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Diffstat (limited to 'lib/Analysis/IPA/InlineCost.cpp')
| -rw-r--r-- | lib/Analysis/IPA/InlineCost.cpp | 1237 |
1 files changed, 1237 insertions, 0 deletions
diff --git a/lib/Analysis/IPA/InlineCost.cpp b/lib/Analysis/IPA/InlineCost.cpp new file mode 100644 index 0000000..cd211c4 --- /dev/null +++ b/lib/Analysis/IPA/InlineCost.cpp @@ -0,0 +1,1237 @@ +//===- 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/ADT/STLExtras.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/ConstantFolding.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/TargetTransformInfo.h" +#include "llvm/IR/CallingConv.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/GlobalAlias.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Operator.h" +#include "llvm/InstVisitor.h" +#include "llvm/Support/CallSite.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/GetElementPtrTypeIterator.h" +#include "llvm/Support/raw_ostream.h" + +using namespace llvm; + +STATISTIC(NumCallsAnalyzed, "Number of call sites analyzed"); + +namespace { + +class CallAnalyzer : public InstVisitor<CallAnalyzer, bool> { + typedef InstVisitor<CallAnalyzer, bool> Base; + friend class InstVisitor<CallAnalyzer, bool>; + + // DataLayout if available, or null. + const DataLayout *const TD; + + /// The TargetTransformInfo available for this compilation. + const TargetTransformInfo &TTI; + + // The called function. + Function &F; + + int Threshold; + int Cost; + + bool IsCallerRecursive; + bool IsRecursiveCall; + bool ExposesReturnsTwice; + bool HasDynamicAlloca; + bool ContainsNoDuplicateCall; + + /// 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<Value *, Constant *> 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<Value *, Value *> 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<Value *, int> SROAArgCosts; + + // Keep track of values which map to a pointer base and constant offset. + DenseMap<Value *, std::pair<Value *, APInt> > ConstantOffsetPtrs; + + // Custom simplification helper routines. + bool isAllocaDerivedArg(Value *V); + bool lookupSROAArgAndCost(Value *V, Value *&Arg, + DenseMap<Value *, int>::iterator &CostIt); + void disableSROA(DenseMap<Value *, int>::iterator CostIt); + void disableSROA(Value *V); + void accumulateSROACost(DenseMap<Value *, int>::iterator CostIt, + int InstructionCost); + bool handleSROACandidate(bool IsSROAValid, + DenseMap<Value *, int>::iterator CostIt, + int InstructionCost); + bool isGEPOffsetConstant(GetElementPtrInst &GEP); + bool accumulateGEPOffset(GEPOperator &GEP, APInt &Offset); + bool simplifyCallSite(Function *F, CallSite CS); + 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 visitExtractValue(ExtractValueInst &I); + bool visitInsertValue(InsertValueInst &I); + bool visitCallSite(CallSite CS); + +public: + CallAnalyzer(const DataLayout *TD, const TargetTransformInfo &TTI, + Function &Callee, int Threshold) + : TD(TD), TTI(TTI), F(Callee), Threshold(Threshold), Cost(0), + IsCallerRecursive(false), IsRecursiveCall(false), + ExposesReturnsTwice(false), HasDynamicAlloca(false), + ContainsNoDuplicateCall(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; } + + // 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<Value *, int>::iterator &CostIt) { + if (SROAArgValues.empty() || SROAArgCosts.empty()) + return false; + + DenseMap<Value *, Value *>::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<Value *, int>::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<Value *, int>::iterator CostIt; + if (lookupSROAArgAndCost(V, SROAArg, CostIt)) + disableSROA(CostIt); +} + +/// \brief Accumulate the given cost for a particular SROA candidate. +void CallAnalyzer::accumulateSROACost(DenseMap<Value *, int>::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<Value *, int>::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<Constant>(*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 IntPtrWidth = TD->getPointerSizeInBits(); + 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<ConstantInt>(GTI.getOperand()); + if (!OpC) + if (Constant *SimpleOp = SimplifiedValues.lookup(GTI.getOperand())) + OpC = dyn_cast<ConstantInt>(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<StructType>(*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. + if (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<Value *, int>::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<Value *, APInt> 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<GEPOperator>(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. + Constant *COp = dyn_cast<Constant>(I.getOperand(0)); + if (!COp) + COp = SimplifiedValues.lookup(I.getOperand(0)); + if (COp) + if (Constant *C = ConstantExpr::getBitCast(COp, I.getType())) { + SimplifiedValues[&I] = C; + return true; + } + + // Track base/offsets through casts + std::pair<Value *, APInt> 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<Value *, int>::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. + Constant *COp = dyn_cast<Constant>(I.getOperand(0)); + if (!COp) + COp = SimplifiedValues.lookup(I.getOperand(0)); + if (COp) + 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(); + if (TD && IntegerSize >= TD->getPointerSizeInBits()) { + std::pair<Value *, APInt> 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<Value *, int>::iterator CostIt; + if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) + SROAArgValues[&I] = SROAArg; + + return TargetTransformInfo::TCC_Free == TTI.getUserCost(&I); +} + +bool CallAnalyzer::visitIntToPtr(IntToPtrInst &I) { + // Propagate constants through ptrtoint. + Constant *COp = dyn_cast<Constant>(I.getOperand(0)); + if (!COp) + COp = SimplifiedValues.lookup(I.getOperand(0)); + if (COp) + 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(); + if (TD && IntegerSize <= TD->getPointerSizeInBits()) { + std::pair<Value *, APInt> 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<Value *, int>::iterator CostIt; + if (lookupSROAArgAndCost(Op, SROAArg, CostIt)) + SROAArgValues[&I] = SROAArg; + + return TargetTransformInfo::TCC_Free == TTI.getUserCost(&I); +} + +bool CallAnalyzer::visitCastInst(CastInst &I) { + // Propagate constants through ptrtoint. + Constant *COp = dyn_cast<Constant>(I.getOperand(0)); + if (!COp) + COp = SimplifiedValues.lookup(I.getOperand(0)); + if (COp) + 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 TargetTransformInfo::TCC_Free == TTI.getUserCost(&I); +} + +bool CallAnalyzer::visitUnaryInstruction(UnaryInstruction &I) { + Value *Operand = I.getOperand(0); + Constant *Ops[1] = { dyn_cast<Constant>(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<Constant>(LHS)) + if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS)) + LHS = SimpleLHS; + if (!isa<Constant>(RHS)) + if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS)) + RHS = SimpleRHS; + if (Constant *CLHS = dyn_cast<Constant>(LHS)) + if (Constant *CRHS = dyn_cast<Constant>(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<ConstantPointerNull>(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<Value *, int>::iterator CostIt; + if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) { + if (isa<ConstantPointerNull>(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<Constant>(LHS)) + if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS)) + LHS = SimpleLHS; + if (!isa<Constant>(RHS)) + if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS)) + RHS = SimpleRHS; + Value *SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS, TD); + if (Constant *C = dyn_cast_or_null<Constant>(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<Value *, int>::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<Value *, int>::iterator CostIt; + if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) { + if (I.isSimple()) { + accumulateSROACost(CostIt, InlineConstants::InstrCost); + return true; + } + + disableSROA(CostIt); + } + + return false; +} + +bool CallAnalyzer::visitExtractValue(ExtractValueInst &I) { + // Constant folding for extract value is trivial. + Constant *C = dyn_cast<Constant>(I.getAggregateOperand()); + if (!C) + C = SimplifiedValues.lookup(I.getAggregateOperand()); + if (C) { + SimplifiedValues[&I] = ConstantExpr::getExtractValue(C, I.getIndices()); + return true; + } + + // SROA can look through these but give them a cost. + return false; +} + +bool CallAnalyzer::visitInsertValue(InsertValueInst &I) { + // Constant folding for insert value is trivial. + Constant *AggC = dyn_cast<Constant>(I.getAggregateOperand()); + if (!AggC) + AggC = SimplifiedValues.lookup(I.getAggregateOperand()); + Constant *InsertedC = dyn_cast<Constant>(I.getInsertedValueOperand()); + if (!InsertedC) + InsertedC = SimplifiedValues.lookup(I.getInsertedValueOperand()); + if (AggC && InsertedC) { + SimplifiedValues[&I] = ConstantExpr::getInsertValue(AggC, InsertedC, + I.getIndices()); + return true; + } + + // SROA can look through these but give them a cost. + return false; +} + +/// \brief Try to simplify a call site. +/// +/// Takes a concrete function and callsite and tries to actually simplify it by +/// analyzing the arguments and call itself with instsimplify. Returns true if +/// it has simplified the callsite to some other entity (a constant), making it +/// free. +bool CallAnalyzer::simplifyCallSite(Function *F, CallSite CS) { + // FIXME: Using the instsimplify logic directly for this is inefficient + // because we have to continually rebuild the argument list even when no + // simplifications can be performed. Until that is fixed with remapping + // inside of instsimplify, directly constant fold calls here. + if (!canConstantFoldCallTo(F)) + return false; + + // Try to re-map the arguments to constants. + SmallVector<Constant *, 4> ConstantArgs; + ConstantArgs.reserve(CS.arg_size()); + for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); + I != E; ++I) { + Constant *C = dyn_cast<Constant>(*I); + if (!C) + C = dyn_cast_or_null<Constant>(SimplifiedValues.lookup(*I)); + if (!C) + return false; // This argument doesn't map to a constant. + + ConstantArgs.push_back(C); + } + if (Constant *C = ConstantFoldCall(F, ConstantArgs)) { + SimplifiedValues[CS.getInstruction()] = C; + return true; + } + + return false; +} + +bool CallAnalyzer::visitCallSite(CallSite CS) { + if (CS.isCall() && cast<CallInst>(CS.getInstruction())->canReturnTwice() && + !F.getAttributes().hasAttribute(AttributeSet::FunctionIndex, + Attribute::ReturnsTwice)) { + // This aborts the entire analysis. + ExposesReturnsTwice = true; + return false; + } + if (CS.isCall() && + cast<CallInst>(CS.getInstruction())->hasFnAttr(Attribute::NoDuplicate)) + ContainsNoDuplicateCall = true; + + if (Function *F = CS.getCalledFunction()) { + // When we have a concrete function, first try to simplify it directly. + if (simplifyCallSite(F, CS)) + return true; + + // Next check if it is an intrinsic we know about. + // FIXME: Lift this into part of the InstVisitor. + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(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 (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<InlineAsm>(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<Function>(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, TTI, *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 (TargetTransformInfo::TCC_Free == TTI.getUserCost(&I)) + 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<ExtractElementInst>(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 (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 IntPtrWidth = TD->getPointerSizeInBits(); + 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<Value *, 4> Visited; + Visited.insert(V); + do { + if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) { + if (!GEP->isInBounds() || !accumulateGEPOffset(*GEP, Offset)) + return 0; + V = GEP->getPointerOperand(); + } else if (Operator::getOpcode(V) == Instruction::BitCast) { + V = cast<Operator>(V)->getOperand(0); + } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(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->getContext()); + return cast<ConstantInt>(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 routine. +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; + + // Perform some tweaks to the cost and threshold based on the direct + // callsite information. + + // 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<PointerType>(CS.getArgument(I)->getType()); + unsigned TypeSize = TD->getTypeSizeInBits(PTy->getElementType()); + unsigned PointerSize = TD->getPointerSizeInBits(); + // 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. + bool OnlyOneCallAndLocalLinkage = F.hasLocalLinkage() && F.hasOneUse() && + &F == CS.getCalledFunction(); + if (OnlyOneCallAndLocalLinkage) + 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<InvokeInst>(Instr)) { + if (isa<UnreachableInst>(II->getNormalDest()->begin())) + Threshold = 1; + } else if (isa<UnreachableInst>(++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<Value>(*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<Constant>(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<AllocaInst>(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<BasicBlock *, SmallVector<BasicBlock *, 16>, + SmallPtrSet<BasicBlock *, 16> > 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 (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<IndirectBrInst>(TI)) + return false; + + if (!HasReturn && isa<ReturnInst>(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<BranchInst>(TI)) { + if (BI->isConditional()) { + Value *Cond = BI->getCondition(); + if (ConstantInt *SimpleCond + = dyn_cast_or_null<ConstantInt>(SimplifiedValues.lookup(Cond))) { + BBWorklist.insert(BI->getSuccessor(SimpleCond->isZero() ? 1 : 0)); + continue; + } + } + } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + Value *Cond = SI->getCondition(); + if (ConstantInt *SimpleCond + = dyn_cast_or_null<ConstantInt>(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; + } + } + + // If this is a noduplicate call, we can still inline as long as + // inlining this would cause the removal of the caller (so the instruction + // is not actually duplicated, just moved). + if (!OnlyOneCallAndLocalLinkage && ContainsNoDuplicateCall) + return false; + + Threshold += VectorBonus; + + return 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); + DEBUG_PRINT_STAT(ContainsNoDuplicateCall); +#undef DEBUG_PRINT_STAT +} +#endif + +INITIALIZE_PASS_BEGIN(InlineCostAnalysis, "inline-cost", "Inline Cost Analysis", + true, true) +INITIALIZE_AG_DEPENDENCY(TargetTransformInfo) +INITIALIZE_PASS_END(InlineCostAnalysis, "inline-cost", "Inline Cost Analysis", + true, true) + +char InlineCostAnalysis::ID = 0; + +InlineCostAnalysis::InlineCostAnalysis() : CallGraphSCCPass(ID), TD(0) {} + +InlineCostAnalysis::~InlineCostAnalysis() {} + +void InlineCostAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesAll(); + AU.addRequired<TargetTransformInfo>(); + CallGraphSCCPass::getAnalysisUsage(AU); +} + +bool InlineCostAnalysis::runOnSCC(CallGraphSCC &SCC) { + TD = getAnalysisIfAvailable<DataLayout>(); + TTI = &getAnalysis<TargetTransformInfo>(); + return false; +} + +InlineCost InlineCostAnalysis::getInlineCost(CallSite CS, int Threshold) { + return getInlineCost(CS, CS.getCalledFunction(), Threshold); +} + +InlineCost InlineCostAnalysis::getInlineCost(CallSite CS, Function *Callee, + int Threshold) { + // Cannot inline indirect calls. + if (!Callee) + return llvm::InlineCost::getNever(); + + // Calls to functions with always-inline attributes should be inlined + // whenever possible. + if (Callee->getAttributes().hasAttribute(AttributeSet::FunctionIndex, + Attribute::AlwaysInline)) { + if (isInlineViable(*Callee)) + return llvm::InlineCost::getAlways(); + return llvm::InlineCost::getNever(); + } + + // 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->mayBeOverridden() || + Callee->getAttributes().hasAttribute(AttributeSet::FunctionIndex, + Attribute::NoInline) || + CS.isNoInline()) + return llvm::InlineCost::getNever(); + + DEBUG(llvm::dbgs() << " Analyzing call of " << Callee->getName() + << "...\n"); + + CallAnalyzer CA(TD, *TTI, *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.getCost() >= CA.getThreshold()) + return InlineCost::getAlways(); + + return llvm::InlineCost::get(CA.getCost(), CA.getThreshold()); +} + +bool InlineCostAnalysis::isInlineViable(Function &F) { + bool ReturnsTwice = + F.getAttributes().hasAttribute(AttributeSet::FunctionIndex, + Attribute::ReturnsTwice); + for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) { + // Disallow inlining of functions which contain an indirect branch. + if (isa<IndirectBrInst>(BI->getTerminator())) + return false; + + for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE; + ++II) { + CallSite CS(II); + if (!CS) + continue; + + // Disallow recursive calls. + if (&F == CS.getCalledFunction()) + return false; + + // Disallow calls which expose returns-twice to a function not previously + // attributed as such. + if (!ReturnsTwice && CS.isCall() && + cast<CallInst>(CS.getInstruction())->canReturnTwice()) + return false; + } + } + + return true; +} |