAPhi && Kind != RK_IntegerMinMax && Kind != RK_FloatMinMax &&
120 hasMultipleUsesOf(Cur, VisitedInsts))
123 // All inputs to a PHI node must be a reduction value.
124 if (IsAPhi && Cur != Phi && !areAllUsesIn(Cur, VisitedInsts))
127 if (Kind == RK_IntegerMinMax &&
128 (isa<ICmpInst>(Cur) || isa<SelectInst>(Cur)))
129 ++NumCmpSelectPatternInst;
130 if (Kind == RK_FloatMinMax && (isa<FCmpInst>(Cur) || isa<SelectInst>(Cur)))
131 ++NumCmpSelectPatternInst;
133 // Check whether we found a reduction operator.
134 FoundReduxOp |= !IsAPhi;
136 // Process users of current instruction. Push non-PHI nodes after PHI nodes
137 // onto the stack. This way we are going to have seen all inputs to PHI
138 // nodes once we get to them.
139 SmallVector<Instruction *, 8> NonPHIs;
140 SmallVector<Instruction *, 8> PHIs;
141 for (User *U : Cur->users()) {
142 Instruction *UI = cast<Instruction>(U);
144 // Check if we found the exit user.
145 BasicBlock *Parent = UI->getParent();
146 if (!TheLoop->contains(Parent)) {
147 // Exit if you find multiple outside users or if the header phi node is
148 // being used. In this case the user uses the value of the previous
149 // iteration, in which case we would loose "VF-1" iterations of the
150 // reduction operation if we vectorize.
151 if (ExitInstruction != nullptr || Cur == Phi)
154 // The instruction used by an outside user must be the last instruction
155 // before we feed back to the reduction phi. Otherwise, we loose VF-1
156 // operations on the value.
157 if (std::find(Phi->op_begin(), Phi->op_end(), Cur) == Phi->op_end())
160 ExitInstruction = Cur;
164 // Process instructions only once (termination). Each reduction cycle
165 // value must only be used once, except by phi nodes and min/max
166 // reductions which are represented as a cmp followed by a select.
167 ReductionInstDesc IgnoredVal(false, nullptr);
168 if (VisitedInsts.insert(UI).second) {
169 if (isa<PHINode>(UI))
172 NonPHIs.push_back(UI);
173 } else if (!isa<PHINode>(UI) &&
174 ((!isa<FCmpInst>(UI) && !isa<ICmpInst>(UI) &&
175 !isa<SelectInst>(UI)) ||
176 !isMinMaxSelectCmpPattern(UI, IgnoredVal).isReduction()))
179 // Remember that we completed the cycle.
181 FoundStartPHI = true;
183 Worklist.append(PHIs.begin(), PHIs.end());
184 Worklist.append(NonPHIs.begin(), NonPHIs.end());
187 // This means we have seen one but not the other instruction of the
188 // pattern or more than just a select and cmp.
189 if ((Kind == RK_IntegerMinMax || Kind == RK_FloatMinMax) &&
190 NumCmpSelectPatternInst != 2)
193 if (!FoundStartPHI || !FoundReduxOp || !ExitInstruction)
196 // We found a reduction var if we have reached the original phi node and we
197 // only have a single instruction with out-of-loop users.
199 // The ExitInstruction(Instruction which is allowed to have out-of-loop users)
200 // is saved as part of the ReductionDescriptor.
202 // Save the description of this reduction variable.
203 ReductionDescriptor RD(RdxStart, ExitInstruction, Kind,
204 ReduxDesc.getMinMaxKind());
211 /// Returns true if the instruction is a Select(ICmp(X, Y), X, Y) instruction
212 /// pattern corresponding to a min(X, Y) or max(X, Y).
214 ReductionDescriptor::isMinMaxSelectCmpPattern(Instruction *I,
215 ReductionInstDesc &Prev) {
217 assert((isa<ICmpInst>(I) || isa<FCmpInst>(I) || isa<SelectInst>(I)) &&
218 "Expect a select instruction");
219 Instruction *Cmp = nullptr;
220 SelectInst *Select = nullptr;
222 // We must handle the select(cmp()) as a single instruction. Advance to the
224 if ((Cmp = dyn_cast<ICmpInst>(I)) || (Cmp = dyn_cast<FCmpInst>(I))) {
225 if (!Cmp->hasOneUse() || !(Select = dyn_cast<SelectInst>(*I->user_begin())))
226 return ReductionInstDesc(false, I);
227 return ReductionInstDesc(Select, Prev.getMinMaxKind());
230 // Only handle single use cases for now.
231 if (!(Select = dyn_cast<SelectInst>(I)))
232 return ReductionInstDesc(false, I);
233 if (!(Cmp = dyn_cast<ICmpInst>(I->getOperand(0))) &&
234 !(Cmp = dyn_cast<FCmpInst>(I->getOperand(0))))
235 return ReductionInstDesc(false, I);
236 if (!Cmp->hasOneUse())
237 return ReductionInstDesc(false, I);
242 // Look for a min/max pattern.
243 if (m_UMin(m_Value(CmpLeft), m_Value(CmpRight)).match(Select))
244 return ReductionInstDesc(Select, ReductionInstDesc::MRK_UIntMin);
245 else if (m_UMax(m_Value(CmpLeft), m_Value(CmpRight)).match(Select))
246 return ReductionInstDesc(Select, ReductionInstDesc::MRK_UIntMax);
247 else if (m_SMax(m_Value(CmpLeft), m_Value(CmpRight)).match(Select))
248 return ReductionInstDesc(Select, ReductionInstDesc::MRK_SIntMax);
249 else if (m_SMin(m_Value(CmpLeft), m_Value(CmpRight)).match(Select))
250 return ReductionInstDesc(Select, ReductionInstDesc::MRK_SIntMin);
251 else if (m_OrdFMin(m_Value(CmpLeft), m_Value(CmpRight)).match(Select))
252 return ReductionInstDesc(Select, ReductionInstDesc::MRK_FloatMin);
253 else if (m_OrdFMax(m_Value(CmpLeft), m_Value(CmpRight)).match(Select))
254 return ReductionInstDesc(Select, ReductionInstDesc::MRK_FloatMax);
255 else if (m_UnordFMin(m_Value(CmpLeft), m_Value(CmpRight)).match(Select))
256 return ReductionInstDesc(Select, ReductionInstDesc::MRK_FloatMin);
257 else if (m_UnordFMax(m_Value(CmpLeft), m_Value(CmpRight)).match(Select))
258 return ReductionInstDesc(Select, ReductionInstDesc::MRK_FloatMax);
260 return ReductionInstDesc(false, I);
263 ReductionInstDesc ReductionDescriptor::isReductionInstr(Instruction *I,
265 ReductionInstDesc &Prev,
266 bool HasFunNoNaNAttr) {
267 bool FP = I->getType()->isFloatingPointTy();
268 bool FastMath = FP && I->hasUnsafeAlgebra();
269 switch (I->getOpcode()) {
271 return ReductionInstDesc(false, I);
272 case Instruction::PHI:
274 (Kind != RK_FloatMult && Kind != RK_FloatAdd && Kind != RK_FloatMinMax))
275 return ReductionInstDesc(false, I);
276 return ReductionInstDesc(I, Prev.getMinMaxKind());
277 case Instruction::Sub:
278 case Instruction::Add:
279 return ReductionInstDesc(Kind == RK_IntegerAdd, I);
280 case Instruction::Mul:
281 return ReductionInstDesc(Kind == RK_IntegerMult, I);
282 case Instruction::And:
283 return ReductionInstDesc(Kind == RK_IntegerAnd, I);
284 case Instruction::Or:
285 return ReductionInstDesc(Kind == RK_IntegerOr, I);
286 case Instruction::Xor:
287 return ReductionInstDesc(Kind == RK_IntegerXor, I);
288 case Instruction::FMul:
289 return ReductionInstDesc(Kind == RK_FloatMult && FastMath, I);
290 case Instruction::FSub:
291 case Instruction::FAdd:
292 return ReductionInstDesc(Kind == RK_FloatAdd && FastMath, I);
293 case Instruction::FCmp:
294 case Instruction::ICmp:
295 case Instruction::Select:
296 if (Kind != RK_IntegerMinMax &&
297 (!HasFunNoNaNAttr || Kind != RK_FloatMinMax))
298 return ReductionInstDesc(false, I);
299 return isMinMaxSelectCmpPattern(I, Prev);
303 bool ReductionDescriptor::hasMultipleUsesOf(
304 Instruction *I, SmallPtrSetImpl<Instruction *> &Insts) {
305 unsigned NumUses = 0;
306 for (User::op_iterator Use = I->op_begin(), E = I->op_end(); Use != E;
308 if (Insts.count(dyn_cast<Instruction>(*Use)))
316 bool ReductionDescriptor::isReductionPHI(PHINode *Phi, Loop *TheLoop,
317 ReductionDescriptor &RedDes) {
319 bool HasFunNoNaNAttr = false;
320 BasicBlock *Header = TheLoop->getHeader();
321 Function &F = *Header->getParent();
322 if (F.hasFnAttribute("no-nans-fp-math"))
324 F.getFnAttribute("no-nans-fp-math").getValueAsString() == "true";
326 if (AddReductionVar(Phi, RK_IntegerAdd, TheLoop, HasFunNoNaNAttr, RedDes)) {
327 DEBUG(dbgs() << "Found an ADD reduction PHI." << *Phi << "\n");
330 if (AddReductionVar(Phi, RK_IntegerMult, TheLoop, HasFunNoNaNAttr, RedDes)) {
331 DEBUG(dbgs() << "Found a MUL reduction PHI." << *Phi << "\n");
334 if (AddReductionVar(Phi, RK_IntegerOr, TheLoop, HasFunNoNaNAttr, RedDes)) {
335 DEBUG(dbgs() << "Found an OR reduction PHI." << *Phi << "\n");
338 if (AddReductionVar(Phi, RK_IntegerAnd, TheLoop, HasFunNoNaNAttr, RedDes)) {
339 DEBUG(dbgs() << "Found an AND reduction PHI." << *Phi << "\n");
342 if (AddReductionVar(Phi, RK_IntegerXor, TheLoop, HasFunNoNaNAttr, RedDes)) {
343 DEBUG(dbgs() << "Found a XOR reduction PHI." << *Phi << "\n");
346 if (AddReductionVar(Phi, RK_IntegerMinMax, TheLoop, HasFunNoNaNAttr,
348 DEBUG(dbgs() << "Found a MINMAX reduction PHI." << *Phi << "\n");
351 if (AddReductionVar(Phi, RK_FloatMult, TheLoop, HasFunNoNaNAttr, RedDes)) {
352 DEBUG(dbgs() << "Found an FMult reduction PHI." << *Phi << "\n");
355 if (AddReductionVar(Phi, RK_FloatAdd, TheLoop, HasFunNoNaNAttr, RedDes)) {
356 DEBUG(dbgs() << "Found an FAdd reduction PHI." << *Phi << "\n");
359 if (AddReductionVar(Phi, RK_FloatMinMax, TheLoop, HasFunNoNaNAttr, RedDes)) {
360 DEBUG(dbgs() << "Found an float MINMAX reduction PHI." << *Phi << "\n");
363 // Not a reduction of known type.
367 /// This function returns the identity element (or neutral element) for
369 Constant *ReductionDescriptor::getReductionIdentity(ReductionKind K, Type *Tp) {
374 // Adding, Xoring, Oring zero to a number does not change it.
375 return ConstantInt::get(Tp, 0);
377 // Multiplying a number by 1 does not change it.
378 return ConstantInt::get(Tp, 1);
380 // AND-ing a number with an all-1 value does not change it.
381 return ConstantInt::get(Tp, -1, true);
383 // Multiplying a number by 1 does not change it.
384 return ConstantFP::get(Tp, 1.0L);
386 // Adding zero to a number does not change it.
387 return ConstantFP::get(Tp, 0.0L);
389 llvm_unreachable("Unknown reduction kind");
393 /// This function translates the reduction kind to an LLVM binary operator.
394 unsigned ReductionDescriptor::getReductionBinOp(ReductionKind Kind) {
397 return Instruction::Add;
399 return Instruction::Mul;
401 return Instruction::Or;
403 return Instruction::And;
405 return Instruction::Xor;
407 return Instruction::FMul;
409 return Instruction::FAdd;
410 case RK_IntegerMinMax:
411 return Instruction::ICmp;
413 return Instruction::FCmp;
415 llvm_unreachable("Unknown reduction operation");
420 ReductionDescriptor::createMinMaxOp(IRBuilder<> &Builder,
421 ReductionInstDesc::MinMaxReductionKind RK,
422 Value *Left, Value *Right) {
423 CmpInst::Predicate P = CmpInst::ICMP_NE;
426 llvm_unreachable("Unknown min/max reduction kind");
427 case ReductionInstDesc::MRK_UIntMin:
428 P = CmpInst::ICMP_ULT;
430 case ReductionInstDesc::MRK_UIntMax:
431 P = CmpInst::ICMP_UGT;
433 case ReductionInstDesc::MRK_SIntMin:
434 P = CmpInst::ICMP_SLT;
436 case ReductionInstDesc::MRK_SIntMax:
437 P = CmpInst::ICMP_SGT;
439 case ReductionInstDesc::MRK_FloatMin:
440 P = CmpInst::FCMP_OLT;
442 case ReductionInstDesc::MRK_FloatMax:
443 P = CmpInst::FCMP_OGT;
448 if (RK == ReductionInstDesc::MRK_FloatMin ||
449 RK == ReductionInstDesc::MRK_FloatMax)
450 Cmp = Builder.CreateFCmp(P, Left, Right, "rdx.minmax.cmp");
452 Cmp = Builder.CreateICmp(P, Left, Right, "rdx.minmax.cmp");
454 Value *Select = Builder.CreateSelect(Cmp, Left, Right, "rdx.minmax.select");
458 bool llvm::isInductionPHI(PHINode *Phi, ScalarEvolution *SE,
459 ConstantInt *&StepValue) {
460 Type *PhiTy = Phi->getType();
461 // We only handle integer and pointer inductions variables.
462 if (!PhiTy->isIntegerTy() && !PhiTy->isPointerTy())
465 // Check that the PHI is consecutive.
466 const SCEV *PhiScev = SE->getSCEV(Phi);
467 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PhiScev);
469 DEBUG(dbgs() << "LV: PHI is not a poly recurrence.\n");
473 const SCEV *Step = AR->getStepRecurrence(*SE);
474 // Calculate the pointer stride and check if it is consecutive.
475 const SCEVConstant *C = dyn_cast<SCEVConstant>(Step);
479 ConstantInt *CV = C->getValue();
480 if (PhiTy->isIntegerTy()) {
485 assert(PhiTy->isPointerTy() && "The PHI must be a pointer");
486 Type *PointerElementType = PhiTy->getPointerElementType();
487 // The pointer stride cannot be determined if the pointer element type is not
489 if (!PointerElementType->isSized())
492 const DataLayout &DL = Phi->getModule()->getDataLayout();
493 int64_t Size = static_cast<int64_t>(DL.getTypeAllocSize(PointerElementType));
494 int64_t CVSize = CV->getSExtValue();
497 StepValue = ConstantInt::getSigned(CV->getType(), CVSize / Size);