1 //===- IROutliner.h - Extract similar IR regions into functions ------------==// 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 // \file 10 // The interface file for the IROutliner which is used by the IROutliner Pass. 11 // 12 // The outliner uses the IRSimilarityIdentifier to identify the similar regions 13 // of code. It evaluates each set of IRSimilarityCandidates with an estimate of 14 // whether it will provide code size reduction. Each region is extracted using 15 // the code extractor. These extracted functions are consolidated into a single 16 // function and called from the extracted call site. 17 // 18 // For example: 19 // \code 20 // %1 = add i32 %a, %b 21 // %2 = add i32 %b, %a 22 // %3 = add i32 %b, %a 23 // %4 = add i32 %a, %b 24 // \endcode 25 // would become function 26 // \code 27 // define internal void outlined_ir_function(i32 %0, i32 %1) { 28 // %1 = add i32 %0, %1 29 // %2 = add i32 %1, %0 30 // ret void 31 // } 32 // \endcode 33 // with calls: 34 // \code 35 // call void outlined_ir_function(i32 %a, i32 %b) 36 // call void outlined_ir_function(i32 %b, i32 %a) 37 // \endcode 38 // 39 //===----------------------------------------------------------------------===// 40 41 #ifndef LLVM_TRANSFORMS_IPO_IROUTLINER_H 42 #define LLVM_TRANSFORMS_IPO_IROUTLINER_H 43 44 #include "llvm/Analysis/IRSimilarityIdentifier.h" 45 #include "llvm/IR/PassManager.h" 46 #include "llvm/IR/ValueMap.h" 47 #include "llvm/Support/InstructionCost.h" 48 #include "llvm/Transforms/Utils/CodeExtractor.h" 49 #include <set> 50 51 struct OutlinableGroup; 52 53 namespace llvm { 54 using namespace IRSimilarity; 55 56 class Module; 57 class TargetTransformInfo; 58 class OptimizationRemarkEmitter; 59 60 /// The OutlinableRegion holds all the information for a specific region, or 61 /// sequence of instructions. This includes what values need to be hoisted to 62 /// arguments from the extracted function, inputs and outputs to the region, and 63 /// mapping from the extracted function arguments to overall function arguments. 64 struct OutlinableRegion { 65 /// Describes the region of code. 66 IRSimilarityCandidate *Candidate; 67 68 /// If this region is outlined, the front and back IRInstructionData could 69 /// potentially become invalidated if the only new instruction is a call. 70 /// This ensures that we replace in the instruction in the IRInstructionData. 71 IRInstructionData *NewFront = nullptr; 72 IRInstructionData *NewBack = nullptr; 73 74 /// The number of extracted inputs from the CodeExtractor. 75 unsigned NumExtractedInputs; 76 77 /// The corresponding BasicBlock with the appropriate stores for this 78 /// OutlinableRegion in the overall function. 79 unsigned OutputBlockNum; 80 81 /// Mapping the extracted argument number to the argument number in the 82 /// overall function. Since there will be inputs, such as elevated constants 83 /// that are not the same in each region in a SimilarityGroup, or values that 84 /// cannot be sunk into the extracted section in every region, we must keep 85 /// track of which extracted argument maps to which overall argument. 86 DenseMap<unsigned, unsigned> ExtractedArgToAgg; 87 DenseMap<unsigned, unsigned> AggArgToExtracted; 88 89 /// Mapping of the argument number in the deduplicated function 90 /// to a given constant, which is used when creating the arguments to the call 91 /// to the newly created deduplicated function. This is handled separately 92 /// since the CodeExtractor does not recognize constants. 93 DenseMap<unsigned, Constant *> AggArgToConstant; 94 95 /// The global value numbers that are used as outputs for this section. Once 96 /// extracted, each output will be stored to an output register. This 97 /// documents the global value numbers that are used in this pattern. 98 SmallVector<unsigned, 4> GVNStores; 99 100 /// Used to create an outlined function. 101 CodeExtractor *CE = nullptr; 102 103 /// The call site of the extracted region. 104 CallInst *Call = nullptr; 105 106 /// The function for the extracted region. 107 Function *ExtractedFunction = nullptr; 108 109 /// Flag for whether we have split out the IRSimilarityCanidate. That is, 110 /// make the region contained the IRSimilarityCandidate its own BasicBlock. 111 bool CandidateSplit = false; 112 113 /// Flag for whether we should not consider this region for extraction. 114 bool IgnoreRegion = false; 115 116 /// The BasicBlock that is before the start of the region BasicBlock, 117 /// only defined when the region has been split. 118 BasicBlock *PrevBB = nullptr; 119 120 /// The BasicBlock that contains the starting instruction of the region. 121 BasicBlock *StartBB = nullptr; 122 123 /// The BasicBlock that contains the ending instruction of the region. 124 BasicBlock *EndBB = nullptr; 125 126 /// The BasicBlock that is after the start of the region BasicBlock, 127 /// only defined when the region has been split. 128 BasicBlock *FollowBB = nullptr; 129 130 /// The Outlinable Group that contains this region and structurally similar 131 /// regions to this region. 132 OutlinableGroup *Parent = nullptr; 133 134 OutlinableRegion(IRSimilarityCandidate &C, OutlinableGroup &Group) 135 : Candidate(&C), Parent(&Group) { 136 StartBB = C.getStartBB(); 137 EndBB = C.getEndBB(); 138 } 139 140 /// For the contained region, split the parent BasicBlock at the starting and 141 /// ending instructions of the contained IRSimilarityCandidate. 142 void splitCandidate(); 143 144 /// For the contained region, reattach the BasicBlock at the starting and 145 /// ending instructions of the contained IRSimilarityCandidate, or if the 146 /// function has been extracted, the start and end of the BasicBlock 147 /// containing the called function. 148 void reattachCandidate(); 149 150 /// Get the size of the code removed from the region. 151 /// 152 /// \param [in] TTI - The TargetTransformInfo for the parent function. 153 /// \returns the code size of the region 154 InstructionCost getBenefit(TargetTransformInfo &TTI); 155 }; 156 157 /// This class is a pass that identifies similarity in a Module, extracts 158 /// instances of the similarity, and then consolidating the similar regions 159 /// in an effort to reduce code size. It uses the IRSimilarityIdentifier pass 160 /// to identify the similar regions of code, and then extracts the similar 161 /// sections into a single function. See the above for an example as to 162 /// how code is extracted and consolidated into a single function. 163 class IROutliner { 164 public: 165 IROutliner(function_ref<TargetTransformInfo &(Function &)> GTTI, 166 function_ref<IRSimilarityIdentifier &(Module &)> GIRSI, 167 function_ref<OptimizationRemarkEmitter &(Function &)> GORE) 168 : getTTI(GTTI), getIRSI(GIRSI), getORE(GORE) {} 169 bool run(Module &M); 170 171 private: 172 /// Find repeated similar code sequences in \p M and outline them into new 173 /// Functions. 174 /// 175 /// \param [in] M - The module to outline from. 176 /// \returns The number of Functions created. 177 unsigned doOutline(Module &M); 178 179 /// Remove all the IRSimilarityCandidates from \p CandidateVec that have 180 /// instructions contained in a previously outlined region and put the 181 /// remaining regions in \p CurrentGroup. 182 /// 183 /// \param [in] CandidateVec - List of similarity candidates for regions with 184 /// the same similarity structure. 185 /// \param [in,out] CurrentGroup - Contains the potential sections to 186 /// be outlined. 187 void 188 pruneIncompatibleRegions(std::vector<IRSimilarityCandidate> &CandidateVec, 189 OutlinableGroup &CurrentGroup); 190 191 /// Create the function based on the overall types found in the current 192 /// regions being outlined. 193 /// 194 /// \param M - The module to outline from. 195 /// \param [in,out] CG - The OutlinableGroup for the regions to be outlined. 196 /// \param [in] FunctionNameSuffix - How many functions have we previously 197 /// created. 198 /// \returns the newly created function. 199 Function *createFunction(Module &M, OutlinableGroup &CG, 200 unsigned FunctionNameSuffix); 201 202 /// Identify the needed extracted inputs in a section, and add to the overall 203 /// function if needed. 204 /// 205 /// \param [in] M - The module to outline from. 206 /// \param [in,out] Region - The region to be extracted. 207 /// \param [in] NotSame - The global value numbers of the Values in the region 208 /// that do not have the same Constant in each strucutrally similar region. 209 void findAddInputsOutputs(Module &M, OutlinableRegion &Region, 210 DenseSet<unsigned> &NotSame); 211 212 /// Find the number of instructions that will be removed by extracting the 213 /// OutlinableRegions in \p CurrentGroup. 214 /// 215 /// \param [in] CurrentGroup - The collection of OutlinableRegions to be 216 /// analyzed. 217 /// \returns the number of outlined instructions across all regions. 218 InstructionCost findBenefitFromAllRegions(OutlinableGroup &CurrentGroup); 219 220 /// Find the number of instructions that will be added by reloading arguments. 221 /// 222 /// \param [in] CurrentGroup - The collection of OutlinableRegions to be 223 /// analyzed. 224 /// \returns the number of added reload instructions across all regions. 225 InstructionCost findCostOutputReloads(OutlinableGroup &CurrentGroup); 226 227 /// Find the cost and the benefit of \p CurrentGroup and save it back to 228 /// \p CurrentGroup. 229 /// 230 /// \param [in] M - The module being analyzed 231 /// \param [in,out] CurrentGroup - The overall outlined section 232 void findCostBenefit(Module &M, OutlinableGroup &CurrentGroup); 233 234 /// Update the output mapping based on the load instruction, and the outputs 235 /// of the extracted function. 236 /// 237 /// \param Region - The region extracted 238 /// \param Outputs - The outputs from the extracted function. 239 /// \param LI - The load instruction used to update the mapping. 240 void updateOutputMapping(OutlinableRegion &Region, 241 ArrayRef<Value *> Outputs, LoadInst *LI); 242 243 /// Extract \p Region into its own function. 244 /// 245 /// \param [in] Region - The region to be extracted into its own function. 246 /// \returns True if it was successfully outlined. 247 bool extractSection(OutlinableRegion &Region); 248 249 /// For the similarities found, and the extracted sections, create a single 250 /// outlined function with appropriate output blocks as necessary. 251 /// 252 /// \param [in] M - The module to outline from 253 /// \param [in] CurrentGroup - The set of extracted sections to consolidate. 254 /// \param [in,out] FuncsToRemove - List of functions to remove from the 255 /// module after outlining is completed. 256 /// \param [in,out] OutlinedFunctionNum - the number of new outlined 257 /// functions. 258 void deduplicateExtractedSections(Module &M, OutlinableGroup &CurrentGroup, 259 std::vector<Function *> &FuncsToRemove, 260 unsigned &OutlinedFunctionNum); 261 262 /// If true, enables us to outline from functions that have LinkOnceFromODR 263 /// linkages. 264 bool OutlineFromLinkODRs = false; 265 266 /// If false, we do not worry if the cost is greater than the benefit. This 267 /// is for debugging and testing, so that we can test small cases to ensure 268 /// that the outlining is being done correctly. 269 bool CostModel = true; 270 271 /// The set of outlined Instructions, identified by their location in the 272 /// sequential ordering of instructions in a Module. 273 DenseSet<unsigned> Outlined; 274 275 /// TargetTransformInfo lambda for target specific information. 276 function_ref<TargetTransformInfo &(Function &)> getTTI; 277 278 /// A mapping from newly created reloaded output values to the original value. 279 /// If an value is replace by an output from an outlined region, this maps 280 /// that Value, back to its original Value. 281 DenseMap<Value *, Value *> OutputMappings; 282 283 /// IRSimilarityIdentifier lambda to retrieve IRSimilarityIdentifier. 284 function_ref<IRSimilarityIdentifier &(Module &)> getIRSI; 285 286 /// The optimization remark emitter for the pass. 287 function_ref<OptimizationRemarkEmitter &(Function &)> getORE; 288 289 /// The memory allocator used to allocate the CodeExtractors. 290 SpecificBumpPtrAllocator<CodeExtractor> ExtractorAllocator; 291 292 /// The memory allocator used to allocate the OutlinableRegions. 293 SpecificBumpPtrAllocator<OutlinableRegion> RegionAllocator; 294 295 /// The memory allocator used to allocate new IRInstructionData. 296 SpecificBumpPtrAllocator<IRInstructionData> InstDataAllocator; 297 298 /// Custom InstVisitor to classify different instructions for whether it can 299 /// be analyzed for similarity. This is needed as there may be instruction we 300 /// can identify as having similarity, but are more complicated to outline. 301 struct InstructionAllowed : public InstVisitor<InstructionAllowed, bool> { 302 InstructionAllowed() {} 303 304 // TODO: Determine a scheme to resolve when the label is similar enough. 305 bool visitBranchInst(BranchInst &BI) { return false; } 306 // TODO: Determine a scheme to resolve when the labels are similar enough. 307 bool visitPHINode(PHINode &PN) { return false; } 308 // TODO: Handle allocas. 309 bool visitAllocaInst(AllocaInst &AI) { return false; } 310 // VAArg instructions are not allowed since this could cause difficulty when 311 // differentiating between different sets of variable instructions in 312 // the deduplicated outlined regions. 313 bool visitVAArgInst(VAArgInst &VI) { return false; } 314 // We exclude all exception handling cases since they are so context 315 // dependent. 316 bool visitLandingPadInst(LandingPadInst &LPI) { return false; } 317 bool visitFuncletPadInst(FuncletPadInst &FPI) { return false; } 318 // DebugInfo should be included in the regions, but should not be 319 // analyzed for similarity as it has no bearing on the outcome of the 320 // program. 321 bool visitDbgInfoIntrinsic(DbgInfoIntrinsic &DII) { return true; } 322 // TODO: Handle specific intrinsics individually from those that can be 323 // handled. 324 bool IntrinsicInst(IntrinsicInst &II) { return false; } 325 // We only handle CallInsts that are not indirect, since we cannot guarantee 326 // that they have a name in these cases. 327 bool visitCallInst(CallInst &CI) { 328 Function *F = CI.getCalledFunction(); 329 if (!F || CI.isIndirectCall() || !F->hasName()) 330 return false; 331 return true; 332 } 333 // TODO: Handle FreezeInsts. Since a frozen value could be frozen inside 334 // the outlined region, and then returned as an output, this will have to be 335 // handled differently. 336 bool visitFreezeInst(FreezeInst &CI) { return false; } 337 // TODO: We do not current handle similarity that changes the control flow. 338 bool visitInvokeInst(InvokeInst &II) { return false; } 339 // TODO: We do not current handle similarity that changes the control flow. 340 bool visitCallBrInst(CallBrInst &CBI) { return false; } 341 // TODO: Handle interblock similarity. 342 bool visitTerminator(Instruction &I) { return false; } 343 bool visitInstruction(Instruction &I) { return true; } 344 }; 345 346 /// A InstVisitor used to exclude certain instructions from being outlined. 347 InstructionAllowed InstructionClassifier; 348 }; 349 350 /// Pass to outline similar regions. 351 class IROutlinerPass : public PassInfoMixin<IROutlinerPass> { 352 public: 353 PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM); 354 }; 355 356 } // end namespace llvm 357 358 #endif // LLVM_TRANSFORMS_IPO_IROUTLINER_H 359