GCStrategy.cpp revision 4ec2258ffb495d7ce00177e447740ef1123a27db
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/CodeGen/MachineFrameInfo.h" 23#include "llvm/CodeGen/MachineFunctionPass.h" 24#include "llvm/CodeGen/MachineInstrBuilder.h" 25#include "llvm/CodeGen/MachineModuleInfo.h" 26#include "llvm/Target/TargetFrameInfo.h" 27#include "llvm/Target/TargetInstrInfo.h" 28#include "llvm/Target/TargetMachine.h" 29#include "llvm/Target/TargetRegisterInfo.h" 30#include "llvm/Support/Debug.h" 31#include "llvm/Support/ErrorHandling.h" 32#include "llvm/Support/raw_ostream.h" 33 34using namespace llvm; 35 36namespace { 37 38 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or 39 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as 40 /// directed by the GCStrategy. It also performs automatic root initialization 41 /// and custom intrinsic lowering. 42 class LowerIntrinsics : public FunctionPass { 43 static bool NeedsDefaultLoweringPass(const GCStrategy &C); 44 static bool NeedsCustomLoweringPass(const GCStrategy &C); 45 static bool CouldBecomeSafePoint(Instruction *I); 46 bool PerformDefaultLowering(Function &F, GCStrategy &Coll); 47 static bool InsertRootInitializers(Function &F, 48 AllocaInst **Roots, unsigned Count); 49 50 public: 51 static char ID; 52 53 LowerIntrinsics(); 54 const char *getPassName() const; 55 void getAnalysisUsage(AnalysisUsage &AU) const; 56 57 bool doInitialization(Module &M); 58 bool runOnFunction(Function &F); 59 }; 60 61 62 /// MachineCodeAnalysis - This is a target-independent pass over the machine 63 /// function representation to identify safe points for the garbage collector 64 /// in the machine code. It inserts labels at safe points and populates a 65 /// GCMetadata record for each function. 66 class MachineCodeAnalysis : public MachineFunctionPass { 67 const TargetMachine *TM; 68 GCFunctionInfo *FI; 69 MachineModuleInfo *MMI; 70 const TargetInstrInfo *TII; 71 72 void FindSafePoints(MachineFunction &MF); 73 void VisitCallPoint(MachineBasicBlock::iterator MI); 74 MCSymbol *InsertLabel(MachineBasicBlock &MBB, 75 MachineBasicBlock::iterator MI, 76 DebugLoc DL) const; 77 78 void FindStackOffsets(MachineFunction &MF); 79 80 public: 81 static char ID; 82 83 MachineCodeAnalysis(); 84 const char *getPassName() const; 85 void getAnalysisUsage(AnalysisUsage &AU) const; 86 87 bool runOnMachineFunction(MachineFunction &MF); 88 }; 89 90} 91 92// ----------------------------------------------------------------------------- 93 94GCStrategy::GCStrategy() : 95 NeededSafePoints(0), 96 CustomReadBarriers(false), 97 CustomWriteBarriers(false), 98 CustomRoots(false), 99 InitRoots(true), 100 UsesMetadata(false) 101{} 102 103GCStrategy::~GCStrategy() { 104 for (iterator I = begin(), E = end(); I != E; ++I) 105 delete *I; 106 107 Functions.clear(); 108} 109 110bool GCStrategy::initializeCustomLowering(Module &M) { return false; } 111 112bool GCStrategy::performCustomLowering(Function &F) { 113 dbgs() << "gc " << getName() << " must override performCustomLowering.\n"; 114 llvm_unreachable(0); 115 return 0; 116} 117 118GCFunctionInfo *GCStrategy::insertFunctionInfo(const Function &F) { 119 GCFunctionInfo *FI = new GCFunctionInfo(F, *this); 120 Functions.push_back(FI); 121 return FI; 122} 123 124// ----------------------------------------------------------------------------- 125 126FunctionPass *llvm::createGCLoweringPass() { 127 return new LowerIntrinsics(); 128} 129 130char LowerIntrinsics::ID = 0; 131 132LowerIntrinsics::LowerIntrinsics() 133 : FunctionPass(&ID) {} 134 135const char *LowerIntrinsics::getPassName() const { 136 return "Lower Garbage Collection Instructions"; 137} 138 139void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const { 140 FunctionPass::getAnalysisUsage(AU); 141 AU.addRequired<GCModuleInfo>(); 142} 143 144/// doInitialization - If this module uses the GC intrinsics, find them now. 145bool LowerIntrinsics::doInitialization(Module &M) { 146 // FIXME: This is rather antisocial in the context of a JIT since it performs 147 // work against the entire module. But this cannot be done at 148 // runFunction time (initializeCustomLowering likely needs to change 149 // the module). 150 GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>(); 151 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?"); 152 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 153 if (!I->isDeclaration() && I->hasGC()) 154 MI->getFunctionInfo(*I); // Instantiate the GC strategy. 155 156 bool MadeChange = false; 157 for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I) 158 if (NeedsCustomLoweringPass(**I)) 159 if ((*I)->initializeCustomLowering(M)) 160 MadeChange = true; 161 162 return MadeChange; 163} 164 165bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots, 166 unsigned Count) { 167 // Scroll past alloca instructions. 168 BasicBlock::iterator IP = F.getEntryBlock().begin(); 169 while (isa<AllocaInst>(IP)) ++IP; 170 171 // Search for initializers in the initial BB. 172 SmallPtrSet<AllocaInst*,16> InitedRoots; 173 for (; !CouldBecomeSafePoint(IP); ++IP) 174 if (StoreInst *SI = dyn_cast<StoreInst>(IP)) 175 if (AllocaInst *AI = 176 dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts())) 177 InitedRoots.insert(AI); 178 179 // Add root initializers. 180 bool MadeChange = false; 181 182 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I) 183 if (!InitedRoots.count(*I)) { 184 StoreInst* SI = new StoreInst(ConstantPointerNull::get(cast<PointerType>( 185 cast<PointerType>((*I)->getType())->getElementType())), 186 *I); 187 SI->insertAfter(*I); 188 MadeChange = true; 189 } 190 191 return MadeChange; 192} 193 194bool LowerIntrinsics::NeedsDefaultLoweringPass(const GCStrategy &C) { 195 // Default lowering is necessary only if read or write barriers have a default 196 // action. The default for roots is no action. 197 return !C.customWriteBarrier() 198 || !C.customReadBarrier() 199 || C.initializeRoots(); 200} 201 202bool LowerIntrinsics::NeedsCustomLoweringPass(const GCStrategy &C) { 203 // Custom lowering is only necessary if enabled for some action. 204 return C.customWriteBarrier() 205 || C.customReadBarrier() 206 || C.customRoots(); 207} 208 209/// CouldBecomeSafePoint - Predicate to conservatively determine whether the 210/// instruction could introduce a safe point. 211bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) { 212 // The natural definition of instructions which could introduce safe points 213 // are: 214 // 215 // - call, invoke (AfterCall, BeforeCall) 216 // - phis (Loops) 217 // - invoke, ret, unwind (Exit) 218 // 219 // However, instructions as seemingly inoccuous as arithmetic can become 220 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead 221 // it is necessary to take a conservative approach. 222 223 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) || 224 isa<StoreInst>(I) || isa<LoadInst>(I)) 225 return false; 226 227 // llvm.gcroot is safe because it doesn't do anything at runtime. 228 if (CallInst *CI = dyn_cast<CallInst>(I)) 229 if (Function *F = CI->getCalledFunction()) 230 if (unsigned IID = F->getIntrinsicID()) 231 if (IID == Intrinsic::gcroot) 232 return false; 233 234 return true; 235} 236 237/// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores. 238/// Leave gcroot intrinsics; the code generator needs to see those. 239bool LowerIntrinsics::runOnFunction(Function &F) { 240 // Quick exit for functions that do not use GC. 241 if (!F.hasGC()) 242 return false; 243 244 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F); 245 GCStrategy &S = FI.getStrategy(); 246 247 bool MadeChange = false; 248 249 if (NeedsDefaultLoweringPass(S)) 250 MadeChange |= PerformDefaultLowering(F, S); 251 252 if (NeedsCustomLoweringPass(S)) 253 MadeChange |= S.performCustomLowering(F); 254 255 return MadeChange; 256} 257 258bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) { 259 bool LowerWr = !S.customWriteBarrier(); 260 bool LowerRd = !S.customReadBarrier(); 261 bool InitRoots = S.initializeRoots(); 262 263 SmallVector<AllocaInst*,32> Roots; 264 265 bool MadeChange = false; 266 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 267 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) { 268 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) { 269 Function *F = CI->getCalledFunction(); 270 switch (F->getIntrinsicID()) { 271 case Intrinsic::gcwrite: 272 if (LowerWr) { 273 // Replace a write barrier with a simple store. 274 Value *St = new StoreInst(CI->getOperand(0), CI->getOperand(2), CI); 275 CI->replaceAllUsesWith(St); 276 CI->eraseFromParent(); 277 } 278 break; 279 case Intrinsic::gcread: 280 if (LowerRd) { 281 // Replace a read barrier with a simple load. 282 Value *Ld = new LoadInst(CI->getOperand(1), "", CI); 283 Ld->takeName(CI); 284 CI->replaceAllUsesWith(Ld); 285 CI->eraseFromParent(); 286 } 287 break; 288 case Intrinsic::gcroot: 289 if (InitRoots) { 290 // Initialize the GC root, but do not delete the intrinsic. The 291 // backend needs the intrinsic to flag the stack slot. 292 Roots.push_back(cast<AllocaInst>( 293 CI->getOperand(0)->stripPointerCasts())); 294 } 295 break; 296 default: 297 continue; 298 } 299 300 MadeChange = true; 301 } 302 } 303 } 304 305 if (Roots.size()) 306 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size()); 307 308 return MadeChange; 309} 310 311// ----------------------------------------------------------------------------- 312 313FunctionPass *llvm::createGCMachineCodeAnalysisPass() { 314 return new MachineCodeAnalysis(); 315} 316 317char MachineCodeAnalysis::ID = 0; 318 319MachineCodeAnalysis::MachineCodeAnalysis() 320 : MachineFunctionPass(&ID) {} 321 322const char *MachineCodeAnalysis::getPassName() const { 323 return "Analyze Machine Code For Garbage Collection"; 324} 325 326void MachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 327 MachineFunctionPass::getAnalysisUsage(AU); 328 AU.setPreservesAll(); 329 AU.addRequired<MachineModuleInfo>(); 330 AU.addRequired<GCModuleInfo>(); 331} 332 333MCSymbol *MachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB, 334 MachineBasicBlock::iterator MI, 335 DebugLoc DL) const { 336 MCSymbol *Label = MBB.getParent()->getContext().CreateTempSymbol(); 337 BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label); 338 return Label; 339} 340 341void MachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) { 342 // Find the return address (next instruction), too, so as to bracket the call 343 // instruction. 344 MachineBasicBlock::iterator RAI = CI; 345 ++RAI; 346 347 if (FI->getStrategy().needsSafePoint(GC::PreCall)) 348 FI->addSafePoint(GC::PreCall, InsertLabel(*CI->getParent(), CI, 349 CI->getDebugLoc())); 350 351 if (FI->getStrategy().needsSafePoint(GC::PostCall)) 352 FI->addSafePoint(GC::PostCall, InsertLabel(*CI->getParent(), RAI, 353 CI->getDebugLoc())); 354} 355 356void MachineCodeAnalysis::FindSafePoints(MachineFunction &MF) { 357 for (MachineFunction::iterator BBI = MF.begin(), 358 BBE = MF.end(); BBI != BBE; ++BBI) 359 for (MachineBasicBlock::iterator MI = BBI->begin(), 360 ME = BBI->end(); MI != ME; ++MI) 361 if (MI->getDesc().isCall()) 362 VisitCallPoint(MI); 363} 364 365void MachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) { 366 const TargetRegisterInfo *TRI = TM->getRegisterInfo(); 367 assert(TRI && "TargetRegisterInfo not available!"); 368 369 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(), 370 RE = FI->roots_end(); RI != RE; ++RI) 371 RI->StackOffset = TRI->getFrameIndexOffset(MF, RI->Num); 372} 373 374bool MachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) { 375 // Quick exit for functions that do not use GC. 376 if (!MF.getFunction()->hasGC()) 377 return false; 378 379 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction()); 380 if (!FI->getStrategy().needsSafePoints()) 381 return false; 382 383 TM = &MF.getTarget(); 384 MMI = &getAnalysis<MachineModuleInfo>(); 385 TII = TM->getInstrInfo(); 386 387 // Find the size of the stack frame. 388 FI->setFrameSize(MF.getFrameInfo()->getStackSize()); 389 390 // Find all safe points. 391 FindSafePoints(MF); 392 393 // Find the stack offsets for all roots. 394 FindStackOffsets(MF); 395 396 return false; 397} 398