| File: | build/source/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp |
| Warning: | line 475, column 7 Value stored to 'Added' is never read |
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| 1 | //===- FunctionSpecialization.cpp - Function Specialization ---------------===// |
| 2 | // |
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | // See https://llvm.org/LICENSE.txt for license information. |
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | // |
| 7 | //===----------------------------------------------------------------------===// |
| 8 | // |
| 9 | // This specialises functions with constant parameters. Constant parameters |
| 10 | // like function pointers and constant globals are propagated to the callee by |
| 11 | // specializing the function. The main benefit of this pass at the moment is |
| 12 | // that indirect calls are transformed into direct calls, which provides inline |
| 13 | // opportunities that the inliner would not have been able to achieve. That's |
| 14 | // why function specialisation is run before the inliner in the optimisation |
| 15 | // pipeline; that is by design. Otherwise, we would only benefit from constant |
| 16 | // passing, which is a valid use-case too, but hasn't been explored much in |
| 17 | // terms of performance uplifts, cost-model and compile-time impact. |
| 18 | // |
| 19 | // Current limitations: |
| 20 | // - It does not yet handle integer ranges. We do support "literal constants", |
| 21 | // but that's off by default under an option. |
| 22 | // - The cost-model could be further looked into (it mainly focuses on inlining |
| 23 | // benefits), |
| 24 | // |
| 25 | // Ideas: |
| 26 | // - With a function specialization attribute for arguments, we could have |
| 27 | // a direct way to steer function specialization, avoiding the cost-model, |
| 28 | // and thus control compile-times / code-size. |
| 29 | // |
| 30 | // Todos: |
| 31 | // - Specializing recursive functions relies on running the transformation a |
| 32 | // number of times, which is controlled by option |
| 33 | // `func-specialization-max-iters`. Thus, increasing this value and the |
| 34 | // number of iterations, will linearly increase the number of times recursive |
| 35 | // functions get specialized, see also the discussion in |
| 36 | // https://reviews.llvm.org/D106426 for details. Perhaps there is a |
| 37 | // compile-time friendlier way to control/limit the number of specialisations |
| 38 | // for recursive functions. |
| 39 | // - Don't transform the function if function specialization does not trigger; |
| 40 | // the SCCPSolver may make IR changes. |
| 41 | // |
| 42 | // References: |
| 43 | // - 2021 LLVM Dev Mtg “Introducing function specialisation, and can we enable |
| 44 | // it by default?”, https://www.youtube.com/watch?v=zJiCjeXgV5Q |
| 45 | // |
| 46 | //===----------------------------------------------------------------------===// |
| 47 | |
| 48 | #include "llvm/ADT/Statistic.h" |
| 49 | #include "llvm/Analysis/CodeMetrics.h" |
| 50 | #include "llvm/Analysis/InlineCost.h" |
| 51 | #include "llvm/Analysis/LoopInfo.h" |
| 52 | #include "llvm/Analysis/TargetTransformInfo.h" |
| 53 | #include "llvm/Analysis/ValueLattice.h" |
| 54 | #include "llvm/Analysis/ValueLatticeUtils.h" |
| 55 | #include "llvm/IR/IntrinsicInst.h" |
| 56 | #include "llvm/Transforms/Scalar/SCCP.h" |
| 57 | #include "llvm/Transforms/Utils/Cloning.h" |
| 58 | #include "llvm/Transforms/Utils/SCCPSolver.h" |
| 59 | #include "llvm/Transforms/Utils/SizeOpts.h" |
| 60 | #include <cmath> |
| 61 | |
| 62 | using namespace llvm; |
| 63 | |
| 64 | #define DEBUG_TYPE"function-specialization" "function-specialization" |
| 65 | |
| 66 | STATISTIC(NumFuncSpecialized, "Number of functions specialized")static llvm::Statistic NumFuncSpecialized = {"function-specialization" , "NumFuncSpecialized", "Number of functions specialized"}; |
| 67 | |
| 68 | static cl::opt<bool> ForceFunctionSpecialization( |
| 69 | "force-function-specialization", cl::init(false), cl::Hidden, |
| 70 | cl::desc("Force function specialization for every call site with a " |
| 71 | "constant argument")); |
| 72 | |
| 73 | static cl::opt<unsigned> FuncSpecializationMaxIters( |
| 74 | "func-specialization-max-iters", cl::Hidden, |
| 75 | cl::desc("The maximum number of iterations function specialization is run"), |
| 76 | cl::init(1)); |
| 77 | |
| 78 | static cl::opt<unsigned> MaxClonesThreshold( |
| 79 | "func-specialization-max-clones", cl::Hidden, |
| 80 | cl::desc("The maximum number of clones allowed for a single function " |
| 81 | "specialization"), |
| 82 | cl::init(3)); |
| 83 | |
| 84 | static cl::opt<unsigned> SmallFunctionThreshold( |
| 85 | "func-specialization-size-threshold", cl::Hidden, |
| 86 | cl::desc("Don't specialize functions that have less than this theshold " |
| 87 | "number of instructions"), |
| 88 | cl::init(100)); |
| 89 | |
| 90 | static cl::opt<unsigned> |
| 91 | AvgLoopIterationCount("func-specialization-avg-iters-cost", cl::Hidden, |
| 92 | cl::desc("Average loop iteration count cost"), |
| 93 | cl::init(10)); |
| 94 | |
| 95 | static cl::opt<bool> SpecializeOnAddresses( |
| 96 | "func-specialization-on-address", cl::init(false), cl::Hidden, |
| 97 | cl::desc("Enable function specialization on the address of global values")); |
| 98 | |
| 99 | // Disabled by default as it can significantly increase compilation times. |
| 100 | // Running nikic's compile time tracker on x86 with instruction count as the |
| 101 | // metric shows 3-4% regression for SPASS while being neutral for all other |
| 102 | // benchmarks of the llvm test suite. |
| 103 | // |
| 104 | // https://llvm-compile-time-tracker.com |
| 105 | // https://github.com/nikic/llvm-compile-time-tracker |
| 106 | static cl::opt<bool> EnableSpecializationForLiteralConstant( |
| 107 | "function-specialization-for-literal-constant", cl::init(false), cl::Hidden, |
| 108 | cl::desc("Enable specialization of functions that take a literal constant " |
| 109 | "as an argument.")); |
| 110 | |
| 111 | namespace { |
| 112 | // Bookkeeping struct to pass data from the analysis and profitability phase |
| 113 | // to the actual transform helper functions. |
| 114 | struct SpecializationInfo { |
| 115 | SmallVector<ArgInfo, 8> Args; // Stores the {formal,actual} argument pairs. |
| 116 | InstructionCost Gain; // Profitability: Gain = Bonus - Cost. |
| 117 | }; |
| 118 | } // Anonymous namespace |
| 119 | |
| 120 | using FuncList = SmallVectorImpl<Function *>; |
| 121 | using CallArgBinding = std::pair<CallBase *, Constant *>; |
| 122 | using CallSpecBinding = std::pair<CallBase *, SpecializationInfo>; |
| 123 | // We are using MapVector because it guarantees deterministic iteration |
| 124 | // order across executions. |
| 125 | using SpecializationMap = SmallMapVector<CallBase *, SpecializationInfo, 8>; |
| 126 | |
| 127 | // Helper to check if \p LV is either a constant or a constant |
| 128 | // range with a single element. This should cover exactly the same cases as the |
| 129 | // old ValueLatticeElement::isConstant() and is intended to be used in the |
| 130 | // transition to ValueLatticeElement. |
| 131 | static bool isConstant(const ValueLatticeElement &LV) { |
| 132 | return LV.isConstant() || |
| 133 | (LV.isConstantRange() && LV.getConstantRange().isSingleElement()); |
| 134 | } |
| 135 | |
| 136 | // Helper to check if \p LV is either overdefined or a constant int. |
| 137 | static bool isOverdefined(const ValueLatticeElement &LV) { |
| 138 | return !LV.isUnknownOrUndef() && !isConstant(LV); |
| 139 | } |
| 140 | |
| 141 | static Constant *getPromotableAlloca(AllocaInst *Alloca, CallInst *Call) { |
| 142 | Value *StoreValue = nullptr; |
| 143 | for (auto *User : Alloca->users()) { |
| 144 | // We can't use llvm::isAllocaPromotable() as that would fail because of |
| 145 | // the usage in the CallInst, which is what we check here. |
| 146 | if (User == Call) |
| 147 | continue; |
| 148 | if (auto *Bitcast = dyn_cast<BitCastInst>(User)) { |
| 149 | if (!Bitcast->hasOneUse() || *Bitcast->user_begin() != Call) |
| 150 | return nullptr; |
| 151 | continue; |
| 152 | } |
| 153 | |
| 154 | if (auto *Store = dyn_cast<StoreInst>(User)) { |
| 155 | // This is a duplicate store, bail out. |
| 156 | if (StoreValue || Store->isVolatile()) |
| 157 | return nullptr; |
| 158 | StoreValue = Store->getValueOperand(); |
| 159 | continue; |
| 160 | } |
| 161 | // Bail if there is any other unknown usage. |
| 162 | return nullptr; |
| 163 | } |
| 164 | return dyn_cast_or_null<Constant>(StoreValue); |
| 165 | } |
| 166 | |
| 167 | // A constant stack value is an AllocaInst that has a single constant |
| 168 | // value stored to it. Return this constant if such an alloca stack value |
| 169 | // is a function argument. |
| 170 | static Constant *getConstantStackValue(CallInst *Call, Value *Val, |
| 171 | SCCPSolver &Solver) { |
| 172 | if (!Val) |
| 173 | return nullptr; |
| 174 | Val = Val->stripPointerCasts(); |
| 175 | if (auto *ConstVal = dyn_cast<ConstantInt>(Val)) |
| 176 | return ConstVal; |
| 177 | auto *Alloca = dyn_cast<AllocaInst>(Val); |
| 178 | if (!Alloca || !Alloca->getAllocatedType()->isIntegerTy()) |
| 179 | return nullptr; |
| 180 | return getPromotableAlloca(Alloca, Call); |
| 181 | } |
| 182 | |
| 183 | // To support specializing recursive functions, it is important to propagate |
| 184 | // constant arguments because after a first iteration of specialisation, a |
| 185 | // reduced example may look like this: |
| 186 | // |
| 187 | // define internal void @RecursiveFn(i32* arg1) { |
| 188 | // %temp = alloca i32, align 4 |
| 189 | // store i32 2 i32* %temp, align 4 |
| 190 | // call void @RecursiveFn.1(i32* nonnull %temp) |
| 191 | // ret void |
| 192 | // } |
| 193 | // |
| 194 | // Before a next iteration, we need to propagate the constant like so |
| 195 | // which allows further specialization in next iterations. |
| 196 | // |
| 197 | // @funcspec.arg = internal constant i32 2 |
| 198 | // |
| 199 | // define internal void @someFunc(i32* arg1) { |
| 200 | // call void @otherFunc(i32* nonnull @funcspec.arg) |
| 201 | // ret void |
| 202 | // } |
| 203 | // |
| 204 | static void constantArgPropagation(FuncList &WorkList, Module &M, |
| 205 | SCCPSolver &Solver) { |
| 206 | // Iterate over the argument tracked functions see if there |
| 207 | // are any new constant values for the call instruction via |
| 208 | // stack variables. |
| 209 | for (auto *F : WorkList) { |
| 210 | |
| 211 | for (auto *User : F->users()) { |
| 212 | |
| 213 | auto *Call = dyn_cast<CallInst>(User); |
| 214 | if (!Call) |
| 215 | continue; |
| 216 | |
| 217 | bool Changed = false; |
| 218 | for (const Use &U : Call->args()) { |
| 219 | unsigned Idx = Call->getArgOperandNo(&U); |
| 220 | Value *ArgOp = Call->getArgOperand(Idx); |
| 221 | Type *ArgOpType = ArgOp->getType(); |
| 222 | |
| 223 | if (!Call->onlyReadsMemory(Idx) || !ArgOpType->isPointerTy()) |
| 224 | continue; |
| 225 | |
| 226 | auto *ConstVal = getConstantStackValue(Call, ArgOp, Solver); |
| 227 | if (!ConstVal) |
| 228 | continue; |
| 229 | |
| 230 | Value *GV = new GlobalVariable(M, ConstVal->getType(), true, |
| 231 | GlobalValue::InternalLinkage, ConstVal, |
| 232 | "funcspec.arg"); |
| 233 | if (ArgOpType != ConstVal->getType()) |
| 234 | GV = ConstantExpr::getBitCast(cast<Constant>(GV), ArgOpType); |
| 235 | |
| 236 | Call->setArgOperand(Idx, GV); |
| 237 | Changed = true; |
| 238 | } |
| 239 | |
| 240 | // Add the changed CallInst to Solver Worklist |
| 241 | if (Changed) |
| 242 | Solver.visitCall(*Call); |
| 243 | } |
| 244 | } |
| 245 | } |
| 246 | |
| 247 | // ssa_copy intrinsics are introduced by the SCCP solver. These intrinsics |
| 248 | // interfere with the constantArgPropagation optimization. |
| 249 | static void removeSSACopy(Function &F) { |
| 250 | for (BasicBlock &BB : F) { |
| 251 | for (Instruction &Inst : llvm::make_early_inc_range(BB)) { |
| 252 | auto *II = dyn_cast<IntrinsicInst>(&Inst); |
| 253 | if (!II) |
| 254 | continue; |
| 255 | if (II->getIntrinsicID() != Intrinsic::ssa_copy) |
| 256 | continue; |
| 257 | Inst.replaceAllUsesWith(II->getOperand(0)); |
| 258 | Inst.eraseFromParent(); |
| 259 | } |
| 260 | } |
| 261 | } |
| 262 | |
| 263 | static void removeSSACopy(Module &M) { |
| 264 | for (Function &F : M) |
| 265 | removeSSACopy(F); |
| 266 | } |
| 267 | |
| 268 | namespace { |
| 269 | class FunctionSpecializer { |
| 270 | |
| 271 | /// The IPSCCP Solver. |
| 272 | SCCPSolver &Solver; |
| 273 | |
| 274 | /// Analysis manager, needed to invalidate analyses. |
| 275 | FunctionAnalysisManager *FAM; |
| 276 | |
| 277 | /// Analyses used to help determine if a function should be specialized. |
| 278 | std::function<AssumptionCache &(Function &)> GetAC; |
| 279 | std::function<TargetTransformInfo &(Function &)> GetTTI; |
| 280 | std::function<TargetLibraryInfo &(Function &)> GetTLI; |
| 281 | |
| 282 | SmallPtrSet<Function *, 4> SpecializedFuncs; |
| 283 | SmallPtrSet<Function *, 4> FullySpecialized; |
| 284 | SmallVector<Instruction *> ReplacedWithConstant; |
| 285 | DenseMap<Function *, CodeMetrics> FunctionMetrics; |
| 286 | |
| 287 | public: |
| 288 | FunctionSpecializer(SCCPSolver &Solver, FunctionAnalysisManager *FAM, |
| 289 | std::function<AssumptionCache &(Function &)> GetAC, |
| 290 | std::function<TargetTransformInfo &(Function &)> GetTTI, |
| 291 | std::function<TargetLibraryInfo &(Function &)> GetTLI) |
| 292 | : Solver(Solver), FAM(FAM), GetAC(GetAC), GetTTI(GetTTI), GetTLI(GetTLI) { |
| 293 | } |
| 294 | |
| 295 | ~FunctionSpecializer() { |
| 296 | // Eliminate dead code. |
| 297 | removeDeadInstructions(); |
| 298 | removeDeadFunctions(); |
| 299 | } |
| 300 | |
| 301 | /// Attempt to specialize functions in the module to enable constant |
| 302 | /// propagation across function boundaries. |
| 303 | /// |
| 304 | /// \returns true if at least one function is specialized. |
| 305 | bool specializeFunctions(FuncList &Candidates, FuncList &WorkList) { |
| 306 | bool Changed = false; |
| 307 | for (auto *F : Candidates) { |
| 308 | if (!isCandidateFunction(F)) |
| 309 | continue; |
| 310 | |
| 311 | auto Cost = getSpecializationCost(F); |
| 312 | if (!Cost.isValid()) { |
| 313 | LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Invalid specialization cost.\n" ; } } while (false) |
| 314 | dbgs() << "FnSpecialization: Invalid specialization cost.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Invalid specialization cost.\n" ; } } while (false); |
| 315 | continue; |
| 316 | } |
| 317 | |
| 318 | LLVM_DEBUG(dbgs() << "FnSpecialization: Specialization cost for "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specialization cost for " << F->getName() << " is " << Cost << "\n"; } } while (false) |
| 319 | << F->getName() << " is " << Cost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specialization cost for " << F->getName() << " is " << Cost << "\n"; } } while (false); |
| 320 | |
| 321 | SmallVector<CallSpecBinding, 8> Specializations; |
| 322 | if (!findSpecializations(F, Cost, Specializations)) { |
| 323 | LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: No possible specializations found\n" ; } } while (false) |
| 324 | dbgs() << "FnSpecialization: No possible specializations found\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: No possible specializations found\n" ; } } while (false); |
| 325 | continue; |
| 326 | } |
| 327 | |
| 328 | Changed = true; |
| 329 | for (auto &Entry : Specializations) |
| 330 | specializeFunction(F, Entry.second, WorkList); |
| 331 | } |
| 332 | |
| 333 | updateSpecializedFuncs(Candidates, WorkList); |
| 334 | NumFuncSpecialized += NbFunctionsSpecialized; |
| 335 | return Changed; |
| 336 | } |
| 337 | |
| 338 | void removeDeadInstructions() { |
| 339 | for (auto *I : ReplacedWithConstant) { |
| 340 | LLVM_DEBUG(dbgs() << "FnSpecialization: Removing dead instruction " << *Ido { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Removing dead instruction " << *I << "\n"; } } while (false) |
| 341 | << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Removing dead instruction " << *I << "\n"; } } while (false); |
| 342 | I->eraseFromParent(); |
| 343 | } |
| 344 | ReplacedWithConstant.clear(); |
| 345 | } |
| 346 | |
| 347 | void removeDeadFunctions() { |
| 348 | for (auto *F : FullySpecialized) { |
| 349 | LLVM_DEBUG(dbgs() << "FnSpecialization: Removing dead function "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Removing dead function " << F->getName() << "\n"; } } while (false) |
| 350 | << F->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Removing dead function " << F->getName() << "\n"; } } while (false); |
| 351 | if (FAM) |
| 352 | FAM->clear(*F, F->getName()); |
| 353 | F->eraseFromParent(); |
| 354 | } |
| 355 | FullySpecialized.clear(); |
| 356 | } |
| 357 | |
| 358 | bool tryToReplaceWithConstant(Value *V) { |
| 359 | if (!V->getType()->isSingleValueType() || isa<CallBase>(V) || |
| 360 | V->user_empty()) |
| 361 | return false; |
| 362 | |
| 363 | const ValueLatticeElement &IV = Solver.getLatticeValueFor(V); |
| 364 | if (isOverdefined(IV)) |
| 365 | return false; |
| 366 | auto *Const = |
| 367 | isConstant(IV) ? Solver.getConstant(IV) : UndefValue::get(V->getType()); |
| 368 | |
| 369 | LLVM_DEBUG(dbgs() << "FnSpecialization: Replacing " << *Vdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Replacing " << *V << "\nFnSpecialization: with " << *Const << "\n"; } } while (false) |
| 370 | << "\nFnSpecialization: with " << *Const << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Replacing " << *V << "\nFnSpecialization: with " << *Const << "\n"; } } while (false); |
| 371 | |
| 372 | // Record uses of V to avoid visiting irrelevant uses of const later. |
| 373 | SmallVector<Instruction *> UseInsts; |
| 374 | for (auto *U : V->users()) |
| 375 | if (auto *I = dyn_cast<Instruction>(U)) |
| 376 | if (Solver.isBlockExecutable(I->getParent())) |
| 377 | UseInsts.push_back(I); |
| 378 | |
| 379 | V->replaceAllUsesWith(Const); |
| 380 | |
| 381 | for (auto *I : UseInsts) |
| 382 | Solver.visit(I); |
| 383 | |
| 384 | // Remove the instruction from Block and Solver. |
| 385 | if (auto *I = dyn_cast<Instruction>(V)) { |
| 386 | if (I->isSafeToRemove()) { |
| 387 | ReplacedWithConstant.push_back(I); |
| 388 | Solver.removeLatticeValueFor(I); |
| 389 | } |
| 390 | } |
| 391 | return true; |
| 392 | } |
| 393 | |
| 394 | private: |
| 395 | // The number of functions specialised, used for collecting statistics and |
| 396 | // also in the cost model. |
| 397 | unsigned NbFunctionsSpecialized = 0; |
| 398 | |
| 399 | // Compute the code metrics for function \p F. |
| 400 | CodeMetrics &analyzeFunction(Function *F) { |
| 401 | auto I = FunctionMetrics.insert({F, CodeMetrics()}); |
| 402 | CodeMetrics &Metrics = I.first->second; |
| 403 | if (I.second) { |
| 404 | // The code metrics were not cached. |
| 405 | SmallPtrSet<const Value *, 32> EphValues; |
| 406 | CodeMetrics::collectEphemeralValues(F, &(GetAC)(*F), EphValues); |
| 407 | for (BasicBlock &BB : *F) |
| 408 | Metrics.analyzeBasicBlock(&BB, (GetTTI)(*F), EphValues); |
| 409 | |
| 410 | LLVM_DEBUG(dbgs() << "FnSpecialization: Code size of function "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Code size of function " << F->getName() << " is " << Metrics.NumInsts << " instructions\n"; } } while (false) |
| 411 | << F->getName() << " is " << Metrics.NumInstsdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Code size of function " << F->getName() << " is " << Metrics.NumInsts << " instructions\n"; } } while (false) |
| 412 | << " instructions\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Code size of function " << F->getName() << " is " << Metrics.NumInsts << " instructions\n"; } } while (false); |
| 413 | } |
| 414 | return Metrics; |
| 415 | } |
| 416 | |
| 417 | /// Clone the function \p F and remove the ssa_copy intrinsics added by |
| 418 | /// the SCCPSolver in the cloned version. |
| 419 | Function *cloneCandidateFunction(Function *F, ValueToValueMapTy &Mappings) { |
| 420 | Function *Clone = CloneFunction(F, Mappings); |
| 421 | removeSSACopy(*Clone); |
| 422 | return Clone; |
| 423 | } |
| 424 | |
| 425 | /// This function decides whether it's worthwhile to specialize function |
| 426 | /// \p F based on the known constant values its arguments can take on. It |
| 427 | /// only discovers potential specialization opportunities without actually |
| 428 | /// applying them. |
| 429 | /// |
| 430 | /// \returns true if any specializations have been found. |
| 431 | bool findSpecializations(Function *F, InstructionCost Cost, |
| 432 | SmallVectorImpl<CallSpecBinding> &WorkList) { |
| 433 | // Get a list of interesting arguments. |
| 434 | SmallVector<Argument *, 4> Args; |
| 435 | for (Argument &Arg : F->args()) |
| 436 | if (isArgumentInteresting(&Arg)) |
| 437 | Args.push_back(&Arg); |
| 438 | |
| 439 | if (!Args.size()) |
| 440 | return false; |
| 441 | |
| 442 | // Find all the call sites for the function. |
| 443 | SpecializationMap Specializations; |
| 444 | for (User *U : F->users()) { |
| 445 | if (!isa<CallInst>(U) && !isa<InvokeInst>(U)) |
| 446 | continue; |
| 447 | auto &CS = *cast<CallBase>(U); |
| 448 | // If the call site has attribute minsize set, that callsite won't be |
| 449 | // specialized. |
| 450 | if (CS.hasFnAttr(Attribute::MinSize)) |
| 451 | continue; |
| 452 | |
| 453 | // If the parent of the call site will never be executed, we don't need |
| 454 | // to worry about the passed value. |
| 455 | if (!Solver.isBlockExecutable(CS.getParent())) |
| 456 | continue; |
| 457 | |
| 458 | // Examine arguments and create specialization candidates from call sites |
| 459 | // with constant arguments. |
| 460 | bool Added = false; |
| 461 | for (Argument *A : Args) { |
| 462 | Constant *C = getCandidateConstant(CS.getArgOperand(A->getArgNo())); |
| 463 | if (!C) |
| 464 | continue; |
| 465 | |
| 466 | if (!Added) { |
| 467 | Specializations[&CS] = {{}, 0 - Cost}; |
| 468 | Added = true; |
| 469 | } |
| 470 | |
| 471 | SpecializationInfo &S = Specializations.back().second; |
| 472 | S.Gain += getSpecializationBonus(A, C, Solver.getLoopInfo(*F)); |
| 473 | S.Args.push_back({A, C}); |
| 474 | } |
| 475 | Added = false; |
Value stored to 'Added' is never read | |
| 476 | } |
| 477 | |
| 478 | // Remove unprofitable specializations. |
| 479 | if (!ForceFunctionSpecialization) |
| 480 | Specializations.remove_if( |
| 481 | [](const auto &Entry) { return Entry.second.Gain <= 0; }); |
| 482 | |
| 483 | // Clear the MapVector and return the underlying vector. |
| 484 | WorkList = Specializations.takeVector(); |
| 485 | |
| 486 | // Sort the candidates in descending order. |
| 487 | llvm::stable_sort(WorkList, [](const auto &L, const auto &R) { |
| 488 | return L.second.Gain > R.second.Gain; |
| 489 | }); |
| 490 | |
| 491 | // Truncate the worklist to 'MaxClonesThreshold' candidates if necessary. |
| 492 | if (WorkList.size() > MaxClonesThreshold) { |
| 493 | LLVM_DEBUG(dbgs() << "FnSpecialization: Number of candidates exceed "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Number of candidates exceed " << "the maximum number of clones threshold.\n" << "FnSpecialization: Truncating worklist to " << MaxClonesThreshold << " candidates.\n"; } } while (false) |
| 494 | << "the maximum number of clones threshold.\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Number of candidates exceed " << "the maximum number of clones threshold.\n" << "FnSpecialization: Truncating worklist to " << MaxClonesThreshold << " candidates.\n"; } } while (false) |
| 495 | << "FnSpecialization: Truncating worklist to "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Number of candidates exceed " << "the maximum number of clones threshold.\n" << "FnSpecialization: Truncating worklist to " << MaxClonesThreshold << " candidates.\n"; } } while (false) |
| 496 | << MaxClonesThreshold << " candidates.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Number of candidates exceed " << "the maximum number of clones threshold.\n" << "FnSpecialization: Truncating worklist to " << MaxClonesThreshold << " candidates.\n"; } } while (false); |
| 497 | WorkList.erase(WorkList.begin() + MaxClonesThreshold, WorkList.end()); |
| 498 | } |
| 499 | |
| 500 | LLVM_DEBUG(dbgs() << "FnSpecialization: Specializations for function "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 501 | << F->getName() << "\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 502 | for (const auto &Entrydo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 503 | : WorkList) {do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 504 | dbgs() << "FnSpecialization: Gain = " << Entry.second.Gaindo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 505 | << "\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 506 | for (const ArgInfo &Arg : Entry.second.Args)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 507 | dbgs() << "FnSpecialization: FormalArg = "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 508 | << Arg.Formal->getNameOrAsOperand()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 509 | << ", ActualArg = "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 510 | << Arg.Actual->getNameOrAsOperand() << "\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false) |
| 511 | })do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Specializations for function " << F->getName() << "\n"; for (const auto & Entry : WorkList) { dbgs() << "FnSpecialization: Gain = " << Entry.second.Gain << "\n"; for (const ArgInfo &Arg : Entry.second.Args) dbgs() << "FnSpecialization: FormalArg = " << Arg.Formal->getNameOrAsOperand() << ", ActualArg = " << Arg.Actual->getNameOrAsOperand() << "\n"; } ; } } while (false); |
| 512 | |
| 513 | return !WorkList.empty(); |
| 514 | } |
| 515 | |
| 516 | bool isCandidateFunction(Function *F) { |
| 517 | // Do not specialize the cloned function again. |
| 518 | if (SpecializedFuncs.contains(F)) |
| 519 | return false; |
| 520 | |
| 521 | // If we're optimizing the function for size, we shouldn't specialize it. |
| 522 | if (F->hasOptSize() || |
| 523 | shouldOptimizeForSize(F, nullptr, nullptr, PGSOQueryType::IRPass)) |
| 524 | return false; |
| 525 | |
| 526 | // Exit if the function is not executable. There's no point in specializing |
| 527 | // a dead function. |
| 528 | if (!Solver.isBlockExecutable(&F->getEntryBlock())) |
| 529 | return false; |
| 530 | |
| 531 | // It wastes time to specialize a function which would get inlined finally. |
| 532 | if (F->hasFnAttribute(Attribute::AlwaysInline)) |
| 533 | return false; |
| 534 | |
| 535 | LLVM_DEBUG(dbgs() << "FnSpecialization: Try function: " << F->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Try function: " << F->getName() << "\n"; } } while (false) |
| 536 | << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Try function: " << F->getName() << "\n"; } } while (false); |
| 537 | return true; |
| 538 | } |
| 539 | |
| 540 | void specializeFunction(Function *F, SpecializationInfo &S, |
| 541 | FuncList &WorkList) { |
| 542 | ValueToValueMapTy Mappings; |
| 543 | Function *Clone = cloneCandidateFunction(F, Mappings); |
| 544 | |
| 545 | // Rewrite calls to the function so that they call the clone instead. |
| 546 | rewriteCallSites(Clone, S.Args, Mappings); |
| 547 | |
| 548 | // Initialize the lattice state of the arguments of the function clone, |
| 549 | // marking the argument on which we specialized the function constant |
| 550 | // with the given value. |
| 551 | Solver.markArgInFuncSpecialization(Clone, S.Args); |
| 552 | |
| 553 | // Mark all the specialized functions |
| 554 | WorkList.push_back(Clone); |
| 555 | NbFunctionsSpecialized++; |
| 556 | |
| 557 | // If the function has been completely specialized, the original function |
| 558 | // is no longer needed. Mark it unreachable. |
| 559 | if (F->getNumUses() == 0 || all_of(F->users(), [F](User *U) { |
| 560 | if (auto *CS = dyn_cast<CallBase>(U)) |
| 561 | return CS->getFunction() == F; |
| 562 | return false; |
| 563 | })) { |
| 564 | Solver.markFunctionUnreachable(F); |
| 565 | FullySpecialized.insert(F); |
| 566 | } |
| 567 | } |
| 568 | |
| 569 | /// Compute and return the cost of specializing function \p F. |
| 570 | InstructionCost getSpecializationCost(Function *F) { |
| 571 | CodeMetrics &Metrics = analyzeFunction(F); |
| 572 | // If the code metrics reveal that we shouldn't duplicate the function, we |
| 573 | // shouldn't specialize it. Set the specialization cost to Invalid. |
| 574 | // Or if the lines of codes implies that this function is easy to get |
| 575 | // inlined so that we shouldn't specialize it. |
| 576 | if (Metrics.notDuplicatable || !Metrics.NumInsts.isValid() || |
| 577 | (!ForceFunctionSpecialization && |
| 578 | !F->hasFnAttribute(Attribute::NoInline) && |
| 579 | Metrics.NumInsts < SmallFunctionThreshold)) |
| 580 | return InstructionCost::getInvalid(); |
| 581 | |
| 582 | // Otherwise, set the specialization cost to be the cost of all the |
| 583 | // instructions in the function and penalty for specializing more functions. |
| 584 | unsigned Penalty = NbFunctionsSpecialized + 1; |
| 585 | return Metrics.NumInsts * InlineConstants::getInstrCost() * Penalty; |
| 586 | } |
| 587 | |
| 588 | InstructionCost getUserBonus(User *U, llvm::TargetTransformInfo &TTI, |
| 589 | const LoopInfo &LI) { |
| 590 | auto *I = dyn_cast_or_null<Instruction>(U); |
| 591 | // If not an instruction we do not know how to evaluate. |
| 592 | // Keep minimum possible cost for now so that it doesnt affect |
| 593 | // specialization. |
| 594 | if (!I) |
| 595 | return std::numeric_limits<unsigned>::min(); |
| 596 | |
| 597 | InstructionCost Cost = |
| 598 | TTI.getInstructionCost(U, TargetTransformInfo::TCK_SizeAndLatency); |
| 599 | |
| 600 | // Increase the cost if it is inside the loop. |
| 601 | unsigned LoopDepth = LI.getLoopDepth(I->getParent()); |
| 602 | Cost *= std::pow((double)AvgLoopIterationCount, LoopDepth); |
| 603 | |
| 604 | // Traverse recursively if there are more uses. |
| 605 | // TODO: Any other instructions to be added here? |
| 606 | if (I->mayReadFromMemory() || I->isCast()) |
| 607 | for (auto *User : I->users()) |
| 608 | Cost += getUserBonus(User, TTI, LI); |
| 609 | |
| 610 | return Cost; |
| 611 | } |
| 612 | |
| 613 | /// Compute a bonus for replacing argument \p A with constant \p C. |
| 614 | InstructionCost getSpecializationBonus(Argument *A, Constant *C, |
| 615 | const LoopInfo &LI) { |
| 616 | Function *F = A->getParent(); |
| 617 | auto &TTI = (GetTTI)(*F); |
| 618 | LLVM_DEBUG(dbgs() << "FnSpecialization: Analysing bonus for constant: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Analysing bonus for constant: " << C->getNameOrAsOperand() << "\n"; } } while (false) |
| 619 | << C->getNameOrAsOperand() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Analysing bonus for constant: " << C->getNameOrAsOperand() << "\n"; } } while (false); |
| 620 | |
| 621 | InstructionCost TotalCost = 0; |
| 622 | for (auto *U : A->users()) { |
| 623 | TotalCost += getUserBonus(U, TTI, LI); |
| 624 | LLVM_DEBUG(dbgs() << "FnSpecialization: User cost ";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: User cost " ; TotalCost.print(dbgs()); dbgs() << " for: " << * U << "\n"; } } while (false) |
| 625 | TotalCost.print(dbgs()); dbgs() << " for: " << *U << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: User cost " ; TotalCost.print(dbgs()); dbgs() << " for: " << * U << "\n"; } } while (false); |
| 626 | } |
| 627 | |
| 628 | // The below heuristic is only concerned with exposing inlining |
| 629 | // opportunities via indirect call promotion. If the argument is not a |
| 630 | // (potentially casted) function pointer, give up. |
| 631 | Function *CalledFunction = dyn_cast<Function>(C->stripPointerCasts()); |
| 632 | if (!CalledFunction) |
| 633 | return TotalCost; |
| 634 | |
| 635 | // Get TTI for the called function (used for the inline cost). |
| 636 | auto &CalleeTTI = (GetTTI)(*CalledFunction); |
| 637 | |
| 638 | // Look at all the call sites whose called value is the argument. |
| 639 | // Specializing the function on the argument would allow these indirect |
| 640 | // calls to be promoted to direct calls. If the indirect call promotion |
| 641 | // would likely enable the called function to be inlined, specializing is a |
| 642 | // good idea. |
| 643 | int Bonus = 0; |
| 644 | for (User *U : A->users()) { |
| 645 | if (!isa<CallInst>(U) && !isa<InvokeInst>(U)) |
| 646 | continue; |
| 647 | auto *CS = cast<CallBase>(U); |
| 648 | if (CS->getCalledOperand() != A) |
| 649 | continue; |
| 650 | |
| 651 | // Get the cost of inlining the called function at this call site. Note |
| 652 | // that this is only an estimate. The called function may eventually |
| 653 | // change in a way that leads to it not being inlined here, even though |
| 654 | // inlining looks profitable now. For example, one of its called |
| 655 | // functions may be inlined into it, making the called function too large |
| 656 | // to be inlined into this call site. |
| 657 | // |
| 658 | // We apply a boost for performing indirect call promotion by increasing |
| 659 | // the default threshold by the threshold for indirect calls. |
| 660 | auto Params = getInlineParams(); |
| 661 | Params.DefaultThreshold += InlineConstants::IndirectCallThreshold; |
| 662 | InlineCost IC = |
| 663 | getInlineCost(*CS, CalledFunction, Params, CalleeTTI, GetAC, GetTLI); |
| 664 | |
| 665 | // We clamp the bonus for this call to be between zero and the default |
| 666 | // threshold. |
| 667 | if (IC.isAlways()) |
| 668 | Bonus += Params.DefaultThreshold; |
| 669 | else if (IC.isVariable() && IC.getCostDelta() > 0) |
| 670 | Bonus += IC.getCostDelta(); |
| 671 | |
| 672 | LLVM_DEBUG(dbgs() << "FnSpecialization: Inlining bonus " << Bonusdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Inlining bonus " << Bonus << " for user " << *U << "\n" ; } } while (false) |
| 673 | << " for user " << *U << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Inlining bonus " << Bonus << " for user " << *U << "\n" ; } } while (false); |
| 674 | } |
| 675 | |
| 676 | return TotalCost + Bonus; |
| 677 | } |
| 678 | |
| 679 | /// Determine if it is possible to specialise the function for constant values |
| 680 | /// of the formal parameter \p A. |
| 681 | bool isArgumentInteresting(Argument *A) { |
| 682 | // No point in specialization if the argument is unused. |
| 683 | if (A->user_empty()) |
| 684 | return false; |
| 685 | |
| 686 | // For now, don't attempt to specialize functions based on the values of |
| 687 | // composite types. |
| 688 | Type *ArgTy = A->getType(); |
| 689 | if (!ArgTy->isSingleValueType()) |
| 690 | return false; |
| 691 | |
| 692 | // Specialization of integer and floating point types needs to be explicitly |
| 693 | // enabled. |
| 694 | if (!EnableSpecializationForLiteralConstant && |
| 695 | (ArgTy->isIntegerTy() || ArgTy->isFloatingPointTy())) |
| 696 | return false; |
| 697 | |
| 698 | // SCCP solver does not record an argument that will be constructed on |
| 699 | // stack. |
| 700 | if (A->hasByValAttr() && !A->getParent()->onlyReadsMemory()) |
| 701 | return false; |
| 702 | |
| 703 | // Check the lattice value and decide if we should attemt to specialize, |
| 704 | // based on this argument. No point in specialization, if the lattice value |
| 705 | // is already a constant. |
| 706 | const ValueLatticeElement &LV = Solver.getLatticeValueFor(A); |
| 707 | if (LV.isUnknownOrUndef() || LV.isConstant() || |
| 708 | (LV.isConstantRange() && LV.getConstantRange().isSingleElement())) { |
| 709 | LLVM_DEBUG(dbgs() << "FnSpecialization: Nothing to do, argument "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Nothing to do, argument " << A->getNameOrAsOperand() << " is already constant\n" ; } } while (false) |
| 710 | << A->getNameOrAsOperand() << " is already constant\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Nothing to do, argument " << A->getNameOrAsOperand() << " is already constant\n" ; } } while (false); |
| 711 | return false; |
| 712 | } |
| 713 | |
| 714 | return true; |
| 715 | } |
| 716 | |
| 717 | /// Check if the valuy \p V (an actual argument) is a constant or can only |
| 718 | /// have a constant value. Return that constant. |
| 719 | Constant *getCandidateConstant(Value *V) { |
| 720 | if (isa<PoisonValue>(V)) |
| 721 | return nullptr; |
| 722 | |
| 723 | // TrackValueOfGlobalVariable only tracks scalar global variables. |
| 724 | if (auto *GV = dyn_cast<GlobalVariable>(V)) { |
| 725 | // Check if we want to specialize on the address of non-constant |
| 726 | // global values. |
| 727 | if (!GV->isConstant() && !SpecializeOnAddresses) |
| 728 | return nullptr; |
| 729 | |
| 730 | if (!GV->getValueType()->isSingleValueType()) |
| 731 | return nullptr; |
| 732 | } |
| 733 | |
| 734 | // Select for possible specialisation values that are constants or |
| 735 | // are deduced to be constants or constant ranges with a single element. |
| 736 | Constant *C = dyn_cast<Constant>(V); |
| 737 | if (!C) { |
| 738 | const ValueLatticeElement &LV = Solver.getLatticeValueFor(V); |
| 739 | if (LV.isConstant()) |
| 740 | C = LV.getConstant(); |
| 741 | else if (LV.isConstantRange() && |
| 742 | LV.getConstantRange().isSingleElement()) { |
| 743 | assert(V->getType()->isIntegerTy() && "Non-integral constant range")(static_cast <bool> (V->getType()->isIntegerTy() && "Non-integral constant range") ? void (0) : __assert_fail ("V->getType()->isIntegerTy() && \"Non-integral constant range\"" , "llvm/lib/Transforms/IPO/FunctionSpecialization.cpp", 743, __extension__ __PRETTY_FUNCTION__)); |
| 744 | C = Constant::getIntegerValue( |
| 745 | V->getType(), *LV.getConstantRange().getSingleElement()); |
| 746 | } else |
| 747 | return nullptr; |
| 748 | } |
| 749 | |
| 750 | LLVM_DEBUG(dbgs() << "FnSpecialization: Found interesting argument "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Found interesting argument " << V->getNameOrAsOperand() << "\n"; } } while (false) |
| 751 | << V->getNameOrAsOperand() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Found interesting argument " << V->getNameOrAsOperand() << "\n"; } } while (false); |
| 752 | |
| 753 | return C; |
| 754 | } |
| 755 | |
| 756 | /// Rewrite calls to function \p F to call function \p Clone instead. |
| 757 | /// |
| 758 | /// This function modifies calls to function \p F as long as the actual |
| 759 | /// arguments match those in \p Args. Note that for recursive calls we |
| 760 | /// need to compare against the cloned formal arguments. |
| 761 | /// |
| 762 | /// Callsites that have been marked with the MinSize function attribute won't |
| 763 | /// be specialized and rewritten. |
| 764 | void rewriteCallSites(Function *Clone, const SmallVectorImpl<ArgInfo> &Args, |
| 765 | ValueToValueMapTy &Mappings) { |
| 766 | assert(!Args.empty() && "Specialization without arguments")(static_cast <bool> (!Args.empty() && "Specialization without arguments" ) ? void (0) : __assert_fail ("!Args.empty() && \"Specialization without arguments\"" , "llvm/lib/Transforms/IPO/FunctionSpecialization.cpp", 766, __extension__ __PRETTY_FUNCTION__)); |
| 767 | Function *F = Args[0].Formal->getParent(); |
| 768 | |
| 769 | SmallVector<CallBase *, 8> CallSitesToRewrite; |
| 770 | for (auto *U : F->users()) { |
| 771 | if (!isa<CallInst>(U) && !isa<InvokeInst>(U)) |
| 772 | continue; |
| 773 | auto &CS = *cast<CallBase>(U); |
| 774 | if (!CS.getCalledFunction() || CS.getCalledFunction() != F) |
| 775 | continue; |
| 776 | CallSitesToRewrite.push_back(&CS); |
| 777 | } |
| 778 | |
| 779 | LLVM_DEBUG(dbgs() << "FnSpecialization: Replacing call sites of "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Replacing call sites of " << F->getName() << " with " << Clone-> getName() << "\n"; } } while (false) |
| 780 | << F->getName() << " with " << Clone->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Replacing call sites of " << F->getName() << " with " << Clone-> getName() << "\n"; } } while (false); |
| 781 | |
| 782 | for (auto *CS : CallSitesToRewrite) { |
| 783 | LLVM_DEBUG(dbgs() << "FnSpecialization: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: " << CS->getFunction()->getName() << " ->" << *CS << "\n"; } } while (false) |
| 784 | << CS->getFunction()->getName() << " ->" << *CSdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: " << CS->getFunction()->getName() << " ->" << *CS << "\n"; } } while (false) |
| 785 | << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: " << CS->getFunction()->getName() << " ->" << *CS << "\n"; } } while (false); |
| 786 | if (/* recursive call */ |
| 787 | (CS->getFunction() == Clone && |
| 788 | all_of(Args, |
| 789 | [CS, &Mappings](const ArgInfo &Arg) { |
| 790 | unsigned ArgNo = Arg.Formal->getArgNo(); |
| 791 | return CS->getArgOperand(ArgNo) == Mappings[Arg.Formal]; |
| 792 | })) || |
| 793 | /* normal call */ |
| 794 | all_of(Args, [CS](const ArgInfo &Arg) { |
| 795 | unsigned ArgNo = Arg.Formal->getArgNo(); |
| 796 | return CS->getArgOperand(ArgNo) == Arg.Actual; |
| 797 | })) { |
| 798 | CS->setCalledFunction(Clone); |
| 799 | Solver.markOverdefined(CS); |
| 800 | } |
| 801 | } |
| 802 | } |
| 803 | |
| 804 | void updateSpecializedFuncs(FuncList &Candidates, FuncList &WorkList) { |
| 805 | for (auto *F : WorkList) { |
| 806 | SpecializedFuncs.insert(F); |
| 807 | |
| 808 | // Initialize the state of the newly created functions, marking them |
| 809 | // argument-tracked and executable. |
| 810 | if (F->hasExactDefinition() && !F->hasFnAttribute(Attribute::Naked)) |
| 811 | Solver.addTrackedFunction(F); |
| 812 | |
| 813 | Solver.addArgumentTrackedFunction(F); |
| 814 | Candidates.push_back(F); |
| 815 | Solver.markBlockExecutable(&F->front()); |
| 816 | |
| 817 | // Replace the function arguments for the specialized functions. |
| 818 | for (Argument &Arg : F->args()) |
| 819 | if (!Arg.use_empty() && tryToReplaceWithConstant(&Arg)) |
| 820 | LLVM_DEBUG(dbgs() << "FnSpecialization: Replaced constant argument: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Replaced constant argument: " << Arg.getNameOrAsOperand() << "\n"; } } while ( false) |
| 821 | << Arg.getNameOrAsOperand() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Replaced constant argument: " << Arg.getNameOrAsOperand() << "\n"; } } while ( false); |
| 822 | } |
| 823 | } |
| 824 | }; |
| 825 | } // namespace |
| 826 | |
| 827 | bool llvm::runFunctionSpecialization( |
| 828 | Module &M, FunctionAnalysisManager *FAM, const DataLayout &DL, |
| 829 | std::function<TargetLibraryInfo &(Function &)> GetTLI, |
| 830 | std::function<TargetTransformInfo &(Function &)> GetTTI, |
| 831 | std::function<AssumptionCache &(Function &)> GetAC, |
| 832 | function_ref<AnalysisResultsForFn(Function &)> GetAnalysis) { |
| 833 | SCCPSolver Solver(DL, GetTLI, M.getContext()); |
| 834 | FunctionSpecializer FS(Solver, FAM, GetAC, GetTTI, GetTLI); |
| 835 | bool Changed = false; |
| 836 | |
| 837 | // Loop over all functions, marking arguments to those with their addresses |
| 838 | // taken or that are external as overdefined. |
| 839 | for (Function &F : M) { |
| 840 | if (F.isDeclaration()) |
| 841 | continue; |
| 842 | if (F.hasFnAttribute(Attribute::NoDuplicate)) |
| 843 | continue; |
| 844 | |
| 845 | LLVM_DEBUG(dbgs() << "\nFnSpecialization: Analysing decl: " << F.getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "\nFnSpecialization: Analysing decl: " << F.getName() << "\n"; } } while (false) |
| 846 | << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "\nFnSpecialization: Analysing decl: " << F.getName() << "\n"; } } while (false); |
| 847 | Solver.addAnalysis(F, GetAnalysis(F)); |
| 848 | |
| 849 | // Determine if we can track the function's arguments. If so, add the |
| 850 | // function to the solver's set of argument-tracked functions. |
| 851 | if (canTrackArgumentsInterprocedurally(&F)) { |
| 852 | LLVM_DEBUG(dbgs() << "FnSpecialization: Can track arguments\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Can track arguments\n" ; } } while (false); |
| 853 | Solver.addArgumentTrackedFunction(&F); |
| 854 | continue; |
| 855 | } else { |
| 856 | LLVM_DEBUG(dbgs() << "FnSpecialization: Can't track arguments!\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Can't track arguments!\n" << "FnSpecialization: Doesn't have local linkage, or " << "has its address taken\n"; } } while (false) |
| 857 | << "FnSpecialization: Doesn't have local linkage, or "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Can't track arguments!\n" << "FnSpecialization: Doesn't have local linkage, or " << "has its address taken\n"; } } while (false) |
| 858 | << "has its address taken\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Can't track arguments!\n" << "FnSpecialization: Doesn't have local linkage, or " << "has its address taken\n"; } } while (false); |
| 859 | } |
| 860 | |
| 861 | // Assume the function is called. |
| 862 | Solver.markBlockExecutable(&F.front()); |
| 863 | |
| 864 | // Assume nothing about the incoming arguments. |
| 865 | for (Argument &AI : F.args()) |
| 866 | Solver.markOverdefined(&AI); |
| 867 | } |
| 868 | |
| 869 | // Determine if we can track any of the module's global variables. If so, add |
| 870 | // the global variables we can track to the solver's set of tracked global |
| 871 | // variables. |
| 872 | for (GlobalVariable &G : M.globals()) { |
| 873 | G.removeDeadConstantUsers(); |
| 874 | if (canTrackGlobalVariableInterprocedurally(&G)) |
| 875 | Solver.trackValueOfGlobalVariable(&G); |
| 876 | } |
| 877 | |
| 878 | auto &TrackedFuncs = Solver.getArgumentTrackedFunctions(); |
| 879 | SmallVector<Function *, 16> FuncDecls(TrackedFuncs.begin(), |
| 880 | TrackedFuncs.end()); |
| 881 | |
| 882 | // No tracked functions, so nothing to do: don't run the solver and remove |
| 883 | // the ssa_copy intrinsics that may have been introduced. |
| 884 | if (TrackedFuncs.empty()) { |
| 885 | removeSSACopy(M); |
| 886 | return false; |
| 887 | } |
| 888 | |
| 889 | // Solve for constants. |
| 890 | auto RunSCCPSolver = [&](auto &WorkList) { |
| 891 | bool ResolvedUndefs = true; |
| 892 | |
| 893 | while (ResolvedUndefs) { |
| 894 | // Not running the solver unnecessary is checked in regression test |
| 895 | // nothing-to-do.ll, so if this debug message is changed, this regression |
| 896 | // test needs updating too. |
| 897 | LLVM_DEBUG(dbgs() << "FnSpecialization: Running solver\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Running solver\n" ; } } while (false); |
| 898 | |
| 899 | Solver.solve(); |
| 900 | LLVM_DEBUG(dbgs() << "FnSpecialization: Resolving undefs\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Resolving undefs\n" ; } } while (false); |
| 901 | ResolvedUndefs = false; |
| 902 | for (Function *F : WorkList) |
| 903 | if (Solver.resolvedUndefsIn(*F)) |
| 904 | ResolvedUndefs = true; |
| 905 | } |
| 906 | |
| 907 | for (auto *F : WorkList) { |
| 908 | for (BasicBlock &BB : *F) { |
| 909 | if (!Solver.isBlockExecutable(&BB)) |
| 910 | continue; |
| 911 | // FIXME: The solver may make changes to the function here, so set |
| 912 | // Changed, even if later function specialization does not trigger. |
| 913 | for (auto &I : make_early_inc_range(BB)) |
| 914 | Changed |= FS.tryToReplaceWithConstant(&I); |
| 915 | } |
| 916 | } |
| 917 | }; |
| 918 | |
| 919 | #ifndef NDEBUG |
| 920 | LLVM_DEBUG(dbgs() << "FnSpecialization: Worklist fn decls:\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Worklist fn decls:\n" ; } } while (false); |
| 921 | for (auto *F : FuncDecls) |
| 922 | LLVM_DEBUG(dbgs() << "FnSpecialization: *) " << F->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: *) " << F->getName() << "\n"; } } while (false); |
| 923 | #endif |
| 924 | |
| 925 | // Initially resolve the constants in all the argument tracked functions. |
| 926 | RunSCCPSolver(FuncDecls); |
| 927 | |
| 928 | SmallVector<Function *, 8> WorkList; |
| 929 | unsigned I = 0; |
| 930 | while (FuncSpecializationMaxIters != I++ && |
| 931 | FS.specializeFunctions(FuncDecls, WorkList)) { |
| 932 | LLVM_DEBUG(dbgs() << "FnSpecialization: Finished iteration " << I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Finished iteration " << I << "\n"; } } while (false); |
| 933 | |
| 934 | // Run the solver for the specialized functions. |
| 935 | RunSCCPSolver(WorkList); |
| 936 | |
| 937 | // Replace some unresolved constant arguments. |
| 938 | constantArgPropagation(FuncDecls, M, Solver); |
| 939 | |
| 940 | WorkList.clear(); |
| 941 | Changed = true; |
| 942 | } |
| 943 | |
| 944 | LLVM_DEBUG(dbgs() << "FnSpecialization: Number of specializations = "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Number of specializations = " << NumFuncSpecialized << "\n"; } } while (false) |
| 945 | << NumFuncSpecialized << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("function-specialization")) { dbgs() << "FnSpecialization: Number of specializations = " << NumFuncSpecialized << "\n"; } } while (false); |
| 946 | |
| 947 | // Remove any ssa_copy intrinsics that may have been introduced. |
| 948 | removeSSACopy(M); |
| 949 | return Changed; |
| 950 | } |