GCStrategy.cpp revision 4d6ccb5f68cd7c6418a209f1fa4dbade569e4493
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// MachineCodeAnalysis identifies the GC safe points in the machine code. Roots 14// 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 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; 56 void getAnalysisUsage(AnalysisUsage &AU) const; 57 58 bool doInitialization(Module &M); 59 bool runOnFunction(Function &F); 60 }; 61 62 63 /// MachineCodeAnalysis - 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 MachineCodeAnalysis : 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 MachineCodeAnalysis(); 85 const char *getPassName() const; 86 void getAnalysisUsage(AnalysisUsage &AU) const; 87 88 bool runOnMachineFunction(MachineFunction &MF); 89 }; 90 91} 92 93// ----------------------------------------------------------------------------- 94 95GCStrategy::GCStrategy() : 96 NeededSafePoints(0), 97 CustomReadBarriers(false), 98 CustomWriteBarriers(false), 99 CustomRoots(false), 100 CustomSafePoints(false), 101 InitRoots(true), 102 UsesMetadata(false) 103{} 104 105GCStrategy::~GCStrategy() { 106 for (iterator I = begin(), E = end(); I != E; ++I) 107 delete *I; 108 109 Functions.clear(); 110} 111 112bool GCStrategy::initializeCustomLowering(Module &M) { return false; } 113 114bool GCStrategy::performCustomLowering(Function &F) { 115 dbgs() << "gc " << getName() << " must override performCustomLowering.\n"; 116 llvm_unreachable(0); 117} 118 119 120bool GCStrategy::findCustomSafePoints(GCFunctionInfo& FI, MachineFunction &F) { 121 dbgs() << "gc " << getName() << " must override findCustomSafePoints.\n"; 122 llvm_unreachable(0); 123} 124 125 126GCFunctionInfo *GCStrategy::insertFunctionInfo(const Function &F) { 127 GCFunctionInfo *FI = new GCFunctionInfo(F, *this); 128 Functions.push_back(FI); 129 return FI; 130} 131 132// ----------------------------------------------------------------------------- 133 134INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering", 135 false, false) 136INITIALIZE_PASS_DEPENDENCY(GCModuleInfo) 137INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false) 138 139FunctionPass *llvm::createGCLoweringPass() { 140 return new LowerIntrinsics(); 141} 142 143char LowerIntrinsics::ID = 0; 144 145LowerIntrinsics::LowerIntrinsics() 146 : FunctionPass(ID) { 147 initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry()); 148 } 149 150const char *LowerIntrinsics::getPassName() const { 151 return "Lower Garbage Collection Instructions"; 152} 153 154void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const { 155 FunctionPass::getAnalysisUsage(AU); 156 AU.addRequired<GCModuleInfo>(); 157 AU.addPreserved<DominatorTree>(); 158} 159 160/// doInitialization - If this module uses the GC intrinsics, find them now. 161bool LowerIntrinsics::doInitialization(Module &M) { 162 // FIXME: This is rather antisocial in the context of a JIT since it performs 163 // work against the entire module. But this cannot be done at 164 // runFunction time (initializeCustomLowering likely needs to change 165 // the module). 166 GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>(); 167 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?"); 168 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 169 if (!I->isDeclaration() && I->hasGC()) 170 MI->getFunctionInfo(*I); // Instantiate the GC strategy. 171 172 bool MadeChange = false; 173 for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I) 174 if (NeedsCustomLoweringPass(**I)) 175 if ((*I)->initializeCustomLowering(M)) 176 MadeChange = true; 177 178 return MadeChange; 179} 180 181bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots, 182 unsigned Count) { 183 // Scroll past alloca instructions. 184 BasicBlock::iterator IP = F.getEntryBlock().begin(); 185 while (isa<AllocaInst>(IP)) ++IP; 186 187 // Search for initializers in the initial BB. 188 SmallPtrSet<AllocaInst*,16> InitedRoots; 189 for (; !CouldBecomeSafePoint(IP); ++IP) 190 if (StoreInst *SI = dyn_cast<StoreInst>(IP)) 191 if (AllocaInst *AI = 192 dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts())) 193 InitedRoots.insert(AI); 194 195 // Add root initializers. 196 bool MadeChange = false; 197 198 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I) 199 if (!InitedRoots.count(*I)) { 200 StoreInst* SI = new StoreInst(ConstantPointerNull::get(cast<PointerType>( 201 cast<PointerType>((*I)->getType())->getElementType())), 202 *I); 203 SI->insertAfter(*I); 204 MadeChange = true; 205 } 206 207 return MadeChange; 208} 209 210bool LowerIntrinsics::NeedsDefaultLoweringPass(const GCStrategy &C) { 211 // Default lowering is necessary only if read or write barriers have a default 212 // action. The default for roots is no action. 213 return !C.customWriteBarrier() 214 || !C.customReadBarrier() 215 || C.initializeRoots(); 216} 217 218bool LowerIntrinsics::NeedsCustomLoweringPass(const GCStrategy &C) { 219 // Custom lowering is only necessary if enabled for some action. 220 return C.customWriteBarrier() 221 || C.customReadBarrier() 222 || C.customRoots(); 223} 224 225/// CouldBecomeSafePoint - Predicate to conservatively determine whether the 226/// instruction could introduce a safe point. 227bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) { 228 // The natural definition of instructions which could introduce safe points 229 // are: 230 // 231 // - call, invoke (AfterCall, BeforeCall) 232 // - phis (Loops) 233 // - invoke, ret, unwind (Exit) 234 // 235 // However, instructions as seemingly inoccuous as arithmetic can become 236 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead 237 // it is necessary to take a conservative approach. 238 239 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) || 240 isa<StoreInst>(I) || isa<LoadInst>(I)) 241 return false; 242 243 // llvm.gcroot is safe because it doesn't do anything at runtime. 244 if (CallInst *CI = dyn_cast<CallInst>(I)) 245 if (Function *F = CI->getCalledFunction()) 246 if (unsigned IID = F->getIntrinsicID()) 247 if (IID == Intrinsic::gcroot) 248 return false; 249 250 return true; 251} 252 253/// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores. 254/// Leave gcroot intrinsics; the code generator needs to see those. 255bool LowerIntrinsics::runOnFunction(Function &F) { 256 // Quick exit for functions that do not use GC. 257 if (!F.hasGC()) 258 return false; 259 260 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F); 261 GCStrategy &S = FI.getStrategy(); 262 263 bool MadeChange = false; 264 265 if (NeedsDefaultLoweringPass(S)) 266 MadeChange |= PerformDefaultLowering(F, S); 267 268 bool UseCustomLoweringPass = NeedsCustomLoweringPass(S); 269 if (UseCustomLoweringPass) 270 MadeChange |= S.performCustomLowering(F); 271 272 // Custom lowering may modify the CFG, so dominators must be recomputed. 273 if (UseCustomLoweringPass) { 274 if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) 275 DT->DT->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 337FunctionPass *llvm::createGCMachineCodeAnalysisPass() { 338 return new MachineCodeAnalysis(); 339} 340 341char MachineCodeAnalysis::ID = 0; 342 343MachineCodeAnalysis::MachineCodeAnalysis() 344 : MachineFunctionPass(ID) {} 345 346const char *MachineCodeAnalysis::getPassName() const { 347 return "Analyze Machine Code For Garbage Collection"; 348} 349 350void MachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 351 MachineFunctionPass::getAnalysisUsage(AU); 352 AU.setPreservesAll(); 353 AU.addRequired<MachineModuleInfo>(); 354 AU.addRequired<GCModuleInfo>(); 355} 356 357MCSymbol *MachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB, 358 MachineBasicBlock::iterator MI, 359 DebugLoc DL) const { 360 MCSymbol *Label = MBB.getParent()->getContext().CreateTempSymbol(); 361 BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label); 362 return Label; 363} 364 365void MachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) { 366 // Find the return address (next instruction), too, so as to bracket the call 367 // instruction. 368 MachineBasicBlock::iterator RAI = CI; 369 ++RAI; 370 371 if (FI->getStrategy().needsSafePoint(GC::PreCall)) { 372 MCSymbol* Label = InsertLabel(*CI->getParent(), CI, CI->getDebugLoc()); 373 FI->addSafePoint(GC::PreCall, Label, CI->getDebugLoc()); 374 } 375 376 if (FI->getStrategy().needsSafePoint(GC::PostCall)) { 377 MCSymbol* Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc()); 378 FI->addSafePoint(GC::PostCall, Label, CI->getDebugLoc()); 379 } 380} 381 382void MachineCodeAnalysis::FindSafePoints(MachineFunction &MF) { 383 for (MachineFunction::iterator BBI = MF.begin(), 384 BBE = MF.end(); BBI != BBE; ++BBI) 385 for (MachineBasicBlock::iterator MI = BBI->begin(), 386 ME = BBI->end(); MI != ME; ++MI) 387 if (MI->isCall()) 388 VisitCallPoint(MI); 389} 390 391void MachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) { 392 const TargetFrameLowering *TFI = TM->getFrameLowering(); 393 assert(TFI && "TargetRegisterInfo not available!"); 394 395 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(), 396 RE = FI->roots_end(); RI != RE; ++RI) 397 RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num); 398} 399 400bool MachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) { 401 // Quick exit for functions that do not use GC. 402 if (!MF.getFunction()->hasGC()) 403 return false; 404 405 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction()); 406 if (!FI->getStrategy().needsSafePoints()) 407 return false; 408 409 TM = &MF.getTarget(); 410 MMI = &getAnalysis<MachineModuleInfo>(); 411 TII = TM->getInstrInfo(); 412 413 // Find the size of the stack frame. 414 FI->setFrameSize(MF.getFrameInfo()->getStackSize()); 415 416 // Find all safe points. 417 if (FI->getStrategy().customSafePoints()) { 418 FI->getStrategy().findCustomSafePoints(*FI, MF); 419 } else { 420 FindSafePoints(MF); 421 } 422 423 // Find the stack offsets for all roots. 424 FindStackOffsets(MF); 425 426 return false; 427} 428