1 //===- Transform/Utils/CodeExtractor.h - Code extraction util ---*- C++ -*-===// 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 // A utility to support extracting code from one function into its own 10 // stand-alone function. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_TRANSFORMS_UTILS_CODEEXTRACTOR_H 15 #define LLVM_TRANSFORMS_UTILS_CODEEXTRACTOR_H 16 17 #include "llvm/ADT/ArrayRef.h" 18 #include "llvm/ADT/DenseMap.h" 19 #include "llvm/ADT/SetVector.h" 20 #include <limits> 21 22 namespace llvm { 23 24 template <typename PtrType> class SmallPtrSetImpl; 25 class AllocaInst; 26 class BasicBlock; 27 class BlockFrequency; 28 class BlockFrequencyInfo; 29 class BranchProbabilityInfo; 30 class AssumptionCache; 31 class CallInst; 32 class DominatorTree; 33 class Function; 34 class Instruction; 35 class Loop; 36 class Module; 37 class Type; 38 class Value; 39 40 /// A cache for the CodeExtractor analysis. The operation \ref 41 /// CodeExtractor::extractCodeRegion is guaranteed not to invalidate this 42 /// object. This object should conservatively be considered invalid if any 43 /// other mutating operations on the IR occur. 44 /// 45 /// Constructing this object is O(n) in the size of the function. 46 class CodeExtractorAnalysisCache { 47 /// The allocas in the function. 48 SmallVector<AllocaInst *, 16> Allocas; 49 50 /// Base memory addresses of load/store instructions, grouped by block. 51 DenseMap<BasicBlock *, DenseSet<Value *>> BaseMemAddrs; 52 53 /// Blocks which contain instructions which may have unknown side-effects 54 /// on memory. 55 DenseSet<BasicBlock *> SideEffectingBlocks; 56 57 void findSideEffectInfoForBlock(BasicBlock &BB); 58 59 public: 60 CodeExtractorAnalysisCache(Function &F); 61 62 /// Get the allocas in the function at the time the analysis was created. 63 /// Note that some of these allocas may no longer be present in the function, 64 /// due to \ref CodeExtractor::extractCodeRegion. getAllocas()65 ArrayRef<AllocaInst *> getAllocas() const { return Allocas; } 66 67 /// Check whether \p BB contains an instruction thought to load from, store 68 /// to, or otherwise clobber the alloca \p Addr. 69 bool doesBlockContainClobberOfAddr(BasicBlock &BB, AllocaInst *Addr) const; 70 }; 71 72 /// Utility class for extracting code into a new function. 73 /// 74 /// This utility provides a simple interface for extracting some sequence of 75 /// code into its own function, replacing it with a call to that function. It 76 /// also provides various methods to query about the nature and result of 77 /// such a transformation. 78 /// 79 /// The rough algorithm used is: 80 /// 1) Find both the inputs and outputs for the extracted region. 81 /// 2) Pass the inputs as arguments, remapping them within the extracted 82 /// function to arguments. 83 /// 3) Add allocas for any scalar outputs, adding all of the outputs' allocas 84 /// as arguments, and inserting stores to the arguments for any scalars. 85 class CodeExtractor { 86 using ValueSet = SetVector<Value *>; 87 88 // Various bits of state computed on construction. 89 DominatorTree *const DT; 90 const bool AggregateArgs; 91 BlockFrequencyInfo *BFI; 92 BranchProbabilityInfo *BPI; 93 AssumptionCache *AC; 94 95 // A block outside of the extraction set where any intermediate 96 // allocations will be placed inside. If this is null, allocations 97 // will be placed in the entry block of the function. 98 BasicBlock *AllocationBlock; 99 100 // If true, varargs functions can be extracted. 101 bool AllowVarArgs; 102 103 // Bits of intermediate state computed at various phases of extraction. 104 SetVector<BasicBlock *> Blocks; 105 unsigned NumExitBlocks = std::numeric_limits<unsigned>::max(); 106 Type *RetTy; 107 108 // Mapping from the original exit blocks, to the new blocks inside 109 // the function. 110 SmallVector<BasicBlock *, 4> OldTargets; 111 112 // Suffix to use when creating extracted function (appended to the original 113 // function name + "."). If empty, the default is to use the entry block 114 // label, if non-empty, otherwise "extracted". 115 std::string Suffix; 116 117 // If true, the outlined function has aggregate argument in zero address 118 // space. 119 bool ArgsInZeroAddressSpace; 120 121 public: 122 /// Create a code extractor for a sequence of blocks. 123 /// 124 /// Given a sequence of basic blocks where the first block in the sequence 125 /// dominates the rest, prepare a code extractor object for pulling this 126 /// sequence out into its new function. When a DominatorTree is also given, 127 /// extra checking and transformations are enabled. If AllowVarArgs is true, 128 /// vararg functions can be extracted. This is safe, if all vararg handling 129 /// code is extracted, including vastart. If AllowAlloca is true, then 130 /// extraction of blocks containing alloca instructions would be possible, 131 /// however code extractor won't validate whether extraction is legal. 132 /// Any new allocations will be placed in the AllocationBlock, unless 133 /// it is null, in which case it will be placed in the entry block of 134 /// the function from which the code is being extracted. 135 /// If ArgsInZeroAddressSpace param is set to true, then the aggregate 136 /// param pointer of the outlined function is declared in zero address 137 /// space. 138 CodeExtractor(ArrayRef<BasicBlock *> BBs, DominatorTree *DT = nullptr, 139 bool AggregateArgs = false, BlockFrequencyInfo *BFI = nullptr, 140 BranchProbabilityInfo *BPI = nullptr, 141 AssumptionCache *AC = nullptr, bool AllowVarArgs = false, 142 bool AllowAlloca = false, 143 BasicBlock *AllocationBlock = nullptr, 144 std::string Suffix = "", bool ArgsInZeroAddressSpace = false); 145 146 /// Create a code extractor for a loop body. 147 /// 148 /// Behaves just like the generic code sequence constructor, but uses the 149 /// block sequence of the loop. 150 CodeExtractor(DominatorTree &DT, Loop &L, bool AggregateArgs = false, 151 BlockFrequencyInfo *BFI = nullptr, 152 BranchProbabilityInfo *BPI = nullptr, 153 AssumptionCache *AC = nullptr, 154 std::string Suffix = ""); 155 156 /// Perform the extraction, returning the new function. 157 /// 158 /// Returns zero when called on a CodeExtractor instance where isEligible 159 /// returns false. 160 Function *extractCodeRegion(const CodeExtractorAnalysisCache &CEAC); 161 162 /// Perform the extraction, returning the new function and providing an 163 /// interface to see what was categorized as inputs and outputs. 164 /// 165 /// \param CEAC - Cache to speed up operations for the CodeExtractor when 166 /// hoisting, and extracting lifetime values and assumes. 167 /// \param Inputs [out] - filled with values marked as inputs to the 168 /// newly outlined function. 169 /// \param Outputs [out] - filled with values marked as outputs to the 170 /// newly outlined function. 171 /// \returns zero when called on a CodeExtractor instance where isEligible 172 /// returns false. 173 Function *extractCodeRegion(const CodeExtractorAnalysisCache &CEAC, 174 ValueSet &Inputs, ValueSet &Outputs); 175 176 /// Verify that assumption cache isn't stale after a region is extracted. 177 /// Returns true when verifier finds errors. AssumptionCache is passed as 178 /// parameter to make this function stateless. 179 static bool verifyAssumptionCache(const Function &OldFunc, 180 const Function &NewFunc, 181 AssumptionCache *AC); 182 183 /// Test whether this code extractor is eligible. 184 /// 185 /// Based on the blocks used when constructing the code extractor, 186 /// determine whether it is eligible for extraction. 187 /// 188 /// Checks that varargs handling (with vastart and vaend) is only done in 189 /// the outlined blocks. 190 bool isEligible() const; 191 192 /// Compute the set of input values and output values for the code. 193 /// 194 /// These can be used either when performing the extraction or to evaluate 195 /// the expected size of a call to the extracted function. Note that this 196 /// work cannot be cached between the two as once we decide to extract 197 /// a code sequence, that sequence is modified, including changing these 198 /// sets, before extraction occurs. These modifications won't have any 199 /// significant impact on the cost however. 200 void findInputsOutputs(ValueSet &Inputs, ValueSet &Outputs, 201 const ValueSet &Allocas) const; 202 203 /// Check if life time marker nodes can be hoisted/sunk into the outline 204 /// region. 205 /// 206 /// Returns true if it is safe to do the code motion. 207 bool 208 isLegalToShrinkwrapLifetimeMarkers(const CodeExtractorAnalysisCache &CEAC, 209 Instruction *AllocaAddr) const; 210 211 /// Find the set of allocas whose life ranges are contained within the 212 /// outlined region. 213 /// 214 /// Allocas which have life_time markers contained in the outlined region 215 /// should be pushed to the outlined function. The address bitcasts that 216 /// are used by the lifetime markers are also candidates for shrink- 217 /// wrapping. The instructions that need to be sunk are collected in 218 /// 'Allocas'. 219 void findAllocas(const CodeExtractorAnalysisCache &CEAC, 220 ValueSet &SinkCands, ValueSet &HoistCands, 221 BasicBlock *&ExitBlock) const; 222 223 /// Find or create a block within the outline region for placing hoisted 224 /// code. 225 /// 226 /// CommonExitBlock is block outside the outline region. It is the common 227 /// successor of blocks inside the region. If there exists a single block 228 /// inside the region that is the predecessor of CommonExitBlock, that block 229 /// will be returned. Otherwise CommonExitBlock will be split and the 230 /// original block will be added to the outline region. 231 BasicBlock *findOrCreateBlockForHoisting(BasicBlock *CommonExitBlock); 232 233 /// Exclude a value from aggregate argument passing when extracting a code 234 /// region, passing it instead as a scalar. 235 void excludeArgFromAggregate(Value *Arg); 236 237 private: 238 struct LifetimeMarkerInfo { 239 bool SinkLifeStart = false; 240 bool HoistLifeEnd = false; 241 Instruction *LifeStart = nullptr; 242 Instruction *LifeEnd = nullptr; 243 }; 244 245 ValueSet ExcludeArgsFromAggregate; 246 247 LifetimeMarkerInfo 248 getLifetimeMarkers(const CodeExtractorAnalysisCache &CEAC, 249 Instruction *Addr, BasicBlock *ExitBlock) const; 250 251 void severSplitPHINodesOfEntry(BasicBlock *&Header); 252 void severSplitPHINodesOfExits(const SetVector<BasicBlock *> &Exits); 253 void splitReturnBlocks(); 254 255 Function *constructFunction(const ValueSet &inputs, 256 const ValueSet &outputs, 257 BasicBlock *header, 258 BasicBlock *newRootNode, BasicBlock *newHeader, 259 Function *oldFunction, Module *M); 260 261 void moveCodeToFunction(Function *newFunction); 262 263 void calculateNewCallTerminatorWeights( 264 BasicBlock *CodeReplacer, 265 DenseMap<BasicBlock *, BlockFrequency> &ExitWeights, 266 BranchProbabilityInfo *BPI); 267 268 CallInst *emitCallAndSwitchStatement(Function *newFunction, 269 BasicBlock *newHeader, 270 ValueSet &inputs, ValueSet &outputs); 271 }; 272 273 } // end namespace llvm 274 275 #endif // LLVM_TRANSFORMS_UTILS_CODEEXTRACTOR_H 276