| //===- FunctionSpecialization.cpp - Function Specialization ---------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This specialises functions with constant parameters. Constant parameters |
| // like function pointers and constant globals are propagated to the callee by |
| // specializing the function. The main benefit of this pass at the moment is |
| // that indirect calls are transformed into direct calls, which provides inline |
| // opportunities that the inliner would not have been able to achieve. That's |
| // why function specialisation is run before the inliner in the optimisation |
| // pipeline; that is by design. Otherwise, we would only benefit from constant |
| // passing, which is a valid use-case too, but hasn't been explored much in |
| // terms of performance uplifts, cost-model and compile-time impact. |
| // |
| // Current limitations: |
| // - It does not yet handle integer ranges. We do support "literal constants", |
| // but that's off by default under an option. |
| // - The cost-model could be further looked into (it mainly focuses on inlining |
| // benefits), |
| // |
| // Ideas: |
| // - With a function specialization attribute for arguments, we could have |
| // a direct way to steer function specialization, avoiding the cost-model, |
| // and thus control compile-times / code-size. |
| // |
| // Todos: |
| // - Specializing recursive functions relies on running the transformation a |
| // number of times, which is controlled by option |
| // `func-specialization-max-iters`. Thus, increasing this value and the |
| // number of iterations, will linearly increase the number of times recursive |
| // functions get specialized, see also the discussion in |
| // https://reviews.llvm.org/D106426 for details. Perhaps there is a |
| // compile-time friendlier way to control/limit the number of specialisations |
| // for recursive functions. |
| // - Don't transform the function if function specialization does not trigger; |
| // the SCCPSolver may make IR changes. |
| // |
| // References: |
| // - 2021 LLVM Dev Mtg “Introducing function specialisation, and can we enable |
| // it by default?”, https://www.youtube.com/watch?v=zJiCjeXgV5Q |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/IPO/FunctionSpecialization.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/CodeMetrics.h" |
| #include "llvm/Analysis/InlineCost.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/TargetTransformInfo.h" |
| #include "llvm/Analysis/ValueLattice.h" |
| #include "llvm/Analysis/ValueLatticeUtils.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/Transforms/Scalar/SCCP.h" |
| #include "llvm/Transforms/Utils/Cloning.h" |
| #include "llvm/Transforms/Utils/SCCPSolver.h" |
| #include "llvm/Transforms/Utils/SizeOpts.h" |
| #include <cmath> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "function-specialization" |
| |
| STATISTIC(NumFuncSpecialized, "Number of functions specialized"); |
| |
| static cl::opt<bool> ForceFunctionSpecialization( |
| "force-function-specialization", cl::init(false), cl::Hidden, |
| cl::desc("Force function specialization for every call site with a " |
| "constant argument")); |
| |
| static cl::opt<unsigned> MaxClonesThreshold( |
| "func-specialization-max-clones", cl::Hidden, |
| cl::desc("The maximum number of clones allowed for a single function " |
| "specialization"), |
| cl::init(3)); |
| |
| static cl::opt<unsigned> SmallFunctionThreshold( |
| "func-specialization-size-threshold", cl::Hidden, |
| cl::desc("Don't specialize functions that have less than this theshold " |
| "number of instructions"), |
| cl::init(100)); |
| |
| static cl::opt<unsigned> |
| AvgLoopIterationCount("func-specialization-avg-iters-cost", cl::Hidden, |
| cl::desc("Average loop iteration count cost"), |
| cl::init(10)); |
| |
| static cl::opt<bool> SpecializeOnAddresses( |
| "func-specialization-on-address", cl::init(false), cl::Hidden, |
| cl::desc("Enable function specialization on the address of global values")); |
| |
| // Disabled by default as it can significantly increase compilation times. |
| // |
| // https://llvm-compile-time-tracker.com |
| // https://github.com/nikic/llvm-compile-time-tracker |
| static cl::opt<bool> EnableSpecializationForLiteralConstant( |
| "function-specialization-for-literal-constant", cl::init(false), cl::Hidden, |
| cl::desc("Enable specialization of functions that take a literal constant " |
| "as an argument.")); |
| |
| Constant *FunctionSpecializer::getPromotableAlloca(AllocaInst *Alloca, |
| CallInst *Call) { |
| Value *StoreValue = nullptr; |
| for (auto *User : Alloca->users()) { |
| // We can't use llvm::isAllocaPromotable() as that would fail because of |
| // the usage in the CallInst, which is what we check here. |
| if (User == Call) |
| continue; |
| if (auto *Bitcast = dyn_cast<BitCastInst>(User)) { |
| if (!Bitcast->hasOneUse() || *Bitcast->user_begin() != Call) |
| return nullptr; |
| continue; |
| } |
| |
| if (auto *Store = dyn_cast<StoreInst>(User)) { |
| // This is a duplicate store, bail out. |
| if (StoreValue || Store->isVolatile()) |
| return nullptr; |
| StoreValue = Store->getValueOperand(); |
| continue; |
| } |
| // Bail if there is any other unknown usage. |
| return nullptr; |
| } |
| return getCandidateConstant(StoreValue); |
| } |
| |
| // A constant stack value is an AllocaInst that has a single constant |
| // value stored to it. Return this constant if such an alloca stack value |
| // is a function argument. |
| Constant *FunctionSpecializer::getConstantStackValue(CallInst *Call, |
| Value *Val) { |
| if (!Val) |
| return nullptr; |
| Val = Val->stripPointerCasts(); |
| if (auto *ConstVal = dyn_cast<ConstantInt>(Val)) |
| return ConstVal; |
| auto *Alloca = dyn_cast<AllocaInst>(Val); |
| if (!Alloca || !Alloca->getAllocatedType()->isIntegerTy()) |
| return nullptr; |
| return getPromotableAlloca(Alloca, Call); |
| } |
| |
| // To support specializing recursive functions, it is important to propagate |
| // constant arguments because after a first iteration of specialisation, a |
| // reduced example may look like this: |
| // |
| // define internal void @RecursiveFn(i32* arg1) { |
| // %temp = alloca i32, align 4 |
| // store i32 2 i32* %temp, align 4 |
| // call void @RecursiveFn.1(i32* nonnull %temp) |
| // ret void |
| // } |
| // |
| // Before a next iteration, we need to propagate the constant like so |
| // which allows further specialization in next iterations. |
| // |
| // @funcspec.arg = internal constant i32 2 |
| // |
| // define internal void @someFunc(i32* arg1) { |
| // call void @otherFunc(i32* nonnull @funcspec.arg) |
| // ret void |
| // } |
| // |
| void FunctionSpecializer::promoteConstantStackValues() { |
| // Iterate over the argument tracked functions see if there |
| // are any new constant values for the call instruction via |
| // stack variables. |
| for (Function &F : M) { |
| if (!Solver.isArgumentTrackedFunction(&F)) |
| continue; |
| |
| for (auto *User : F.users()) { |
| |
| auto *Call = dyn_cast<CallInst>(User); |
| if (!Call) |
| continue; |
| |
| if (!Solver.isBlockExecutable(Call->getParent())) |
| continue; |
| |
| bool Changed = false; |
| for (const Use &U : Call->args()) { |
| unsigned Idx = Call->getArgOperandNo(&U); |
| Value *ArgOp = Call->getArgOperand(Idx); |
| Type *ArgOpType = ArgOp->getType(); |
| |
| if (!Call->onlyReadsMemory(Idx) || !ArgOpType->isPointerTy()) |
| continue; |
| |
| auto *ConstVal = getConstantStackValue(Call, ArgOp); |
| if (!ConstVal) |
| continue; |
| |
| Value *GV = new GlobalVariable(M, ConstVal->getType(), true, |
| GlobalValue::InternalLinkage, ConstVal, |
| "funcspec.arg"); |
| if (ArgOpType != ConstVal->getType()) |
| GV = ConstantExpr::getBitCast(cast<Constant>(GV), ArgOpType); |
| |
| Call->setArgOperand(Idx, GV); |
| Changed = true; |
| } |
| |
| // Add the changed CallInst to Solver Worklist |
| if (Changed) |
| Solver.visitCall(*Call); |
| } |
| } |
| } |
| |
| // ssa_copy intrinsics are introduced by the SCCP solver. These intrinsics |
| // interfere with the promoteConstantStackValues() optimization. |
| static void removeSSACopy(Function &F) { |
| for (BasicBlock &BB : F) { |
| for (Instruction &Inst : llvm::make_early_inc_range(BB)) { |
| auto *II = dyn_cast<IntrinsicInst>(&Inst); |
| if (!II) |
| continue; |
| if (II->getIntrinsicID() != Intrinsic::ssa_copy) |
| continue; |
| Inst.replaceAllUsesWith(II->getOperand(0)); |
| Inst.eraseFromParent(); |
| } |
| } |
| } |
| |
| /// Remove any ssa_copy intrinsics that may have been introduced. |
| void FunctionSpecializer::cleanUpSSA() { |
| for (Function *F : SpecializedFuncs) |
| removeSSACopy(*F); |
| } |
| |
| |
| template <> struct llvm::DenseMapInfo<SpecSig> { |
| static inline SpecSig getEmptyKey() { return {~0U, {}}; } |
| |
| static inline SpecSig getTombstoneKey() { return {~1U, {}}; } |
| |
| static unsigned getHashValue(const SpecSig &S) { |
| return static_cast<unsigned>(hash_value(S)); |
| } |
| |
| static bool isEqual(const SpecSig &LHS, const SpecSig &RHS) { |
| return LHS == RHS; |
| } |
| }; |
| |
| /// Attempt to specialize functions in the module to enable constant |
| /// propagation across function boundaries. |
| /// |
| /// \returns true if at least one function is specialized. |
| bool FunctionSpecializer::run() { |
| // Find possible specializations for each function. |
| SpecMap SM; |
| SmallVector<Spec, 32> AllSpecs; |
| unsigned NumCandidates = 0; |
| for (Function &F : M) { |
| if (!isCandidateFunction(&F)) |
| continue; |
| |
| auto Cost = getSpecializationCost(&F); |
| if (!Cost.isValid()) { |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Invalid specialization cost for " |
| << F.getName() << "\n"); |
| continue; |
| } |
| |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Specialization cost for " |
| << F.getName() << " is " << Cost << "\n"); |
| |
| if (!findSpecializations(&F, Cost, AllSpecs, SM)) { |
| LLVM_DEBUG( |
| dbgs() << "FnSpecialization: No possible specializations found for " |
| << F.getName() << "\n"); |
| continue; |
| } |
| |
| ++NumCandidates; |
| } |
| |
| if (!NumCandidates) { |
| LLVM_DEBUG( |
| dbgs() |
| << "FnSpecialization: No possible specializations found in module\n"); |
| return false; |
| } |
| |
| // Choose the most profitable specialisations, which fit in the module |
| // specialization budget, which is derived from maximum number of |
| // specializations per specialization candidate function. |
| auto CompareGain = [&AllSpecs](unsigned I, unsigned J) { |
| return AllSpecs[I].Gain > AllSpecs[J].Gain; |
| }; |
| const unsigned NSpecs = |
| std::min(NumCandidates * MaxClonesThreshold, unsigned(AllSpecs.size())); |
| SmallVector<unsigned> BestSpecs(NSpecs + 1); |
| std::iota(BestSpecs.begin(), BestSpecs.begin() + NSpecs, 0); |
| if (AllSpecs.size() > NSpecs) { |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Number of candidates exceed " |
| << "the maximum number of clones threshold.\n" |
| << "FnSpecialization: Specializing the " |
| << NSpecs |
| << " most profitable candidates.\n"); |
| std::make_heap(BestSpecs.begin(), BestSpecs.begin() + NSpecs, CompareGain); |
| for (unsigned I = NSpecs, N = AllSpecs.size(); I < N; ++I) { |
| BestSpecs[NSpecs] = I; |
| std::push_heap(BestSpecs.begin(), BestSpecs.end(), CompareGain); |
| std::pop_heap(BestSpecs.begin(), BestSpecs.end(), CompareGain); |
| } |
| } |
| |
| LLVM_DEBUG(dbgs() << "FnSpecialization: List of specializations \n"; |
| for (unsigned I = 0; I < NSpecs; ++I) { |
| const Spec &S = AllSpecs[BestSpecs[I]]; |
| dbgs() << "FnSpecialization: Function " << S.F->getName() |
| << " , gain " << S.Gain << "\n"; |
| for (const ArgInfo &Arg : S.Sig.Args) |
| dbgs() << "FnSpecialization: FormalArg = " |
| << Arg.Formal->getNameOrAsOperand() |
| << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() |
| << "\n"; |
| }); |
| |
| // Create the chosen specializations. |
| SmallPtrSet<Function *, 8> OriginalFuncs; |
| SmallVector<Function *> Clones; |
| for (unsigned I = 0; I < NSpecs; ++I) { |
| Spec &S = AllSpecs[BestSpecs[I]]; |
| S.Clone = createSpecialization(S.F, S.Sig); |
| |
| // Update the known call sites to call the clone. |
| for (CallBase *Call : S.CallSites) { |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Redirecting " << *Call |
| << " to call " << S.Clone->getName() << "\n"); |
| Call->setCalledFunction(S.Clone); |
| } |
| |
| Clones.push_back(S.Clone); |
| OriginalFuncs.insert(S.F); |
| } |
| |
| Solver.solveWhileResolvedUndefsIn(Clones); |
| |
| // Update the rest of the call sites - these are the recursive calls, calls |
| // to discarded specialisations and calls that may match a specialisation |
| // after the solver runs. |
| for (Function *F : OriginalFuncs) { |
| auto [Begin, End] = SM[F]; |
| updateCallSites(F, AllSpecs.begin() + Begin, AllSpecs.begin() + End); |
| } |
| |
| promoteConstantStackValues(); |
| LLVM_DEBUG(if (NbFunctionsSpecialized) dbgs() |
| << "FnSpecialization: Specialized " << NbFunctionsSpecialized |
| << " functions in module " << M.getName() << "\n"); |
| |
| NumFuncSpecialized += NbFunctionsSpecialized; |
| return true; |
| } |
| |
| void FunctionSpecializer::removeDeadFunctions() { |
| for (Function *F : FullySpecialized) { |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Removing dead function " |
| << F->getName() << "\n"); |
| if (FAM) |
| FAM->clear(*F, F->getName()); |
| F->eraseFromParent(); |
| } |
| FullySpecialized.clear(); |
| } |
| |
| // Compute the code metrics for function \p F. |
| CodeMetrics &FunctionSpecializer::analyzeFunction(Function *F) { |
| auto I = FunctionMetrics.insert({F, CodeMetrics()}); |
| CodeMetrics &Metrics = I.first->second; |
| if (I.second) { |
| // The code metrics were not cached. |
| SmallPtrSet<const Value *, 32> EphValues; |
| CodeMetrics::collectEphemeralValues(F, &(GetAC)(*F), EphValues); |
| for (BasicBlock &BB : *F) |
| Metrics.analyzeBasicBlock(&BB, (GetTTI)(*F), EphValues); |
| |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Code size of function " |
| << F->getName() << " is " << Metrics.NumInsts |
| << " instructions\n"); |
| } |
| return Metrics; |
| } |
| |
| /// Clone the function \p F and remove the ssa_copy intrinsics added by |
| /// the SCCPSolver in the cloned version. |
| static Function *cloneCandidateFunction(Function *F) { |
| ValueToValueMapTy Mappings; |
| Function *Clone = CloneFunction(F, Mappings); |
| removeSSACopy(*Clone); |
| return Clone; |
| } |
| |
| bool FunctionSpecializer::findSpecializations(Function *F, InstructionCost Cost, |
| SmallVectorImpl<Spec> &AllSpecs, |
| SpecMap &SM) { |
| // A mapping from a specialisation signature to the index of the respective |
| // entry in the all specialisation array. Used to ensure uniqueness of |
| // specialisations. |
| DenseMap<SpecSig, unsigned> UM; |
| |
| // Get a list of interesting arguments. |
| SmallVector<Argument *> Args; |
| for (Argument &Arg : F->args()) |
| if (isArgumentInteresting(&Arg)) |
| Args.push_back(&Arg); |
| |
| if (Args.empty()) |
| return false; |
| |
| bool Found = false; |
| for (User *U : F->users()) { |
| if (!isa<CallInst>(U) && !isa<InvokeInst>(U)) |
| continue; |
| auto &CS = *cast<CallBase>(U); |
| |
| // The user instruction does not call our function. |
| if (CS.getCalledFunction() != F) |
| continue; |
| |
| // If the call site has attribute minsize set, that callsite won't be |
| // specialized. |
| if (CS.hasFnAttr(Attribute::MinSize)) |
| continue; |
| |
| // If the parent of the call site will never be executed, we don't need |
| // to worry about the passed value. |
| if (!Solver.isBlockExecutable(CS.getParent())) |
| continue; |
| |
| // Examine arguments and create a specialisation candidate from the |
| // constant operands of this call site. |
| SpecSig S; |
| for (Argument *A : Args) { |
| Constant *C = getCandidateConstant(CS.getArgOperand(A->getArgNo())); |
| if (!C) |
| continue; |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Found interesting argument " |
| << A->getName() << " : " << C->getNameOrAsOperand() |
| << "\n"); |
| S.Args.push_back({A, C}); |
| } |
| |
| if (S.Args.empty()) |
| continue; |
| |
| // Check if we have encountered the same specialisation already. |
| if (auto It = UM.find(S); It != UM.end()) { |
| // Existing specialisation. Add the call to the list to rewrite, unless |
| // it's a recursive call. A specialisation, generated because of a |
| // recursive call may end up as not the best specialisation for all |
| // the cloned instances of this call, which result from specialising |
| // functions. Hence we don't rewrite the call directly, but match it with |
| // the best specialisation once all specialisations are known. |
| if (CS.getFunction() == F) |
| continue; |
| const unsigned Index = It->second; |
| AllSpecs[Index].CallSites.push_back(&CS); |
| } else { |
| // Calculate the specialisation gain. |
| InstructionCost Gain = 0 - Cost; |
| for (ArgInfo &A : S.Args) |
| Gain += |
| getSpecializationBonus(A.Formal, A.Actual, Solver.getLoopInfo(*F)); |
| |
| // Discard unprofitable specialisations. |
| if (!ForceFunctionSpecialization && Gain <= 0) |
| continue; |
| |
| // Create a new specialisation entry. |
| auto &Spec = AllSpecs.emplace_back(F, S, Gain); |
| if (CS.getFunction() != F) |
| Spec.CallSites.push_back(&CS); |
| const unsigned Index = AllSpecs.size() - 1; |
| UM[S] = Index; |
| if (auto [It, Inserted] = SM.try_emplace(F, Index, Index + 1); !Inserted) |
| It->second.second = Index + 1; |
| Found = true; |
| } |
| } |
| |
| return Found; |
| } |
| |
| bool FunctionSpecializer::isCandidateFunction(Function *F) { |
| if (F->isDeclaration()) |
| return false; |
| |
| if (F->hasFnAttribute(Attribute::NoDuplicate)) |
| return false; |
| |
| if (!Solver.isArgumentTrackedFunction(F)) |
| return false; |
| |
| // Do not specialize the cloned function again. |
| if (SpecializedFuncs.contains(F)) |
| return false; |
| |
| // If we're optimizing the function for size, we shouldn't specialize it. |
| if (F->hasOptSize() || |
| shouldOptimizeForSize(F, nullptr, nullptr, PGSOQueryType::IRPass)) |
| return false; |
| |
| // Exit if the function is not executable. There's no point in specializing |
| // a dead function. |
| if (!Solver.isBlockExecutable(&F->getEntryBlock())) |
| return false; |
| |
| // It wastes time to specialize a function which would get inlined finally. |
| if (F->hasFnAttribute(Attribute::AlwaysInline)) |
| return false; |
| |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Try function: " << F->getName() |
| << "\n"); |
| return true; |
| } |
| |
| Function *FunctionSpecializer::createSpecialization(Function *F, const SpecSig &S) { |
| Function *Clone = cloneCandidateFunction(F); |
| |
| // Initialize the lattice state of the arguments of the function clone, |
| // marking the argument on which we specialized the function constant |
| // with the given value. |
| Solver.markArgInFuncSpecialization(Clone, S.Args); |
| |
| Solver.addArgumentTrackedFunction(Clone); |
| Solver.markBlockExecutable(&Clone->front()); |
| |
| // Mark all the specialized functions |
| SpecializedFuncs.insert(Clone); |
| NbFunctionsSpecialized++; |
| |
| return Clone; |
| } |
| |
| /// Compute and return the cost of specializing function \p F. |
| InstructionCost FunctionSpecializer::getSpecializationCost(Function *F) { |
| CodeMetrics &Metrics = analyzeFunction(F); |
| // If the code metrics reveal that we shouldn't duplicate the function, we |
| // shouldn't specialize it. Set the specialization cost to Invalid. |
| // Or if the lines of codes implies that this function is easy to get |
| // inlined so that we shouldn't specialize it. |
| if (Metrics.notDuplicatable || !Metrics.NumInsts.isValid() || |
| (!ForceFunctionSpecialization && |
| !F->hasFnAttribute(Attribute::NoInline) && |
| Metrics.NumInsts < SmallFunctionThreshold)) |
| return InstructionCost::getInvalid(); |
| |
| // Otherwise, set the specialization cost to be the cost of all the |
| // instructions in the function. |
| return Metrics.NumInsts * InlineConstants::getInstrCost(); |
| } |
| |
| static InstructionCost getUserBonus(User *U, llvm::TargetTransformInfo &TTI, |
| const LoopInfo &LI) { |
| auto *I = dyn_cast_or_null<Instruction>(U); |
| // If not an instruction we do not know how to evaluate. |
| // Keep minimum possible cost for now so that it doesnt affect |
| // specialization. |
| if (!I) |
| return std::numeric_limits<unsigned>::min(); |
| |
| InstructionCost Cost = |
| TTI.getInstructionCost(U, TargetTransformInfo::TCK_SizeAndLatency); |
| |
| // Increase the cost if it is inside the loop. |
| unsigned LoopDepth = LI.getLoopDepth(I->getParent()); |
| Cost *= std::pow((double)AvgLoopIterationCount, LoopDepth); |
| |
| // Traverse recursively if there are more uses. |
| // TODO: Any other instructions to be added here? |
| if (I->mayReadFromMemory() || I->isCast()) |
| for (auto *User : I->users()) |
| Cost += getUserBonus(User, TTI, LI); |
| |
| return Cost; |
| } |
| |
| /// Compute a bonus for replacing argument \p A with constant \p C. |
| InstructionCost |
| FunctionSpecializer::getSpecializationBonus(Argument *A, Constant *C, |
| const LoopInfo &LI) { |
| Function *F = A->getParent(); |
| auto &TTI = (GetTTI)(*F); |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Analysing bonus for constant: " |
| << C->getNameOrAsOperand() << "\n"); |
| |
| InstructionCost TotalCost = 0; |
| for (auto *U : A->users()) { |
| TotalCost += getUserBonus(U, TTI, LI); |
| LLVM_DEBUG(dbgs() << "FnSpecialization: User cost "; |
| TotalCost.print(dbgs()); dbgs() << " for: " << *U << "\n"); |
| } |
| |
| // The below heuristic is only concerned with exposing inlining |
| // opportunities via indirect call promotion. If the argument is not a |
| // (potentially casted) function pointer, give up. |
| Function *CalledFunction = dyn_cast<Function>(C->stripPointerCasts()); |
| if (!CalledFunction) |
| return TotalCost; |
| |
| // Get TTI for the called function (used for the inline cost). |
| auto &CalleeTTI = (GetTTI)(*CalledFunction); |
| |
| // Look at all the call sites whose called value is the argument. |
| // Specializing the function on the argument would allow these indirect |
| // calls to be promoted to direct calls. If the indirect call promotion |
| // would likely enable the called function to be inlined, specializing is a |
| // good idea. |
| int Bonus = 0; |
| for (User *U : A->users()) { |
| if (!isa<CallInst>(U) && !isa<InvokeInst>(U)) |
| continue; |
| auto *CS = cast<CallBase>(U); |
| if (CS->getCalledOperand() != A) |
| continue; |
| if (CS->getFunctionType() != CalledFunction->getFunctionType()) |
| continue; |
| |
| // Get the cost of inlining the called function at this call site. Note |
| // that this is only an estimate. The called function may eventually |
| // change in a way that leads to it not being inlined here, even though |
| // inlining looks profitable now. For example, one of its called |
| // functions may be inlined into it, making the called function too large |
| // to be inlined into this call site. |
| // |
| // We apply a boost for performing indirect call promotion by increasing |
| // the default threshold by the threshold for indirect calls. |
| auto Params = getInlineParams(); |
| Params.DefaultThreshold += InlineConstants::IndirectCallThreshold; |
| InlineCost IC = |
| getInlineCost(*CS, CalledFunction, Params, CalleeTTI, GetAC, GetTLI); |
| |
| // We clamp the bonus for this call to be between zero and the default |
| // threshold. |
| if (IC.isAlways()) |
| Bonus += Params.DefaultThreshold; |
| else if (IC.isVariable() && IC.getCostDelta() > 0) |
| Bonus += IC.getCostDelta(); |
| |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Inlining bonus " << Bonus |
| << " for user " << *U << "\n"); |
| } |
| |
| return TotalCost + Bonus; |
| } |
| |
| /// Determine if it is possible to specialise the function for constant values |
| /// of the formal parameter \p A. |
| bool FunctionSpecializer::isArgumentInteresting(Argument *A) { |
| // No point in specialization if the argument is unused. |
| if (A->user_empty()) |
| return false; |
| |
| // For now, don't attempt to specialize functions based on the values of |
| // composite types. |
| Type *ArgTy = A->getType(); |
| if (!ArgTy->isSingleValueType()) |
| return false; |
| |
| // Specialization of integer and floating point types needs to be explicitly |
| // enabled. |
| if (!EnableSpecializationForLiteralConstant && |
| (ArgTy->isIntegerTy() || ArgTy->isFloatingPointTy())) |
| return false; |
| |
| // SCCP solver does not record an argument that will be constructed on |
| // stack. |
| if (A->hasByValAttr() && !A->getParent()->onlyReadsMemory()) |
| return false; |
| |
| // Check the lattice value and decide if we should attemt to specialize, |
| // based on this argument. No point in specialization, if the lattice value |
| // is already a constant. |
| const ValueLatticeElement &LV = Solver.getLatticeValueFor(A); |
| if (LV.isUnknownOrUndef() || LV.isConstant() || |
| (LV.isConstantRange() && LV.getConstantRange().isSingleElement())) { |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Nothing to do, parameter " |
| << A->getNameOrAsOperand() << " is already constant\n"); |
| return false; |
| } |
| |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Found interesting parameter " |
| << A->getNameOrAsOperand() << "\n"); |
| |
| return true; |
| } |
| |
| /// Check if the valuy \p V (an actual argument) is a constant or can only |
| /// have a constant value. Return that constant. |
| Constant *FunctionSpecializer::getCandidateConstant(Value *V) { |
| if (isa<PoisonValue>(V)) |
| return nullptr; |
| |
| // TrackValueOfGlobalVariable only tracks scalar global variables. |
| if (auto *GV = dyn_cast<GlobalVariable>(V)) { |
| // Check if we want to specialize on the address of non-constant |
| // global values. |
| if (!GV->isConstant() && !SpecializeOnAddresses) |
| return nullptr; |
| |
| if (!GV->getValueType()->isSingleValueType()) |
| return nullptr; |
| } |
| |
| // Select for possible specialisation values that are constants or |
| // are deduced to be constants or constant ranges with a single element. |
| Constant *C = dyn_cast<Constant>(V); |
| if (!C) { |
| const ValueLatticeElement &LV = Solver.getLatticeValueFor(V); |
| if (LV.isConstant()) |
| C = LV.getConstant(); |
| else if (LV.isConstantRange() && LV.getConstantRange().isSingleElement()) { |
| assert(V->getType()->isIntegerTy() && "Non-integral constant range"); |
| C = Constant::getIntegerValue(V->getType(), |
| *LV.getConstantRange().getSingleElement()); |
| } else |
| return nullptr; |
| } |
| |
| return C; |
| } |
| |
| void FunctionSpecializer::updateCallSites(Function *F, const Spec *Begin, |
| const Spec *End) { |
| // Collect the call sites that need updating. |
| SmallVector<CallBase *> ToUpdate; |
| for (User *U : F->users()) |
| if (auto *CS = dyn_cast<CallBase>(U); |
| CS && CS->getCalledFunction() == F && |
| Solver.isBlockExecutable(CS->getParent())) |
| ToUpdate.push_back(CS); |
| |
| unsigned NCallsLeft = ToUpdate.size(); |
| for (CallBase *CS : ToUpdate) { |
| bool ShouldDecrementCount = CS->getFunction() == F; |
| |
| // Find the best matching specialisation. |
| const Spec *BestSpec = nullptr; |
| for (const Spec &S : make_range(Begin, End)) { |
| if (!S.Clone || (BestSpec && S.Gain <= BestSpec->Gain)) |
| continue; |
| |
| if (any_of(S.Sig.Args, [CS, this](const ArgInfo &Arg) { |
| unsigned ArgNo = Arg.Formal->getArgNo(); |
| return getCandidateConstant(CS->getArgOperand(ArgNo)) != Arg.Actual; |
| })) |
| continue; |
| |
| BestSpec = &S; |
| } |
| |
| if (BestSpec) { |
| LLVM_DEBUG(dbgs() << "FnSpecialization: Redirecting " << *CS |
| << " to call " << BestSpec->Clone->getName() << "\n"); |
| CS->setCalledFunction(BestSpec->Clone); |
| ShouldDecrementCount = true; |
| } |
| |
| if (ShouldDecrementCount) |
| --NCallsLeft; |
| } |
| |
| // If the function has been completely specialized, the original function |
| // is no longer needed. Mark it unreachable. |
| if (NCallsLeft == 0) { |
| Solver.markFunctionUnreachable(F); |
| FullySpecialized.insert(F); |
| } |
| } |