1 //===- LoopStrengthReduce.cpp - Strength Reduce IVs in Loops --------------===//
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 transformation analyzes and transforms the induction variables (and
11 // computations derived from them) into forms suitable for efficient execution
14 // This pass performs a strength reduction on array references inside loops that
15 // have as one or more of their components the loop induction variable, it
16 // rewrites expressions to take advantage of scaled-index addressing modes
17 // available on the target, and it performs a variety of other optimizations
18 // related to loop induction variables.
20 // Terminology note: this code has a lot of handling for "post-increment" or
21 // "post-inc" users. This is not talking about post-increment addressing modes;
22 // it is instead talking about code like this:
24 // %i = phi [ 0, %entry ], [ %i.next, %latch ]
26 // %i.next = add %i, 1
27 // %c = icmp eq %i.next, %n
29 // The SCEV for %i is {0,+,1}<%L>. The SCEV for %i.next is {1,+,1}<%L>, however
30 // it's useful to think about these as the same register, with some uses using
31 // the value of the register before the add and some using // it after. In this
32 // example, the icmp is a post-increment user, since it uses %i.next, which is
33 // the value of the induction variable after the increment. The other common
34 // case of post-increment users is users outside the loop.
36 // TODO: More sophistication in the way Formulae are generated and filtered.
38 // TODO: Handle multiple loops at a time.
40 // TODO: Should TargetLowering::AddrMode::BaseGV be changed to a ConstantExpr
41 // instead of a GlobalValue?
43 // TODO: When truncation is free, truncate ICmp users' operands to make it a
44 // smaller encoding (on x86 at least).
46 // TODO: When a negated register is used by an add (such as in a list of
47 // multiple base registers, or as the increment expression in an addrec),
48 // we may not actually need both reg and (-1 * reg) in registers; the
49 // negation can be implemented by using a sub instead of an add. The
50 // lack of support for taking this into consideration when making
51 // register pressure decisions is partly worked around by the "Special"
54 //===----------------------------------------------------------------------===//
56 #define DEBUG_TYPE "loop-reduce"
57 #include "llvm/Transforms/Scalar.h"
58 #include "llvm/Constants.h"
59 #include "llvm/Instructions.h"
60 #include "llvm/IntrinsicInst.h"
61 #include "llvm/DerivedTypes.h"
62 #include "llvm/Analysis/IVUsers.h"
63 #include "llvm/Analysis/Dominators.h"
64 #include "llvm/Analysis/LoopPass.h"
65 #include "llvm/Analysis/ScalarEvolutionExpander.h"
66 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
67 #include "llvm/Transforms/Utils/Local.h"
68 #include "llvm/ADT/SmallBitVector.h"
69 #include "llvm/ADT/SetVector.h"
70 #include "llvm/ADT/DenseSet.h"
71 #include "llvm/Support/Debug.h"
72 #include "llvm/Support/ValueHandle.h"
73 #include "llvm/Support/raw_ostream.h"
74 #include "llvm/Target/TargetLowering.h"
80 /// RegSortData - This class holds data which is used to order reuse candidates.
83 /// UsedByIndices - This represents the set of LSRUse indices which reference
84 /// a particular register.
85 SmallBitVector UsedByIndices;
89 void print(raw_ostream &OS) const;
95 void RegSortData::print(raw_ostream &OS) const {
96 OS << "[NumUses=" << UsedByIndices.count() << ']';
99 void RegSortData::dump() const {
100 print(errs()); errs() << '\n';
105 /// RegUseTracker - Map register candidates to information about how they are
107 class RegUseTracker {
108 typedef DenseMap<const SCEV *, RegSortData> RegUsesTy;
111 SmallVector<const SCEV *, 16> RegSequence;
114 void CountRegister(const SCEV *Reg, size_t LUIdx);
116 bool isRegUsedByUsesOtherThan(const SCEV *Reg, size_t LUIdx) const;
118 const SmallBitVector &getUsedByIndices(const SCEV *Reg) const;
122 typedef SmallVectorImpl<const SCEV *>::iterator iterator;
123 typedef SmallVectorImpl<const SCEV *>::const_iterator const_iterator;
124 iterator begin() { return RegSequence.begin(); }
125 iterator end() { return RegSequence.end(); }
126 const_iterator begin() const { return RegSequence.begin(); }
127 const_iterator end() const { return RegSequence.end(); }
133 RegUseTracker::CountRegister(const SCEV *Reg, size_t LUIdx) {
134 std::pair<RegUsesTy::iterator, bool> Pair =
135 RegUses.insert(std::make_pair(Reg, RegSortData()));
136 RegSortData &RSD = Pair.first->second;
138 RegSequence.push_back(Reg);
139 RSD.UsedByIndices.resize(std::max(RSD.UsedByIndices.size(), LUIdx + 1));
140 RSD.UsedByIndices.set(LUIdx);
144 RegUseTracker::isRegUsedByUsesOtherThan(const SCEV *Reg, size_t LUIdx) const {
145 if (!RegUses.count(Reg)) return false;
146 const SmallBitVector &UsedByIndices =
147 RegUses.find(Reg)->second.UsedByIndices;
148 int i = UsedByIndices.find_first();
149 if (i == -1) return false;
150 if ((size_t)i != LUIdx) return true;
151 return UsedByIndices.find_next(i) != -1;
154 const SmallBitVector &RegUseTracker::getUsedByIndices(const SCEV *Reg) const {
155 RegUsesTy::const_iterator I = RegUses.find(Reg);
156 assert(I != RegUses.end() && "Unknown register!");
157 return I->second.UsedByIndices;
160 void RegUseTracker::clear() {
167 /// Formula - This class holds information that describes a formula for
168 /// computing satisfying a use. It may include broken-out immediates and scaled
171 /// AM - This is used to represent complex addressing, as well as other kinds
172 /// of interesting uses.
173 TargetLowering::AddrMode AM;
175 /// BaseRegs - The list of "base" registers for this use. When this is
176 /// non-empty, AM.HasBaseReg should be set to true.
177 SmallVector<const SCEV *, 2> BaseRegs;
179 /// ScaledReg - The 'scaled' register for this use. This should be non-null
180 /// when AM.Scale is not zero.
181 const SCEV *ScaledReg;
183 Formula() : ScaledReg(0) {}
185 void InitialMatch(const SCEV *S, Loop *L,
186 ScalarEvolution &SE, DominatorTree &DT);
188 unsigned getNumRegs() const;
189 const Type *getType() const;
191 bool referencesReg(const SCEV *S) const;
192 bool hasRegsUsedByUsesOtherThan(size_t LUIdx,
193 const RegUseTracker &RegUses) const;
195 void print(raw_ostream &OS) const;
201 /// DoInitialMatch - Recurrsion helper for InitialMatch.
202 static void DoInitialMatch(const SCEV *S, Loop *L,
203 SmallVectorImpl<const SCEV *> &Good,
204 SmallVectorImpl<const SCEV *> &Bad,
205 ScalarEvolution &SE, DominatorTree &DT) {
206 // Collect expressions which properly dominate the loop header.
207 if (S->properlyDominates(L->getHeader(), &DT)) {
212 // Look at add operands.
213 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
214 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
216 DoInitialMatch(*I, L, Good, Bad, SE, DT);
220 // Look at addrec operands.
221 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
222 if (!AR->getStart()->isZero()) {
223 DoInitialMatch(AR->getStart(), L, Good, Bad, SE, DT);
224 DoInitialMatch(SE.getAddRecExpr(SE.getIntegerSCEV(0, AR->getType()),
225 AR->getStepRecurrence(SE),
227 L, Good, Bad, SE, DT);
231 // Handle a multiplication by -1 (negation) if it didn't fold.
232 if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S))
233 if (Mul->getOperand(0)->isAllOnesValue()) {
234 SmallVector<const SCEV *, 4> Ops(Mul->op_begin()+1, Mul->op_end());
235 const SCEV *NewMul = SE.getMulExpr(Ops);
237 SmallVector<const SCEV *, 4> MyGood;
238 SmallVector<const SCEV *, 4> MyBad;
239 DoInitialMatch(NewMul, L, MyGood, MyBad, SE, DT);
240 const SCEV *NegOne = SE.getSCEV(ConstantInt::getAllOnesValue(
241 SE.getEffectiveSCEVType(NewMul->getType())));
242 for (SmallVectorImpl<const SCEV *>::const_iterator I = MyGood.begin(),
243 E = MyGood.end(); I != E; ++I)
244 Good.push_back(SE.getMulExpr(NegOne, *I));
245 for (SmallVectorImpl<const SCEV *>::const_iterator I = MyBad.begin(),
246 E = MyBad.end(); I != E; ++I)
247 Bad.push_back(SE.getMulExpr(NegOne, *I));
251 // Ok, we can't do anything interesting. Just stuff the whole thing into a
252 // register and hope for the best.
256 /// InitialMatch - Incorporate loop-variant parts of S into this Formula,
257 /// attempting to keep all loop-invariant and loop-computable values in a
258 /// single base register.
259 void Formula::InitialMatch(const SCEV *S, Loop *L,
260 ScalarEvolution &SE, DominatorTree &DT) {
261 SmallVector<const SCEV *, 4> Good;
262 SmallVector<const SCEV *, 4> Bad;
263 DoInitialMatch(S, L, Good, Bad, SE, DT);
265 BaseRegs.push_back(SE.getAddExpr(Good));
266 AM.HasBaseReg = true;
269 BaseRegs.push_back(SE.getAddExpr(Bad));
270 AM.HasBaseReg = true;
274 /// getNumRegs - Return the total number of register operands used by this
275 /// formula. This does not include register uses implied by non-constant
277 unsigned Formula::getNumRegs() const {
278 return !!ScaledReg + BaseRegs.size();
281 /// getType - Return the type of this formula, if it has one, or null
282 /// otherwise. This type is meaningless except for the bit size.
283 const Type *Formula::getType() const {
284 return !BaseRegs.empty() ? BaseRegs.front()->getType() :
285 ScaledReg ? ScaledReg->getType() :
286 AM.BaseGV ? AM.BaseGV->getType() :
290 /// referencesReg - Test if this formula references the given register.
291 bool Formula::referencesReg(const SCEV *S) const {
292 return S == ScaledReg ||
293 std::find(BaseRegs.begin(), BaseRegs.end(), S) != BaseRegs.end();
296 /// hasRegsUsedByUsesOtherThan - Test whether this formula uses registers
297 /// which are used by uses other than the use with the given index.
298 bool Formula::hasRegsUsedByUsesOtherThan(size_t LUIdx,
299 const RegUseTracker &RegUses) const {
301 if (RegUses.isRegUsedByUsesOtherThan(ScaledReg, LUIdx))
303 for (SmallVectorImpl<const SCEV *>::const_iterator I = BaseRegs.begin(),
304 E = BaseRegs.end(); I != E; ++I)
305 if (RegUses.isRegUsedByUsesOtherThan(*I, LUIdx))
310 void Formula::print(raw_ostream &OS) const {
313 if (!First) OS << " + "; else First = false;
314 WriteAsOperand(OS, AM.BaseGV, /*PrintType=*/false);
316 if (AM.BaseOffs != 0) {
317 if (!First) OS << " + "; else First = false;
320 for (SmallVectorImpl<const SCEV *>::const_iterator I = BaseRegs.begin(),
321 E = BaseRegs.end(); I != E; ++I) {
322 if (!First) OS << " + "; else First = false;
323 OS << "reg(" << **I << ')';
326 if (!First) OS << " + "; else First = false;
327 OS << AM.Scale << "*reg(";
336 void Formula::dump() const {
337 print(errs()); errs() << '\n';
340 /// getSDiv - Return an expression for LHS /s RHS, if it can be determined,
341 /// or null otherwise. If IgnoreSignificantBits is true, expressions like
342 /// (X * Y) /s Y are simplified to Y, ignoring that the multiplication may
343 /// overflow, which is useful when the result will be used in a context where
344 /// the most significant bits are ignored.
345 static const SCEV *getSDiv(const SCEV *LHS, const SCEV *RHS,
347 bool IgnoreSignificantBits = false) {
348 // Handle the trivial case, which works for any SCEV type.
350 return SE.getIntegerSCEV(1, LHS->getType());
352 // Handle x /s -1 as x * -1, to give ScalarEvolution a chance to do some
354 if (RHS->isAllOnesValue())
355 return SE.getMulExpr(LHS, RHS);
357 // Check for a division of a constant by a constant.
358 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(LHS)) {
359 const SCEVConstant *RC = dyn_cast<SCEVConstant>(RHS);
362 if (C->getValue()->getValue().srem(RC->getValue()->getValue()) != 0)
364 return SE.getConstant(C->getValue()->getValue()
365 .sdiv(RC->getValue()->getValue()));
368 // Distribute the sdiv over addrec operands.
369 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS)) {
370 const SCEV *Start = getSDiv(AR->getStart(), RHS, SE,
371 IgnoreSignificantBits);
372 if (!Start) return 0;
373 const SCEV *Step = getSDiv(AR->getStepRecurrence(SE), RHS, SE,
374 IgnoreSignificantBits);
376 return SE.getAddRecExpr(Start, Step, AR->getLoop());
379 // Distribute the sdiv over add operands.
380 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(LHS)) {
381 SmallVector<const SCEV *, 8> Ops;
382 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
384 const SCEV *Op = getSDiv(*I, RHS, SE,
385 IgnoreSignificantBits);
389 return SE.getAddExpr(Ops);
392 // Check for a multiply operand that we can pull RHS out of.
393 if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(LHS))
394 if (IgnoreSignificantBits || Mul->hasNoSignedWrap()) {
395 SmallVector<const SCEV *, 4> Ops;
397 for (SCEVMulExpr::op_iterator I = Mul->op_begin(), E = Mul->op_end();
400 if (const SCEV *Q = getSDiv(*I, RHS, SE, IgnoreSignificantBits)) {
407 return Found ? SE.getMulExpr(Ops) : 0;
410 // Otherwise we don't know.
414 /// ExtractImmediate - If S involves the addition of a constant integer value,
415 /// return that integer value, and mutate S to point to a new SCEV with that
417 static int64_t ExtractImmediate(const SCEV *&S, ScalarEvolution &SE) {
418 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S)) {
419 if (C->getValue()->getValue().getMinSignedBits() <= 64) {
420 S = SE.getIntegerSCEV(0, C->getType());
421 return C->getValue()->getSExtValue();
423 } else if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
424 SmallVector<const SCEV *, 8> NewOps(Add->op_begin(), Add->op_end());
425 int64_t Result = ExtractImmediate(NewOps.front(), SE);
426 S = SE.getAddExpr(NewOps);
428 } else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
429 SmallVector<const SCEV *, 8> NewOps(AR->op_begin(), AR->op_end());
430 int64_t Result = ExtractImmediate(NewOps.front(), SE);
431 S = SE.getAddRecExpr(NewOps, AR->getLoop());
437 /// ExtractSymbol - If S involves the addition of a GlobalValue address,
438 /// return that symbol, and mutate S to point to a new SCEV with that
440 static GlobalValue *ExtractSymbol(const SCEV *&S, ScalarEvolution &SE) {
441 if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
442 if (GlobalValue *GV = dyn_cast<GlobalValue>(U->getValue())) {
443 S = SE.getIntegerSCEV(0, GV->getType());
446 } else if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
447 SmallVector<const SCEV *, 8> NewOps(Add->op_begin(), Add->op_end());
448 GlobalValue *Result = ExtractSymbol(NewOps.back(), SE);
449 S = SE.getAddExpr(NewOps);
451 } else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
452 SmallVector<const SCEV *, 8> NewOps(AR->op_begin(), AR->op_end());
453 GlobalValue *Result = ExtractSymbol(NewOps.front(), SE);
454 S = SE.getAddRecExpr(NewOps, AR->getLoop());
460 /// isAddressUse - Returns true if the specified instruction is using the
461 /// specified value as an address.
462 static bool isAddressUse(Instruction *Inst, Value *OperandVal) {
463 bool isAddress = isa<LoadInst>(Inst);
464 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
465 if (SI->getOperand(1) == OperandVal)
467 } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
468 // Addressing modes can also be folded into prefetches and a variety
470 switch (II->getIntrinsicID()) {
472 case Intrinsic::prefetch:
473 case Intrinsic::x86_sse2_loadu_dq:
474 case Intrinsic::x86_sse2_loadu_pd:
475 case Intrinsic::x86_sse_loadu_ps:
476 case Intrinsic::x86_sse_storeu_ps:
477 case Intrinsic::x86_sse2_storeu_pd:
478 case Intrinsic::x86_sse2_storeu_dq:
479 case Intrinsic::x86_sse2_storel_dq:
480 if (II->getOperand(1) == OperandVal)
488 /// getAccessType - Return the type of the memory being accessed.
489 static const Type *getAccessType(const Instruction *Inst) {
490 const Type *AccessTy = Inst->getType();
491 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst))
492 AccessTy = SI->getOperand(0)->getType();
493 else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
494 // Addressing modes can also be folded into prefetches and a variety
496 switch (II->getIntrinsicID()) {
498 case Intrinsic::x86_sse_storeu_ps:
499 case Intrinsic::x86_sse2_storeu_pd:
500 case Intrinsic::x86_sse2_storeu_dq:
501 case Intrinsic::x86_sse2_storel_dq:
502 AccessTy = II->getOperand(1)->getType();
507 // All pointers have the same requirements, so canonicalize them to an
508 // arbitrary pointer type to minimize variation.
509 if (const PointerType *PTy = dyn_cast<PointerType>(AccessTy))
510 AccessTy = PointerType::get(IntegerType::get(PTy->getContext(), 1),
511 PTy->getAddressSpace());
516 /// DeleteTriviallyDeadInstructions - If any of the instructions is the
517 /// specified set are trivially dead, delete them and see if this makes any of
518 /// their operands subsequently dead.
520 DeleteTriviallyDeadInstructions(SmallVectorImpl<WeakVH> &DeadInsts) {
521 bool Changed = false;
523 while (!DeadInsts.empty()) {
524 Instruction *I = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val());
526 if (I == 0 || !isInstructionTriviallyDead(I))
529 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
530 if (Instruction *U = dyn_cast<Instruction>(*OI)) {
533 DeadInsts.push_back(U);
536 I->eraseFromParent();
545 /// Cost - This class is used to measure and compare candidate formulae.
547 /// TODO: Some of these could be merged. Also, a lexical ordering
548 /// isn't always optimal.
552 unsigned NumBaseAdds;
558 : NumRegs(0), AddRecCost(0), NumIVMuls(0), NumBaseAdds(0), ImmCost(0),
561 unsigned getNumRegs() const { return NumRegs; }
563 bool operator<(const Cost &Other) const;
567 void RateFormula(const Formula &F,
568 SmallPtrSet<const SCEV *, 16> &Regs,
569 const DenseSet<const SCEV *> &VisitedRegs,
571 const SmallVectorImpl<int64_t> &Offsets,
572 ScalarEvolution &SE, DominatorTree &DT);
574 void print(raw_ostream &OS) const;
578 void RateRegister(const SCEV *Reg,
579 SmallPtrSet<const SCEV *, 16> &Regs,
581 ScalarEvolution &SE, DominatorTree &DT);
582 void RatePrimaryRegister(const SCEV *Reg,
583 SmallPtrSet<const SCEV *, 16> &Regs,
585 ScalarEvolution &SE, DominatorTree &DT);
590 /// RateRegister - Tally up interesting quantities from the given register.
591 void Cost::RateRegister(const SCEV *Reg,
592 SmallPtrSet<const SCEV *, 16> &Regs,
594 ScalarEvolution &SE, DominatorTree &DT) {
595 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Reg)) {
596 if (AR->getLoop() == L)
597 AddRecCost += 1; /// TODO: This should be a function of the stride.
599 // If this is an addrec for a loop that's already been visited by LSR,
600 // don't second-guess its addrec phi nodes. LSR isn't currently smart
601 // enough to reason about more than one loop at a time. Consider these
602 // registers free and leave them alone.
603 else if (L->contains(AR->getLoop()) ||
604 (!AR->getLoop()->contains(L) &&
605 DT.dominates(L->getHeader(), AR->getLoop()->getHeader()))) {
606 for (BasicBlock::iterator I = AR->getLoop()->getHeader()->begin();
607 PHINode *PN = dyn_cast<PHINode>(I); ++I)
608 if (SE.isSCEVable(PN->getType()) &&
609 (SE.getEffectiveSCEVType(PN->getType()) ==
610 SE.getEffectiveSCEVType(AR->getType())) &&
611 SE.getSCEV(PN) == AR)
614 // If this isn't one of the addrecs that the loop already has, it
615 // would require a costly new phi and add. TODO: This isn't
616 // precisely modeled right now.
618 if (!Regs.count(AR->getStart()))
619 RateRegister(AR->getStart(), Regs, L, SE, DT);
622 // Add the step value register, if it needs one.
623 // TODO: The non-affine case isn't precisely modeled here.
624 if (!AR->isAffine() || !isa<SCEVConstant>(AR->getOperand(1)))
625 if (!Regs.count(AR->getStart()))
626 RateRegister(AR->getOperand(1), Regs, L, SE, DT);
630 // Rough heuristic; favor registers which don't require extra setup
631 // instructions in the preheader.
632 if (!isa<SCEVUnknown>(Reg) &&
633 !isa<SCEVConstant>(Reg) &&
634 !(isa<SCEVAddRecExpr>(Reg) &&
635 (isa<SCEVUnknown>(cast<SCEVAddRecExpr>(Reg)->getStart()) ||
636 isa<SCEVConstant>(cast<SCEVAddRecExpr>(Reg)->getStart()))))
640 /// RatePrimaryRegister - Record this register in the set. If we haven't seen it
642 void Cost::RatePrimaryRegister(const SCEV *Reg,
643 SmallPtrSet<const SCEV *, 16> &Regs,
645 ScalarEvolution &SE, DominatorTree &DT) {
646 if (Regs.insert(Reg))
647 RateRegister(Reg, Regs, L, SE, DT);
650 void Cost::RateFormula(const Formula &F,
651 SmallPtrSet<const SCEV *, 16> &Regs,
652 const DenseSet<const SCEV *> &VisitedRegs,
654 const SmallVectorImpl<int64_t> &Offsets,
655 ScalarEvolution &SE, DominatorTree &DT) {
656 // Tally up the registers.
657 if (const SCEV *ScaledReg = F.ScaledReg) {
658 if (VisitedRegs.count(ScaledReg)) {
662 RatePrimaryRegister(ScaledReg, Regs, L, SE, DT);
664 for (SmallVectorImpl<const SCEV *>::const_iterator I = F.BaseRegs.begin(),
665 E = F.BaseRegs.end(); I != E; ++I) {
666 const SCEV *BaseReg = *I;
667 if (VisitedRegs.count(BaseReg)) {
671 RatePrimaryRegister(BaseReg, Regs, L, SE, DT);
673 NumIVMuls += isa<SCEVMulExpr>(BaseReg) &&
674 BaseReg->hasComputableLoopEvolution(L);
677 if (F.BaseRegs.size() > 1)
678 NumBaseAdds += F.BaseRegs.size() - 1;
680 // Tally up the non-zero immediates.
681 for (SmallVectorImpl<int64_t>::const_iterator I = Offsets.begin(),
682 E = Offsets.end(); I != E; ++I) {
683 int64_t Offset = (uint64_t)*I + F.AM.BaseOffs;
685 ImmCost += 64; // Handle symbolic values conservatively.
686 // TODO: This should probably be the pointer size.
687 else if (Offset != 0)
688 ImmCost += APInt(64, Offset, true).getMinSignedBits();
692 /// Loose - Set this cost to a loosing value.
702 /// operator< - Choose the lower cost.
703 bool Cost::operator<(const Cost &Other) const {
704 if (NumRegs != Other.NumRegs)
705 return NumRegs < Other.NumRegs;
706 if (AddRecCost != Other.AddRecCost)
707 return AddRecCost < Other.AddRecCost;
708 if (NumIVMuls != Other.NumIVMuls)
709 return NumIVMuls < Other.NumIVMuls;
710 if (NumBaseAdds != Other.NumBaseAdds)
711 return NumBaseAdds < Other.NumBaseAdds;
712 if (ImmCost != Other.ImmCost)
713 return ImmCost < Other.ImmCost;
714 if (SetupCost != Other.SetupCost)
715 return SetupCost < Other.SetupCost;
719 void Cost::print(raw_ostream &OS) const {
720 OS << NumRegs << " reg" << (NumRegs == 1 ? "" : "s");
722 OS << ", with addrec cost " << AddRecCost;
724 OS << ", plus " << NumIVMuls << " IV mul" << (NumIVMuls == 1 ? "" : "s");
725 if (NumBaseAdds != 0)
726 OS << ", plus " << NumBaseAdds << " base add"
727 << (NumBaseAdds == 1 ? "" : "s");
729 OS << ", plus " << ImmCost << " imm cost";
731 OS << ", plus " << SetupCost << " setup cost";
734 void Cost::dump() const {
735 print(errs()); errs() << '\n';
740 /// LSRFixup - An operand value in an instruction which is to be replaced
741 /// with some equivalent, possibly strength-reduced, replacement.
743 /// UserInst - The instruction which will be updated.
744 Instruction *UserInst;
746 /// OperandValToReplace - The operand of the instruction which will
747 /// be replaced. The operand may be used more than once; every instance
748 /// will be replaced.
749 Value *OperandValToReplace;
751 /// PostIncLoop - If this user is to use the post-incremented value of an
752 /// induction variable, this variable is non-null and holds the loop
753 /// associated with the induction variable.
754 const Loop *PostIncLoop;
756 /// LUIdx - The index of the LSRUse describing the expression which
757 /// this fixup needs, minus an offset (below).
760 /// Offset - A constant offset to be added to the LSRUse expression.
761 /// This allows multiple fixups to share the same LSRUse with different
762 /// offsets, for example in an unrolled loop.
767 void print(raw_ostream &OS) const;
774 : UserInst(0), OperandValToReplace(0), PostIncLoop(0),
775 LUIdx(~size_t(0)), Offset(0) {}
777 void LSRFixup::print(raw_ostream &OS) const {
779 // Store is common and interesting enough to be worth special-casing.
780 if (StoreInst *Store = dyn_cast<StoreInst>(UserInst)) {
782 WriteAsOperand(OS, Store->getOperand(0), /*PrintType=*/false);
783 } else if (UserInst->getType()->isVoidTy())
784 OS << UserInst->getOpcodeName();
786 WriteAsOperand(OS, UserInst, /*PrintType=*/false);
788 OS << ", OperandValToReplace=";
789 WriteAsOperand(OS, OperandValToReplace, /*PrintType=*/false);
792 OS << ", PostIncLoop=";
793 WriteAsOperand(OS, PostIncLoop->getHeader(), /*PrintType=*/false);
796 if (LUIdx != ~size_t(0))
797 OS << ", LUIdx=" << LUIdx;
800 OS << ", Offset=" << Offset;
803 void LSRFixup::dump() const {
804 print(errs()); errs() << '\n';
809 /// UniquifierDenseMapInfo - A DenseMapInfo implementation for holding
810 /// DenseMaps and DenseSets of sorted SmallVectors of const SCEV*.
811 struct UniquifierDenseMapInfo {
812 static SmallVector<const SCEV *, 2> getEmptyKey() {
813 SmallVector<const SCEV *, 2> V;
814 V.push_back(reinterpret_cast<const SCEV *>(-1));
818 static SmallVector<const SCEV *, 2> getTombstoneKey() {
819 SmallVector<const SCEV *, 2> V;
820 V.push_back(reinterpret_cast<const SCEV *>(-2));
824 static unsigned getHashValue(const SmallVector<const SCEV *, 2> &V) {
826 for (SmallVectorImpl<const SCEV *>::const_iterator I = V.begin(),
827 E = V.end(); I != E; ++I)
828 Result ^= DenseMapInfo<const SCEV *>::getHashValue(*I);
832 static bool isEqual(const SmallVector<const SCEV *, 2> &LHS,
833 const SmallVector<const SCEV *, 2> &RHS) {
838 /// LSRUse - This class holds the state that LSR keeps for each use in
839 /// IVUsers, as well as uses invented by LSR itself. It includes information
840 /// about what kinds of things can be folded into the user, information about
841 /// the user itself, and information about how the use may be satisfied.
842 /// TODO: Represent multiple users of the same expression in common?
844 DenseSet<SmallVector<const SCEV *, 2>, UniquifierDenseMapInfo> Uniquifier;
847 /// KindType - An enum for a kind of use, indicating what types of
848 /// scaled and immediate operands it might support.
850 Basic, ///< A normal use, with no folding.
851 Special, ///< A special case of basic, allowing -1 scales.
852 Address, ///< An address use; folding according to TargetLowering
853 ICmpZero ///< An equality icmp with both operands folded into one.
854 // TODO: Add a generic icmp too?
858 const Type *AccessTy;
860 SmallVector<int64_t, 8> Offsets;
864 /// AllFixupsOutsideLoop - This records whether all of the fixups using this
865 /// LSRUse are outside of the loop, in which case some special-case heuristics
867 bool AllFixupsOutsideLoop;
869 /// Formulae - A list of ways to build a value that can satisfy this user.
870 /// After the list is populated, one of these is selected heuristically and
871 /// used to formulate a replacement for OperandValToReplace in UserInst.
872 SmallVector<Formula, 12> Formulae;
874 /// Regs - The set of register candidates used by all formulae in this LSRUse.
875 SmallPtrSet<const SCEV *, 4> Regs;
877 LSRUse(KindType K, const Type *T) : Kind(K), AccessTy(T),
878 MinOffset(INT64_MAX),
879 MaxOffset(INT64_MIN),
880 AllFixupsOutsideLoop(true) {}
882 bool InsertFormula(size_t LUIdx, const Formula &F);
886 void print(raw_ostream &OS) const;
890 /// InsertFormula - If the given formula has not yet been inserted, add it to
891 /// the list, and return true. Return false otherwise.
892 bool LSRUse::InsertFormula(size_t LUIdx, const Formula &F) {
893 SmallVector<const SCEV *, 2> Key = F.BaseRegs;
894 if (F.ScaledReg) Key.push_back(F.ScaledReg);
895 // Unstable sort by host order ok, because this is only used for uniquifying.
896 std::sort(Key.begin(), Key.end());
898 if (!Uniquifier.insert(Key).second)
901 // Using a register to hold the value of 0 is not profitable.
902 assert((!F.ScaledReg || !F.ScaledReg->isZero()) &&
903 "Zero allocated in a scaled register!");
905 for (SmallVectorImpl<const SCEV *>::const_iterator I =
906 F.BaseRegs.begin(), E = F.BaseRegs.end(); I != E; ++I)
907 assert(!(*I)->isZero() && "Zero allocated in a base register!");
910 // Add the formula to the list.
911 Formulae.push_back(F);
913 // Record registers now being used by this use.
914 if (F.ScaledReg) Regs.insert(F.ScaledReg);
915 Regs.insert(F.BaseRegs.begin(), F.BaseRegs.end());
920 void LSRUse::print(raw_ostream &OS) const {
921 OS << "LSR Use: Kind=";
923 case Basic: OS << "Basic"; break;
924 case Special: OS << "Special"; break;
925 case ICmpZero: OS << "ICmpZero"; break;
928 if (isa<PointerType>(AccessTy))
929 OS << "pointer"; // the full pointer type could be really verbose
935 for (SmallVectorImpl<int64_t>::const_iterator I = Offsets.begin(),
936 E = Offsets.end(); I != E; ++I) {
943 if (AllFixupsOutsideLoop)
944 OS << ", all-fixups-outside-loop";
947 void LSRUse::dump() const {
948 print(errs()); errs() << '\n';
951 /// isLegalUse - Test whether the use described by AM is "legal", meaning it can
952 /// be completely folded into the user instruction at isel time. This includes
953 /// address-mode folding and special icmp tricks.
954 static bool isLegalUse(const TargetLowering::AddrMode &AM,
955 LSRUse::KindType Kind, const Type *AccessTy,
956 const TargetLowering *TLI) {
958 case LSRUse::Address:
959 // If we have low-level target information, ask the target if it can
960 // completely fold this address.
961 if (TLI) return TLI->isLegalAddressingMode(AM, AccessTy);
963 // Otherwise, just guess that reg+reg addressing is legal.
964 return !AM.BaseGV && AM.BaseOffs == 0 && AM.Scale <= 1;
966 case LSRUse::ICmpZero:
967 // There's not even a target hook for querying whether it would be legal to
968 // fold a GV into an ICmp.
972 // ICmp only has two operands; don't allow more than two non-trivial parts.
973 if (AM.Scale != 0 && AM.HasBaseReg && AM.BaseOffs != 0)
976 // ICmp only supports no scale or a -1 scale, as we can "fold" a -1 scale by
977 // putting the scaled register in the other operand of the icmp.
978 if (AM.Scale != 0 && AM.Scale != -1)
981 // If we have low-level target information, ask the target if it can fold an
982 // integer immediate on an icmp.
983 if (AM.BaseOffs != 0) {
984 if (TLI) return TLI->isLegalICmpImmediate(-AM.BaseOffs);
991 // Only handle single-register values.
992 return !AM.BaseGV && AM.Scale == 0 && AM.BaseOffs == 0;
994 case LSRUse::Special:
995 // Only handle -1 scales, or no scale.
996 return AM.Scale == 0 || AM.Scale == -1;
1002 static bool isLegalUse(TargetLowering::AddrMode AM,
1003 int64_t MinOffset, int64_t MaxOffset,
1004 LSRUse::KindType Kind, const Type *AccessTy,
1005 const TargetLowering *TLI) {
1006 // Check for overflow.
1007 if (((int64_t)((uint64_t)AM.BaseOffs + MinOffset) > AM.BaseOffs) !=
1010 AM.BaseOffs = (uint64_t)AM.BaseOffs + MinOffset;
1011 if (isLegalUse(AM, Kind, AccessTy, TLI)) {
1012 AM.BaseOffs = (uint64_t)AM.BaseOffs - MinOffset;
1013 // Check for overflow.
1014 if (((int64_t)((uint64_t)AM.BaseOffs + MaxOffset) > AM.BaseOffs) !=
1017 AM.BaseOffs = (uint64_t)AM.BaseOffs + MaxOffset;
1018 return isLegalUse(AM, Kind, AccessTy, TLI);
1023 static bool isAlwaysFoldable(int64_t BaseOffs,
1024 GlobalValue *BaseGV,
1026 LSRUse::KindType Kind, const Type *AccessTy,
1027 const TargetLowering *TLI,
1028 ScalarEvolution &SE) {
1029 // Fast-path: zero is always foldable.
1030 if (BaseOffs == 0 && !BaseGV) return true;
1032 // Conservatively, create an address with an immediate and a
1033 // base and a scale.
1034 TargetLowering::AddrMode AM;
1035 AM.BaseOffs = BaseOffs;
1037 AM.HasBaseReg = HasBaseReg;
1038 AM.Scale = Kind == LSRUse::ICmpZero ? -1 : 1;
1040 return isLegalUse(AM, Kind, AccessTy, TLI);
1043 static bool isAlwaysFoldable(const SCEV *S,
1044 int64_t MinOffset, int64_t MaxOffset,
1046 LSRUse::KindType Kind, const Type *AccessTy,
1047 const TargetLowering *TLI,
1048 ScalarEvolution &SE) {
1049 // Fast-path: zero is always foldable.
1050 if (S->isZero()) return true;
1052 // Conservatively, create an address with an immediate and a
1053 // base and a scale.
1054 int64_t BaseOffs = ExtractImmediate(S, SE);
1055 GlobalValue *BaseGV = ExtractSymbol(S, SE);
1057 // If there's anything else involved, it's not foldable.
1058 if (!S->isZero()) return false;
1060 // Fast-path: zero is always foldable.
1061 if (BaseOffs == 0 && !BaseGV) return true;
1063 // Conservatively, create an address with an immediate and a
1064 // base and a scale.
1065 TargetLowering::AddrMode AM;
1066 AM.BaseOffs = BaseOffs;
1068 AM.HasBaseReg = HasBaseReg;
1069 AM.Scale = Kind == LSRUse::ICmpZero ? -1 : 1;
1071 return isLegalUse(AM, MinOffset, MaxOffset, Kind, AccessTy, TLI);
1074 /// FormulaSorter - This class implements an ordering for formulae which sorts
1075 /// the by their standalone cost.
1076 class FormulaSorter {
1077 /// These two sets are kept empty, so that we compute standalone costs.
1078 DenseSet<const SCEV *> VisitedRegs;
1079 SmallPtrSet<const SCEV *, 16> Regs;
1082 ScalarEvolution &SE;
1086 FormulaSorter(Loop *l, LSRUse &lu, ScalarEvolution &se, DominatorTree &dt)
1087 : L(l), LU(&lu), SE(se), DT(dt) {}
1089 bool operator()(const Formula &A, const Formula &B) {
1091 CostA.RateFormula(A, Regs, VisitedRegs, L, LU->Offsets, SE, DT);
1094 CostB.RateFormula(B, Regs, VisitedRegs, L, LU->Offsets, SE, DT);
1096 return CostA < CostB;
1100 /// LSRInstance - This class holds state for the main loop strength reduction
1104 ScalarEvolution &SE;
1106 const TargetLowering *const TLI;
1110 /// IVIncInsertPos - This is the insert position that the current loop's
1111 /// induction variable increment should be placed. In simple loops, this is
1112 /// the latch block's terminator. But in more complicated cases, this is a
1113 /// position which will dominate all the in-loop post-increment users.
1114 Instruction *IVIncInsertPos;
1116 /// Factors - Interesting factors between use strides.
1117 SmallSetVector<int64_t, 8> Factors;
1119 /// Types - Interesting use types, to facilitate truncation reuse.
1120 SmallSetVector<const Type *, 4> Types;
1122 /// Fixups - The list of operands which are to be replaced.
1123 SmallVector<LSRFixup, 16> Fixups;
1125 /// Uses - The list of interesting uses.
1126 SmallVector<LSRUse, 16> Uses;
1128 /// RegUses - Track which uses use which register candidates.
1129 RegUseTracker RegUses;
1131 void OptimizeShadowIV();
1132 bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse);
1133 ICmpInst *OptimizeMax(ICmpInst *Cond, IVStrideUse* &CondUse);
1134 bool OptimizeLoopTermCond();
1136 void CollectInterestingTypesAndFactors();
1137 void CollectFixupsAndInitialFormulae();
1139 LSRFixup &getNewFixup() {
1140 Fixups.push_back(LSRFixup());
1141 return Fixups.back();
1144 // Support for sharing of LSRUses between LSRFixups.
1145 typedef DenseMap<const SCEV *, size_t> UseMapTy;
1148 bool reconcileNewOffset(LSRUse &LU, int64_t NewOffset,
1149 LSRUse::KindType Kind, const Type *AccessTy);
1151 std::pair<size_t, int64_t> getUse(const SCEV *&Expr,
1152 LSRUse::KindType Kind,
1153 const Type *AccessTy);
1156 void InsertInitialFormula(const SCEV *S, Loop *L, LSRUse &LU, size_t LUIdx);
1157 void InsertSupplementalFormula(const SCEV *S, LSRUse &LU, size_t LUIdx);
1158 void CountRegisters(const Formula &F, size_t LUIdx);
1159 bool InsertFormula(LSRUse &LU, unsigned LUIdx, const Formula &F);
1161 void CollectLoopInvariantFixupsAndFormulae();
1163 void GenerateReassociations(LSRUse &LU, unsigned LUIdx, Formula Base,
1164 unsigned Depth = 0);
1165 void GenerateCombinations(LSRUse &LU, unsigned LUIdx, Formula Base);
1166 void GenerateSymbolicOffsets(LSRUse &LU, unsigned LUIdx, Formula Base);
1167 void GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx, Formula Base);
1168 void GenerateICmpZeroScales(LSRUse &LU, unsigned LUIdx, Formula Base);
1169 void GenerateScales(LSRUse &LU, unsigned LUIdx, Formula Base);
1170 void GenerateTruncates(LSRUse &LU, unsigned LUIdx, Formula Base);
1171 void GenerateCrossUseConstantOffsets();
1172 void GenerateAllReuseFormulae();
1174 void FilterOutUndesirableDedicatedRegisters();
1175 void NarrowSearchSpaceUsingHeuristics();
1177 void SolveRecurse(SmallVectorImpl<const Formula *> &Solution,
1179 SmallVectorImpl<const Formula *> &Workspace,
1180 const Cost &CurCost,
1181 const SmallPtrSet<const SCEV *, 16> &CurRegs,
1182 DenseSet<const SCEV *> &VisitedRegs) const;
1183 void Solve(SmallVectorImpl<const Formula *> &Solution) const;
1185 Value *Expand(const LSRFixup &LF,
1187 BasicBlock::iterator IP, Loop *L, Instruction *IVIncInsertPos,
1188 SCEVExpander &Rewriter,
1189 SmallVectorImpl<WeakVH> &DeadInsts,
1190 ScalarEvolution &SE, DominatorTree &DT) const;
1191 void Rewrite(const LSRFixup &LF,
1193 Loop *L, Instruction *IVIncInsertPos,
1194 SCEVExpander &Rewriter,
1195 SmallVectorImpl<WeakVH> &DeadInsts,
1196 ScalarEvolution &SE, DominatorTree &DT,
1198 void ImplementSolution(const SmallVectorImpl<const Formula *> &Solution,
1201 LSRInstance(const TargetLowering *tli, Loop *l, Pass *P);
1203 bool getChanged() const { return Changed; }
1205 void print_factors_and_types(raw_ostream &OS) const;
1206 void print_fixups(raw_ostream &OS) const;
1207 void print_uses(raw_ostream &OS) const;
1208 void print(raw_ostream &OS) const;
1214 /// OptimizeShadowIV - If IV is used in a int-to-float cast
1215 /// inside the loop then try to eliminate the cast opeation.
1216 void LSRInstance::OptimizeShadowIV() {
1217 const SCEV *BackedgeTakenCount = SE.getBackedgeTakenCount(L);
1218 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
1221 for (IVUsers::const_iterator UI = IU.begin(), E = IU.end();
1222 UI != E; /* empty */) {
1223 IVUsers::const_iterator CandidateUI = UI;
1225 Instruction *ShadowUse = CandidateUI->getUser();
1226 const Type *DestTy = NULL;
1228 /* If shadow use is a int->float cast then insert a second IV
1229 to eliminate this cast.
1231 for (unsigned i = 0; i < n; ++i)
1237 for (unsigned i = 0; i < n; ++i, ++d)
1240 if (UIToFPInst *UCast = dyn_cast<UIToFPInst>(CandidateUI->getUser()))
1241 DestTy = UCast->getDestTy();
1242 else if (SIToFPInst *SCast = dyn_cast<SIToFPInst>(CandidateUI->getUser()))
1243 DestTy = SCast->getDestTy();
1244 if (!DestTy) continue;
1247 // If target does not support DestTy natively then do not apply
1248 // this transformation.
1249 EVT DVT = TLI->getValueType(DestTy);
1250 if (!TLI->isTypeLegal(DVT)) continue;
1253 PHINode *PH = dyn_cast<PHINode>(ShadowUse->getOperand(0));
1255 if (PH->getNumIncomingValues() != 2) continue;
1257 const Type *SrcTy = PH->getType();
1258 int Mantissa = DestTy->getFPMantissaWidth();
1259 if (Mantissa == -1) continue;
1260 if ((int)SE.getTypeSizeInBits(SrcTy) > Mantissa)
1263 unsigned Entry, Latch;
1264 if (PH->getIncomingBlock(0) == L->getLoopPreheader()) {
1272 ConstantInt *Init = dyn_cast<ConstantInt>(PH->getIncomingValue(Entry));
1273 if (!Init) continue;
1274 Constant *NewInit = ConstantFP::get(DestTy, Init->getZExtValue());
1276 BinaryOperator *Incr =
1277 dyn_cast<BinaryOperator>(PH->getIncomingValue(Latch));
1278 if (!Incr) continue;
1279 if (Incr->getOpcode() != Instruction::Add
1280 && Incr->getOpcode() != Instruction::Sub)
1283 /* Initialize new IV, double d = 0.0 in above example. */
1284 ConstantInt *C = NULL;
1285 if (Incr->getOperand(0) == PH)
1286 C = dyn_cast<ConstantInt>(Incr->getOperand(1));
1287 else if (Incr->getOperand(1) == PH)
1288 C = dyn_cast<ConstantInt>(Incr->getOperand(0));
1294 // Ignore negative constants, as the code below doesn't handle them
1295 // correctly. TODO: Remove this restriction.
1296 if (!C->getValue().isStrictlyPositive()) continue;
1298 /* Add new PHINode. */
1299 PHINode *NewPH = PHINode::Create(DestTy, "IV.S.", PH);
1301 /* create new increment. '++d' in above example. */
1302 Constant *CFP = ConstantFP::get(DestTy, C->getZExtValue());
1303 BinaryOperator *NewIncr =
1304 BinaryOperator::Create(Incr->getOpcode() == Instruction::Add ?
1305 Instruction::FAdd : Instruction::FSub,
1306 NewPH, CFP, "IV.S.next.", Incr);
1308 NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry));
1309 NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch));
1311 /* Remove cast operation */
1312 ShadowUse->replaceAllUsesWith(NewPH);
1313 ShadowUse->eraseFromParent();
1318 /// FindIVUserForCond - If Cond has an operand that is an expression of an IV,
1319 /// set the IV user and stride information and return true, otherwise return
1321 bool LSRInstance::FindIVUserForCond(ICmpInst *Cond,
1322 IVStrideUse *&CondUse) {
1323 for (IVUsers::iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI)
1324 if (UI->getUser() == Cond) {
1325 // NOTE: we could handle setcc instructions with multiple uses here, but
1326 // InstCombine does it as well for simple uses, it's not clear that it
1327 // occurs enough in real life to handle.
1334 /// OptimizeMax - Rewrite the loop's terminating condition if it uses
1335 /// a max computation.
1337 /// This is a narrow solution to a specific, but acute, problem. For loops
1343 /// } while (++i < n);
1345 /// the trip count isn't just 'n', because 'n' might not be positive. And
1346 /// unfortunately this can come up even for loops where the user didn't use
1347 /// a C do-while loop. For example, seemingly well-behaved top-test loops
1348 /// will commonly be lowered like this:
1354 /// } while (++i < n);
1357 /// and then it's possible for subsequent optimization to obscure the if
1358 /// test in such a way that indvars can't find it.
1360 /// When indvars can't find the if test in loops like this, it creates a
1361 /// max expression, which allows it to give the loop a canonical
1362 /// induction variable:
1365 /// max = n < 1 ? 1 : n;
1368 /// } while (++i != max);
1370 /// Canonical induction variables are necessary because the loop passes
1371 /// are designed around them. The most obvious example of this is the
1372 /// LoopInfo analysis, which doesn't remember trip count values. It
1373 /// expects to be able to rediscover the trip count each time it is
1374 /// needed, and it does this using a simple analysis that only succeeds if
1375 /// the loop has a canonical induction variable.
1377 /// However, when it comes time to generate code, the maximum operation
1378 /// can be quite costly, especially if it's inside of an outer loop.
1380 /// This function solves this problem by detecting this type of loop and
1381 /// rewriting their conditions from ICMP_NE back to ICMP_SLT, and deleting
1382 /// the instructions for the maximum computation.
1384 ICmpInst *LSRInstance::OptimizeMax(ICmpInst *Cond, IVStrideUse* &CondUse) {
1385 // Check that the loop matches the pattern we're looking for.
1386 if (Cond->getPredicate() != CmpInst::ICMP_EQ &&
1387 Cond->getPredicate() != CmpInst::ICMP_NE)
1390 SelectInst *Sel = dyn_cast<SelectInst>(Cond->getOperand(1));
1391 if (!Sel || !Sel->hasOneUse()) return Cond;
1393 const SCEV *BackedgeTakenCount = SE.getBackedgeTakenCount(L);
1394 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
1396 const SCEV *One = SE.getIntegerSCEV(1, BackedgeTakenCount->getType());
1398 // Add one to the backedge-taken count to get the trip count.
1399 const SCEV *IterationCount = SE.getAddExpr(BackedgeTakenCount, One);
1401 // Check for a max calculation that matches the pattern.
1402 if (!isa<SCEVSMaxExpr>(IterationCount) && !isa<SCEVUMaxExpr>(IterationCount))
1404 const SCEVNAryExpr *Max = cast<SCEVNAryExpr>(IterationCount);
1405 if (Max != SE.getSCEV(Sel)) return Cond;
1407 // To handle a max with more than two operands, this optimization would
1408 // require additional checking and setup.
1409 if (Max->getNumOperands() != 2)
1412 const SCEV *MaxLHS = Max->getOperand(0);
1413 const SCEV *MaxRHS = Max->getOperand(1);
1414 if (!MaxLHS || MaxLHS != One) return Cond;
1415 // Check the relevant induction variable for conformance to
1417 const SCEV *IV = SE.getSCEV(Cond->getOperand(0));
1418 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
1419 if (!AR || !AR->isAffine() ||
1420 AR->getStart() != One ||
1421 AR->getStepRecurrence(SE) != One)
1424 assert(AR->getLoop() == L &&
1425 "Loop condition operand is an addrec in a different loop!");
1427 // Check the right operand of the select, and remember it, as it will
1428 // be used in the new comparison instruction.
1430 if (SE.getSCEV(Sel->getOperand(1)) == MaxRHS)
1431 NewRHS = Sel->getOperand(1);
1432 else if (SE.getSCEV(Sel->getOperand(2)) == MaxRHS)
1433 NewRHS = Sel->getOperand(2);
1434 if (!NewRHS) return Cond;
1436 // Determine the new comparison opcode. It may be signed or unsigned,
1437 // and the original comparison may be either equality or inequality.
1438 CmpInst::Predicate Pred =
1439 isa<SCEVSMaxExpr>(Max) ? CmpInst::ICMP_SLT : CmpInst::ICMP_ULT;
1440 if (Cond->getPredicate() == CmpInst::ICMP_EQ)
1441 Pred = CmpInst::getInversePredicate(Pred);
1443 // Ok, everything looks ok to change the condition into an SLT or SGE and
1444 // delete the max calculation.
1446 new ICmpInst(Cond, Pred, Cond->getOperand(0), NewRHS, "scmp");
1448 // Delete the max calculation instructions.
1449 Cond->replaceAllUsesWith(NewCond);
1450 CondUse->setUser(NewCond);
1451 Instruction *Cmp = cast<Instruction>(Sel->getOperand(0));
1452 Cond->eraseFromParent();
1453 Sel->eraseFromParent();
1454 if (Cmp->use_empty())
1455 Cmp->eraseFromParent();
1459 /// OptimizeLoopTermCond - Change loop terminating condition to use the
1460 /// postinc iv when possible.
1462 LSRInstance::OptimizeLoopTermCond() {
1463 SmallPtrSet<Instruction *, 4> PostIncs;
1465 BasicBlock *LatchBlock = L->getLoopLatch();
1466 SmallVector<BasicBlock*, 8> ExitingBlocks;
1467 L->getExitingBlocks(ExitingBlocks);
1469 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
1470 BasicBlock *ExitingBlock = ExitingBlocks[i];
1472 // Get the terminating condition for the loop if possible. If we
1473 // can, we want to change it to use a post-incremented version of its
1474 // induction variable, to allow coalescing the live ranges for the IV into
1475 // one register value.
1477 BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
1480 // FIXME: Overly conservative, termination condition could be an 'or' etc..
1481 if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition()))
1484 // Search IVUsesByStride to find Cond's IVUse if there is one.
1485 IVStrideUse *CondUse = 0;
1486 ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
1487 if (!FindIVUserForCond(Cond, CondUse))
1490 // If the trip count is computed in terms of a max (due to ScalarEvolution
1491 // being unable to find a sufficient guard, for example), change the loop
1492 // comparison to use SLT or ULT instead of NE.
1493 // One consequence of doing this now is that it disrupts the count-down
1494 // optimization. That's not always a bad thing though, because in such
1495 // cases it may still be worthwhile to avoid a max.
1496 Cond = OptimizeMax(Cond, CondUse);
1498 // If this exiting block dominates the latch block, it may also use
1499 // the post-inc value if it won't be shared with other uses.
1500 // Check for dominance.
1501 if (!DT.dominates(ExitingBlock, LatchBlock))
1504 // Conservatively avoid trying to use the post-inc value in non-latch
1505 // exits if there may be pre-inc users in intervening blocks.
1506 if (LatchBlock != ExitingBlock) {
1507 // Without target lowering, we won't be able to query about valid reuse.
1511 for (IVUsers::const_iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI)
1512 // Test if the use is reachable from the exiting block. This dominator
1513 // query is a conservative approximation of reachability.
1514 if (&*UI != CondUse &&
1515 !DT.properlyDominates(UI->getUser()->getParent(), ExitingBlock)) {
1516 // Conservatively assume there may be reuse if the quotient of their
1517 // strides could be a legal scale.
1518 const SCEV *A = CondUse->getStride();
1519 const SCEV *B = UI->getStride();
1520 if (SE.getTypeSizeInBits(A->getType()) !=
1521 SE.getTypeSizeInBits(B->getType())) {
1522 if (SE.getTypeSizeInBits(A->getType()) >
1523 SE.getTypeSizeInBits(B->getType()))
1524 B = SE.getSignExtendExpr(B, A->getType());
1526 A = SE.getSignExtendExpr(A, B->getType());
1528 if (const SCEVConstant *D =
1529 dyn_cast_or_null<SCEVConstant>(getSDiv(B, A, SE))) {
1530 // Stride of one or negative one can have reuse with non-addresses.
1531 if (D->getValue()->isOne() ||
1532 D->getValue()->isAllOnesValue())
1533 goto decline_post_inc;
1534 // Avoid weird situations.
1535 if (D->getValue()->getValue().getMinSignedBits() >= 64 ||
1536 D->getValue()->getValue().isMinSignedValue())
1537 goto decline_post_inc;
1538 // Check for possible scaled-address reuse.
1539 const Type *AccessTy = getAccessType(UI->getUser());
1540 TargetLowering::AddrMode AM;
1541 AM.Scale = D->getValue()->getSExtValue();
1542 if (TLI->isLegalAddressingMode(AM, AccessTy))
1543 goto decline_post_inc;
1544 AM.Scale = -AM.Scale;
1545 if (TLI->isLegalAddressingMode(AM, AccessTy))
1546 goto decline_post_inc;
1551 DEBUG(dbgs() << " Change loop exiting icmp to use postinc iv: "
1554 // It's possible for the setcc instruction to be anywhere in the loop, and
1555 // possible for it to have multiple users. If it is not immediately before
1556 // the exiting block branch, move it.
1557 if (&*++BasicBlock::iterator(Cond) != TermBr) {
1558 if (Cond->hasOneUse()) {
1559 Cond->moveBefore(TermBr);
1561 // Clone the terminating condition and insert into the loopend.
1562 ICmpInst *OldCond = Cond;
1563 Cond = cast<ICmpInst>(Cond->clone());
1564 Cond->setName(L->getHeader()->getName() + ".termcond");
1565 ExitingBlock->getInstList().insert(TermBr, Cond);
1567 // Clone the IVUse, as the old use still exists!
1568 CondUse = &IU.AddUser(CondUse->getStride(), CondUse->getOffset(),
1569 Cond, CondUse->getOperandValToReplace());
1570 TermBr->replaceUsesOfWith(OldCond, Cond);
1574 // If we get to here, we know that we can transform the setcc instruction to
1575 // use the post-incremented version of the IV, allowing us to coalesce the
1576 // live ranges for the IV correctly.
1577 CondUse->setOffset(SE.getMinusSCEV(CondUse->getOffset(),
1578 CondUse->getStride()));
1579 CondUse->setIsUseOfPostIncrementedValue(true);
1582 PostIncs.insert(Cond);
1586 // Determine an insertion point for the loop induction variable increment. It
1587 // must dominate all the post-inc comparisons we just set up, and it must
1588 // dominate the loop latch edge.
1589 IVIncInsertPos = L->getLoopLatch()->getTerminator();
1590 for (SmallPtrSet<Instruction *, 4>::const_iterator I = PostIncs.begin(),
1591 E = PostIncs.end(); I != E; ++I) {
1593 DT.findNearestCommonDominator(IVIncInsertPos->getParent(),
1595 if (BB == (*I)->getParent())
1596 IVIncInsertPos = *I;
1597 else if (BB != IVIncInsertPos->getParent())
1598 IVIncInsertPos = BB->getTerminator();
1605 LSRInstance::reconcileNewOffset(LSRUse &LU, int64_t NewOffset,
1606 LSRUse::KindType Kind, const Type *AccessTy) {
1607 int64_t NewMinOffset = LU.MinOffset;
1608 int64_t NewMaxOffset = LU.MaxOffset;
1609 const Type *NewAccessTy = AccessTy;
1611 // Check for a mismatched kind. It's tempting to collapse mismatched kinds to
1612 // something conservative, however this can pessimize in the case that one of
1613 // the uses will have all its uses outside the loop, for example.
1614 if (LU.Kind != Kind)
1616 // Conservatively assume HasBaseReg is true for now.
1617 if (NewOffset < LU.MinOffset) {
1618 if (!isAlwaysFoldable(LU.MaxOffset - NewOffset, 0, /*HasBaseReg=*/true,
1619 Kind, AccessTy, TLI, SE))
1621 NewMinOffset = NewOffset;
1622 } else if (NewOffset > LU.MaxOffset) {
1623 if (!isAlwaysFoldable(NewOffset - LU.MinOffset, 0, /*HasBaseReg=*/true,
1624 Kind, AccessTy, TLI, SE))
1626 NewMaxOffset = NewOffset;
1628 // Check for a mismatched access type, and fall back conservatively as needed.
1629 if (Kind == LSRUse::Address && AccessTy != LU.AccessTy)
1630 NewAccessTy = Type::getVoidTy(AccessTy->getContext());
1633 LU.MinOffset = NewMinOffset;
1634 LU.MaxOffset = NewMaxOffset;
1635 LU.AccessTy = NewAccessTy;
1636 if (NewOffset != LU.Offsets.back())
1637 LU.Offsets.push_back(NewOffset);
1641 /// getUse - Return an LSRUse index and an offset value for a fixup which
1642 /// needs the given expression, with the given kind and optional access type.
1643 /// Either reuse an exisitng use or create a new one, as needed.
1644 std::pair<size_t, int64_t>
1645 LSRInstance::getUse(const SCEV *&Expr,
1646 LSRUse::KindType Kind, const Type *AccessTy) {
1647 const SCEV *Copy = Expr;
1648 int64_t Offset = ExtractImmediate(Expr, SE);
1650 // Basic uses can't accept any offset, for example.
1651 if (!isAlwaysFoldable(Offset, 0, /*HasBaseReg=*/true,
1652 Kind, AccessTy, TLI, SE)) {
1657 std::pair<UseMapTy::iterator, bool> P =
1658 UseMap.insert(std::make_pair(Expr, 0));
1660 // A use already existed with this base.
1661 size_t LUIdx = P.first->second;
1662 LSRUse &LU = Uses[LUIdx];
1663 if (reconcileNewOffset(LU, Offset, Kind, AccessTy))
1665 return std::make_pair(LUIdx, Offset);
1668 // Create a new use.
1669 size_t LUIdx = Uses.size();
1670 P.first->second = LUIdx;
1671 Uses.push_back(LSRUse(Kind, AccessTy));
1672 LSRUse &LU = Uses[LUIdx];
1674 // We don't need to track redundant offsets, but we don't need to go out
1675 // of our way here to avoid them.
1676 if (LU.Offsets.empty() || Offset != LU.Offsets.back())
1677 LU.Offsets.push_back(Offset);
1679 LU.MinOffset = Offset;
1680 LU.MaxOffset = Offset;
1681 return std::make_pair(LUIdx, Offset);
1684 void LSRInstance::CollectInterestingTypesAndFactors() {
1685 SmallSetVector<const SCEV *, 4> Strides;
1687 // Collect interesting types and factors.
1688 for (IVUsers::const_iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI) {
1689 const SCEV *Stride = UI->getStride();
1691 // Collect interesting types.
1692 Types.insert(SE.getEffectiveSCEVType(Stride->getType()));
1694 // Collect interesting factors.
1695 for (SmallSetVector<const SCEV *, 4>::const_iterator NewStrideIter =
1696 Strides.begin(), SEnd = Strides.end(); NewStrideIter != SEnd;
1698 const SCEV *OldStride = Stride;
1699 const SCEV *NewStride = *NewStrideIter;
1700 if (OldStride == NewStride)
1703 if (SE.getTypeSizeInBits(OldStride->getType()) !=
1704 SE.getTypeSizeInBits(NewStride->getType())) {
1705 if (SE.getTypeSizeInBits(OldStride->getType()) >
1706 SE.getTypeSizeInBits(NewStride->getType()))
1707 NewStride = SE.getSignExtendExpr(NewStride, OldStride->getType());
1709 OldStride = SE.getSignExtendExpr(OldStride, NewStride->getType());
1711 if (const SCEVConstant *Factor =
1712 dyn_cast_or_null<SCEVConstant>(getSDiv(NewStride, OldStride,
1714 if (Factor->getValue()->getValue().getMinSignedBits() <= 64)
1715 Factors.insert(Factor->getValue()->getValue().getSExtValue());
1716 } else if (const SCEVConstant *Factor =
1717 dyn_cast_or_null<SCEVConstant>(getSDiv(OldStride, NewStride,
1719 if (Factor->getValue()->getValue().getMinSignedBits() <= 64)
1720 Factors.insert(Factor->getValue()->getValue().getSExtValue());
1723 Strides.insert(Stride);
1726 // If all uses use the same type, don't bother looking for truncation-based
1728 if (Types.size() == 1)
1731 DEBUG(print_factors_and_types(dbgs()));
1734 void LSRInstance::CollectFixupsAndInitialFormulae() {
1735 for (IVUsers::const_iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI) {
1737 LSRFixup &LF = getNewFixup();
1738 LF.UserInst = UI->getUser();
1739 LF.OperandValToReplace = UI->getOperandValToReplace();
1740 if (UI->isUseOfPostIncrementedValue())
1743 LSRUse::KindType Kind = LSRUse::Basic;
1744 const Type *AccessTy = 0;
1745 if (isAddressUse(LF.UserInst, LF.OperandValToReplace)) {
1746 Kind = LSRUse::Address;
1747 AccessTy = getAccessType(LF.UserInst);
1750 const SCEV *S = IU.getCanonicalExpr(*UI);
1752 // Equality (== and !=) ICmps are special. We can rewrite (i == N) as
1753 // (N - i == 0), and this allows (N - i) to be the expression that we work
1754 // with rather than just N or i, so we can consider the register
1755 // requirements for both N and i at the same time. Limiting this code to
1756 // equality icmps is not a problem because all interesting loops use
1757 // equality icmps, thanks to IndVarSimplify.
1758 if (ICmpInst *CI = dyn_cast<ICmpInst>(LF.UserInst))
1759 if (CI->isEquality()) {
1760 // Swap the operands if needed to put the OperandValToReplace on the
1761 // left, for consistency.
1762 Value *NV = CI->getOperand(1);
1763 if (NV == LF.OperandValToReplace) {
1764 CI->setOperand(1, CI->getOperand(0));
1765 CI->setOperand(0, NV);
1768 // x == y --> x - y == 0
1769 const SCEV *N = SE.getSCEV(NV);
1770 if (N->isLoopInvariant(L)) {
1771 Kind = LSRUse::ICmpZero;
1772 S = SE.getMinusSCEV(N, S);
1775 // -1 and the negations of all interesting strides (except the negation
1776 // of -1) are now also interesting.
1777 for (size_t i = 0, e = Factors.size(); i != e; ++i)
1778 if (Factors[i] != -1)
1779 Factors.insert(-(uint64_t)Factors[i]);
1783 // Set up the initial formula for this use.
1784 std::pair<size_t, int64_t> P = getUse(S, Kind, AccessTy);
1786 LF.Offset = P.second;
1787 LSRUse &LU = Uses[LF.LUIdx];
1788 LU.AllFixupsOutsideLoop &= !L->contains(LF.UserInst);
1790 // If this is the first use of this LSRUse, give it a formula.
1791 if (LU.Formulae.empty()) {
1792 InsertInitialFormula(S, L, LU, LF.LUIdx);
1793 CountRegisters(LU.Formulae.back(), LF.LUIdx);
1797 DEBUG(print_fixups(dbgs()));
1801 LSRInstance::InsertInitialFormula(const SCEV *S, Loop *L,
1802 LSRUse &LU, size_t LUIdx) {
1804 F.InitialMatch(S, L, SE, DT);
1805 bool Inserted = InsertFormula(LU, LUIdx, F);
1806 assert(Inserted && "Initial formula already exists!"); (void)Inserted;
1810 LSRInstance::InsertSupplementalFormula(const SCEV *S,
1811 LSRUse &LU, size_t LUIdx) {
1813 F.BaseRegs.push_back(S);
1814 F.AM.HasBaseReg = true;
1815 bool Inserted = InsertFormula(LU, LUIdx, F);
1816 assert(Inserted && "Supplemental formula already exists!"); (void)Inserted;
1819 /// CountRegisters - Note which registers are used by the given formula,
1820 /// updating RegUses.
1821 void LSRInstance::CountRegisters(const Formula &F, size_t LUIdx) {
1823 RegUses.CountRegister(F.ScaledReg, LUIdx);
1824 for (SmallVectorImpl<const SCEV *>::const_iterator I = F.BaseRegs.begin(),
1825 E = F.BaseRegs.end(); I != E; ++I)
1826 RegUses.CountRegister(*I, LUIdx);
1829 /// InsertFormula - If the given formula has not yet been inserted, add it to
1830 /// the list, and return true. Return false otherwise.
1831 bool LSRInstance::InsertFormula(LSRUse &LU, unsigned LUIdx, const Formula &F) {
1832 if (!LU.InsertFormula(LUIdx, F))
1835 CountRegisters(F, LUIdx);
1839 /// CollectLoopInvariantFixupsAndFormulae - Check for other uses of
1840 /// loop-invariant values which we're tracking. These other uses will pin these
1841 /// values in registers, making them less profitable for elimination.
1842 /// TODO: This currently misses non-constant addrec step registers.
1843 /// TODO: Should this give more weight to users inside the loop?
1845 LSRInstance::CollectLoopInvariantFixupsAndFormulae() {
1846 SmallVector<const SCEV *, 8> Worklist(RegUses.begin(), RegUses.end());
1847 SmallPtrSet<const SCEV *, 8> Inserted;
1849 while (!Worklist.empty()) {
1850 const SCEV *S = Worklist.pop_back_val();
1852 if (const SCEVNAryExpr *N = dyn_cast<SCEVNAryExpr>(S))
1853 Worklist.insert(Worklist.end(), N->op_begin(), N->op_end());
1854 else if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))
1855 Worklist.push_back(C->getOperand());
1856 else if (const SCEVUDivExpr *D = dyn_cast<SCEVUDivExpr>(S)) {
1857 Worklist.push_back(D->getLHS());
1858 Worklist.push_back(D->getRHS());
1859 } else if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
1860 if (!Inserted.insert(U)) continue;
1861 const Value *V = U->getValue();
1862 if (const Instruction *Inst = dyn_cast<Instruction>(V))
1863 if (L->contains(Inst)) continue;
1864 for (Value::use_const_iterator UI = V->use_begin(), UE = V->use_end();
1866 const Instruction *UserInst = dyn_cast<Instruction>(*UI);
1867 // Ignore non-instructions.
1870 // Ignore instructions in other functions (as can happen with
1872 if (UserInst->getParent()->getParent() != L->getHeader()->getParent())
1874 // Ignore instructions not dominated by the loop.
1875 const BasicBlock *UseBB = !isa<PHINode>(UserInst) ?
1876 UserInst->getParent() :
1877 cast<PHINode>(UserInst)->getIncomingBlock(
1878 PHINode::getIncomingValueNumForOperand(UI.getOperandNo()));
1879 if (!DT.dominates(L->getHeader(), UseBB))
1881 // Ignore uses which are part of other SCEV expressions, to avoid
1882 // analyzing them multiple times.
1883 if (SE.isSCEVable(UserInst->getType()) &&
1884 !isa<SCEVUnknown>(SE.getSCEV(const_cast<Instruction *>(UserInst))))
1886 // Ignore icmp instructions which are already being analyzed.
1887 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UserInst)) {
1888 unsigned OtherIdx = !UI.getOperandNo();
1889 Value *OtherOp = const_cast<Value *>(ICI->getOperand(OtherIdx));
1890 if (SE.getSCEV(OtherOp)->hasComputableLoopEvolution(L))
1894 LSRFixup &LF = getNewFixup();
1895 LF.UserInst = const_cast<Instruction *>(UserInst);
1896 LF.OperandValToReplace = UI.getUse();
1897 std::pair<size_t, int64_t> P = getUse(S, LSRUse::Basic, 0);
1899 LF.Offset = P.second;
1900 LSRUse &LU = Uses[LF.LUIdx];
1901 LU.AllFixupsOutsideLoop &= L->contains(LF.UserInst);
1902 InsertSupplementalFormula(U, LU, LF.LUIdx);
1903 CountRegisters(LU.Formulae.back(), Uses.size() - 1);
1910 /// CollectSubexprs - Split S into subexpressions which can be pulled out into
1911 /// separate registers. If C is non-null, multiply each subexpression by C.
1912 static void CollectSubexprs(const SCEV *S, const SCEVConstant *C,
1913 SmallVectorImpl<const SCEV *> &Ops,
1914 ScalarEvolution &SE) {
1915 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
1916 // Break out add operands.
1917 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
1919 CollectSubexprs(*I, C, Ops, SE);
1921 } else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
1922 // Split a non-zero base out of an addrec.
1923 if (!AR->getStart()->isZero()) {
1924 CollectSubexprs(SE.getAddRecExpr(SE.getIntegerSCEV(0, AR->getType()),
1925 AR->getStepRecurrence(SE),
1926 AR->getLoop()), C, Ops, SE);
1927 CollectSubexprs(AR->getStart(), C, Ops, SE);
1930 } else if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) {
1931 // Break (C * (a + b + c)) into C*a + C*b + C*c.
1932 if (Mul->getNumOperands() == 2)
1933 if (const SCEVConstant *Op0 =
1934 dyn_cast<SCEVConstant>(Mul->getOperand(0))) {
1935 CollectSubexprs(Mul->getOperand(1),
1936 C ? cast<SCEVConstant>(SE.getMulExpr(C, Op0)) : Op0,
1942 // Otherwise use the value itself.
1943 Ops.push_back(C ? SE.getMulExpr(C, S) : S);
1946 /// GenerateReassociations - Split out subexpressions from adds and the bases of
1948 void LSRInstance::GenerateReassociations(LSRUse &LU, unsigned LUIdx,
1951 // Arbitrarily cap recursion to protect compile time.
1952 if (Depth >= 3) return;
1954 for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i) {
1955 const SCEV *BaseReg = Base.BaseRegs[i];
1957 SmallVector<const SCEV *, 8> AddOps;
1958 CollectSubexprs(BaseReg, 0, AddOps, SE);
1959 if (AddOps.size() == 1) continue;
1961 for (SmallVectorImpl<const SCEV *>::const_iterator J = AddOps.begin(),
1962 JE = AddOps.end(); J != JE; ++J) {
1963 // Don't pull a constant into a register if the constant could be folded
1964 // into an immediate field.
1965 if (isAlwaysFoldable(*J, LU.MinOffset, LU.MaxOffset,
1966 Base.getNumRegs() > 1,
1967 LU.Kind, LU.AccessTy, TLI, SE))
1970 // Collect all operands except *J.
1971 SmallVector<const SCEV *, 8> InnerAddOps;
1972 for (SmallVectorImpl<const SCEV *>::const_iterator K = AddOps.begin(),
1973 KE = AddOps.end(); K != KE; ++K)
1975 InnerAddOps.push_back(*K);
1977 // Don't leave just a constant behind in a register if the constant could
1978 // be folded into an immediate field.
1979 if (InnerAddOps.size() == 1 &&
1980 isAlwaysFoldable(InnerAddOps[0], LU.MinOffset, LU.MaxOffset,
1981 Base.getNumRegs() > 1,
1982 LU.Kind, LU.AccessTy, TLI, SE))
1986 F.BaseRegs[i] = SE.getAddExpr(InnerAddOps);
1987 F.BaseRegs.push_back(*J);
1988 if (InsertFormula(LU, LUIdx, F))
1989 // If that formula hadn't been seen before, recurse to find more like
1991 GenerateReassociations(LU, LUIdx, LU.Formulae.back(), Depth+1);
1996 /// GenerateCombinations - Generate a formula consisting of all of the
1997 /// loop-dominating registers added into a single register.
1998 void LSRInstance::GenerateCombinations(LSRUse &LU, unsigned LUIdx,
2000 // This method is only intersting on a plurality of registers.
2001 if (Base.BaseRegs.size() <= 1) return;
2005 SmallVector<const SCEV *, 4> Ops;
2006 for (SmallVectorImpl<const SCEV *>::const_iterator
2007 I = Base.BaseRegs.begin(), E = Base.BaseRegs.end(); I != E; ++I) {
2008 const SCEV *BaseReg = *I;
2009 if (BaseReg->properlyDominates(L->getHeader(), &DT) &&
2010 !BaseReg->hasComputableLoopEvolution(L))
2011 Ops.push_back(BaseReg);
2013 F.BaseRegs.push_back(BaseReg);
2015 if (Ops.size() > 1) {
2016 F.BaseRegs.push_back(SE.getAddExpr(Ops));
2017 (void)InsertFormula(LU, LUIdx, F);
2021 /// GenerateSymbolicOffsets - Generate reuse formulae using symbolic offsets.
2022 void LSRInstance::GenerateSymbolicOffsets(LSRUse &LU, unsigned LUIdx,
2024 // We can't add a symbolic offset if the address already contains one.
2025 if (Base.AM.BaseGV) return;
2027 for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i) {
2028 const SCEV *G = Base.BaseRegs[i];
2029 GlobalValue *GV = ExtractSymbol(G, SE);
2030 if (G->isZero() || !GV)
2034 if (!isLegalUse(F.AM, LU.MinOffset, LU.MaxOffset,
2035 LU.Kind, LU.AccessTy, TLI))
2038 (void)InsertFormula(LU, LUIdx, F);
2042 /// GenerateConstantOffsets - Generate reuse formulae using symbolic offsets.
2043 void LSRInstance::GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx,
2045 // TODO: For now, just add the min and max offset, because it usually isn't
2046 // worthwhile looking at everything inbetween.
2047 SmallVector<int64_t, 4> Worklist;
2048 Worklist.push_back(LU.MinOffset);
2049 if (LU.MaxOffset != LU.MinOffset)
2050 Worklist.push_back(LU.MaxOffset);
2052 for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i) {
2053 const SCEV *G = Base.BaseRegs[i];
2055 for (SmallVectorImpl<int64_t>::const_iterator I = Worklist.begin(),
2056 E = Worklist.end(); I != E; ++I) {
2058 F.AM.BaseOffs = (uint64_t)Base.AM.BaseOffs - *I;
2059 if (isLegalUse(F.AM, LU.MinOffset - *I, LU.MaxOffset - *I,
2060 LU.Kind, LU.AccessTy, TLI)) {
2061 F.BaseRegs[i] = SE.getAddExpr(G, SE.getIntegerSCEV(*I, G->getType()));
2063 (void)InsertFormula(LU, LUIdx, F);
2067 int64_t Imm = ExtractImmediate(G, SE);
2068 if (G->isZero() || Imm == 0)
2071 F.AM.BaseOffs = (uint64_t)F.AM.BaseOffs + Imm;
2072 if (!isLegalUse(F.AM, LU.MinOffset, LU.MaxOffset,
2073 LU.Kind, LU.AccessTy, TLI))
2076 (void)InsertFormula(LU, LUIdx, F);
2080 /// GenerateICmpZeroScales - For ICmpZero, check to see if we can scale up
2081 /// the comparison. For example, x == y -> x*c == y*c.
2082 void LSRInstance::GenerateICmpZeroScales(LSRUse &LU, unsigned LUIdx,
2084 if (LU.Kind != LSRUse::ICmpZero) return;
2086 // Determine the integer type for the base formula.
2087 const Type *IntTy = Base.getType();
2089 if (SE.getTypeSizeInBits(IntTy) > 64) return;
2091 // Don't do this if there is more than one offset.
2092 if (LU.MinOffset != LU.MaxOffset) return;
2094 assert(!Base.AM.BaseGV && "ICmpZero use is not legal!");
2096 // Check each interesting stride.
2097 for (SmallSetVector<int64_t, 8>::const_iterator
2098 I = Factors.begin(), E = Factors.end(); I != E; ++I) {
2099 int64_t Factor = *I;
2102 // Check that the multiplication doesn't overflow.
2103 F.AM.BaseOffs = (uint64_t)Base.AM.BaseOffs * Factor;
2104 if ((int64_t)F.AM.BaseOffs / Factor != Base.AM.BaseOffs)
2107 // Check that multiplying with the use offset doesn't overflow.
2108 int64_t Offset = LU.MinOffset;
2109 Offset = (uint64_t)Offset * Factor;
2110 if ((int64_t)Offset / Factor != LU.MinOffset)
2113 // Check that this scale is legal.
2114 if (!isLegalUse(F.AM, Offset, Offset, LU.Kind, LU.AccessTy, TLI))
2117 // Compensate for the use having MinOffset built into it.
2118 F.AM.BaseOffs = (uint64_t)F.AM.BaseOffs + Offset - LU.MinOffset;
2120 const SCEV *FactorS = SE.getIntegerSCEV(Factor, IntTy);
2122 // Check that multiplying with each base register doesn't overflow.
2123 for (size_t i = 0, e = F.BaseRegs.size(); i != e; ++i) {
2124 F.BaseRegs[i] = SE.getMulExpr(F.BaseRegs[i], FactorS);
2125 if (getSDiv(F.BaseRegs[i], FactorS, SE) != Base.BaseRegs[i])
2129 // Check that multiplying with the scaled register doesn't overflow.
2131 F.ScaledReg = SE.getMulExpr(F.ScaledReg, FactorS);
2132 if (getSDiv(F.ScaledReg, FactorS, SE) != Base.ScaledReg)
2136 // If we make it here and it's legal, add it.
2137 (void)InsertFormula(LU, LUIdx, F);
2142 /// GenerateScales - Generate stride factor reuse formulae by making use of
2143 /// scaled-offset address modes, for example.
2144 void LSRInstance::GenerateScales(LSRUse &LU, unsigned LUIdx,
2146 // Determine the integer type for the base formula.
2147 const Type *IntTy = Base.getType();
2150 // If this Formula already has a scaled register, we can't add another one.
2151 if (Base.AM.Scale != 0) return;
2153 // Check each interesting stride.
2154 for (SmallSetVector<int64_t, 8>::const_iterator
2155 I = Factors.begin(), E = Factors.end(); I != E; ++I) {
2156 int64_t Factor = *I;
2158 Base.AM.Scale = Factor;
2159 Base.AM.HasBaseReg = Base.BaseRegs.size() > 1;
2160 // Check whether this scale is going to be legal.
2161 if (!isLegalUse(Base.AM, LU.MinOffset, LU.MaxOffset,
2162 LU.Kind, LU.AccessTy, TLI)) {
2163 // As a special-case, handle special out-of-loop Basic users specially.
2164 // TODO: Reconsider this special case.
2165 if (LU.Kind == LSRUse::Basic &&
2166 isLegalUse(Base.AM, LU.MinOffset, LU.MaxOffset,
2167 LSRUse::Special, LU.AccessTy, TLI) &&
2168 LU.AllFixupsOutsideLoop)
2169 LU.Kind = LSRUse::Special;
2173 // For an ICmpZero, negating a solitary base register won't lead to
2175 if (LU.Kind == LSRUse::ICmpZero &&
2176 !Base.AM.HasBaseReg && Base.AM.BaseOffs == 0 && !Base.AM.BaseGV)
2178 // For each addrec base reg, apply the scale, if possible.
2179 for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i)
2180 if (const SCEVAddRecExpr *AR =
2181 dyn_cast<SCEVAddRecExpr>(Base.BaseRegs[i])) {
2182 const SCEV *FactorS = SE.getIntegerSCEV(Factor, IntTy);
2183 if (FactorS->isZero())
2185 // Divide out the factor, ignoring high bits, since we'll be
2186 // scaling the value back up in the end.
2187 if (const SCEV *Quotient = getSDiv(AR, FactorS, SE, true)) {
2188 // TODO: This could be optimized to avoid all the copying.
2190 F.ScaledReg = Quotient;
2191 std::swap(F.BaseRegs[i], F.BaseRegs.back());
2192 F.BaseRegs.pop_back();
2193 (void)InsertFormula(LU, LUIdx, F);
2199 /// GenerateTruncates - Generate reuse formulae from different IV types.
2200 void LSRInstance::GenerateTruncates(LSRUse &LU, unsigned LUIdx,
2202 // This requires TargetLowering to tell us which truncates are free.
2205 // Don't bother truncating symbolic values.
2206 if (Base.AM.BaseGV) return;
2208 // Determine the integer type for the base formula.
2209 const Type *DstTy = Base.getType();
2211 DstTy = SE.getEffectiveSCEVType(DstTy);
2213 for (SmallSetVector<const Type *, 4>::const_iterator
2214 I = Types.begin(), E = Types.end(); I != E; ++I) {
2215 const Type *SrcTy = *I;
2216 if (SrcTy != DstTy && TLI->isTruncateFree(SrcTy, DstTy)) {
2219 if (F.ScaledReg) F.ScaledReg = SE.getAnyExtendExpr(F.ScaledReg, *I);
2220 for (SmallVectorImpl<const SCEV *>::iterator J = F.BaseRegs.begin(),
2221 JE = F.BaseRegs.end(); J != JE; ++J)
2222 *J = SE.getAnyExtendExpr(*J, SrcTy);
2224 // TODO: This assumes we've done basic processing on all uses and
2225 // have an idea what the register usage is.
2226 if (!F.hasRegsUsedByUsesOtherThan(LUIdx, RegUses))
2229 (void)InsertFormula(LU, LUIdx, F);
2236 /// WorkItem - Helper class for GenerateConstantOffsetReuse. It's used to
2237 /// defer modifications so that the search phase doesn't have to worry about
2238 /// the data structures moving underneath it.
2242 const SCEV *OrigReg;
2244 WorkItem(size_t LI, int64_t I, const SCEV *R)
2245 : LUIdx(LI), Imm(I), OrigReg(R) {}
2247 void print(raw_ostream &OS) const;
2253 void WorkItem::print(raw_ostream &OS) const {
2254 OS << "in formulae referencing " << *OrigReg << " in use " << LUIdx
2255 << " , add offset " << Imm;
2258 void WorkItem::dump() const {
2259 print(errs()); errs() << '\n';
2262 /// GenerateCrossUseConstantOffsets - Look for registers which are a constant
2263 /// distance apart and try to form reuse opportunities between them.
2264 void LSRInstance::GenerateCrossUseConstantOffsets() {
2265 // Group the registers by their value without any added constant offset.
2266 typedef std::map<int64_t, const SCEV *> ImmMapTy;
2267 typedef DenseMap<const SCEV *, ImmMapTy> RegMapTy;
2269 DenseMap<const SCEV *, SmallBitVector> UsedByIndicesMap;
2270 SmallVector<const SCEV *, 8> Sequence;
2271 for (RegUseTracker::const_iterator I = RegUses.begin(), E = RegUses.end();
2273 const SCEV *Reg = *I;
2274 int64_t Imm = ExtractImmediate(Reg, SE);
2275 std::pair<RegMapTy::iterator, bool> Pair =
2276 Map.insert(std::make_pair(Reg, ImmMapTy()));
2278 Sequence.push_back(Reg);
2279 Pair.first->second.insert(std::make_pair(Imm, *I));
2280 UsedByIndicesMap[Reg] |= RegUses.getUsedByIndices(*I);
2283 // Now examine each set of registers with the same base value. Build up
2284 // a list of work to do and do the work in a separate step so that we're
2285 // not adding formulae and register counts while we're searching.
2286 SmallVector<WorkItem, 32> WorkItems;
2287 SmallSet<std::pair<size_t, int64_t>, 32> UniqueItems;
2288 for (SmallVectorImpl<const SCEV *>::const_iterator I = Sequence.begin(),
2289 E = Sequence.end(); I != E; ++I) {
2290 const SCEV *Reg = *I;
2291 const ImmMapTy &Imms = Map.find(Reg)->second;
2293 // It's not worthwhile looking for reuse if there's only one offset.
2294 if (Imms.size() == 1)
2297 DEBUG(dbgs() << "Generating cross-use offsets for " << *Reg << ':';
2298 for (ImmMapTy::const_iterator J = Imms.begin(), JE = Imms.end();
2300 dbgs() << ' ' << J->first;
2303 // Examine each offset.
2304 for (ImmMapTy::const_iterator J = Imms.begin(), JE = Imms.end();
2306 const SCEV *OrigReg = J->second;
2308 int64_t JImm = J->first;
2309 const SmallBitVector &UsedByIndices = RegUses.getUsedByIndices(OrigReg);
2311 if (!isa<SCEVConstant>(OrigReg) &&
2312 UsedByIndicesMap[Reg].count() == 1) {
2313 DEBUG(dbgs() << "Skipping cross-use reuse for " << *OrigReg << '\n');
2317 // Conservatively examine offsets between this orig reg a few selected
2319 ImmMapTy::const_iterator OtherImms[] = {
2320 Imms.begin(), prior(Imms.end()),
2321 Imms.upper_bound((Imms.begin()->first + prior(Imms.end())->first) / 2)
2323 for (size_t i = 0, e = array_lengthof(OtherImms); i != e; ++i) {
2324 ImmMapTy::const_iterator M = OtherImms[i];
2325 if (M == J || M == JE) continue;
2327 // Compute the difference between the two.
2328 int64_t Imm = (uint64_t)JImm - M->first;
2329 for (int LUIdx = UsedByIndices.find_first(); LUIdx != -1;
2330 LUIdx = UsedByIndices.find_next(LUIdx))
2331 // Make a memo of this use, offset, and register tuple.
2332 if (UniqueItems.insert(std::make_pair(LUIdx, Imm)))
2333 WorkItems.push_back(WorkItem(LUIdx, Imm, OrigReg));
2340 UsedByIndicesMap.clear();
2341 UniqueItems.clear();
2343 // Now iterate through the worklist and add new formulae.
2344 for (SmallVectorImpl<WorkItem>::const_iterator I = WorkItems.begin(),
2345 E = WorkItems.end(); I != E; ++I) {
2346 const WorkItem &WI = *I;
2347 size_t LUIdx = WI.LUIdx;
2348 LSRUse &LU = Uses[LUIdx];
2349 int64_t Imm = WI.Imm;
2350 const SCEV *OrigReg = WI.OrigReg;
2352 const Type *IntTy = SE.getEffectiveSCEVType(OrigReg->getType());
2353 const SCEV *NegImmS = SE.getSCEV(ConstantInt::get(IntTy, -(uint64_t)Imm));
2354 unsigned BitWidth = SE.getTypeSizeInBits(IntTy);
2356 // TODO: Use a more targetted data structure.
2357 for (size_t L = 0, LE = LU.Formulae.size(); L != LE; ++L) {
2358 Formula F = LU.Formulae[L];
2359 // Use the immediate in the scaled register.
2360 if (F.ScaledReg == OrigReg) {
2361 int64_t Offs = (uint64_t)F.AM.BaseOffs +
2362 Imm * (uint64_t)F.AM.Scale;
2363 // Don't create 50 + reg(-50).
2364 if (F.referencesReg(SE.getSCEV(
2365 ConstantInt::get(IntTy, -(uint64_t)Offs))))
2368 NewF.AM.BaseOffs = Offs;
2369 if (!isLegalUse(NewF.AM, LU.MinOffset, LU.MaxOffset,
2370 LU.Kind, LU.AccessTy, TLI))
2372 NewF.ScaledReg = SE.getAddExpr(NegImmS, NewF.ScaledReg);
2374 // If the new scale is a constant in a register, and adding the constant
2375 // value to the immediate would produce a value closer to zero than the
2376 // immediate itself, then the formula isn't worthwhile.
2377 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(NewF.ScaledReg))
2378 if (C->getValue()->getValue().isNegative() !=
2379 (NewF.AM.BaseOffs < 0) &&
2380 (C->getValue()->getValue().abs() * APInt(BitWidth, F.AM.Scale))
2381 .ule(APInt(BitWidth, NewF.AM.BaseOffs).abs()))
2385 (void)InsertFormula(LU, LUIdx, NewF);
2387 // Use the immediate in a base register.
2388 for (size_t N = 0, NE = F.BaseRegs.size(); N != NE; ++N) {
2389 const SCEV *BaseReg = F.BaseRegs[N];
2390 if (BaseReg != OrigReg)
2393 NewF.AM.BaseOffs = (uint64_t)NewF.AM.BaseOffs + Imm;
2394 if (!isLegalUse(NewF.AM, LU.MinOffset, LU.MaxOffset,
2395 LU.Kind, LU.AccessTy, TLI))
2397 NewF.BaseRegs[N] = SE.getAddExpr(NegImmS, BaseReg);
2399 // If the new formula has a constant in a register, and adding the
2400 // constant value to the immediate would produce a value closer to
2401 // zero than the immediate itself, then the formula isn't worthwhile.
2402 for (SmallVectorImpl<const SCEV *>::const_iterator
2403 J = NewF.BaseRegs.begin(), JE = NewF.BaseRegs.end();
2405 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(*J))
2406 if (C->getValue()->getValue().isNegative() !=
2407 (NewF.AM.BaseOffs < 0) &&
2408 C->getValue()->getValue().abs()
2409 .ule(APInt(BitWidth, NewF.AM.BaseOffs).abs()))
2413 (void)InsertFormula(LU, LUIdx, NewF);
2422 /// GenerateAllReuseFormulae - Generate formulae for each use.
2424 LSRInstance::GenerateAllReuseFormulae() {
2425 // This is split into two loops so that hasRegsUsedByUsesOtherThan
2426 // queries are more precise.
2427 for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
2428 LSRUse &LU = Uses[LUIdx];
2429 for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
2430 GenerateReassociations(LU, LUIdx, LU.Formulae[i]);
2431 for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
2432 GenerateCombinations(LU, LUIdx, LU.Formulae[i]);
2434 for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
2435 LSRUse &LU = Uses[LUIdx];
2436 for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
2437 GenerateSymbolicOffsets(LU, LUIdx, LU.Formulae[i]);
2438 for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
2439 GenerateConstantOffsets(LU, LUIdx, LU.Formulae[i]);
2440 for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
2441 GenerateICmpZeroScales(LU, LUIdx, LU.Formulae[i]);
2442 for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
2443 GenerateScales(LU, LUIdx, LU.Formulae[i]);
2444 for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
2445 GenerateTruncates(LU, LUIdx, LU.Formulae[i]);
2448 GenerateCrossUseConstantOffsets();
2451 /// If their are multiple formulae with the same set of registers used
2452 /// by other uses, pick the best one and delete the others.
2453 void LSRInstance::FilterOutUndesirableDedicatedRegisters() {
2455 bool Changed = false;
2458 // Collect the best formula for each unique set of shared registers. This
2459 // is reset for each use.
2460 typedef DenseMap<SmallVector<const SCEV *, 2>, size_t, UniquifierDenseMapInfo>
2462 BestFormulaeTy BestFormulae;
2464 for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
2465 LSRUse &LU = Uses[LUIdx];
2466 FormulaSorter Sorter(L, LU, SE, DT);
2468 // Clear out the set of used regs; it will be recomputed.
2471 for (size_t FIdx = 0, NumForms = LU.Formulae.size();
2472 FIdx != NumForms; ++FIdx) {
2473 Formula &F = LU.Formulae[FIdx];
2475 SmallVector<const SCEV *, 2> Key;
2476 for (SmallVectorImpl<const SCEV *>::const_iterator J = F.BaseRegs.begin(),
2477 JE = F.BaseRegs.end(); J != JE; ++J) {
2478 const SCEV *Reg = *J;
2479 if (RegUses.isRegUsedByUsesOtherThan(Reg, LUIdx))
2483 RegUses.isRegUsedByUsesOtherThan(F.ScaledReg, LUIdx))
2484 Key.push_back(F.ScaledReg);
2485 // Unstable sort by host order ok, because this is only used for
2487 std::sort(Key.begin(), Key.end());
2489 std::pair<BestFormulaeTy::const_iterator, bool> P =
2490 BestFormulae.insert(std::make_pair(Key, FIdx));
2492 Formula &Best = LU.Formulae[P.first->second];
2493 if (Sorter.operator()(F, Best))
2495 DEBUG(dbgs() << "Filtering out "; F.print(dbgs());
2497 " in favor of "; Best.print(dbgs());
2502 std::swap(F, LU.Formulae.back());
2503 LU.Formulae.pop_back();
2508 if (F.ScaledReg) LU.Regs.insert(F.ScaledReg);
2509 LU.Regs.insert(F.BaseRegs.begin(), F.BaseRegs.end());
2511 BestFormulae.clear();
2514 DEBUG(if (Changed) {
2516 "After filtering out undesirable candidates:\n";
2521 /// NarrowSearchSpaceUsingHeuristics - If there are an extrordinary number of
2522 /// formulae to choose from, use some rough heuristics to prune down the number
2523 /// of formulae. This keeps the main solver from taking an extrordinary amount
2524 /// of time in some worst-case scenarios.
2525 void LSRInstance::NarrowSearchSpaceUsingHeuristics() {
2526 // This is a rough guess that seems to work fairly well.
2527 const size_t Limit = UINT16_MAX;
2529 SmallPtrSet<const SCEV *, 4> Taken;
2531 // Estimate the worst-case number of solutions we might consider. We almost
2532 // never consider this many solutions because we prune the search space,
2533 // but the pruning isn't always sufficient.
2535 for (SmallVectorImpl<LSRUse>::const_iterator I = Uses.begin(),
2536 E = Uses.end(); I != E; ++I) {
2537 size_t FSize = I->Formulae.size();
2538 if (FSize >= Limit) {
2549 // Ok, we have too many of formulae on our hands to conveniently handle.
2550 // Use a rough heuristic to thin out the list.
2552 // Pick the register which is used by the most LSRUses, which is likely
2553 // to be a good reuse register candidate.
2554 const SCEV *Best = 0;
2555 unsigned BestNum = 0;
2556 for (RegUseTracker::const_iterator I = RegUses.begin(), E = RegUses.end();
2558 const SCEV *Reg = *I;
2559 if (Taken.count(Reg))
2564 unsigned Count = RegUses.getUsedByIndices(Reg).count();
2565 if (Count > BestNum) {
2572 DEBUG(dbgs() << "Narrowing the search space by assuming " << *Best
2573 << " will yeild profitable reuse.\n");
2576 // In any use with formulae which references this register, delete formulae
2577 // which don't reference it.
2578 for (SmallVectorImpl<LSRUse>::iterator I = Uses.begin(),
2579 E = Uses.end(); I != E; ++I) {
2581 if (!LU.Regs.count(Best)) continue;
2583 // Clear out the set of used regs; it will be recomputed.
2586 for (size_t i = 0, e = LU.Formulae.size(); i != e; ++i) {
2587 Formula &F = LU.Formulae[i];
2588 if (!F.referencesReg(Best)) {
2589 DEBUG(dbgs() << " Deleting "; F.print(dbgs()); dbgs() << '\n');
2590 std::swap(LU.Formulae.back(), F);
2591 LU.Formulae.pop_back();
2597 if (F.ScaledReg) LU.Regs.insert(F.ScaledReg);
2598 LU.Regs.insert(F.BaseRegs.begin(), F.BaseRegs.end());
2602 DEBUG(dbgs() << "After pre-selection:\n";
2603 print_uses(dbgs()));
2607 /// SolveRecurse - This is the recursive solver.
2608 void LSRInstance::SolveRecurse(SmallVectorImpl<const Formula *> &Solution,
2610 SmallVectorImpl<const Formula *> &Workspace,
2611 const Cost &CurCost,
2612 const SmallPtrSet<const SCEV *, 16> &CurRegs,
2613 DenseSet<const SCEV *> &VisitedRegs) const {
2616 // - use more aggressive filtering
2617 // - sort the formula so that the most profitable solutions are found first
2618 // - sort the uses too
2620 // - dont compute a cost, and then compare. compare while computing a cost
2622 // - track register sets with SmallBitVector
2624 const LSRUse &LU = Uses[Workspace.size()];
2626 // If this use references any register that's already a part of the
2627 // in-progress solution, consider it a requirement that a formula must
2628 // reference that register in order to be considered. This prunes out
2629 // unprofitable searching.
2630 SmallSetVector<const SCEV *, 4> ReqRegs;
2631 for (SmallPtrSet<const SCEV *, 16>::const_iterator I = CurRegs.begin(),
2632 E = CurRegs.end(); I != E; ++I)
2633 if (LU.Regs.count(*I))
2636 bool AnySatisfiedReqRegs = false;
2637 SmallPtrSet<const SCEV *, 16> NewRegs;
2640 for (SmallVectorImpl<Formula>::const_iterator I = LU.Formulae.begin(),
2641 E = LU.Formulae.end(); I != E; ++I) {
2642 const Formula &F = *I;
2644 // Ignore formulae which do not use any of the required registers.
2645 for (SmallSetVector<const SCEV *, 4>::const_iterator J = ReqRegs.begin(),
2646 JE = ReqRegs.end(); J != JE; ++J) {
2647 const SCEV *Reg = *J;
2648 if ((!F.ScaledReg || F.ScaledReg != Reg) &&
2649 std::find(F.BaseRegs.begin(), F.BaseRegs.end(), Reg) ==
2653 AnySatisfiedReqRegs = true;
2655 // Evaluate the cost of the current formula. If it's already worse than
2656 // the current best, prune the search at that point.
2659 NewCost.RateFormula(F, NewRegs, VisitedRegs, L, LU.Offsets, SE, DT);
2660 if (NewCost < SolutionCost) {
2661 Workspace.push_back(&F);
2662 if (Workspace.size() != Uses.size()) {
2663 SolveRecurse(Solution, SolutionCost, Workspace, NewCost,
2664 NewRegs, VisitedRegs);
2665 if (F.getNumRegs() == 1 && Workspace.size() == 1)
2666 VisitedRegs.insert(F.ScaledReg ? F.ScaledReg : F.BaseRegs[0]);
2668 DEBUG(dbgs() << "New best at "; NewCost.print(dbgs());
2669 dbgs() << ". Regs:";
2670 for (SmallPtrSet<const SCEV *, 16>::const_iterator
2671 I = NewRegs.begin(), E = NewRegs.end(); I != E; ++I)
2672 dbgs() << ' ' << **I;
2675 SolutionCost = NewCost;
2676 Solution = Workspace;
2678 Workspace.pop_back();
2683 // If none of the formulae had all of the required registers, relax the
2684 // constraint so that we don't exclude all formulae.
2685 if (!AnySatisfiedReqRegs) {
2691 void LSRInstance::Solve(SmallVectorImpl<const Formula *> &Solution) const {
2692 SmallVector<const Formula *, 8> Workspace;
2694 SolutionCost.Loose();
2696 SmallPtrSet<const SCEV *, 16> CurRegs;
2697 DenseSet<const SCEV *> VisitedRegs;
2698 Workspace.reserve(Uses.size());
2700 SolveRecurse(Solution, SolutionCost, Workspace, CurCost,
2701 CurRegs, VisitedRegs);
2703 // Ok, we've now made all our decisions.
2704 DEBUG(dbgs() << "\n"
2705 "The chosen solution requires "; SolutionCost.print(dbgs());
2707 for (size_t i = 0, e = Uses.size(); i != e; ++i) {
2709 Uses[i].print(dbgs());
2712 Solution[i]->print(dbgs());
2717 /// getImmediateDominator - A handy utility for the specific DominatorTree
2718 /// query that we need here.
2720 static BasicBlock *getImmediateDominator(BasicBlock *BB, DominatorTree &DT) {
2721 DomTreeNode *Node = DT.getNode(BB);
2722 if (!Node) return 0;
2723 Node = Node->getIDom();
2724 if (!Node) return 0;
2725 return Node->getBlock();
2728 Value *LSRInstance::Expand(const LSRFixup &LF,
2730 BasicBlock::iterator IP,
2731 Loop *L, Instruction *IVIncInsertPos,
2732 SCEVExpander &Rewriter,
2733 SmallVectorImpl<WeakVH> &DeadInsts,
2734 ScalarEvolution &SE, DominatorTree &DT) const {
2735 const LSRUse &LU = Uses[LF.LUIdx];
2737 // Then, collect some instructions which we will remain dominated by when
2738 // expanding the replacement. These must be dominated by any operands that
2739 // will be required in the expansion.
2740 SmallVector<Instruction *, 4> Inputs;
2741 if (Instruction *I = dyn_cast<Instruction>(LF.OperandValToReplace))
2742 Inputs.push_back(I);
2743 if (LU.Kind == LSRUse::ICmpZero)
2744 if (Instruction *I =
2745 dyn_cast<Instruction>(cast<ICmpInst>(LF.UserInst)->getOperand(1)))
2746 Inputs.push_back(I);
2747 if (LF.PostIncLoop && !L->contains(LF.UserInst))
2748 Inputs.push_back(L->getLoopLatch()->getTerminator());
2750 // Then, climb up the immediate dominator tree as far as we can go while
2751 // still being dominated by the input positions.
2753 bool AllDominate = true;
2754 Instruction *BetterPos = 0;
2755 BasicBlock *IDom = getImmediateDominator(IP->getParent(), DT);
2757 Instruction *Tentative = IDom->getTerminator();
2758 for (SmallVectorImpl<Instruction *>::const_iterator I = Inputs.begin(),
2759 E = Inputs.end(); I != E; ++I) {
2760 Instruction *Inst = *I;
2761 if (Inst == Tentative || !DT.dominates(Inst, Tentative)) {
2762 AllDominate = false;
2765 if (IDom == Inst->getParent() &&
2766 (!BetterPos || DT.dominates(BetterPos, Inst)))
2767 BetterPos = next(BasicBlock::iterator(Inst));
2776 while (isa<PHINode>(IP)) ++IP;
2778 // Inform the Rewriter if we have a post-increment use, so that it can
2779 // perform an advantageous expansion.
2780 Rewriter.setPostInc(LF.PostIncLoop);
2782 // This is the type that the user actually needs.
2783 const Type *OpTy = LF.OperandValToReplace->getType();
2784 // This will be the type that we'll initially expand to.
2785 const Type *Ty = F.getType();
2787 // No type known; just expand directly to the ultimate type.
2789 else if (SE.getEffectiveSCEVType(Ty) == SE.getEffectiveSCEVType(OpTy))
2790 // Expand directly to the ultimate type if it's the right size.
2792 // This is the type to do integer arithmetic in.
2793 const Type *IntTy = SE.getEffectiveSCEVType(Ty);
2795 // Build up a list of operands to add together to form the full base.
2796 SmallVector<const SCEV *, 8> Ops;
2798 // Expand the BaseRegs portion.
2799 for (SmallVectorImpl<const SCEV *>::const_iterator I = F.BaseRegs.begin(),
2800 E = F.BaseRegs.end(); I != E; ++I) {
2801 const SCEV *Reg = *I;
2802 assert(!Reg->isZero() && "Zero allocated in a base register!");
2804 // If we're expanding for a post-inc user for the add-rec's loop, make the
2805 // post-inc adjustment.
2806 const SCEV *Start = Reg;
2807 while (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Start)) {
2808 if (AR->getLoop() == LF.PostIncLoop) {
2809 Reg = SE.getAddExpr(Reg, AR->getStepRecurrence(SE));
2810 // If the user is inside the loop, insert the code after the increment
2811 // so that it is dominated by its operand.
2812 if (L->contains(LF.UserInst))
2813 IP = IVIncInsertPos;
2816 Start = AR->getStart();
2819 Ops.push_back(SE.getUnknown(Rewriter.expandCodeFor(Reg, 0, IP)));
2822 // Expand the ScaledReg portion.
2823 Value *ICmpScaledV = 0;
2824 if (F.AM.Scale != 0) {
2825 const SCEV *ScaledS = F.ScaledReg;
2827 // If we're expanding for a post-inc user for the add-rec's loop, make the
2828 // post-inc adjustment.
2829 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(ScaledS))
2830 if (AR->getLoop() == LF.PostIncLoop)
2831 ScaledS = SE.getAddExpr(ScaledS, AR->getStepRecurrence(SE));
2833 if (LU.Kind == LSRUse::ICmpZero) {
2834 // An interesting way of "folding" with an icmp is to use a negated
2835 // scale, which we'll implement by inserting it into the other operand
2837 assert(F.AM.Scale == -1 &&
2838 "The only scale supported by ICmpZero uses is -1!");
2839 ICmpScaledV = Rewriter.expandCodeFor(ScaledS, 0, IP);
2841 // Otherwise just expand the scaled register and an explicit scale,
2842 // which is expected to be matched as part of the address.
2843 ScaledS = SE.getUnknown(Rewriter.expandCodeFor(ScaledS, 0, IP));
2844 ScaledS = SE.getMulExpr(ScaledS,
2845 SE.getIntegerSCEV(F.AM.Scale,
2846 ScaledS->getType()));
2847 Ops.push_back(ScaledS);
2851 // Expand the immediate portions.
2853 Ops.push_back(SE.getSCEV(F.AM.BaseGV));
2854 int64_t Offset = (uint64_t)F.AM.BaseOffs + LF.Offset;
2856 if (LU.Kind == LSRUse::ICmpZero) {
2857 // The other interesting way of "folding" with an ICmpZero is to use a
2858 // negated immediate.
2860 ICmpScaledV = ConstantInt::get(IntTy, -Offset);
2862 Ops.push_back(SE.getUnknown(ICmpScaledV));
2863 ICmpScaledV = ConstantInt::get(IntTy, Offset);
2866 // Just add the immediate values. These again are expected to be matched
2867 // as part of the address.
2868 Ops.push_back(SE.getIntegerSCEV(Offset, IntTy));
2872 // Emit instructions summing all the operands.
2873 const SCEV *FullS = Ops.empty() ?
2874 SE.getIntegerSCEV(0, IntTy) :
2876 Value *FullV = Rewriter.expandCodeFor(FullS, Ty, IP);
2878 // We're done expanding now, so reset the rewriter.
2879 Rewriter.setPostInc(0);
2881 // An ICmpZero Formula represents an ICmp which we're handling as a
2882 // comparison against zero. Now that we've expanded an expression for that
2883 // form, update the ICmp's other operand.
2884 if (LU.Kind == LSRUse::ICmpZero) {
2885 ICmpInst *CI = cast<ICmpInst>(LF.UserInst);
2886 DeadInsts.push_back(CI->getOperand(1));
2887 assert(!F.AM.BaseGV && "ICmp does not support folding a global value and "
2888 "a scale at the same time!");
2889 if (F.AM.Scale == -1) {
2890 if (ICmpScaledV->getType() != OpTy) {
2892 CastInst::Create(CastInst::getCastOpcode(ICmpScaledV, false,
2894 ICmpScaledV, OpTy, "tmp", CI);
2897 CI->setOperand(1, ICmpScaledV);
2899 assert(F.AM.Scale == 0 &&
2900 "ICmp does not support folding a global value and "
2901 "a scale at the same time!");
2902 Constant *C = ConstantInt::getSigned(SE.getEffectiveSCEVType(OpTy),
2904 if (C->getType() != OpTy)
2905 C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
2909 CI->setOperand(1, C);
2916 /// Rewrite - Emit instructions for the leading candidate expression for this
2917 /// LSRUse (this is called "expanding"), and update the UserInst to reference
2918 /// the newly expanded value.
2919 void LSRInstance::Rewrite(const LSRFixup &LF,
2921 Loop *L, Instruction *IVIncInsertPos,
2922 SCEVExpander &Rewriter,
2923 SmallVectorImpl<WeakVH> &DeadInsts,
2924 ScalarEvolution &SE, DominatorTree &DT,
2926 const Type *OpTy = LF.OperandValToReplace->getType();
2928 // First, find an insertion point that dominates UserInst. For PHI nodes,
2929 // find the nearest block which dominates all the relevant uses.
2930 if (PHINode *PN = dyn_cast<PHINode>(LF.UserInst)) {
2931 DenseMap<BasicBlock *, Value *> Inserted;
2932 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
2933 if (PN->getIncomingValue(i) == LF.OperandValToReplace) {
2934 BasicBlock *BB = PN->getIncomingBlock(i);
2936 // If this is a critical edge, split the edge so that we do not insert
2937 // the code on all predecessor/successor paths. We do this unless this
2938 // is the canonical backedge for this loop, which complicates post-inc
2940 if (e != 1 && BB->getTerminator()->getNumSuccessors() > 1 &&
2941 !isa<IndirectBrInst>(BB->getTerminator()) &&
2942 (PN->getParent() != L->getHeader() || !L->contains(BB))) {
2943 // Split the critical edge.
2944 BasicBlock *NewBB = SplitCriticalEdge(BB, PN->getParent(), P);
2946 // If PN is outside of the loop and BB is in the loop, we want to
2947 // move the block to be immediately before the PHI block, not
2948 // immediately after BB.
2949 if (L->contains(BB) && !L->contains(PN))
2950 NewBB->moveBefore(PN->getParent());
2952 // Splitting the edge can reduce the number of PHI entries we have.
2953 e = PN->getNumIncomingValues();
2955 i = PN->getBasicBlockIndex(BB);
2958 std::pair<DenseMap<BasicBlock *, Value *>::iterator, bool> Pair =
2959 Inserted.insert(std::make_pair(BB, static_cast<Value *>(0)));
2961 PN->setIncomingValue(i, Pair.first->second);
2963 Value *FullV = Expand(LF, F, BB->getTerminator(), L, IVIncInsertPos,
2964 Rewriter, DeadInsts, SE, DT);
2966 // If this is reuse-by-noop-cast, insert the noop cast.
2967 if (FullV->getType() != OpTy)
2969 CastInst::Create(CastInst::getCastOpcode(FullV, false,
2971 FullV, LF.OperandValToReplace->getType(),
2972 "tmp", BB->getTerminator());
2974 PN->setIncomingValue(i, FullV);
2975 Pair.first->second = FullV;
2979 Value *FullV = Expand(LF, F, LF.UserInst, L, IVIncInsertPos,
2980 Rewriter, DeadInsts, SE, DT);
2982 // If this is reuse-by-noop-cast, insert the noop cast.
2983 if (FullV->getType() != OpTy) {
2985 CastInst::Create(CastInst::getCastOpcode(FullV, false, OpTy, false),
2986 FullV, OpTy, "tmp", LF.UserInst);
2990 // Update the user. ICmpZero is handled specially here (for now) because
2991 // Expand may have updated one of the operands of the icmp already, and
2992 // its new value may happen to be equal to LF.OperandValToReplace, in
2993 // which case doing replaceUsesOfWith leads to replacing both operands
2994 // with the same value. TODO: Reorganize this.
2995 if (Uses[LF.LUIdx].Kind == LSRUse::ICmpZero)
2996 LF.UserInst->setOperand(0, FullV);
2998 LF.UserInst->replaceUsesOfWith(LF.OperandValToReplace, FullV);
3001 DeadInsts.push_back(LF.OperandValToReplace);
3005 LSRInstance::ImplementSolution(const SmallVectorImpl<const Formula *> &Solution,
3007 // Keep track of instructions we may have made dead, so that
3008 // we can remove them after we are done working.
3009 SmallVector<WeakVH, 16> DeadInsts;
3011 SCEVExpander Rewriter(SE);
3012 Rewriter.disableCanonicalMode();
3013 Rewriter.setIVIncInsertPos(L, IVIncInsertPos);
3015 // Expand the new value definitions and update the users.
3016 for (size_t i = 0, e = Fixups.size(); i != e; ++i) {
3017 size_t LUIdx = Fixups[i].LUIdx;
3019 Rewrite(Fixups[i], *Solution[LUIdx], L, IVIncInsertPos, Rewriter,
3020 DeadInsts, SE, DT, P);
3025 // Clean up after ourselves. This must be done before deleting any
3029 Changed |= DeleteTriviallyDeadInstructions(DeadInsts);
3032 LSRInstance::LSRInstance(const TargetLowering *tli, Loop *l, Pass *P)
3033 : IU(P->getAnalysis<IVUsers>()),
3034 SE(P->getAnalysis<ScalarEvolution>()),
3035 DT(P->getAnalysis<DominatorTree>()),
3036 TLI(tli), L(l), Changed(false), IVIncInsertPos(0) {
3038 // If LoopSimplify form is not available, stay out of trouble.
3039 if (!L->isLoopSimplifyForm()) return;
3041 // If there's no interesting work to be done, bail early.
3042 if (IU.empty()) return;
3044 DEBUG(dbgs() << "\nLSR on loop ";
3045 WriteAsOperand(dbgs(), L->getHeader(), /*PrintType=*/false);
3048 /// OptimizeShadowIV - If IV is used in a int-to-float cast
3049 /// inside the loop then try to eliminate the cast opeation.
3052 // Change loop terminating condition to use the postinc iv when possible.
3053 Changed |= OptimizeLoopTermCond();
3055 CollectInterestingTypesAndFactors();
3056 CollectFixupsAndInitialFormulae();
3057 CollectLoopInvariantFixupsAndFormulae();
3059 DEBUG(dbgs() << "LSR found " << Uses.size() << " uses:\n";
3060 print_uses(dbgs()));
3062 // Now use the reuse data to generate a bunch of interesting ways
3063 // to formulate the values needed for the uses.
3064 GenerateAllReuseFormulae();
3066 DEBUG(dbgs() << "\n"
3067 "After generating reuse formulae:\n";
3068 print_uses(dbgs()));
3070 FilterOutUndesirableDedicatedRegisters();
3071 NarrowSearchSpaceUsingHeuristics();
3073 SmallVector<const Formula *, 8> Solution;
3075 assert(Solution.size() == Uses.size() && "Malformed solution!");
3077 // Release memory that is no longer needed.
3083 // Formulae should be legal.
3084 for (SmallVectorImpl<LSRUse>::const_iterator I = Uses.begin(),
3085 E = Uses.end(); I != E; ++I) {
3086 const LSRUse &LU = *I;
3087 for (SmallVectorImpl<Formula>::const_iterator J = LU.Formulae.begin(),
3088 JE = LU.Formulae.end(); J != JE; ++J)
3089 assert(isLegalUse(J->AM, LU.MinOffset, LU.MaxOffset,
3090 LU.Kind, LU.AccessTy, TLI) &&
3091 "Illegal formula generated!");
3095 // Now that we've decided what we want, make it so.
3096 ImplementSolution(Solution, P);
3099 void LSRInstance::print_factors_and_types(raw_ostream &OS) const {
3100 if (Factors.empty() && Types.empty()) return;
3102 OS << "LSR has identified the following interesting factors and types: ";
3105 for (SmallSetVector<int64_t, 8>::const_iterator
3106 I = Factors.begin(), E = Factors.end(); I != E; ++I) {
3107 if (!First) OS << ", ";
3112 for (SmallSetVector<const Type *, 4>::const_iterator
3113 I = Types.begin(), E = Types.end(); I != E; ++I) {
3114 if (!First) OS << ", ";
3116 OS << '(' << **I << ')';
3121 void LSRInstance::print_fixups(raw_ostream &OS) const {
3122 OS << "LSR is examining the following fixup sites:\n";
3123 for (SmallVectorImpl<LSRFixup>::const_iterator I = Fixups.begin(),
3124 E = Fixups.end(); I != E; ++I) {
3125 const LSRFixup &LF = *I;
3132 void LSRInstance::print_uses(raw_ostream &OS) const {
3133 OS << "LSR is examining the following uses:\n";
3134 for (SmallVectorImpl<LSRUse>::const_iterator I = Uses.begin(),
3135 E = Uses.end(); I != E; ++I) {
3136 const LSRUse &LU = *I;
3140 for (SmallVectorImpl<Formula>::const_iterator J = LU.Formulae.begin(),
3141 JE = LU.Formulae.end(); J != JE; ++J) {
3149 void LSRInstance::print(raw_ostream &OS) const {
3150 print_factors_and_types(OS);
3155 void LSRInstance::dump() const {
3156 print(errs()); errs() << '\n';
3161 class LoopStrengthReduce : public LoopPass {
3162 /// TLI - Keep a pointer of a TargetLowering to consult for determining
3163 /// transformation profitability.
3164 const TargetLowering *const TLI;
3167 static char ID; // Pass ID, replacement for typeid
3168 explicit LoopStrengthReduce(const TargetLowering *tli = 0);
3171 bool runOnLoop(Loop *L, LPPassManager &LPM);
3172 void getAnalysisUsage(AnalysisUsage &AU) const;
3177 char LoopStrengthReduce::ID = 0;
3178 static RegisterPass<LoopStrengthReduce>
3179 X("loop-reduce", "Loop Strength Reduction");
3181 Pass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) {
3182 return new LoopStrengthReduce(TLI);
3185 LoopStrengthReduce::LoopStrengthReduce(const TargetLowering *tli)
3186 : LoopPass(&ID), TLI(tli) {}
3188 void LoopStrengthReduce::getAnalysisUsage(AnalysisUsage &AU) const {
3189 // We split critical edges, so we change the CFG. However, we do update
3190 // many analyses if they are around.
3191 AU.addPreservedID(LoopSimplifyID);
3192 AU.addPreserved<LoopInfo>();
3193 AU.addPreserved("domfrontier");
3195 AU.addRequiredID(LoopSimplifyID);
3196 AU.addRequired<DominatorTree>();
3197 AU.addPreserved<DominatorTree>();
3198 AU.addRequired<ScalarEvolution>();
3199 AU.addPreserved<ScalarEvolution>();
3200 AU.addRequired<IVUsers>();
3201 AU.addPreserved<IVUsers>();
3204 bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager & /*LPM*/) {
3205 bool Changed = false;
3207 // Run the main LSR transformation.
3208 Changed |= LSRInstance(TLI, L, this).getChanged();
3210 // At this point, it is worth checking to see if any recurrence PHIs are also
3211 // dead, so that we can remove them as well.
3212 Changed |= DeleteDeadPHIs(L->getHeader());