| File: | src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp |
| Warning: | line 337, column 3 Called C++ object pointer is null |
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| 1 | //===- DFAJumpThreading.cpp - Threads a switch statement inside a loop ----===// | ||||
| 2 | // | ||||
| 3 | // The LLVM Compiler Infrastructure | ||||
| 4 | // | ||||
| 5 | // This file is distributed under the University of Illinois Open Source | ||||
| 6 | // License. See LICENSE.TXT for details. | ||||
| 7 | // | ||||
| 8 | //===----------------------------------------------------------------------===// | ||||
| 9 | // | ||||
| 10 | // Transform each threading path to effectively jump thread the DFA. For | ||||
| 11 | // example, the CFG below could be transformed as follows, where the cloned | ||||
| 12 | // blocks unconditionally branch to the next correct case based on what is | ||||
| 13 | // identified in the analysis. | ||||
| 14 | // | ||||
| 15 | // sw.bb sw.bb | ||||
| 16 | // / | \ / | \ | ||||
| 17 | // case1 case2 case3 case1 case2 case3 | ||||
| 18 | // \ | / | | | | ||||
| 19 | // determinator det.2 det.3 det.1 | ||||
| 20 | // br sw.bb / | \ | ||||
| 21 | // sw.bb.2 sw.bb.3 sw.bb.1 | ||||
| 22 | // br case2 br case3 br case1ยง | ||||
| 23 | // | ||||
| 24 | // Definitions and Terminology: | ||||
| 25 | // | ||||
| 26 | // * Threading path: | ||||
| 27 | // a list of basic blocks, the exit state, and the block that determines | ||||
| 28 | // the next state, for which the following notation will be used: | ||||
| 29 | // < path of BBs that form a cycle > [ state, determinator ] | ||||
| 30 | // | ||||
| 31 | // * Predictable switch: | ||||
| 32 | // The switch variable is always a known constant so that all conditional | ||||
| 33 | // jumps based on switch variable can be converted to unconditional jump. | ||||
| 34 | // | ||||
| 35 | // * Determinator: | ||||
| 36 | // The basic block that determines the next state of the DFA. | ||||
| 37 | // | ||||
| 38 | // Representing the optimization in C-like pseudocode: the code pattern on the | ||||
| 39 | // left could functionally be transformed to the right pattern if the switch | ||||
| 40 | // condition is predictable. | ||||
| 41 | // | ||||
| 42 | // X = A goto A | ||||
| 43 | // for (...) A: | ||||
| 44 | // switch (X) ... | ||||
| 45 | // case A goto B | ||||
| 46 | // X = B B: | ||||
| 47 | // case B ... | ||||
| 48 | // X = C goto C | ||||
| 49 | // | ||||
| 50 | // The pass first checks that switch variable X is decided by the control flow | ||||
| 51 | // path taken in the loop; for example, in case B, the next value of X is | ||||
| 52 | // decided to be C. It then enumerates through all paths in the loop and labels | ||||
| 53 | // the basic blocks where the next state is decided. | ||||
| 54 | // | ||||
| 55 | // Using this information it creates new paths that unconditionally branch to | ||||
| 56 | // the next case. This involves cloning code, so it only gets triggered if the | ||||
| 57 | // amount of code duplicated is below a threshold. | ||||
| 58 | // | ||||
| 59 | //===----------------------------------------------------------------------===// | ||||
| 60 | |||||
| 61 | #include "llvm/Transforms/Scalar/DFAJumpThreading.h" | ||||
| 62 | #include "llvm/ADT/APInt.h" | ||||
| 63 | #include "llvm/ADT/DenseMap.h" | ||||
| 64 | #include "llvm/ADT/DepthFirstIterator.h" | ||||
| 65 | #include "llvm/ADT/SmallSet.h" | ||||
| 66 | #include "llvm/ADT/Statistic.h" | ||||
| 67 | #include "llvm/Analysis/AssumptionCache.h" | ||||
| 68 | #include "llvm/Analysis/CodeMetrics.h" | ||||
| 69 | #include "llvm/Analysis/LoopIterator.h" | ||||
| 70 | #include "llvm/Analysis/OptimizationRemarkEmitter.h" | ||||
| 71 | #include "llvm/Analysis/TargetTransformInfo.h" | ||||
| 72 | #include "llvm/IR/CFG.h" | ||||
| 73 | #include "llvm/IR/Constants.h" | ||||
| 74 | #include "llvm/IR/IntrinsicInst.h" | ||||
| 75 | #include "llvm/IR/Verifier.h" | ||||
| 76 | #include "llvm/InitializePasses.h" | ||||
| 77 | #include "llvm/Pass.h" | ||||
| 78 | #include "llvm/Support/CommandLine.h" | ||||
| 79 | #include "llvm/Support/Debug.h" | ||||
| 80 | #include "llvm/Transforms/Scalar.h" | ||||
| 81 | #include "llvm/Transforms/Utils/BasicBlockUtils.h" | ||||
| 82 | #include "llvm/Transforms/Utils/Cloning.h" | ||||
| 83 | #include "llvm/Transforms/Utils/SSAUpdaterBulk.h" | ||||
| 84 | #include "llvm/Transforms/Utils/ValueMapper.h" | ||||
| 85 | #include <algorithm> | ||||
| 86 | #include <deque> | ||||
| 87 | #include <unordered_map> | ||||
| 88 | #include <unordered_set> | ||||
| 89 | |||||
| 90 | using namespace llvm; | ||||
| 91 | |||||
| 92 | #define DEBUG_TYPE"dfa-jump-threading" "dfa-jump-threading" | ||||
| 93 | |||||
| 94 | STATISTIC(NumTransforms, "Number of transformations done")static llvm::Statistic NumTransforms = {"dfa-jump-threading", "NumTransforms", "Number of transformations done"}; | ||||
| 95 | STATISTIC(NumCloned, "Number of blocks cloned")static llvm::Statistic NumCloned = {"dfa-jump-threading", "NumCloned" , "Number of blocks cloned"}; | ||||
| 96 | STATISTIC(NumPaths, "Number of individual paths threaded")static llvm::Statistic NumPaths = {"dfa-jump-threading", "NumPaths" , "Number of individual paths threaded"}; | ||||
| 97 | |||||
| 98 | static cl::opt<bool> | ||||
| 99 | ClViewCfgBefore("dfa-jump-view-cfg-before", | ||||
| 100 | cl::desc("View the CFG before DFA Jump Threading"), | ||||
| 101 | cl::Hidden, cl::init(false)); | ||||
| 102 | |||||
| 103 | static cl::opt<unsigned> MaxPathLength( | ||||
| 104 | "dfa-max-path-length", | ||||
| 105 | cl::desc("Max number of blocks searched to find a threading path"), | ||||
| 106 | cl::Hidden, cl::init(20)); | ||||
| 107 | |||||
| 108 | static cl::opt<unsigned> | ||||
| 109 | CostThreshold("dfa-cost-threshold", | ||||
| 110 | cl::desc("Maximum cost accepted for the transformation"), | ||||
| 111 | cl::Hidden, cl::init(50)); | ||||
| 112 | |||||
| 113 | namespace { | ||||
| 114 | |||||
| 115 | class SelectInstToUnfold { | ||||
| 116 | SelectInst *SI; | ||||
| 117 | PHINode *SIUse; | ||||
| 118 | |||||
| 119 | public: | ||||
| 120 | SelectInstToUnfold(SelectInst *SI, PHINode *SIUse) : SI(SI), SIUse(SIUse) {} | ||||
| 121 | |||||
| 122 | SelectInst *getInst() { return SI; } | ||||
| 123 | PHINode *getUse() { return SIUse; } | ||||
| 124 | |||||
| 125 | explicit operator bool() const { return SI && SIUse; } | ||||
| 126 | }; | ||||
| 127 | |||||
| 128 | void unfold(DomTreeUpdater *DTU, SelectInstToUnfold SIToUnfold, | ||||
| 129 | std::vector<SelectInstToUnfold> *NewSIsToUnfold, | ||||
| 130 | std::vector<BasicBlock *> *NewBBs); | ||||
| 131 | |||||
| 132 | class DFAJumpThreading { | ||||
| 133 | public: | ||||
| 134 | DFAJumpThreading(AssumptionCache *AC, DominatorTree *DT, | ||||
| 135 | TargetTransformInfo *TTI, OptimizationRemarkEmitter *ORE) | ||||
| 136 | : AC(AC), DT(DT), TTI(TTI), ORE(ORE) {} | ||||
| 137 | |||||
| 138 | bool run(Function &F); | ||||
| 139 | |||||
| 140 | private: | ||||
| 141 | void | ||||
| 142 | unfoldSelectInstrs(DominatorTree *DT, | ||||
| 143 | const SmallVector<SelectInstToUnfold, 4> &SelectInsts) { | ||||
| 144 | DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager); | ||||
| 145 | SmallVector<SelectInstToUnfold, 4> Stack; | ||||
| 146 | for (SelectInstToUnfold SIToUnfold : SelectInsts) | ||||
| 147 | Stack.push_back(SIToUnfold); | ||||
| 148 | |||||
| 149 | while (!Stack.empty()) { | ||||
| 150 | SelectInstToUnfold SIToUnfold = Stack.back(); | ||||
| 151 | Stack.pop_back(); | ||||
| 152 | |||||
| 153 | std::vector<SelectInstToUnfold> NewSIsToUnfold; | ||||
| 154 | std::vector<BasicBlock *> NewBBs; | ||||
| 155 | unfold(&DTU, SIToUnfold, &NewSIsToUnfold, &NewBBs); | ||||
| 156 | |||||
| 157 | // Put newly discovered select instructions into the work list. | ||||
| 158 | for (const SelectInstToUnfold &NewSIToUnfold : NewSIsToUnfold) | ||||
| 159 | Stack.push_back(NewSIToUnfold); | ||||
| 160 | } | ||||
| 161 | } | ||||
| 162 | |||||
| 163 | AssumptionCache *AC; | ||||
| 164 | DominatorTree *DT; | ||||
| 165 | TargetTransformInfo *TTI; | ||||
| 166 | OptimizationRemarkEmitter *ORE; | ||||
| 167 | }; | ||||
| 168 | |||||
| 169 | class DFAJumpThreadingLegacyPass : public FunctionPass { | ||||
| 170 | public: | ||||
| 171 | static char ID; // Pass identification | ||||
| 172 | DFAJumpThreadingLegacyPass() : FunctionPass(ID) {} | ||||
| 173 | |||||
| 174 | void getAnalysisUsage(AnalysisUsage &AU) const override { | ||||
| 175 | AU.addRequired<AssumptionCacheTracker>(); | ||||
| 176 | AU.addRequired<DominatorTreeWrapperPass>(); | ||||
| 177 | AU.addRequired<TargetTransformInfoWrapperPass>(); | ||||
| 178 | AU.addRequired<OptimizationRemarkEmitterWrapperPass>(); | ||||
| 179 | } | ||||
| 180 | |||||
| 181 | bool runOnFunction(Function &F) override { | ||||
| 182 | if (skipFunction(F)) | ||||
| 183 | return false; | ||||
| 184 | |||||
| 185 | AssumptionCache *AC = | ||||
| 186 | &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); | ||||
| 187 | DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); | ||||
| 188 | TargetTransformInfo *TTI = | ||||
| 189 | &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); | ||||
| 190 | OptimizationRemarkEmitter *ORE = | ||||
| 191 | &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE(); | ||||
| 192 | |||||
| 193 | return DFAJumpThreading(AC, DT, TTI, ORE).run(F); | ||||
| 194 | } | ||||
| 195 | }; | ||||
| 196 | } // end anonymous namespace | ||||
| 197 | |||||
| 198 | char DFAJumpThreadingLegacyPass::ID = 0; | ||||
| 199 | INITIALIZE_PASS_BEGIN(DFAJumpThreadingLegacyPass, "dfa-jump-threading",static void *initializeDFAJumpThreadingLegacyPassPassOnce(PassRegistry &Registry) { | ||||
| 200 | "DFA Jump Threading", false, false)static void *initializeDFAJumpThreadingLegacyPassPassOnce(PassRegistry &Registry) { | ||||
| 201 | INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)initializeAssumptionCacheTrackerPass(Registry); | ||||
| 202 | INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry); | ||||
| 203 | INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)initializeTargetTransformInfoWrapperPassPass(Registry); | ||||
| 204 | INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)initializeOptimizationRemarkEmitterWrapperPassPass(Registry); | ||||
| 205 | INITIALIZE_PASS_END(DFAJumpThreadingLegacyPass, "dfa-jump-threading",PassInfo *PI = new PassInfo( "DFA Jump Threading", "dfa-jump-threading" , &DFAJumpThreadingLegacyPass::ID, PassInfo::NormalCtor_t (callDefaultCtor<DFAJumpThreadingLegacyPass>), false, false ); Registry.registerPass(*PI, true); return PI; } static llvm ::once_flag InitializeDFAJumpThreadingLegacyPassPassFlag; void llvm::initializeDFAJumpThreadingLegacyPassPass(PassRegistry & Registry) { llvm::call_once(InitializeDFAJumpThreadingLegacyPassPassFlag , initializeDFAJumpThreadingLegacyPassPassOnce, std::ref(Registry )); } | ||||
| 206 | "DFA Jump Threading", false, false)PassInfo *PI = new PassInfo( "DFA Jump Threading", "dfa-jump-threading" , &DFAJumpThreadingLegacyPass::ID, PassInfo::NormalCtor_t (callDefaultCtor<DFAJumpThreadingLegacyPass>), false, false ); Registry.registerPass(*PI, true); return PI; } static llvm ::once_flag InitializeDFAJumpThreadingLegacyPassPassFlag; void llvm::initializeDFAJumpThreadingLegacyPassPass(PassRegistry & Registry) { llvm::call_once(InitializeDFAJumpThreadingLegacyPassPassFlag , initializeDFAJumpThreadingLegacyPassPassOnce, std::ref(Registry )); } | ||||
| 207 | |||||
| 208 | // Public interface to the DFA Jump Threading pass | ||||
| 209 | FunctionPass *llvm::createDFAJumpThreadingPass() { | ||||
| 210 | return new DFAJumpThreadingLegacyPass(); | ||||
| 211 | } | ||||
| 212 | |||||
| 213 | namespace { | ||||
| 214 | |||||
| 215 | /// Create a new basic block and sink \p SIToSink into it. | ||||
| 216 | void createBasicBlockAndSinkSelectInst( | ||||
| 217 | DomTreeUpdater *DTU, SelectInst *SI, PHINode *SIUse, SelectInst *SIToSink, | ||||
| 218 | BasicBlock *EndBlock, StringRef NewBBName, BasicBlock **NewBlock, | ||||
| 219 | BranchInst **NewBranch, std::vector<SelectInstToUnfold> *NewSIsToUnfold, | ||||
| 220 | std::vector<BasicBlock *> *NewBBs) { | ||||
| 221 | assert(SIToSink->hasOneUse())((void)0); | ||||
| 222 | assert(NewBlock)((void)0); | ||||
| 223 | assert(NewBranch)((void)0); | ||||
| 224 | *NewBlock = BasicBlock::Create(SI->getContext(), NewBBName, | ||||
| 225 | EndBlock->getParent(), EndBlock); | ||||
| 226 | NewBBs->push_back(*NewBlock); | ||||
| 227 | *NewBranch = BranchInst::Create(EndBlock, *NewBlock); | ||||
| 228 | SIToSink->moveBefore(*NewBranch); | ||||
| 229 | NewSIsToUnfold->push_back(SelectInstToUnfold(SIToSink, SIUse)); | ||||
| 230 | DTU->applyUpdates({{DominatorTree::Insert, *NewBlock, EndBlock}}); | ||||
| 231 | } | ||||
| 232 | |||||
| 233 | /// Unfold the select instruction held in \p SIToUnfold by replacing it with | ||||
| 234 | /// control flow. | ||||
| 235 | /// | ||||
| 236 | /// Put newly discovered select instructions into \p NewSIsToUnfold. Put newly | ||||
| 237 | /// created basic blocks into \p NewBBs. | ||||
| 238 | /// | ||||
| 239 | /// TODO: merge it with CodeGenPrepare::optimizeSelectInst() if possible. | ||||
| 240 | void unfold(DomTreeUpdater *DTU, SelectInstToUnfold SIToUnfold, | ||||
| 241 | std::vector<SelectInstToUnfold> *NewSIsToUnfold, | ||||
| 242 | std::vector<BasicBlock *> *NewBBs) { | ||||
| 243 | SelectInst *SI = SIToUnfold.getInst(); | ||||
| 244 | PHINode *SIUse = SIToUnfold.getUse(); | ||||
| 245 | BasicBlock *StartBlock = SI->getParent(); | ||||
| 246 | BasicBlock *EndBlock = SIUse->getParent(); | ||||
| 247 | BranchInst *StartBlockTerm = | ||||
| 248 | dyn_cast<BranchInst>(StartBlock->getTerminator()); | ||||
| 249 | |||||
| 250 | assert(StartBlockTerm && StartBlockTerm->isUnconditional())((void)0); | ||||
| 251 | assert(SI->hasOneUse())((void)0); | ||||
| 252 | |||||
| 253 | // These are the new basic blocks for the conditional branch. | ||||
| 254 | // At least one will become an actual new basic block. | ||||
| 255 | BasicBlock *TrueBlock = nullptr; | ||||
| 256 | BasicBlock *FalseBlock = nullptr; | ||||
| 257 | BranchInst *TrueBranch = nullptr; | ||||
| 258 | BranchInst *FalseBranch = nullptr; | ||||
| 259 | |||||
| 260 | // Sink select instructions to be able to unfold them later. | ||||
| 261 | if (SelectInst *SIOp
| ||||
| 262 | createBasicBlockAndSinkSelectInst(DTU, SI, SIUse, SIOp, EndBlock, | ||||
| 263 | "si.unfold.true", &TrueBlock, &TrueBranch, | ||||
| 264 | NewSIsToUnfold, NewBBs); | ||||
| 265 | } | ||||
| 266 | if (SelectInst *SIOp
| ||||
| 267 | createBasicBlockAndSinkSelectInst(DTU, SI, SIUse, SIOp, EndBlock, | ||||
| 268 | "si.unfold.false", &FalseBlock, | ||||
| 269 | &FalseBranch, NewSIsToUnfold, NewBBs); | ||||
| 270 | } | ||||
| 271 | |||||
| 272 | // If there was nothing to sink, then arbitrarily choose the 'false' side | ||||
| 273 | // for a new input value to the PHI. | ||||
| 274 | if (!TrueBlock
| ||||
| 275 | FalseBlock = BasicBlock::Create(SI->getContext(), "si.unfold.false", | ||||
| 276 | EndBlock->getParent(), EndBlock); | ||||
| 277 | NewBBs->push_back(FalseBlock); | ||||
| 278 | BranchInst::Create(EndBlock, FalseBlock); | ||||
| 279 | DTU->applyUpdates({{DominatorTree::Insert, FalseBlock, EndBlock}}); | ||||
| 280 | } | ||||
| 281 | |||||
| 282 | // Insert the real conditional branch based on the original condition. | ||||
| 283 | // If we did not create a new block for one of the 'true' or 'false' paths | ||||
| 284 | // of the condition, it means that side of the branch goes to the end block | ||||
| 285 | // directly and the path originates from the start block from the point of | ||||
| 286 | // view of the new PHI. | ||||
| 287 | BasicBlock *TT = EndBlock; | ||||
| 288 | BasicBlock *FT = EndBlock; | ||||
| 289 | if (TrueBlock
| ||||
| 290 | // A diamond. | ||||
| 291 | TT = TrueBlock; | ||||
| 292 | FT = FalseBlock; | ||||
| 293 | |||||
| 294 | // Update the phi node of SI. | ||||
| 295 | SIUse->removeIncomingValue(StartBlock, /* DeletePHIIfEmpty = */ false); | ||||
| 296 | SIUse->addIncoming(SI->getTrueValue(), TrueBlock); | ||||
| 297 | SIUse->addIncoming(SI->getFalseValue(), FalseBlock); | ||||
| 298 | |||||
| 299 | // Update any other PHI nodes in EndBlock. | ||||
| 300 | for (PHINode &Phi : EndBlock->phis()) { | ||||
| 301 | if (&Phi != SIUse) { | ||||
| 302 | Phi.addIncoming(Phi.getIncomingValueForBlock(StartBlock), TrueBlock); | ||||
| 303 | Phi.addIncoming(Phi.getIncomingValueForBlock(StartBlock), FalseBlock); | ||||
| 304 | } | ||||
| 305 | } | ||||
| 306 | } else { | ||||
| 307 | BasicBlock *NewBlock = nullptr; | ||||
| 308 | Value *SIOp1 = SI->getTrueValue(); | ||||
| 309 | Value *SIOp2 = SI->getFalseValue(); | ||||
| 310 | |||||
| 311 | // A triangle pointing right. | ||||
| 312 | if (!TrueBlock
| ||||
| 313 | NewBlock = FalseBlock; | ||||
| 314 | FT = FalseBlock; | ||||
| 315 | } | ||||
| 316 | // A triangle pointing left. | ||||
| 317 | else { | ||||
| 318 | NewBlock = TrueBlock; | ||||
| 319 | TT = TrueBlock; | ||||
| 320 | std::swap(SIOp1, SIOp2); | ||||
| 321 | } | ||||
| 322 | |||||
| 323 | // Update the phi node of SI. | ||||
| 324 | for (unsigned Idx = 0; Idx < SIUse->getNumIncomingValues(); ++Idx) { | ||||
| 325 | if (SIUse->getIncomingBlock(Idx) == StartBlock) | ||||
| 326 | SIUse->setIncomingValue(Idx, SIOp1); | ||||
| 327 | } | ||||
| 328 | SIUse->addIncoming(SIOp2, NewBlock); | ||||
| 329 | |||||
| 330 | // Update any other PHI nodes in EndBlock. | ||||
| 331 | for (auto II = EndBlock->begin(); PHINode *Phi = dyn_cast<PHINode>(II); | ||||
| 332 | ++II) { | ||||
| 333 | if (Phi != SIUse) | ||||
| 334 | Phi->addIncoming(Phi->getIncomingValueForBlock(StartBlock), NewBlock); | ||||
| 335 | } | ||||
| 336 | } | ||||
| 337 | StartBlockTerm->eraseFromParent(); | ||||
| |||||
| 338 | BranchInst::Create(TT, FT, SI->getCondition(), StartBlock); | ||||
| 339 | DTU->applyUpdates({{DominatorTree::Insert, StartBlock, TT}, | ||||
| 340 | {DominatorTree::Insert, StartBlock, FT}}); | ||||
| 341 | |||||
| 342 | // The select is now dead. | ||||
| 343 | SI->eraseFromParent(); | ||||
| 344 | } | ||||
| 345 | |||||
| 346 | struct ClonedBlock { | ||||
| 347 | BasicBlock *BB; | ||||
| 348 | uint64_t State; ///< \p State corresponds to the next value of a switch stmnt. | ||||
| 349 | }; | ||||
| 350 | |||||
| 351 | typedef std::deque<BasicBlock *> PathType; | ||||
| 352 | typedef std::vector<PathType> PathsType; | ||||
| 353 | typedef std::set<const BasicBlock *> VisitedBlocks; | ||||
| 354 | typedef std::vector<ClonedBlock> CloneList; | ||||
| 355 | |||||
| 356 | // This data structure keeps track of all blocks that have been cloned. If two | ||||
| 357 | // different ThreadingPaths clone the same block for a certain state it should | ||||
| 358 | // be reused, and it can be looked up in this map. | ||||
| 359 | typedef DenseMap<BasicBlock *, CloneList> DuplicateBlockMap; | ||||
| 360 | |||||
| 361 | // This map keeps track of all the new definitions for an instruction. This | ||||
| 362 | // information is needed when restoring SSA form after cloning blocks. | ||||
| 363 | typedef DenseMap<Instruction *, std::vector<Instruction *>> DefMap; | ||||
| 364 | |||||
| 365 | inline raw_ostream &operator<<(raw_ostream &OS, const PathType &Path) { | ||||
| 366 | OS << "< "; | ||||
| 367 | for (const BasicBlock *BB : Path) { | ||||
| 368 | std::string BBName; | ||||
| 369 | if (BB->hasName()) | ||||
| 370 | raw_string_ostream(BBName) << BB->getName(); | ||||
| 371 | else | ||||
| 372 | raw_string_ostream(BBName) << BB; | ||||
| 373 | OS << BBName << " "; | ||||
| 374 | } | ||||
| 375 | OS << ">"; | ||||
| 376 | return OS; | ||||
| 377 | } | ||||
| 378 | |||||
| 379 | /// ThreadingPath is a path in the control flow of a loop that can be threaded | ||||
| 380 | /// by cloning necessary basic blocks and replacing conditional branches with | ||||
| 381 | /// unconditional ones. A threading path includes a list of basic blocks, the | ||||
| 382 | /// exit state, and the block that determines the next state. | ||||
| 383 | struct ThreadingPath { | ||||
| 384 | /// Exit value is DFA's exit state for the given path. | ||||
| 385 | uint64_t getExitValue() const { return ExitVal; } | ||||
| 386 | void setExitValue(const ConstantInt *V) { | ||||
| 387 | ExitVal = V->getZExtValue(); | ||||
| 388 | IsExitValSet = true; | ||||
| 389 | } | ||||
| 390 | bool isExitValueSet() const { return IsExitValSet; } | ||||
| 391 | |||||
| 392 | /// Determinator is the basic block that determines the next state of the DFA. | ||||
| 393 | const BasicBlock *getDeterminatorBB() const { return DBB; } | ||||
| 394 | void setDeterminator(const BasicBlock *BB) { DBB = BB; } | ||||
| 395 | |||||
| 396 | /// Path is a list of basic blocks. | ||||
| 397 | const PathType &getPath() const { return Path; } | ||||
| 398 | void setPath(const PathType &NewPath) { Path = NewPath; } | ||||
| 399 | |||||
| 400 | void print(raw_ostream &OS) const { | ||||
| 401 | OS << Path << " [ " << ExitVal << ", " << DBB->getName() << " ]"; | ||||
| 402 | } | ||||
| 403 | |||||
| 404 | private: | ||||
| 405 | PathType Path; | ||||
| 406 | uint64_t ExitVal; | ||||
| 407 | const BasicBlock *DBB = nullptr; | ||||
| 408 | bool IsExitValSet = false; | ||||
| 409 | }; | ||||
| 410 | |||||
| 411 | #ifndef NDEBUG1 | ||||
| 412 | inline raw_ostream &operator<<(raw_ostream &OS, const ThreadingPath &TPath) { | ||||
| 413 | TPath.print(OS); | ||||
| 414 | return OS; | ||||
| 415 | } | ||||
| 416 | #endif | ||||
| 417 | |||||
| 418 | struct MainSwitch { | ||||
| 419 | MainSwitch(SwitchInst *SI, OptimizationRemarkEmitter *ORE) { | ||||
| 420 | if (isPredictable(SI)) { | ||||
| 421 | Instr = SI; | ||||
| 422 | } else { | ||||
| 423 | ORE->emit([&]() { | ||||
| 424 | return OptimizationRemarkMissed(DEBUG_TYPE"dfa-jump-threading", "SwitchNotPredictable", SI) | ||||
| 425 | << "Switch instruction is not predictable."; | ||||
| 426 | }); | ||||
| 427 | } | ||||
| 428 | } | ||||
| 429 | |||||
| 430 | virtual ~MainSwitch() = default; | ||||
| 431 | |||||
| 432 | SwitchInst *getInstr() const { return Instr; } | ||||
| 433 | const SmallVector<SelectInstToUnfold, 4> getSelectInsts() { | ||||
| 434 | return SelectInsts; | ||||
| 435 | } | ||||
| 436 | |||||
| 437 | private: | ||||
| 438 | /// Do a use-def chain traversal. Make sure the value of the switch variable | ||||
| 439 | /// is always a known constant. This means that all conditional jumps based on | ||||
| 440 | /// switch variable can be converted to unconditional jumps. | ||||
| 441 | bool isPredictable(const SwitchInst *SI) { | ||||
| 442 | std::deque<Instruction *> Q; | ||||
| 443 | SmallSet<Value *, 16> SeenValues; | ||||
| 444 | SelectInsts.clear(); | ||||
| 445 | |||||
| 446 | Value *FirstDef = SI->getOperand(0); | ||||
| 447 | auto *Inst = dyn_cast<Instruction>(FirstDef); | ||||
| 448 | |||||
| 449 | // If this is a function argument or another non-instruction, then give up. | ||||
| 450 | // We are interested in loop local variables. | ||||
| 451 | if (!Inst) | ||||
| 452 | return false; | ||||
| 453 | |||||
| 454 | // Require the first definition to be a PHINode | ||||
| 455 | if (!isa<PHINode>(Inst)) | ||||
| 456 | return false; | ||||
| 457 | |||||
| 458 | LLVM_DEBUG(dbgs() << "\tisPredictable() FirstDef: " << *Inst << "\n")do { } while (false); | ||||
| 459 | |||||
| 460 | Q.push_back(Inst); | ||||
| 461 | SeenValues.insert(FirstDef); | ||||
| 462 | |||||
| 463 | while (!Q.empty()) { | ||||
| 464 | Instruction *Current = Q.front(); | ||||
| 465 | Q.pop_front(); | ||||
| 466 | |||||
| 467 | if (auto *Phi = dyn_cast<PHINode>(Current)) { | ||||
| 468 | for (Value *Incoming : Phi->incoming_values()) { | ||||
| 469 | if (!isPredictableValue(Incoming, SeenValues)) | ||||
| 470 | return false; | ||||
| 471 | addInstToQueue(Incoming, Q, SeenValues); | ||||
| 472 | } | ||||
| 473 | LLVM_DEBUG(dbgs() << "\tisPredictable() phi: " << *Phi << "\n")do { } while (false); | ||||
| 474 | } else if (SelectInst *SelI = dyn_cast<SelectInst>(Current)) { | ||||
| 475 | if (!isValidSelectInst(SelI)) | ||||
| 476 | return false; | ||||
| 477 | if (!isPredictableValue(SelI->getTrueValue(), SeenValues) || | ||||
| 478 | !isPredictableValue(SelI->getFalseValue(), SeenValues)) { | ||||
| 479 | return false; | ||||
| 480 | } | ||||
| 481 | addInstToQueue(SelI->getTrueValue(), Q, SeenValues); | ||||
| 482 | addInstToQueue(SelI->getFalseValue(), Q, SeenValues); | ||||
| 483 | LLVM_DEBUG(dbgs() << "\tisPredictable() select: " << *SelI << "\n")do { } while (false); | ||||
| 484 | if (auto *SelIUse = dyn_cast<PHINode>(SelI->user_back())) | ||||
| 485 | SelectInsts.push_back(SelectInstToUnfold(SelI, SelIUse)); | ||||
| 486 | } else { | ||||
| 487 | // If it is neither a phi nor a select, then we give up. | ||||
| 488 | return false; | ||||
| 489 | } | ||||
| 490 | } | ||||
| 491 | |||||
| 492 | return true; | ||||
| 493 | } | ||||
| 494 | |||||
| 495 | bool isPredictableValue(Value *InpVal, SmallSet<Value *, 16> &SeenValues) { | ||||
| 496 | if (SeenValues.find(InpVal) != SeenValues.end()) | ||||
| 497 | return true; | ||||
| 498 | |||||
| 499 | if (isa<ConstantInt>(InpVal)) | ||||
| 500 | return true; | ||||
| 501 | |||||
| 502 | // If this is a function argument or another non-instruction, then give up. | ||||
| 503 | if (!isa<Instruction>(InpVal)) | ||||
| 504 | return false; | ||||
| 505 | |||||
| 506 | return true; | ||||
| 507 | } | ||||
| 508 | |||||
| 509 | void addInstToQueue(Value *Val, std::deque<Instruction *> &Q, | ||||
| 510 | SmallSet<Value *, 16> &SeenValues) { | ||||
| 511 | if (SeenValues.find(Val) != SeenValues.end()) | ||||
| 512 | return; | ||||
| 513 | if (Instruction *I = dyn_cast<Instruction>(Val)) | ||||
| 514 | Q.push_back(I); | ||||
| 515 | SeenValues.insert(Val); | ||||
| 516 | } | ||||
| 517 | |||||
| 518 | bool isValidSelectInst(SelectInst *SI) { | ||||
| 519 | if (!SI->hasOneUse()) | ||||
| 520 | return false; | ||||
| 521 | |||||
| 522 | Instruction *SIUse = dyn_cast<Instruction>(SI->user_back()); | ||||
| 523 | // The use of the select inst should be either a phi or another select. | ||||
| 524 | if (!SIUse && !(isa<PHINode>(SIUse) || isa<SelectInst>(SIUse))) | ||||
| 525 | return false; | ||||
| 526 | |||||
| 527 | BasicBlock *SIBB = SI->getParent(); | ||||
| 528 | |||||
| 529 | // Currently, we can only expand select instructions in basic blocks with | ||||
| 530 | // one successor. | ||||
| 531 | BranchInst *SITerm = dyn_cast<BranchInst>(SIBB->getTerminator()); | ||||
| 532 | if (!SITerm || !SITerm->isUnconditional()) | ||||
| 533 | return false; | ||||
| 534 | |||||
| 535 | if (isa<PHINode>(SIUse) && | ||||
| 536 | SIBB->getSingleSuccessor() != dyn_cast<Instruction>(SIUse)->getParent()) | ||||
| 537 | return false; | ||||
| 538 | |||||
| 539 | // If select will not be sunk during unfolding, and it is in the same basic | ||||
| 540 | // block as another state defining select, then cannot unfold both. | ||||
| 541 | for (SelectInstToUnfold SIToUnfold : SelectInsts) { | ||||
| 542 | SelectInst *PrevSI = SIToUnfold.getInst(); | ||||
| 543 | if (PrevSI->getTrueValue() != SI && PrevSI->getFalseValue() != SI && | ||||
| 544 | PrevSI->getParent() == SI->getParent()) | ||||
| 545 | return false; | ||||
| 546 | } | ||||
| 547 | |||||
| 548 | return true; | ||||
| 549 | } | ||||
| 550 | |||||
| 551 | SwitchInst *Instr = nullptr; | ||||
| 552 | SmallVector<SelectInstToUnfold, 4> SelectInsts; | ||||
| 553 | }; | ||||
| 554 | |||||
| 555 | struct AllSwitchPaths { | ||||
| 556 | AllSwitchPaths(const MainSwitch *MSwitch, OptimizationRemarkEmitter *ORE) | ||||
| 557 | : Switch(MSwitch->getInstr()), SwitchBlock(Switch->getParent()), | ||||
| 558 | ORE(ORE) {} | ||||
| 559 | |||||
| 560 | std::vector<ThreadingPath> &getThreadingPaths() { return TPaths; } | ||||
| 561 | unsigned getNumThreadingPaths() { return TPaths.size(); } | ||||
| 562 | SwitchInst *getSwitchInst() { return Switch; } | ||||
| 563 | BasicBlock *getSwitchBlock() { return SwitchBlock; } | ||||
| 564 | |||||
| 565 | void run() { | ||||
| 566 | VisitedBlocks Visited; | ||||
| 567 | PathsType LoopPaths = paths(SwitchBlock, Visited, /* PathDepth = */ 1); | ||||
| 568 | StateDefMap StateDef = getStateDefMap(); | ||||
| 569 | |||||
| 570 | for (PathType Path : LoopPaths) { | ||||
| 571 | ThreadingPath TPath; | ||||
| 572 | |||||
| 573 | const BasicBlock *PrevBB = Path.back(); | ||||
| 574 | for (const BasicBlock *BB : Path) { | ||||
| 575 | if (StateDef.count(BB) != 0) { | ||||
| 576 | const PHINode *Phi = dyn_cast<PHINode>(StateDef[BB]); | ||||
| 577 | assert(Phi && "Expected a state-defining instr to be a phi node.")((void)0); | ||||
| 578 | |||||
| 579 | const Value *V = Phi->getIncomingValueForBlock(PrevBB); | ||||
| 580 | if (const ConstantInt *C = dyn_cast<const ConstantInt>(V)) { | ||||
| 581 | TPath.setExitValue(C); | ||||
| 582 | TPath.setDeterminator(BB); | ||||
| 583 | TPath.setPath(Path); | ||||
| 584 | } | ||||
| 585 | } | ||||
| 586 | |||||
| 587 | // Switch block is the determinator, this is the final exit value. | ||||
| 588 | if (TPath.isExitValueSet() && BB == Path.front()) | ||||
| 589 | break; | ||||
| 590 | |||||
| 591 | PrevBB = BB; | ||||
| 592 | } | ||||
| 593 | |||||
| 594 | if (TPath.isExitValueSet()) | ||||
| 595 | TPaths.push_back(TPath); | ||||
| 596 | } | ||||
| 597 | } | ||||
| 598 | |||||
| 599 | private: | ||||
| 600 | // Value: an instruction that defines a switch state; | ||||
| 601 | // Key: the parent basic block of that instruction. | ||||
| 602 | typedef DenseMap<const BasicBlock *, const PHINode *> StateDefMap; | ||||
| 603 | |||||
| 604 | PathsType paths(BasicBlock *BB, VisitedBlocks &Visited, | ||||
| 605 | unsigned PathDepth) const { | ||||
| 606 | PathsType Res; | ||||
| 607 | |||||
| 608 | // Stop exploring paths after visiting MaxPathLength blocks | ||||
| 609 | if (PathDepth > MaxPathLength) { | ||||
| 610 | ORE->emit([&]() { | ||||
| 611 | return OptimizationRemarkAnalysis(DEBUG_TYPE"dfa-jump-threading", "MaxPathLengthReached", | ||||
| 612 | Switch) | ||||
| 613 | << "Exploration stopped after visiting MaxPathLength=" | ||||
| 614 | << ore::NV("MaxPathLength", MaxPathLength) << " blocks."; | ||||
| 615 | }); | ||||
| 616 | return Res; | ||||
| 617 | } | ||||
| 618 | |||||
| 619 | Visited.insert(BB); | ||||
| 620 | |||||
| 621 | // Some blocks have multiple edges to the same successor, and this set | ||||
| 622 | // is used to prevent a duplicate path from being generated | ||||
| 623 | SmallSet<BasicBlock *, 4> Successors; | ||||
| 624 | |||||
| 625 | for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) { | ||||
| 626 | BasicBlock *Succ = *SI; | ||||
| 627 | |||||
| 628 | if (Successors.find(Succ) != Successors.end()) | ||||
| 629 | continue; | ||||
| 630 | Successors.insert(Succ); | ||||
| 631 | |||||
| 632 | // Found a cycle through the SwitchBlock | ||||
| 633 | if (Succ == SwitchBlock) { | ||||
| 634 | Res.push_back({BB}); | ||||
| 635 | continue; | ||||
| 636 | } | ||||
| 637 | |||||
| 638 | // We have encountered a cycle, do not get caught in it | ||||
| 639 | if (Visited.find(Succ) != Visited.end()) | ||||
| 640 | continue; | ||||
| 641 | |||||
| 642 | PathsType SuccPaths = paths(Succ, Visited, PathDepth + 1); | ||||
| 643 | for (PathType Path : SuccPaths) { | ||||
| 644 | PathType NewPath(Path); | ||||
| 645 | NewPath.push_front(BB); | ||||
| 646 | Res.push_back(NewPath); | ||||
| 647 | } | ||||
| 648 | } | ||||
| 649 | // This block could now be visited again from a different predecessor. Note | ||||
| 650 | // that this will result in exponential runtime. Subpaths could possibly be | ||||
| 651 | // cached but it takes a lot of memory to store them. | ||||
| 652 | Visited.erase(BB); | ||||
| 653 | return Res; | ||||
| 654 | } | ||||
| 655 | |||||
| 656 | /// Walk the use-def chain and collect all the state-defining instructions. | ||||
| 657 | StateDefMap getStateDefMap() const { | ||||
| 658 | StateDefMap Res; | ||||
| 659 | |||||
| 660 | Value *FirstDef = Switch->getOperand(0); | ||||
| 661 | |||||
| 662 | assert(isa<PHINode>(FirstDef) && "After select unfolding, all state "((void)0) | ||||
| 663 | "definitions are expected to be phi "((void)0) | ||||
| 664 | "nodes.")((void)0); | ||||
| 665 | |||||
| 666 | SmallVector<PHINode *, 8> Stack; | ||||
| 667 | Stack.push_back(dyn_cast<PHINode>(FirstDef)); | ||||
| 668 | SmallSet<Value *, 16> SeenValues; | ||||
| 669 | |||||
| 670 | while (!Stack.empty()) { | ||||
| 671 | PHINode *CurPhi = Stack.back(); | ||||
| 672 | Stack.pop_back(); | ||||
| 673 | |||||
| 674 | Res[CurPhi->getParent()] = CurPhi; | ||||
| 675 | SeenValues.insert(CurPhi); | ||||
| 676 | |||||
| 677 | for (Value *Incoming : CurPhi->incoming_values()) { | ||||
| 678 | if (Incoming == FirstDef || isa<ConstantInt>(Incoming) || | ||||
| 679 | SeenValues.find(Incoming) != SeenValues.end()) { | ||||
| 680 | continue; | ||||
| 681 | } | ||||
| 682 | |||||
| 683 | assert(isa<PHINode>(Incoming) && "After select unfolding, all state "((void)0) | ||||
| 684 | "definitions are expected to be phi "((void)0) | ||||
| 685 | "nodes.")((void)0); | ||||
| 686 | |||||
| 687 | Stack.push_back(cast<PHINode>(Incoming)); | ||||
| 688 | } | ||||
| 689 | } | ||||
| 690 | |||||
| 691 | return Res; | ||||
| 692 | } | ||||
| 693 | |||||
| 694 | SwitchInst *Switch; | ||||
| 695 | BasicBlock *SwitchBlock; | ||||
| 696 | OptimizationRemarkEmitter *ORE; | ||||
| 697 | std::vector<ThreadingPath> TPaths; | ||||
| 698 | }; | ||||
| 699 | |||||
| 700 | struct TransformDFA { | ||||
| 701 | TransformDFA(AllSwitchPaths *SwitchPaths, DominatorTree *DT, | ||||
| 702 | AssumptionCache *AC, TargetTransformInfo *TTI, | ||||
| 703 | OptimizationRemarkEmitter *ORE, | ||||
| 704 | SmallPtrSet<const Value *, 32> EphValues) | ||||
| 705 | : SwitchPaths(SwitchPaths), DT(DT), AC(AC), TTI(TTI), ORE(ORE), | ||||
| 706 | EphValues(EphValues) {} | ||||
| 707 | |||||
| 708 | void run() { | ||||
| 709 | if (isLegalAndProfitableToTransform()) { | ||||
| 710 | createAllExitPaths(); | ||||
| 711 | NumTransforms++; | ||||
| 712 | } | ||||
| 713 | } | ||||
| 714 | |||||
| 715 | private: | ||||
| 716 | /// This function performs both a legality check and profitability check at | ||||
| 717 | /// the same time since it is convenient to do so. It iterates through all | ||||
| 718 | /// blocks that will be cloned, and keeps track of the duplication cost. It | ||||
| 719 | /// also returns false if it is illegal to clone some required block. | ||||
| 720 | bool isLegalAndProfitableToTransform() { | ||||
| 721 | CodeMetrics Metrics; | ||||
| 722 | SwitchInst *Switch = SwitchPaths->getSwitchInst(); | ||||
| 723 | |||||
| 724 | // Note that DuplicateBlockMap is not being used as intended here. It is | ||||
| 725 | // just being used to ensure (BB, State) pairs are only counted once. | ||||
| 726 | DuplicateBlockMap DuplicateMap; | ||||
| 727 | |||||
| 728 | for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) { | ||||
| 729 | PathType PathBBs = TPath.getPath(); | ||||
| 730 | uint64_t NextState = TPath.getExitValue(); | ||||
| 731 | const BasicBlock *Determinator = TPath.getDeterminatorBB(); | ||||
| 732 | |||||
| 733 | // Update Metrics for the Switch block, this is always cloned | ||||
| 734 | BasicBlock *BB = SwitchPaths->getSwitchBlock(); | ||||
| 735 | BasicBlock *VisitedBB = getClonedBB(BB, NextState, DuplicateMap); | ||||
| 736 | if (!VisitedBB) { | ||||
| 737 | Metrics.analyzeBasicBlock(BB, *TTI, EphValues); | ||||
| 738 | DuplicateMap[BB].push_back({BB, NextState}); | ||||
| 739 | } | ||||
| 740 | |||||
| 741 | // If the Switch block is the Determinator, then we can continue since | ||||
| 742 | // this is the only block that is cloned and we already counted for it. | ||||
| 743 | if (PathBBs.front() == Determinator) | ||||
| 744 | continue; | ||||
| 745 | |||||
| 746 | // Otherwise update Metrics for all blocks that will be cloned. If any | ||||
| 747 | // block is already cloned and would be reused, don't double count it. | ||||
| 748 | auto DetIt = std::find(PathBBs.begin(), PathBBs.end(), Determinator); | ||||
| 749 | for (auto BBIt = DetIt; BBIt != PathBBs.end(); BBIt++) { | ||||
| 750 | BB = *BBIt; | ||||
| 751 | VisitedBB = getClonedBB(BB, NextState, DuplicateMap); | ||||
| 752 | if (VisitedBB) | ||||
| 753 | continue; | ||||
| 754 | Metrics.analyzeBasicBlock(BB, *TTI, EphValues); | ||||
| 755 | DuplicateMap[BB].push_back({BB, NextState}); | ||||
| 756 | } | ||||
| 757 | |||||
| 758 | if (Metrics.notDuplicatable) { | ||||
| 759 | LLVM_DEBUG(dbgs() << "DFA Jump Threading: Not jump threading, contains "do { } while (false) | ||||
| 760 | << "non-duplicatable instructions.\n")do { } while (false); | ||||
| 761 | ORE->emit([&]() { | ||||
| 762 | return OptimizationRemarkMissed(DEBUG_TYPE"dfa-jump-threading", "NonDuplicatableInst", | ||||
| 763 | Switch) | ||||
| 764 | << "Contains non-duplicatable instructions."; | ||||
| 765 | }); | ||||
| 766 | return false; | ||||
| 767 | } | ||||
| 768 | |||||
| 769 | if (Metrics.convergent) { | ||||
| 770 | LLVM_DEBUG(dbgs() << "DFA Jump Threading: Not jump threading, contains "do { } while (false) | ||||
| 771 | << "convergent instructions.\n")do { } while (false); | ||||
| 772 | ORE->emit([&]() { | ||||
| 773 | return OptimizationRemarkMissed(DEBUG_TYPE"dfa-jump-threading", "ConvergentInst", Switch) | ||||
| 774 | << "Contains convergent instructions."; | ||||
| 775 | }); | ||||
| 776 | return false; | ||||
| 777 | } | ||||
| 778 | } | ||||
| 779 | |||||
| 780 | unsigned DuplicationCost = 0; | ||||
| 781 | |||||
| 782 | unsigned JumpTableSize = 0; | ||||
| 783 | TTI->getEstimatedNumberOfCaseClusters(*Switch, JumpTableSize, nullptr, | ||||
| 784 | nullptr); | ||||
| 785 | if (JumpTableSize == 0) { | ||||
| 786 | // Factor in the number of conditional branches reduced from jump | ||||
| 787 | // threading. Assume that lowering the switch block is implemented by | ||||
| 788 | // using binary search, hence the LogBase2(). | ||||
| 789 | unsigned CondBranches = | ||||
| 790 | APInt(32, Switch->getNumSuccessors()).ceilLogBase2(); | ||||
| 791 | DuplicationCost = Metrics.NumInsts / CondBranches; | ||||
| 792 | } else { | ||||
| 793 | // Compared with jump tables, the DFA optimizer removes an indirect branch | ||||
| 794 | // on each loop iteration, thus making branch prediction more precise. The | ||||
| 795 | // more branch targets there are, the more likely it is for the branch | ||||
| 796 | // predictor to make a mistake, and the more benefit there is in the DFA | ||||
| 797 | // optimizer. Thus, the more branch targets there are, the lower is the | ||||
| 798 | // cost of the DFA opt. | ||||
| 799 | DuplicationCost = Metrics.NumInsts / JumpTableSize; | ||||
| 800 | } | ||||
| 801 | |||||
| 802 | LLVM_DEBUG(dbgs() << "\nDFA Jump Threading: Cost to jump thread block "do { } while (false) | ||||
| 803 | << SwitchPaths->getSwitchBlock()->getName()do { } while (false) | ||||
| 804 | << " is: " << DuplicationCost << "\n\n")do { } while (false); | ||||
| 805 | |||||
| 806 | if (DuplicationCost > CostThreshold) { | ||||
| 807 | LLVM_DEBUG(dbgs() << "Not jump threading, duplication cost exceeds the "do { } while (false) | ||||
| 808 | << "cost threshold.\n")do { } while (false); | ||||
| 809 | ORE->emit([&]() { | ||||
| 810 | return OptimizationRemarkMissed(DEBUG_TYPE"dfa-jump-threading", "NotProfitable", Switch) | ||||
| 811 | << "Duplication cost exceeds the cost threshold (cost=" | ||||
| 812 | << ore::NV("Cost", DuplicationCost) | ||||
| 813 | << ", threshold=" << ore::NV("Threshold", CostThreshold) << ")."; | ||||
| 814 | }); | ||||
| 815 | return false; | ||||
| 816 | } | ||||
| 817 | |||||
| 818 | ORE->emit([&]() { | ||||
| 819 | return OptimizationRemark(DEBUG_TYPE"dfa-jump-threading", "JumpThreaded", Switch) | ||||
| 820 | << "Switch statement jump-threaded."; | ||||
| 821 | }); | ||||
| 822 | |||||
| 823 | return true; | ||||
| 824 | } | ||||
| 825 | |||||
| 826 | /// Transform each threading path to effectively jump thread the DFA. | ||||
| 827 | void createAllExitPaths() { | ||||
| 828 | DomTreeUpdater DTU(*DT, DomTreeUpdater::UpdateStrategy::Eager); | ||||
| 829 | |||||
| 830 | // Move the switch block to the end of the path, since it will be duplicated | ||||
| 831 | BasicBlock *SwitchBlock = SwitchPaths->getSwitchBlock(); | ||||
| 832 | for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) { | ||||
| 833 | LLVM_DEBUG(dbgs() << TPath << "\n")do { } while (false); | ||||
| 834 | PathType NewPath(TPath.getPath()); | ||||
| 835 | NewPath.push_back(SwitchBlock); | ||||
| 836 | TPath.setPath(NewPath); | ||||
| 837 | } | ||||
| 838 | |||||
| 839 | // Transform the ThreadingPaths and keep track of the cloned values | ||||
| 840 | DuplicateBlockMap DuplicateMap; | ||||
| 841 | DefMap NewDefs; | ||||
| 842 | |||||
| 843 | SmallSet<BasicBlock *, 16> BlocksToClean; | ||||
| 844 | for (BasicBlock *BB : successors(SwitchBlock)) | ||||
| 845 | BlocksToClean.insert(BB); | ||||
| 846 | |||||
| 847 | for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) { | ||||
| 848 | createExitPath(NewDefs, TPath, DuplicateMap, BlocksToClean, &DTU); | ||||
| 849 | NumPaths++; | ||||
| 850 | } | ||||
| 851 | |||||
| 852 | // After all paths are cloned, now update the last successor of the cloned | ||||
| 853 | // path so it skips over the switch statement | ||||
| 854 | for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) | ||||
| 855 | updateLastSuccessor(TPath, DuplicateMap, &DTU); | ||||
| 856 | |||||
| 857 | // For each instruction that was cloned and used outside, update its uses | ||||
| 858 | updateSSA(NewDefs); | ||||
| 859 | |||||
| 860 | // Clean PHI Nodes for the newly created blocks | ||||
| 861 | for (BasicBlock *BB : BlocksToClean) | ||||
| 862 | cleanPhiNodes(BB); | ||||
| 863 | } | ||||
| 864 | |||||
| 865 | /// For a specific ThreadingPath \p Path, create an exit path starting from | ||||
| 866 | /// the determinator block. | ||||
| 867 | /// | ||||
| 868 | /// To remember the correct destination, we have to duplicate blocks | ||||
| 869 | /// corresponding to each state. Also update the terminating instruction of | ||||
| 870 | /// the predecessors, and phis in the successor blocks. | ||||
| 871 | void createExitPath(DefMap &NewDefs, ThreadingPath &Path, | ||||
| 872 | DuplicateBlockMap &DuplicateMap, | ||||
| 873 | SmallSet<BasicBlock *, 16> &BlocksToClean, | ||||
| 874 | DomTreeUpdater *DTU) { | ||||
| 875 | uint64_t NextState = Path.getExitValue(); | ||||
| 876 | const BasicBlock *Determinator = Path.getDeterminatorBB(); | ||||
| 877 | PathType PathBBs = Path.getPath(); | ||||
| 878 | |||||
| 879 | // Don't select the placeholder block in front | ||||
| 880 | if (PathBBs.front() == Determinator) | ||||
| 881 | PathBBs.pop_front(); | ||||
| 882 | |||||
| 883 | auto DetIt = std::find(PathBBs.begin(), PathBBs.end(), Determinator); | ||||
| 884 | auto Prev = std::prev(DetIt); | ||||
| 885 | BasicBlock *PrevBB = *Prev; | ||||
| 886 | for (auto BBIt = DetIt; BBIt != PathBBs.end(); BBIt++) { | ||||
| 887 | BasicBlock *BB = *BBIt; | ||||
| 888 | BlocksToClean.insert(BB); | ||||
| 889 | |||||
| 890 | // We already cloned BB for this NextState, now just update the branch | ||||
| 891 | // and continue. | ||||
| 892 | BasicBlock *NextBB = getClonedBB(BB, NextState, DuplicateMap); | ||||
| 893 | if (NextBB) { | ||||
| 894 | updatePredecessor(PrevBB, BB, NextBB, DTU); | ||||
| 895 | PrevBB = NextBB; | ||||
| 896 | continue; | ||||
| 897 | } | ||||
| 898 | |||||
| 899 | // Clone the BB and update the successor of Prev to jump to the new block | ||||
| 900 | BasicBlock *NewBB = cloneBlockAndUpdatePredecessor( | ||||
| 901 | BB, PrevBB, NextState, DuplicateMap, NewDefs, DTU); | ||||
| 902 | DuplicateMap[BB].push_back({NewBB, NextState}); | ||||
| 903 | BlocksToClean.insert(NewBB); | ||||
| 904 | PrevBB = NewBB; | ||||
| 905 | } | ||||
| 906 | } | ||||
| 907 | |||||
| 908 | /// Restore SSA form after cloning blocks. | ||||
| 909 | /// | ||||
| 910 | /// Each cloned block creates new defs for a variable, and the uses need to be | ||||
| 911 | /// updated to reflect this. The uses may be replaced with a cloned value, or | ||||
| 912 | /// some derived phi instruction. Note that all uses of a value defined in the | ||||
| 913 | /// same block were already remapped when cloning the block. | ||||
| 914 | void updateSSA(DefMap &NewDefs) { | ||||
| 915 | SSAUpdaterBulk SSAUpdate; | ||||
| 916 | SmallVector<Use *, 16> UsesToRename; | ||||
| 917 | |||||
| 918 | for (auto KV : NewDefs) { | ||||
| 919 | Instruction *I = KV.first; | ||||
| 920 | BasicBlock *BB = I->getParent(); | ||||
| 921 | std::vector<Instruction *> Cloned = KV.second; | ||||
| 922 | |||||
| 923 | // Scan all uses of this instruction to see if it is used outside of its | ||||
| 924 | // block, and if so, record them in UsesToRename. | ||||
| 925 | for (Use &U : I->uses()) { | ||||
| 926 | Instruction *User = cast<Instruction>(U.getUser()); | ||||
| 927 | if (PHINode *UserPN = dyn_cast<PHINode>(User)) { | ||||
| 928 | if (UserPN->getIncomingBlock(U) == BB) | ||||
| 929 | continue; | ||||
| 930 | } else if (User->getParent() == BB) { | ||||
| 931 | continue; | ||||
| 932 | } | ||||
| 933 | |||||
| 934 | UsesToRename.push_back(&U); | ||||
| 935 | } | ||||
| 936 | |||||
| 937 | // If there are no uses outside the block, we're done with this | ||||
| 938 | // instruction. | ||||
| 939 | if (UsesToRename.empty()) | ||||
| 940 | continue; | ||||
| 941 | LLVM_DEBUG(dbgs() << "DFA-JT: Renaming non-local uses of: " << *Ido { } while (false) | ||||
| 942 | << "\n")do { } while (false); | ||||
| 943 | |||||
| 944 | // We found a use of I outside of BB. Rename all uses of I that are | ||||
| 945 | // outside its block to be uses of the appropriate PHI node etc. See | ||||
| 946 | // ValuesInBlocks with the values we know. | ||||
| 947 | unsigned VarNum = SSAUpdate.AddVariable(I->getName(), I->getType()); | ||||
| 948 | SSAUpdate.AddAvailableValue(VarNum, BB, I); | ||||
| 949 | for (Instruction *New : Cloned) | ||||
| 950 | SSAUpdate.AddAvailableValue(VarNum, New->getParent(), New); | ||||
| 951 | |||||
| 952 | while (!UsesToRename.empty()) | ||||
| 953 | SSAUpdate.AddUse(VarNum, UsesToRename.pop_back_val()); | ||||
| 954 | |||||
| 955 | LLVM_DEBUG(dbgs() << "\n")do { } while (false); | ||||
| 956 | } | ||||
| 957 | // SSAUpdater handles phi placement and renaming uses with the appropriate | ||||
| 958 | // value. | ||||
| 959 | SSAUpdate.RewriteAllUses(DT); | ||||
| 960 | } | ||||
| 961 | |||||
| 962 | /// Clones a basic block, and adds it to the CFG. | ||||
| 963 | /// | ||||
| 964 | /// This function also includes updating phi nodes in the successors of the | ||||
| 965 | /// BB, and remapping uses that were defined locally in the cloned BB. | ||||
| 966 | BasicBlock *cloneBlockAndUpdatePredecessor(BasicBlock *BB, BasicBlock *PrevBB, | ||||
| 967 | uint64_t NextState, | ||||
| 968 | DuplicateBlockMap &DuplicateMap, | ||||
| 969 | DefMap &NewDefs, | ||||
| 970 | DomTreeUpdater *DTU) { | ||||
| 971 | ValueToValueMapTy VMap; | ||||
| 972 | BasicBlock *NewBB = CloneBasicBlock( | ||||
| 973 | BB, VMap, ".jt" + std::to_string(NextState), BB->getParent()); | ||||
| 974 | NewBB->moveAfter(BB); | ||||
| 975 | NumCloned++; | ||||
| 976 | |||||
| 977 | for (Instruction &I : *NewBB) { | ||||
| 978 | // Do not remap operands of PHINode in case a definition in BB is an | ||||
| 979 | // incoming value to a phi in the same block. This incoming value will | ||||
| 980 | // be renamed later while restoring SSA. | ||||
| 981 | if (isa<PHINode>(&I)) | ||||
| 982 | continue; | ||||
| 983 | RemapInstruction(&I, VMap, | ||||
| 984 | RF_IgnoreMissingLocals | RF_NoModuleLevelChanges); | ||||
| 985 | if (AssumeInst *II = dyn_cast<AssumeInst>(&I)) | ||||
| 986 | AC->registerAssumption(II); | ||||
| 987 | } | ||||
| 988 | |||||
| 989 | updateSuccessorPhis(BB, NewBB, NextState, VMap, DuplicateMap); | ||||
| 990 | updatePredecessor(PrevBB, BB, NewBB, DTU); | ||||
| 991 | updateDefMap(NewDefs, VMap); | ||||
| 992 | |||||
| 993 | // Add all successors to the DominatorTree | ||||
| 994 | SmallPtrSet<BasicBlock *, 4> SuccSet; | ||||
| 995 | for (auto *SuccBB : successors(NewBB)) { | ||||
| 996 | if (SuccSet.insert(SuccBB).second) | ||||
| 997 | DTU->applyUpdates({{DominatorTree::Insert, NewBB, SuccBB}}); | ||||
| 998 | } | ||||
| 999 | SuccSet.clear(); | ||||
| 1000 | return NewBB; | ||||
| 1001 | } | ||||
| 1002 | |||||
| 1003 | /// Update the phi nodes in BB's successors. | ||||
| 1004 | /// | ||||
| 1005 | /// This means creating a new incoming value from NewBB with the new | ||||
| 1006 | /// instruction wherever there is an incoming value from BB. | ||||
| 1007 | void updateSuccessorPhis(BasicBlock *BB, BasicBlock *ClonedBB, | ||||
| 1008 | uint64_t NextState, ValueToValueMapTy &VMap, | ||||
| 1009 | DuplicateBlockMap &DuplicateMap) { | ||||
| 1010 | std::vector<BasicBlock *> BlocksToUpdate; | ||||
| 1011 | |||||
| 1012 | // If BB is the last block in the path, we can simply update the one case | ||||
| 1013 | // successor that will be reached. | ||||
| 1014 | if (BB == SwitchPaths->getSwitchBlock()) { | ||||
| 1015 | SwitchInst *Switch = SwitchPaths->getSwitchInst(); | ||||
| 1016 | BasicBlock *NextCase = getNextCaseSuccessor(Switch, NextState); | ||||
| 1017 | BlocksToUpdate.push_back(NextCase); | ||||
| 1018 | BasicBlock *ClonedSucc = getClonedBB(NextCase, NextState, DuplicateMap); | ||||
| 1019 | if (ClonedSucc) | ||||
| 1020 | BlocksToUpdate.push_back(ClonedSucc); | ||||
| 1021 | } | ||||
| 1022 | // Otherwise update phis in all successors. | ||||
| 1023 | else { | ||||
| 1024 | for (BasicBlock *Succ : successors(BB)) { | ||||
| 1025 | BlocksToUpdate.push_back(Succ); | ||||
| 1026 | |||||
| 1027 | // Check if a successor has already been cloned for the particular exit | ||||
| 1028 | // value. In this case if a successor was already cloned, the phi nodes | ||||
| 1029 | // in the cloned block should be updated directly. | ||||
| 1030 | BasicBlock *ClonedSucc = getClonedBB(Succ, NextState, DuplicateMap); | ||||
| 1031 | if (ClonedSucc) | ||||
| 1032 | BlocksToUpdate.push_back(ClonedSucc); | ||||
| 1033 | } | ||||
| 1034 | } | ||||
| 1035 | |||||
| 1036 | // If there is a phi with an incoming value from BB, create a new incoming | ||||
| 1037 | // value for the new predecessor ClonedBB. The value will either be the same | ||||
| 1038 | // value from BB or a cloned value. | ||||
| 1039 | for (BasicBlock *Succ : BlocksToUpdate) { | ||||
| 1040 | for (auto II = Succ->begin(); PHINode *Phi = dyn_cast<PHINode>(II); | ||||
| 1041 | ++II) { | ||||
| 1042 | Value *Incoming = Phi->getIncomingValueForBlock(BB); | ||||
| 1043 | if (Incoming) { | ||||
| 1044 | if (isa<Constant>(Incoming)) { | ||||
| 1045 | Phi->addIncoming(Incoming, ClonedBB); | ||||
| 1046 | continue; | ||||
| 1047 | } | ||||
| 1048 | Value *ClonedVal = VMap[Incoming]; | ||||
| 1049 | if (ClonedVal) | ||||
| 1050 | Phi->addIncoming(ClonedVal, ClonedBB); | ||||
| 1051 | else | ||||
| 1052 | Phi->addIncoming(Incoming, ClonedBB); | ||||
| 1053 | } | ||||
| 1054 | } | ||||
| 1055 | } | ||||
| 1056 | } | ||||
| 1057 | |||||
| 1058 | /// Sets the successor of PrevBB to be NewBB instead of OldBB. Note that all | ||||
| 1059 | /// other successors are kept as well. | ||||
| 1060 | void updatePredecessor(BasicBlock *PrevBB, BasicBlock *OldBB, | ||||
| 1061 | BasicBlock *NewBB, DomTreeUpdater *DTU) { | ||||
| 1062 | // When a path is reused, there is a chance that predecessors were already | ||||
| 1063 | // updated before. Check if the predecessor needs to be updated first. | ||||
| 1064 | if (!isPredecessor(OldBB, PrevBB)) | ||||
| 1065 | return; | ||||
| 1066 | |||||
| 1067 | Instruction *PrevTerm = PrevBB->getTerminator(); | ||||
| 1068 | for (unsigned Idx = 0; Idx < PrevTerm->getNumSuccessors(); Idx++) { | ||||
| 1069 | if (PrevTerm->getSuccessor(Idx) == OldBB) { | ||||
| 1070 | OldBB->removePredecessor(PrevBB, /* KeepOneInputPHIs = */ true); | ||||
| 1071 | PrevTerm->setSuccessor(Idx, NewBB); | ||||
| 1072 | } | ||||
| 1073 | } | ||||
| 1074 | DTU->applyUpdates({{DominatorTree::Delete, PrevBB, OldBB}, | ||||
| 1075 | {DominatorTree::Insert, PrevBB, NewBB}}); | ||||
| 1076 | } | ||||
| 1077 | |||||
| 1078 | /// Add new value mappings to the DefMap to keep track of all new definitions | ||||
| 1079 | /// for a particular instruction. These will be used while updating SSA form. | ||||
| 1080 | void updateDefMap(DefMap &NewDefs, ValueToValueMapTy &VMap) { | ||||
| 1081 | for (auto Entry : VMap) { | ||||
| 1082 | Instruction *Inst = | ||||
| 1083 | dyn_cast<Instruction>(const_cast<Value *>(Entry.first)); | ||||
| 1084 | if (!Inst || !Entry.second || isa<BranchInst>(Inst) || | ||||
| 1085 | isa<SwitchInst>(Inst)) { | ||||
| 1086 | continue; | ||||
| 1087 | } | ||||
| 1088 | |||||
| 1089 | Instruction *Cloned = dyn_cast<Instruction>(Entry.second); | ||||
| 1090 | if (!Cloned) | ||||
| 1091 | continue; | ||||
| 1092 | |||||
| 1093 | if (NewDefs.find(Inst) == NewDefs.end()) | ||||
| 1094 | NewDefs[Inst] = {Cloned}; | ||||
| 1095 | else | ||||
| 1096 | NewDefs[Inst].push_back(Cloned); | ||||
| 1097 | } | ||||
| 1098 | } | ||||
| 1099 | |||||
| 1100 | /// Update the last branch of a particular cloned path to point to the correct | ||||
| 1101 | /// case successor. | ||||
| 1102 | /// | ||||
| 1103 | /// Note that this is an optional step and would have been done in later | ||||
| 1104 | /// optimizations, but it makes the CFG significantly easier to work with. | ||||
| 1105 | void updateLastSuccessor(ThreadingPath &TPath, | ||||
| 1106 | DuplicateBlockMap &DuplicateMap, | ||||
| 1107 | DomTreeUpdater *DTU) { | ||||
| 1108 | uint64_t NextState = TPath.getExitValue(); | ||||
| 1109 | BasicBlock *BB = TPath.getPath().back(); | ||||
| 1110 | BasicBlock *LastBlock = getClonedBB(BB, NextState, DuplicateMap); | ||||
| 1111 | |||||
| 1112 | // Note multiple paths can end at the same block so check that it is not | ||||
| 1113 | // updated yet | ||||
| 1114 | if (!isa<SwitchInst>(LastBlock->getTerminator())) | ||||
| 1115 | return; | ||||
| 1116 | SwitchInst *Switch = cast<SwitchInst>(LastBlock->getTerminator()); | ||||
| 1117 | BasicBlock *NextCase = getNextCaseSuccessor(Switch, NextState); | ||||
| 1118 | |||||
| 1119 | std::vector<DominatorTree::UpdateType> DTUpdates; | ||||
| 1120 | SmallPtrSet<BasicBlock *, 4> SuccSet; | ||||
| 1121 | for (BasicBlock *Succ : successors(LastBlock)) { | ||||
| 1122 | if (Succ != NextCase && SuccSet.insert(Succ).second) | ||||
| 1123 | DTUpdates.push_back({DominatorTree::Delete, LastBlock, Succ}); | ||||
| 1124 | } | ||||
| 1125 | |||||
| 1126 | Switch->eraseFromParent(); | ||||
| 1127 | BranchInst::Create(NextCase, LastBlock); | ||||
| 1128 | |||||
| 1129 | DTU->applyUpdates(DTUpdates); | ||||
| 1130 | } | ||||
| 1131 | |||||
| 1132 | /// After cloning blocks, some of the phi nodes have extra incoming values | ||||
| 1133 | /// that are no longer used. This function removes them. | ||||
| 1134 | void cleanPhiNodes(BasicBlock *BB) { | ||||
| 1135 | // If BB is no longer reachable, remove any remaining phi nodes | ||||
| 1136 | if (pred_empty(BB)) { | ||||
| 1137 | std::vector<PHINode *> PhiToRemove; | ||||
| 1138 | for (auto II = BB->begin(); PHINode *Phi = dyn_cast<PHINode>(II); ++II) { | ||||
| 1139 | PhiToRemove.push_back(Phi); | ||||
| 1140 | } | ||||
| 1141 | for (PHINode *PN : PhiToRemove) { | ||||
| 1142 | PN->replaceAllUsesWith(UndefValue::get(PN->getType())); | ||||
| 1143 | PN->eraseFromParent(); | ||||
| 1144 | } | ||||
| 1145 | return; | ||||
| 1146 | } | ||||
| 1147 | |||||
| 1148 | // Remove any incoming values that come from an invalid predecessor | ||||
| 1149 | for (auto II = BB->begin(); PHINode *Phi = dyn_cast<PHINode>(II); ++II) { | ||||
| 1150 | std::vector<BasicBlock *> BlocksToRemove; | ||||
| 1151 | for (BasicBlock *IncomingBB : Phi->blocks()) { | ||||
| 1152 | if (!isPredecessor(BB, IncomingBB)) | ||||
| 1153 | BlocksToRemove.push_back(IncomingBB); | ||||
| 1154 | } | ||||
| 1155 | for (BasicBlock *BB : BlocksToRemove) | ||||
| 1156 | Phi->removeIncomingValue(BB); | ||||
| 1157 | } | ||||
| 1158 | } | ||||
| 1159 | |||||
| 1160 | /// Checks if BB was already cloned for a particular next state value. If it | ||||
| 1161 | /// was then it returns this cloned block, and otherwise null. | ||||
| 1162 | BasicBlock *getClonedBB(BasicBlock *BB, uint64_t NextState, | ||||
| 1163 | DuplicateBlockMap &DuplicateMap) { | ||||
| 1164 | CloneList ClonedBBs = DuplicateMap[BB]; | ||||
| 1165 | |||||
| 1166 | // Find an entry in the CloneList with this NextState. If it exists then | ||||
| 1167 | // return the corresponding BB | ||||
| 1168 | auto It = llvm::find_if(ClonedBBs, [NextState](const ClonedBlock &C) { | ||||
| 1169 | return C.State == NextState; | ||||
| 1170 | }); | ||||
| 1171 | return It != ClonedBBs.end() ? (*It).BB : nullptr; | ||||
| 1172 | } | ||||
| 1173 | |||||
| 1174 | /// Helper to get the successor corresponding to a particular case value for | ||||
| 1175 | /// a switch statement. | ||||
| 1176 | BasicBlock *getNextCaseSuccessor(SwitchInst *Switch, uint64_t NextState) { | ||||
| 1177 | BasicBlock *NextCase = nullptr; | ||||
| 1178 | for (auto Case : Switch->cases()) { | ||||
| 1179 | if (Case.getCaseValue()->getZExtValue() == NextState) { | ||||
| 1180 | NextCase = Case.getCaseSuccessor(); | ||||
| 1181 | break; | ||||
| 1182 | } | ||||
| 1183 | } | ||||
| 1184 | if (!NextCase) | ||||
| 1185 | NextCase = Switch->getDefaultDest(); | ||||
| 1186 | return NextCase; | ||||
| 1187 | } | ||||
| 1188 | |||||
| 1189 | /// Returns true if IncomingBB is a predecessor of BB. | ||||
| 1190 | bool isPredecessor(BasicBlock *BB, BasicBlock *IncomingBB) { | ||||
| 1191 | return llvm::find(predecessors(BB), IncomingBB) != pred_end(BB); | ||||
| 1192 | } | ||||
| 1193 | |||||
| 1194 | AllSwitchPaths *SwitchPaths; | ||||
| 1195 | DominatorTree *DT; | ||||
| 1196 | AssumptionCache *AC; | ||||
| 1197 | TargetTransformInfo *TTI; | ||||
| 1198 | OptimizationRemarkEmitter *ORE; | ||||
| 1199 | SmallPtrSet<const Value *, 32> EphValues; | ||||
| 1200 | std::vector<ThreadingPath> TPaths; | ||||
| 1201 | }; | ||||
| 1202 | |||||
| 1203 | bool DFAJumpThreading::run(Function &F) { | ||||
| 1204 | LLVM_DEBUG(dbgs() << "\nDFA Jump threading: " << F.getName() << "\n")do { } while (false); | ||||
| 1205 | |||||
| 1206 | if (F.hasOptSize()) { | ||||
| 1207 | LLVM_DEBUG(dbgs() << "Skipping due to the 'minsize' attribute\n")do { } while (false); | ||||
| 1208 | return false; | ||||
| 1209 | } | ||||
| 1210 | |||||
| 1211 | if (ClViewCfgBefore) | ||||
| 1212 | F.viewCFG(); | ||||
| 1213 | |||||
| 1214 | SmallVector<AllSwitchPaths, 2> ThreadableLoops; | ||||
| 1215 | bool MadeChanges = false; | ||||
| 1216 | |||||
| 1217 | for (BasicBlock &BB : F) { | ||||
| 1218 | auto *SI = dyn_cast<SwitchInst>(BB.getTerminator()); | ||||
| 1219 | if (!SI
| ||||
| 1220 | continue; | ||||
| 1221 | |||||
| 1222 | LLVM_DEBUG(dbgs() << "\nCheck if SwitchInst in BB " << BB.getName()do { } while (false) | ||||
| 1223 | << " is predictable\n")do { } while (false); | ||||
| 1224 | MainSwitch Switch(SI, ORE); | ||||
| 1225 | |||||
| 1226 | if (!Switch.getInstr()) | ||||
| 1227 | continue; | ||||
| 1228 | |||||
| 1229 | LLVM_DEBUG(dbgs() << "\nSwitchInst in BB " << BB.getName() << " is a "do { } while (false) | ||||
| 1230 | << "candidate for jump threading\n")do { } while (false); | ||||
| 1231 | LLVM_DEBUG(SI->dump())do { } while (false); | ||||
| 1232 | |||||
| 1233 | unfoldSelectInstrs(DT, Switch.getSelectInsts()); | ||||
| 1234 | if (!Switch.getSelectInsts().empty()) | ||||
| 1235 | MadeChanges = true; | ||||
| 1236 | |||||
| 1237 | AllSwitchPaths SwitchPaths(&Switch, ORE); | ||||
| 1238 | SwitchPaths.run(); | ||||
| 1239 | |||||
| 1240 | if (SwitchPaths.getNumThreadingPaths() > 0) { | ||||
| 1241 | ThreadableLoops.push_back(SwitchPaths); | ||||
| 1242 | |||||
| 1243 | // For the time being limit this optimization to occurring once in a | ||||
| 1244 | // function since it can change the CFG significantly. This is not a | ||||
| 1245 | // strict requirement but it can cause buggy behavior if there is an | ||||
| 1246 | // overlap of blocks in different opportunities. There is a lot of room to | ||||
| 1247 | // experiment with catching more opportunities here. | ||||
| 1248 | break; | ||||
| 1249 | } | ||||
| 1250 | } | ||||
| 1251 | |||||
| 1252 | SmallPtrSet<const Value *, 32> EphValues; | ||||
| 1253 | if (ThreadableLoops.size() > 0) | ||||
| 1254 | CodeMetrics::collectEphemeralValues(&F, AC, EphValues); | ||||
| 1255 | |||||
| 1256 | for (AllSwitchPaths SwitchPaths : ThreadableLoops) { | ||||
| 1257 | TransformDFA Transform(&SwitchPaths, DT, AC, TTI, ORE, EphValues); | ||||
| 1258 | Transform.run(); | ||||
| 1259 | MadeChanges = true; | ||||
| 1260 | } | ||||
| 1261 | |||||
| 1262 | #ifdef EXPENSIVE_CHECKS | ||||
| 1263 | assert(DT->verify(DominatorTree::VerificationLevel::Full))((void)0); | ||||
| 1264 | verifyFunction(F, &dbgs()); | ||||
| 1265 | #endif | ||||
| 1266 | |||||
| 1267 | return MadeChanges; | ||||
| 1268 | } | ||||
| 1269 | |||||
| 1270 | } // end anonymous namespace | ||||
| 1271 | |||||
| 1272 | /// Integrate with the new Pass Manager | ||||
| 1273 | PreservedAnalyses DFAJumpThreadingPass::run(Function &F, | ||||
| 1274 | FunctionAnalysisManager &AM) { | ||||
| 1275 | AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F); | ||||
| 1276 | DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F); | ||||
| 1277 | TargetTransformInfo &TTI = AM.getResult<TargetIRAnalysis>(F); | ||||
| 1278 | OptimizationRemarkEmitter ORE(&F); | ||||
| 1279 | |||||
| 1280 | if (!DFAJumpThreading(&AC, &DT, &TTI, &ORE).run(F)) | ||||
| |||||
| 1281 | return PreservedAnalyses::all(); | ||||
| 1282 | |||||
| 1283 | PreservedAnalyses PA; | ||||
| 1284 | PA.preserve<DominatorTreeAnalysis>(); | ||||
| 1285 | return PA; | ||||
| 1286 | } |