//===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis ------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file contains the implementation of the scalar evolution expander, // which is used to generate the code corresponding to a given scalar evolution // expression. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/ScalarEvolutionExpander.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallSet.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/TargetTransformInfo.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Module.h" #include "llvm/IR/PatternMatch.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" using namespace llvm; using namespace PatternMatch; /// ReuseOrCreateCast - Arrange for there to be a cast of V to Ty at IP, /// reusing an existing cast if a suitable one exists, moving an existing /// cast if a suitable one exists but isn't in the right place, or /// creating a new one. Value *SCEVExpander::ReuseOrCreateCast(Value *V, Type *Ty, Instruction::CastOps Op, BasicBlock::iterator IP) { // This function must be called with the builder having a valid insertion // point. It doesn't need to be the actual IP where the uses of the returned // cast will be added, but it must dominate such IP. // We use this precondition to produce a cast that will dominate all its // uses. In particular, this is crucial for the case where the builder's // insertion point *is* the point where we were asked to put the cast. // Since we don't know the builder's insertion point is actually // where the uses will be added (only that it dominates it), we are // not allowed to move it. BasicBlock::iterator BIP = Builder.GetInsertPoint(); Instruction *Ret = nullptr; // Check to see if there is already a cast! for (User *U : V->users()) if (U->getType() == Ty) if (CastInst *CI = dyn_cast(U)) if (CI->getOpcode() == Op) { // If the cast isn't where we want it, create a new cast at IP. // Likewise, do not reuse a cast at BIP because it must dominate // instructions that might be inserted before BIP. if (BasicBlock::iterator(CI) != IP || BIP == IP) { // Create a new cast, and leave the old cast in place in case // it is being used as an insert point. Clear its operand // so that it doesn't hold anything live. Ret = CastInst::Create(Op, V, Ty, "", &*IP); Ret->takeName(CI); CI->replaceAllUsesWith(Ret); CI->setOperand(0, UndefValue::get(V->getType())); break; } Ret = CI; break; } // Create a new cast. if (!Ret) Ret = CastInst::Create(Op, V, Ty, V->getName(), &*IP); // We assert at the end of the function since IP might point to an // instruction with different dominance properties than a cast // (an invoke for example) and not dominate BIP (but the cast does). assert(SE.DT.dominates(Ret, &*BIP)); rememberInstruction(Ret); return Ret; } static BasicBlock::iterator findInsertPointAfter(Instruction *I, BasicBlock *MustDominate) { BasicBlock::iterator IP = ++I->getIterator(); if (auto *II = dyn_cast(I)) IP = II->getNormalDest()->begin(); while (isa(IP)) ++IP; if (isa(IP) || isa(IP)) { ++IP; } else if (isa(IP)) { IP = MustDominate->getFirstInsertionPt(); } else { assert(!IP->isEHPad() && "unexpected eh pad!"); } return IP; } /// InsertNoopCastOfTo - Insert a cast of V to the specified type, /// which must be possible with a noop cast, doing what we can to share /// the casts. Value *SCEVExpander::InsertNoopCastOfTo(Value *V, Type *Ty) { Instruction::CastOps Op = CastInst::getCastOpcode(V, false, Ty, false); assert((Op == Instruction::BitCast || Op == Instruction::PtrToInt || Op == Instruction::IntToPtr) && "InsertNoopCastOfTo cannot perform non-noop casts!"); assert(SE.getTypeSizeInBits(V->getType()) == SE.getTypeSizeInBits(Ty) && "InsertNoopCastOfTo cannot change sizes!"); // Short-circuit unnecessary bitcasts. if (Op == Instruction::BitCast) { if (V->getType() == Ty) return V; if (CastInst *CI = dyn_cast(V)) { if (CI->getOperand(0)->getType() == Ty) return CI->getOperand(0); } } // Short-circuit unnecessary inttoptr<->ptrtoint casts. if ((Op == Instruction::PtrToInt || Op == Instruction::IntToPtr) && SE.getTypeSizeInBits(Ty) == SE.getTypeSizeInBits(V->getType())) { if (CastInst *CI = dyn_cast(V)) if ((CI->getOpcode() == Instruction::PtrToInt || CI->getOpcode() == Instruction::IntToPtr) && SE.getTypeSizeInBits(CI->getType()) == SE.getTypeSizeInBits(CI->getOperand(0)->getType())) return CI->getOperand(0); if (ConstantExpr *CE = dyn_cast(V)) if ((CE->getOpcode() == Instruction::PtrToInt || CE->getOpcode() == Instruction::IntToPtr) && SE.getTypeSizeInBits(CE->getType()) == SE.getTypeSizeInBits(CE->getOperand(0)->getType())) return CE->getOperand(0); } // Fold a cast of a constant. if (Constant *C = dyn_cast(V)) return ConstantExpr::getCast(Op, C, Ty); // Cast the argument at the beginning of the entry block, after // any bitcasts of other arguments. if (Argument *A = dyn_cast(V)) { BasicBlock::iterator IP = A->getParent()->getEntryBlock().begin(); while ((isa(IP) && isa(cast(IP)->getOperand(0)) && cast(IP)->getOperand(0) != A) || isa(IP)) ++IP; return ReuseOrCreateCast(A, Ty, Op, IP); } // Cast the instruction immediately after the instruction. Instruction *I = cast(V); BasicBlock::iterator IP = findInsertPointAfter(I, Builder.GetInsertBlock()); return ReuseOrCreateCast(I, Ty, Op, IP); } /// InsertBinop - Insert the specified binary operator, doing a small amount /// of work to avoid inserting an obviously redundant operation. Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS) { // Fold a binop with constant operands. if (Constant *CLHS = dyn_cast(LHS)) if (Constant *CRHS = dyn_cast(RHS)) return ConstantExpr::get(Opcode, CLHS, CRHS); // Do a quick scan to see if we have this binop nearby. If so, reuse it. unsigned ScanLimit = 6; BasicBlock::iterator BlockBegin = Builder.GetInsertBlock()->begin(); // Scanning starts from the last instruction before the insertion point. BasicBlock::iterator IP = Builder.GetInsertPoint(); if (IP != BlockBegin) { --IP; for (; ScanLimit; --IP, --ScanLimit) { // Don't count dbg.value against the ScanLimit, to avoid perturbing the // generated code. if (isa(IP)) ScanLimit++; // Conservatively, do not use any instruction which has any of wrap/exact // flags installed. // TODO: Instead of simply disable poison instructions we can be clever // here and match SCEV to this instruction. auto canGeneratePoison = [](Instruction *I) { if (isa(I) && (I->hasNoSignedWrap() || I->hasNoUnsignedWrap())) return true; if (isa(I) && I->isExact()) return true; return false; }; if (IP->getOpcode() == (unsigned)Opcode && IP->getOperand(0) == LHS && IP->getOperand(1) == RHS && !canGeneratePoison(&*IP)) return &*IP; if (IP == BlockBegin) break; } } // Save the original insertion point so we can restore it when we're done. DebugLoc Loc = Builder.GetInsertPoint()->getDebugLoc(); SCEVInsertPointGuard Guard(Builder, this); // Move the insertion point out of as many loops as we can. while (const Loop *L = SE.LI.getLoopFor(Builder.GetInsertBlock())) { if (!L->isLoopInvariant(LHS) || !L->isLoopInvariant(RHS)) break; BasicBlock *Preheader = L->getLoopPreheader(); if (!Preheader) break; // Ok, move up a level. Builder.SetInsertPoint(Preheader->getTerminator()); } // If we haven't found this binop, insert it. Instruction *BO = cast(Builder.CreateBinOp(Opcode, LHS, RHS)); BO->setDebugLoc(Loc); rememberInstruction(BO); return BO; } /// FactorOutConstant - Test if S is divisible by Factor, using signed /// division. If so, update S with Factor divided out and return true. /// S need not be evenly divisible if a reasonable remainder can be /// computed. /// TODO: When ScalarEvolution gets a SCEVSDivExpr, this can be made /// unnecessary; in its place, just signed-divide Ops[i] by the scale and /// check to see if the divide was folded. static bool FactorOutConstant(const SCEV *&S, const SCEV *&Remainder, const SCEV *Factor, ScalarEvolution &SE, const DataLayout &DL) { // Everything is divisible by one. if (Factor->isOne()) return true; // x/x == 1. if (S == Factor) { S = SE.getConstant(S->getType(), 1); return true; } // For a Constant, check for a multiple of the given factor. if (const SCEVConstant *C = dyn_cast(S)) { // 0/x == 0. if (C->isZero()) return true; // Check for divisibility. if (const SCEVConstant *FC = dyn_cast(Factor)) { ConstantInt *CI = ConstantInt::get(SE.getContext(), C->getAPInt().sdiv(FC->getAPInt())); // If the quotient is zero and the remainder is non-zero, reject // the value at this scale. It will be considered for subsequent // smaller scales. if (!CI->isZero()) { const SCEV *Div = SE.getConstant(CI); S = Div; Remainder = SE.getAddExpr( Remainder, SE.getConstant(C->getAPInt().srem(FC->getAPInt()))); return true; } } } // In a Mul, check if there is a constant operand which is a multiple // of the given factor. if (const SCEVMulExpr *M = dyn_cast(S)) { // Size is known, check if there is a constant operand which is a multiple // of the given factor. If so, we can factor it. const SCEVConstant *FC = cast(Factor); if (const SCEVConstant *C = dyn_cast(M->getOperand(0))) if (!C->getAPInt().srem(FC->getAPInt())) { SmallVector NewMulOps(M->op_begin(), M->op_end()); NewMulOps[0] = SE.getConstant(C->getAPInt().sdiv(FC->getAPInt())); S = SE.getMulExpr(NewMulOps); return true; } } // In an AddRec, check if both start and step are divisible. if (const SCEVAddRecExpr *A = dyn_cast(S)) { const SCEV *Step = A->getStepRecurrence(SE); const SCEV *StepRem = SE.getConstant(Step->getType(), 0); if (!FactorOutConstant(Step, StepRem, Factor, SE, DL)) return false; if (!StepRem->isZero()) return false; const SCEV *Start = A->getStart(); if (!FactorOutConstant(Start, Remainder, Factor, SE, DL)) return false; S = SE.getAddRecExpr(Start, Step, A->getLoop(), A->getNoWrapFlags(SCEV::FlagNW)); return true; } return false; } /// SimplifyAddOperands - Sort and simplify a list of add operands. NumAddRecs /// is the number of SCEVAddRecExprs present, which are kept at the end of /// the list. /// static void SimplifyAddOperands(SmallVectorImpl &Ops, Type *Ty, ScalarEvolution &SE) { unsigned NumAddRecs = 0; for (unsigned i = Ops.size(); i > 0 && isa(Ops[i-1]); --i) ++NumAddRecs; // Group Ops into non-addrecs and addrecs. SmallVector NoAddRecs(Ops.begin(), Ops.end() - NumAddRecs); SmallVector AddRecs(Ops.end() - NumAddRecs, Ops.end()); // Let ScalarEvolution sort and simplify the non-addrecs list. const SCEV *Sum = NoAddRecs.empty() ? SE.getConstant(Ty, 0) : SE.getAddExpr(NoAddRecs); // If it returned an add, use the operands. Otherwise it simplified // the sum into a single value, so just use that. Ops.clear(); if (const SCEVAddExpr *Add = dyn_cast(Sum)) Ops.append(Add->op_begin(), Add->op_end()); else if (!Sum->isZero()) Ops.push_back(Sum); // Then append the addrecs. Ops.append(AddRecs.begin(), AddRecs.end()); } /// SplitAddRecs - Flatten a list of add operands, moving addrec start values /// out to the top level. For example, convert {a + b,+,c} to a, b, {0,+,d}. /// This helps expose more opportunities for folding parts of the expressions /// into GEP indices. /// static void SplitAddRecs(SmallVectorImpl &Ops, Type *Ty, ScalarEvolution &SE) { // Find the addrecs. SmallVector AddRecs; for (unsigned i = 0, e = Ops.size(); i != e; ++i) while (const SCEVAddRecExpr *A = dyn_cast(Ops[i])) { const SCEV *Start = A->getStart(); if (Start->isZero()) break; const SCEV *Zero = SE.getConstant(Ty, 0); AddRecs.push_back(SE.getAddRecExpr(Zero, A->getStepRecurrence(SE), A->getLoop(), A->getNoWrapFlags(SCEV::FlagNW))); if (const SCEVAddExpr *Add = dyn_cast(Start)) { Ops[i] = Zero; Ops.append(Add->op_begin(), Add->op_end()); e += Add->getNumOperands(); } else { Ops[i] = Start; } } if (!AddRecs.empty()) { // Add the addrecs onto the end of the list. Ops.append(AddRecs.begin(), AddRecs.end()); // Resort the operand list, moving any constants to the front. SimplifyAddOperands(Ops, Ty, SE); } } /// expandAddToGEP - Expand an addition expression with a pointer type into /// a GEP instead of using ptrtoint+arithmetic+inttoptr. This helps /// BasicAliasAnalysis and other passes analyze the result. See the rules /// for getelementptr vs. inttoptr in /// http://llvm.org/docs/LangRef.html#pointeraliasing /// for details. /// /// Design note: The correctness of using getelementptr here depends on /// ScalarEvolution not recognizing inttoptr and ptrtoint operators, as /// they may introduce pointer arithmetic which may not be safely converted /// into getelementptr. /// /// Design note: It might seem desirable for this function to be more /// loop-aware. If some of the indices are loop-invariant while others /// aren't, it might seem desirable to emit multiple GEPs, keeping the /// loop-invariant portions of the overall computation outside the loop. /// However, there are a few reasons this is not done here. Hoisting simple /// arithmetic is a low-level optimization that often isn't very /// important until late in the optimization process. In fact, passes /// like InstructionCombining will combine GEPs, even if it means /// pushing loop-invariant computation down into loops, so even if the /// GEPs were split here, the work would quickly be undone. The /// LoopStrengthReduction pass, which is usually run quite late (and /// after the last InstructionCombining pass), takes care of hoisting /// loop-invariant portions of expressions, after considering what /// can be folded using target addressing modes. /// Value *SCEVExpander::expandAddToGEP(const SCEV *const *op_begin, const SCEV *const *op_end, PointerType *PTy, Type *Ty, Value *V) { Type *OriginalElTy = PTy->getElementType(); Type *ElTy = OriginalElTy; SmallVector GepIndices; SmallVector Ops(op_begin, op_end); bool AnyNonZeroIndices = false; // Split AddRecs up into parts as either of the parts may be usable // without the other. SplitAddRecs(Ops, Ty, SE); Type *IntPtrTy = DL.getIntPtrType(PTy); // Descend down the pointer's type and attempt to convert the other // operands into GEP indices, at each level. The first index in a GEP // indexes into the array implied by the pointer operand; the rest of // the indices index into the element or field type selected by the // preceding index. for (;;) { // If the scale size is not 0, attempt to factor out a scale for // array indexing. SmallVector ScaledOps; if (ElTy->isSized()) { const SCEV *ElSize = SE.getSizeOfExpr(IntPtrTy, ElTy); if (!ElSize->isZero()) { SmallVector NewOps; for (const SCEV *Op : Ops) { const SCEV *Remainder = SE.getConstant(Ty, 0); if (FactorOutConstant(Op, Remainder, ElSize, SE, DL)) { // Op now has ElSize factored out. ScaledOps.push_back(Op); if (!Remainder->isZero()) NewOps.push_back(Remainder); AnyNonZeroIndices = true; } else { // The operand was not divisible, so add it to the list of operands // we'll scan next iteration. NewOps.push_back(Op); } } // If we made any changes, update Ops. if (!ScaledOps.empty()) { Ops = NewOps; SimplifyAddOperands(Ops, Ty, SE); } } } // Record the scaled array index for this level of the type. If // we didn't find any operands that could be factored, tentatively // assume that element zero was selected (since the zero offset // would obviously be folded away). Value *Scaled = ScaledOps.empty() ? Constant::getNullValue(Ty) : expandCodeFor(SE.getAddExpr(ScaledOps), Ty); GepIndices.push_back(Scaled); // Collect struct field index operands. while (StructType *STy = dyn_cast(ElTy)) { bool FoundFieldNo = false; // An empty struct has no fields. if (STy->getNumElements() == 0) break; // Field offsets are known. See if a constant offset falls within any of // the struct fields. if (Ops.empty()) break; if (const SCEVConstant *C = dyn_cast(Ops[0])) if (SE.getTypeSizeInBits(C->getType()) <= 64) { const StructLayout &SL = *DL.getStructLayout(STy); uint64_t FullOffset = C->getValue()->getZExtValue(); if (FullOffset < SL.getSizeInBytes()) { unsigned ElIdx = SL.getElementContainingOffset(FullOffset); GepIndices.push_back( ConstantInt::get(Type::getInt32Ty(Ty->getContext()), ElIdx)); ElTy = STy->getTypeAtIndex(ElIdx); Ops[0] = SE.getConstant(Ty, FullOffset - SL.getElementOffset(ElIdx)); AnyNonZeroIndices = true; FoundFieldNo = true; } } // If no struct field offsets were found, tentatively assume that // field zero was selected (since the zero offset would obviously // be folded away). if (!FoundFieldNo) { ElTy = STy->getTypeAtIndex(0u); GepIndices.push_back( Constant::getNullValue(Type::getInt32Ty(Ty->getContext()))); } } if (ArrayType *ATy = dyn_cast(ElTy)) ElTy = ATy->getElementType(); else break; } // If none of the operands were convertible to proper GEP indices, cast // the base to i8* and do an ugly getelementptr with that. It's still // better than ptrtoint+arithmetic+inttoptr at least. if (!AnyNonZeroIndices) { // Cast the base to i8*. V = InsertNoopCastOfTo(V, Type::getInt8PtrTy(Ty->getContext(), PTy->getAddressSpace())); assert(!isa(V) || SE.DT.dominates(cast(V), &*Builder.GetInsertPoint())); // Expand the operands for a plain byte offset. Value *Idx = expandCodeFor(SE.getAddExpr(Ops), Ty); // Fold a GEP with constant operands. if (Constant *CLHS = dyn_cast(V)) if (Constant *CRHS = dyn_cast(Idx)) return ConstantExpr::getGetElementPtr(Type::getInt8Ty(Ty->getContext()), CLHS, CRHS); // Do a quick scan to see if we have this GEP nearby. If so, reuse it. unsigned ScanLimit = 6; BasicBlock::iterator BlockBegin = Builder.GetInsertBlock()->begin(); // Scanning starts from the last instruction before the insertion point. BasicBlock::iterator IP = Builder.GetInsertPoint(); if (IP != BlockBegin) { --IP; for (; ScanLimit; --IP, --ScanLimit) { // Don't count dbg.value against the ScanLimit, to avoid perturbing the // generated code. if (isa(IP)) ScanLimit++; if (IP->getOpcode() == Instruction::GetElementPtr && IP->getOperand(0) == V && IP->getOperand(1) == Idx) return &*IP; if (IP == BlockBegin) break; } } // Save the original insertion point so we can restore it when we're done. SCEVInsertPointGuard Guard(Builder, this); // Move the insertion point out of as many loops as we can. while (const Loop *L = SE.LI.getLoopFor(Builder.GetInsertBlock())) { if (!L->isLoopInvariant(V) || !L->isLoopInvariant(Idx)) break; BasicBlock *Preheader = L->getLoopPreheader(); if (!Preheader) break; // Ok, move up a level. Builder.SetInsertPoint(Preheader->getTerminator()); } // Emit a GEP. Value *GEP = Builder.CreateGEP(Builder.getInt8Ty(), V, Idx, "uglygep"); rememberInstruction(GEP); return GEP; } { SCEVInsertPointGuard Guard(Builder, this); // Move the insertion point out of as many loops as we can. while (const Loop *L = SE.LI.getLoopFor(Builder.GetInsertBlock())) { if (!L->isLoopInvariant(V)) break; bool AnyIndexNotLoopInvariant = any_of( GepIndices, [L](Value *Op) { return !L->isLoopInvariant(Op); }); if (AnyIndexNotLoopInvariant) break; BasicBlock *Preheader = L->getLoopPreheader(); if (!Preheader) break; // Ok, move up a level. Builder.SetInsertPoint(Preheader->getTerminator()); } // Insert a pretty getelementptr. Note that this GEP is not marked inbounds, // because ScalarEvolution may have changed the address arithmetic to // compute a value which is beyond the end of the allocated object. Value *Casted = V; if (V->getType() != PTy) Casted = InsertNoopCastOfTo(Casted, PTy); Value *GEP = Builder.CreateGEP(OriginalElTy, Casted, GepIndices, "scevgep"); Ops.push_back(SE.getUnknown(GEP)); rememberInstruction(GEP); } return expand(SE.getAddExpr(Ops)); } /// PickMostRelevantLoop - Given two loops pick the one that's most relevant for /// SCEV expansion. If they are nested, this is the most nested. If they are /// neighboring, pick the later. static const Loop *PickMostRelevantLoop(const Loop *A, const Loop *B, DominatorTree &DT) { if (!A) return B; if (!B) return A; if (A->contains(B)) return B; if (B->contains(A)) return A; if (DT.dominates(A->getHeader(), B->getHeader())) return B; if (DT.dominates(B->getHeader(), A->getHeader())) return A; return A; // Arbitrarily break the tie. } /// getRelevantLoop - Get the most relevant loop associated with the given /// expression, according to PickMostRelevantLoop. const Loop *SCEVExpander::getRelevantLoop(const SCEV *S) { // Test whether we've already computed the most relevant loop for this SCEV. auto Pair = RelevantLoops.insert(std::make_pair(S, nullptr)); if (!Pair.second) return Pair.first->second; if (isa(S)) // A constant has no relevant loops. return nullptr; if (const SCEVUnknown *U = dyn_cast(S)) { if (const Instruction *I = dyn_cast(U->getValue())) return Pair.first->second = SE.LI.getLoopFor(I->getParent()); // A non-instruction has no relevant loops. return nullptr; } if (const SCEVNAryExpr *N = dyn_cast(S)) { const Loop *L = nullptr; if (const SCEVAddRecExpr *AR = dyn_cast(S)) L = AR->getLoop(); for (const SCEV *Op : N->operands()) L = PickMostRelevantLoop(L, getRelevantLoop(Op), SE.DT); return RelevantLoops[N] = L; } if (const SCEVCastExpr *C = dyn_cast(S)) { const Loop *Result = getRelevantLoop(C->getOperand()); return RelevantLoops[C] = Result; } if (const SCEVUDivExpr *D = dyn_cast(S)) { const Loop *Result = PickMostRelevantLoop( getRelevantLoop(D->getLHS()), getRelevantLoop(D->getRHS()), SE.DT); return RelevantLoops[D] = Result; } llvm_unreachable("Unexpected SCEV type!"); } namespace { /// LoopCompare - Compare loops by PickMostRelevantLoop. class LoopCompare { DominatorTree &DT; public: explicit LoopCompare(DominatorTree &dt) : DT(dt) {} bool operator()(std::pair LHS, std::pair RHS) const { // Keep pointer operands sorted at the end. if (LHS.second->getType()->isPointerTy() != RHS.second->getType()->isPointerTy()) return LHS.second->getType()->isPointerTy(); // Compare loops with PickMostRelevantLoop. if (LHS.first != RHS.first) return PickMostRelevantLoop(LHS.first, RHS.first, DT) != LHS.first; // If one operand is a non-constant negative and the other is not, // put the non-constant negative on the right so that a sub can // be used instead of a negate and add. if (LHS.second->isNonConstantNegative()) { if (!RHS.second->isNonConstantNegative()) return false; } else if (RHS.second->isNonConstantNegative()) return true; // Otherwise they are equivalent according to this comparison. return false; } }; } Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) { Type *Ty = SE.getEffectiveSCEVType(S->getType()); // Collect all the add operands in a loop, along with their associated loops. // Iterate in reverse so that constants are emitted last, all else equal, and // so that pointer operands are inserted first, which the code below relies on // to form more involved GEPs. SmallVector, 8> OpsAndLoops; for (std::reverse_iterator I(S->op_end()), E(S->op_begin()); I != E; ++I) OpsAndLoops.push_back(std::make_pair(getRelevantLoop(*I), *I)); // Sort by loop. Use a stable sort so that constants follow non-constants and // pointer operands precede non-pointer operands. std::stable_sort(OpsAndLoops.begin(), OpsAndLoops.end(), LoopCompare(SE.DT)); // Emit instructions to add all the operands. Hoist as much as possible // out of loops, and form meaningful getelementptrs where possible. Value *Sum = nullptr; for (auto I = OpsAndLoops.begin(), E = OpsAndLoops.end(); I != E;) { const Loop *CurLoop = I->first; const SCEV *Op = I->second; if (!Sum) { // This is the first operand. Just expand it. Sum = expand(Op); ++I; } else if (PointerType *PTy = dyn_cast(Sum->getType())) { // The running sum expression is a pointer. Try to form a getelementptr // at this level with that as the base. SmallVector NewOps; for (; I != E && I->first == CurLoop; ++I) { // If the operand is SCEVUnknown and not instructions, peek through // it, to enable more of it to be folded into the GEP. const SCEV *X = I->second; if (const SCEVUnknown *U = dyn_cast(X)) if (!isa(U->getValue())) X = SE.getSCEV(U->getValue()); NewOps.push_back(X); } Sum = expandAddToGEP(NewOps.begin(), NewOps.end(), PTy, Ty, Sum); } else if (PointerType *PTy = dyn_cast(Op->getType())) { // The running sum is an integer, and there's a pointer at this level. // Try to form a getelementptr. If the running sum is instructions, // use a SCEVUnknown to avoid re-analyzing them. SmallVector NewOps; NewOps.push_back(isa(Sum) ? SE.getUnknown(Sum) : SE.getSCEV(Sum)); for (++I; I != E && I->first == CurLoop; ++I) NewOps.push_back(I->second); Sum = expandAddToGEP(NewOps.begin(), NewOps.end(), PTy, Ty, expand(Op)); } else if (Op->isNonConstantNegative()) { // Instead of doing a negate and add, just do a subtract. Value *W = expandCodeFor(SE.getNegativeSCEV(Op), Ty); Sum = InsertNoopCastOfTo(Sum, Ty); Sum = InsertBinop(Instruction::Sub, Sum, W); ++I; } else { // A simple add. Value *W = expandCodeFor(Op, Ty); Sum = InsertNoopCastOfTo(Sum, Ty); // Canonicalize a constant to the RHS. if (isa(Sum)) std::swap(Sum, W); Sum = InsertBinop(Instruction::Add, Sum, W); ++I; } } return Sum; } Value *SCEVExpander::visitMulExpr(const SCEVMulExpr *S) { Type *Ty = SE.getEffectiveSCEVType(S->getType()); // Collect all the mul operands in a loop, along with their associated loops. // Iterate in reverse so that constants are emitted last, all else equal. SmallVector, 8> OpsAndLoops; for (std::reverse_iterator I(S->op_end()), E(S->op_begin()); I != E; ++I) OpsAndLoops.push_back(std::make_pair(getRelevantLoop(*I), *I)); // Sort by loop. Use a stable sort so that constants follow non-constants. std::stable_sort(OpsAndLoops.begin(), OpsAndLoops.end(), LoopCompare(SE.DT)); // Emit instructions to mul all the operands. Hoist as much as possible // out of loops. Value *Prod = nullptr; auto I = OpsAndLoops.begin(); // Expand the calculation of X pow N in the following manner: // Let N = P1 + P2 + ... + PK, where all P are powers of 2. Then: // X pow N = (X pow P1) * (X pow P2) * ... * (X pow PK). const auto ExpandOpBinPowN = [this, &I, &OpsAndLoops, &Ty]() { auto E = I; // Calculate how many times the same operand from the same loop is included // into this power. uint64_t Exponent = 0; const uint64_t MaxExponent = UINT64_MAX >> 1; // No one sane will ever try to calculate such huge exponents, but if we // need this, we stop on UINT64_MAX / 2 because we need to exit the loop // below when the power of 2 exceeds our Exponent, and we want it to be // 1u << 31 at most to not deal with unsigned overflow. while (E != OpsAndLoops.end() && *I == *E && Exponent != MaxExponent) { ++Exponent; ++E; } assert(Exponent > 0 && "Trying to calculate a zeroth exponent of operand?"); // Calculate powers with exponents 1, 2, 4, 8 etc. and include those of them // that are needed into the result. Value *P = expandCodeFor(I->second, Ty); Value *Result = nullptr; if (Exponent & 1) Result = P; for (uint64_t BinExp = 2; BinExp <= Exponent; BinExp <<= 1) { P = InsertBinop(Instruction::Mul, P, P); if (Exponent & BinExp) Result = Result ? InsertBinop(Instruction::Mul, Result, P) : P; } I = E; assert(Result && "Nothing was expanded?"); return Result; }; while (I != OpsAndLoops.end()) { if (!Prod) { // This is the first operand. Just expand it. Prod = ExpandOpBinPowN(); } else if (I->second->isAllOnesValue()) { // Instead of doing a multiply by negative one, just do a negate. Prod = InsertNoopCastOfTo(Prod, Ty); Prod = InsertBinop(Instruction::Sub, Constant::getNullValue(Ty), Prod); ++I; } else { // A simple mul. Value *W = ExpandOpBinPowN(); Prod = InsertNoopCastOfTo(Prod, Ty); // Canonicalize a constant to the RHS. if (isa(Prod)) std::swap(Prod, W); const APInt *RHS; if (match(W, m_Power2(RHS))) { // Canonicalize Prod*(1<isVectorTy() && "vector types are not SCEVable"); Prod = InsertBinop(Instruction::Shl, Prod, ConstantInt::get(Ty, RHS->logBase2())); } else { Prod = InsertBinop(Instruction::Mul, Prod, W); } } } return Prod; } Value *SCEVExpander::visitUDivExpr(const SCEVUDivExpr *S) { Type *Ty = SE.getEffectiveSCEVType(S->getType()); Value *LHS = expandCodeFor(S->getLHS(), Ty); if (const SCEVConstant *SC = dyn_cast(S->getRHS())) { const APInt &RHS = SC->getAPInt(); if (RHS.isPowerOf2()) return InsertBinop(Instruction::LShr, LHS, ConstantInt::get(Ty, RHS.logBase2())); } Value *RHS = expandCodeFor(S->getRHS(), Ty); return InsertBinop(Instruction::UDiv, LHS, RHS); } /// Move parts of Base into Rest to leave Base with the minimal /// expression that provides a pointer operand suitable for a /// GEP expansion. static void ExposePointerBase(const SCEV *&Base, const SCEV *&Rest, ScalarEvolution &SE) { while (const SCEVAddRecExpr *A = dyn_cast(Base)) { Base = A->getStart(); Rest = SE.getAddExpr(Rest, SE.getAddRecExpr(SE.getConstant(A->getType(), 0), A->getStepRecurrence(SE), A->getLoop(), A->getNoWrapFlags(SCEV::FlagNW))); } if (const SCEVAddExpr *A = dyn_cast(Base)) { Base = A->getOperand(A->getNumOperands()-1); SmallVector NewAddOps(A->op_begin(), A->op_end()); NewAddOps.back() = Rest; Rest = SE.getAddExpr(NewAddOps); ExposePointerBase(Base, Rest, SE); } } /// Determine if this is a well-behaved chain of instructions leading back to /// the PHI. If so, it may be reused by expanded expressions. bool SCEVExpander::isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L) { if (IncV->getNumOperands() == 0 || isa(IncV) || (isa(IncV) && !isa(IncV))) return false; // If any of the operands don't dominate the insert position, bail. // Addrec operands are always loop-invariant, so this can only happen // if there are instructions which haven't been hoisted. if (L == IVIncInsertLoop) { for (User::op_iterator OI = IncV->op_begin()+1, OE = IncV->op_end(); OI != OE; ++OI) if (Instruction *OInst = dyn_cast(OI)) if (!SE.DT.dominates(OInst, IVIncInsertPos)) return false; } // Advance to the next instruction. IncV = dyn_cast(IncV->getOperand(0)); if (!IncV) return false; if (IncV->mayHaveSideEffects()) return false; if (IncV == PN) return true; return isNormalAddRecExprPHI(PN, IncV, L); } /// getIVIncOperand returns an induction variable increment's induction /// variable operand. /// /// If allowScale is set, any type of GEP is allowed as long as the nonIV /// operands dominate InsertPos. /// /// If allowScale is not set, ensure that a GEP increment conforms to one of the /// simple patterns generated by getAddRecExprPHILiterally and /// expandAddtoGEP. If the pattern isn't recognized, return NULL. Instruction *SCEVExpander::getIVIncOperand(Instruction *IncV, Instruction *InsertPos, bool allowScale) { if (IncV == InsertPos) return nullptr; switch (IncV->getOpcode()) { default: return nullptr; // Check for a simple Add/Sub or GEP of a loop invariant step. case Instruction::Add: case Instruction::Sub: { Instruction *OInst = dyn_cast(IncV->getOperand(1)); if (!OInst || SE.DT.dominates(OInst, InsertPos)) return dyn_cast(IncV->getOperand(0)); return nullptr; } case Instruction::BitCast: return dyn_cast(IncV->getOperand(0)); case Instruction::GetElementPtr: for (auto I = IncV->op_begin() + 1, E = IncV->op_end(); I != E; ++I) { if (isa(*I)) continue; if (Instruction *OInst = dyn_cast(*I)) { if (!SE.DT.dominates(OInst, InsertPos)) return nullptr; } if (allowScale) { // allow any kind of GEP as long as it can be hoisted. continue; } // This must be a pointer addition of constants (pretty), which is already // handled, or some number of address-size elements (ugly). Ugly geps // have 2 operands. i1* is used by the expander to represent an // address-size element. if (IncV->getNumOperands() != 2) return nullptr; unsigned AS = cast(IncV->getType())->getAddressSpace(); if (IncV->getType() != Type::getInt1PtrTy(SE.getContext(), AS) && IncV->getType() != Type::getInt8PtrTy(SE.getContext(), AS)) return nullptr; break; } return dyn_cast(IncV->getOperand(0)); } } /// If the insert point of the current builder or any of the builders on the /// stack of saved builders has 'I' as its insert point, update it to point to /// the instruction after 'I'. This is intended to be used when the instruction /// 'I' is being moved. If this fixup is not done and 'I' is moved to a /// different block, the inconsistent insert point (with a mismatched /// Instruction and Block) can lead to an instruction being inserted in a block /// other than its parent. void SCEVExpander::fixupInsertPoints(Instruction *I) { BasicBlock::iterator It(*I); BasicBlock::iterator NewInsertPt = std::next(It); if (Builder.GetInsertPoint() == It) Builder.SetInsertPoint(&*NewInsertPt); for (auto *InsertPtGuard : InsertPointGuards) if (InsertPtGuard->GetInsertPoint() == It) InsertPtGuard->SetInsertPoint(NewInsertPt); } /// hoistStep - Attempt to hoist a simple IV increment above InsertPos to make /// it available to other uses in this loop. Recursively hoist any operands, /// until we reach a value that dominates InsertPos. bool SCEVExpander::hoistIVInc(Instruction *IncV, Instruction *InsertPos) { if (SE.DT.dominates(IncV, InsertPos)) return true; // InsertPos must itself dominate IncV so that IncV's new position satisfies // its existing users. if (isa(InsertPos) || !SE.DT.dominates(InsertPos->getParent(), IncV->getParent())) return false; if (!SE.LI.movementPreservesLCSSAForm(IncV, InsertPos)) return false; // Check that the chain of IV operands leading back to Phi can be hoisted. SmallVector IVIncs; for(;;) { Instruction *Oper = getIVIncOperand(IncV, InsertPos, /*allowScale*/true); if (!Oper) return false; // IncV is safe to hoist. IVIncs.push_back(IncV); IncV = Oper; if (SE.DT.dominates(IncV, InsertPos)) break; } for (auto I = IVIncs.rbegin(), E = IVIncs.rend(); I != E; ++I) { fixupInsertPoints(*I); (*I)->moveBefore(InsertPos); } return true; } /// Determine if this cyclic phi is in a form that would have been generated by /// LSR. We don't care if the phi was actually expanded in this pass, as long /// as it is in a low-cost form, for example, no implied multiplication. This /// should match any patterns generated by getAddRecExprPHILiterally and /// expandAddtoGEP. bool SCEVExpander::isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L) { for(Instruction *IVOper = IncV; (IVOper = getIVIncOperand(IVOper, L->getLoopPreheader()->getTerminator(), /*allowScale=*/false));) { if (IVOper == PN) return true; } return false; } /// expandIVInc - Expand an IV increment at Builder's current InsertPos. /// Typically this is the LatchBlock terminator or IVIncInsertPos, but we may /// need to materialize IV increments elsewhere to handle difficult situations. Value *SCEVExpander::expandIVInc(PHINode *PN, Value *StepV, const Loop *L, Type *ExpandTy, Type *IntTy, bool useSubtract) { Value *IncV; // If the PHI is a pointer, use a GEP, otherwise use an add or sub. if (ExpandTy->isPointerTy()) { PointerType *GEPPtrTy = cast(ExpandTy); // If the step isn't constant, don't use an implicitly scaled GEP, because // that would require a multiply inside the loop. if (!isa(StepV)) GEPPtrTy = PointerType::get(Type::getInt1Ty(SE.getContext()), GEPPtrTy->getAddressSpace()); const SCEV *const StepArray[1] = { SE.getSCEV(StepV) }; IncV = expandAddToGEP(StepArray, StepArray+1, GEPPtrTy, IntTy, PN); if (IncV->getType() != PN->getType()) { IncV = Builder.CreateBitCast(IncV, PN->getType()); rememberInstruction(IncV); } } else { IncV = useSubtract ? Builder.CreateSub(PN, StepV, Twine(IVName) + ".iv.next") : Builder.CreateAdd(PN, StepV, Twine(IVName) + ".iv.next"); rememberInstruction(IncV); } return IncV; } /// \brief Hoist the addrec instruction chain rooted in the loop phi above the /// position. This routine assumes that this is possible (has been checked). void SCEVExpander::hoistBeforePos(DominatorTree *DT, Instruction *InstToHoist, Instruction *Pos, PHINode *LoopPhi) { do { if (DT->dominates(InstToHoist, Pos)) break; // Make sure the increment is where we want it. But don't move it // down past a potential existing post-inc user. fixupInsertPoints(InstToHoist); InstToHoist->moveBefore(Pos); Pos = InstToHoist; InstToHoist = cast(InstToHoist->getOperand(0)); } while (InstToHoist != LoopPhi); } /// \brief Check whether we can cheaply express the requested SCEV in terms of /// the available PHI SCEV by truncation and/or inversion of the step. static bool canBeCheaplyTransformed(ScalarEvolution &SE, const SCEVAddRecExpr *Phi, const SCEVAddRecExpr *Requested, bool &InvertStep) { Type *PhiTy = SE.getEffectiveSCEVType(Phi->getType()); Type *RequestedTy = SE.getEffectiveSCEVType(Requested->getType()); if (RequestedTy->getIntegerBitWidth() > PhiTy->getIntegerBitWidth()) return false; // Try truncate it if necessary. Phi = dyn_cast(SE.getTruncateOrNoop(Phi, RequestedTy)); if (!Phi) return false; // Check whether truncation will help. if (Phi == Requested) { InvertStep = false; return true; } // Check whether inverting will help: {R,+,-1} == R - {0,+,1}. if (SE.getAddExpr(Requested->getStart(), SE.getNegativeSCEV(Requested)) == Phi) { InvertStep = true; return true; } return false; } static bool IsIncrementNSW(ScalarEvolution &SE, const SCEVAddRecExpr *AR) { if (!isa(AR->getType())) return false; unsigned BitWidth = cast(AR->getType())->getBitWidth(); Type *WideTy = IntegerType::get(AR->getType()->getContext(), BitWidth * 2); const SCEV *Step = AR->getStepRecurrence(SE); const SCEV *OpAfterExtend = SE.getAddExpr(SE.getSignExtendExpr(Step, WideTy), SE.getSignExtendExpr(AR, WideTy)); const SCEV *ExtendAfterOp = SE.getSignExtendExpr(SE.getAddExpr(AR, Step), WideTy); return ExtendAfterOp == OpAfterExtend; } static bool IsIncrementNUW(ScalarEvolution &SE, const SCEVAddRecExpr *AR) { if (!isa(AR->getType())) return false; unsigned BitWidth = cast(AR->getType())->getBitWidth(); Type *WideTy = IntegerType::get(AR->getType()->getContext(), BitWidth * 2); const SCEV *Step = AR->getStepRecurrence(SE); const SCEV *OpAfterExtend = SE.getAddExpr(SE.getZeroExtendExpr(Step, WideTy), SE.getZeroExtendExpr(AR, WideTy)); const SCEV *ExtendAfterOp = SE.getZeroExtendExpr(SE.getAddExpr(AR, Step), WideTy); return ExtendAfterOp == OpAfterExtend; } /// getAddRecExprPHILiterally - Helper for expandAddRecExprLiterally. Expand /// the base addrec, which is the addrec without any non-loop-dominating /// values, and return the PHI. PHINode * SCEVExpander::getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized, const Loop *L, Type *ExpandTy, Type *IntTy, Type *&TruncTy, bool &InvertStep) { assert((!IVIncInsertLoop||IVIncInsertPos) && "Uninitialized insert position"); // Reuse a previously-inserted PHI, if present. BasicBlock *LatchBlock = L->getLoopLatch(); if (LatchBlock) { PHINode *AddRecPhiMatch = nullptr; Instruction *IncV = nullptr; TruncTy = nullptr; InvertStep = false; // Only try partially matching scevs that need truncation and/or // step-inversion if we know this loop is outside the current loop. bool TryNonMatchingSCEV = IVIncInsertLoop && SE.DT.properlyDominates(LatchBlock, IVIncInsertLoop->getHeader()); for (PHINode &PN : L->getHeader()->phis()) { if (!SE.isSCEVable(PN.getType())) continue; const SCEVAddRecExpr *PhiSCEV = dyn_cast(SE.getSCEV(&PN)); if (!PhiSCEV) continue; bool IsMatchingSCEV = PhiSCEV == Normalized; // We only handle truncation and inversion of phi recurrences for the // expanded expression if the expanded expression's loop dominates the // loop we insert to. Check now, so we can bail out early. if (!IsMatchingSCEV && !TryNonMatchingSCEV) continue; Instruction *TempIncV = cast(PN.getIncomingValueForBlock(LatchBlock)); // Check whether we can reuse this PHI node. if (LSRMode) { if (!isExpandedAddRecExprPHI(&PN, TempIncV, L)) continue; if (L == IVIncInsertLoop && !hoistIVInc(TempIncV, IVIncInsertPos)) continue; } else { if (!isNormalAddRecExprPHI(&PN, TempIncV, L)) continue; } // Stop if we have found an exact match SCEV. if (IsMatchingSCEV) { IncV = TempIncV; TruncTy = nullptr; InvertStep = false; AddRecPhiMatch = &PN; break; } // Try whether the phi can be translated into the requested form // (truncated and/or offset by a constant). if ((!TruncTy || InvertStep) && canBeCheaplyTransformed(SE, PhiSCEV, Normalized, InvertStep)) { // Record the phi node. But don't stop we might find an exact match // later. AddRecPhiMatch = &PN; IncV = TempIncV; TruncTy = SE.getEffectiveSCEVType(Normalized->getType()); } } if (AddRecPhiMatch) { // Potentially, move the increment. We have made sure in // isExpandedAddRecExprPHI or hoistIVInc that this is possible. if (L == IVIncInsertLoop) hoistBeforePos(&SE.DT, IncV, IVIncInsertPos, AddRecPhiMatch); // Ok, the add recurrence looks usable. // Remember this PHI, even in post-inc mode. InsertedValues.insert(AddRecPhiMatch); // Remember the increment. rememberInstruction(IncV); return AddRecPhiMatch; } } // Save the original insertion point so we can restore it when we're done. SCEVInsertPointGuard Guard(Builder, this); // Another AddRec may need to be recursively expanded below. For example, if // this AddRec is quadratic, the StepV may itself be an AddRec in this // loop. Remove this loop from the PostIncLoops set before expanding such // AddRecs. Otherwise, we cannot find a valid position for the step // (i.e. StepV can never dominate its loop header). Ideally, we could do // SavedIncLoops.swap(PostIncLoops), but we generally have a single element, // so it's not worth implementing SmallPtrSet::swap. PostIncLoopSet SavedPostIncLoops = PostIncLoops; PostIncLoops.clear(); // Expand code for the start value into the loop preheader. assert(L->getLoopPreheader() && "Can't expand add recurrences without a loop preheader!"); Value *StartV = expandCodeFor(Normalized->getStart(), ExpandTy, L->getLoopPreheader()->getTerminator()); // StartV must have been be inserted into L's preheader to dominate the new // phi. assert(!isa(StartV) || SE.DT.properlyDominates(cast(StartV)->getParent(), L->getHeader())); // Expand code for the step value. Do this before creating the PHI so that PHI // reuse code doesn't see an incomplete PHI. const SCEV *Step = Normalized->getStepRecurrence(SE); // If the stride is negative, insert a sub instead of an add for the increment // (unless it's a constant, because subtracts of constants are canonicalized // to adds). bool useSubtract = !ExpandTy->isPointerTy() && Step->isNonConstantNegative(); if (useSubtract) Step = SE.getNegativeSCEV(Step); // Expand the step somewhere that dominates the loop header. Value *StepV = expandCodeFor(Step, IntTy, &L->getHeader()->front()); // The no-wrap behavior proved by IsIncrement(NUW|NSW) is only applicable if // we actually do emit an addition. It does not apply if we emit a // subtraction. bool IncrementIsNUW = !useSubtract && IsIncrementNUW(SE, Normalized); bool IncrementIsNSW = !useSubtract && IsIncrementNSW(SE, Normalized); // Create the PHI. BasicBlock *Header = L->getHeader(); Builder.SetInsertPoint(Header, Header->begin()); pred_iterator HPB = pred_begin(Header), HPE = pred_end(Header); PHINode *PN = Builder.CreatePHI(ExpandTy, std::distance(HPB, HPE), Twine(IVName) + ".iv"); rememberInstruction(PN); // Create the step instructions and populate the PHI. for (pred_iterator HPI = HPB; HPI != HPE; ++HPI) { BasicBlock *Pred = *HPI; // Add a start value. if (!L->contains(Pred)) { PN->addIncoming(StartV, Pred); continue; } // Create a step value and add it to the PHI. // If IVIncInsertLoop is non-null and equal to the addrec's loop, insert the // instructions at IVIncInsertPos. Instruction *InsertPos = L == IVIncInsertLoop ? IVIncInsertPos : Pred->getTerminator(); Builder.SetInsertPoint(InsertPos); Value *IncV = expandIVInc(PN, StepV, L, ExpandTy, IntTy, useSubtract); if (isa(IncV)) { if (IncrementIsNUW) cast(IncV)->setHasNoUnsignedWrap(); if (IncrementIsNSW) cast(IncV)->setHasNoSignedWrap(); } PN->addIncoming(IncV, Pred); } // After expanding subexpressions, restore the PostIncLoops set so the caller // can ensure that IVIncrement dominates the current uses. PostIncLoops = SavedPostIncLoops; // Remember this PHI, even in post-inc mode. InsertedValues.insert(PN); return PN; } Value *SCEVExpander::expandAddRecExprLiterally(const SCEVAddRecExpr *S) { Type *STy = S->getType(); Type *IntTy = SE.getEffectiveSCEVType(STy); const Loop *L = S->getLoop(); // Determine a normalized form of this expression, which is the expression // before any post-inc adjustment is made. const SCEVAddRecExpr *Normalized = S; if (PostIncLoops.count(L)) { PostIncLoopSet Loops; Loops.insert(L); Normalized = cast(normalizeForPostIncUse(S, Loops, SE)); } // Strip off any non-loop-dominating component from the addrec start. const SCEV *Start = Normalized->getStart(); const SCEV *PostLoopOffset = nullptr; if (!SE.properlyDominates(Start, L->getHeader())) { PostLoopOffset = Start; Start = SE.getConstant(Normalized->getType(), 0); Normalized = cast( SE.getAddRecExpr(Start, Normalized->getStepRecurrence(SE), Normalized->getLoop(), Normalized->getNoWrapFlags(SCEV::FlagNW))); } // Strip off any non-loop-dominating component from the addrec step. const SCEV *Step = Normalized->getStepRecurrence(SE); const SCEV *PostLoopScale = nullptr; if (!SE.dominates(Step, L->getHeader())) { PostLoopScale = Step; Step = SE.getConstant(Normalized->getType(), 1); if (!Start->isZero()) { // The normalization below assumes that Start is constant zero, so if // it isn't re-associate Start to PostLoopOffset. assert(!PostLoopOffset && "Start not-null but PostLoopOffset set?"); PostLoopOffset = Start; Start = SE.getConstant(Normalized->getType(), 0); } Normalized = cast(SE.getAddRecExpr( Start, Step, Normalized->getLoop(), Normalized->getNoWrapFlags(SCEV::FlagNW))); } // Expand the core addrec. If we need post-loop scaling, force it to // expand to an integer type to avoid the need for additional casting. Type *ExpandTy = PostLoopScale ? IntTy : STy; // We can't use a pointer type for the addrec if the pointer type is // non-integral. Type *AddRecPHIExpandTy = DL.isNonIntegralPointerType(STy) ? Normalized->getType() : ExpandTy; // In some cases, we decide to reuse an existing phi node but need to truncate // it and/or invert the step. Type *TruncTy = nullptr; bool InvertStep = false; PHINode *PN = getAddRecExprPHILiterally(Normalized, L, AddRecPHIExpandTy, IntTy, TruncTy, InvertStep); // Accommodate post-inc mode, if necessary. Value *Result; if (!PostIncLoops.count(L)) Result = PN; else { // In PostInc mode, use the post-incremented value. BasicBlock *LatchBlock = L->getLoopLatch(); assert(LatchBlock && "PostInc mode requires a unique loop latch!"); Result = PN->getIncomingValueForBlock(LatchBlock); // For an expansion to use the postinc form, the client must call // expandCodeFor with an InsertPoint that is either outside the PostIncLoop // or dominated by IVIncInsertPos. if (isa(Result) && !SE.DT.dominates(cast(Result), &*Builder.GetInsertPoint())) { // The induction variable's postinc expansion does not dominate this use. // IVUsers tries to prevent this case, so it is rare. However, it can // happen when an IVUser outside the loop is not dominated by the latch // block. Adjusting IVIncInsertPos before expansion begins cannot handle // all cases. Consider a phi outide whose operand is replaced during // expansion with the value of the postinc user. Without fundamentally // changing the way postinc users are tracked, the only remedy is // inserting an extra IV increment. StepV might fold into PostLoopOffset, // but hopefully expandCodeFor handles that. bool useSubtract = !ExpandTy->isPointerTy() && Step->isNonConstantNegative(); if (useSubtract) Step = SE.getNegativeSCEV(Step); Value *StepV; { // Expand the step somewhere that dominates the loop header. SCEVInsertPointGuard Guard(Builder, this); StepV = expandCodeFor(Step, IntTy, &L->getHeader()->front()); } Result = expandIVInc(PN, StepV, L, ExpandTy, IntTy, useSubtract); } } // We have decided to reuse an induction variable of a dominating loop. Apply // truncation and/or invertion of the step. if (TruncTy) { Type *ResTy = Result->getType(); // Normalize the result type. if (ResTy != SE.getEffectiveSCEVType(ResTy)) Result = InsertNoopCastOfTo(Result, SE.getEffectiveSCEVType(ResTy)); // Truncate the result. if (TruncTy != Result->getType()) { Result = Builder.CreateTrunc(Result, TruncTy); rememberInstruction(Result); } // Invert the result. if (InvertStep) { Result = Builder.CreateSub(expandCodeFor(Normalized->getStart(), TruncTy), Result); rememberInstruction(Result); } } // Re-apply any non-loop-dominating scale. if (PostLoopScale) { assert(S->isAffine() && "Can't linearly scale non-affine recurrences."); Result = InsertNoopCastOfTo(Result, IntTy); Result = Builder.CreateMul(Result, expandCodeFor(PostLoopScale, IntTy)); rememberInstruction(Result); } // Re-apply any non-loop-dominating offset. if (PostLoopOffset) { if (PointerType *PTy = dyn_cast(ExpandTy)) { if (Result->getType()->isIntegerTy()) { Value *Base = expandCodeFor(PostLoopOffset, ExpandTy); const SCEV *const OffsetArray[1] = {SE.getUnknown(Result)}; Result = expandAddToGEP(OffsetArray, OffsetArray + 1, PTy, IntTy, Base); } else { const SCEV *const OffsetArray[1] = {PostLoopOffset}; Result = expandAddToGEP(OffsetArray, OffsetArray + 1, PTy, IntTy, Result); } } else { Result = InsertNoopCastOfTo(Result, IntTy); Result = Builder.CreateAdd(Result, expandCodeFor(PostLoopOffset, IntTy)); rememberInstruction(Result); } } return Result; } Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) { if (!CanonicalMode) return expandAddRecExprLiterally(S); Type *Ty = SE.getEffectiveSCEVType(S->getType()); const Loop *L = S->getLoop(); // First check for an existing canonical IV in a suitable type. PHINode *CanonicalIV = nullptr; if (PHINode *PN = L->getCanonicalInductionVariable()) if (SE.getTypeSizeInBits(PN->getType()) >= SE.getTypeSizeInBits(Ty)) CanonicalIV = PN; // Rewrite an AddRec in terms of the canonical induction variable, if // its type is more narrow. if (CanonicalIV && SE.getTypeSizeInBits(CanonicalIV->getType()) > SE.getTypeSizeInBits(Ty)) { SmallVector NewOps(S->getNumOperands()); for (unsigned i = 0, e = S->getNumOperands(); i != e; ++i) NewOps[i] = SE.getAnyExtendExpr(S->op_begin()[i], CanonicalIV->getType()); Value *V = expand(SE.getAddRecExpr(NewOps, S->getLoop(), S->getNoWrapFlags(SCEV::FlagNW))); BasicBlock::iterator NewInsertPt = findInsertPointAfter(cast(V), Builder.GetInsertBlock()); V = expandCodeFor(SE.getTruncateExpr(SE.getUnknown(V), Ty), nullptr, &*NewInsertPt); return V; } // {X,+,F} --> X + {0,+,F} if (!S->getStart()->isZero()) { SmallVector NewOps(S->op_begin(), S->op_end()); NewOps[0] = SE.getConstant(Ty, 0); const SCEV *Rest = SE.getAddRecExpr(NewOps, L, S->getNoWrapFlags(SCEV::FlagNW)); // Turn things like ptrtoint+arithmetic+inttoptr into GEP. See the // comments on expandAddToGEP for details. const SCEV *Base = S->getStart(); const SCEV *RestArray[1] = { Rest }; // Dig into the expression to find the pointer base for a GEP. ExposePointerBase(Base, RestArray[0], SE); // If we found a pointer, expand the AddRec with a GEP. if (PointerType *PTy = dyn_cast(Base->getType())) { // Make sure the Base isn't something exotic, such as a multiplied // or divided pointer value. In those cases, the result type isn't // actually a pointer type. if (!isa(Base) && !isa(Base)) { Value *StartV = expand(Base); assert(StartV->getType() == PTy && "Pointer type mismatch for GEP!"); return expandAddToGEP(RestArray, RestArray+1, PTy, Ty, StartV); } } // Just do a normal add. Pre-expand the operands to suppress folding. // // The LHS and RHS values are factored out of the expand call to make the // output independent of the argument evaluation order. const SCEV *AddExprLHS = SE.getUnknown(expand(S->getStart())); const SCEV *AddExprRHS = SE.getUnknown(expand(Rest)); return expand(SE.getAddExpr(AddExprLHS, AddExprRHS)); } // If we don't yet have a canonical IV, create one. if (!CanonicalIV) { // Create and insert the PHI node for the induction variable in the // specified loop. BasicBlock *Header = L->getHeader(); pred_iterator HPB = pred_begin(Header), HPE = pred_end(Header); CanonicalIV = PHINode::Create(Ty, std::distance(HPB, HPE), "indvar", &Header->front()); rememberInstruction(CanonicalIV); SmallSet PredSeen; Constant *One = ConstantInt::get(Ty, 1); for (pred_iterator HPI = HPB; HPI != HPE; ++HPI) { BasicBlock *HP = *HPI; if (!PredSeen.insert(HP).second) { // There must be an incoming value for each predecessor, even the // duplicates! CanonicalIV->addIncoming(CanonicalIV->getIncomingValueForBlock(HP), HP); continue; } if (L->contains(HP)) { // Insert a unit add instruction right before the terminator // corresponding to the back-edge. Instruction *Add = BinaryOperator::CreateAdd(CanonicalIV, One, "indvar.next", HP->getTerminator()); Add->setDebugLoc(HP->getTerminator()->getDebugLoc()); rememberInstruction(Add); CanonicalIV->addIncoming(Add, HP); } else { CanonicalIV->addIncoming(Constant::getNullValue(Ty), HP); } } } // {0,+,1} --> Insert a canonical induction variable into the loop! if (S->isAffine() && S->getOperand(1)->isOne()) { assert(Ty == SE.getEffectiveSCEVType(CanonicalIV->getType()) && "IVs with types different from the canonical IV should " "already have been handled!"); return CanonicalIV; } // {0,+,F} --> {0,+,1} * F // If this is a simple linear addrec, emit it now as a special case. if (S->isAffine()) // {0,+,F} --> i*F return expand(SE.getTruncateOrNoop( SE.getMulExpr(SE.getUnknown(CanonicalIV), SE.getNoopOrAnyExtend(S->getOperand(1), CanonicalIV->getType())), Ty)); // If this is a chain of recurrences, turn it into a closed form, using the // folders, then expandCodeFor the closed form. This allows the folders to // simplify the expression without having to build a bunch of special code // into this folder. const SCEV *IH = SE.getUnknown(CanonicalIV); // Get I as a "symbolic" SCEV. // Promote S up to the canonical IV type, if the cast is foldable. const SCEV *NewS = S; const SCEV *Ext = SE.getNoopOrAnyExtend(S, CanonicalIV->getType()); if (isa(Ext)) NewS = Ext; const SCEV *V = cast(NewS)->evaluateAtIteration(IH, SE); //cerr << "Evaluated: " << *this << "\n to: " << *V << "\n"; // Truncate the result down to the original type, if needed. const SCEV *T = SE.getTruncateOrNoop(V, Ty); return expand(T); } Value *SCEVExpander::visitTruncateExpr(const SCEVTruncateExpr *S) { Type *Ty = SE.getEffectiveSCEVType(S->getType()); Value *V = expandCodeFor(S->getOperand(), SE.getEffectiveSCEVType(S->getOperand()->getType())); Value *I = Builder.CreateTrunc(V, Ty); rememberInstruction(I); return I; } Value *SCEVExpander::visitZeroExtendExpr(const SCEVZeroExtendExpr *S) { Type *Ty = SE.getEffectiveSCEVType(S->getType()); Value *V = expandCodeFor(S->getOperand(), SE.getEffectiveSCEVType(S->getOperand()->getType())); Value *I = Builder.CreateZExt(V, Ty); rememberInstruction(I); return I; } Value *SCEVExpander::visitSignExtendExpr(const SCEVSignExtendExpr *S) { Type *Ty = SE.getEffectiveSCEVType(S->getType()); Value *V = expandCodeFor(S->getOperand(), SE.getEffectiveSCEVType(S->getOperand()->getType())); Value *I = Builder.CreateSExt(V, Ty); rememberInstruction(I); return I; } Value *SCEVExpander::visitSMaxExpr(const SCEVSMaxExpr *S) { Value *LHS = expand(S->getOperand(S->getNumOperands()-1)); Type *Ty = LHS->getType(); for (int i = S->getNumOperands()-2; i >= 0; --i) { // In the case of mixed integer and pointer types, do the // rest of the comparisons as integer. if (S->getOperand(i)->getType() != Ty) { Ty = SE.getEffectiveSCEVType(Ty); LHS = InsertNoopCastOfTo(LHS, Ty); } Value *RHS = expandCodeFor(S->getOperand(i), Ty); Value *ICmp = Builder.CreateICmpSGT(LHS, RHS); rememberInstruction(ICmp); Value *Sel = Builder.CreateSelect(ICmp, LHS, RHS, "smax"); rememberInstruction(Sel); LHS = Sel; } // In the case of mixed integer and pointer types, cast the // final result back to the pointer type. if (LHS->getType() != S->getType()) LHS = InsertNoopCastOfTo(LHS, S->getType()); return LHS; } Value *SCEVExpander::visitUMaxExpr(const SCEVUMaxExpr *S) { Value *LHS = expand(S->getOperand(S->getNumOperands()-1)); Type *Ty = LHS->getType(); for (int i = S->getNumOperands()-2; i >= 0; --i) { // In the case of mixed integer and pointer types, do the // rest of the comparisons as integer. if (S->getOperand(i)->getType() != Ty) { Ty = SE.getEffectiveSCEVType(Ty); LHS = InsertNoopCastOfTo(LHS, Ty); } Value *RHS = expandCodeFor(S->getOperand(i), Ty); Value *ICmp = Builder.CreateICmpUGT(LHS, RHS); rememberInstruction(ICmp); Value *Sel = Builder.CreateSelect(ICmp, LHS, RHS, "umax"); rememberInstruction(Sel); LHS = Sel; } // In the case of mixed integer and pointer types, cast the // final result back to the pointer type. if (LHS->getType() != S->getType()) LHS = InsertNoopCastOfTo(LHS, S->getType()); return LHS; } Value *SCEVExpander::expandCodeFor(const SCEV *SH, Type *Ty, Instruction *IP) { setInsertPoint(IP); return expandCodeFor(SH, Ty); } Value *SCEVExpander::expandCodeFor(const SCEV *SH, Type *Ty) { // Expand the code for this SCEV. Value *V = expand(SH); if (Ty) { assert(SE.getTypeSizeInBits(Ty) == SE.getTypeSizeInBits(SH->getType()) && "non-trivial casts should be done with the SCEVs directly!"); V = InsertNoopCastOfTo(V, Ty); } return V; } ScalarEvolution::ValueOffsetPair SCEVExpander::FindValueInExprValueMap(const SCEV *S, const Instruction *InsertPt) { SetVector *Set = SE.getSCEVValues(S); // If the expansion is not in CanonicalMode, and the SCEV contains any // sub scAddRecExpr type SCEV, it is required to expand the SCEV literally. if (CanonicalMode || !SE.containsAddRecurrence(S)) { // If S is scConstant, it may be worse to reuse an existing Value. if (S->getSCEVType() != scConstant && Set) { // Choose a Value from the set which dominates the insertPt. // insertPt should be inside the Value's parent loop so as not to break // the LCSSA form. for (auto const &VOPair : *Set) { Value *V = VOPair.first; ConstantInt *Offset = VOPair.second; Instruction *EntInst = nullptr; if (V && isa(V) && (EntInst = cast(V)) && S->getType() == V->getType() && EntInst->getFunction() == InsertPt->getFunction() && SE.DT.dominates(EntInst, InsertPt) && (SE.LI.getLoopFor(EntInst->getParent()) == nullptr || SE.LI.getLoopFor(EntInst->getParent())->contains(InsertPt))) return {V, Offset}; } } } return {nullptr, nullptr}; } // The expansion of SCEV will either reuse a previous Value in ExprValueMap, // or expand the SCEV literally. Specifically, if the expansion is in LSRMode, // and the SCEV contains any sub scAddRecExpr type SCEV, it will be expanded // literally, to prevent LSR's transformed SCEV from being reverted. Otherwise, // the expansion will try to reuse Value from ExprValueMap, and only when it // fails, expand the SCEV literally. Value *SCEVExpander::expand(const SCEV *S) { // Compute an insertion point for this SCEV object. Hoist the instructions // as far out in the loop nest as possible. Instruction *InsertPt = &*Builder.GetInsertPoint(); for (Loop *L = SE.LI.getLoopFor(Builder.GetInsertBlock());; L = L->getParentLoop()) if (SE.isLoopInvariant(S, L)) { if (!L) break; if (BasicBlock *Preheader = L->getLoopPreheader()) InsertPt = Preheader->getTerminator(); else { // LSR sets the insertion point for AddRec start/step values to the // block start to simplify value reuse, even though it's an invalid // position. SCEVExpander must correct for this in all cases. InsertPt = &*L->getHeader()->getFirstInsertionPt(); } } else { // We can move insertion point only if there is no div or rem operations // otherwise we are risky to move it over the check for zero denominator. auto SafeToHoist = [](const SCEV *S) { return !SCEVExprContains(S, [](const SCEV *S) { if (const auto *D = dyn_cast(S)) { if (const auto *SC = dyn_cast(D->getRHS())) // Division by non-zero constants can be hoisted. return SC->getValue()->isZero(); // All other divisions should not be moved as they may be // divisions by zero and should be kept within the // conditions of the surrounding loops that guard their // execution (see PR35406). return true; } return false; }); }; // If the SCEV is computable at this level, insert it into the header // after the PHIs (and after any other instructions that we've inserted // there) so that it is guaranteed to dominate any user inside the loop. if (L && SE.hasComputableLoopEvolution(S, L) && !PostIncLoops.count(L) && SafeToHoist(S)) InsertPt = &*L->getHeader()->getFirstInsertionPt(); while (InsertPt->getIterator() != Builder.GetInsertPoint() && (isInsertedInstruction(InsertPt) || isa(InsertPt))) { InsertPt = &*std::next(InsertPt->getIterator()); } break; } // Check to see if we already expanded this here. auto I = InsertedExpressions.find(std::make_pair(S, InsertPt)); if (I != InsertedExpressions.end()) return I->second; SCEVInsertPointGuard Guard(Builder, this); Builder.SetInsertPoint(InsertPt); // Expand the expression into instructions. ScalarEvolution::ValueOffsetPair VO = FindValueInExprValueMap(S, InsertPt); Value *V = VO.first; if (!V) V = visit(S); else if (VO.second) { if (PointerType *Vty = dyn_cast(V->getType())) { Type *Ety = Vty->getPointerElementType(); int64_t Offset = VO.second->getSExtValue(); int64_t ESize = SE.getTypeSizeInBits(Ety); if ((Offset * 8) % ESize == 0) { ConstantInt *Idx = ConstantInt::getSigned(VO.second->getType(), -(Offset * 8) / ESize); V = Builder.CreateGEP(Ety, V, Idx, "scevgep"); } else { ConstantInt *Idx = ConstantInt::getSigned(VO.second->getType(), -Offset); unsigned AS = Vty->getAddressSpace(); V = Builder.CreateBitCast(V, Type::getInt8PtrTy(SE.getContext(), AS)); V = Builder.CreateGEP(Type::getInt8Ty(SE.getContext()), V, Idx, "uglygep"); V = Builder.CreateBitCast(V, Vty); } } else { V = Builder.CreateSub(V, VO.second); } } // Remember the expanded value for this SCEV at this location. // // This is independent of PostIncLoops. The mapped value simply materializes // the expression at this insertion point. If the mapped value happened to be // a postinc expansion, it could be reused by a non-postinc user, but only if // its insertion point was already at the head of the loop. InsertedExpressions[std::make_pair(S, InsertPt)] = V; return V; } void SCEVExpander::rememberInstruction(Value *I) { if (!PostIncLoops.empty()) InsertedPostIncValues.insert(I); else InsertedValues.insert(I); } /// getOrInsertCanonicalInductionVariable - This method returns the /// canonical induction variable of the specified type for the specified /// loop (inserting one if there is none). A canonical induction variable /// starts at zero and steps by one on each iteration. PHINode * SCEVExpander::getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty) { assert(Ty->isIntegerTy() && "Can only insert integer induction variables!"); // Build a SCEV for {0,+,1}. // Conservatively use FlagAnyWrap for now. const SCEV *H = SE.getAddRecExpr(SE.getConstant(Ty, 0), SE.getConstant(Ty, 1), L, SCEV::FlagAnyWrap); // Emit code for it. SCEVInsertPointGuard Guard(Builder, this); PHINode *V = cast(expandCodeFor(H, nullptr, &L->getHeader()->front())); return V; } /// replaceCongruentIVs - Check for congruent phis in this loop header and /// replace them with their most canonical representative. Return the number of /// phis eliminated. /// /// This does not depend on any SCEVExpander state but should be used in /// the same context that SCEVExpander is used. unsigned SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT, SmallVectorImpl &DeadInsts, const TargetTransformInfo *TTI) { // Find integer phis in order of increasing width. SmallVector Phis; for (PHINode &PN : L->getHeader()->phis()) Phis.push_back(&PN); if (TTI) std::sort(Phis.begin(), Phis.end(), [](Value *LHS, Value *RHS) { // Put pointers at the back and make sure pointer < pointer = false. if (!LHS->getType()->isIntegerTy() || !RHS->getType()->isIntegerTy()) return RHS->getType()->isIntegerTy() && !LHS->getType()->isIntegerTy(); return RHS->getType()->getPrimitiveSizeInBits() < LHS->getType()->getPrimitiveSizeInBits(); }); unsigned NumElim = 0; DenseMap ExprToIVMap; // Process phis from wide to narrow. Map wide phis to their truncation // so narrow phis can reuse them. for (PHINode *Phi : Phis) { auto SimplifyPHINode = [&](PHINode *PN) -> Value * { if (Value *V = SimplifyInstruction(PN, {DL, &SE.TLI, &SE.DT, &SE.AC})) return V; if (!SE.isSCEVable(PN->getType())) return nullptr; auto *Const = dyn_cast(SE.getSCEV(PN)); if (!Const) return nullptr; return Const->getValue(); }; // Fold constant phis. They may be congruent to other constant phis and // would confuse the logic below that expects proper IVs. if (Value *V = SimplifyPHINode(Phi)) { if (V->getType() != Phi->getType()) continue; Phi->replaceAllUsesWith(V); DeadInsts.emplace_back(Phi); ++NumElim; DEBUG_WITH_TYPE(DebugType, dbgs() << "INDVARS: Eliminated constant iv: " << *Phi << '\n'); continue; } if (!SE.isSCEVable(Phi->getType())) continue; PHINode *&OrigPhiRef = ExprToIVMap[SE.getSCEV(Phi)]; if (!OrigPhiRef) { OrigPhiRef = Phi; if (Phi->getType()->isIntegerTy() && TTI && TTI->isTruncateFree(Phi->getType(), Phis.back()->getType())) { // This phi can be freely truncated to the narrowest phi type. Map the // truncated expression to it so it will be reused for narrow types. const SCEV *TruncExpr = SE.getTruncateExpr(SE.getSCEV(Phi), Phis.back()->getType()); ExprToIVMap[TruncExpr] = Phi; } continue; } // Replacing a pointer phi with an integer phi or vice-versa doesn't make // sense. if (OrigPhiRef->getType()->isPointerTy() != Phi->getType()->isPointerTy()) continue; if (BasicBlock *LatchBlock = L->getLoopLatch()) { Instruction *OrigInc = dyn_cast( OrigPhiRef->getIncomingValueForBlock(LatchBlock)); Instruction *IsomorphicInc = dyn_cast(Phi->getIncomingValueForBlock(LatchBlock)); if (OrigInc && IsomorphicInc) { // If this phi has the same width but is more canonical, replace the // original with it. As part of the "more canonical" determination, // respect a prior decision to use an IV chain. if (OrigPhiRef->getType() == Phi->getType() && !(ChainedPhis.count(Phi) || isExpandedAddRecExprPHI(OrigPhiRef, OrigInc, L)) && (ChainedPhis.count(Phi) || isExpandedAddRecExprPHI(Phi, IsomorphicInc, L))) { std::swap(OrigPhiRef, Phi); std::swap(OrigInc, IsomorphicInc); } // Replacing the congruent phi is sufficient because acyclic // redundancy elimination, CSE/GVN, should handle the // rest. However, once SCEV proves that a phi is congruent, // it's often the head of an IV user cycle that is isomorphic // with the original phi. It's worth eagerly cleaning up the // common case of a single IV increment so that DeleteDeadPHIs // can remove cycles that had postinc uses. const SCEV *TruncExpr = SE.getTruncateOrNoop(SE.getSCEV(OrigInc), IsomorphicInc->getType()); if (OrigInc != IsomorphicInc && TruncExpr == SE.getSCEV(IsomorphicInc) && SE.LI.replacementPreservesLCSSAForm(IsomorphicInc, OrigInc) && hoistIVInc(OrigInc, IsomorphicInc)) { DEBUG_WITH_TYPE(DebugType, dbgs() << "INDVARS: Eliminated congruent iv.inc: " << *IsomorphicInc << '\n'); Value *NewInc = OrigInc; if (OrigInc->getType() != IsomorphicInc->getType()) { Instruction *IP = nullptr; if (PHINode *PN = dyn_cast(OrigInc)) IP = &*PN->getParent()->getFirstInsertionPt(); else IP = OrigInc->getNextNode(); IRBuilder<> Builder(IP); Builder.SetCurrentDebugLocation(IsomorphicInc->getDebugLoc()); NewInc = Builder.CreateTruncOrBitCast( OrigInc, IsomorphicInc->getType(), IVName); } IsomorphicInc->replaceAllUsesWith(NewInc); DeadInsts.emplace_back(IsomorphicInc); } } } DEBUG_WITH_TYPE(DebugType, dbgs() << "INDVARS: Eliminated congruent iv: " << *Phi << '\n'); ++NumElim; Value *NewIV = OrigPhiRef; if (OrigPhiRef->getType() != Phi->getType()) { IRBuilder<> Builder(&*L->getHeader()->getFirstInsertionPt()); Builder.SetCurrentDebugLocation(Phi->getDebugLoc()); NewIV = Builder.CreateTruncOrBitCast(OrigPhiRef, Phi->getType(), IVName); } Phi->replaceAllUsesWith(NewIV); DeadInsts.emplace_back(Phi); } return NumElim; } Value *SCEVExpander::getExactExistingExpansion(const SCEV *S, const Instruction *At, Loop *L) { Optional VO = getRelatedExistingExpansion(S, At, L); if (VO && VO.getValue().second == nullptr) return VO.getValue().first; return nullptr; } Optional SCEVExpander::getRelatedExistingExpansion(const SCEV *S, const Instruction *At, Loop *L) { using namespace llvm::PatternMatch; SmallVector ExitingBlocks; L->getExitingBlocks(ExitingBlocks); // Look for suitable value in simple conditions at the loop exits. for (BasicBlock *BB : ExitingBlocks) { ICmpInst::Predicate Pred; Instruction *LHS, *RHS; BasicBlock *TrueBB, *FalseBB; if (!match(BB->getTerminator(), m_Br(m_ICmp(Pred, m_Instruction(LHS), m_Instruction(RHS)), TrueBB, FalseBB))) continue; if (SE.getSCEV(LHS) == S && SE.DT.dominates(LHS, At)) return ScalarEvolution::ValueOffsetPair(LHS, nullptr); if (SE.getSCEV(RHS) == S && SE.DT.dominates(RHS, At)) return ScalarEvolution::ValueOffsetPair(RHS, nullptr); } // Use expand's logic which is used for reusing a previous Value in // ExprValueMap. ScalarEvolution::ValueOffsetPair VO = FindValueInExprValueMap(S, At); if (VO.first) return VO; // There is potential to make this significantly smarter, but this simple // heuristic already gets some interesting cases. // Can not find suitable value. return None; } bool SCEVExpander::isHighCostExpansionHelper( const SCEV *S, Loop *L, const Instruction *At, SmallPtrSetImpl &Processed) { // If we can find an existing value for this scev available at the point "At" // then consider the expression cheap. if (At && getRelatedExistingExpansion(S, At, L)) return false; // Zero/One operand expressions switch (S->getSCEVType()) { case scUnknown: case scConstant: return false; case scTruncate: return isHighCostExpansionHelper(cast(S)->getOperand(), L, At, Processed); case scZeroExtend: return isHighCostExpansionHelper(cast(S)->getOperand(), L, At, Processed); case scSignExtend: return isHighCostExpansionHelper(cast(S)->getOperand(), L, At, Processed); } if (!Processed.insert(S).second) return false; if (auto *UDivExpr = dyn_cast(S)) { // If the divisor is a power of two and the SCEV type fits in a native // integer, consider the division cheap irrespective of whether it occurs in // the user code since it can be lowered into a right shift. if (auto *SC = dyn_cast(UDivExpr->getRHS())) if (SC->getAPInt().isPowerOf2()) { const DataLayout &DL = L->getHeader()->getParent()->getParent()->getDataLayout(); unsigned Width = cast(UDivExpr->getType())->getBitWidth(); return DL.isIllegalInteger(Width); } // UDivExpr is very likely a UDiv that ScalarEvolution's HowFarToZero or // HowManyLessThans produced to compute a precise expression, rather than a // UDiv from the user's code. If we can't find a UDiv in the code with some // simple searching, assume the former consider UDivExpr expensive to // compute. BasicBlock *ExitingBB = L->getExitingBlock(); if (!ExitingBB) return true; // At the beginning of this function we already tried to find existing value // for plain 'S'. Now try to lookup 'S + 1' since it is common pattern // involving division. This is just a simple search heuristic. if (!At) At = &ExitingBB->back(); if (!getRelatedExistingExpansion( SE.getAddExpr(S, SE.getConstant(S->getType(), 1)), At, L)) return true; } // HowManyLessThans uses a Max expression whenever the loop is not guarded by // the exit condition. if (isa(S) || isa(S)) return true; // Recurse past nary expressions, which commonly occur in the // BackedgeTakenCount. They may already exist in program code, and if not, // they are not too expensive rematerialize. if (const SCEVNAryExpr *NAry = dyn_cast(S)) { for (auto *Op : NAry->operands()) if (isHighCostExpansionHelper(Op, L, At, Processed)) return true; } // If we haven't recognized an expensive SCEV pattern, assume it's an // expression produced by program code. return false; } Value *SCEVExpander::expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *IP) { assert(IP); switch (Pred->getKind()) { case SCEVPredicate::P_Union: return expandUnionPredicate(cast(Pred), IP); case SCEVPredicate::P_Equal: return expandEqualPredicate(cast(Pred), IP); case SCEVPredicate::P_Wrap: { auto *AddRecPred = cast(Pred); return expandWrapPredicate(AddRecPred, IP); } } llvm_unreachable("Unknown SCEV predicate type"); } Value *SCEVExpander::expandEqualPredicate(const SCEVEqualPredicate *Pred, Instruction *IP) { Value *Expr0 = expandCodeFor(Pred->getLHS(), Pred->getLHS()->getType(), IP); Value *Expr1 = expandCodeFor(Pred->getRHS(), Pred->getRHS()->getType(), IP); Builder.SetInsertPoint(IP); auto *I = Builder.CreateICmpNE(Expr0, Expr1, "ident.check"); return I; } Value *SCEVExpander::generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc, bool Signed) { assert(AR->isAffine() && "Cannot generate RT check for " "non-affine expression"); SCEVUnionPredicate Pred; const SCEV *ExitCount = SE.getPredicatedBackedgeTakenCount(AR->getLoop(), Pred); assert(ExitCount != SE.getCouldNotCompute() && "Invalid loop count"); const SCEV *Step = AR->getStepRecurrence(SE); const SCEV *Start = AR->getStart(); unsigned SrcBits = SE.getTypeSizeInBits(ExitCount->getType()); unsigned DstBits = SE.getTypeSizeInBits(AR->getType()); // The expression {Start,+,Step} has nusw/nssw if // Step < 0, Start - |Step| * Backedge <= Start // Step >= 0, Start + |Step| * Backedge > Start // and |Step| * Backedge doesn't unsigned overflow. IntegerType *CountTy = IntegerType::get(Loc->getContext(), SrcBits); Builder.SetInsertPoint(Loc); Value *TripCountVal = expandCodeFor(ExitCount, CountTy, Loc); IntegerType *Ty = IntegerType::get(Loc->getContext(), SE.getTypeSizeInBits(AR->getType())); Value *StepValue = expandCodeFor(Step, Ty, Loc); Value *NegStepValue = expandCodeFor(SE.getNegativeSCEV(Step), Ty, Loc); Value *StartValue = expandCodeFor(Start, Ty, Loc); ConstantInt *Zero = ConstantInt::get(Loc->getContext(), APInt::getNullValue(DstBits)); Builder.SetInsertPoint(Loc); // Compute |Step| Value *StepCompare = Builder.CreateICmp(ICmpInst::ICMP_SLT, StepValue, Zero); Value *AbsStep = Builder.CreateSelect(StepCompare, NegStepValue, StepValue); // Get the backedge taken count and truncate or extended to the AR type. Value *TruncTripCount = Builder.CreateZExtOrTrunc(TripCountVal, Ty); auto *MulF = Intrinsic::getDeclaration(Loc->getModule(), Intrinsic::umul_with_overflow, Ty); // Compute |Step| * Backedge CallInst *Mul = Builder.CreateCall(MulF, {AbsStep, TruncTripCount}, "mul"); Value *MulV = Builder.CreateExtractValue(Mul, 0, "mul.result"); Value *OfMul = Builder.CreateExtractValue(Mul, 1, "mul.overflow"); // Compute: // Start + |Step| * Backedge < Start // Start - |Step| * Backedge > Start Value *Add = Builder.CreateAdd(StartValue, MulV); Value *Sub = Builder.CreateSub(StartValue, MulV); Value *EndCompareGT = Builder.CreateICmp( Signed ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT, Sub, StartValue); Value *EndCompareLT = Builder.CreateICmp( Signed ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, Add, StartValue); // Select the answer based on the sign of Step. Value *EndCheck = Builder.CreateSelect(StepCompare, EndCompareGT, EndCompareLT); // If the backedge taken count type is larger than the AR type, // check that we don't drop any bits by truncating it. If we are // droping bits, then we have overflow (unless the step is zero). if (SE.getTypeSizeInBits(CountTy) > SE.getTypeSizeInBits(Ty)) { auto MaxVal = APInt::getMaxValue(DstBits).zext(SrcBits); auto *BackedgeCheck = Builder.CreateICmp(ICmpInst::ICMP_UGT, TripCountVal, ConstantInt::get(Loc->getContext(), MaxVal)); BackedgeCheck = Builder.CreateAnd( BackedgeCheck, Builder.CreateICmp(ICmpInst::ICMP_NE, StepValue, Zero)); EndCheck = Builder.CreateOr(EndCheck, BackedgeCheck); } EndCheck = Builder.CreateOr(EndCheck, OfMul); return EndCheck; } Value *SCEVExpander::expandWrapPredicate(const SCEVWrapPredicate *Pred, Instruction *IP) { const auto *A = cast(Pred->getExpr()); Value *NSSWCheck = nullptr, *NUSWCheck = nullptr; // Add a check for NUSW if (Pred->getFlags() & SCEVWrapPredicate::IncrementNUSW) NUSWCheck = generateOverflowCheck(A, IP, false); // Add a check for NSSW if (Pred->getFlags() & SCEVWrapPredicate::IncrementNSSW) NSSWCheck = generateOverflowCheck(A, IP, true); if (NUSWCheck && NSSWCheck) return Builder.CreateOr(NUSWCheck, NSSWCheck); if (NUSWCheck) return NUSWCheck; if (NSSWCheck) return NSSWCheck; return ConstantInt::getFalse(IP->getContext()); } Value *SCEVExpander::expandUnionPredicate(const SCEVUnionPredicate *Union, Instruction *IP) { auto *BoolType = IntegerType::get(IP->getContext(), 1); Value *Check = ConstantInt::getNullValue(BoolType); // Loop over all checks in this set. for (auto Pred : Union->getPredicates()) { auto *NextCheck = expandCodeForPredicate(Pred, IP); Builder.SetInsertPoint(IP); Check = Builder.CreateOr(Check, NextCheck); } return Check; } namespace { // Search for a SCEV subexpression that is not safe to expand. Any expression // that may expand to a !isSafeToSpeculativelyExecute value is unsafe, namely // UDiv expressions. We don't know if the UDiv is derived from an IR divide // instruction, but the important thing is that we prove the denominator is // nonzero before expansion. // // IVUsers already checks that IV-derived expressions are safe. So this check is // only needed when the expression includes some subexpression that is not IV // derived. // // Currently, we only allow division by a nonzero constant here. If this is // inadequate, we could easily allow division by SCEVUnknown by using // ValueTracking to check isKnownNonZero(). // // We cannot generally expand recurrences unless the step dominates the loop // header. The expander handles the special case of affine recurrences by // scaling the recurrence outside the loop, but this technique isn't generally // applicable. Expanding a nested recurrence outside a loop requires computing // binomial coefficients. This could be done, but the recurrence has to be in a // perfectly reduced form, which can't be guaranteed. struct SCEVFindUnsafe { ScalarEvolution &SE; bool IsUnsafe; SCEVFindUnsafe(ScalarEvolution &se): SE(se), IsUnsafe(false) {} bool follow(const SCEV *S) { if (const SCEVUDivExpr *D = dyn_cast(S)) { const SCEVConstant *SC = dyn_cast(D->getRHS()); if (!SC || SC->getValue()->isZero()) { IsUnsafe = true; return false; } } if (const SCEVAddRecExpr *AR = dyn_cast(S)) { const SCEV *Step = AR->getStepRecurrence(SE); if (!AR->isAffine() && !SE.dominates(Step, AR->getLoop()->getHeader())) { IsUnsafe = true; return false; } } return true; } bool isDone() const { return IsUnsafe; } }; } namespace llvm { bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE) { SCEVFindUnsafe Search(SE); visitAll(S, Search); return !Search.IsUnsafe; } bool isSafeToExpandAt(const SCEV *S, const Instruction *InsertionPoint, ScalarEvolution &SE) { return isSafeToExpand(S, SE) && SE.dominates(S, InsertionPoint->getParent()); } }