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view lib/Transforms/Scalar/LoopStrengthReduce.cpp @ 83:60c9769439b8
LLVM 3.7
author | Tatsuki IHA <e125716@ie.u-ryukyu.ac.jp> |
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date | Wed, 18 Feb 2015 14:55:36 +0900 |
parents | 54457678186b |
children | afa8332a0e37 |
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//===- LoopStrengthReduce.cpp - Strength Reduce IVs in Loops --------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This transformation analyzes and transforms the induction variables (and // computations derived from them) into forms suitable for efficient execution // on the target. // // This pass performs a strength reduction on array references inside loops that // have as one or more of their components the loop induction variable, it // rewrites expressions to take advantage of scaled-index addressing modes // available on the target, and it performs a variety of other optimizations // related to loop induction variables. // // Terminology note: this code has a lot of handling for "post-increment" or // "post-inc" users. This is not talking about post-increment addressing modes; // it is instead talking about code like this: // // %i = phi [ 0, %entry ], [ %i.next, %latch ] // ... // %i.next = add %i, 1 // %c = icmp eq %i.next, %n // // The SCEV for %i is {0,+,1}<%L>. The SCEV for %i.next is {1,+,1}<%L>, however // it's useful to think about these as the same register, with some uses using // the value of the register before the add and some using // it after. In this // example, the icmp is a post-increment user, since it uses %i.next, which is // the value of the induction variable after the increment. The other common // case of post-increment users is users outside the loop. // // TODO: More sophistication in the way Formulae are generated and filtered. // // TODO: Handle multiple loops at a time. // // TODO: Should the addressing mode BaseGV be changed to a ConstantExpr instead // of a GlobalValue? // // TODO: When truncation is free, truncate ICmp users' operands to make it a // smaller encoding (on x86 at least). // // TODO: When a negated register is used by an add (such as in a list of // multiple base registers, or as the increment expression in an addrec), // we may not actually need both reg and (-1 * reg) in registers; the // negation can be implemented by using a sub instead of an add. The // lack of support for taking this into consideration when making // register pressure decisions is partly worked around by the "Special" // use kind. // //===----------------------------------------------------------------------===// #include "llvm/Transforms/Scalar.h" #include "llvm/ADT/DenseSet.h" #include "llvm/ADT/Hashing.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SetVector.h" #include "llvm/ADT/SmallBitVector.h" #include "llvm/Analysis/IVUsers.h" #include "llvm/Analysis/LoopPass.h" #include "llvm/Analysis/ScalarEvolutionExpander.h" #include "llvm/Analysis/TargetTransformInfo.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/ValueHandle.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/Transforms/Utils/Local.h" #include <algorithm> using namespace llvm; #define DEBUG_TYPE "loop-reduce" /// MaxIVUsers is an arbitrary threshold that provides an early opportunitiy for /// bail out. This threshold is far beyond the number of users that LSR can /// conceivably solve, so it should not affect generated code, but catches the /// worst cases before LSR burns too much compile time and stack space. static const unsigned MaxIVUsers = 200; // Temporary flag to cleanup congruent phis after LSR phi expansion. // It's currently disabled until we can determine whether it's truly useful or // not. The flag should be removed after the v3.0 release. // This is now needed for ivchains. static cl::opt<bool> EnablePhiElim( "enable-lsr-phielim", cl::Hidden, cl::init(true), cl::desc("Enable LSR phi elimination")); #ifndef NDEBUG // Stress test IV chain generation. static cl::opt<bool> StressIVChain( "stress-ivchain", cl::Hidden, cl::init(false), cl::desc("Stress test LSR IV chains")); #else static bool StressIVChain = false; #endif namespace { /// RegSortData - This class holds data which is used to order reuse candidates. class RegSortData { public: /// UsedByIndices - This represents the set of LSRUse indices which reference /// a particular register. SmallBitVector UsedByIndices; RegSortData() {} void print(raw_ostream &OS) const; void dump() const; }; } void RegSortData::print(raw_ostream &OS) const { OS << "[NumUses=" << UsedByIndices.count() << ']'; } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void RegSortData::dump() const { print(errs()); errs() << '\n'; } #endif namespace { /// RegUseTracker - Map register candidates to information about how they are /// used. class RegUseTracker { typedef DenseMap<const SCEV *, RegSortData> RegUsesTy; RegUsesTy RegUsesMap; SmallVector<const SCEV *, 16> RegSequence; public: void CountRegister(const SCEV *Reg, size_t LUIdx); void DropRegister(const SCEV *Reg, size_t LUIdx); void SwapAndDropUse(size_t LUIdx, size_t LastLUIdx); bool isRegUsedByUsesOtherThan(const SCEV *Reg, size_t LUIdx) const; const SmallBitVector &getUsedByIndices(const SCEV *Reg) const; void clear(); typedef SmallVectorImpl<const SCEV *>::iterator iterator; typedef SmallVectorImpl<const SCEV *>::const_iterator const_iterator; iterator begin() { return RegSequence.begin(); } iterator end() { return RegSequence.end(); } const_iterator begin() const { return RegSequence.begin(); } const_iterator end() const { return RegSequence.end(); } }; } void RegUseTracker::CountRegister(const SCEV *Reg, size_t LUIdx) { std::pair<RegUsesTy::iterator, bool> Pair = RegUsesMap.insert(std::make_pair(Reg, RegSortData())); RegSortData &RSD = Pair.first->second; if (Pair.second) RegSequence.push_back(Reg); RSD.UsedByIndices.resize(std::max(RSD.UsedByIndices.size(), LUIdx + 1)); RSD.UsedByIndices.set(LUIdx); } void RegUseTracker::DropRegister(const SCEV *Reg, size_t LUIdx) { RegUsesTy::iterator It = RegUsesMap.find(Reg); assert(It != RegUsesMap.end()); RegSortData &RSD = It->second; assert(RSD.UsedByIndices.size() > LUIdx); RSD.UsedByIndices.reset(LUIdx); } void RegUseTracker::SwapAndDropUse(size_t LUIdx, size_t LastLUIdx) { assert(LUIdx <= LastLUIdx); // Update RegUses. The data structure is not optimized for this purpose; // we must iterate through it and update each of the bit vectors. for (RegUsesTy::iterator I = RegUsesMap.begin(), E = RegUsesMap.end(); I != E; ++I) { SmallBitVector &UsedByIndices = I->second.UsedByIndices; if (LUIdx < UsedByIndices.size()) UsedByIndices[LUIdx] = LastLUIdx < UsedByIndices.size() ? UsedByIndices[LastLUIdx] : 0; UsedByIndices.resize(std::min(UsedByIndices.size(), LastLUIdx)); } } bool RegUseTracker::isRegUsedByUsesOtherThan(const SCEV *Reg, size_t LUIdx) const { RegUsesTy::const_iterator I = RegUsesMap.find(Reg); if (I == RegUsesMap.end()) return false; const SmallBitVector &UsedByIndices = I->second.UsedByIndices; int i = UsedByIndices.find_first(); if (i == -1) return false; if ((size_t)i != LUIdx) return true; return UsedByIndices.find_next(i) != -1; } const SmallBitVector &RegUseTracker::getUsedByIndices(const SCEV *Reg) const { RegUsesTy::const_iterator I = RegUsesMap.find(Reg); assert(I != RegUsesMap.end() && "Unknown register!"); return I->second.UsedByIndices; } void RegUseTracker::clear() { RegUsesMap.clear(); RegSequence.clear(); } namespace { /// Formula - This class holds information that describes a formula for /// computing satisfying a use. It may include broken-out immediates and scaled /// registers. struct Formula { /// Global base address used for complex addressing. GlobalValue *BaseGV; /// Base offset for complex addressing. int64_t BaseOffset; /// Whether any complex addressing has a base register. bool HasBaseReg; /// The scale of any complex addressing. int64_t Scale; /// BaseRegs - The list of "base" registers for this use. When this is /// non-empty. The canonical representation of a formula is /// 1. BaseRegs.size > 1 implies ScaledReg != NULL and /// 2. ScaledReg != NULL implies Scale != 1 || !BaseRegs.empty(). /// #1 enforces that the scaled register is always used when at least two /// registers are needed by the formula: e.g., reg1 + reg2 is reg1 + 1 * reg2. /// #2 enforces that 1 * reg is reg. /// This invariant can be temporarly broken while building a formula. /// However, every formula inserted into the LSRInstance must be in canonical /// form. SmallVector<const SCEV *, 4> BaseRegs; /// ScaledReg - The 'scaled' register for this use. This should be non-null /// when Scale is not zero. const SCEV *ScaledReg; /// UnfoldedOffset - An additional constant offset which added near the /// use. This requires a temporary register, but the offset itself can /// live in an add immediate field rather than a register. int64_t UnfoldedOffset; Formula() : BaseGV(nullptr), BaseOffset(0), HasBaseReg(false), Scale(0), ScaledReg(nullptr), UnfoldedOffset(0) {} void InitialMatch(const SCEV *S, Loop *L, ScalarEvolution &SE); bool isCanonical() const; void Canonicalize(); bool Unscale(); size_t getNumRegs() const; Type *getType() const; void DeleteBaseReg(const SCEV *&S); bool referencesReg(const SCEV *S) const; bool hasRegsUsedByUsesOtherThan(size_t LUIdx, const RegUseTracker &RegUses) const; void print(raw_ostream &OS) const; void dump() const; }; } /// DoInitialMatch - Recursion helper for InitialMatch. static void DoInitialMatch(const SCEV *S, Loop *L, SmallVectorImpl<const SCEV *> &Good, SmallVectorImpl<const SCEV *> &Bad, ScalarEvolution &SE) { // Collect expressions which properly dominate the loop header. if (SE.properlyDominates(S, L->getHeader())) { Good.push_back(S); return; } // Look at add operands. if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end(); I != E; ++I) DoInitialMatch(*I, L, Good, Bad, SE); return; } // Look at addrec operands. if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) if (!AR->getStart()->isZero()) { DoInitialMatch(AR->getStart(), L, Good, Bad, SE); DoInitialMatch(SE.getAddRecExpr(SE.getConstant(AR->getType(), 0), AR->getStepRecurrence(SE), // FIXME: AR->getNoWrapFlags() AR->getLoop(), SCEV::FlagAnyWrap), L, Good, Bad, SE); return; } // Handle a multiplication by -1 (negation) if it didn't fold. if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) if (Mul->getOperand(0)->isAllOnesValue()) { SmallVector<const SCEV *, 4> Ops(Mul->op_begin()+1, Mul->op_end()); const SCEV *NewMul = SE.getMulExpr(Ops); SmallVector<const SCEV *, 4> MyGood; SmallVector<const SCEV *, 4> MyBad; DoInitialMatch(NewMul, L, MyGood, MyBad, SE); const SCEV *NegOne = SE.getSCEV(ConstantInt::getAllOnesValue( SE.getEffectiveSCEVType(NewMul->getType()))); for (SmallVectorImpl<const SCEV *>::const_iterator I = MyGood.begin(), E = MyGood.end(); I != E; ++I) Good.push_back(SE.getMulExpr(NegOne, *I)); for (SmallVectorImpl<const SCEV *>::const_iterator I = MyBad.begin(), E = MyBad.end(); I != E; ++I) Bad.push_back(SE.getMulExpr(NegOne, *I)); return; } // Ok, we can't do anything interesting. Just stuff the whole thing into a // register and hope for the best. Bad.push_back(S); } /// InitialMatch - Incorporate loop-variant parts of S into this Formula, /// attempting to keep all loop-invariant and loop-computable values in a /// single base register. void Formula::InitialMatch(const SCEV *S, Loop *L, ScalarEvolution &SE) { SmallVector<const SCEV *, 4> Good; SmallVector<const SCEV *, 4> Bad; DoInitialMatch(S, L, Good, Bad, SE); if (!Good.empty()) { const SCEV *Sum = SE.getAddExpr(Good); if (!Sum->isZero()) BaseRegs.push_back(Sum); HasBaseReg = true; } if (!Bad.empty()) { const SCEV *Sum = SE.getAddExpr(Bad); if (!Sum->isZero()) BaseRegs.push_back(Sum); HasBaseReg = true; } Canonicalize(); } /// \brief Check whether or not this formula statisfies the canonical /// representation. /// \see Formula::BaseRegs. bool Formula::isCanonical() const { if (ScaledReg) return Scale != 1 || !BaseRegs.empty(); return BaseRegs.size() <= 1; } /// \brief Helper method to morph a formula into its canonical representation. /// \see Formula::BaseRegs. /// Every formula having more than one base register, must use the ScaledReg /// field. Otherwise, we would have to do special cases everywhere in LSR /// to treat reg1 + reg2 + ... the same way as reg1 + 1*reg2 + ... /// On the other hand, 1*reg should be canonicalized into reg. void Formula::Canonicalize() { if (isCanonical()) return; // So far we did not need this case. This is easy to implement but it is // useless to maintain dead code. Beside it could hurt compile time. assert(!BaseRegs.empty() && "1*reg => reg, should not be needed."); // Keep the invariant sum in BaseRegs and one of the variant sum in ScaledReg. ScaledReg = BaseRegs.back(); BaseRegs.pop_back(); Scale = 1; size_t BaseRegsSize = BaseRegs.size(); size_t Try = 0; // If ScaledReg is an invariant, try to find a variant expression. while (Try < BaseRegsSize && !isa<SCEVAddRecExpr>(ScaledReg)) std::swap(ScaledReg, BaseRegs[Try++]); } /// \brief Get rid of the scale in the formula. /// In other words, this method morphes reg1 + 1*reg2 into reg1 + reg2. /// \return true if it was possible to get rid of the scale, false otherwise. /// \note After this operation the formula may not be in the canonical form. bool Formula::Unscale() { if (Scale != 1) return false; Scale = 0; BaseRegs.push_back(ScaledReg); ScaledReg = nullptr; return true; } /// getNumRegs - Return the total number of register operands used by this /// formula. This does not include register uses implied by non-constant /// addrec strides. size_t Formula::getNumRegs() const { return !!ScaledReg + BaseRegs.size(); } /// getType - Return the type of this formula, if it has one, or null /// otherwise. This type is meaningless except for the bit size. Type *Formula::getType() const { return !BaseRegs.empty() ? BaseRegs.front()->getType() : ScaledReg ? ScaledReg->getType() : BaseGV ? BaseGV->getType() : nullptr; } /// DeleteBaseReg - Delete the given base reg from the BaseRegs list. void Formula::DeleteBaseReg(const SCEV *&S) { if (&S != &BaseRegs.back()) std::swap(S, BaseRegs.back()); BaseRegs.pop_back(); } /// referencesReg - Test if this formula references the given register. bool Formula::referencesReg(const SCEV *S) const { return S == ScaledReg || std::find(BaseRegs.begin(), BaseRegs.end(), S) != BaseRegs.end(); } /// hasRegsUsedByUsesOtherThan - Test whether this formula uses registers /// which are used by uses other than the use with the given index. bool Formula::hasRegsUsedByUsesOtherThan(size_t LUIdx, const RegUseTracker &RegUses) const { if (ScaledReg) if (RegUses.isRegUsedByUsesOtherThan(ScaledReg, LUIdx)) return true; for (SmallVectorImpl<const SCEV *>::const_iterator I = BaseRegs.begin(), E = BaseRegs.end(); I != E; ++I) if (RegUses.isRegUsedByUsesOtherThan(*I, LUIdx)) return true; return false; } void Formula::print(raw_ostream &OS) const { bool First = true; if (BaseGV) { if (!First) OS << " + "; else First = false; BaseGV->printAsOperand(OS, /*PrintType=*/false); } if (BaseOffset != 0) { if (!First) OS << " + "; else First = false; OS << BaseOffset; } for (SmallVectorImpl<const SCEV *>::const_iterator I = BaseRegs.begin(), E = BaseRegs.end(); I != E; ++I) { if (!First) OS << " + "; else First = false; OS << "reg(" << **I << ')'; } if (HasBaseReg && BaseRegs.empty()) { if (!First) OS << " + "; else First = false; OS << "**error: HasBaseReg**"; } else if (!HasBaseReg && !BaseRegs.empty()) { if (!First) OS << " + "; else First = false; OS << "**error: !HasBaseReg**"; } if (Scale != 0) { if (!First) OS << " + "; else First = false; OS << Scale << "*reg("; if (ScaledReg) OS << *ScaledReg; else OS << "<unknown>"; OS << ')'; } if (UnfoldedOffset != 0) { if (!First) OS << " + "; OS << "imm(" << UnfoldedOffset << ')'; } } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void Formula::dump() const { print(errs()); errs() << '\n'; } #endif /// isAddRecSExtable - Return true if the given addrec can be sign-extended /// without changing its value. static bool isAddRecSExtable(const SCEVAddRecExpr *AR, ScalarEvolution &SE) { Type *WideTy = IntegerType::get(SE.getContext(), SE.getTypeSizeInBits(AR->getType()) + 1); return isa<SCEVAddRecExpr>(SE.getSignExtendExpr(AR, WideTy)); } /// isAddSExtable - Return true if the given add can be sign-extended /// without changing its value. static bool isAddSExtable(const SCEVAddExpr *A, ScalarEvolution &SE) { Type *WideTy = IntegerType::get(SE.getContext(), SE.getTypeSizeInBits(A->getType()) + 1); return isa<SCEVAddExpr>(SE.getSignExtendExpr(A, WideTy)); } /// isMulSExtable - Return true if the given mul can be sign-extended /// without changing its value. static bool isMulSExtable(const SCEVMulExpr *M, ScalarEvolution &SE) { Type *WideTy = IntegerType::get(SE.getContext(), SE.getTypeSizeInBits(M->getType()) * M->getNumOperands()); return isa<SCEVMulExpr>(SE.getSignExtendExpr(M, WideTy)); } /// getExactSDiv - Return an expression for LHS /s RHS, if it can be determined /// and if the remainder is known to be zero, or null otherwise. If /// IgnoreSignificantBits is true, expressions like (X * Y) /s Y are simplified /// to Y, ignoring that the multiplication may overflow, which is useful when /// the result will be used in a context where the most significant bits are /// ignored. static const SCEV *getExactSDiv(const SCEV *LHS, const SCEV *RHS, ScalarEvolution &SE, bool IgnoreSignificantBits = false) { // Handle the trivial case, which works for any SCEV type. if (LHS == RHS) return SE.getConstant(LHS->getType(), 1); // Handle a few RHS special cases. const SCEVConstant *RC = dyn_cast<SCEVConstant>(RHS); if (RC) { const APInt &RA = RC->getValue()->getValue(); // Handle x /s -1 as x * -1, to give ScalarEvolution a chance to do // some folding. if (RA.isAllOnesValue()) return SE.getMulExpr(LHS, RC); // Handle x /s 1 as x. if (RA == 1) return LHS; } // Check for a division of a constant by a constant. if (const SCEVConstant *C = dyn_cast<SCEVConstant>(LHS)) { if (!RC) return nullptr; const APInt &LA = C->getValue()->getValue(); const APInt &RA = RC->getValue()->getValue(); if (LA.srem(RA) != 0) return nullptr; return SE.getConstant(LA.sdiv(RA)); } // Distribute the sdiv over addrec operands, if the addrec doesn't overflow. if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS)) { if (IgnoreSignificantBits || isAddRecSExtable(AR, SE)) { const SCEV *Step = getExactSDiv(AR->getStepRecurrence(SE), RHS, SE, IgnoreSignificantBits); if (!Step) return nullptr; const SCEV *Start = getExactSDiv(AR->getStart(), RHS, SE, IgnoreSignificantBits); if (!Start) return nullptr; // FlagNW is independent of the start value, step direction, and is // preserved with smaller magnitude steps. // FIXME: AR->getNoWrapFlags(SCEV::FlagNW) return SE.getAddRecExpr(Start, Step, AR->getLoop(), SCEV::FlagAnyWrap); } return nullptr; } // Distribute the sdiv over add operands, if the add doesn't overflow. if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(LHS)) { if (IgnoreSignificantBits || isAddSExtable(Add, SE)) { SmallVector<const SCEV *, 8> Ops; for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end(); I != E; ++I) { const SCEV *Op = getExactSDiv(*I, RHS, SE, IgnoreSignificantBits); if (!Op) return nullptr; Ops.push_back(Op); } return SE.getAddExpr(Ops); } return nullptr; } // Check for a multiply operand that we can pull RHS out of. if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(LHS)) { if (IgnoreSignificantBits || isMulSExtable(Mul, SE)) { SmallVector<const SCEV *, 4> Ops; bool Found = false; for (SCEVMulExpr::op_iterator I = Mul->op_begin(), E = Mul->op_end(); I != E; ++I) { const SCEV *S = *I; if (!Found) if (const SCEV *Q = getExactSDiv(S, RHS, SE, IgnoreSignificantBits)) { S = Q; Found = true; } Ops.push_back(S); } return Found ? SE.getMulExpr(Ops) : nullptr; } return nullptr; } // Otherwise we don't know. return nullptr; } /// ExtractImmediate - If S involves the addition of a constant integer value, /// return that integer value, and mutate S to point to a new SCEV with that /// value excluded. static int64_t ExtractImmediate(const SCEV *&S, ScalarEvolution &SE) { if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S)) { if (C->getValue()->getValue().getMinSignedBits() <= 64) { S = SE.getConstant(C->getType(), 0); return C->getValue()->getSExtValue(); } } else if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { SmallVector<const SCEV *, 8> NewOps(Add->op_begin(), Add->op_end()); int64_t Result = ExtractImmediate(NewOps.front(), SE); if (Result != 0) S = SE.getAddExpr(NewOps); return Result; } else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { SmallVector<const SCEV *, 8> NewOps(AR->op_begin(), AR->op_end()); int64_t Result = ExtractImmediate(NewOps.front(), SE); if (Result != 0) S = SE.getAddRecExpr(NewOps, AR->getLoop(), // FIXME: AR->getNoWrapFlags(SCEV::FlagNW) SCEV::FlagAnyWrap); return Result; } return 0; } /// ExtractSymbol - If S involves the addition of a GlobalValue address, /// return that symbol, and mutate S to point to a new SCEV with that /// value excluded. static GlobalValue *ExtractSymbol(const SCEV *&S, ScalarEvolution &SE) { if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) { if (GlobalValue *GV = dyn_cast<GlobalValue>(U->getValue())) { S = SE.getConstant(GV->getType(), 0); return GV; } } else if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { SmallVector<const SCEV *, 8> NewOps(Add->op_begin(), Add->op_end()); GlobalValue *Result = ExtractSymbol(NewOps.back(), SE); if (Result) S = SE.getAddExpr(NewOps); return Result; } else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { SmallVector<const SCEV *, 8> NewOps(AR->op_begin(), AR->op_end()); GlobalValue *Result = ExtractSymbol(NewOps.front(), SE); if (Result) S = SE.getAddRecExpr(NewOps, AR->getLoop(), // FIXME: AR->getNoWrapFlags(SCEV::FlagNW) SCEV::FlagAnyWrap); return Result; } return nullptr; } /// isAddressUse - Returns true if the specified instruction is using the /// specified value as an address. static bool isAddressUse(Instruction *Inst, Value *OperandVal) { bool isAddress = isa<LoadInst>(Inst); if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { if (SI->getOperand(1) == OperandVal) isAddress = true; } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) { // Addressing modes can also be folded into prefetches and a variety // of intrinsics. switch (II->getIntrinsicID()) { default: break; case Intrinsic::prefetch: case Intrinsic::x86_sse_storeu_ps: case Intrinsic::x86_sse2_storeu_pd: case Intrinsic::x86_sse2_storeu_dq: case Intrinsic::x86_sse2_storel_dq: if (II->getArgOperand(0) == OperandVal) isAddress = true; break; } } return isAddress; } /// getAccessType - Return the type of the memory being accessed. static Type *getAccessType(const Instruction *Inst) { Type *AccessTy = Inst->getType(); if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) AccessTy = SI->getOperand(0)->getType(); else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) { // Addressing modes can also be folded into prefetches and a variety // of intrinsics. switch (II->getIntrinsicID()) { default: break; case Intrinsic::x86_sse_storeu_ps: case Intrinsic::x86_sse2_storeu_pd: case Intrinsic::x86_sse2_storeu_dq: case Intrinsic::x86_sse2_storel_dq: AccessTy = II->getArgOperand(0)->getType(); break; } } // All pointers have the same requirements, so canonicalize them to an // arbitrary pointer type to minimize variation. if (PointerType *PTy = dyn_cast<PointerType>(AccessTy)) AccessTy = PointerType::get(IntegerType::get(PTy->getContext(), 1), PTy->getAddressSpace()); return AccessTy; } /// isExistingPhi - Return true if this AddRec is already a phi in its loop. static bool isExistingPhi(const SCEVAddRecExpr *AR, ScalarEvolution &SE) { for (BasicBlock::iterator I = AR->getLoop()->getHeader()->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I) { if (SE.isSCEVable(PN->getType()) && (SE.getEffectiveSCEVType(PN->getType()) == SE.getEffectiveSCEVType(AR->getType())) && SE.getSCEV(PN) == AR) return true; } return false; } /// Check if expanding this expression is likely to incur significant cost. This /// is tricky because SCEV doesn't track which expressions are actually computed /// by the current IR. /// /// We currently allow expansion of IV increments that involve adds, /// multiplication by constants, and AddRecs from existing phis. /// /// TODO: Allow UDivExpr if we can find an existing IV increment that is an /// obvious multiple of the UDivExpr. static bool isHighCostExpansion(const SCEV *S, SmallPtrSetImpl<const SCEV*> &Processed, ScalarEvolution &SE) { // Zero/One operand expressions switch (S->getSCEVType()) { case scUnknown: case scConstant: return false; case scTruncate: return isHighCostExpansion(cast<SCEVTruncateExpr>(S)->getOperand(), Processed, SE); case scZeroExtend: return isHighCostExpansion(cast<SCEVZeroExtendExpr>(S)->getOperand(), Processed, SE); case scSignExtend: return isHighCostExpansion(cast<SCEVSignExtendExpr>(S)->getOperand(), Processed, SE); } if (!Processed.insert(S).second) return false; if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end(); I != E; ++I) { if (isHighCostExpansion(*I, Processed, SE)) return true; } return false; } if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) { if (Mul->getNumOperands() == 2) { // Multiplication by a constant is ok if (isa<SCEVConstant>(Mul->getOperand(0))) return isHighCostExpansion(Mul->getOperand(1), Processed, SE); // If we have the value of one operand, check if an existing // multiplication already generates this expression. if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(Mul->getOperand(1))) { Value *UVal = U->getValue(); for (User *UR : UVal->users()) { // If U is a constant, it may be used by a ConstantExpr. Instruction *UI = dyn_cast<Instruction>(UR); if (UI && UI->getOpcode() == Instruction::Mul && SE.isSCEVable(UI->getType())) { return SE.getSCEV(UI) == Mul; } } } } } if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { if (isExistingPhi(AR, SE)) return false; } // Fow now, consider any other type of expression (div/mul/min/max) high cost. return true; } /// DeleteTriviallyDeadInstructions - If any of the instructions is the /// specified set are trivially dead, delete them and see if this makes any of /// their operands subsequently dead. static bool DeleteTriviallyDeadInstructions(SmallVectorImpl<WeakVH> &DeadInsts) { bool Changed = false; while (!DeadInsts.empty()) { Value *V = DeadInsts.pop_back_val(); Instruction *I = dyn_cast_or_null<Instruction>(V); if (!I || !isInstructionTriviallyDead(I)) continue; for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) if (Instruction *U = dyn_cast<Instruction>(*OI)) { *OI = nullptr; if (U->use_empty()) DeadInsts.push_back(U); } I->eraseFromParent(); Changed = true; } return Changed; } namespace { class LSRUse; } /// \brief Check if the addressing mode defined by \p F is completely /// folded in \p LU at isel time. /// This includes address-mode folding and special icmp tricks. /// This function returns true if \p LU can accommodate what \p F /// defines and up to 1 base + 1 scaled + offset. /// In other words, if \p F has several base registers, this function may /// still return true. Therefore, users still need to account for /// additional base registers and/or unfolded offsets to derive an /// accurate cost model. static bool isAMCompletelyFolded(const TargetTransformInfo &TTI, const LSRUse &LU, const Formula &F); // Get the cost of the scaling factor used in F for LU. static unsigned getScalingFactorCost(const TargetTransformInfo &TTI, const LSRUse &LU, const Formula &F); namespace { /// Cost - This class is used to measure and compare candidate formulae. class Cost { /// TODO: Some of these could be merged. Also, a lexical ordering /// isn't always optimal. unsigned NumRegs; unsigned AddRecCost; unsigned NumIVMuls; unsigned NumBaseAdds; unsigned ImmCost; unsigned SetupCost; unsigned ScaleCost; public: Cost() : NumRegs(0), AddRecCost(0), NumIVMuls(0), NumBaseAdds(0), ImmCost(0), SetupCost(0), ScaleCost(0) {} bool operator<(const Cost &Other) const; void Lose(); #ifndef NDEBUG // Once any of the metrics loses, they must all remain losers. bool isValid() { return ((NumRegs | AddRecCost | NumIVMuls | NumBaseAdds | ImmCost | SetupCost | ScaleCost) != ~0u) || ((NumRegs & AddRecCost & NumIVMuls & NumBaseAdds & ImmCost & SetupCost & ScaleCost) == ~0u); } #endif bool isLoser() { assert(isValid() && "invalid cost"); return NumRegs == ~0u; } void RateFormula(const TargetTransformInfo &TTI, const Formula &F, SmallPtrSetImpl<const SCEV *> &Regs, const DenseSet<const SCEV *> &VisitedRegs, const Loop *L, const SmallVectorImpl<int64_t> &Offsets, ScalarEvolution &SE, DominatorTree &DT, const LSRUse &LU, SmallPtrSetImpl<const SCEV *> *LoserRegs = nullptr); void print(raw_ostream &OS) const; void dump() const; private: void RateRegister(const SCEV *Reg, SmallPtrSetImpl<const SCEV *> &Regs, const Loop *L, ScalarEvolution &SE, DominatorTree &DT); void RatePrimaryRegister(const SCEV *Reg, SmallPtrSetImpl<const SCEV *> &Regs, const Loop *L, ScalarEvolution &SE, DominatorTree &DT, SmallPtrSetImpl<const SCEV *> *LoserRegs); }; } /// RateRegister - Tally up interesting quantities from the given register. void Cost::RateRegister(const SCEV *Reg, SmallPtrSetImpl<const SCEV *> &Regs, const Loop *L, ScalarEvolution &SE, DominatorTree &DT) { if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Reg)) { // If this is an addrec for another loop, don't second-guess its addrec phi // nodes. LSR isn't currently smart enough to reason about more than one // loop at a time. LSR has already run on inner loops, will not run on outer // loops, and cannot be expected to change sibling loops. if (AR->getLoop() != L) { // If the AddRec exists, consider it's register free and leave it alone. if (isExistingPhi(AR, SE)) return; // Otherwise, do not consider this formula at all. Lose(); return; } AddRecCost += 1; /// TODO: This should be a function of the stride. // Add the step value register, if it needs one. // TODO: The non-affine case isn't precisely modeled here. if (!AR->isAffine() || !isa<SCEVConstant>(AR->getOperand(1))) { if (!Regs.count(AR->getOperand(1))) { RateRegister(AR->getOperand(1), Regs, L, SE, DT); if (isLoser()) return; } } } ++NumRegs; // Rough heuristic; favor registers which don't require extra setup // instructions in the preheader. if (!isa<SCEVUnknown>(Reg) && !isa<SCEVConstant>(Reg) && !(isa<SCEVAddRecExpr>(Reg) && (isa<SCEVUnknown>(cast<SCEVAddRecExpr>(Reg)->getStart()) || isa<SCEVConstant>(cast<SCEVAddRecExpr>(Reg)->getStart())))) ++SetupCost; NumIVMuls += isa<SCEVMulExpr>(Reg) && SE.hasComputableLoopEvolution(Reg, L); } /// RatePrimaryRegister - Record this register in the set. If we haven't seen it /// before, rate it. Optional LoserRegs provides a way to declare any formula /// that refers to one of those regs an instant loser. void Cost::RatePrimaryRegister(const SCEV *Reg, SmallPtrSetImpl<const SCEV *> &Regs, const Loop *L, ScalarEvolution &SE, DominatorTree &DT, SmallPtrSetImpl<const SCEV *> *LoserRegs) { if (LoserRegs && LoserRegs->count(Reg)) { Lose(); return; } if (Regs.insert(Reg).second) { RateRegister(Reg, Regs, L, SE, DT); if (LoserRegs && isLoser()) LoserRegs->insert(Reg); } } void Cost::RateFormula(const TargetTransformInfo &TTI, const Formula &F, SmallPtrSetImpl<const SCEV *> &Regs, const DenseSet<const SCEV *> &VisitedRegs, const Loop *L, const SmallVectorImpl<int64_t> &Offsets, ScalarEvolution &SE, DominatorTree &DT, const LSRUse &LU, SmallPtrSetImpl<const SCEV *> *LoserRegs) { assert(F.isCanonical() && "Cost is accurate only for canonical formula"); // Tally up the registers. if (const SCEV *ScaledReg = F.ScaledReg) { if (VisitedRegs.count(ScaledReg)) { Lose(); return; } RatePrimaryRegister(ScaledReg, Regs, L, SE, DT, LoserRegs); if (isLoser()) return; } for (SmallVectorImpl<const SCEV *>::const_iterator I = F.BaseRegs.begin(), E = F.BaseRegs.end(); I != E; ++I) { const SCEV *BaseReg = *I; if (VisitedRegs.count(BaseReg)) { Lose(); return; } RatePrimaryRegister(BaseReg, Regs, L, SE, DT, LoserRegs); if (isLoser()) return; } // Determine how many (unfolded) adds we'll need inside the loop. size_t NumBaseParts = F.getNumRegs(); if (NumBaseParts > 1) // Do not count the base and a possible second register if the target // allows to fold 2 registers. NumBaseAdds += NumBaseParts - (1 + (F.Scale && isAMCompletelyFolded(TTI, LU, F))); NumBaseAdds += (F.UnfoldedOffset != 0); // Accumulate non-free scaling amounts. ScaleCost += getScalingFactorCost(TTI, LU, F); // Tally up the non-zero immediates. for (SmallVectorImpl<int64_t>::const_iterator I = Offsets.begin(), E = Offsets.end(); I != E; ++I) { int64_t Offset = (uint64_t)*I + F.BaseOffset; if (F.BaseGV) ImmCost += 64; // Handle symbolic values conservatively. // TODO: This should probably be the pointer size. else if (Offset != 0) ImmCost += APInt(64, Offset, true).getMinSignedBits(); } assert(isValid() && "invalid cost"); } /// Lose - Set this cost to a losing value. void Cost::Lose() { NumRegs = ~0u; AddRecCost = ~0u; NumIVMuls = ~0u; NumBaseAdds = ~0u; ImmCost = ~0u; SetupCost = ~0u; ScaleCost = ~0u; } /// operator< - Choose the lower cost. bool Cost::operator<(const Cost &Other) const { return std::tie(NumRegs, AddRecCost, NumIVMuls, NumBaseAdds, ScaleCost, ImmCost, SetupCost) < std::tie(Other.NumRegs, Other.AddRecCost, Other.NumIVMuls, Other.NumBaseAdds, Other.ScaleCost, Other.ImmCost, Other.SetupCost); } void Cost::print(raw_ostream &OS) const { OS << NumRegs << " reg" << (NumRegs == 1 ? "" : "s"); if (AddRecCost != 0) OS << ", with addrec cost " << AddRecCost; if (NumIVMuls != 0) OS << ", plus " << NumIVMuls << " IV mul" << (NumIVMuls == 1 ? "" : "s"); if (NumBaseAdds != 0) OS << ", plus " << NumBaseAdds << " base add" << (NumBaseAdds == 1 ? "" : "s"); if (ScaleCost != 0) OS << ", plus " << ScaleCost << " scale cost"; if (ImmCost != 0) OS << ", plus " << ImmCost << " imm cost"; if (SetupCost != 0) OS << ", plus " << SetupCost << " setup cost"; } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void Cost::dump() const { print(errs()); errs() << '\n'; } #endif namespace { /// LSRFixup - An operand value in an instruction which is to be replaced /// with some equivalent, possibly strength-reduced, replacement. struct LSRFixup { /// UserInst - The instruction which will be updated. Instruction *UserInst; /// OperandValToReplace - The operand of the instruction which will /// be replaced. The operand may be used more than once; every instance /// will be replaced. Value *OperandValToReplace; /// PostIncLoops - If this user is to use the post-incremented value of an /// induction variable, this variable is non-null and holds the loop /// associated with the induction variable. PostIncLoopSet PostIncLoops; /// LUIdx - The index of the LSRUse describing the expression which /// this fixup needs, minus an offset (below). size_t LUIdx; /// Offset - A constant offset to be added to the LSRUse expression. /// This allows multiple fixups to share the same LSRUse with different /// offsets, for example in an unrolled loop. int64_t Offset; bool isUseFullyOutsideLoop(const Loop *L) const; LSRFixup(); void print(raw_ostream &OS) const; void dump() const; }; } LSRFixup::LSRFixup() : UserInst(nullptr), OperandValToReplace(nullptr), LUIdx(~size_t(0)), Offset(0) {} /// isUseFullyOutsideLoop - Test whether this fixup always uses its /// value outside of the given loop. bool LSRFixup::isUseFullyOutsideLoop(const Loop *L) const { // PHI nodes use their value in their incoming blocks. if (const PHINode *PN = dyn_cast<PHINode>(UserInst)) { for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) if (PN->getIncomingValue(i) == OperandValToReplace && L->contains(PN->getIncomingBlock(i))) return false; return true; } return !L->contains(UserInst); } void LSRFixup::print(raw_ostream &OS) const { OS << "UserInst="; // Store is common and interesting enough to be worth special-casing. if (StoreInst *Store = dyn_cast<StoreInst>(UserInst)) { OS << "store "; Store->getOperand(0)->printAsOperand(OS, /*PrintType=*/false); } else if (UserInst->getType()->isVoidTy()) OS << UserInst->getOpcodeName(); else UserInst->printAsOperand(OS, /*PrintType=*/false); OS << ", OperandValToReplace="; OperandValToReplace->printAsOperand(OS, /*PrintType=*/false); for (PostIncLoopSet::const_iterator I = PostIncLoops.begin(), E = PostIncLoops.end(); I != E; ++I) { OS << ", PostIncLoop="; (*I)->getHeader()->printAsOperand(OS, /*PrintType=*/false); } if (LUIdx != ~size_t(0)) OS << ", LUIdx=" << LUIdx; if (Offset != 0) OS << ", Offset=" << Offset; } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void LSRFixup::dump() const { print(errs()); errs() << '\n'; } #endif namespace { /// UniquifierDenseMapInfo - A DenseMapInfo implementation for holding /// DenseMaps and DenseSets of sorted SmallVectors of const SCEV*. struct UniquifierDenseMapInfo { static SmallVector<const SCEV *, 4> getEmptyKey() { SmallVector<const SCEV *, 4> V; V.push_back(reinterpret_cast<const SCEV *>(-1)); return V; } static SmallVector<const SCEV *, 4> getTombstoneKey() { SmallVector<const SCEV *, 4> V; V.push_back(reinterpret_cast<const SCEV *>(-2)); return V; } static unsigned getHashValue(const SmallVector<const SCEV *, 4> &V) { return static_cast<unsigned>(hash_combine_range(V.begin(), V.end())); } static bool isEqual(const SmallVector<const SCEV *, 4> &LHS, const SmallVector<const SCEV *, 4> &RHS) { return LHS == RHS; } }; /// LSRUse - This class holds the state that LSR keeps for each use in /// IVUsers, as well as uses invented by LSR itself. It includes information /// about what kinds of things can be folded into the user, information about /// the user itself, and information about how the use may be satisfied. /// TODO: Represent multiple users of the same expression in common? class LSRUse { DenseSet<SmallVector<const SCEV *, 4>, UniquifierDenseMapInfo> Uniquifier; public: /// KindType - An enum for a kind of use, indicating what types of /// scaled and immediate operands it might support. enum KindType { Basic, ///< A normal use, with no folding. Special, ///< A special case of basic, allowing -1 scales. Address, ///< An address use; folding according to TargetLowering ICmpZero ///< An equality icmp with both operands folded into one. // TODO: Add a generic icmp too? }; typedef PointerIntPair<const SCEV *, 2, KindType> SCEVUseKindPair; KindType Kind; Type *AccessTy; SmallVector<int64_t, 8> Offsets; int64_t MinOffset; int64_t MaxOffset; /// AllFixupsOutsideLoop - This records whether all of the fixups using this /// LSRUse are outside of the loop, in which case some special-case heuristics /// may be used. bool AllFixupsOutsideLoop; /// RigidFormula is set to true to guarantee that this use will be associated /// with a single formula--the one that initially matched. Some SCEV /// expressions cannot be expanded. This allows LSR to consider the registers /// used by those expressions without the need to expand them later after /// changing the formula. bool RigidFormula; /// WidestFixupType - This records the widest use type for any fixup using /// this LSRUse. FindUseWithSimilarFormula can't consider uses with different /// max fixup widths to be equivalent, because the narrower one may be relying /// on the implicit truncation to truncate away bogus bits. Type *WidestFixupType; /// Formulae - A list of ways to build a value that can satisfy this user. /// After the list is populated, one of these is selected heuristically and /// used to formulate a replacement for OperandValToReplace in UserInst. SmallVector<Formula, 12> Formulae; /// Regs - The set of register candidates used by all formulae in this LSRUse. SmallPtrSet<const SCEV *, 4> Regs; LSRUse(KindType K, Type *T) : Kind(K), AccessTy(T), MinOffset(INT64_MAX), MaxOffset(INT64_MIN), AllFixupsOutsideLoop(true), RigidFormula(false), WidestFixupType(nullptr) {} bool HasFormulaWithSameRegs(const Formula &F) const; bool InsertFormula(const Formula &F); void DeleteFormula(Formula &F); void RecomputeRegs(size_t LUIdx, RegUseTracker &Reguses); void print(raw_ostream &OS) const; void dump() const; }; } /// HasFormula - Test whether this use as a formula which has the same /// registers as the given formula. bool LSRUse::HasFormulaWithSameRegs(const Formula &F) const { SmallVector<const SCEV *, 4> Key = F.BaseRegs; if (F.ScaledReg) Key.push_back(F.ScaledReg); // Unstable sort by host order ok, because this is only used for uniquifying. std::sort(Key.begin(), Key.end()); return Uniquifier.count(Key); } /// InsertFormula - If the given formula has not yet been inserted, add it to /// the list, and return true. Return false otherwise. /// The formula must be in canonical form. bool LSRUse::InsertFormula(const Formula &F) { assert(F.isCanonical() && "Invalid canonical representation"); if (!Formulae.empty() && RigidFormula) return false; SmallVector<const SCEV *, 4> Key = F.BaseRegs; if (F.ScaledReg) Key.push_back(F.ScaledReg); // Unstable sort by host order ok, because this is only used for uniquifying. std::sort(Key.begin(), Key.end()); if (!Uniquifier.insert(Key).second) return false; // Using a register to hold the value of 0 is not profitable. assert((!F.ScaledReg || !F.ScaledReg->isZero()) && "Zero allocated in a scaled register!"); #ifndef NDEBUG for (SmallVectorImpl<const SCEV *>::const_iterator I = F.BaseRegs.begin(), E = F.BaseRegs.end(); I != E; ++I) assert(!(*I)->isZero() && "Zero allocated in a base register!"); #endif // Add the formula to the list. Formulae.push_back(F); // Record registers now being used by this use. Regs.insert(F.BaseRegs.begin(), F.BaseRegs.end()); if (F.ScaledReg) Regs.insert(F.ScaledReg); return true; } /// DeleteFormula - Remove the given formula from this use's list. void LSRUse::DeleteFormula(Formula &F) { if (&F != &Formulae.back()) std::swap(F, Formulae.back()); Formulae.pop_back(); } /// RecomputeRegs - Recompute the Regs field, and update RegUses. void LSRUse::RecomputeRegs(size_t LUIdx, RegUseTracker &RegUses) { // Now that we've filtered out some formulae, recompute the Regs set. SmallPtrSet<const SCEV *, 4> OldRegs = Regs; Regs.clear(); for (SmallVectorImpl<Formula>::const_iterator I = Formulae.begin(), E = Formulae.end(); I != E; ++I) { const Formula &F = *I; if (F.ScaledReg) Regs.insert(F.ScaledReg); Regs.insert(F.BaseRegs.begin(), F.BaseRegs.end()); } // Update the RegTracker. for (const SCEV *S : OldRegs) if (!Regs.count(S)) RegUses.DropRegister(S, LUIdx); } void LSRUse::print(raw_ostream &OS) const { OS << "LSR Use: Kind="; switch (Kind) { case Basic: OS << "Basic"; break; case Special: OS << "Special"; break; case ICmpZero: OS << "ICmpZero"; break; case Address: OS << "Address of "; if (AccessTy->isPointerTy()) OS << "pointer"; // the full pointer type could be really verbose else OS << *AccessTy; } OS << ", Offsets={"; for (SmallVectorImpl<int64_t>::const_iterator I = Offsets.begin(), E = Offsets.end(); I != E; ++I) { OS << *I; if (std::next(I) != E) OS << ','; } OS << '}'; if (AllFixupsOutsideLoop) OS << ", all-fixups-outside-loop"; if (WidestFixupType) OS << ", widest fixup type: " << *WidestFixupType; } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void LSRUse::dump() const { print(errs()); errs() << '\n'; } #endif static bool isAMCompletelyFolded(const TargetTransformInfo &TTI, LSRUse::KindType Kind, Type *AccessTy, GlobalValue *BaseGV, int64_t BaseOffset, bool HasBaseReg, int64_t Scale) { switch (Kind) { case LSRUse::Address: return TTI.isLegalAddressingMode(AccessTy, BaseGV, BaseOffset, HasBaseReg, Scale); // Otherwise, just guess that reg+reg addressing is legal. //return ; case LSRUse::ICmpZero: // There's not even a target hook for querying whether it would be legal to // fold a GV into an ICmp. if (BaseGV) return false; // ICmp only has two operands; don't allow more than two non-trivial parts. if (Scale != 0 && HasBaseReg && BaseOffset != 0) return false; // ICmp only supports no scale or a -1 scale, as we can "fold" a -1 scale by // putting the scaled register in the other operand of the icmp. if (Scale != 0 && Scale != -1) return false; // If we have low-level target information, ask the target if it can fold an // integer immediate on an icmp. if (BaseOffset != 0) { // We have one of: // ICmpZero BaseReg + BaseOffset => ICmp BaseReg, -BaseOffset // ICmpZero -1*ScaleReg + BaseOffset => ICmp ScaleReg, BaseOffset // Offs is the ICmp immediate. if (Scale == 0) // The cast does the right thing with INT64_MIN. BaseOffset = -(uint64_t)BaseOffset; return TTI.isLegalICmpImmediate(BaseOffset); } // ICmpZero BaseReg + -1*ScaleReg => ICmp BaseReg, ScaleReg return true; case LSRUse::Basic: // Only handle single-register values. return !BaseGV && Scale == 0 && BaseOffset == 0; case LSRUse::Special: // Special case Basic to handle -1 scales. return !BaseGV && (Scale == 0 || Scale == -1) && BaseOffset == 0; } llvm_unreachable("Invalid LSRUse Kind!"); } static bool isAMCompletelyFolded(const TargetTransformInfo &TTI, int64_t MinOffset, int64_t MaxOffset, LSRUse::KindType Kind, Type *AccessTy, GlobalValue *BaseGV, int64_t BaseOffset, bool HasBaseReg, int64_t Scale) { // Check for overflow. if (((int64_t)((uint64_t)BaseOffset + MinOffset) > BaseOffset) != (MinOffset > 0)) return false; MinOffset = (uint64_t)BaseOffset + MinOffset; if (((int64_t)((uint64_t)BaseOffset + MaxOffset) > BaseOffset) != (MaxOffset > 0)) return false; MaxOffset = (uint64_t)BaseOffset + MaxOffset; return isAMCompletelyFolded(TTI, Kind, AccessTy, BaseGV, MinOffset, HasBaseReg, Scale) && isAMCompletelyFolded(TTI, Kind, AccessTy, BaseGV, MaxOffset, HasBaseReg, Scale); } static bool isAMCompletelyFolded(const TargetTransformInfo &TTI, int64_t MinOffset, int64_t MaxOffset, LSRUse::KindType Kind, Type *AccessTy, const Formula &F) { // For the purpose of isAMCompletelyFolded either having a canonical formula // or a scale not equal to zero is correct. // Problems may arise from non canonical formulae having a scale == 0. // Strictly speaking it would best to just rely on canonical formulae. // However, when we generate the scaled formulae, we first check that the // scaling factor is profitable before computing the actual ScaledReg for // compile time sake. assert((F.isCanonical() || F.Scale != 0)); return isAMCompletelyFolded(TTI, MinOffset, MaxOffset, Kind, AccessTy, F.BaseGV, F.BaseOffset, F.HasBaseReg, F.Scale); } /// isLegalUse - Test whether we know how to expand the current formula. static bool isLegalUse(const TargetTransformInfo &TTI, int64_t MinOffset, int64_t MaxOffset, LSRUse::KindType Kind, Type *AccessTy, GlobalValue *BaseGV, int64_t BaseOffset, bool HasBaseReg, int64_t Scale) { // We know how to expand completely foldable formulae. return isAMCompletelyFolded(TTI, MinOffset, MaxOffset, Kind, AccessTy, BaseGV, BaseOffset, HasBaseReg, Scale) || // Or formulae that use a base register produced by a sum of base // registers. (Scale == 1 && isAMCompletelyFolded(TTI, MinOffset, MaxOffset, Kind, AccessTy, BaseGV, BaseOffset, true, 0)); } static bool isLegalUse(const TargetTransformInfo &TTI, int64_t MinOffset, int64_t MaxOffset, LSRUse::KindType Kind, Type *AccessTy, const Formula &F) { return isLegalUse(TTI, MinOffset, MaxOffset, Kind, AccessTy, F.BaseGV, F.BaseOffset, F.HasBaseReg, F.Scale); } static bool isAMCompletelyFolded(const TargetTransformInfo &TTI, const LSRUse &LU, const Formula &F) { return isAMCompletelyFolded(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, F.BaseGV, F.BaseOffset, F.HasBaseReg, F.Scale); } static unsigned getScalingFactorCost(const TargetTransformInfo &TTI, const LSRUse &LU, const Formula &F) { if (!F.Scale) return 0; // If the use is not completely folded in that instruction, we will have to // pay an extra cost only for scale != 1. if (!isAMCompletelyFolded(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, F)) return F.Scale != 1; switch (LU.Kind) { case LSRUse::Address: { // Check the scaling factor cost with both the min and max offsets. int ScaleCostMinOffset = TTI.getScalingFactorCost(LU.AccessTy, F.BaseGV, F.BaseOffset + LU.MinOffset, F.HasBaseReg, F.Scale); int ScaleCostMaxOffset = TTI.getScalingFactorCost(LU.AccessTy, F.BaseGV, F.BaseOffset + LU.MaxOffset, F.HasBaseReg, F.Scale); assert(ScaleCostMinOffset >= 0 && ScaleCostMaxOffset >= 0 && "Legal addressing mode has an illegal cost!"); return std::max(ScaleCostMinOffset, ScaleCostMaxOffset); } case LSRUse::ICmpZero: case LSRUse::Basic: case LSRUse::Special: // The use is completely folded, i.e., everything is folded into the // instruction. return 0; } llvm_unreachable("Invalid LSRUse Kind!"); } static bool isAlwaysFoldable(const TargetTransformInfo &TTI, LSRUse::KindType Kind, Type *AccessTy, GlobalValue *BaseGV, int64_t BaseOffset, bool HasBaseReg) { // Fast-path: zero is always foldable. if (BaseOffset == 0 && !BaseGV) return true; // Conservatively, create an address with an immediate and a // base and a scale. int64_t Scale = Kind == LSRUse::ICmpZero ? -1 : 1; // Canonicalize a scale of 1 to a base register if the formula doesn't // already have a base register. if (!HasBaseReg && Scale == 1) { Scale = 0; HasBaseReg = true; } return isAMCompletelyFolded(TTI, Kind, AccessTy, BaseGV, BaseOffset, HasBaseReg, Scale); } static bool isAlwaysFoldable(const TargetTransformInfo &TTI, ScalarEvolution &SE, int64_t MinOffset, int64_t MaxOffset, LSRUse::KindType Kind, Type *AccessTy, const SCEV *S, bool HasBaseReg) { // Fast-path: zero is always foldable. if (S->isZero()) return true; // Conservatively, create an address with an immediate and a // base and a scale. int64_t BaseOffset = ExtractImmediate(S, SE); GlobalValue *BaseGV = ExtractSymbol(S, SE); // If there's anything else involved, it's not foldable. if (!S->isZero()) return false; // Fast-path: zero is always foldable. if (BaseOffset == 0 && !BaseGV) return true; // Conservatively, create an address with an immediate and a // base and a scale. int64_t Scale = Kind == LSRUse::ICmpZero ? -1 : 1; return isAMCompletelyFolded(TTI, MinOffset, MaxOffset, Kind, AccessTy, BaseGV, BaseOffset, HasBaseReg, Scale); } namespace { /// IVInc - An individual increment in a Chain of IV increments. /// Relate an IV user to an expression that computes the IV it uses from the IV /// used by the previous link in the Chain. /// /// For the head of a chain, IncExpr holds the absolute SCEV expression for the /// original IVOperand. The head of the chain's IVOperand is only valid during /// chain collection, before LSR replaces IV users. During chain generation, /// IncExpr can be used to find the new IVOperand that computes the same /// expression. struct IVInc { Instruction *UserInst; Value* IVOperand; const SCEV *IncExpr; IVInc(Instruction *U, Value *O, const SCEV *E): UserInst(U), IVOperand(O), IncExpr(E) {} }; // IVChain - The list of IV increments in program order. // We typically add the head of a chain without finding subsequent links. struct IVChain { SmallVector<IVInc,1> Incs; const SCEV *ExprBase; IVChain() : ExprBase(nullptr) {} IVChain(const IVInc &Head, const SCEV *Base) : Incs(1, Head), ExprBase(Base) {} typedef SmallVectorImpl<IVInc>::const_iterator const_iterator; // begin - return the first increment in the chain. const_iterator begin() const { assert(!Incs.empty()); return std::next(Incs.begin()); } const_iterator end() const { return Incs.end(); } // hasIncs - Returns true if this chain contains any increments. bool hasIncs() const { return Incs.size() >= 2; } // add - Add an IVInc to the end of this chain. void add(const IVInc &X) { Incs.push_back(X); } // tailUserInst - Returns the last UserInst in the chain. Instruction *tailUserInst() const { return Incs.back().UserInst; } // isProfitableIncrement - Returns true if IncExpr can be profitably added to // this chain. bool isProfitableIncrement(const SCEV *OperExpr, const SCEV *IncExpr, ScalarEvolution&); }; /// ChainUsers - Helper for CollectChains to track multiple IV increment uses. /// Distinguish between FarUsers that definitely cross IV increments and /// NearUsers that may be used between IV increments. struct ChainUsers { SmallPtrSet<Instruction*, 4> FarUsers; SmallPtrSet<Instruction*, 4> NearUsers; }; /// LSRInstance - This class holds state for the main loop strength reduction /// logic. class LSRInstance { IVUsers &IU; ScalarEvolution &SE; DominatorTree &DT; LoopInfo &LI; const TargetTransformInfo &TTI; Loop *const L; bool Changed; /// IVIncInsertPos - This is the insert position that the current loop's /// induction variable increment should be placed. In simple loops, this is /// the latch block's terminator. But in more complicated cases, this is a /// position which will dominate all the in-loop post-increment users. Instruction *IVIncInsertPos; /// Factors - Interesting factors between use strides. SmallSetVector<int64_t, 8> Factors; /// Types - Interesting use types, to facilitate truncation reuse. SmallSetVector<Type *, 4> Types; /// Fixups - The list of operands which are to be replaced. SmallVector<LSRFixup, 16> Fixups; /// Uses - The list of interesting uses. SmallVector<LSRUse, 16> Uses; /// RegUses - Track which uses use which register candidates. RegUseTracker RegUses; // Limit the number of chains to avoid quadratic behavior. We don't expect to // have more than a few IV increment chains in a loop. Missing a Chain falls // back to normal LSR behavior for those uses. static const unsigned MaxChains = 8; /// IVChainVec - IV users can form a chain of IV increments. SmallVector<IVChain, MaxChains> IVChainVec; /// IVIncSet - IV users that belong to profitable IVChains. SmallPtrSet<Use*, MaxChains> IVIncSet; void OptimizeShadowIV(); bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse); ICmpInst *OptimizeMax(ICmpInst *Cond, IVStrideUse* &CondUse); void OptimizeLoopTermCond(); void ChainInstruction(Instruction *UserInst, Instruction *IVOper, SmallVectorImpl<ChainUsers> &ChainUsersVec); void FinalizeChain(IVChain &Chain); void CollectChains(); void GenerateIVChain(const IVChain &Chain, SCEVExpander &Rewriter, SmallVectorImpl<WeakVH> &DeadInsts); void CollectInterestingTypesAndFactors(); void CollectFixupsAndInitialFormulae(); LSRFixup &getNewFixup() { Fixups.push_back(LSRFixup()); return Fixups.back(); } // Support for sharing of LSRUses between LSRFixups. typedef DenseMap<LSRUse::SCEVUseKindPair, size_t> UseMapTy; UseMapTy UseMap; bool reconcileNewOffset(LSRUse &LU, int64_t NewOffset, bool HasBaseReg, LSRUse::KindType Kind, Type *AccessTy); std::pair<size_t, int64_t> getUse(const SCEV *&Expr, LSRUse::KindType Kind, Type *AccessTy); void DeleteUse(LSRUse &LU, size_t LUIdx); LSRUse *FindUseWithSimilarFormula(const Formula &F, const LSRUse &OrigLU); void InsertInitialFormula(const SCEV *S, LSRUse &LU, size_t LUIdx); void InsertSupplementalFormula(const SCEV *S, LSRUse &LU, size_t LUIdx); void CountRegisters(const Formula &F, size_t LUIdx); bool InsertFormula(LSRUse &LU, unsigned LUIdx, const Formula &F); void CollectLoopInvariantFixupsAndFormulae(); void GenerateReassociations(LSRUse &LU, unsigned LUIdx, Formula Base, unsigned Depth = 0); void GenerateReassociationsImpl(LSRUse &LU, unsigned LUIdx, const Formula &Base, unsigned Depth, size_t Idx, bool IsScaledReg = false); void GenerateCombinations(LSRUse &LU, unsigned LUIdx, Formula Base); void GenerateSymbolicOffsetsImpl(LSRUse &LU, unsigned LUIdx, const Formula &Base, size_t Idx, bool IsScaledReg = false); void GenerateSymbolicOffsets(LSRUse &LU, unsigned LUIdx, Formula Base); void GenerateConstantOffsetsImpl(LSRUse &LU, unsigned LUIdx, const Formula &Base, const SmallVectorImpl<int64_t> &Worklist, size_t Idx, bool IsScaledReg = false); void GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx, Formula Base); void GenerateICmpZeroScales(LSRUse &LU, unsigned LUIdx, Formula Base); void GenerateScales(LSRUse &LU, unsigned LUIdx, Formula Base); void GenerateTruncates(LSRUse &LU, unsigned LUIdx, Formula Base); void GenerateCrossUseConstantOffsets(); void GenerateAllReuseFormulae(); void FilterOutUndesirableDedicatedRegisters(); size_t EstimateSearchSpaceComplexity() const; void NarrowSearchSpaceByDetectingSupersets(); void NarrowSearchSpaceByCollapsingUnrolledCode(); void NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters(); void NarrowSearchSpaceByPickingWinnerRegs(); void NarrowSearchSpaceUsingHeuristics(); void SolveRecurse(SmallVectorImpl<const Formula *> &Solution, Cost &SolutionCost, SmallVectorImpl<const Formula *> &Workspace, const Cost &CurCost, const SmallPtrSet<const SCEV *, 16> &CurRegs, DenseSet<const SCEV *> &VisitedRegs) const; void Solve(SmallVectorImpl<const Formula *> &Solution) const; BasicBlock::iterator HoistInsertPosition(BasicBlock::iterator IP, const SmallVectorImpl<Instruction *> &Inputs) const; BasicBlock::iterator AdjustInsertPositionForExpand(BasicBlock::iterator IP, const LSRFixup &LF, const LSRUse &LU, SCEVExpander &Rewriter) const; Value *Expand(const LSRFixup &LF, const Formula &F, BasicBlock::iterator IP, SCEVExpander &Rewriter, SmallVectorImpl<WeakVH> &DeadInsts) const; void RewriteForPHI(PHINode *PN, const LSRFixup &LF, const Formula &F, SCEVExpander &Rewriter, SmallVectorImpl<WeakVH> &DeadInsts, Pass *P) const; void Rewrite(const LSRFixup &LF, const Formula &F, SCEVExpander &Rewriter, SmallVectorImpl<WeakVH> &DeadInsts, Pass *P) const; void ImplementSolution(const SmallVectorImpl<const Formula *> &Solution, Pass *P); public: LSRInstance(Loop *L, Pass *P); bool getChanged() const { return Changed; } void print_factors_and_types(raw_ostream &OS) const; void print_fixups(raw_ostream &OS) const; void print_uses(raw_ostream &OS) const; void print(raw_ostream &OS) const; void dump() const; }; } /// OptimizeShadowIV - If IV is used in a int-to-float cast /// inside the loop then try to eliminate the cast operation. void LSRInstance::OptimizeShadowIV() { const SCEV *BackedgeTakenCount = SE.getBackedgeTakenCount(L); if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) return; for (IVUsers::const_iterator UI = IU.begin(), E = IU.end(); UI != E; /* empty */) { IVUsers::const_iterator CandidateUI = UI; ++UI; Instruction *ShadowUse = CandidateUI->getUser(); Type *DestTy = nullptr; bool IsSigned = false; /* If shadow use is a int->float cast then insert a second IV to eliminate this cast. for (unsigned i = 0; i < n; ++i) foo((double)i); is transformed into double d = 0.0; for (unsigned i = 0; i < n; ++i, ++d) foo(d); */ if (UIToFPInst *UCast = dyn_cast<UIToFPInst>(CandidateUI->getUser())) { IsSigned = false; DestTy = UCast->getDestTy(); } else if (SIToFPInst *SCast = dyn_cast<SIToFPInst>(CandidateUI->getUser())) { IsSigned = true; DestTy = SCast->getDestTy(); } if (!DestTy) continue; // If target does not support DestTy natively then do not apply // this transformation. if (!TTI.isTypeLegal(DestTy)) continue; PHINode *PH = dyn_cast<PHINode>(ShadowUse->getOperand(0)); if (!PH) continue; if (PH->getNumIncomingValues() != 2) continue; Type *SrcTy = PH->getType(); int Mantissa = DestTy->getFPMantissaWidth(); if (Mantissa == -1) continue; if ((int)SE.getTypeSizeInBits(SrcTy) > Mantissa) continue; unsigned Entry, Latch; if (PH->getIncomingBlock(0) == L->getLoopPreheader()) { Entry = 0; Latch = 1; } else { Entry = 1; Latch = 0; } ConstantInt *Init = dyn_cast<ConstantInt>(PH->getIncomingValue(Entry)); if (!Init) continue; Constant *NewInit = ConstantFP::get(DestTy, IsSigned ? (double)Init->getSExtValue() : (double)Init->getZExtValue()); BinaryOperator *Incr = dyn_cast<BinaryOperator>(PH->getIncomingValue(Latch)); if (!Incr) continue; if (Incr->getOpcode() != Instruction::Add && Incr->getOpcode() != Instruction::Sub) continue; /* Initialize new IV, double d = 0.0 in above example. */ ConstantInt *C = nullptr; if (Incr->getOperand(0) == PH) C = dyn_cast<ConstantInt>(Incr->getOperand(1)); else if (Incr->getOperand(1) == PH) C = dyn_cast<ConstantInt>(Incr->getOperand(0)); else continue; if (!C) continue; // Ignore negative constants, as the code below doesn't handle them // correctly. TODO: Remove this restriction. if (!C->getValue().isStrictlyPositive()) continue; /* Add new PHINode. */ PHINode *NewPH = PHINode::Create(DestTy, 2, "IV.S.", PH); /* create new increment. '++d' in above example. */ Constant *CFP = ConstantFP::get(DestTy, C->getZExtValue()); BinaryOperator *NewIncr = BinaryOperator::Create(Incr->getOpcode() == Instruction::Add ? Instruction::FAdd : Instruction::FSub, NewPH, CFP, "IV.S.next.", Incr); NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry)); NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch)); /* Remove cast operation */ ShadowUse->replaceAllUsesWith(NewPH); ShadowUse->eraseFromParent(); Changed = true; break; } } /// FindIVUserForCond - If Cond has an operand that is an expression of an IV, /// set the IV user and stride information and return true, otherwise return /// false. bool LSRInstance::FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse) { for (IVUsers::iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI) if (UI->getUser() == Cond) { // NOTE: we could handle setcc instructions with multiple uses here, but // InstCombine does it as well for simple uses, it's not clear that it // occurs enough in real life to handle. CondUse = UI; return true; } return false; } /// OptimizeMax - Rewrite the loop's terminating condition if it uses /// a max computation. /// /// This is a narrow solution to a specific, but acute, problem. For loops /// like this: /// /// i = 0; /// do { /// p[i] = 0.0; /// } while (++i < n); /// /// the trip count isn't just 'n', because 'n' might not be positive. And /// unfortunately this can come up even for loops where the user didn't use /// a C do-while loop. For example, seemingly well-behaved top-test loops /// will commonly be lowered like this: // /// if (n > 0) { /// i = 0; /// do { /// p[i] = 0.0; /// } while (++i < n); /// } /// /// and then it's possible for subsequent optimization to obscure the if /// test in such a way that indvars can't find it. /// /// When indvars can't find the if test in loops like this, it creates a /// max expression, which allows it to give the loop a canonical /// induction variable: /// /// i = 0; /// max = n < 1 ? 1 : n; /// do { /// p[i] = 0.0; /// } while (++i != max); /// /// Canonical induction variables are necessary because the loop passes /// are designed around them. The most obvious example of this is the /// LoopInfo analysis, which doesn't remember trip count values. It /// expects to be able to rediscover the trip count each time it is /// needed, and it does this using a simple analysis that only succeeds if /// the loop has a canonical induction variable. /// /// However, when it comes time to generate code, the maximum operation /// can be quite costly, especially if it's inside of an outer loop. /// /// This function solves this problem by detecting this type of loop and /// rewriting their conditions from ICMP_NE back to ICMP_SLT, and deleting /// the instructions for the maximum computation. /// ICmpInst *LSRInstance::OptimizeMax(ICmpInst *Cond, IVStrideUse* &CondUse) { // Check that the loop matches the pattern we're looking for. if (Cond->getPredicate() != CmpInst::ICMP_EQ && Cond->getPredicate() != CmpInst::ICMP_NE) return Cond; SelectInst *Sel = dyn_cast<SelectInst>(Cond->getOperand(1)); if (!Sel || !Sel->hasOneUse()) return Cond; const SCEV *BackedgeTakenCount = SE.getBackedgeTakenCount(L); if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) return Cond; const SCEV *One = SE.getConstant(BackedgeTakenCount->getType(), 1); // Add one to the backedge-taken count to get the trip count. const SCEV *IterationCount = SE.getAddExpr(One, BackedgeTakenCount); if (IterationCount != SE.getSCEV(Sel)) return Cond; // Check for a max calculation that matches the pattern. There's no check // for ICMP_ULE here because the comparison would be with zero, which // isn't interesting. CmpInst::Predicate Pred = ICmpInst::BAD_ICMP_PREDICATE; const SCEVNAryExpr *Max = nullptr; if (const SCEVSMaxExpr *S = dyn_cast<SCEVSMaxExpr>(BackedgeTakenCount)) { Pred = ICmpInst::ICMP_SLE; Max = S; } else if (const SCEVSMaxExpr *S = dyn_cast<SCEVSMaxExpr>(IterationCount)) { Pred = ICmpInst::ICMP_SLT; Max = S; } else if (const SCEVUMaxExpr *U = dyn_cast<SCEVUMaxExpr>(IterationCount)) { Pred = ICmpInst::ICMP_ULT; Max = U; } else { // No match; bail. return Cond; } // To handle a max with more than two operands, this optimization would // require additional checking and setup. if (Max->getNumOperands() != 2) return Cond; const SCEV *MaxLHS = Max->getOperand(0); const SCEV *MaxRHS = Max->getOperand(1); // ScalarEvolution canonicalizes constants to the left. For < and >, look // for a comparison with 1. For <= and >=, a comparison with zero. if (!MaxLHS || (ICmpInst::isTrueWhenEqual(Pred) ? !MaxLHS->isZero() : (MaxLHS != One))) return Cond; // Check the relevant induction variable for conformance to // the pattern. const SCEV *IV = SE.getSCEV(Cond->getOperand(0)); const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV); if (!AR || !AR->isAffine() || AR->getStart() != One || AR->getStepRecurrence(SE) != One) return Cond; assert(AR->getLoop() == L && "Loop condition operand is an addrec in a different loop!"); // Check the right operand of the select, and remember it, as it will // be used in the new comparison instruction. Value *NewRHS = nullptr; if (ICmpInst::isTrueWhenEqual(Pred)) { // Look for n+1, and grab n. if (AddOperator *BO = dyn_cast<AddOperator>(Sel->getOperand(1))) if (ConstantInt *BO1 = dyn_cast<ConstantInt>(BO->getOperand(1))) if (BO1->isOne() && SE.getSCEV(BO->getOperand(0)) == MaxRHS) NewRHS = BO->getOperand(0); if (AddOperator *BO = dyn_cast<AddOperator>(Sel->getOperand(2))) if (ConstantInt *BO1 = dyn_cast<ConstantInt>(BO->getOperand(1))) if (BO1->isOne() && SE.getSCEV(BO->getOperand(0)) == MaxRHS) NewRHS = BO->getOperand(0); if (!NewRHS) return Cond; } else if (SE.getSCEV(Sel->getOperand(1)) == MaxRHS) NewRHS = Sel->getOperand(1); else if (SE.getSCEV(Sel->getOperand(2)) == MaxRHS) NewRHS = Sel->getOperand(2); else if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(MaxRHS)) NewRHS = SU->getValue(); else // Max doesn't match expected pattern. return Cond; // Determine the new comparison opcode. It may be signed or unsigned, // and the original comparison may be either equality or inequality. if (Cond->getPredicate() == CmpInst::ICMP_EQ) Pred = CmpInst::getInversePredicate(Pred); // Ok, everything looks ok to change the condition into an SLT or SGE and // delete the max calculation. ICmpInst *NewCond = new ICmpInst(Cond, Pred, Cond->getOperand(0), NewRHS, "scmp"); // Delete the max calculation instructions. Cond->replaceAllUsesWith(NewCond); CondUse->setUser(NewCond); Instruction *Cmp = cast<Instruction>(Sel->getOperand(0)); Cond->eraseFromParent(); Sel->eraseFromParent(); if (Cmp->use_empty()) Cmp->eraseFromParent(); return NewCond; } /// OptimizeLoopTermCond - Change loop terminating condition to use the /// postinc iv when possible. void LSRInstance::OptimizeLoopTermCond() { SmallPtrSet<Instruction *, 4> PostIncs; BasicBlock *LatchBlock = L->getLoopLatch(); SmallVector<BasicBlock*, 8> ExitingBlocks; L->getExitingBlocks(ExitingBlocks); for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) { BasicBlock *ExitingBlock = ExitingBlocks[i]; // Get the terminating condition for the loop if possible. If we // can, we want to change it to use a post-incremented version of its // induction variable, to allow coalescing the live ranges for the IV into // one register value. BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator()); if (!TermBr) continue; // FIXME: Overly conservative, termination condition could be an 'or' etc.. if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition())) continue; // Search IVUsesByStride to find Cond's IVUse if there is one. IVStrideUse *CondUse = nullptr; ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition()); if (!FindIVUserForCond(Cond, CondUse)) continue; // If the trip count is computed in terms of a max (due to ScalarEvolution // being unable to find a sufficient guard, for example), change the loop // comparison to use SLT or ULT instead of NE. // One consequence of doing this now is that it disrupts the count-down // optimization. That's not always a bad thing though, because in such // cases it may still be worthwhile to avoid a max. Cond = OptimizeMax(Cond, CondUse); // If this exiting block dominates the latch block, it may also use // the post-inc value if it won't be shared with other uses. // Check for dominance. if (!DT.dominates(ExitingBlock, LatchBlock)) continue; // Conservatively avoid trying to use the post-inc value in non-latch // exits if there may be pre-inc users in intervening blocks. if (LatchBlock != ExitingBlock) for (IVUsers::const_iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI) // Test if the use is reachable from the exiting block. This dominator // query is a conservative approximation of reachability. if (&*UI != CondUse && !DT.properlyDominates(UI->getUser()->getParent(), ExitingBlock)) { // Conservatively assume there may be reuse if the quotient of their // strides could be a legal scale. const SCEV *A = IU.getStride(*CondUse, L); const SCEV *B = IU.getStride(*UI, L); if (!A || !B) continue; if (SE.getTypeSizeInBits(A->getType()) != SE.getTypeSizeInBits(B->getType())) { if (SE.getTypeSizeInBits(A->getType()) > SE.getTypeSizeInBits(B->getType())) B = SE.getSignExtendExpr(B, A->getType()); else A = SE.getSignExtendExpr(A, B->getType()); } if (const SCEVConstant *D = dyn_cast_or_null<SCEVConstant>(getExactSDiv(B, A, SE))) { const ConstantInt *C = D->getValue(); // Stride of one or negative one can have reuse with non-addresses. if (C->isOne() || C->isAllOnesValue()) goto decline_post_inc; // Avoid weird situations. if (C->getValue().getMinSignedBits() >= 64 || C->getValue().isMinSignedValue()) goto decline_post_inc; // Check for possible scaled-address reuse. Type *AccessTy = getAccessType(UI->getUser()); int64_t Scale = C->getSExtValue(); if (TTI.isLegalAddressingMode(AccessTy, /*BaseGV=*/ nullptr, /*BaseOffset=*/ 0, /*HasBaseReg=*/ false, Scale)) goto decline_post_inc; Scale = -Scale; if (TTI.isLegalAddressingMode(AccessTy, /*BaseGV=*/ nullptr, /*BaseOffset=*/ 0, /*HasBaseReg=*/ false, Scale)) goto decline_post_inc; } } DEBUG(dbgs() << " Change loop exiting icmp to use postinc iv: " << *Cond << '\n'); // It's possible for the setcc instruction to be anywhere in the loop, and // possible for it to have multiple users. If it is not immediately before // the exiting block branch, move it. if (&*++BasicBlock::iterator(Cond) != TermBr) { if (Cond->hasOneUse()) { Cond->moveBefore(TermBr); } else { // Clone the terminating condition and insert into the loopend. ICmpInst *OldCond = Cond; Cond = cast<ICmpInst>(Cond->clone()); Cond->setName(L->getHeader()->getName() + ".termcond"); ExitingBlock->getInstList().insert(TermBr, Cond); // Clone the IVUse, as the old use still exists! CondUse = &IU.AddUser(Cond, CondUse->getOperandValToReplace()); TermBr->replaceUsesOfWith(OldCond, Cond); } } // If we get to here, we know that we can transform the setcc instruction to // use the post-incremented version of the IV, allowing us to coalesce the // live ranges for the IV correctly. CondUse->transformToPostInc(L); Changed = true; PostIncs.insert(Cond); decline_post_inc:; } // Determine an insertion point for the loop induction variable increment. It // must dominate all the post-inc comparisons we just set up, and it must // dominate the loop latch edge. IVIncInsertPos = L->getLoopLatch()->getTerminator(); for (Instruction *Inst : PostIncs) { BasicBlock *BB = DT.findNearestCommonDominator(IVIncInsertPos->getParent(), Inst->getParent()); if (BB == Inst->getParent()) IVIncInsertPos = Inst; else if (BB != IVIncInsertPos->getParent()) IVIncInsertPos = BB->getTerminator(); } } /// reconcileNewOffset - Determine if the given use can accommodate a fixup /// at the given offset and other details. If so, update the use and /// return true. bool LSRInstance::reconcileNewOffset(LSRUse &LU, int64_t NewOffset, bool HasBaseReg, LSRUse::KindType Kind, Type *AccessTy) { int64_t NewMinOffset = LU.MinOffset; int64_t NewMaxOffset = LU.MaxOffset; Type *NewAccessTy = AccessTy; // Check for a mismatched kind. It's tempting to collapse mismatched kinds to // something conservative, however this can pessimize in the case that one of // the uses will have all its uses outside the loop, for example. if (LU.Kind != Kind) return false; // Check for a mismatched access type, and fall back conservatively as needed. // TODO: Be less conservative when the type is similar and can use the same // addressing modes. if (Kind == LSRUse::Address && AccessTy != LU.AccessTy) NewAccessTy = Type::getVoidTy(AccessTy->getContext()); // Conservatively assume HasBaseReg is true for now. if (NewOffset < LU.MinOffset) { if (!isAlwaysFoldable(TTI, Kind, NewAccessTy, /*BaseGV=*/nullptr, LU.MaxOffset - NewOffset, HasBaseReg)) return false; NewMinOffset = NewOffset; } else if (NewOffset > LU.MaxOffset) { if (!isAlwaysFoldable(TTI, Kind, NewAccessTy, /*BaseGV=*/nullptr, NewOffset - LU.MinOffset, HasBaseReg)) return false; NewMaxOffset = NewOffset; } // Update the use. LU.MinOffset = NewMinOffset; LU.MaxOffset = NewMaxOffset; LU.AccessTy = NewAccessTy; if (NewOffset != LU.Offsets.back()) LU.Offsets.push_back(NewOffset); return true; } /// getUse - Return an LSRUse index and an offset value for a fixup which /// needs the given expression, with the given kind and optional access type. /// Either reuse an existing use or create a new one, as needed. std::pair<size_t, int64_t> LSRInstance::getUse(const SCEV *&Expr, LSRUse::KindType Kind, Type *AccessTy) { const SCEV *Copy = Expr; int64_t Offset = ExtractImmediate(Expr, SE); // Basic uses can't accept any offset, for example. if (!isAlwaysFoldable(TTI, Kind, AccessTy, /*BaseGV=*/ nullptr, Offset, /*HasBaseReg=*/ true)) { Expr = Copy; Offset = 0; } std::pair<UseMapTy::iterator, bool> P = UseMap.insert(std::make_pair(LSRUse::SCEVUseKindPair(Expr, Kind), 0)); if (!P.second) { // A use already existed with this base. size_t LUIdx = P.first->second; LSRUse &LU = Uses[LUIdx]; if (reconcileNewOffset(LU, Offset, /*HasBaseReg=*/true, Kind, AccessTy)) // Reuse this use. return std::make_pair(LUIdx, Offset); } // Create a new use. size_t LUIdx = Uses.size(); P.first->second = LUIdx; Uses.push_back(LSRUse(Kind, AccessTy)); LSRUse &LU = Uses[LUIdx]; // We don't need to track redundant offsets, but we don't need to go out // of our way here to avoid them. if (LU.Offsets.empty() || Offset != LU.Offsets.back()) LU.Offsets.push_back(Offset); LU.MinOffset = Offset; LU.MaxOffset = Offset; return std::make_pair(LUIdx, Offset); } /// DeleteUse - Delete the given use from the Uses list. void LSRInstance::DeleteUse(LSRUse &LU, size_t LUIdx) { if (&LU != &Uses.back()) std::swap(LU, Uses.back()); Uses.pop_back(); // Update RegUses. RegUses.SwapAndDropUse(LUIdx, Uses.size()); } /// FindUseWithFormula - Look for a use distinct from OrigLU which is has /// a formula that has the same registers as the given formula. LSRUse * LSRInstance::FindUseWithSimilarFormula(const Formula &OrigF, const LSRUse &OrigLU) { // Search all uses for the formula. This could be more clever. for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) { LSRUse &LU = Uses[LUIdx]; // Check whether this use is close enough to OrigLU, to see whether it's // worthwhile looking through its formulae. // Ignore ICmpZero uses because they may contain formulae generated by // GenerateICmpZeroScales, in which case adding fixup offsets may // be invalid. if (&LU != &OrigLU && LU.Kind != LSRUse::ICmpZero && LU.Kind == OrigLU.Kind && OrigLU.AccessTy == LU.AccessTy && LU.WidestFixupType == OrigLU.WidestFixupType && LU.HasFormulaWithSameRegs(OrigF)) { // Scan through this use's formulae. for (SmallVectorImpl<Formula>::const_iterator I = LU.Formulae.begin(), E = LU.Formulae.end(); I != E; ++I) { const Formula &F = *I; // Check to see if this formula has the same registers and symbols // as OrigF. if (F.BaseRegs == OrigF.BaseRegs && F.ScaledReg == OrigF.ScaledReg && F.BaseGV == OrigF.BaseGV && F.Scale == OrigF.Scale && F.UnfoldedOffset == OrigF.UnfoldedOffset) { if (F.BaseOffset == 0) return &LU; // This is the formula where all the registers and symbols matched; // there aren't going to be any others. Since we declined it, we // can skip the rest of the formulae and proceed to the next LSRUse. break; } } } } // Nothing looked good. return nullptr; } void LSRInstance::CollectInterestingTypesAndFactors() { SmallSetVector<const SCEV *, 4> Strides; // Collect interesting types and strides. SmallVector<const SCEV *, 4> Worklist; for (IVUsers::const_iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI) { const SCEV *Expr = IU.getExpr(*UI); // Collect interesting types. Types.insert(SE.getEffectiveSCEVType(Expr->getType())); // Add strides for mentioned loops. Worklist.push_back(Expr); do { const SCEV *S = Worklist.pop_back_val(); if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { if (AR->getLoop() == L) Strides.insert(AR->getStepRecurrence(SE)); Worklist.push_back(AR->getStart()); } else if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { Worklist.append(Add->op_begin(), Add->op_end()); } } while (!Worklist.empty()); } // Compute interesting factors from the set of interesting strides. for (SmallSetVector<const SCEV *, 4>::const_iterator I = Strides.begin(), E = Strides.end(); I != E; ++I) for (SmallSetVector<const SCEV *, 4>::const_iterator NewStrideIter = std::next(I); NewStrideIter != E; ++NewStrideIter) { const SCEV *OldStride = *I; const SCEV *NewStride = *NewStrideIter; if (SE.getTypeSizeInBits(OldStride->getType()) != SE.getTypeSizeInBits(NewStride->getType())) { if (SE.getTypeSizeInBits(OldStride->getType()) > SE.getTypeSizeInBits(NewStride->getType())) NewStride = SE.getSignExtendExpr(NewStride, OldStride->getType()); else OldStride = SE.getSignExtendExpr(OldStride, NewStride->getType()); } if (const SCEVConstant *Factor = dyn_cast_or_null<SCEVConstant>(getExactSDiv(NewStride, OldStride, SE, true))) { if (Factor->getValue()->getValue().getMinSignedBits() <= 64) Factors.insert(Factor->getValue()->getValue().getSExtValue()); } else if (const SCEVConstant *Factor = dyn_cast_or_null<SCEVConstant>(getExactSDiv(OldStride, NewStride, SE, true))) { if (Factor->getValue()->getValue().getMinSignedBits() <= 64) Factors.insert(Factor->getValue()->getValue().getSExtValue()); } } // If all uses use the same type, don't bother looking for truncation-based // reuse. if (Types.size() == 1) Types.clear(); DEBUG(print_factors_and_types(dbgs())); } /// findIVOperand - Helper for CollectChains that finds an IV operand (computed /// by an AddRec in this loop) within [OI,OE) or returns OE. If IVUsers mapped /// Instructions to IVStrideUses, we could partially skip this. static User::op_iterator findIVOperand(User::op_iterator OI, User::op_iterator OE, Loop *L, ScalarEvolution &SE) { for(; OI != OE; ++OI) { if (Instruction *Oper = dyn_cast<Instruction>(*OI)) { if (!SE.isSCEVable(Oper->getType())) continue; if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(Oper))) { if (AR->getLoop() == L) break; } } } return OI; } /// getWideOperand - IVChain logic must consistenctly peek base TruncInst /// operands, so wrap it in a convenient helper. static Value *getWideOperand(Value *Oper) { if (TruncInst *Trunc = dyn_cast<TruncInst>(Oper)) return Trunc->getOperand(0); return Oper; } /// isCompatibleIVType - Return true if we allow an IV chain to include both /// types. static bool isCompatibleIVType(Value *LVal, Value *RVal) { Type *LType = LVal->getType(); Type *RType = RVal->getType(); return (LType == RType) || (LType->isPointerTy() && RType->isPointerTy()); } /// getExprBase - Return an approximation of this SCEV expression's "base", or /// NULL for any constant. Returning the expression itself is /// conservative. Returning a deeper subexpression is more precise and valid as /// long as it isn't less complex than another subexpression. For expressions /// involving multiple unscaled values, we need to return the pointer-type /// SCEVUnknown. This avoids forming chains across objects, such as: /// PrevOper==a[i], IVOper==b[i], IVInc==b-a. /// /// Since SCEVUnknown is the rightmost type, and pointers are the rightmost /// SCEVUnknown, we simply return the rightmost SCEV operand. static const SCEV *getExprBase(const SCEV *S) { switch (S->getSCEVType()) { default: // uncluding scUnknown. return S; case scConstant: return nullptr; case scTruncate: return getExprBase(cast<SCEVTruncateExpr>(S)->getOperand()); case scZeroExtend: return getExprBase(cast<SCEVZeroExtendExpr>(S)->getOperand()); case scSignExtend: return getExprBase(cast<SCEVSignExtendExpr>(S)->getOperand()); case scAddExpr: { // Skip over scaled operands (scMulExpr) to follow add operands as long as // there's nothing more complex. // FIXME: not sure if we want to recognize negation. const SCEVAddExpr *Add = cast<SCEVAddExpr>(S); for (std::reverse_iterator<SCEVAddExpr::op_iterator> I(Add->op_end()), E(Add->op_begin()); I != E; ++I) { const SCEV *SubExpr = *I; if (SubExpr->getSCEVType() == scAddExpr) return getExprBase(SubExpr); if (SubExpr->getSCEVType() != scMulExpr) return SubExpr; } return S; // all operands are scaled, be conservative. } case scAddRecExpr: return getExprBase(cast<SCEVAddRecExpr>(S)->getStart()); } } /// Return true if the chain increment is profitable to expand into a loop /// invariant value, which may require its own register. A profitable chain /// increment will be an offset relative to the same base. We allow such offsets /// to potentially be used as chain increment as long as it's not obviously /// expensive to expand using real instructions. bool IVChain::isProfitableIncrement(const SCEV *OperExpr, const SCEV *IncExpr, ScalarEvolution &SE) { // Aggressively form chains when -stress-ivchain. if (StressIVChain) return true; // Do not replace a constant offset from IV head with a nonconstant IV // increment. if (!isa<SCEVConstant>(IncExpr)) { const SCEV *HeadExpr = SE.getSCEV(getWideOperand(Incs[0].IVOperand)); if (isa<SCEVConstant>(SE.getMinusSCEV(OperExpr, HeadExpr))) return 0; } SmallPtrSet<const SCEV*, 8> Processed; return !isHighCostExpansion(IncExpr, Processed, SE); } /// Return true if the number of registers needed for the chain is estimated to /// be less than the number required for the individual IV users. First prohibit /// any IV users that keep the IV live across increments (the Users set should /// be empty). Next count the number and type of increments in the chain. /// /// Chaining IVs can lead to considerable code bloat if ISEL doesn't /// effectively use postinc addressing modes. Only consider it profitable it the /// increments can be computed in fewer registers when chained. /// /// TODO: Consider IVInc free if it's already used in another chains. static bool isProfitableChain(IVChain &Chain, SmallPtrSetImpl<Instruction*> &Users, ScalarEvolution &SE, const TargetTransformInfo &TTI) { if (StressIVChain) return true; if (!Chain.hasIncs()) return false; if (!Users.empty()) { DEBUG(dbgs() << "Chain: " << *Chain.Incs[0].UserInst << " users:\n"; for (Instruction *Inst : Users) { dbgs() << " " << *Inst << "\n"; }); return false; } assert(!Chain.Incs.empty() && "empty IV chains are not allowed"); // The chain itself may require a register, so intialize cost to 1. int cost = 1; // A complete chain likely eliminates the need for keeping the original IV in // a register. LSR does not currently know how to form a complete chain unless // the header phi already exists. if (isa<PHINode>(Chain.tailUserInst()) && SE.getSCEV(Chain.tailUserInst()) == Chain.Incs[0].IncExpr) { --cost; } const SCEV *LastIncExpr = nullptr; unsigned NumConstIncrements = 0; unsigned NumVarIncrements = 0; unsigned NumReusedIncrements = 0; for (IVChain::const_iterator I = Chain.begin(), E = Chain.end(); I != E; ++I) { if (I->IncExpr->isZero()) continue; // Incrementing by zero or some constant is neutral. We assume constants can // be folded into an addressing mode or an add's immediate operand. if (isa<SCEVConstant>(I->IncExpr)) { ++NumConstIncrements; continue; } if (I->IncExpr == LastIncExpr) ++NumReusedIncrements; else ++NumVarIncrements; LastIncExpr = I->IncExpr; } // An IV chain with a single increment is handled by LSR's postinc // uses. However, a chain with multiple increments requires keeping the IV's // value live longer than it needs to be if chained. if (NumConstIncrements > 1) --cost; // Materializing increment expressions in the preheader that didn't exist in // the original code may cost a register. For example, sign-extended array // indices can produce ridiculous increments like this: // IV + ((sext i32 (2 * %s) to i64) + (-1 * (sext i32 %s to i64))) cost += NumVarIncrements; // Reusing variable increments likely saves a register to hold the multiple of // the stride. cost -= NumReusedIncrements; DEBUG(dbgs() << "Chain: " << *Chain.Incs[0].UserInst << " Cost: " << cost << "\n"); return cost < 0; } /// ChainInstruction - Add this IV user to an existing chain or make it the head /// of a new chain. void LSRInstance::ChainInstruction(Instruction *UserInst, Instruction *IVOper, SmallVectorImpl<ChainUsers> &ChainUsersVec) { // When IVs are used as types of varying widths, they are generally converted // to a wider type with some uses remaining narrow under a (free) trunc. Value *const NextIV = getWideOperand(IVOper); const SCEV *const OperExpr = SE.getSCEV(NextIV); const SCEV *const OperExprBase = getExprBase(OperExpr); // Visit all existing chains. Check if its IVOper can be computed as a // profitable loop invariant increment from the last link in the Chain. unsigned ChainIdx = 0, NChains = IVChainVec.size(); const SCEV *LastIncExpr = nullptr; for (; ChainIdx < NChains; ++ChainIdx) { IVChain &Chain = IVChainVec[ChainIdx]; // Prune the solution space aggressively by checking that both IV operands // are expressions that operate on the same unscaled SCEVUnknown. This // "base" will be canceled by the subsequent getMinusSCEV call. Checking // first avoids creating extra SCEV expressions. if (!StressIVChain && Chain.ExprBase != OperExprBase) continue; Value *PrevIV = getWideOperand(Chain.Incs.back().IVOperand); if (!isCompatibleIVType(PrevIV, NextIV)) continue; // A phi node terminates a chain. if (isa<PHINode>(UserInst) && isa<PHINode>(Chain.tailUserInst())) continue; // The increment must be loop-invariant so it can be kept in a register. const SCEV *PrevExpr = SE.getSCEV(PrevIV); const SCEV *IncExpr = SE.getMinusSCEV(OperExpr, PrevExpr); if (!SE.isLoopInvariant(IncExpr, L)) continue; if (Chain.isProfitableIncrement(OperExpr, IncExpr, SE)) { LastIncExpr = IncExpr; break; } } // If we haven't found a chain, create a new one, unless we hit the max. Don't // bother for phi nodes, because they must be last in the chain. if (ChainIdx == NChains) { if (isa<PHINode>(UserInst)) return; if (NChains >= MaxChains && !StressIVChain) { DEBUG(dbgs() << "IV Chain Limit\n"); return; } LastIncExpr = OperExpr; // IVUsers may have skipped over sign/zero extensions. We don't currently // attempt to form chains involving extensions unless they can be hoisted // into this loop's AddRec. if (!isa<SCEVAddRecExpr>(LastIncExpr)) return; ++NChains; IVChainVec.push_back(IVChain(IVInc(UserInst, IVOper, LastIncExpr), OperExprBase)); ChainUsersVec.resize(NChains); DEBUG(dbgs() << "IV Chain#" << ChainIdx << " Head: (" << *UserInst << ") IV=" << *LastIncExpr << "\n"); } else { DEBUG(dbgs() << "IV Chain#" << ChainIdx << " Inc: (" << *UserInst << ") IV+" << *LastIncExpr << "\n"); // Add this IV user to the end of the chain. IVChainVec[ChainIdx].add(IVInc(UserInst, IVOper, LastIncExpr)); } IVChain &Chain = IVChainVec[ChainIdx]; SmallPtrSet<Instruction*,4> &NearUsers = ChainUsersVec[ChainIdx].NearUsers; // This chain's NearUsers become FarUsers. if (!LastIncExpr->isZero()) { ChainUsersVec[ChainIdx].FarUsers.insert(NearUsers.begin(), NearUsers.end()); NearUsers.clear(); } // All other uses of IVOperand become near uses of the chain. // We currently ignore intermediate values within SCEV expressions, assuming // they will eventually be used be the current chain, or can be computed // from one of the chain increments. To be more precise we could // transitively follow its user and only add leaf IV users to the set. for (User *U : IVOper->users()) { Instruction *OtherUse = dyn_cast<Instruction>(U); if (!OtherUse) continue; // Uses in the chain will no longer be uses if the chain is formed. // Include the head of the chain in this iteration (not Chain.begin()). IVChain::const_iterator IncIter = Chain.Incs.begin(); IVChain::const_iterator IncEnd = Chain.Incs.end(); for( ; IncIter != IncEnd; ++IncIter) { if (IncIter->UserInst == OtherUse) break; } if (IncIter != IncEnd) continue; if (SE.isSCEVable(OtherUse->getType()) && !isa<SCEVUnknown>(SE.getSCEV(OtherUse)) && IU.isIVUserOrOperand(OtherUse)) { continue; } NearUsers.insert(OtherUse); } // Since this user is part of the chain, it's no longer considered a use // of the chain. ChainUsersVec[ChainIdx].FarUsers.erase(UserInst); } /// CollectChains - Populate the vector of Chains. /// /// This decreases ILP at the architecture level. Targets with ample registers, /// multiple memory ports, and no register renaming probably don't want /// this. However, such targets should probably disable LSR altogether. /// /// The job of LSR is to make a reasonable choice of induction variables across /// the loop. Subsequent passes can easily "unchain" computation exposing more /// ILP *within the loop* if the target wants it. /// /// Finding the best IV chain is potentially a scheduling problem. Since LSR /// will not reorder memory operations, it will recognize this as a chain, but /// will generate redundant IV increments. Ideally this would be corrected later /// by a smart scheduler: /// = A[i] /// = A[i+x] /// A[i] = /// A[i+x] = /// /// TODO: Walk the entire domtree within this loop, not just the path to the /// loop latch. This will discover chains on side paths, but requires /// maintaining multiple copies of the Chains state. void LSRInstance::CollectChains() { DEBUG(dbgs() << "Collecting IV Chains.\n"); SmallVector<ChainUsers, 8> ChainUsersVec; SmallVector<BasicBlock *,8> LatchPath; BasicBlock *LoopHeader = L->getHeader(); for (DomTreeNode *Rung = DT.getNode(L->getLoopLatch()); Rung->getBlock() != LoopHeader; Rung = Rung->getIDom()) { LatchPath.push_back(Rung->getBlock()); } LatchPath.push_back(LoopHeader); // Walk the instruction stream from the loop header to the loop latch. for (SmallVectorImpl<BasicBlock *>::reverse_iterator BBIter = LatchPath.rbegin(), BBEnd = LatchPath.rend(); BBIter != BBEnd; ++BBIter) { for (BasicBlock::iterator I = (*BBIter)->begin(), E = (*BBIter)->end(); I != E; ++I) { // Skip instructions that weren't seen by IVUsers analysis. if (isa<PHINode>(I) || !IU.isIVUserOrOperand(I)) continue; // Ignore users that are part of a SCEV expression. This way we only // consider leaf IV Users. This effectively rediscovers a portion of // IVUsers analysis but in program order this time. if (SE.isSCEVable(I->getType()) && !isa<SCEVUnknown>(SE.getSCEV(I))) continue; // Remove this instruction from any NearUsers set it may be in. for (unsigned ChainIdx = 0, NChains = IVChainVec.size(); ChainIdx < NChains; ++ChainIdx) { ChainUsersVec[ChainIdx].NearUsers.erase(I); } // Search for operands that can be chained. SmallPtrSet<Instruction*, 4> UniqueOperands; User::op_iterator IVOpEnd = I->op_end(); User::op_iterator IVOpIter = findIVOperand(I->op_begin(), IVOpEnd, L, SE); while (IVOpIter != IVOpEnd) { Instruction *IVOpInst = cast<Instruction>(*IVOpIter); if (UniqueOperands.insert(IVOpInst).second) ChainInstruction(I, IVOpInst, ChainUsersVec); IVOpIter = findIVOperand(std::next(IVOpIter), IVOpEnd, L, SE); } } // Continue walking down the instructions. } // Continue walking down the domtree. // Visit phi backedges to determine if the chain can generate the IV postinc. for (BasicBlock::iterator I = L->getHeader()->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I) { if (!SE.isSCEVable(PN->getType())) continue; Instruction *IncV = dyn_cast<Instruction>(PN->getIncomingValueForBlock(L->getLoopLatch())); if (IncV) ChainInstruction(PN, IncV, ChainUsersVec); } // Remove any unprofitable chains. unsigned ChainIdx = 0; for (unsigned UsersIdx = 0, NChains = IVChainVec.size(); UsersIdx < NChains; ++UsersIdx) { if (!isProfitableChain(IVChainVec[UsersIdx], ChainUsersVec[UsersIdx].FarUsers, SE, TTI)) continue; // Preserve the chain at UsesIdx. if (ChainIdx != UsersIdx) IVChainVec[ChainIdx] = IVChainVec[UsersIdx]; FinalizeChain(IVChainVec[ChainIdx]); ++ChainIdx; } IVChainVec.resize(ChainIdx); } void LSRInstance::FinalizeChain(IVChain &Chain) { assert(!Chain.Incs.empty() && "empty IV chains are not allowed"); DEBUG(dbgs() << "Final Chain: " << *Chain.Incs[0].UserInst << "\n"); for (IVChain::const_iterator I = Chain.begin(), E = Chain.end(); I != E; ++I) { DEBUG(dbgs() << " Inc: " << *I->UserInst << "\n"); User::op_iterator UseI = std::find(I->UserInst->op_begin(), I->UserInst->op_end(), I->IVOperand); assert(UseI != I->UserInst->op_end() && "cannot find IV operand"); IVIncSet.insert(UseI); } } /// Return true if the IVInc can be folded into an addressing mode. static bool canFoldIVIncExpr(const SCEV *IncExpr, Instruction *UserInst, Value *Operand, const TargetTransformInfo &TTI) { const SCEVConstant *IncConst = dyn_cast<SCEVConstant>(IncExpr); if (!IncConst || !isAddressUse(UserInst, Operand)) return false; if (IncConst->getValue()->getValue().getMinSignedBits() > 64) return false; int64_t IncOffset = IncConst->getValue()->getSExtValue(); if (!isAlwaysFoldable(TTI, LSRUse::Address, getAccessType(UserInst), /*BaseGV=*/ nullptr, IncOffset, /*HaseBaseReg=*/ false)) return false; return true; } /// GenerateIVChains - Generate an add or subtract for each IVInc in a chain to /// materialize the IV user's operand from the previous IV user's operand. void LSRInstance::GenerateIVChain(const IVChain &Chain, SCEVExpander &Rewriter, SmallVectorImpl<WeakVH> &DeadInsts) { // Find the new IVOperand for the head of the chain. It may have been replaced // by LSR. const IVInc &Head = Chain.Incs[0]; User::op_iterator IVOpEnd = Head.UserInst->op_end(); // findIVOperand returns IVOpEnd if it can no longer find a valid IV user. User::op_iterator IVOpIter = findIVOperand(Head.UserInst->op_begin(), IVOpEnd, L, SE); Value *IVSrc = nullptr; while (IVOpIter != IVOpEnd) { IVSrc = getWideOperand(*IVOpIter); // If this operand computes the expression that the chain needs, we may use // it. (Check this after setting IVSrc which is used below.) // // Note that if Head.IncExpr is wider than IVSrc, then this phi is too // narrow for the chain, so we can no longer use it. We do allow using a // wider phi, assuming the LSR checked for free truncation. In that case we // should already have a truncate on this operand such that // getSCEV(IVSrc) == IncExpr. if (SE.getSCEV(*IVOpIter) == Head.IncExpr || SE.getSCEV(IVSrc) == Head.IncExpr) { break; } IVOpIter = findIVOperand(std::next(IVOpIter), IVOpEnd, L, SE); } if (IVOpIter == IVOpEnd) { // Gracefully give up on this chain. DEBUG(dbgs() << "Concealed chain head: " << *Head.UserInst << "\n"); return; } DEBUG(dbgs() << "Generate chain at: " << *IVSrc << "\n"); Type *IVTy = IVSrc->getType(); Type *IntTy = SE.getEffectiveSCEVType(IVTy); const SCEV *LeftOverExpr = nullptr; for (IVChain::const_iterator IncI = Chain.begin(), IncE = Chain.end(); IncI != IncE; ++IncI) { Instruction *InsertPt = IncI->UserInst; if (isa<PHINode>(InsertPt)) InsertPt = L->getLoopLatch()->getTerminator(); // IVOper will replace the current IV User's operand. IVSrc is the IV // value currently held in a register. Value *IVOper = IVSrc; if (!IncI->IncExpr->isZero()) { // IncExpr was the result of subtraction of two narrow values, so must // be signed. const SCEV *IncExpr = SE.getNoopOrSignExtend(IncI->IncExpr, IntTy); LeftOverExpr = LeftOverExpr ? SE.getAddExpr(LeftOverExpr, IncExpr) : IncExpr; } if (LeftOverExpr && !LeftOverExpr->isZero()) { // Expand the IV increment. Rewriter.clearPostInc(); Value *IncV = Rewriter.expandCodeFor(LeftOverExpr, IntTy, InsertPt); const SCEV *IVOperExpr = SE.getAddExpr(SE.getUnknown(IVSrc), SE.getUnknown(IncV)); IVOper = Rewriter.expandCodeFor(IVOperExpr, IVTy, InsertPt); // If an IV increment can't be folded, use it as the next IV value. if (!canFoldIVIncExpr(LeftOverExpr, IncI->UserInst, IncI->IVOperand, TTI)) { assert(IVTy == IVOper->getType() && "inconsistent IV increment type"); IVSrc = IVOper; LeftOverExpr = nullptr; } } Type *OperTy = IncI->IVOperand->getType(); if (IVTy != OperTy) { assert(SE.getTypeSizeInBits(IVTy) >= SE.getTypeSizeInBits(OperTy) && "cannot extend a chained IV"); IRBuilder<> Builder(InsertPt); IVOper = Builder.CreateTruncOrBitCast(IVOper, OperTy, "lsr.chain"); } IncI->UserInst->replaceUsesOfWith(IncI->IVOperand, IVOper); DeadInsts.push_back(IncI->IVOperand); } // If LSR created a new, wider phi, we may also replace its postinc. We only // do this if we also found a wide value for the head of the chain. if (isa<PHINode>(Chain.tailUserInst())) { for (BasicBlock::iterator I = L->getHeader()->begin(); PHINode *Phi = dyn_cast<PHINode>(I); ++I) { if (!isCompatibleIVType(Phi, IVSrc)) continue; Instruction *PostIncV = dyn_cast<Instruction>( Phi->getIncomingValueForBlock(L->getLoopLatch())); if (!PostIncV || (SE.getSCEV(PostIncV) != SE.getSCEV(IVSrc))) continue; Value *IVOper = IVSrc; Type *PostIncTy = PostIncV->getType(); if (IVTy != PostIncTy) { assert(PostIncTy->isPointerTy() && "mixing int/ptr IV types"); IRBuilder<> Builder(L->getLoopLatch()->getTerminator()); Builder.SetCurrentDebugLocation(PostIncV->getDebugLoc()); IVOper = Builder.CreatePointerCast(IVSrc, PostIncTy, "lsr.chain"); } Phi->replaceUsesOfWith(PostIncV, IVOper); DeadInsts.push_back(PostIncV); } } } void LSRInstance::CollectFixupsAndInitialFormulae() { for (IVUsers::const_iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI) { Instruction *UserInst = UI->getUser(); // Skip IV users that are part of profitable IV Chains. User::op_iterator UseI = std::find(UserInst->op_begin(), UserInst->op_end(), UI->getOperandValToReplace()); assert(UseI != UserInst->op_end() && "cannot find IV operand"); if (IVIncSet.count(UseI)) continue; // Record the uses. LSRFixup &LF = getNewFixup(); LF.UserInst = UserInst; LF.OperandValToReplace = UI->getOperandValToReplace(); LF.PostIncLoops = UI->getPostIncLoops(); LSRUse::KindType Kind = LSRUse::Basic; Type *AccessTy = nullptr; if (isAddressUse(LF.UserInst, LF.OperandValToReplace)) { Kind = LSRUse::Address; AccessTy = getAccessType(LF.UserInst); } const SCEV *S = IU.getExpr(*UI); // Equality (== and !=) ICmps are special. We can rewrite (i == N) as // (N - i == 0), and this allows (N - i) to be the expression that we work // with rather than just N or i, so we can consider the register // requirements for both N and i at the same time. Limiting this code to // equality icmps is not a problem because all interesting loops use // equality icmps, thanks to IndVarSimplify. if (ICmpInst *CI = dyn_cast<ICmpInst>(LF.UserInst)) if (CI->isEquality()) { // Swap the operands if needed to put the OperandValToReplace on the // left, for consistency. Value *NV = CI->getOperand(1); if (NV == LF.OperandValToReplace) { CI->setOperand(1, CI->getOperand(0)); CI->setOperand(0, NV); NV = CI->getOperand(1); Changed = true; } // x == y --> x - y == 0 const SCEV *N = SE.getSCEV(NV); if (SE.isLoopInvariant(N, L) && isSafeToExpand(N, SE)) { // S is normalized, so normalize N before folding it into S // to keep the result normalized. N = TransformForPostIncUse(Normalize, N, CI, nullptr, LF.PostIncLoops, SE, DT); Kind = LSRUse::ICmpZero; S = SE.getMinusSCEV(N, S); } // -1 and the negations of all interesting strides (except the negation // of -1) are now also interesting. for (size_t i = 0, e = Factors.size(); i != e; ++i) if (Factors[i] != -1) Factors.insert(-(uint64_t)Factors[i]); Factors.insert(-1); } // Set up the initial formula for this use. std::pair<size_t, int64_t> P = getUse(S, Kind, AccessTy); LF.LUIdx = P.first; LF.Offset = P.second; LSRUse &LU = Uses[LF.LUIdx]; LU.AllFixupsOutsideLoop &= LF.isUseFullyOutsideLoop(L); if (!LU.WidestFixupType || SE.getTypeSizeInBits(LU.WidestFixupType) < SE.getTypeSizeInBits(LF.OperandValToReplace->getType())) LU.WidestFixupType = LF.OperandValToReplace->getType(); // If this is the first use of this LSRUse, give it a formula. if (LU.Formulae.empty()) { InsertInitialFormula(S, LU, LF.LUIdx); CountRegisters(LU.Formulae.back(), LF.LUIdx); } } DEBUG(print_fixups(dbgs())); } /// InsertInitialFormula - Insert a formula for the given expression into /// the given use, separating out loop-variant portions from loop-invariant /// and loop-computable portions. void LSRInstance::InsertInitialFormula(const SCEV *S, LSRUse &LU, size_t LUIdx) { // Mark uses whose expressions cannot be expanded. if (!isSafeToExpand(S, SE)) LU.RigidFormula = true; Formula F; F.InitialMatch(S, L, SE); bool Inserted = InsertFormula(LU, LUIdx, F); assert(Inserted && "Initial formula already exists!"); (void)Inserted; } /// InsertSupplementalFormula - Insert a simple single-register formula for /// the given expression into the given use. void LSRInstance::InsertSupplementalFormula(const SCEV *S, LSRUse &LU, size_t LUIdx) { Formula F; F.BaseRegs.push_back(S); F.HasBaseReg = true; bool Inserted = InsertFormula(LU, LUIdx, F); assert(Inserted && "Supplemental formula already exists!"); (void)Inserted; } /// CountRegisters - Note which registers are used by the given formula, /// updating RegUses. void LSRInstance::CountRegisters(const Formula &F, size_t LUIdx) { if (F.ScaledReg) RegUses.CountRegister(F.ScaledReg, LUIdx); for (SmallVectorImpl<const SCEV *>::const_iterator I = F.BaseRegs.begin(), E = F.BaseRegs.end(); I != E; ++I) RegUses.CountRegister(*I, LUIdx); } /// InsertFormula - If the given formula has not yet been inserted, add it to /// the list, and return true. Return false otherwise. bool LSRInstance::InsertFormula(LSRUse &LU, unsigned LUIdx, const Formula &F) { // Do not insert formula that we will not be able to expand. assert(isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, F) && "Formula is illegal"); if (!LU.InsertFormula(F)) return false; CountRegisters(F, LUIdx); return true; } /// CollectLoopInvariantFixupsAndFormulae - Check for other uses of /// loop-invariant values which we're tracking. These other uses will pin these /// values in registers, making them less profitable for elimination. /// TODO: This currently misses non-constant addrec step registers. /// TODO: Should this give more weight to users inside the loop? void LSRInstance::CollectLoopInvariantFixupsAndFormulae() { SmallVector<const SCEV *, 8> Worklist(RegUses.begin(), RegUses.end()); SmallPtrSet<const SCEV *, 32> Visited; while (!Worklist.empty()) { const SCEV *S = Worklist.pop_back_val(); // Don't process the same SCEV twice if (!Visited.insert(S).second) continue; if (const SCEVNAryExpr *N = dyn_cast<SCEVNAryExpr>(S)) Worklist.append(N->op_begin(), N->op_end()); else if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S)) Worklist.push_back(C->getOperand()); else if (const SCEVUDivExpr *D = dyn_cast<SCEVUDivExpr>(S)) { Worklist.push_back(D->getLHS()); Worklist.push_back(D->getRHS()); } else if (const SCEVUnknown *US = dyn_cast<SCEVUnknown>(S)) { const Value *V = US->getValue(); if (const Instruction *Inst = dyn_cast<Instruction>(V)) { // Look for instructions defined outside the loop. if (L->contains(Inst)) continue; } else if (isa<UndefValue>(V)) // Undef doesn't have a live range, so it doesn't matter. continue; for (const Use &U : V->uses()) { const Instruction *UserInst = dyn_cast<Instruction>(U.getUser()); // Ignore non-instructions. if (!UserInst) continue; // Ignore instructions in other functions (as can happen with // Constants). if (UserInst->getParent()->getParent() != L->getHeader()->getParent()) continue; // Ignore instructions not dominated by the loop. const BasicBlock *UseBB = !isa<PHINode>(UserInst) ? UserInst->getParent() : cast<PHINode>(UserInst)->getIncomingBlock( PHINode::getIncomingValueNumForOperand(U.getOperandNo())); if (!DT.dominates(L->getHeader(), UseBB)) continue; // Ignore uses which are part of other SCEV expressions, to avoid // analyzing them multiple times. if (SE.isSCEVable(UserInst->getType())) { const SCEV *UserS = SE.getSCEV(const_cast<Instruction *>(UserInst)); // If the user is a no-op, look through to its uses. if (!isa<SCEVUnknown>(UserS)) continue; if (UserS == US) { Worklist.push_back( SE.getUnknown(const_cast<Instruction *>(UserInst))); continue; } } // Ignore icmp instructions which are already being analyzed. if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UserInst)) { unsigned OtherIdx = !U.getOperandNo(); Value *OtherOp = const_cast<Value *>(ICI->getOperand(OtherIdx)); if (SE.hasComputableLoopEvolution(SE.getSCEV(OtherOp), L)) continue; } LSRFixup &LF = getNewFixup(); LF.UserInst = const_cast<Instruction *>(UserInst); LF.OperandValToReplace = U; std::pair<size_t, int64_t> P = getUse(S, LSRUse::Basic, nullptr); LF.LUIdx = P.first; LF.Offset = P.second; LSRUse &LU = Uses[LF.LUIdx]; LU.AllFixupsOutsideLoop &= LF.isUseFullyOutsideLoop(L); if (!LU.WidestFixupType || SE.getTypeSizeInBits(LU.WidestFixupType) < SE.getTypeSizeInBits(LF.OperandValToReplace->getType())) LU.WidestFixupType = LF.OperandValToReplace->getType(); InsertSupplementalFormula(US, LU, LF.LUIdx); CountRegisters(LU.Formulae.back(), Uses.size() - 1); break; } } } } /// CollectSubexprs - Split S into subexpressions which can be pulled out into /// separate registers. If C is non-null, multiply each subexpression by C. /// /// Return remainder expression after factoring the subexpressions captured by /// Ops. If Ops is complete, return NULL. static const SCEV *CollectSubexprs(const SCEV *S, const SCEVConstant *C, SmallVectorImpl<const SCEV *> &Ops, const Loop *L, ScalarEvolution &SE, unsigned Depth = 0) { // Arbitrarily cap recursion to protect compile time. if (Depth >= 3) return S; if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { // Break out add operands. for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end(); I != E; ++I) { const SCEV *Remainder = CollectSubexprs(*I, C, Ops, L, SE, Depth+1); if (Remainder) Ops.push_back(C ? SE.getMulExpr(C, Remainder) : Remainder); } return nullptr; } else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { // Split a non-zero base out of an addrec. if (AR->getStart()->isZero()) return S; const SCEV *Remainder = CollectSubexprs(AR->getStart(), C, Ops, L, SE, Depth+1); // Split the non-zero AddRec unless it is part of a nested recurrence that // does not pertain to this loop. if (Remainder && (AR->getLoop() == L || !isa<SCEVAddRecExpr>(Remainder))) { Ops.push_back(C ? SE.getMulExpr(C, Remainder) : Remainder); Remainder = nullptr; } if (Remainder != AR->getStart()) { if (!Remainder) Remainder = SE.getConstant(AR->getType(), 0); return SE.getAddRecExpr(Remainder, AR->getStepRecurrence(SE), AR->getLoop(), //FIXME: AR->getNoWrapFlags(SCEV::FlagNW) SCEV::FlagAnyWrap); } } else if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) { // Break (C * (a + b + c)) into C*a + C*b + C*c. if (Mul->getNumOperands() != 2) return S; if (const SCEVConstant *Op0 = dyn_cast<SCEVConstant>(Mul->getOperand(0))) { C = C ? cast<SCEVConstant>(SE.getMulExpr(C, Op0)) : Op0; const SCEV *Remainder = CollectSubexprs(Mul->getOperand(1), C, Ops, L, SE, Depth+1); if (Remainder) Ops.push_back(SE.getMulExpr(C, Remainder)); return nullptr; } } return S; } /// \brief Helper function for LSRInstance::GenerateReassociations. void LSRInstance::GenerateReassociationsImpl(LSRUse &LU, unsigned LUIdx, const Formula &Base, unsigned Depth, size_t Idx, bool IsScaledReg) { const SCEV *BaseReg = IsScaledReg ? Base.ScaledReg : Base.BaseRegs[Idx]; SmallVector<const SCEV *, 8> AddOps; const SCEV *Remainder = CollectSubexprs(BaseReg, nullptr, AddOps, L, SE); if (Remainder) AddOps.push_back(Remainder); if (AddOps.size() == 1) return; for (SmallVectorImpl<const SCEV *>::const_iterator J = AddOps.begin(), JE = AddOps.end(); J != JE; ++J) { // Loop-variant "unknown" values are uninteresting; we won't be able to // do anything meaningful with them. if (isa<SCEVUnknown>(*J) && !SE.isLoopInvariant(*J, L)) continue; // Don't pull a constant into a register if the constant could be folded // into an immediate field. if (isAlwaysFoldable(TTI, SE, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, *J, Base.getNumRegs() > 1)) continue; // Collect all operands except *J. SmallVector<const SCEV *, 8> InnerAddOps( ((const SmallVector<const SCEV *, 8> &)AddOps).begin(), J); InnerAddOps.append(std::next(J), ((const SmallVector<const SCEV *, 8> &)AddOps).end()); // Don't leave just a constant behind in a register if the constant could // be folded into an immediate field. if (InnerAddOps.size() == 1 && isAlwaysFoldable(TTI, SE, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, InnerAddOps[0], Base.getNumRegs() > 1)) continue; const SCEV *InnerSum = SE.getAddExpr(InnerAddOps); if (InnerSum->isZero()) continue; Formula F = Base; // Add the remaining pieces of the add back into the new formula. const SCEVConstant *InnerSumSC = dyn_cast<SCEVConstant>(InnerSum); if (InnerSumSC && SE.getTypeSizeInBits(InnerSumSC->getType()) <= 64 && TTI.isLegalAddImmediate((uint64_t)F.UnfoldedOffset + InnerSumSC->getValue()->getZExtValue())) { F.UnfoldedOffset = (uint64_t)F.UnfoldedOffset + InnerSumSC->getValue()->getZExtValue(); if (IsScaledReg) F.ScaledReg = nullptr; else F.BaseRegs.erase(F.BaseRegs.begin() + Idx); } else if (IsScaledReg) F.ScaledReg = InnerSum; else F.BaseRegs[Idx] = InnerSum; // Add J as its own register, or an unfolded immediate. const SCEVConstant *SC = dyn_cast<SCEVConstant>(*J); if (SC && SE.getTypeSizeInBits(SC->getType()) <= 64 && TTI.isLegalAddImmediate((uint64_t)F.UnfoldedOffset + SC->getValue()->getZExtValue())) F.UnfoldedOffset = (uint64_t)F.UnfoldedOffset + SC->getValue()->getZExtValue(); else F.BaseRegs.push_back(*J); // We may have changed the number of register in base regs, adjust the // formula accordingly. F.Canonicalize(); if (InsertFormula(LU, LUIdx, F)) // If that formula hadn't been seen before, recurse to find more like // it. GenerateReassociations(LU, LUIdx, LU.Formulae.back(), Depth + 1); } } /// GenerateReassociations - Split out subexpressions from adds and the bases of /// addrecs. void LSRInstance::GenerateReassociations(LSRUse &LU, unsigned LUIdx, Formula Base, unsigned Depth) { assert(Base.isCanonical() && "Input must be in the canonical form"); // Arbitrarily cap recursion to protect compile time. if (Depth >= 3) return; for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i) GenerateReassociationsImpl(LU, LUIdx, Base, Depth, i); if (Base.Scale == 1) GenerateReassociationsImpl(LU, LUIdx, Base, Depth, /* Idx */ -1, /* IsScaledReg */ true); } /// GenerateCombinations - Generate a formula consisting of all of the /// loop-dominating registers added into a single register. void LSRInstance::GenerateCombinations(LSRUse &LU, unsigned LUIdx, Formula Base) { // This method is only interesting on a plurality of registers. if (Base.BaseRegs.size() + (Base.Scale == 1) <= 1) return; // Flatten the representation, i.e., reg1 + 1*reg2 => reg1 + reg2, before // processing the formula. Base.Unscale(); Formula F = Base; F.BaseRegs.clear(); SmallVector<const SCEV *, 4> Ops; for (SmallVectorImpl<const SCEV *>::const_iterator I = Base.BaseRegs.begin(), E = Base.BaseRegs.end(); I != E; ++I) { const SCEV *BaseReg = *I; if (SE.properlyDominates(BaseReg, L->getHeader()) && !SE.hasComputableLoopEvolution(BaseReg, L)) Ops.push_back(BaseReg); else F.BaseRegs.push_back(BaseReg); } if (Ops.size() > 1) { const SCEV *Sum = SE.getAddExpr(Ops); // TODO: If Sum is zero, it probably means ScalarEvolution missed an // opportunity to fold something. For now, just ignore such cases // rather than proceed with zero in a register. if (!Sum->isZero()) { F.BaseRegs.push_back(Sum); F.Canonicalize(); (void)InsertFormula(LU, LUIdx, F); } } } /// \brief Helper function for LSRInstance::GenerateSymbolicOffsets. void LSRInstance::GenerateSymbolicOffsetsImpl(LSRUse &LU, unsigned LUIdx, const Formula &Base, size_t Idx, bool IsScaledReg) { const SCEV *G = IsScaledReg ? Base.ScaledReg : Base.BaseRegs[Idx]; GlobalValue *GV = ExtractSymbol(G, SE); if (G->isZero() || !GV) return; Formula F = Base; F.BaseGV = GV; if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, F)) return; if (IsScaledReg) F.ScaledReg = G; else F.BaseRegs[Idx] = G; (void)InsertFormula(LU, LUIdx, F); } /// GenerateSymbolicOffsets - Generate reuse formulae using symbolic offsets. void LSRInstance::GenerateSymbolicOffsets(LSRUse &LU, unsigned LUIdx, Formula Base) { // We can't add a symbolic offset if the address already contains one. if (Base.BaseGV) return; for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i) GenerateSymbolicOffsetsImpl(LU, LUIdx, Base, i); if (Base.Scale == 1) GenerateSymbolicOffsetsImpl(LU, LUIdx, Base, /* Idx */ -1, /* IsScaledReg */ true); } /// \brief Helper function for LSRInstance::GenerateConstantOffsets. void LSRInstance::GenerateConstantOffsetsImpl( LSRUse &LU, unsigned LUIdx, const Formula &Base, const SmallVectorImpl<int64_t> &Worklist, size_t Idx, bool IsScaledReg) { const SCEV *G = IsScaledReg ? Base.ScaledReg : Base.BaseRegs[Idx]; for (SmallVectorImpl<int64_t>::const_iterator I = Worklist.begin(), E = Worklist.end(); I != E; ++I) { Formula F = Base; F.BaseOffset = (uint64_t)Base.BaseOffset - *I; if (isLegalUse(TTI, LU.MinOffset - *I, LU.MaxOffset - *I, LU.Kind, LU.AccessTy, F)) { // Add the offset to the base register. const SCEV *NewG = SE.getAddExpr(SE.getConstant(G->getType(), *I), G); // If it cancelled out, drop the base register, otherwise update it. if (NewG->isZero()) { if (IsScaledReg) { F.Scale = 0; F.ScaledReg = nullptr; } else F.DeleteBaseReg(F.BaseRegs[Idx]); F.Canonicalize(); } else if (IsScaledReg) F.ScaledReg = NewG; else F.BaseRegs[Idx] = NewG; (void)InsertFormula(LU, LUIdx, F); } } int64_t Imm = ExtractImmediate(G, SE); if (G->isZero() || Imm == 0) return; Formula F = Base; F.BaseOffset = (uint64_t)F.BaseOffset + Imm; if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, F)) return; if (IsScaledReg) F.ScaledReg = G; else F.BaseRegs[Idx] = G; (void)InsertFormula(LU, LUIdx, F); } /// GenerateConstantOffsets - Generate reuse formulae using symbolic offsets. void LSRInstance::GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx, Formula Base) { // TODO: For now, just add the min and max offset, because it usually isn't // worthwhile looking at everything inbetween. SmallVector<int64_t, 2> Worklist; Worklist.push_back(LU.MinOffset); if (LU.MaxOffset != LU.MinOffset) Worklist.push_back(LU.MaxOffset); for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i) GenerateConstantOffsetsImpl(LU, LUIdx, Base, Worklist, i); if (Base.Scale == 1) GenerateConstantOffsetsImpl(LU, LUIdx, Base, Worklist, /* Idx */ -1, /* IsScaledReg */ true); } /// GenerateICmpZeroScales - For ICmpZero, check to see if we can scale up /// the comparison. For example, x == y -> x*c == y*c. void LSRInstance::GenerateICmpZeroScales(LSRUse &LU, unsigned LUIdx, Formula Base) { if (LU.Kind != LSRUse::ICmpZero) return; // Determine the integer type for the base formula. Type *IntTy = Base.getType(); if (!IntTy) return; if (SE.getTypeSizeInBits(IntTy) > 64) return; // Don't do this if there is more than one offset. if (LU.MinOffset != LU.MaxOffset) return; assert(!Base.BaseGV && "ICmpZero use is not legal!"); // Check each interesting stride. for (SmallSetVector<int64_t, 8>::const_iterator I = Factors.begin(), E = Factors.end(); I != E; ++I) { int64_t Factor = *I; // Check that the multiplication doesn't overflow. if (Base.BaseOffset == INT64_MIN && Factor == -1) continue; int64_t NewBaseOffset = (uint64_t)Base.BaseOffset * Factor; if (NewBaseOffset / Factor != Base.BaseOffset) continue; // If the offset will be truncated at this use, check that it is in bounds. if (!IntTy->isPointerTy() && !ConstantInt::isValueValidForType(IntTy, NewBaseOffset)) continue; // Check that multiplying with the use offset doesn't overflow. int64_t Offset = LU.MinOffset; if (Offset == INT64_MIN && Factor == -1) continue; Offset = (uint64_t)Offset * Factor; if (Offset / Factor != LU.MinOffset) continue; // If the offset will be truncated at this use, check that it is in bounds. if (!IntTy->isPointerTy() && !ConstantInt::isValueValidForType(IntTy, Offset)) continue; Formula F = Base; F.BaseOffset = NewBaseOffset; // Check that this scale is legal. if (!isLegalUse(TTI, Offset, Offset, LU.Kind, LU.AccessTy, F)) continue; // Compensate for the use having MinOffset built into it. F.BaseOffset = (uint64_t)F.BaseOffset + Offset - LU.MinOffset; const SCEV *FactorS = SE.getConstant(IntTy, Factor); // Check that multiplying with each base register doesn't overflow. for (size_t i = 0, e = F.BaseRegs.size(); i != e; ++i) { F.BaseRegs[i] = SE.getMulExpr(F.BaseRegs[i], FactorS); if (getExactSDiv(F.BaseRegs[i], FactorS, SE) != Base.BaseRegs[i]) goto next; } // Check that multiplying with the scaled register doesn't overflow. if (F.ScaledReg) { F.ScaledReg = SE.getMulExpr(F.ScaledReg, FactorS); if (getExactSDiv(F.ScaledReg, FactorS, SE) != Base.ScaledReg) continue; } // Check that multiplying with the unfolded offset doesn't overflow. if (F.UnfoldedOffset != 0) { if (F.UnfoldedOffset == INT64_MIN && Factor == -1) continue; F.UnfoldedOffset = (uint64_t)F.UnfoldedOffset * Factor; if (F.UnfoldedOffset / Factor != Base.UnfoldedOffset) continue; // If the offset will be truncated, check that it is in bounds. if (!IntTy->isPointerTy() && !ConstantInt::isValueValidForType(IntTy, F.UnfoldedOffset)) continue; } // If we make it here and it's legal, add it. (void)InsertFormula(LU, LUIdx, F); next:; } } /// GenerateScales - Generate stride factor reuse formulae by making use of /// scaled-offset address modes, for example. void LSRInstance::GenerateScales(LSRUse &LU, unsigned LUIdx, Formula Base) { // Determine the integer type for the base formula. Type *IntTy = Base.getType(); if (!IntTy) return; // If this Formula already has a scaled register, we can't add another one. // Try to unscale the formula to generate a better scale. if (Base.Scale != 0 && !Base.Unscale()) return; assert(Base.Scale == 0 && "Unscale did not did its job!"); // Check each interesting stride. for (SmallSetVector<int64_t, 8>::const_iterator I = Factors.begin(), E = Factors.end(); I != E; ++I) { int64_t Factor = *I; Base.Scale = Factor; Base.HasBaseReg = Base.BaseRegs.size() > 1; // Check whether this scale is going to be legal. if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, Base)) { // As a special-case, handle special out-of-loop Basic users specially. // TODO: Reconsider this special case. if (LU.Kind == LSRUse::Basic && isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LSRUse::Special, LU.AccessTy, Base) && LU.AllFixupsOutsideLoop) LU.Kind = LSRUse::Special; else continue; } // For an ICmpZero, negating a solitary base register won't lead to // new solutions. if (LU.Kind == LSRUse::ICmpZero && !Base.HasBaseReg && Base.BaseOffset == 0 && !Base.BaseGV) continue; // For each addrec base reg, apply the scale, if possible. for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i) if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Base.BaseRegs[i])) { const SCEV *FactorS = SE.getConstant(IntTy, Factor); if (FactorS->isZero()) continue; // Divide out the factor, ignoring high bits, since we'll be // scaling the value back up in the end. if (const SCEV *Quotient = getExactSDiv(AR, FactorS, SE, true)) { // TODO: This could be optimized to avoid all the copying. Formula F = Base; F.ScaledReg = Quotient; F.DeleteBaseReg(F.BaseRegs[i]); // The canonical representation of 1*reg is reg, which is already in // Base. In that case, do not try to insert the formula, it will be // rejected anyway. if (F.Scale == 1 && F.BaseRegs.empty()) continue; (void)InsertFormula(LU, LUIdx, F); } } } } /// GenerateTruncates - Generate reuse formulae from different IV types. void LSRInstance::GenerateTruncates(LSRUse &LU, unsigned LUIdx, Formula Base) { // Don't bother truncating symbolic values. if (Base.BaseGV) return; // Determine the integer type for the base formula. Type *DstTy = Base.getType(); if (!DstTy) return; DstTy = SE.getEffectiveSCEVType(DstTy); for (SmallSetVector<Type *, 4>::const_iterator I = Types.begin(), E = Types.end(); I != E; ++I) { Type *SrcTy = *I; if (SrcTy != DstTy && TTI.isTruncateFree(SrcTy, DstTy)) { Formula F = Base; if (F.ScaledReg) F.ScaledReg = SE.getAnyExtendExpr(F.ScaledReg, *I); for (SmallVectorImpl<const SCEV *>::iterator J = F.BaseRegs.begin(), JE = F.BaseRegs.end(); J != JE; ++J) *J = SE.getAnyExtendExpr(*J, SrcTy); // TODO: This assumes we've done basic processing on all uses and // have an idea what the register usage is. if (!F.hasRegsUsedByUsesOtherThan(LUIdx, RegUses)) continue; (void)InsertFormula(LU, LUIdx, F); } } } namespace { /// WorkItem - Helper class for GenerateCrossUseConstantOffsets. It's used to /// defer modifications so that the search phase doesn't have to worry about /// the data structures moving underneath it. struct WorkItem { size_t LUIdx; int64_t Imm; const SCEV *OrigReg; WorkItem(size_t LI, int64_t I, const SCEV *R) : LUIdx(LI), Imm(I), OrigReg(R) {} void print(raw_ostream &OS) const; void dump() const; }; } void WorkItem::print(raw_ostream &OS) const { OS << "in formulae referencing " << *OrigReg << " in use " << LUIdx << " , add offset " << Imm; } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void WorkItem::dump() const { print(errs()); errs() << '\n'; } #endif /// GenerateCrossUseConstantOffsets - Look for registers which are a constant /// distance apart and try to form reuse opportunities between them. void LSRInstance::GenerateCrossUseConstantOffsets() { // Group the registers by their value without any added constant offset. typedef std::map<int64_t, const SCEV *> ImmMapTy; typedef DenseMap<const SCEV *, ImmMapTy> RegMapTy; RegMapTy Map; DenseMap<const SCEV *, SmallBitVector> UsedByIndicesMap; SmallVector<const SCEV *, 8> Sequence; for (RegUseTracker::const_iterator I = RegUses.begin(), E = RegUses.end(); I != E; ++I) { const SCEV *Reg = *I; int64_t Imm = ExtractImmediate(Reg, SE); std::pair<RegMapTy::iterator, bool> Pair = Map.insert(std::make_pair(Reg, ImmMapTy())); if (Pair.second) Sequence.push_back(Reg); Pair.first->second.insert(std::make_pair(Imm, *I)); UsedByIndicesMap[Reg] |= RegUses.getUsedByIndices(*I); } // Now examine each set of registers with the same base value. Build up // a list of work to do and do the work in a separate step so that we're // not adding formulae and register counts while we're searching. SmallVector<WorkItem, 32> WorkItems; SmallSet<std::pair<size_t, int64_t>, 32> UniqueItems; for (SmallVectorImpl<const SCEV *>::const_iterator I = Sequence.begin(), E = Sequence.end(); I != E; ++I) { const SCEV *Reg = *I; const ImmMapTy &Imms = Map.find(Reg)->second; // It's not worthwhile looking for reuse if there's only one offset. if (Imms.size() == 1) continue; DEBUG(dbgs() << "Generating cross-use offsets for " << *Reg << ':'; for (ImmMapTy::const_iterator J = Imms.begin(), JE = Imms.end(); J != JE; ++J) dbgs() << ' ' << J->first; dbgs() << '\n'); // Examine each offset. for (ImmMapTy::const_iterator J = Imms.begin(), JE = Imms.end(); J != JE; ++J) { const SCEV *OrigReg = J->second; int64_t JImm = J->first; const SmallBitVector &UsedByIndices = RegUses.getUsedByIndices(OrigReg); if (!isa<SCEVConstant>(OrigReg) && UsedByIndicesMap[Reg].count() == 1) { DEBUG(dbgs() << "Skipping cross-use reuse for " << *OrigReg << '\n'); continue; } // Conservatively examine offsets between this orig reg a few selected // other orig regs. ImmMapTy::const_iterator OtherImms[] = { Imms.begin(), std::prev(Imms.end()), Imms.lower_bound((Imms.begin()->first + std::prev(Imms.end())->first) / 2) }; for (size_t i = 0, e = array_lengthof(OtherImms); i != e; ++i) { ImmMapTy::const_iterator M = OtherImms[i]; if (M == J || M == JE) continue; // Compute the difference between the two. int64_t Imm = (uint64_t)JImm - M->first; for (int LUIdx = UsedByIndices.find_first(); LUIdx != -1; LUIdx = UsedByIndices.find_next(LUIdx)) // Make a memo of this use, offset, and register tuple. if (UniqueItems.insert(std::make_pair(LUIdx, Imm)).second) WorkItems.push_back(WorkItem(LUIdx, Imm, OrigReg)); } } } Map.clear(); Sequence.clear(); UsedByIndicesMap.clear(); UniqueItems.clear(); // Now iterate through the worklist and add new formulae. for (SmallVectorImpl<WorkItem>::const_iterator I = WorkItems.begin(), E = WorkItems.end(); I != E; ++I) { const WorkItem &WI = *I; size_t LUIdx = WI.LUIdx; LSRUse &LU = Uses[LUIdx]; int64_t Imm = WI.Imm; const SCEV *OrigReg = WI.OrigReg; Type *IntTy = SE.getEffectiveSCEVType(OrigReg->getType()); const SCEV *NegImmS = SE.getSCEV(ConstantInt::get(IntTy, -(uint64_t)Imm)); unsigned BitWidth = SE.getTypeSizeInBits(IntTy); // TODO: Use a more targeted data structure. for (size_t L = 0, LE = LU.Formulae.size(); L != LE; ++L) { Formula F = LU.Formulae[L]; // FIXME: The code for the scaled and unscaled registers looks // very similar but slightly different. Investigate if they // could be merged. That way, we would not have to unscale the // Formula. F.Unscale(); // Use the immediate in the scaled register. if (F.ScaledReg == OrigReg) { int64_t Offset = (uint64_t)F.BaseOffset + Imm * (uint64_t)F.Scale; // Don't create 50 + reg(-50). if (F.referencesReg(SE.getSCEV( ConstantInt::get(IntTy, -(uint64_t)Offset)))) continue; Formula NewF = F; NewF.BaseOffset = Offset; if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, NewF)) continue; NewF.ScaledReg = SE.getAddExpr(NegImmS, NewF.ScaledReg); // If the new scale is a constant in a register, and adding the constant // value to the immediate would produce a value closer to zero than the // immediate itself, then the formula isn't worthwhile. if (const SCEVConstant *C = dyn_cast<SCEVConstant>(NewF.ScaledReg)) if (C->getValue()->isNegative() != (NewF.BaseOffset < 0) && (C->getValue()->getValue().abs() * APInt(BitWidth, F.Scale)) .ule(abs64(NewF.BaseOffset))) continue; // OK, looks good. NewF.Canonicalize(); (void)InsertFormula(LU, LUIdx, NewF); } else { // Use the immediate in a base register. for (size_t N = 0, NE = F.BaseRegs.size(); N != NE; ++N) { const SCEV *BaseReg = F.BaseRegs[N]; if (BaseReg != OrigReg) continue; Formula NewF = F; NewF.BaseOffset = (uint64_t)NewF.BaseOffset + Imm; if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, NewF)) { if (!TTI.isLegalAddImmediate((uint64_t)NewF.UnfoldedOffset + Imm)) continue; NewF = F; NewF.UnfoldedOffset = (uint64_t)NewF.UnfoldedOffset + Imm; } NewF.BaseRegs[N] = SE.getAddExpr(NegImmS, BaseReg); // If the new formula has a constant in a register, and adding the // constant value to the immediate would produce a value closer to // zero than the immediate itself, then the formula isn't worthwhile. for (SmallVectorImpl<const SCEV *>::const_iterator J = NewF.BaseRegs.begin(), JE = NewF.BaseRegs.end(); J != JE; ++J) if (const SCEVConstant *C = dyn_cast<SCEVConstant>(*J)) if ((C->getValue()->getValue() + NewF.BaseOffset).abs().slt( abs64(NewF.BaseOffset)) && (C->getValue()->getValue() + NewF.BaseOffset).countTrailingZeros() >= countTrailingZeros<uint64_t>(NewF.BaseOffset)) goto skip_formula; // Ok, looks good. NewF.Canonicalize(); (void)InsertFormula(LU, LUIdx, NewF); break; skip_formula:; } } } } } /// GenerateAllReuseFormulae - Generate formulae for each use. void LSRInstance::GenerateAllReuseFormulae() { // This is split into multiple loops so that hasRegsUsedByUsesOtherThan // queries are more precise. for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) { LSRUse &LU = Uses[LUIdx]; for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i) GenerateReassociations(LU, LUIdx, LU.Formulae[i]); for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i) GenerateCombinations(LU, LUIdx, LU.Formulae[i]); } for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) { LSRUse &LU = Uses[LUIdx]; for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i) GenerateSymbolicOffsets(LU, LUIdx, LU.Formulae[i]); for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i) GenerateConstantOffsets(LU, LUIdx, LU.Formulae[i]); for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i) GenerateICmpZeroScales(LU, LUIdx, LU.Formulae[i]); for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i) GenerateScales(LU, LUIdx, LU.Formulae[i]); } for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) { LSRUse &LU = Uses[LUIdx]; for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i) GenerateTruncates(LU, LUIdx, LU.Formulae[i]); } GenerateCrossUseConstantOffsets(); DEBUG(dbgs() << "\n" "After generating reuse formulae:\n"; print_uses(dbgs())); } /// If there are multiple formulae with the same set of registers used /// by other uses, pick the best one and delete the others. void LSRInstance::FilterOutUndesirableDedicatedRegisters() { DenseSet<const SCEV *> VisitedRegs; SmallPtrSet<const SCEV *, 16> Regs; SmallPtrSet<const SCEV *, 16> LoserRegs; #ifndef NDEBUG bool ChangedFormulae = false; #endif // Collect the best formula for each unique set of shared registers. This // is reset for each use. typedef DenseMap<SmallVector<const SCEV *, 4>, size_t, UniquifierDenseMapInfo> BestFormulaeTy; BestFormulaeTy BestFormulae; for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) { LSRUse &LU = Uses[LUIdx]; DEBUG(dbgs() << "Filtering for use "; LU.print(dbgs()); dbgs() << '\n'); bool Any = false; for (size_t FIdx = 0, NumForms = LU.Formulae.size(); FIdx != NumForms; ++FIdx) { Formula &F = LU.Formulae[FIdx]; // Some formulas are instant losers. For example, they may depend on // nonexistent AddRecs from other loops. These need to be filtered // immediately, otherwise heuristics could choose them over others leading // to an unsatisfactory solution. Passing LoserRegs into RateFormula here // avoids the need to recompute this information across formulae using the // same bad AddRec. Passing LoserRegs is also essential unless we remove // the corresponding bad register from the Regs set. Cost CostF; Regs.clear(); CostF.RateFormula(TTI, F, Regs, VisitedRegs, L, LU.Offsets, SE, DT, LU, &LoserRegs); if (CostF.isLoser()) { // During initial formula generation, undesirable formulae are generated // by uses within other loops that have some non-trivial address mode or // use the postinc form of the IV. LSR needs to provide these formulae // as the basis of rediscovering the desired formula that uses an AddRec // corresponding to the existing phi. Once all formulae have been // generated, these initial losers may be pruned. DEBUG(dbgs() << " Filtering loser "; F.print(dbgs()); dbgs() << "\n"); } else { SmallVector<const SCEV *, 4> Key; for (SmallVectorImpl<const SCEV *>::const_iterator J = F.BaseRegs.begin(), JE = F.BaseRegs.end(); J != JE; ++J) { const SCEV *Reg = *J; if (RegUses.isRegUsedByUsesOtherThan(Reg, LUIdx)) Key.push_back(Reg); } if (F.ScaledReg && RegUses.isRegUsedByUsesOtherThan(F.ScaledReg, LUIdx)) Key.push_back(F.ScaledReg); // Unstable sort by host order ok, because this is only used for // uniquifying. std::sort(Key.begin(), Key.end()); std::pair<BestFormulaeTy::const_iterator, bool> P = BestFormulae.insert(std::make_pair(Key, FIdx)); if (P.second) continue; Formula &Best = LU.Formulae[P.first->second]; Cost CostBest; Regs.clear(); CostBest.RateFormula(TTI, Best, Regs, VisitedRegs, L, LU.Offsets, SE, DT, LU); if (CostF < CostBest) std::swap(F, Best); DEBUG(dbgs() << " Filtering out formula "; F.print(dbgs()); dbgs() << "\n" " in favor of formula "; Best.print(dbgs()); dbgs() << '\n'); } #ifndef NDEBUG ChangedFormulae = true; #endif LU.DeleteFormula(F); --FIdx; --NumForms; Any = true; } // Now that we've filtered out some formulae, recompute the Regs set. if (Any) LU.RecomputeRegs(LUIdx, RegUses); // Reset this to prepare for the next use. BestFormulae.clear(); } DEBUG(if (ChangedFormulae) { dbgs() << "\n" "After filtering out undesirable candidates:\n"; print_uses(dbgs()); }); } // This is a rough guess that seems to work fairly well. static const size_t ComplexityLimit = UINT16_MAX; /// EstimateSearchSpaceComplexity - Estimate the worst-case number of /// solutions the solver might have to consider. It almost never considers /// this many solutions because it prune the search space, but the pruning /// isn't always sufficient. size_t LSRInstance::EstimateSearchSpaceComplexity() const { size_t Power = 1; for (SmallVectorImpl<LSRUse>::const_iterator I = Uses.begin(), E = Uses.end(); I != E; ++I) { size_t FSize = I->Formulae.size(); if (FSize >= ComplexityLimit) { Power = ComplexityLimit; break; } Power *= FSize; if (Power >= ComplexityLimit) break; } return Power; } /// NarrowSearchSpaceByDetectingSupersets - When one formula uses a superset /// of the registers of another formula, it won't help reduce register /// pressure (though it may not necessarily hurt register pressure); remove /// it to simplify the system. void LSRInstance::NarrowSearchSpaceByDetectingSupersets() { if (EstimateSearchSpaceComplexity() >= ComplexityLimit) { DEBUG(dbgs() << "The search space is too complex.\n"); DEBUG(dbgs() << "Narrowing the search space by eliminating formulae " "which use a superset of registers used by other " "formulae.\n"); for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) { LSRUse &LU = Uses[LUIdx]; bool Any = false; for (size_t i = 0, e = LU.Formulae.size(); i != e; ++i) { Formula &F = LU.Formulae[i]; // Look for a formula with a constant or GV in a register. If the use // also has a formula with that same value in an immediate field, // delete the one that uses a register. for (SmallVectorImpl<const SCEV *>::const_iterator I = F.BaseRegs.begin(), E = F.BaseRegs.end(); I != E; ++I) { if (const SCEVConstant *C = dyn_cast<SCEVConstant>(*I)) { Formula NewF = F; NewF.BaseOffset += C->getValue()->getSExtValue(); NewF.BaseRegs.erase(NewF.BaseRegs.begin() + (I - F.BaseRegs.begin())); if (LU.HasFormulaWithSameRegs(NewF)) { DEBUG(dbgs() << " Deleting "; F.print(dbgs()); dbgs() << '\n'); LU.DeleteFormula(F); --i; --e; Any = true; break; } } else if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(*I)) { if (GlobalValue *GV = dyn_cast<GlobalValue>(U->getValue())) if (!F.BaseGV) { Formula NewF = F; NewF.BaseGV = GV; NewF.BaseRegs.erase(NewF.BaseRegs.begin() + (I - F.BaseRegs.begin())); if (LU.HasFormulaWithSameRegs(NewF)) { DEBUG(dbgs() << " Deleting "; F.print(dbgs()); dbgs() << '\n'); LU.DeleteFormula(F); --i; --e; Any = true; break; } } } } } if (Any) LU.RecomputeRegs(LUIdx, RegUses); } DEBUG(dbgs() << "After pre-selection:\n"; print_uses(dbgs())); } } /// NarrowSearchSpaceByCollapsingUnrolledCode - When there are many registers /// for expressions like A, A+1, A+2, etc., allocate a single register for /// them. void LSRInstance::NarrowSearchSpaceByCollapsingUnrolledCode() { if (EstimateSearchSpaceComplexity() < ComplexityLimit) return; DEBUG(dbgs() << "The search space is too complex.\n" "Narrowing the search space by assuming that uses separated " "by a constant offset will use the same registers.\n"); // This is especially useful for unrolled loops. for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) { LSRUse &LU = Uses[LUIdx]; for (SmallVectorImpl<Formula>::const_iterator I = LU.Formulae.begin(), E = LU.Formulae.end(); I != E; ++I) { const Formula &F = *I; if (F.BaseOffset == 0 || (F.Scale != 0 && F.Scale != 1)) continue; LSRUse *LUThatHas = FindUseWithSimilarFormula(F, LU); if (!LUThatHas) continue; if (!reconcileNewOffset(*LUThatHas, F.BaseOffset, /*HasBaseReg=*/ false, LU.Kind, LU.AccessTy)) continue; DEBUG(dbgs() << " Deleting use "; LU.print(dbgs()); dbgs() << '\n'); LUThatHas->AllFixupsOutsideLoop &= LU.AllFixupsOutsideLoop; // Update the relocs to reference the new use. for (SmallVectorImpl<LSRFixup>::iterator I = Fixups.begin(), E = Fixups.end(); I != E; ++I) { LSRFixup &Fixup = *I; if (Fixup.LUIdx == LUIdx) { Fixup.LUIdx = LUThatHas - &Uses.front(); Fixup.Offset += F.BaseOffset; // Add the new offset to LUThatHas' offset list. if (LUThatHas->Offsets.back() != Fixup.Offset) { LUThatHas->Offsets.push_back(Fixup.Offset); if (Fixup.Offset > LUThatHas->MaxOffset) LUThatHas->MaxOffset = Fixup.Offset; if (Fixup.Offset < LUThatHas->MinOffset) LUThatHas->MinOffset = Fixup.Offset; } DEBUG(dbgs() << "New fixup has offset " << Fixup.Offset << '\n'); } if (Fixup.LUIdx == NumUses-1) Fixup.LUIdx = LUIdx; } // Delete formulae from the new use which are no longer legal. bool Any = false; for (size_t i = 0, e = LUThatHas->Formulae.size(); i != e; ++i) { Formula &F = LUThatHas->Formulae[i]; if (!isLegalUse(TTI, LUThatHas->MinOffset, LUThatHas->MaxOffset, LUThatHas->Kind, LUThatHas->AccessTy, F)) { DEBUG(dbgs() << " Deleting "; F.print(dbgs()); dbgs() << '\n'); LUThatHas->DeleteFormula(F); --i; --e; Any = true; } } if (Any) LUThatHas->RecomputeRegs(LUThatHas - &Uses.front(), RegUses); // Delete the old use. DeleteUse(LU, LUIdx); --LUIdx; --NumUses; break; } } DEBUG(dbgs() << "After pre-selection:\n"; print_uses(dbgs())); } /// NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters - Call /// FilterOutUndesirableDedicatedRegisters again, if necessary, now that /// we've done more filtering, as it may be able to find more formulae to /// eliminate. void LSRInstance::NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters(){ if (EstimateSearchSpaceComplexity() >= ComplexityLimit) { DEBUG(dbgs() << "The search space is too complex.\n"); DEBUG(dbgs() << "Narrowing the search space by re-filtering out " "undesirable dedicated registers.\n"); FilterOutUndesirableDedicatedRegisters(); DEBUG(dbgs() << "After pre-selection:\n"; print_uses(dbgs())); } } /// NarrowSearchSpaceByPickingWinnerRegs - Pick a register which seems likely /// to be profitable, and then in any use which has any reference to that /// register, delete all formulae which do not reference that register. void LSRInstance::NarrowSearchSpaceByPickingWinnerRegs() { // With all other options exhausted, loop until the system is simple // enough to handle. SmallPtrSet<const SCEV *, 4> Taken; while (EstimateSearchSpaceComplexity() >= ComplexityLimit) { // Ok, we have too many of formulae on our hands to conveniently handle. // Use a rough heuristic to thin out the list. DEBUG(dbgs() << "The search space is too complex.\n"); // Pick the register which is used by the most LSRUses, which is likely // to be a good reuse register candidate. const SCEV *Best = nullptr; unsigned BestNum = 0; for (RegUseTracker::const_iterator I = RegUses.begin(), E = RegUses.end(); I != E; ++I) { const SCEV *Reg = *I; if (Taken.count(Reg)) continue; if (!Best) Best = Reg; else { unsigned Count = RegUses.getUsedByIndices(Reg).count(); if (Count > BestNum) { Best = Reg; BestNum = Count; } } } DEBUG(dbgs() << "Narrowing the search space by assuming " << *Best << " will yield profitable reuse.\n"); Taken.insert(Best); // In any use with formulae which references this register, delete formulae // which don't reference it. for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) { LSRUse &LU = Uses[LUIdx]; if (!LU.Regs.count(Best)) continue; bool Any = false; for (size_t i = 0, e = LU.Formulae.size(); i != e; ++i) { Formula &F = LU.Formulae[i]; if (!F.referencesReg(Best)) { DEBUG(dbgs() << " Deleting "; F.print(dbgs()); dbgs() << '\n'); LU.DeleteFormula(F); --e; --i; Any = true; assert(e != 0 && "Use has no formulae left! Is Regs inconsistent?"); continue; } } if (Any) LU.RecomputeRegs(LUIdx, RegUses); } DEBUG(dbgs() << "After pre-selection:\n"; print_uses(dbgs())); } } /// NarrowSearchSpaceUsingHeuristics - If there are an extraordinary number of /// formulae to choose from, use some rough heuristics to prune down the number /// of formulae. This keeps the main solver from taking an extraordinary amount /// of time in some worst-case scenarios. void LSRInstance::NarrowSearchSpaceUsingHeuristics() { NarrowSearchSpaceByDetectingSupersets(); NarrowSearchSpaceByCollapsingUnrolledCode(); NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters(); NarrowSearchSpaceByPickingWinnerRegs(); } /// SolveRecurse - This is the recursive solver. void LSRInstance::SolveRecurse(SmallVectorImpl<const Formula *> &Solution, Cost &SolutionCost, SmallVectorImpl<const Formula *> &Workspace, const Cost &CurCost, const SmallPtrSet<const SCEV *, 16> &CurRegs, DenseSet<const SCEV *> &VisitedRegs) const { // Some ideas: // - prune more: // - use more aggressive filtering // - sort the formula so that the most profitable solutions are found first // - sort the uses too // - search faster: // - don't compute a cost, and then compare. compare while computing a cost // and bail early. // - track register sets with SmallBitVector const LSRUse &LU = Uses[Workspace.size()]; // If this use references any register that's already a part of the // in-progress solution, consider it a requirement that a formula must // reference that register in order to be considered. This prunes out // unprofitable searching. SmallSetVector<const SCEV *, 4> ReqRegs; for (const SCEV *S : CurRegs) if (LU.Regs.count(S)) ReqRegs.insert(S); SmallPtrSet<const SCEV *, 16> NewRegs; Cost NewCost; for (SmallVectorImpl<Formula>::const_iterator I = LU.Formulae.begin(), E = LU.Formulae.end(); I != E; ++I) { const Formula &F = *I; // Ignore formulae which may not be ideal in terms of register reuse of // ReqRegs. The formula should use all required registers before // introducing new ones. int NumReqRegsToFind = std::min(F.getNumRegs(), ReqRegs.size()); for (SmallSetVector<const SCEV *, 4>::const_iterator J = ReqRegs.begin(), JE = ReqRegs.end(); J != JE; ++J) { const SCEV *Reg = *J; if ((F.ScaledReg && F.ScaledReg == Reg) || std::find(F.BaseRegs.begin(), F.BaseRegs.end(), Reg) != F.BaseRegs.end()) { --NumReqRegsToFind; if (NumReqRegsToFind == 0) break; } } if (NumReqRegsToFind != 0) { // If none of the formulae satisfied the required registers, then we could // clear ReqRegs and try again. Currently, we simply give up in this case. continue; } // Evaluate the cost of the current formula. If it's already worse than // the current best, prune the search at that point. NewCost = CurCost; NewRegs = CurRegs; NewCost.RateFormula(TTI, F, NewRegs, VisitedRegs, L, LU.Offsets, SE, DT, LU); if (NewCost < SolutionCost) { Workspace.push_back(&F); if (Workspace.size() != Uses.size()) { SolveRecurse(Solution, SolutionCost, Workspace, NewCost, NewRegs, VisitedRegs); if (F.getNumRegs() == 1 && Workspace.size() == 1) VisitedRegs.insert(F.ScaledReg ? F.ScaledReg : F.BaseRegs[0]); } else { DEBUG(dbgs() << "New best at "; NewCost.print(dbgs()); dbgs() << ".\n Regs:"; for (const SCEV *S : NewRegs) dbgs() << ' ' << *S; dbgs() << '\n'); SolutionCost = NewCost; Solution = Workspace; } Workspace.pop_back(); } } } /// Solve - Choose one formula from each use. Return the results in the given /// Solution vector. void LSRInstance::Solve(SmallVectorImpl<const Formula *> &Solution) const { SmallVector<const Formula *, 8> Workspace; Cost SolutionCost; SolutionCost.Lose(); Cost CurCost; SmallPtrSet<const SCEV *, 16> CurRegs; DenseSet<const SCEV *> VisitedRegs; Workspace.reserve(Uses.size()); // SolveRecurse does all the work. SolveRecurse(Solution, SolutionCost, Workspace, CurCost, CurRegs, VisitedRegs); if (Solution.empty()) { DEBUG(dbgs() << "\nNo Satisfactory Solution\n"); return; } // Ok, we've now made all our decisions. DEBUG(dbgs() << "\n" "The chosen solution requires "; SolutionCost.print(dbgs()); dbgs() << ":\n"; for (size_t i = 0, e = Uses.size(); i != e; ++i) { dbgs() << " "; Uses[i].print(dbgs()); dbgs() << "\n" " "; Solution[i]->print(dbgs()); dbgs() << '\n'; }); assert(Solution.size() == Uses.size() && "Malformed solution!"); } /// HoistInsertPosition - Helper for AdjustInsertPositionForExpand. Climb up /// the dominator tree far as we can go while still being dominated by the /// input positions. This helps canonicalize the insert position, which /// encourages sharing. BasicBlock::iterator LSRInstance::HoistInsertPosition(BasicBlock::iterator IP, const SmallVectorImpl<Instruction *> &Inputs) const { for (;;) { const Loop *IPLoop = LI.getLoopFor(IP->getParent()); unsigned IPLoopDepth = IPLoop ? IPLoop->getLoopDepth() : 0; BasicBlock *IDom; for (DomTreeNode *Rung = DT.getNode(IP->getParent()); ; ) { if (!Rung) return IP; Rung = Rung->getIDom(); if (!Rung) return IP; IDom = Rung->getBlock(); // Don't climb into a loop though. const Loop *IDomLoop = LI.getLoopFor(IDom); unsigned IDomDepth = IDomLoop ? IDomLoop->getLoopDepth() : 0; if (IDomDepth <= IPLoopDepth && (IDomDepth != IPLoopDepth || IDomLoop == IPLoop)) break; } bool AllDominate = true; Instruction *BetterPos = nullptr; Instruction *Tentative = IDom->getTerminator(); for (SmallVectorImpl<Instruction *>::const_iterator I = Inputs.begin(), E = Inputs.end(); I != E; ++I) { Instruction *Inst = *I; if (Inst == Tentative || !DT.dominates(Inst, Tentative)) { AllDominate = false; break; } // Attempt to find an insert position in the middle of the block, // instead of at the end, so that it can be used for other expansions. if (IDom == Inst->getParent() && (!BetterPos || !DT.dominates(Inst, BetterPos))) BetterPos = std::next(BasicBlock::iterator(Inst)); } if (!AllDominate) break; if (BetterPos) IP = BetterPos; else IP = Tentative; } return IP; } /// AdjustInsertPositionForExpand - Determine an input position which will be /// dominated by the operands and which will dominate the result. BasicBlock::iterator LSRInstance::AdjustInsertPositionForExpand(BasicBlock::iterator LowestIP, const LSRFixup &LF, const LSRUse &LU, SCEVExpander &Rewriter) const { // Collect some instructions which must be dominated by the // expanding replacement. These must be dominated by any operands that // will be required in the expansion. SmallVector<Instruction *, 4> Inputs; if (Instruction *I = dyn_cast<Instruction>(LF.OperandValToReplace)) Inputs.push_back(I); if (LU.Kind == LSRUse::ICmpZero) if (Instruction *I = dyn_cast<Instruction>(cast<ICmpInst>(LF.UserInst)->getOperand(1))) Inputs.push_back(I); if (LF.PostIncLoops.count(L)) { if (LF.isUseFullyOutsideLoop(L)) Inputs.push_back(L->getLoopLatch()->getTerminator()); else Inputs.push_back(IVIncInsertPos); } // The expansion must also be dominated by the increment positions of any // loops it for which it is using post-inc mode. for (PostIncLoopSet::const_iterator I = LF.PostIncLoops.begin(), E = LF.PostIncLoops.end(); I != E; ++I) { const Loop *PIL = *I; if (PIL == L) continue; // Be dominated by the loop exit. SmallVector<BasicBlock *, 4> ExitingBlocks; PIL->getExitingBlocks(ExitingBlocks); if (!ExitingBlocks.empty()) { BasicBlock *BB = ExitingBlocks[0]; for (unsigned i = 1, e = ExitingBlocks.size(); i != e; ++i) BB = DT.findNearestCommonDominator(BB, ExitingBlocks[i]); Inputs.push_back(BB->getTerminator()); } } assert(!isa<PHINode>(LowestIP) && !isa<LandingPadInst>(LowestIP) && !isa<DbgInfoIntrinsic>(LowestIP) && "Insertion point must be a normal instruction"); // Then, climb up the immediate dominator tree as far as we can go while // still being dominated by the input positions. BasicBlock::iterator IP = HoistInsertPosition(LowestIP, Inputs); // Don't insert instructions before PHI nodes. while (isa<PHINode>(IP)) ++IP; // Ignore landingpad instructions. while (isa<LandingPadInst>(IP)) ++IP; // Ignore debug intrinsics. while (isa<DbgInfoIntrinsic>(IP)) ++IP; // Set IP below instructions recently inserted by SCEVExpander. This keeps the // IP consistent across expansions and allows the previously inserted // instructions to be reused by subsequent expansion. while (Rewriter.isInsertedInstruction(IP) && IP != LowestIP) ++IP; return IP; } /// Expand - Emit instructions for the leading candidate expression for this /// LSRUse (this is called "expanding"). Value *LSRInstance::Expand(const LSRFixup &LF, const Formula &F, BasicBlock::iterator IP, SCEVExpander &Rewriter, SmallVectorImpl<WeakVH> &DeadInsts) const { const LSRUse &LU = Uses[LF.LUIdx]; if (LU.RigidFormula) return LF.OperandValToReplace; // Determine an input position which will be dominated by the operands and // which will dominate the result. IP = AdjustInsertPositionForExpand(IP, LF, LU, Rewriter); // Inform the Rewriter if we have a post-increment use, so that it can // perform an advantageous expansion. Rewriter.setPostInc(LF.PostIncLoops); // This is the type that the user actually needs. Type *OpTy = LF.OperandValToReplace->getType(); // This will be the type that we'll initially expand to. Type *Ty = F.getType(); if (!Ty) // No type known; just expand directly to the ultimate type. Ty = OpTy; else if (SE.getEffectiveSCEVType(Ty) == SE.getEffectiveSCEVType(OpTy)) // Expand directly to the ultimate type if it's the right size. Ty = OpTy; // This is the type to do integer arithmetic in. Type *IntTy = SE.getEffectiveSCEVType(Ty); // Build up a list of operands to add together to form the full base. SmallVector<const SCEV *, 8> Ops; // Expand the BaseRegs portion. for (SmallVectorImpl<const SCEV *>::const_iterator I = F.BaseRegs.begin(), E = F.BaseRegs.end(); I != E; ++I) { const SCEV *Reg = *I; assert(!Reg->isZero() && "Zero allocated in a base register!"); // If we're expanding for a post-inc user, make the post-inc adjustment. PostIncLoopSet &Loops = const_cast<PostIncLoopSet &>(LF.PostIncLoops); Reg = TransformForPostIncUse(Denormalize, Reg, LF.UserInst, LF.OperandValToReplace, Loops, SE, DT); Ops.push_back(SE.getUnknown(Rewriter.expandCodeFor(Reg, nullptr, IP))); } // Expand the ScaledReg portion. Value *ICmpScaledV = nullptr; if (F.Scale != 0) { const SCEV *ScaledS = F.ScaledReg; // If we're expanding for a post-inc user, make the post-inc adjustment. PostIncLoopSet &Loops = const_cast<PostIncLoopSet &>(LF.PostIncLoops); ScaledS = TransformForPostIncUse(Denormalize, ScaledS, LF.UserInst, LF.OperandValToReplace, Loops, SE, DT); if (LU.Kind == LSRUse::ICmpZero) { // Expand ScaleReg as if it was part of the base regs. if (F.Scale == 1) Ops.push_back( SE.getUnknown(Rewriter.expandCodeFor(ScaledS, nullptr, IP))); else { // An interesting way of "folding" with an icmp is to use a negated // scale, which we'll implement by inserting it into the other operand // of the icmp. assert(F.Scale == -1 && "The only scale supported by ICmpZero uses is -1!"); ICmpScaledV = Rewriter.expandCodeFor(ScaledS, nullptr, IP); } } else { // Otherwise just expand the scaled register and an explicit scale, // which is expected to be matched as part of the address. // Flush the operand list to suppress SCEVExpander hoisting address modes. // Unless the addressing mode will not be folded. if (!Ops.empty() && LU.Kind == LSRUse::Address && isAMCompletelyFolded(TTI, LU, F)) { Value *FullV = Rewriter.expandCodeFor(SE.getAddExpr(Ops), Ty, IP); Ops.clear(); Ops.push_back(SE.getUnknown(FullV)); } ScaledS = SE.getUnknown(Rewriter.expandCodeFor(ScaledS, nullptr, IP)); if (F.Scale != 1) ScaledS = SE.getMulExpr(ScaledS, SE.getConstant(ScaledS->getType(), F.Scale)); Ops.push_back(ScaledS); } } // Expand the GV portion. if (F.BaseGV) { // Flush the operand list to suppress SCEVExpander hoisting. if (!Ops.empty()) { Value *FullV = Rewriter.expandCodeFor(SE.getAddExpr(Ops), Ty, IP); Ops.clear(); Ops.push_back(SE.getUnknown(FullV)); } Ops.push_back(SE.getUnknown(F.BaseGV)); } // Flush the operand list to suppress SCEVExpander hoisting of both folded and // unfolded offsets. LSR assumes they both live next to their uses. if (!Ops.empty()) { Value *FullV = Rewriter.expandCodeFor(SE.getAddExpr(Ops), Ty, IP); Ops.clear(); Ops.push_back(SE.getUnknown(FullV)); } // Expand the immediate portion. int64_t Offset = (uint64_t)F.BaseOffset + LF.Offset; if (Offset != 0) { if (LU.Kind == LSRUse::ICmpZero) { // The other interesting way of "folding" with an ICmpZero is to use a // negated immediate. if (!ICmpScaledV) ICmpScaledV = ConstantInt::get(IntTy, -(uint64_t)Offset); else { Ops.push_back(SE.getUnknown(ICmpScaledV)); ICmpScaledV = ConstantInt::get(IntTy, Offset); } } else { // Just add the immediate values. These again are expected to be matched // as part of the address. Ops.push_back(SE.getUnknown(ConstantInt::getSigned(IntTy, Offset))); } } // Expand the unfolded offset portion. int64_t UnfoldedOffset = F.UnfoldedOffset; if (UnfoldedOffset != 0) { // Just add the immediate values. Ops.push_back(SE.getUnknown(ConstantInt::getSigned(IntTy, UnfoldedOffset))); } // Emit instructions summing all the operands. const SCEV *FullS = Ops.empty() ? SE.getConstant(IntTy, 0) : SE.getAddExpr(Ops); Value *FullV = Rewriter.expandCodeFor(FullS, Ty, IP); // We're done expanding now, so reset the rewriter. Rewriter.clearPostInc(); // An ICmpZero Formula represents an ICmp which we're handling as a // comparison against zero. Now that we've expanded an expression for that // form, update the ICmp's other operand. if (LU.Kind == LSRUse::ICmpZero) { ICmpInst *CI = cast<ICmpInst>(LF.UserInst); DeadInsts.push_back(CI->getOperand(1)); assert(!F.BaseGV && "ICmp does not support folding a global value and " "a scale at the same time!"); if (F.Scale == -1) { if (ICmpScaledV->getType() != OpTy) { Instruction *Cast = CastInst::Create(CastInst::getCastOpcode(ICmpScaledV, false, OpTy, false), ICmpScaledV, OpTy, "tmp", CI); ICmpScaledV = Cast; } CI->setOperand(1, ICmpScaledV); } else { // A scale of 1 means that the scale has been expanded as part of the // base regs. assert((F.Scale == 0 || F.Scale == 1) && "ICmp does not support folding a global value and " "a scale at the same time!"); Constant *C = ConstantInt::getSigned(SE.getEffectiveSCEVType(OpTy), -(uint64_t)Offset); if (C->getType() != OpTy) C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false, OpTy, false), C, OpTy); CI->setOperand(1, C); } } return FullV; } /// RewriteForPHI - Helper for Rewrite. PHI nodes are special because the use /// of their operands effectively happens in their predecessor blocks, so the /// expression may need to be expanded in multiple places. void LSRInstance::RewriteForPHI(PHINode *PN, const LSRFixup &LF, const Formula &F, SCEVExpander &Rewriter, SmallVectorImpl<WeakVH> &DeadInsts, Pass *P) const { DenseMap<BasicBlock *, Value *> Inserted; for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) if (PN->getIncomingValue(i) == LF.OperandValToReplace) { BasicBlock *BB = PN->getIncomingBlock(i); // If this is a critical edge, split the edge so that we do not insert // the code on all predecessor/successor paths. We do this unless this // is the canonical backedge for this loop, which complicates post-inc // users. if (e != 1 && BB->getTerminator()->getNumSuccessors() > 1 && !isa<IndirectBrInst>(BB->getTerminator())) { BasicBlock *Parent = PN->getParent(); Loop *PNLoop = LI.getLoopFor(Parent); if (!PNLoop || Parent != PNLoop->getHeader()) { // Split the critical edge. BasicBlock *NewBB = nullptr; if (!Parent->isLandingPad()) { NewBB = SplitCriticalEdge(BB, Parent, CriticalEdgeSplittingOptions(&DT, &LI) .setMergeIdenticalEdges() .setDontDeleteUselessPHIs()); } else { SmallVector<BasicBlock*, 2> NewBBs; SplitLandingPadPredecessors(Parent, BB, "", "", NewBBs, /*AliasAnalysis*/ nullptr, &DT, &LI); NewBB = NewBBs[0]; } // If NewBB==NULL, then SplitCriticalEdge refused to split because all // phi predecessors are identical. The simple thing to do is skip // splitting in this case rather than complicate the API. if (NewBB) { // If PN is outside of the loop and BB is in the loop, we want to // move the block to be immediately before the PHI block, not // immediately after BB. if (L->contains(BB) && !L->contains(PN)) NewBB->moveBefore(PN->getParent()); // Splitting the edge can reduce the number of PHI entries we have. e = PN->getNumIncomingValues(); BB = NewBB; i = PN->getBasicBlockIndex(BB); } } } std::pair<DenseMap<BasicBlock *, Value *>::iterator, bool> Pair = Inserted.insert(std::make_pair(BB, static_cast<Value *>(nullptr))); if (!Pair.second) PN->setIncomingValue(i, Pair.first->second); else { Value *FullV = Expand(LF, F, BB->getTerminator(), Rewriter, DeadInsts); // If this is reuse-by-noop-cast, insert the noop cast. Type *OpTy = LF.OperandValToReplace->getType(); if (FullV->getType() != OpTy) FullV = CastInst::Create(CastInst::getCastOpcode(FullV, false, OpTy, false), FullV, LF.OperandValToReplace->getType(), "tmp", BB->getTerminator()); PN->setIncomingValue(i, FullV); Pair.first->second = FullV; } } } /// Rewrite - Emit instructions for the leading candidate expression for this /// LSRUse (this is called "expanding"), and update the UserInst to reference /// the newly expanded value. void LSRInstance::Rewrite(const LSRFixup &LF, const Formula &F, SCEVExpander &Rewriter, SmallVectorImpl<WeakVH> &DeadInsts, Pass *P) const { // First, find an insertion point that dominates UserInst. For PHI nodes, // find the nearest block which dominates all the relevant uses. if (PHINode *PN = dyn_cast<PHINode>(LF.UserInst)) { RewriteForPHI(PN, LF, F, Rewriter, DeadInsts, P); } else { Value *FullV = Expand(LF, F, LF.UserInst, Rewriter, DeadInsts); // If this is reuse-by-noop-cast, insert the noop cast. Type *OpTy = LF.OperandValToReplace->getType(); if (FullV->getType() != OpTy) { Instruction *Cast = CastInst::Create(CastInst::getCastOpcode(FullV, false, OpTy, false), FullV, OpTy, "tmp", LF.UserInst); FullV = Cast; } // Update the user. ICmpZero is handled specially here (for now) because // Expand may have updated one of the operands of the icmp already, and // its new value may happen to be equal to LF.OperandValToReplace, in // which case doing replaceUsesOfWith leads to replacing both operands // with the same value. TODO: Reorganize this. if (Uses[LF.LUIdx].Kind == LSRUse::ICmpZero) LF.UserInst->setOperand(0, FullV); else LF.UserInst->replaceUsesOfWith(LF.OperandValToReplace, FullV); } DeadInsts.push_back(LF.OperandValToReplace); } /// ImplementSolution - Rewrite all the fixup locations with new values, /// following the chosen solution. void LSRInstance::ImplementSolution(const SmallVectorImpl<const Formula *> &Solution, Pass *P) { // Keep track of instructions we may have made dead, so that // we can remove them after we are done working. SmallVector<WeakVH, 16> DeadInsts; SCEVExpander Rewriter(SE, "lsr"); #ifndef NDEBUG Rewriter.setDebugType(DEBUG_TYPE); #endif Rewriter.disableCanonicalMode(); Rewriter.enableLSRMode(); Rewriter.setIVIncInsertPos(L, IVIncInsertPos); // Mark phi nodes that terminate chains so the expander tries to reuse them. for (SmallVectorImpl<IVChain>::const_iterator ChainI = IVChainVec.begin(), ChainE = IVChainVec.end(); ChainI != ChainE; ++ChainI) { if (PHINode *PN = dyn_cast<PHINode>(ChainI->tailUserInst())) Rewriter.setChainedPhi(PN); } // Expand the new value definitions and update the users. for (SmallVectorImpl<LSRFixup>::const_iterator I = Fixups.begin(), E = Fixups.end(); I != E; ++I) { const LSRFixup &Fixup = *I; Rewrite(Fixup, *Solution[Fixup.LUIdx], Rewriter, DeadInsts, P); Changed = true; } for (SmallVectorImpl<IVChain>::const_iterator ChainI = IVChainVec.begin(), ChainE = IVChainVec.end(); ChainI != ChainE; ++ChainI) { GenerateIVChain(*ChainI, Rewriter, DeadInsts); Changed = true; } // Clean up after ourselves. This must be done before deleting any // instructions. Rewriter.clear(); Changed |= DeleteTriviallyDeadInstructions(DeadInsts); } LSRInstance::LSRInstance(Loop *L, Pass *P) : IU(P->getAnalysis<IVUsers>()), SE(P->getAnalysis<ScalarEvolution>()), DT(P->getAnalysis<DominatorTreeWrapperPass>().getDomTree()), LI(P->getAnalysis<LoopInfoWrapperPass>().getLoopInfo()), TTI(P->getAnalysis<TargetTransformInfoWrapperPass>().getTTI( *L->getHeader()->getParent())), L(L), Changed(false), IVIncInsertPos(nullptr) { // If LoopSimplify form is not available, stay out of trouble. if (!L->isLoopSimplifyForm()) return; // If there's no interesting work to be done, bail early. if (IU.empty()) return; // If there's too much analysis to be done, bail early. We won't be able to // model the problem anyway. unsigned NumUsers = 0; for (IVUsers::const_iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI) { if (++NumUsers > MaxIVUsers) { DEBUG(dbgs() << "LSR skipping loop, too many IV Users in " << *L << "\n"); return; } } #ifndef NDEBUG // All dominating loops must have preheaders, or SCEVExpander may not be able // to materialize an AddRecExpr whose Start is an outer AddRecExpr. // // IVUsers analysis should only create users that are dominated by simple loop // headers. Since this loop should dominate all of its users, its user list // should be empty if this loop itself is not within a simple loop nest. for (DomTreeNode *Rung = DT.getNode(L->getLoopPreheader()); Rung; Rung = Rung->getIDom()) { BasicBlock *BB = Rung->getBlock(); const Loop *DomLoop = LI.getLoopFor(BB); if (DomLoop && DomLoop->getHeader() == BB) { assert(DomLoop->getLoopPreheader() && "LSR needs a simplified loop nest"); } } #endif // DEBUG DEBUG(dbgs() << "\nLSR on loop "; L->getHeader()->printAsOperand(dbgs(), /*PrintType=*/false); dbgs() << ":\n"); // First, perform some low-level loop optimizations. OptimizeShadowIV(); OptimizeLoopTermCond(); // If loop preparation eliminates all interesting IV users, bail. if (IU.empty()) return; // Skip nested loops until we can model them better with formulae. if (!L->empty()) { DEBUG(dbgs() << "LSR skipping outer loop " << *L << "\n"); return; } // Start collecting data and preparing for the solver. CollectChains(); CollectInterestingTypesAndFactors(); CollectFixupsAndInitialFormulae(); CollectLoopInvariantFixupsAndFormulae(); assert(!Uses.empty() && "IVUsers reported at least one use"); DEBUG(dbgs() << "LSR found " << Uses.size() << " uses:\n"; print_uses(dbgs())); // Now use the reuse data to generate a bunch of interesting ways // to formulate the values needed for the uses. GenerateAllReuseFormulae(); FilterOutUndesirableDedicatedRegisters(); NarrowSearchSpaceUsingHeuristics(); SmallVector<const Formula *, 8> Solution; Solve(Solution); // Release memory that is no longer needed. Factors.clear(); Types.clear(); RegUses.clear(); if (Solution.empty()) return; #ifndef NDEBUG // Formulae should be legal. for (SmallVectorImpl<LSRUse>::const_iterator I = Uses.begin(), E = Uses.end(); I != E; ++I) { const LSRUse &LU = *I; for (SmallVectorImpl<Formula>::const_iterator J = LU.Formulae.begin(), JE = LU.Formulae.end(); J != JE; ++J) assert(isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, *J) && "Illegal formula generated!"); }; #endif // Now that we've decided what we want, make it so. ImplementSolution(Solution, P); } void LSRInstance::print_factors_and_types(raw_ostream &OS) const { if (Factors.empty() && Types.empty()) return; OS << "LSR has identified the following interesting factors and types: "; bool First = true; for (SmallSetVector<int64_t, 8>::const_iterator I = Factors.begin(), E = Factors.end(); I != E; ++I) { if (!First) OS << ", "; First = false; OS << '*' << *I; } for (SmallSetVector<Type *, 4>::const_iterator I = Types.begin(), E = Types.end(); I != E; ++I) { if (!First) OS << ", "; First = false; OS << '(' << **I << ')'; } OS << '\n'; } void LSRInstance::print_fixups(raw_ostream &OS) const { OS << "LSR is examining the following fixup sites:\n"; for (SmallVectorImpl<LSRFixup>::const_iterator I = Fixups.begin(), E = Fixups.end(); I != E; ++I) { dbgs() << " "; I->print(OS); OS << '\n'; } } void LSRInstance::print_uses(raw_ostream &OS) const { OS << "LSR is examining the following uses:\n"; for (SmallVectorImpl<LSRUse>::const_iterator I = Uses.begin(), E = Uses.end(); I != E; ++I) { const LSRUse &LU = *I; dbgs() << " "; LU.print(OS); OS << '\n'; for (SmallVectorImpl<Formula>::const_iterator J = LU.Formulae.begin(), JE = LU.Formulae.end(); J != JE; ++J) { OS << " "; J->print(OS); OS << '\n'; } } } void LSRInstance::print(raw_ostream &OS) const { print_factors_and_types(OS); print_fixups(OS); print_uses(OS); } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void LSRInstance::dump() const { print(errs()); errs() << '\n'; } #endif namespace { class LoopStrengthReduce : public LoopPass { public: static char ID; // Pass ID, replacement for typeid LoopStrengthReduce(); private: bool runOnLoop(Loop *L, LPPassManager &LPM) override; void getAnalysisUsage(AnalysisUsage &AU) const override; }; } char LoopStrengthReduce::ID = 0; INITIALIZE_PASS_BEGIN(LoopStrengthReduce, "loop-reduce", "Loop Strength Reduction", false, false) INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) INITIALIZE_PASS_DEPENDENCY(IVUsers) INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) INITIALIZE_PASS_DEPENDENCY(LoopSimplify) INITIALIZE_PASS_END(LoopStrengthReduce, "loop-reduce", "Loop Strength Reduction", false, false) Pass *llvm::createLoopStrengthReducePass() { return new LoopStrengthReduce(); } LoopStrengthReduce::LoopStrengthReduce() : LoopPass(ID) { initializeLoopStrengthReducePass(*PassRegistry::getPassRegistry()); } void LoopStrengthReduce::getAnalysisUsage(AnalysisUsage &AU) const { // We split critical edges, so we change the CFG. However, we do update // many analyses if they are around. AU.addPreservedID(LoopSimplifyID); AU.addRequired<LoopInfoWrapperPass>(); AU.addPreserved<LoopInfoWrapperPass>(); AU.addRequiredID(LoopSimplifyID); AU.addRequired<DominatorTreeWrapperPass>(); AU.addPreserved<DominatorTreeWrapperPass>(); AU.addRequired<ScalarEvolution>(); AU.addPreserved<ScalarEvolution>(); // Requiring LoopSimplify a second time here prevents IVUsers from running // twice, since LoopSimplify was invalidated by running ScalarEvolution. AU.addRequiredID(LoopSimplifyID); AU.addRequired<IVUsers>(); AU.addPreserved<IVUsers>(); AU.addRequired<TargetTransformInfoWrapperPass>(); } bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager & /*LPM*/) { if (skipOptnoneFunction(L)) return false; bool Changed = false; // Run the main LSR transformation. Changed |= LSRInstance(L, this).getChanged(); // Remove any extra phis created by processing inner loops. Changed |= DeleteDeadPHIs(L->getHeader()); if (EnablePhiElim && L->isLoopSimplifyForm()) { SmallVector<WeakVH, 16> DeadInsts; SCEVExpander Rewriter(getAnalysis<ScalarEvolution>(), "lsr"); #ifndef NDEBUG Rewriter.setDebugType(DEBUG_TYPE); #endif unsigned numFolded = Rewriter.replaceCongruentIVs( L, &getAnalysis<DominatorTreeWrapperPass>().getDomTree(), DeadInsts, &getAnalysis<TargetTransformInfoWrapperPass>().getTTI( *L->getHeader()->getParent())); if (numFolded) { Changed = true; DeleteTriviallyDeadInstructions(DeadInsts); DeleteDeadPHIs(L->getHeader()); } } return Changed; }