diff options
Diffstat (limited to 'contrib/llvm-project/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp')
-rw-r--r-- | contrib/llvm-project/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp | 779 |
1 files changed, 779 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp b/contrib/llvm-project/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp new file mode 100644 index 000000000000..4a7efb28e853 --- /dev/null +++ b/contrib/llvm-project/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp @@ -0,0 +1,779 @@ +//===- 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); + } +} |