1 //===-- GCStrategy.cpp - Garbage collection infrastructure -----------------===// 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 // This file implements target- and collector-independent garbage collection 11 // infrastructure. 12 // 13 // GCMachineCodeAnalysis identifies the GC safe points in the machine code. 14 // Roots are identified in SelectionDAGISel. 15 // 16 //===----------------------------------------------------------------------===// 17 18 #include "llvm/CodeGen/GCStrategy.h" 19 #include "llvm/CodeGen/Passes.h" 20 #include "llvm/IntrinsicInst.h" 21 #include "llvm/Module.h" 22 #include "llvm/Analysis/Dominators.h" 23 #include "llvm/CodeGen/MachineFrameInfo.h" 24 #include "llvm/CodeGen/MachineFunctionPass.h" 25 #include "llvm/CodeGen/MachineInstrBuilder.h" 26 #include "llvm/CodeGen/MachineModuleInfo.h" 27 #include "llvm/Target/TargetFrameLowering.h" 28 #include "llvm/Target/TargetInstrInfo.h" 29 #include "llvm/Target/TargetMachine.h" 30 #include "llvm/Target/TargetRegisterInfo.h" 31 #include "llvm/Support/Debug.h" 32 #include "llvm/Support/ErrorHandling.h" 33 #include "llvm/Support/raw_ostream.h" 34 35 using namespace llvm; 36 37 namespace { 38 39 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or 40 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as 41 /// directed by the GCStrategy. It also performs automatic root initialization 42 /// and custom intrinsic lowering. 43 class LowerIntrinsics : public FunctionPass { 44 static bool NeedsDefaultLoweringPass(const GCStrategy &C); 45 static bool NeedsCustomLoweringPass(const GCStrategy &C); 46 static bool CouldBecomeSafePoint(Instruction *I); 47 bool PerformDefaultLowering(Function &F, GCStrategy &Coll); 48 static bool InsertRootInitializers(Function &F, 49 AllocaInst **Roots, unsigned Count); 50 51 public: 52 static char ID; 53 54 LowerIntrinsics(); 55 const char *getPassName() const; 56 void getAnalysisUsage(AnalysisUsage &AU) const; 57 58 bool doInitialization(Module &M); 59 bool runOnFunction(Function &F); 60 }; 61 62 63 /// GCMachineCodeAnalysis - This is a target-independent pass over the machine 64 /// function representation to identify safe points for the garbage collector 65 /// in the machine code. It inserts labels at safe points and populates a 66 /// GCMetadata record for each function. 67 class GCMachineCodeAnalysis : public MachineFunctionPass { 68 const TargetMachine *TM; 69 GCFunctionInfo *FI; 70 MachineModuleInfo *MMI; 71 const TargetInstrInfo *TII; 72 73 void FindSafePoints(MachineFunction &MF); 74 void VisitCallPoint(MachineBasicBlock::iterator MI); 75 MCSymbol *InsertLabel(MachineBasicBlock &MBB, 76 MachineBasicBlock::iterator MI, 77 DebugLoc DL) const; 78 79 void FindStackOffsets(MachineFunction &MF); 80 81 public: 82 static char ID; 83 84 GCMachineCodeAnalysis(); 85 void getAnalysisUsage(AnalysisUsage &AU) const; 86 87 bool runOnMachineFunction(MachineFunction &MF); 88 }; 89 90 } 91 92 // ----------------------------------------------------------------------------- 93 94 GCStrategy::GCStrategy() : 95 NeededSafePoints(0), 96 CustomReadBarriers(false), 97 CustomWriteBarriers(false), 98 CustomRoots(false), 99 CustomSafePoints(false), 100 InitRoots(true), 101 UsesMetadata(false) 102 {} 103 104 GCStrategy::~GCStrategy() { 105 for (iterator I = begin(), E = end(); I != E; ++I) 106 delete *I; 107 108 Functions.clear(); 109 } 110 111 bool GCStrategy::initializeCustomLowering(Module &M) { return false; } 112 113 bool GCStrategy::performCustomLowering(Function &F) { 114 dbgs() << "gc " << getName() << " must override performCustomLowering.\n"; 115 llvm_unreachable("must override performCustomLowering"); 116 } 117 118 119 bool GCStrategy::findCustomSafePoints(GCFunctionInfo& FI, MachineFunction &F) { 120 dbgs() << "gc " << getName() << " must override findCustomSafePoints.\n"; 121 llvm_unreachable(0); 122 } 123 124 125 GCFunctionInfo *GCStrategy::insertFunctionInfo(const Function &F) { 126 GCFunctionInfo *FI = new GCFunctionInfo(F, *this); 127 Functions.push_back(FI); 128 return FI; 129 } 130 131 // ----------------------------------------------------------------------------- 132 133 INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering", 134 false, false) 135 INITIALIZE_PASS_DEPENDENCY(GCModuleInfo) 136 INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false) 137 138 FunctionPass *llvm::createGCLoweringPass() { 139 return new LowerIntrinsics(); 140 } 141 142 char LowerIntrinsics::ID = 0; 143 144 LowerIntrinsics::LowerIntrinsics() 145 : FunctionPass(ID) { 146 initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry()); 147 } 148 149 const char *LowerIntrinsics::getPassName() const { 150 return "Lower Garbage Collection Instructions"; 151 } 152 153 void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const { 154 FunctionPass::getAnalysisUsage(AU); 155 AU.addRequired<GCModuleInfo>(); 156 AU.addPreserved<DominatorTree>(); 157 } 158 159 /// doInitialization - If this module uses the GC intrinsics, find them now. 160 bool LowerIntrinsics::doInitialization(Module &M) { 161 // FIXME: This is rather antisocial in the context of a JIT since it performs 162 // work against the entire module. But this cannot be done at 163 // runFunction time (initializeCustomLowering likely needs to change 164 // the module). 165 GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>(); 166 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?"); 167 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 168 if (!I->isDeclaration() && I->hasGC()) 169 MI->getFunctionInfo(*I); // Instantiate the GC strategy. 170 171 bool MadeChange = false; 172 for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I) 173 if (NeedsCustomLoweringPass(**I)) 174 if ((*I)->initializeCustomLowering(M)) 175 MadeChange = true; 176 177 return MadeChange; 178 } 179 180 bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots, 181 unsigned Count) { 182 // Scroll past alloca instructions. 183 BasicBlock::iterator IP = F.getEntryBlock().begin(); 184 while (isa<AllocaInst>(IP)) ++IP; 185 186 // Search for initializers in the initial BB. 187 SmallPtrSet<AllocaInst*,16> InitedRoots; 188 for (; !CouldBecomeSafePoint(IP); ++IP) 189 if (StoreInst *SI = dyn_cast<StoreInst>(IP)) 190 if (AllocaInst *AI = 191 dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts())) 192 InitedRoots.insert(AI); 193 194 // Add root initializers. 195 bool MadeChange = false; 196 197 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I) 198 if (!InitedRoots.count(*I)) { 199 StoreInst* SI = new StoreInst(ConstantPointerNull::get(cast<PointerType>( 200 cast<PointerType>((*I)->getType())->getElementType())), 201 *I); 202 SI->insertAfter(*I); 203 MadeChange = true; 204 } 205 206 return MadeChange; 207 } 208 209 bool LowerIntrinsics::NeedsDefaultLoweringPass(const GCStrategy &C) { 210 // Default lowering is necessary only if read or write barriers have a default 211 // action. The default for roots is no action. 212 return !C.customWriteBarrier() 213 || !C.customReadBarrier() 214 || C.initializeRoots(); 215 } 216 217 bool LowerIntrinsics::NeedsCustomLoweringPass(const GCStrategy &C) { 218 // Custom lowering is only necessary if enabled for some action. 219 return C.customWriteBarrier() 220 || C.customReadBarrier() 221 || C.customRoots(); 222 } 223 224 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the 225 /// instruction could introduce a safe point. 226 bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) { 227 // The natural definition of instructions which could introduce safe points 228 // are: 229 // 230 // - call, invoke (AfterCall, BeforeCall) 231 // - phis (Loops) 232 // - invoke, ret, unwind (Exit) 233 // 234 // However, instructions as seemingly inoccuous as arithmetic can become 235 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead 236 // it is necessary to take a conservative approach. 237 238 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) || 239 isa<StoreInst>(I) || isa<LoadInst>(I)) 240 return false; 241 242 // llvm.gcroot is safe because it doesn't do anything at runtime. 243 if (CallInst *CI = dyn_cast<CallInst>(I)) 244 if (Function *F = CI->getCalledFunction()) 245 if (unsigned IID = F->getIntrinsicID()) 246 if (IID == Intrinsic::gcroot) 247 return false; 248 249 return true; 250 } 251 252 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores. 253 /// Leave gcroot intrinsics; the code generator needs to see those. 254 bool LowerIntrinsics::runOnFunction(Function &F) { 255 // Quick exit for functions that do not use GC. 256 if (!F.hasGC()) 257 return false; 258 259 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F); 260 GCStrategy &S = FI.getStrategy(); 261 262 bool MadeChange = false; 263 264 if (NeedsDefaultLoweringPass(S)) 265 MadeChange |= PerformDefaultLowering(F, S); 266 267 bool UseCustomLoweringPass = NeedsCustomLoweringPass(S); 268 if (UseCustomLoweringPass) 269 MadeChange |= S.performCustomLowering(F); 270 271 // Custom lowering may modify the CFG, so dominators must be recomputed. 272 if (UseCustomLoweringPass) { 273 if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) 274 DT->DT->recalculate(F); 275 } 276 277 return MadeChange; 278 } 279 280 bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) { 281 bool LowerWr = !S.customWriteBarrier(); 282 bool LowerRd = !S.customReadBarrier(); 283 bool InitRoots = S.initializeRoots(); 284 285 SmallVector<AllocaInst*, 32> Roots; 286 287 bool MadeChange = false; 288 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 289 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) { 290 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) { 291 Function *F = CI->getCalledFunction(); 292 switch (F->getIntrinsicID()) { 293 case Intrinsic::gcwrite: 294 if (LowerWr) { 295 // Replace a write barrier with a simple store. 296 Value *St = new StoreInst(CI->getArgOperand(0), 297 CI->getArgOperand(2), CI); 298 CI->replaceAllUsesWith(St); 299 CI->eraseFromParent(); 300 } 301 break; 302 case Intrinsic::gcread: 303 if (LowerRd) { 304 // Replace a read barrier with a simple load. 305 Value *Ld = new LoadInst(CI->getArgOperand(1), "", CI); 306 Ld->takeName(CI); 307 CI->replaceAllUsesWith(Ld); 308 CI->eraseFromParent(); 309 } 310 break; 311 case Intrinsic::gcroot: 312 if (InitRoots) { 313 // Initialize the GC root, but do not delete the intrinsic. The 314 // backend needs the intrinsic to flag the stack slot. 315 Roots.push_back(cast<AllocaInst>( 316 CI->getArgOperand(0)->stripPointerCasts())); 317 } 318 break; 319 default: 320 continue; 321 } 322 323 MadeChange = true; 324 } 325 } 326 } 327 328 if (Roots.size()) 329 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size()); 330 331 return MadeChange; 332 } 333 334 // ----------------------------------------------------------------------------- 335 336 char GCMachineCodeAnalysis::ID = 0; 337 char &llvm::GCMachineCodeAnalysisID = GCMachineCodeAnalysis::ID; 338 339 INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis", 340 "Analyze Machine Code For Garbage Collection", false, false) 341 342 GCMachineCodeAnalysis::GCMachineCodeAnalysis() 343 : MachineFunctionPass(ID) {} 344 345 void GCMachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 346 MachineFunctionPass::getAnalysisUsage(AU); 347 AU.setPreservesAll(); 348 AU.addRequired<MachineModuleInfo>(); 349 AU.addRequired<GCModuleInfo>(); 350 } 351 352 MCSymbol *GCMachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB, 353 MachineBasicBlock::iterator MI, 354 DebugLoc DL) const { 355 MCSymbol *Label = MBB.getParent()->getContext().CreateTempSymbol(); 356 BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label); 357 return Label; 358 } 359 360 void GCMachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) { 361 // Find the return address (next instruction), too, so as to bracket the call 362 // instruction. 363 MachineBasicBlock::iterator RAI = CI; 364 ++RAI; 365 366 if (FI->getStrategy().needsSafePoint(GC::PreCall)) { 367 MCSymbol* Label = InsertLabel(*CI->getParent(), CI, CI->getDebugLoc()); 368 FI->addSafePoint(GC::PreCall, Label, CI->getDebugLoc()); 369 } 370 371 if (FI->getStrategy().needsSafePoint(GC::PostCall)) { 372 MCSymbol* Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc()); 373 FI->addSafePoint(GC::PostCall, Label, CI->getDebugLoc()); 374 } 375 } 376 377 void GCMachineCodeAnalysis::FindSafePoints(MachineFunction &MF) { 378 for (MachineFunction::iterator BBI = MF.begin(), 379 BBE = MF.end(); BBI != BBE; ++BBI) 380 for (MachineBasicBlock::iterator MI = BBI->begin(), 381 ME = BBI->end(); MI != ME; ++MI) 382 if (MI->isCall()) 383 VisitCallPoint(MI); 384 } 385 386 void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) { 387 const TargetFrameLowering *TFI = TM->getFrameLowering(); 388 assert(TFI && "TargetRegisterInfo not available!"); 389 390 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(), 391 RE = FI->roots_end(); RI != RE; ++RI) 392 RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num); 393 } 394 395 bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) { 396 // Quick exit for functions that do not use GC. 397 if (!MF.getFunction()->hasGC()) 398 return false; 399 400 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction()); 401 if (!FI->getStrategy().needsSafePoints()) 402 return false; 403 404 TM = &MF.getTarget(); 405 MMI = &getAnalysis<MachineModuleInfo>(); 406 TII = TM->getInstrInfo(); 407 408 // Find the size of the stack frame. 409 FI->setFrameSize(MF.getFrameInfo()->getStackSize()); 410 411 // Find all safe points. 412 if (FI->getStrategy().customSafePoints()) { 413 FI->getStrategy().findCustomSafePoints(*FI, MF); 414 } else { 415 FindSafePoints(MF); 416 } 417 418 // Find the stack offsets for all roots. 419 FindStackOffsets(MF); 420 421 return false; 422 } 423