GCStrategy.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338
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/MachineFrameInfo.h" 20#include "llvm/CodeGen/MachineFunctionPass.h" 21#include "llvm/CodeGen/MachineInstrBuilder.h" 22#include "llvm/CodeGen/MachineModuleInfo.h" 23#include "llvm/CodeGen/Passes.h" 24#include "llvm/IR/Dominators.h" 25#include "llvm/IR/IntrinsicInst.h" 26#include "llvm/IR/Module.h" 27#include "llvm/Support/Debug.h" 28#include "llvm/Support/ErrorHandling.h" 29#include "llvm/Support/raw_ostream.h" 30#include "llvm/Target/TargetFrameLowering.h" 31#include "llvm/Target/TargetInstrInfo.h" 32#include "llvm/Target/TargetMachine.h" 33#include "llvm/Target/TargetRegisterInfo.h" 34 35using namespace llvm; 36 37namespace { 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 override; 56 void getAnalysisUsage(AnalysisUsage &AU) const override; 57 58 bool doInitialization(Module &M) override; 59 bool runOnFunction(Function &F) override; 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 override; 86 87 bool runOnMachineFunction(MachineFunction &MF) override; 88 }; 89 90} 91 92// ----------------------------------------------------------------------------- 93 94GCStrategy::GCStrategy() : 95 NeededSafePoints(0), 96 CustomReadBarriers(false), 97 CustomWriteBarriers(false), 98 CustomRoots(false), 99 CustomSafePoints(false), 100 InitRoots(true), 101 UsesMetadata(false) 102{} 103 104GCStrategy::~GCStrategy() { 105 for (iterator I = begin(), E = end(); I != E; ++I) 106 delete *I; 107 108 Functions.clear(); 109} 110 111bool GCStrategy::initializeCustomLowering(Module &M) { return false; } 112 113bool GCStrategy::performCustomLowering(Function &F) { 114 dbgs() << "gc " << getName() << " must override performCustomLowering.\n"; 115 llvm_unreachable("must override performCustomLowering"); 116} 117 118 119bool GCStrategy::findCustomSafePoints(GCFunctionInfo& FI, MachineFunction &F) { 120 dbgs() << "gc " << getName() << " must override findCustomSafePoints.\n"; 121 llvm_unreachable(0); 122} 123 124 125GCFunctionInfo *GCStrategy::insertFunctionInfo(const Function &F) { 126 GCFunctionInfo *FI = new GCFunctionInfo(F, *this); 127 Functions.push_back(FI); 128 return FI; 129} 130 131// ----------------------------------------------------------------------------- 132 133INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering", 134 false, false) 135INITIALIZE_PASS_DEPENDENCY(GCModuleInfo) 136INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false) 137 138FunctionPass *llvm::createGCLoweringPass() { 139 return new LowerIntrinsics(); 140} 141 142char LowerIntrinsics::ID = 0; 143 144LowerIntrinsics::LowerIntrinsics() 145 : FunctionPass(ID) { 146 initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry()); 147 } 148 149const char *LowerIntrinsics::getPassName() const { 150 return "Lower Garbage Collection Instructions"; 151} 152 153void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const { 154 FunctionPass::getAnalysisUsage(AU); 155 AU.addRequired<GCModuleInfo>(); 156 AU.addPreserved<DominatorTreeWrapperPass>(); 157} 158 159/// doInitialization - If this module uses the GC intrinsics, find them now. 160bool 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 180bool 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 209bool 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 217bool 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. 226bool 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. 254bool 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 (DominatorTreeWrapperPass *DTWP = 274 getAnalysisIfAvailable<DominatorTreeWrapperPass>()) 275 DTWP->getDomTree().recalculate(F); 276 } 277 278 return MadeChange; 279} 280 281bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) { 282 bool LowerWr = !S.customWriteBarrier(); 283 bool LowerRd = !S.customReadBarrier(); 284 bool InitRoots = S.initializeRoots(); 285 286 SmallVector<AllocaInst*, 32> Roots; 287 288 bool MadeChange = false; 289 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 290 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) { 291 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) { 292 Function *F = CI->getCalledFunction(); 293 switch (F->getIntrinsicID()) { 294 case Intrinsic::gcwrite: 295 if (LowerWr) { 296 // Replace a write barrier with a simple store. 297 Value *St = new StoreInst(CI->getArgOperand(0), 298 CI->getArgOperand(2), CI); 299 CI->replaceAllUsesWith(St); 300 CI->eraseFromParent(); 301 } 302 break; 303 case Intrinsic::gcread: 304 if (LowerRd) { 305 // Replace a read barrier with a simple load. 306 Value *Ld = new LoadInst(CI->getArgOperand(1), "", CI); 307 Ld->takeName(CI); 308 CI->replaceAllUsesWith(Ld); 309 CI->eraseFromParent(); 310 } 311 break; 312 case Intrinsic::gcroot: 313 if (InitRoots) { 314 // Initialize the GC root, but do not delete the intrinsic. The 315 // backend needs the intrinsic to flag the stack slot. 316 Roots.push_back(cast<AllocaInst>( 317 CI->getArgOperand(0)->stripPointerCasts())); 318 } 319 break; 320 default: 321 continue; 322 } 323 324 MadeChange = true; 325 } 326 } 327 } 328 329 if (Roots.size()) 330 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size()); 331 332 return MadeChange; 333} 334 335// ----------------------------------------------------------------------------- 336 337char GCMachineCodeAnalysis::ID = 0; 338char &llvm::GCMachineCodeAnalysisID = GCMachineCodeAnalysis::ID; 339 340INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis", 341 "Analyze Machine Code For Garbage Collection", false, false) 342 343GCMachineCodeAnalysis::GCMachineCodeAnalysis() 344 : MachineFunctionPass(ID) {} 345 346void GCMachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 347 MachineFunctionPass::getAnalysisUsage(AU); 348 AU.setPreservesAll(); 349 AU.addRequired<MachineModuleInfo>(); 350 AU.addRequired<GCModuleInfo>(); 351} 352 353MCSymbol *GCMachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB, 354 MachineBasicBlock::iterator MI, 355 DebugLoc DL) const { 356 MCSymbol *Label = MBB.getParent()->getContext().CreateTempSymbol(); 357 BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label); 358 return Label; 359} 360 361void GCMachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) { 362 // Find the return address (next instruction), too, so as to bracket the call 363 // instruction. 364 MachineBasicBlock::iterator RAI = CI; 365 ++RAI; 366 367 if (FI->getStrategy().needsSafePoint(GC::PreCall)) { 368 MCSymbol* Label = InsertLabel(*CI->getParent(), CI, CI->getDebugLoc()); 369 FI->addSafePoint(GC::PreCall, Label, CI->getDebugLoc()); 370 } 371 372 if (FI->getStrategy().needsSafePoint(GC::PostCall)) { 373 MCSymbol* Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc()); 374 FI->addSafePoint(GC::PostCall, Label, CI->getDebugLoc()); 375 } 376} 377 378void GCMachineCodeAnalysis::FindSafePoints(MachineFunction &MF) { 379 for (MachineFunction::iterator BBI = MF.begin(), 380 BBE = MF.end(); BBI != BBE; ++BBI) 381 for (MachineBasicBlock::iterator MI = BBI->begin(), 382 ME = BBI->end(); MI != ME; ++MI) 383 if (MI->isCall()) 384 VisitCallPoint(MI); 385} 386 387void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) { 388 const TargetFrameLowering *TFI = TM->getFrameLowering(); 389 assert(TFI && "TargetRegisterInfo not available!"); 390 391 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(); 392 RI != FI->roots_end();) { 393 // If the root references a dead object, no need to keep it. 394 if (MF.getFrameInfo()->isDeadObjectIndex(RI->Num)) { 395 RI = FI->removeStackRoot(RI); 396 } else { 397 RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num); 398 ++RI; 399 } 400 } 401} 402 403bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) { 404 // Quick exit for functions that do not use GC. 405 if (!MF.getFunction()->hasGC()) 406 return false; 407 408 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction()); 409 if (!FI->getStrategy().needsSafePoints()) 410 return false; 411 412 TM = &MF.getTarget(); 413 MMI = &getAnalysis<MachineModuleInfo>(); 414 TII = TM->getInstrInfo(); 415 416 // Find the size of the stack frame. 417 FI->setFrameSize(MF.getFrameInfo()->getStackSize()); 418 419 // Find all safe points. 420 if (FI->getStrategy().customSafePoints()) { 421 FI->getStrategy().findCustomSafePoints(*FI, MF); 422 } else { 423 FindSafePoints(MF); 424 } 425 426 // Find the stack offsets for all roots. 427 FindStackOffsets(MF); 428 429 return false; 430} 431