GCStrategy.cpp revision 7d696d80409aad20bb5da0fc4eccab941dd371d4
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/Compiler.h" 31#include "llvm/Support/ErrorHandling.h" 32 33using namespace llvm; 34 35namespace { 36 37 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or 38 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as 39 /// directed by the GCStrategy. It also performs automatic root initialization 40 /// and custom intrinsic lowering. 41 class VISIBILITY_HIDDEN LowerIntrinsics : public FunctionPass { 42 static bool NeedsDefaultLoweringPass(const GCStrategy &C); 43 static bool NeedsCustomLoweringPass(const GCStrategy &C); 44 static bool CouldBecomeSafePoint(Instruction *I); 45 bool PerformDefaultLowering(Function &F, GCStrategy &Coll); 46 static bool InsertRootInitializers(Function &F, 47 AllocaInst **Roots, unsigned Count); 48 49 public: 50 static char ID; 51 52 LowerIntrinsics(); 53 const char *getPassName() const; 54 void getAnalysisUsage(AnalysisUsage &AU) const; 55 56 bool doInitialization(Module &M); 57 bool runOnFunction(Function &F); 58 }; 59 60 61 /// MachineCodeAnalysis - This is a target-independent pass over the machine 62 /// function representation to identify safe points for the garbage collector 63 /// in the machine code. It inserts labels at safe points and populates a 64 /// GCMetadata record for each function. 65 class VISIBILITY_HIDDEN MachineCodeAnalysis : public MachineFunctionPass { 66 const TargetMachine *TM; 67 GCFunctionInfo *FI; 68 MachineModuleInfo *MMI; 69 const TargetInstrInfo *TII; 70 71 void FindSafePoints(MachineFunction &MF); 72 void VisitCallPoint(MachineBasicBlock::iterator MI); 73 unsigned InsertLabel(MachineBasicBlock &MBB, 74 MachineBasicBlock::iterator MI) const; 75 76 void FindStackOffsets(MachineFunction &MF); 77 78 public: 79 static char ID; 80 81 MachineCodeAnalysis(); 82 const char *getPassName() const; 83 void getAnalysisUsage(AnalysisUsage &AU) const; 84 85 bool runOnMachineFunction(MachineFunction &MF); 86 }; 87 88} 89 90// ----------------------------------------------------------------------------- 91 92GCStrategy::GCStrategy() : 93 NeededSafePoints(0), 94 CustomReadBarriers(false), 95 CustomWriteBarriers(false), 96 CustomRoots(false), 97 InitRoots(true), 98 UsesMetadata(false) 99{} 100 101GCStrategy::~GCStrategy() { 102 for (iterator I = begin(), E = end(); I != E; ++I) 103 delete *I; 104 105 Functions.clear(); 106} 107 108bool GCStrategy::initializeCustomLowering(Module &M) { return false; } 109 110bool GCStrategy::performCustomLowering(Function &F) { 111 cerr << "gc " << getName() << " must override performCustomLowering.\n"; 112 llvm_unreachable(); 113 return 0; 114} 115 116GCFunctionInfo *GCStrategy::insertFunctionInfo(const Function &F) { 117 GCFunctionInfo *FI = new GCFunctionInfo(F, *this); 118 Functions.push_back(FI); 119 return FI; 120} 121 122// ----------------------------------------------------------------------------- 123 124FunctionPass *llvm::createGCLoweringPass() { 125 return new LowerIntrinsics(); 126} 127 128char LowerIntrinsics::ID = 0; 129 130LowerIntrinsics::LowerIntrinsics() 131 : FunctionPass(&ID) {} 132 133const char *LowerIntrinsics::getPassName() const { 134 return "Lower Garbage Collection Instructions"; 135} 136 137void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const { 138 FunctionPass::getAnalysisUsage(AU); 139 AU.addRequired<GCModuleInfo>(); 140} 141 142/// doInitialization - If this module uses the GC intrinsics, find them now. 143bool LowerIntrinsics::doInitialization(Module &M) { 144 // FIXME: This is rather antisocial in the context of a JIT since it performs 145 // work against the entire module. But this cannot be done at 146 // runFunction time (initializeCustomLowering likely needs to change 147 // the module). 148 GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>(); 149 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?"); 150 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 151 if (!I->isDeclaration() && I->hasGC()) 152 MI->getFunctionInfo(*I); // Instantiate the GC strategy. 153 154 bool MadeChange = false; 155 for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I) 156 if (NeedsCustomLoweringPass(**I)) 157 if ((*I)->initializeCustomLowering(M)) 158 MadeChange = true; 159 160 return MadeChange; 161} 162 163bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots, 164 unsigned Count) { 165 // Scroll past alloca instructions. 166 BasicBlock::iterator IP = F.getEntryBlock().begin(); 167 while (isa<AllocaInst>(IP)) ++IP; 168 169 // Search for initializers in the initial BB. 170 SmallPtrSet<AllocaInst*,16> InitedRoots; 171 for (; !CouldBecomeSafePoint(IP); ++IP) 172 if (StoreInst *SI = dyn_cast<StoreInst>(IP)) 173 if (AllocaInst *AI = 174 dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts())) 175 InitedRoots.insert(AI); 176 177 // Add root initializers. 178 bool MadeChange = false; 179 180 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I) 181 if (!InitedRoots.count(*I)) { 182 new StoreInst(ConstantPointerNull::get(cast<PointerType>( 183 cast<PointerType>((*I)->getType())->getElementType())), 184 *I, IP); 185 MadeChange = true; 186 } 187 188 return MadeChange; 189} 190 191bool LowerIntrinsics::NeedsDefaultLoweringPass(const GCStrategy &C) { 192 // Default lowering is necessary only if read or write barriers have a default 193 // action. The default for roots is no action. 194 return !C.customWriteBarrier() 195 || !C.customReadBarrier() 196 || C.initializeRoots(); 197} 198 199bool LowerIntrinsics::NeedsCustomLoweringPass(const GCStrategy &C) { 200 // Custom lowering is only necessary if enabled for some action. 201 return C.customWriteBarrier() 202 || C.customReadBarrier() 203 || C.customRoots(); 204} 205 206/// CouldBecomeSafePoint - Predicate to conservatively determine whether the 207/// instruction could introduce a safe point. 208bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) { 209 // The natural definition of instructions which could introduce safe points 210 // are: 211 // 212 // - call, invoke (AfterCall, BeforeCall) 213 // - phis (Loops) 214 // - invoke, ret, unwind (Exit) 215 // 216 // However, instructions as seemingly inoccuous as arithmetic can become 217 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead 218 // it is necessary to take a conservative approach. 219 220 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) || 221 isa<StoreInst>(I) || isa<LoadInst>(I)) 222 return false; 223 224 // llvm.gcroot is safe because it doesn't do anything at runtime. 225 if (CallInst *CI = dyn_cast<CallInst>(I)) 226 if (Function *F = CI->getCalledFunction()) 227 if (unsigned IID = F->getIntrinsicID()) 228 if (IID == Intrinsic::gcroot) 229 return false; 230 231 return true; 232} 233 234/// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores. 235/// Leave gcroot intrinsics; the code generator needs to see those. 236bool LowerIntrinsics::runOnFunction(Function &F) { 237 // Quick exit for functions that do not use GC. 238 if (!F.hasGC()) 239 return false; 240 241 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F); 242 GCStrategy &S = FI.getStrategy(); 243 244 bool MadeChange = false; 245 246 if (NeedsDefaultLoweringPass(S)) 247 MadeChange |= PerformDefaultLowering(F, S); 248 249 if (NeedsCustomLoweringPass(S)) 250 MadeChange |= S.performCustomLowering(F); 251 252 return MadeChange; 253} 254 255bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) { 256 bool LowerWr = !S.customWriteBarrier(); 257 bool LowerRd = !S.customReadBarrier(); 258 bool InitRoots = S.initializeRoots(); 259 260 SmallVector<AllocaInst*,32> Roots; 261 262 bool MadeChange = false; 263 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 264 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) { 265 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) { 266 Function *F = CI->getCalledFunction(); 267 switch (F->getIntrinsicID()) { 268 case Intrinsic::gcwrite: 269 if (LowerWr) { 270 // Replace a write barrier with a simple store. 271 Value *St = new StoreInst(CI->getOperand(1), CI->getOperand(3), CI); 272 CI->replaceAllUsesWith(St); 273 CI->eraseFromParent(); 274 } 275 break; 276 case Intrinsic::gcread: 277 if (LowerRd) { 278 // Replace a read barrier with a simple load. 279 Value *Ld = new LoadInst(CI->getOperand(2), "", CI); 280 Ld->takeName(CI); 281 CI->replaceAllUsesWith(Ld); 282 CI->eraseFromParent(); 283 } 284 break; 285 case Intrinsic::gcroot: 286 if (InitRoots) { 287 // Initialize the GC root, but do not delete the intrinsic. The 288 // backend needs the intrinsic to flag the stack slot. 289 Roots.push_back(cast<AllocaInst>( 290 CI->getOperand(1)->stripPointerCasts())); 291 } 292 break; 293 default: 294 continue; 295 } 296 297 MadeChange = true; 298 } 299 } 300 } 301 302 if (Roots.size()) 303 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size()); 304 305 return MadeChange; 306} 307 308// ----------------------------------------------------------------------------- 309 310FunctionPass *llvm::createGCMachineCodeAnalysisPass() { 311 return new MachineCodeAnalysis(); 312} 313 314char MachineCodeAnalysis::ID = 0; 315 316MachineCodeAnalysis::MachineCodeAnalysis() 317 : MachineFunctionPass(&ID) {} 318 319const char *MachineCodeAnalysis::getPassName() const { 320 return "Analyze Machine Code For Garbage Collection"; 321} 322 323void MachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 324 MachineFunctionPass::getAnalysisUsage(AU); 325 AU.setPreservesAll(); 326 AU.addRequired<MachineModuleInfo>(); 327 AU.addRequired<GCModuleInfo>(); 328} 329 330unsigned MachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB, 331 MachineBasicBlock::iterator MI) const { 332 unsigned Label = MMI->NextLabelID(); 333 // N.B. we assume that MI is *not* equal to the "end()" iterator. 334 BuildMI(MBB, MI, MI->getDebugLoc(), 335 TII->get(TargetInstrInfo::GC_LABEL)).addImm(Label); 336 return Label; 337} 338 339void MachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) { 340 // Find the return address (next instruction), too, so as to bracket the call 341 // instruction. 342 MachineBasicBlock::iterator RAI = CI; 343 ++RAI; 344 345 if (FI->getStrategy().needsSafePoint(GC::PreCall)) 346 FI->addSafePoint(GC::PreCall, InsertLabel(*CI->getParent(), CI)); 347 348 if (FI->getStrategy().needsSafePoint(GC::PostCall)) 349 FI->addSafePoint(GC::PostCall, InsertLabel(*CI->getParent(), RAI)); 350} 351 352void MachineCodeAnalysis::FindSafePoints(MachineFunction &MF) { 353 for (MachineFunction::iterator BBI = MF.begin(), 354 BBE = MF.end(); BBI != BBE; ++BBI) 355 for (MachineBasicBlock::iterator MI = BBI->begin(), 356 ME = BBI->end(); MI != ME; ++MI) 357 if (MI->getDesc().isCall()) 358 VisitCallPoint(MI); 359} 360 361void MachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) { 362 const TargetRegisterInfo *TRI = TM->getRegisterInfo(); 363 assert(TRI && "TargetRegisterInfo not available!"); 364 365 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(), 366 RE = FI->roots_end(); RI != RE; ++RI) 367 RI->StackOffset = TRI->getFrameIndexOffset(MF, RI->Num); 368} 369 370bool MachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) { 371 // Quick exit for functions that do not use GC. 372 if (!MF.getFunction()->hasGC()) 373 return false; 374 375 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction()); 376 if (!FI->getStrategy().needsSafePoints()) 377 return false; 378 379 TM = &MF.getTarget(); 380 MMI = &getAnalysis<MachineModuleInfo>(); 381 TII = TM->getInstrInfo(); 382 383 // Find the size of the stack frame. 384 FI->setFrameSize(MF.getFrameInfo()->getStackSize()); 385 386 // Find all safe points. 387 FindSafePoints(MF); 388 389 // Find the stack offsets for all roots. 390 FindStackOffsets(MF); 391 392 return false; 393} 394