//===- InlineCost.cpp - Cost analysis for inliner -------------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file implements inline cost analysis. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "inline-cost" #include "llvm/Analysis/InlineCost.h" #include "llvm/Analysis/ConstantFolding.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Support/CallSite.h" #include "llvm/Support/Debug.h" #include "llvm/Support/InstVisitor.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/raw_ostream.h" #include "llvm/CallingConv.h" #include "llvm/IntrinsicInst.h" #include "llvm/Operator.h" #include "llvm/GlobalAlias.h" #include "llvm/DataLayout.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SetVector.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/Statistic.h" using namespace llvm; STATISTIC(NumCallsAnalyzed, "Number of call sites analyzed"); namespace { class CallAnalyzer : public InstVisitor { typedef InstVisitor Base; friend class InstVisitor; // DataLayout if available, or null. const DataLayout *const TD; // The called function. Function &F; int Threshold; int Cost; const bool AlwaysInline; bool IsCallerRecursive; bool IsRecursiveCall; bool ExposesReturnsTwice; bool HasDynamicAlloca; /// Number of bytes allocated statically by the callee. uint64_t AllocatedSize; unsigned NumInstructions, NumVectorInstructions; int FiftyPercentVectorBonus, TenPercentVectorBonus; int VectorBonus; // While we walk the potentially-inlined instructions, we build up and // maintain a mapping of simplified values specific to this callsite. The // idea is to propagate any special information we have about arguments to // this call through the inlinable section of the function, and account for // likely simplifications post-inlining. The most important aspect we track // is CFG altering simplifications -- when we prove a basic block dead, that // can cause dramatic shifts in the cost of inlining a function. DenseMap SimplifiedValues; // Keep track of the values which map back (through function arguments) to // allocas on the caller stack which could be simplified through SROA. DenseMap SROAArgValues; // The mapping of caller Alloca values to their accumulated cost savings. If // we have to disable SROA for one of the allocas, this tells us how much // cost must be added. DenseMap SROAArgCosts; // Keep track of values which map to a pointer base and constant offset. DenseMap > ConstantOffsetPtrs; // Custom simplification helper routines. bool isAllocaDerivedArg(Value *V); bool lookupSROAArgAndCost(Value *V, Value *&Arg, DenseMap::iterator &CostIt); void disableSROA(DenseMap::iterator CostIt); void disableSROA(Value *V); void accumulateSROACost(DenseMap::iterator CostIt, int InstructionCost); bool handleSROACandidate(bool IsSROAValid, DenseMap::iterator CostIt, int InstructionCost); bool isGEPOffsetConstant(GetElementPtrInst &GEP); bool accumulateGEPOffset(GEPOperator &GEP, APInt &Offset); ConstantInt *stripAndComputeInBoundsConstantOffsets(Value *&V); // Custom analysis routines. bool analyzeBlock(BasicBlock *BB); // Disable several entry points to the visitor so we don't accidentally use // them by declaring but not defining them here. void visit(Module *); void visit(Module &); void visit(Function *); void visit(Function &); void visit(BasicBlock *); void visit(BasicBlock &); // Provide base case for our instruction visit. bool visitInstruction(Instruction &I); // Our visit overrides. bool visitAlloca(AllocaInst &I); bool visitPHI(PHINode &I); bool visitGetElementPtr(GetElementPtrInst &I); bool visitBitCast(BitCastInst &I); bool visitPtrToInt(PtrToIntInst &I); bool visitIntToPtr(IntToPtrInst &I); bool visitCastInst(CastInst &I); bool visitUnaryInstruction(UnaryInstruction &I); bool visitICmp(ICmpInst &I); bool visitSub(BinaryOperator &I); bool visitBinaryOperator(BinaryOperator &I); bool visitLoad(LoadInst &I); bool visitStore(StoreInst &I); bool visitCallSite(CallSite CS); public: CallAnalyzer(const DataLayout *TD, Function &Callee, int Threshold) : TD(TD), F(Callee), Threshold(Threshold), Cost(0), AlwaysInline(F.getFnAttributes().hasAttribute(Attributes::AlwaysInline)), IsCallerRecursive(false), IsRecursiveCall(false), ExposesReturnsTwice(false), HasDynamicAlloca(false), AllocatedSize(0), NumInstructions(0), NumVectorInstructions(0), FiftyPercentVectorBonus(0), TenPercentVectorBonus(0), VectorBonus(0), NumConstantArgs(0), NumConstantOffsetPtrArgs(0), NumAllocaArgs(0), NumConstantPtrCmps(0), NumConstantPtrDiffs(0), NumInstructionsSimplified(0), SROACostSavings(0), SROACostSavingsLost(0) { } bool analyzeCall(CallSite CS); int getThreshold() { return Threshold; } int getCost() { return Cost; } bool isAlwaysInline() { return AlwaysInline; } // Keep a bunch of stats about the cost savings found so we can print them // out when debugging. unsigned NumConstantArgs; unsigned NumConstantOffsetPtrArgs; unsigned NumAllocaArgs; unsigned NumConstantPtrCmps; unsigned NumConstantPtrDiffs; unsigned NumInstructionsSimplified; unsigned SROACostSavings; unsigned SROACostSavingsLost; void dump(); }; } // namespace /// \brief Test whether the given value is an Alloca-derived function argument. bool CallAnalyzer::isAllocaDerivedArg(Value *V) { return SROAArgValues.count(V); } /// \brief Lookup the SROA-candidate argument and cost iterator which V maps to. /// Returns false if V does not map to a SROA-candidate. bool CallAnalyzer::lookupSROAArgAndCost( Value *V, Value *&Arg, DenseMap::iterator &CostIt) { if (SROAArgValues.empty() || SROAArgCosts.empty()) return false; DenseMap::iterator ArgIt = SROAArgValues.find(V); if (ArgIt == SROAArgValues.end()) return false; Arg = ArgIt->second; CostIt = SROAArgCosts.find(Arg); return CostIt != SROAArgCosts.end(); } /// \brief Disable SROA for the candidate marked by this cost iterator. /// /// This marks the candidate as no longer viable for SROA, and adds the cost /// savings associated with it back into the inline cost measurement. void CallAnalyzer::disableSROA(DenseMap::iterator CostIt) { // If we're no longer able to perform SROA we need to undo its cost savings // and prevent subsequent analysis. Cost += CostIt->second; SROACostSavings -= CostIt->second; SROACostSavingsLost += CostIt->second; SROAArgCosts.erase(CostIt); } /// \brief If 'V' maps to a SROA candidate, disable SROA for it. void CallAnalyzer::disableSROA(Value *V) { Value *SROAArg; DenseMap::iterator CostIt; if (lookupSROAArgAndCost(V, SROAArg, CostIt)) disableSROA(CostIt); } /// \brief Accumulate the given cost for a particular SROA candidate. void CallAnalyzer::accumulateSROACost(DenseMap::iterator CostIt, int InstructionCost) { CostIt->second += InstructionCost; SROACostSavings += InstructionCost; } /// \brief Helper for the common pattern of handling a SROA candidate. /// Either accumulates the cost savings if the SROA remains valid, or disables /// SROA for the candidate. bool CallAnalyzer::handleSROACandidate(bool IsSROAValid, DenseMap::iterator CostIt, int InstructionCost) { if (IsSROAValid) { accumulateSROACost(CostIt, InstructionCost); return true; } disableSROA(CostIt); return false; } /// \brief Check whether a GEP's indices are all constant. /// /// Respects any simplified values known during the analysis of this callsite. bool CallAnalyzer::isGEPOffsetConstant(GetElementPtrInst &GEP) { for (User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end(); I != E; ++I) if (!isa(*I) && !SimplifiedValues.lookup(*I)) return false; return true; } /// \brief Accumulate a constant GEP offset into an APInt if possible. /// /// Returns false if unable to compute the offset for any reason. Respects any /// simplified values known during the analysis of this callsite. bool CallAnalyzer::accumulateGEPOffset(GEPOperator &GEP, APInt &Offset) { if (!TD) return false; unsigned AS = GEP.getPointerAddressSpace(); unsigned IntPtrWidth = TD->getPointerSizeInBits(AS); assert(IntPtrWidth == Offset.getBitWidth()); for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP); GTI != GTE; ++GTI) { ConstantInt *OpC = dyn_cast(GTI.getOperand()); if (!OpC) if (Constant *SimpleOp = SimplifiedValues.lookup(GTI.getOperand())) OpC = dyn_cast(SimpleOp); if (!OpC) return false; if (OpC->isZero()) continue; // Handle a struct index, which adds its field offset to the pointer. if (StructType *STy = dyn_cast(*GTI)) { unsigned ElementIdx = OpC->getZExtValue(); const StructLayout *SL = TD->getStructLayout(STy); Offset += APInt(IntPtrWidth, SL->getElementOffset(ElementIdx)); continue; } APInt TypeSize(IntPtrWidth, TD->getTypeAllocSize(GTI.getIndexedType())); Offset += OpC->getValue().sextOrTrunc(IntPtrWidth) * TypeSize; } return true; } bool CallAnalyzer::visitAlloca(AllocaInst &I) { // FIXME: Check whether inlining will turn a dynamic alloca into a static // alloca, and handle that case. // Accumulate the allocated size. if (I.isStaticAlloca()) { Type *Ty = I.getAllocatedType(); AllocatedSize += (TD ? TD->getTypeAllocSize(Ty) : Ty->getPrimitiveSizeInBits()); } // We will happily inline static alloca instructions or dynamic alloca // instructions in always-inline situations. if (AlwaysInline || I.isStaticAlloca()) return Base::visitAlloca(I); // FIXME: This is overly conservative. Dynamic allocas are inefficient for // a variety of reasons, and so we would like to not inline them into // functions which don't currently have a dynamic alloca. This simply // disables inlining altogether in the presence of a dynamic alloca. HasDynamicAlloca = true; return false; } bool CallAnalyzer::visitPHI(PHINode &I) { // FIXME: We should potentially be tracking values through phi nodes, // especially when they collapse to a single value due to deleted CFG edges // during inlining. // FIXME: We need to propagate SROA *disabling* through phi nodes, even // though we don't want to propagate it's bonuses. The idea is to disable // SROA if it *might* be used in an inappropriate manner. // Phi nodes are always zero-cost. return true; } bool CallAnalyzer::visitGetElementPtr(GetElementPtrInst &I) { Value *SROAArg; DenseMap::iterator CostIt; bool SROACandidate = lookupSROAArgAndCost(I.getPointerOperand(), SROAArg, CostIt); // Try to fold GEPs of constant-offset call site argument pointers. This // requires target data and inbounds GEPs. if (TD && I.isInBounds()) { // Check if we have a base + offset for the pointer. Value *Ptr = I.getPointerOperand(); std::pair BaseAndOffset = ConstantOffsetPtrs.lookup(Ptr); if (BaseAndOffset.first) { // Check if the offset of this GEP is constant, and if so accumulate it // into Offset. if (!accumulateGEPOffset(cast(I), BaseAndOffset.second)) { // Non-constant GEPs aren't folded, and disable SROA. if (SROACandidate) disableSROA(CostIt); return false; } // Add the result as a new mapping to Base + Offset. ConstantOffsetPtrs[&I] = BaseAndOffset; // Also handle SROA candidates here, we already know that the GEP is // all-constant indexed. if (SROACandidate) SROAArgValues[&I] = SROAArg; return true; } } if (isGEPOffsetConstant(I)) { if (SROACandidate) SROAArgValues[&I] = SROAArg; // Constant GEPs are modeled as free. return true; } // Variable GEPs will require math and will disable SROA. if (SROACandidate) disableSROA(CostIt); return false; } bool CallAnalyzer::visitBitCast(BitCastInst &I) { // Propagate constants through bitcasts. if (Constant *COp = dyn_cast(I.getOperand(0))) if (Constant *C = ConstantExpr::getBitCast(COp, I.getType())) { SimplifiedValues[&I] = C; return true; } // Track base/offsets through casts std::pair BaseAndOffset = ConstantOffsetPtrs.lookup(I.getOperand(0)); // Casts don't change the offset, just wrap it up. if (BaseAndOffset.first) ConstantOffsetPtrs[&I] = BaseAndOffset; // Also look for SROA candidates here. Value *SROAArg; DenseMap::iterator CostIt; if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) SROAArgValues[&I] = SROAArg; // Bitcasts are always zero cost. return true; } bool CallAnalyzer::visitPtrToInt(PtrToIntInst &I) { // Propagate constants through ptrtoint. if (Constant *COp = dyn_cast(I.getOperand(0))) if (Constant *C = ConstantExpr::getPtrToInt(COp, I.getType())) { SimplifiedValues[&I] = C; return true; } // Track base/offset pairs when converted to a plain integer provided the // integer is large enough to represent the pointer. unsigned IntegerSize = I.getType()->getScalarSizeInBits(); unsigned AS = I.getPointerAddressSpace(); if (TD && IntegerSize >= TD->getPointerSizeInBits(AS)) { std::pair BaseAndOffset = ConstantOffsetPtrs.lookup(I.getOperand(0)); if (BaseAndOffset.first) ConstantOffsetPtrs[&I] = BaseAndOffset; } // This is really weird. Technically, ptrtoint will disable SROA. However, // unless that ptrtoint is *used* somewhere in the live basic blocks after // inlining, it will be nuked, and SROA should proceed. All of the uses which // would block SROA would also block SROA if applied directly to a pointer, // and so we can just add the integer in here. The only places where SROA is // preserved either cannot fire on an integer, or won't in-and-of themselves // disable SROA (ext) w/o some later use that we would see and disable. Value *SROAArg; DenseMap::iterator CostIt; if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) SROAArgValues[&I] = SROAArg; return isInstructionFree(&I, TD); } bool CallAnalyzer::visitIntToPtr(IntToPtrInst &I) { // Propagate constants through ptrtoint. if (Constant *COp = dyn_cast(I.getOperand(0))) if (Constant *C = ConstantExpr::getIntToPtr(COp, I.getType())) { SimplifiedValues[&I] = C; return true; } // Track base/offset pairs when round-tripped through a pointer without // modifications provided the integer is not too large. Value *Op = I.getOperand(0); unsigned IntegerSize = Op->getType()->getScalarSizeInBits(); unsigned AS = I.getAddressSpace(); if (TD && IntegerSize <= TD->getPointerSizeInBits(AS)) { std::pair BaseAndOffset = ConstantOffsetPtrs.lookup(Op); if (BaseAndOffset.first) ConstantOffsetPtrs[&I] = BaseAndOffset; } // "Propagate" SROA here in the same manner as we do for ptrtoint above. Value *SROAArg; DenseMap::iterator CostIt; if (lookupSROAArgAndCost(Op, SROAArg, CostIt)) SROAArgValues[&I] = SROAArg; return isInstructionFree(&I, TD); } bool CallAnalyzer::visitCastInst(CastInst &I) { // Propagate constants through ptrtoint. if (Constant *COp = dyn_cast(I.getOperand(0))) if (Constant *C = ConstantExpr::getCast(I.getOpcode(), COp, I.getType())) { SimplifiedValues[&I] = C; return true; } // Disable SROA in the face of arbitrary casts we don't whitelist elsewhere. disableSROA(I.getOperand(0)); return isInstructionFree(&I, TD); } bool CallAnalyzer::visitUnaryInstruction(UnaryInstruction &I) { Value *Operand = I.getOperand(0); Constant *Ops[1] = { dyn_cast(Operand) }; if (Ops[0] || (Ops[0] = SimplifiedValues.lookup(Operand))) if (Constant *C = ConstantFoldInstOperands(I.getOpcode(), I.getType(), Ops, TD)) { SimplifiedValues[&I] = C; return true; } // Disable any SROA on the argument to arbitrary unary operators. disableSROA(Operand); return false; } bool CallAnalyzer::visitICmp(ICmpInst &I) { Value *LHS = I.getOperand(0), *RHS = I.getOperand(1); // First try to handle simplified comparisons. if (!isa(LHS)) if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS)) LHS = SimpleLHS; if (!isa(RHS)) if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS)) RHS = SimpleRHS; if (Constant *CLHS = dyn_cast(LHS)) if (Constant *CRHS = dyn_cast(RHS)) if (Constant *C = ConstantExpr::getICmp(I.getPredicate(), CLHS, CRHS)) { SimplifiedValues[&I] = C; return true; } // Otherwise look for a comparison between constant offset pointers with // a common base. Value *LHSBase, *RHSBase; APInt LHSOffset, RHSOffset; llvm::tie(LHSBase, LHSOffset) = ConstantOffsetPtrs.lookup(LHS); if (LHSBase) { llvm::tie(RHSBase, RHSOffset) = ConstantOffsetPtrs.lookup(RHS); if (RHSBase && LHSBase == RHSBase) { // We have common bases, fold the icmp to a constant based on the // offsets. Constant *CLHS = ConstantInt::get(LHS->getContext(), LHSOffset); Constant *CRHS = ConstantInt::get(RHS->getContext(), RHSOffset); if (Constant *C = ConstantExpr::getICmp(I.getPredicate(), CLHS, CRHS)) { SimplifiedValues[&I] = C; ++NumConstantPtrCmps; return true; } } } // If the comparison is an equality comparison with null, we can simplify it // for any alloca-derived argument. if (I.isEquality() && isa(I.getOperand(1))) if (isAllocaDerivedArg(I.getOperand(0))) { // We can actually predict the result of comparisons between an // alloca-derived value and null. Note that this fires regardless of // SROA firing. bool IsNotEqual = I.getPredicate() == CmpInst::ICMP_NE; SimplifiedValues[&I] = IsNotEqual ? ConstantInt::getTrue(I.getType()) : ConstantInt::getFalse(I.getType()); return true; } // Finally check for SROA candidates in comparisons. Value *SROAArg; DenseMap::iterator CostIt; if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) { if (isa(I.getOperand(1))) { accumulateSROACost(CostIt, InlineConstants::InstrCost); return true; } disableSROA(CostIt); } return false; } bool CallAnalyzer::visitSub(BinaryOperator &I) { // Try to handle a special case: we can fold computing the difference of two // constant-related pointers. Value *LHS = I.getOperand(0), *RHS = I.getOperand(1); Value *LHSBase, *RHSBase; APInt LHSOffset, RHSOffset; llvm::tie(LHSBase, LHSOffset) = ConstantOffsetPtrs.lookup(LHS); if (LHSBase) { llvm::tie(RHSBase, RHSOffset) = ConstantOffsetPtrs.lookup(RHS); if (RHSBase && LHSBase == RHSBase) { // We have common bases, fold the subtract to a constant based on the // offsets. Constant *CLHS = ConstantInt::get(LHS->getContext(), LHSOffset); Constant *CRHS = ConstantInt::get(RHS->getContext(), RHSOffset); if (Constant *C = ConstantExpr::getSub(CLHS, CRHS)) { SimplifiedValues[&I] = C; ++NumConstantPtrDiffs; return true; } } } // Otherwise, fall back to the generic logic for simplifying and handling // instructions. return Base::visitSub(I); } bool CallAnalyzer::visitBinaryOperator(BinaryOperator &I) { Value *LHS = I.getOperand(0), *RHS = I.getOperand(1); if (!isa(LHS)) if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS)) LHS = SimpleLHS; if (!isa(RHS)) if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS)) RHS = SimpleRHS; Value *SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS, TD); if (Constant *C = dyn_cast_or_null(SimpleV)) { SimplifiedValues[&I] = C; return true; } // Disable any SROA on arguments to arbitrary, unsimplified binary operators. disableSROA(LHS); disableSROA(RHS); return false; } bool CallAnalyzer::visitLoad(LoadInst &I) { Value *SROAArg; DenseMap::iterator CostIt; if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) { if (I.isSimple()) { accumulateSROACost(CostIt, InlineConstants::InstrCost); return true; } disableSROA(CostIt); } return false; } bool CallAnalyzer::visitStore(StoreInst &I) { Value *SROAArg; DenseMap::iterator CostIt; if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) { if (I.isSimple()) { accumulateSROACost(CostIt, InlineConstants::InstrCost); return true; } disableSROA(CostIt); } return false; } bool CallAnalyzer::visitCallSite(CallSite CS) { if (CS.isCall() && cast(CS.getInstruction())->canReturnTwice() && !F.getFnAttributes().hasAttribute(Attributes::ReturnsTwice)) { // This aborts the entire analysis. ExposesReturnsTwice = true; return false; } if (IntrinsicInst *II = dyn_cast(CS.getInstruction())) { switch (II->getIntrinsicID()) { default: return Base::visitCallSite(CS); case Intrinsic::memset: case Intrinsic::memcpy: case Intrinsic::memmove: // SROA can usually chew through these intrinsics, but they aren't free. return false; } } if (Function *F = CS.getCalledFunction()) { if (F == CS.getInstruction()->getParent()->getParent()) { // This flag will fully abort the analysis, so don't bother with anything // else. IsRecursiveCall = true; return false; } if (!callIsSmall(CS)) { // We account for the average 1 instruction per call argument setup // here. Cost += CS.arg_size() * InlineConstants::InstrCost; // Everything other than inline ASM will also have a significant cost // merely from making the call. if (!isa(CS.getCalledValue())) Cost += InlineConstants::CallPenalty; } return Base::visitCallSite(CS); } // Otherwise we're in a very special case -- an indirect function call. See // if we can be particularly clever about this. Value *Callee = CS.getCalledValue(); // First, pay the price of the argument setup. We account for the average // 1 instruction per call argument setup here. Cost += CS.arg_size() * InlineConstants::InstrCost; // Next, check if this happens to be an indirect function call to a known // function in this inline context. If not, we've done all we can. Function *F = dyn_cast_or_null(SimplifiedValues.lookup(Callee)); if (!F) return Base::visitCallSite(CS); // If we have a constant that we are calling as a function, we can peer // through it and see the function target. This happens not infrequently // during devirtualization and so we want to give it a hefty bonus for // inlining, but cap that bonus in the event that inlining wouldn't pan // out. Pretend to inline the function, with a custom threshold. CallAnalyzer CA(TD, *F, InlineConstants::IndirectCallThreshold); if (CA.analyzeCall(CS)) { // We were able to inline the indirect call! Subtract the cost from the // bonus we want to apply, but don't go below zero. Cost -= std::max(0, InlineConstants::IndirectCallThreshold - CA.getCost()); } return Base::visitCallSite(CS); } bool CallAnalyzer::visitInstruction(Instruction &I) { // Some instructions are free. All of the free intrinsics can also be // handled by SROA, etc. if (isInstructionFree(&I, TD)) return true; // We found something we don't understand or can't handle. Mark any SROA-able // values in the operand list as no longer viable. for (User::op_iterator OI = I.op_begin(), OE = I.op_end(); OI != OE; ++OI) disableSROA(*OI); return false; } /// \brief Analyze a basic block for its contribution to the inline cost. /// /// This method walks the analyzer over every instruction in the given basic /// block and accounts for their cost during inlining at this callsite. It /// aborts early if the threshold has been exceeded or an impossible to inline /// construct has been detected. It returns false if inlining is no longer /// viable, and true if inlining remains viable. bool CallAnalyzer::analyzeBlock(BasicBlock *BB) { for (BasicBlock::iterator I = BB->begin(), E = llvm::prior(BB->end()); I != E; ++I) { ++NumInstructions; if (isa(I) || I->getType()->isVectorTy()) ++NumVectorInstructions; // If the instruction simplified to a constant, there is no cost to this // instruction. Visit the instructions using our InstVisitor to account for // all of the per-instruction logic. The visit tree returns true if we // consumed the instruction in any way, and false if the instruction's base // cost should count against inlining. if (Base::visit(I)) ++NumInstructionsSimplified; else Cost += InlineConstants::InstrCost; // If the visit this instruction detected an uninlinable pattern, abort. if (IsRecursiveCall || ExposesReturnsTwice || HasDynamicAlloca) return false; // If the caller is a recursive function then we don't want to inline // functions which allocate a lot of stack space because it would increase // the caller stack usage dramatically. if (IsCallerRecursive && AllocatedSize > InlineConstants::TotalAllocaSizeRecursiveCaller) return false; if (NumVectorInstructions > NumInstructions/2) VectorBonus = FiftyPercentVectorBonus; else if (NumVectorInstructions > NumInstructions/10) VectorBonus = TenPercentVectorBonus; else VectorBonus = 0; // Check if we've past the threshold so we don't spin in huge basic // blocks that will never inline. if (!AlwaysInline && Cost > (Threshold + VectorBonus)) return false; } return true; } /// \brief Compute the base pointer and cumulative constant offsets for V. /// /// This strips all constant offsets off of V, leaving it the base pointer, and /// accumulates the total constant offset applied in the returned constant. It /// returns 0 if V is not a pointer, and returns the constant '0' if there are /// no constant offsets applied. ConstantInt *CallAnalyzer::stripAndComputeInBoundsConstantOffsets(Value *&V) { if (!TD || !V->getType()->isPointerTy()) return 0; unsigned AS = cast(V->getType())->getAddressSpace();; unsigned IntPtrWidth = TD->getPointerSizeInBits(AS); APInt Offset = APInt::getNullValue(IntPtrWidth); // Even though we don't look through PHI nodes, we could be called on an // instruction in an unreachable block, which may be on a cycle. SmallPtrSet Visited; Visited.insert(V); do { if (GEPOperator *GEP = dyn_cast(V)) { if (!GEP->isInBounds() || !accumulateGEPOffset(*GEP, Offset)) return 0; V = GEP->getPointerOperand(); } else if (Operator::getOpcode(V) == Instruction::BitCast) { V = cast(V)->getOperand(0); } else if (GlobalAlias *GA = dyn_cast(V)) { if (GA->mayBeOverridden()) break; V = GA->getAliasee(); } else { break; } assert(V->getType()->isPointerTy() && "Unexpected operand type!"); } while (Visited.insert(V)); Type *IntPtrTy = TD->getIntPtrType(V->getType()); return cast(ConstantInt::get(IntPtrTy, Offset)); } /// \brief Analyze a call site for potential inlining. /// /// Returns true if inlining this call is viable, and false if it is not /// viable. It computes the cost and adjusts the threshold based on numerous /// factors and heuristics. If this method returns false but the computed cost /// is below the computed threshold, then inlining was forcibly disabled by /// some artifact of the rountine. bool CallAnalyzer::analyzeCall(CallSite CS) { ++NumCallsAnalyzed; // Track whether the post-inlining function would have more than one basic // block. A single basic block is often intended for inlining. Balloon the // threshold by 50% until we pass the single-BB phase. bool SingleBB = true; int SingleBBBonus = Threshold / 2; Threshold += SingleBBBonus; // Unless we are always-inlining, perform some tweaks to the cost and // threshold based on the direct callsite information. if (!AlwaysInline) { // We want to more aggressively inline vector-dense kernels, so up the // threshold, and we'll lower it if the % of vector instructions gets too // low. assert(NumInstructions == 0); assert(NumVectorInstructions == 0); FiftyPercentVectorBonus = Threshold; TenPercentVectorBonus = Threshold / 2; // Give out bonuses per argument, as the instructions setting them up will // be gone after inlining. for (unsigned I = 0, E = CS.arg_size(); I != E; ++I) { if (TD && CS.isByValArgument(I)) { // We approximate the number of loads and stores needed by dividing the // size of the byval type by the target's pointer size. PointerType *PTy = cast(CS.getArgument(I)->getType()); unsigned TypeSize = TD->getTypeSizeInBits(PTy->getElementType()); unsigned AS = PTy->getAddressSpace(); unsigned PointerSize = TD->getPointerSizeInBits(AS); // Ceiling division. unsigned NumStores = (TypeSize + PointerSize - 1) / PointerSize; // If it generates more than 8 stores it is likely to be expanded as an // inline memcpy so we take that as an upper bound. Otherwise we assume // one load and one store per word copied. // FIXME: The maxStoresPerMemcpy setting from the target should be used // here instead of a magic number of 8, but it's not available via // DataLayout. NumStores = std::min(NumStores, 8U); Cost -= 2 * NumStores * InlineConstants::InstrCost; } else { // For non-byval arguments subtract off one instruction per call // argument. Cost -= InlineConstants::InstrCost; } } // If there is only one call of the function, and it has internal linkage, // the cost of inlining it drops dramatically. if (F.hasLocalLinkage() && F.hasOneUse() && &F == CS.getCalledFunction()) Cost += InlineConstants::LastCallToStaticBonus; // If the instruction after the call, or if the normal destination of the // invoke is an unreachable instruction, the function is noreturn. As such, // there is little point in inlining this unless there is literally zero // cost. Instruction *Instr = CS.getInstruction(); if (InvokeInst *II = dyn_cast(Instr)) { if (isa(II->getNormalDest()->begin())) Threshold = 1; } else if (isa(++BasicBlock::iterator(Instr))) Threshold = 1; // If this function uses the coldcc calling convention, prefer not to inline // it. if (F.getCallingConv() == CallingConv::Cold) Cost += InlineConstants::ColdccPenalty; // Check if we're done. This can happen due to bonuses and penalties. if (Cost > Threshold) return false; } if (F.empty()) return true; Function *Caller = CS.getInstruction()->getParent()->getParent(); // Check if the caller function is recursive itself. for (Value::use_iterator U = Caller->use_begin(), E = Caller->use_end(); U != E; ++U) { CallSite Site(cast(*U)); if (!Site) continue; Instruction *I = Site.getInstruction(); if (I->getParent()->getParent() == Caller) { IsCallerRecursive = true; break; } } // Track whether we've seen a return instruction. The first return // instruction is free, as at least one will usually disappear in inlining. bool HasReturn = false; // Populate our simplified values by mapping from function arguments to call // arguments with known important simplifications. CallSite::arg_iterator CAI = CS.arg_begin(); for (Function::arg_iterator FAI = F.arg_begin(), FAE = F.arg_end(); FAI != FAE; ++FAI, ++CAI) { assert(CAI != CS.arg_end()); if (Constant *C = dyn_cast(CAI)) SimplifiedValues[FAI] = C; Value *PtrArg = *CAI; if (ConstantInt *C = stripAndComputeInBoundsConstantOffsets(PtrArg)) { ConstantOffsetPtrs[FAI] = std::make_pair(PtrArg, C->getValue()); // We can SROA any pointer arguments derived from alloca instructions. if (isa(PtrArg)) { SROAArgValues[FAI] = PtrArg; SROAArgCosts[PtrArg] = 0; } } } NumConstantArgs = SimplifiedValues.size(); NumConstantOffsetPtrArgs = ConstantOffsetPtrs.size(); NumAllocaArgs = SROAArgValues.size(); // The worklist of live basic blocks in the callee *after* inlining. We avoid // adding basic blocks of the callee which can be proven to be dead for this // particular call site in order to get more accurate cost estimates. This // requires a somewhat heavyweight iteration pattern: we need to walk the // basic blocks in a breadth-first order as we insert live successors. To // accomplish this, prioritizing for small iterations because we exit after // crossing our threshold, we use a small-size optimized SetVector. typedef SetVector, SmallPtrSet > BBSetVector; BBSetVector BBWorklist; BBWorklist.insert(&F.getEntryBlock()); // Note that we *must not* cache the size, this loop grows the worklist. for (unsigned Idx = 0; Idx != BBWorklist.size(); ++Idx) { // Bail out the moment we cross the threshold. This means we'll under-count // the cost, but only when undercounting doesn't matter. if (!AlwaysInline && Cost > (Threshold + VectorBonus)) break; BasicBlock *BB = BBWorklist[Idx]; if (BB->empty()) continue; // Handle the terminator cost here where we can track returns and other // function-wide constructs. TerminatorInst *TI = BB->getTerminator(); // We never want to inline functions that contain an indirectbr. This is // incorrect because all the blockaddress's (in static global initializers // for example) would be referring to the original function, and this // indirect jump would jump from the inlined copy of the function into the // original function which is extremely undefined behavior. // FIXME: This logic isn't really right; we can safely inline functions // with indirectbr's as long as no other function or global references the // blockaddress of a block within the current function. And as a QOI issue, // if someone is using a blockaddress without an indirectbr, and that // reference somehow ends up in another function or global, we probably // don't want to inline this function. if (isa(TI)) return false; if (!HasReturn && isa(TI)) HasReturn = true; else Cost += InlineConstants::InstrCost; // Analyze the cost of this block. If we blow through the threshold, this // returns false, and we can bail on out. if (!analyzeBlock(BB)) { if (IsRecursiveCall || ExposesReturnsTwice || HasDynamicAlloca) return false; // If the caller is a recursive function then we don't want to inline // functions which allocate a lot of stack space because it would increase // the caller stack usage dramatically. if (IsCallerRecursive && AllocatedSize > InlineConstants::TotalAllocaSizeRecursiveCaller) return false; break; } // Add in the live successors by first checking whether we have terminator // that may be simplified based on the values simplified by this call. if (BranchInst *BI = dyn_cast(TI)) { if (BI->isConditional()) { Value *Cond = BI->getCondition(); if (ConstantInt *SimpleCond = dyn_cast_or_null(SimplifiedValues.lookup(Cond))) { BBWorklist.insert(BI->getSuccessor(SimpleCond->isZero() ? 1 : 0)); continue; } } } else if (SwitchInst *SI = dyn_cast(TI)) { Value *Cond = SI->getCondition(); if (ConstantInt *SimpleCond = dyn_cast_or_null(SimplifiedValues.lookup(Cond))) { BBWorklist.insert(SI->findCaseValue(SimpleCond).getCaseSuccessor()); continue; } } // If we're unable to select a particular successor, just count all of // them. for (unsigned TIdx = 0, TSize = TI->getNumSuccessors(); TIdx != TSize; ++TIdx) BBWorklist.insert(TI->getSuccessor(TIdx)); // If we had any successors at this point, than post-inlining is likely to // have them as well. Note that we assume any basic blocks which existed // due to branches or switches which folded above will also fold after // inlining. if (SingleBB && TI->getNumSuccessors() > 1) { // Take off the bonus we applied to the threshold. Threshold -= SingleBBBonus; SingleBB = false; } } Threshold += VectorBonus; return AlwaysInline || Cost < Threshold; } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) /// \brief Dump stats about this call's analysis. void CallAnalyzer::dump() { #define DEBUG_PRINT_STAT(x) llvm::dbgs() << " " #x ": " << x << "\n" DEBUG_PRINT_STAT(NumConstantArgs); DEBUG_PRINT_STAT(NumConstantOffsetPtrArgs); DEBUG_PRINT_STAT(NumAllocaArgs); DEBUG_PRINT_STAT(NumConstantPtrCmps); DEBUG_PRINT_STAT(NumConstantPtrDiffs); DEBUG_PRINT_STAT(NumInstructionsSimplified); DEBUG_PRINT_STAT(SROACostSavings); DEBUG_PRINT_STAT(SROACostSavingsLost); #undef DEBUG_PRINT_STAT } #endif InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS, int Threshold) { return getInlineCost(CS, CS.getCalledFunction(), Threshold); } InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS, Function *Callee, int Threshold) { // Don't inline functions which can be redefined at link-time to mean // something else. Don't inline functions marked noinline or call sites // marked noinline. if (!Callee || Callee->mayBeOverridden() || Callee->getFnAttributes().hasAttribute(Attributes::NoInline) || CS.isNoInline()) return llvm::InlineCost::getNever(); DEBUG(llvm::dbgs() << " Analyzing call of " << Callee->getName() << "...\n"); CallAnalyzer CA(TD, *Callee, Threshold); bool ShouldInline = CA.analyzeCall(CS); DEBUG(CA.dump()); // Check if there was a reason to force inlining or no inlining. if (!ShouldInline && CA.getCost() < CA.getThreshold()) return InlineCost::getNever(); if (ShouldInline && (CA.isAlwaysInline() || CA.getCost() >= CA.getThreshold())) return InlineCost::getAlways(); return llvm::InlineCost::get(CA.getCost(), CA.getThreshold()); }