lib/CodeGen/GCStrategy.cpp

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