//===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===// // // 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/Support/Debug.h" using namespace llvm; /// 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; } /// 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) || isa(IP)) ++IP; return ReuseOrCreateCast(A, Ty, Op, IP); } // Cast the instruction immediately after the instruction. Instruction *I = cast(V); BasicBlock::iterator IP = I; ++IP; if (InvokeInst *II = dyn_cast(I)) IP = II->getNormalDest()->begin(); while (isa(IP) || isa(IP)) ++IP; 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++; if (IP->getOpcode() == (unsigned)Opcode && IP->getOperand(0) == LHS && IP->getOperand(1) == RHS) 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(); BuilderType::InsertPointGuard Guard(Builder); // 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, 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->getValue()->getValue().sdiv( FC->getValue()->getValue())); // 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->getValue()->getValue().srem( FC->getValue()->getValue()))); 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)) { if (DL) { // With DataLayout, the 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->getValue()->getValue().srem(FC->getValue()->getValue())) { SmallVector NewMulOps(M->op_begin(), M->op_end()); NewMulOps[0] = SE.getConstant(C->getValue()->getValue().sdiv( FC->getValue()->getValue())); S = SE.getMulExpr(NewMulOps); return true; } } else { // Without DataLayout, check if Factor can be factored out of any of the // Mul's operands. If so, we can just remove it. for (unsigned i = 0, e = M->getNumOperands(); i != e; ++i) { const SCEV *SOp = M->getOperand(i); const SCEV *Remainder = SE.getConstant(SOp->getType(), 0); if (FactorOutConstant(SOp, Remainder, Factor, SE, DL) && Remainder->isZero()) { SmallVector NewMulOps(M->op_begin(), M->op_end()); NewMulOps[i] = SOp; 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 *ElTy = PTy->getElementType(); 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 = SE.DL ? SE.DL->getIntPtrType(PTy) : Type::getInt64Ty(PTy->getContext()); // 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 (unsigned i = 0, e = Ops.size(); i != e; ++i) { const SCEV *Op = Ops[i]; const SCEV *Remainder = SE.getConstant(Ty, 0); if (FactorOutConstant(Op, Remainder, ElSize, SE, 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(Ops[i]); } } // 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; if (SE.DL) { // With DataLayout, 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 = *SE.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; } } } else { // Without DataLayout, just check for an offsetof expression of the // appropriate struct type. for (unsigned i = 0, e = Ops.size(); i != e; ++i) if (const SCEVUnknown *U = dyn_cast(Ops[i])) { Type *CTy; Constant *FieldNo; if (U->isOffsetOf(CTy, FieldNo) && CTy == STy) { GepIndices.push_back(FieldNo); ElTy = STy->getTypeAtIndex(cast(FieldNo)->getZExtValue()); Ops[i] = SE.getConstant(Ty, 0); AnyNonZeroIndices = true; FoundFieldNo = true; break; } } } // 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(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. BuilderType::InsertPointGuard Guard(Builder); // 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, Preheader->getTerminator()); } // Emit a GEP. Value *GEP = Builder.CreateGEP(V, Idx, "uglygep"); rememberInstruction(GEP); return GEP; } // Save the original insertion point so we can restore it when we're done. BuilderType::InsertPoint SaveInsertPt = Builder.saveIP(); // 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 = false; for (SmallVectorImpl::const_iterator I = GepIndices.begin(), E = GepIndices.end(); I != E; ++I) if (!L->isLoopInvariant(*I)) { AnyIndexNotLoopInvariant = true; break; } if (AnyIndexNotLoopInvariant) break; BasicBlock *Preheader = L->getLoopPreheader(); if (!Preheader) break; // Ok, move up a level. Builder.SetInsertPoint(Preheader, 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(Casted, GepIndices, "scevgep"); Ops.push_back(SE.getUnknown(GEP)); rememberInstruction(GEP); // Restore the original insert point. Builder.restoreIP(SaveInsertPt); 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. std::pair::iterator, bool> 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 (SCEVNAryExpr::op_iterator I = N->op_begin(), E = N->op_end(); I != E; ++I) L = PickMostRelevantLoop(L, getRelevantLoop(*I), *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 (SmallVectorImpl >::iterator 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; for (SmallVectorImpl >::iterator I = OpsAndLoops.begin(), E = OpsAndLoops.end(); I != E; ) { const SCEV *Op = I->second; if (!Prod) { // This is the first operand. Just expand it. Prod = expand(Op); ++I; } else if (Op->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 = expandCodeFor(Op, Ty); Prod = InsertNoopCastOfTo(Prod, Ty); // Canonicalize a constant to the RHS. if (isa(Prod)) std::swap(Prod, W); Prod = InsertBinop(Instruction::Mul, Prod, W); ++I; } } 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->getValue()->getValue(); 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 (Instruction::op_iterator 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)); } } /// 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; // 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 (SmallVectorImpl::reverse_iterator I = IVIncs.rbegin(), E = IVIncs.rend(); I != E; ++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). static void 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. 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 invertion 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; } /// 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 (BasicBlock::iterator I = L->getHeader()->begin(); PHINode *PN = dyn_cast(I); ++I) { 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. BuilderType::InsertPointGuard Guard(Builder); // 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. Value *StartV = expandCodeFor(Normalized->getStart(), ExpandTy, L->getHeader()->begin()); // StartV must be hoisted 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()->begin()); // 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 (Normalized->getNoWrapFlags(SCEV::FlagNUW)) cast(IncV)->setHasNoUnsignedWrap(); if (Normalized->getNoWrapFlags(SCEV::FlagNSW)) 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(TransformForPostIncUse(Normalize, S, nullptr, nullptr, Loops, SE, *SE.DT)); } // 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); 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; // 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, ExpandTy, 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. BuilderType::InsertPointGuard Guard(Builder); StepV = expandCodeFor(Step, IntTy, L->getHeader()->begin()); } 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)) { 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 = std::next(BasicBlock::iterator(cast(V))); BuilderType::InsertPointGuard Guard(Builder); while (isa(NewInsertPt) || isa(NewInsertPt) || isa(NewInsertPt)) ++NewInsertPt; 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. return expand(SE.getAddExpr(SE.getUnknown(expand(S->getStart())), SE.getUnknown(expand(Rest)))); } // 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->begin()); 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)) 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) { Builder.SetInsertPoint(IP->getParent(), 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; } 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 { // 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)) InsertPt = L->getHeader()->getFirstInsertionPt(); while (InsertPt != Builder.GetInsertPoint() && (isInsertedInstruction(InsertPt) || isa(InsertPt))) { InsertPt = std::next(BasicBlock::iterator(InsertPt)); } break; } // Check to see if we already expanded this here. std::map, TrackingVH >::iterator I = InsertedExpressions.find(std::make_pair(S, InsertPt)); if (I != InsertedExpressions.end()) return I->second; BuilderType::InsertPointGuard Guard(Builder); Builder.SetInsertPoint(InsertPt->getParent(), InsertPt); // Expand the expression into instructions. Value *V = visit(S); // 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. BuilderType::InsertPointGuard Guard(Builder); PHINode *V = cast(expandCodeFor(H, nullptr, L->getHeader()->begin())); 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 (BasicBlock::iterator I = L->getHeader()->begin(); PHINode *Phi = dyn_cast(I); ++I) { Phis.push_back(Phi); } 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. Mapping wide phis to the their truncation // so narrow phis can reuse them. for (SmallVectorImpl::const_iterator PIter = Phis.begin(), PEnd = Phis.end(); PIter != PEnd; ++PIter) { PHINode *Phi = *PIter; // Fold constant phis. They may be congruent to other constant phis and // would confuse the logic below that expects proper IVs. if (Value *V = SimplifyInstruction(Phi, SE.DL, SE.TLI, SE.DT)) { Phi->replaceAllUsesWith(V); DeadInsts.push_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 = cast(OrigPhiRef->getIncomingValueForBlock(LatchBlock)); Instruction *IsomorphicInc = cast(Phi->getIncomingValueForBlock(LatchBlock)); // 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) && ((isa(OrigInc) && isa(IsomorphicInc)) || 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 = isa(OrigInc) ? (Instruction*)L->getHeader()->getFirstInsertionPt() : OrigInc->getNextNode(); IRBuilder<> Builder(IP); Builder.SetCurrentDebugLocation(IsomorphicInc->getDebugLoc()); NewInc = Builder. CreateTruncOrBitCast(OrigInc, IsomorphicInc->getType(), IVName); } IsomorphicInc->replaceAllUsesWith(NewInc); DeadInsts.push_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.push_back(Phi); } return NumElim; } 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; } }