AsmPrinter.cpp

  }
  
  switch (CE->getOpcode()) {
  default:
    // If the code isn't optimized, there may be outstanding folding
    // opportunities. Attempt to fold the expression using TargetData as a
    // last resort before giving up.
    if (Constant *C =
          ConstantFoldConstantExpression(CE, AP.TM.getTargetData()))
      if (C != CE)
        return LowerConstant(C, AP);
#ifndef NDEBUG
    CE->dump();
#endif
    llvm_unreachable("FIXME: Don't support this constant expr");
  case Instruction::GetElementPtr: {
    const TargetData &TD = *AP.TM.getTargetData();
    // Generate a symbolic expression for the byte address
    const Constant *PtrVal = CE->getOperand(0);
    SmallVector<Value*, 8> IdxVec(CE->op_begin()+1, CE->op_end());
    int64_t Offset = TD.getIndexedOffset(PtrVal->getType(), &IdxVec[0],
                                         IdxVec.size());
    
    const MCExpr *Base = LowerConstant(CE->getOperand(0), AP);
    if (Offset == 0)
      return Base;
    
    // Truncate/sext the offset to the pointer size.
    if (TD.getPointerSizeInBits() != 64) {
      int SExtAmount = 64-TD.getPointerSizeInBits();
      Offset = (Offset << SExtAmount) >> SExtAmount;
    }
    
    return MCBinaryExpr::CreateAdd(Base, MCConstantExpr::Create(Offset, Ctx),
                                   Ctx);
  }
      
  case Instruction::Trunc:
    // We emit the value and depend on the assembler to truncate the generated
    // expression properly.  This is important for differences between
    // blockaddress labels.  Since the two labels are in the same function, it
    // is reasonable to treat their delta as a 32-bit value.
    // FALL THROUGH.
  case Instruction::BitCast:
    return LowerConstant(CE->getOperand(0), AP);

  case Instruction::IntToPtr: {
    const TargetData &TD = *AP.TM.getTargetData();
    // Handle casts to pointers by changing them into casts to the appropriate
    // integer type.  This promotes constant folding and simplifies this code.
    Constant *Op = CE->getOperand(0);
    Op = ConstantExpr::getIntegerCast(Op, TD.getIntPtrType(CV->getContext()),
                                      false/*ZExt*/);
    return LowerConstant(Op, AP);
  }
    
  case Instruction::PtrToInt: {
    const TargetData &TD = *AP.TM.getTargetData();
    // Support only foldable casts to/from pointers that can be eliminated by
    // changing the pointer to the appropriately sized integer type.
    Constant *Op = CE->getOperand(0);
    const Type *Ty = CE->getType();

    const MCExpr *OpExpr = LowerConstant(Op, AP);

    // We can emit the pointer value into this slot if the slot is an
    // integer slot equal to the size of the pointer.
    if (TD.getTypeAllocSize(Ty) == TD.getTypeAllocSize(Op->getType()))
      return OpExpr;

    // Otherwise the pointer is smaller than the resultant integer, mask off
    // the high bits so we are sure to get a proper truncation if the input is
    // a constant expr.
    unsigned InBits = TD.getTypeAllocSizeInBits(Op->getType());
    const MCExpr *MaskExpr = MCConstantExpr::Create(~0ULL >> (64-InBits), Ctx);
    return MCBinaryExpr::CreateAnd(OpExpr, MaskExpr, Ctx);
  }
      
  // The MC library also has a right-shift operator, but it isn't consistently
  // signed or unsigned between different targets.
  case Instruction::Add:
  case Instruction::Sub:
  case Instruction::Mul:
  case Instruction::SDiv:
  case Instruction::SRem:
  case Instruction::Shl:
  case Instruction::And:
  case Instruction::Or:
  case Instruction::Xor: {
    const MCExpr *LHS = LowerConstant(CE->getOperand(0), AP);
    const MCExpr *RHS = LowerConstant(CE->getOperand(1), AP);
    switch (CE->getOpcode()) {
    default: llvm_unreachable("Unknown binary operator constant cast expr");
    case Instruction::Add: return MCBinaryExpr::CreateAdd(LHS, RHS, Ctx);
    case Instruction::Sub: return MCBinaryExpr::CreateSub(LHS, RHS, Ctx);
    case Instruction::Mul: return MCBinaryExpr::CreateMul(LHS, RHS, Ctx);
    case Instruction::SDiv: return MCBinaryExpr::CreateDiv(LHS, RHS, Ctx);
    case Instruction::SRem: return MCBinaryExpr::CreateMod(LHS, RHS, Ctx);
    case Instruction::Shl: return MCBinaryExpr::CreateShl(LHS, RHS, Ctx);
    case Instruction::And: return MCBinaryExpr::CreateAnd(LHS, RHS, Ctx);
    case Instruction::Or:  return MCBinaryExpr::CreateOr (LHS, RHS, Ctx);
    case Instruction::Xor: return MCBinaryExpr::CreateXor(LHS, RHS, Ctx);
    }
  }
  }
}

static void EmitGlobalConstantArray(const ConstantArray *CA, unsigned AddrSpace,
                                    AsmPrinter &AP) {
  if (AddrSpace != 0 || !CA->isString()) {
    // Not a string.  Print the values in successive locations
    for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i)
      AP.EmitGlobalConstant(CA->getOperand(i), AddrSpace);
    return;
  }
  
  // Otherwise, it can be emitted as .ascii.
  SmallVector<char, 128> TmpVec;
  TmpVec.reserve(CA->getNumOperands());
  for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i)
    TmpVec.push_back(cast<ConstantInt>(CA->getOperand(i))->getZExtValue());

  AP.OutStreamer.EmitBytes(StringRef(TmpVec.data(), TmpVec.size()), AddrSpace);
}

static void EmitGlobalConstantVector(const ConstantVector *CV,
                                     unsigned AddrSpace, AsmPrinter &AP) {
  for (unsigned i = 0, e = CV->getType()->getNumElements(); i != e; ++i)
    AP.EmitGlobalConstant(CV->getOperand(i), AddrSpace);
}

static void EmitGlobalConstantStruct(const ConstantStruct *CS,
                                     unsigned AddrSpace, AsmPrinter &AP) {
  // Print the fields in successive locations. Pad to align if needed!
  const TargetData *TD = AP.TM.getTargetData();
  unsigned Size = TD->getTypeAllocSize(CS->getType());
  const StructLayout *Layout = TD->getStructLayout(CS->getType());
  uint64_t SizeSoFar = 0;
  for (unsigned i = 0, e = CS->getNumOperands(); i != e; ++i) {
    const Constant *Field = CS->getOperand(i);

    // Check if padding is needed and insert one or more 0s.
    uint64_t FieldSize = TD->getTypeAllocSize(Field->getType());
    uint64_t PadSize = ((i == e-1 ? Size : Layout->getElementOffset(i+1))
                        - Layout->getElementOffset(i)) - FieldSize;
    SizeSoFar += FieldSize + PadSize;

    // Now print the actual field value.
    AP.EmitGlobalConstant(Field, AddrSpace);

    // Insert padding - this may include padding to increase the size of the
    // current field up to the ABI size (if the struct is not packed) as well
    // as padding to ensure that the next field starts at the right offset.
    AP.OutStreamer.EmitZeros(PadSize, AddrSpace);
  }
  assert(SizeSoFar == Layout->getSizeInBytes() &&
         "Layout of constant struct may be incorrect!");
}

static void EmitGlobalConstantUnion(const ConstantUnion *CU, 
                                    unsigned AddrSpace, AsmPrinter &AP) {
  const TargetData *TD = AP.TM.getTargetData();
  unsigned Size = TD->getTypeAllocSize(CU->getType());

  const Constant *Contents = CU->getOperand(0);
  unsigned FilledSize = TD->getTypeAllocSize(Contents->getType());
    
  // Print the actually filled part
  AP.EmitGlobalConstant(Contents, AddrSpace);

  // And pad with enough zeroes
  AP.OutStreamer.EmitZeros(Size-FilledSize, AddrSpace);
}

static void EmitGlobalConstantFP(const ConstantFP *CFP, unsigned AddrSpace,
                                 AsmPrinter &AP) {
  // FP Constants are printed as integer constants to avoid losing
  // precision.
  if (CFP->getType()->isDoubleTy()) {
    if (AP.VerboseAsm) {
      double Val = CFP->getValueAPF().convertToDouble();
      AP.OutStreamer.GetCommentOS() << "double " << Val << '\n';
    }

    uint64_t Val = CFP->getValueAPF().bitcastToAPInt().getZExtValue();
    AP.OutStreamer.EmitIntValue(Val, 8, AddrSpace);
    return;
  }
  
  if (CFP->getType()->isFloatTy()) {
    if (AP.VerboseAsm) {
      float Val = CFP->getValueAPF().convertToFloat();
      AP.OutStreamer.GetCommentOS() << "float " << Val << '\n';
    }
    uint64_t Val = CFP->getValueAPF().bitcastToAPInt().getZExtValue();
    AP.OutStreamer.EmitIntValue(Val, 4, AddrSpace);
    return;
  }
  
  if (CFP->getType()->isX86_FP80Ty()) {
    // all long double variants are printed as hex
    // api needed to prevent premature destruction
    APInt API = CFP->getValueAPF().bitcastToAPInt();
    const uint64_t *p = API.getRawData();
    if (AP.VerboseAsm) {
      // Convert to double so we can print the approximate val as a comment.
      APFloat DoubleVal = CFP->getValueAPF();
      bool ignored;
      DoubleVal.convert(APFloat::IEEEdouble, APFloat::rmNearestTiesToEven,
                        &ignored);
      AP.OutStreamer.GetCommentOS() << "x86_fp80 ~= "
        << DoubleVal.convertToDouble() << '\n';
    }
    
    if (AP.TM.getTargetData()->isBigEndian()) {
      AP.OutStreamer.EmitIntValue(p[1], 2, AddrSpace);
      AP.OutStreamer.EmitIntValue(p[0], 8, AddrSpace);
    } else {
      AP.OutStreamer.EmitIntValue(p[0], 8, AddrSpace);
      AP.OutStreamer.EmitIntValue(p[1], 2, AddrSpace);
    }
    
    // Emit the tail padding for the long double.
    const TargetData &TD = *AP.TM.getTargetData();
    AP.OutStreamer.EmitZeros(TD.getTypeAllocSize(CFP->getType()) -
                             TD.getTypeStoreSize(CFP->getType()), AddrSpace);
    return;
  }
  
  assert(CFP->getType()->isPPC_FP128Ty() &&
         "Floating point constant type not handled");
  // All long double variants are printed as hex api needed to prevent
  // premature destruction.
  APInt API = CFP->getValueAPF().bitcastToAPInt();
  const uint64_t *p = API.getRawData();
  if (AP.TM.getTargetData()->isBigEndian()) {
    AP.OutStreamer.EmitIntValue(p[0], 8, AddrSpace);
    AP.OutStreamer.EmitIntValue(p[1], 8, AddrSpace);
  } else {
    AP.OutStreamer.EmitIntValue(p[1], 8, AddrSpace);
    AP.OutStreamer.EmitIntValue(p[0], 8, AddrSpace);
  }
}

static void EmitGlobalConstantLargeInt(const ConstantInt *CI,
                                       unsigned AddrSpace, AsmPrinter &AP) {
  const TargetData *TD = AP.TM.getTargetData();
  unsigned BitWidth = CI->getBitWidth();
  assert((BitWidth & 63) == 0 && "only support multiples of 64-bits");

  // We don't expect assemblers to support integer data directives
  // for more than 64 bits, so we emit the data in at most 64-bit
  // quantities at a time.
  const uint64_t *RawData = CI->getValue().getRawData();
  for (unsigned i = 0, e = BitWidth / 64; i != e; ++i) {
    uint64_t Val = TD->isBigEndian() ? RawData[e - i - 1] : RawData[i];
    AP.OutStreamer.EmitIntValue(Val, 8, AddrSpace);
  }
}

/// EmitGlobalConstant - Print a general LLVM constant to the .s file.
void AsmPrinter::EmitGlobalConstant(const Constant *CV, unsigned AddrSpace) {
  if (isa<ConstantAggregateZero>(CV) || isa<UndefValue>(CV)) {
    uint64_t Size = TM.getTargetData()->getTypeAllocSize(CV->getType());
    if (Size == 0) Size = 1; // An empty "_foo:" followed by a section is undef.
    return OutStreamer.EmitZeros(Size, AddrSpace);
  }

  if (const ConstantInt *CI = dyn_cast<ConstantInt>(CV)) {
    unsigned Size = TM.getTargetData()->getTypeAllocSize(CV->getType());
    switch (Size) {
    case 1:
    case 2:
    case 4:
    case 8:
      if (VerboseAsm)
        OutStreamer.GetCommentOS() << format("0x%llx\n", CI->getZExtValue());
      OutStreamer.EmitIntValue(CI->getZExtValue(), Size, AddrSpace);
      return;
    default:
      EmitGlobalConstantLargeInt(CI, AddrSpace, *this);
      return;
    }
  }
  
  if (const ConstantArray *CVA = dyn_cast<ConstantArray>(CV))
    return EmitGlobalConstantArray(CVA, AddrSpace, *this);
  
  if (const ConstantStruct *CVS = dyn_cast<ConstantStruct>(CV))
    return EmitGlobalConstantStruct(CVS, AddrSpace, *this);

  if (const ConstantFP *CFP = dyn_cast<ConstantFP>(CV))
    return EmitGlobalConstantFP(CFP, AddrSpace, *this);

  if (isa<ConstantPointerNull>(CV)) {
    unsigned Size = TM.getTargetData()->getTypeAllocSize(CV->getType());
    OutStreamer.EmitIntValue(0, Size, AddrSpace);
    return;
  }
  
  if (const ConstantUnion *CVU = dyn_cast<ConstantUnion>(CV))
    return EmitGlobalConstantUnion(CVU, AddrSpace, *this);
  
  if (const ConstantVector *V = dyn_cast<ConstantVector>(CV))
    return EmitGlobalConstantVector(V, AddrSpace, *this);
  
  // Otherwise, it must be a ConstantExpr.  Lower it to an MCExpr, then emit it
  // thread the streamer with EmitValue.
  OutStreamer.EmitValue(LowerConstant(CV, *this),
                        TM.getTargetData()->getTypeAllocSize(CV->getType()),
                        AddrSpace);
}

void AsmPrinter::EmitMachineConstantPoolValue(MachineConstantPoolValue *MCPV) {
  // Target doesn't support this yet!
  llvm_unreachable("Target does not support EmitMachineConstantPoolValue");
}

void AsmPrinter::printOffset(int64_t Offset, raw_ostream &OS) const {
  if (Offset > 0)
    OS << '+' << Offset;
  else if (Offset < 0)
    OS << Offset;
}


/// EmitImplicitDef - This method emits the specified machine instruction
/// that is an implicit def.
void AsmPrinter::EmitImplicitDef(const MachineInstr *MI) const {
  if (!VerboseAsm) return;
  unsigned RegNo = MI->getOperand(0).getReg();
  OutStreamer.AddComment(Twine("implicit-def: ") +
                         TM.getRegisterInfo()->getName(RegNo));
  OutStreamer.AddBlankLine();
}

void AsmPrinter::EmitKill(const MachineInstr *MI) const {
  if (!VerboseAsm) return;
  
  std::string Str = "kill:";
  for (unsigned n = 0, e = MI->getNumOperands(); n != e; ++n) {
    const MachineOperand &Op = MI->getOperand(n);
    assert(Op.isReg() && "KILL instruction must have only register operands");
    Str += ' ';
    Str += TM.getRegisterInfo()->getName(Op.getReg());
    Str += (Op.isDef() ? "<def>" : "<kill>");
  }
  OutStreamer.AddComment(Str);
  OutStreamer.AddBlankLine();
}

MCSymbol *AsmPrinter::GetBlockAddressSymbol(const BlockAddress *BA) const {
  return MMI->getAddrLabelSymbol(BA->getBasicBlock());
}

MCSymbol *AsmPrinter::GetBlockAddressSymbol(const BasicBlock *BB) const {
  return MMI->getAddrLabelSymbol(BB);
}

/// GetCPISymbol - Return the symbol for the specified constant pool entry.
MCSymbol *AsmPrinter::GetCPISymbol(unsigned CPID) const {
  return OutContext.GetOrCreateSymbol
    (Twine(MAI->getPrivateGlobalPrefix()) + "CPI" + Twine(getFunctionNumber())
     + "_" + Twine(CPID));
}

/// GetJTISymbol - Return the symbol for the specified jump table entry.
MCSymbol *AsmPrinter::GetJTISymbol(unsigned JTID, bool isLinkerPrivate) const {
  return MF->getJTISymbol(JTID, OutContext, isLinkerPrivate);
}

/// GetJTSetSymbol - Return the symbol for the specified jump table .set
/// FIXME: privatize to AsmPrinter.
MCSymbol *AsmPrinter::GetJTSetSymbol(unsigned UID, unsigned MBBID) const {
  return OutContext.GetOrCreateSymbol
  (Twine(MAI->getPrivateGlobalPrefix()) + Twine(getFunctionNumber()) + "_" +
   Twine(UID) + "_set_" + Twine(MBBID));
}

/// GetSymbolWithGlobalValueBase - Return the MCSymbol for a symbol with
/// global value name as its base, with the specified suffix, and where the
/// symbol is forced to have private linkage if ForcePrivate is true.
MCSymbol *AsmPrinter::GetSymbolWithGlobalValueBase(const GlobalValue *GV,
                                                   StringRef Suffix,
                                                   bool ForcePrivate) const {
  SmallString<60> NameStr;
  Mang->getNameWithPrefix(NameStr, GV, ForcePrivate);
  NameStr.append(Suffix.begin(), Suffix.end());
  return OutContext.GetOrCreateSymbol(NameStr.str());
}

/// GetExternalSymbolSymbol - Return the MCSymbol for the specified
/// ExternalSymbol.
MCSymbol *AsmPrinter::GetExternalSymbolSymbol(StringRef Sym) const {
  SmallString<60> NameStr;
  Mang->getNameWithPrefix(NameStr, Sym);
  return OutContext.GetOrCreateSymbol(NameStr.str());
}  



/// PrintParentLoopComment - Print comments about parent loops of this one.
static void PrintParentLoopComment(raw_ostream &OS, const MachineLoop *Loop,
                                   unsigned FunctionNumber) {
  if (Loop == 0) return;
  PrintParentLoopComment(OS, Loop->getParentLoop(), FunctionNumber);
  OS.indent(Loop->getLoopDepth()*2)
    << "Parent Loop BB" << FunctionNumber << "_"
    << Loop->getHeader()->getNumber()
    << " Depth=" << Loop->getLoopDepth() << '\n';
}


/// PrintChildLoopComment - Print comments about child loops within
/// the loop for this basic block, with nesting.
static void PrintChildLoopComment(raw_ostream &OS, const MachineLoop *Loop,
                                  unsigned FunctionNumber) {
  // Add child loop information
  for (MachineLoop::iterator CL = Loop->begin(), E = Loop->end();CL != E; ++CL){
    OS.indent((*CL)->getLoopDepth()*2)
      << "Child Loop BB" << FunctionNumber << "_"
      << (*CL)->getHeader()->getNumber() << " Depth " << (*CL)->getLoopDepth()
      << '\n';
    PrintChildLoopComment(OS, *CL, FunctionNumber);
  }
}

/// EmitBasicBlockLoopComments - Pretty-print comments for basic blocks.
static void EmitBasicBlockLoopComments(const MachineBasicBlock &MBB,
                                       const MachineLoopInfo *LI,
                                       const AsmPrinter &AP) {
  // Add loop depth information
  const MachineLoop *Loop = LI->getLoopFor(&MBB);
  if (Loop == 0) return;
  
  MachineBasicBlock *Header = Loop->getHeader();
  assert(Header && "No header for loop");
  
  // If this block is not a loop header, just print out what is the loop header
  // and return.
  if (Header != &MBB) {
    AP.OutStreamer.AddComment("  in Loop: Header=BB" +
                              Twine(AP.getFunctionNumber())+"_" +
                              Twine(Loop->getHeader()->getNumber())+
                              " Depth="+Twine(Loop->getLoopDepth()));
    return;
  }
  
  // Otherwise, it is a loop header.  Print out information about child and
  // parent loops.
  raw_ostream &OS = AP.OutStreamer.GetCommentOS();
  
  PrintParentLoopComment(OS, Loop->getParentLoop(), AP.getFunctionNumber()); 
  
  OS << "=>";
  OS.indent(Loop->getLoopDepth()*2-2);
  
  OS << "This ";
  if (Loop->empty())
    OS << "Inner ";
  OS << "Loop Header: Depth=" + Twine(Loop->getLoopDepth()) << '\n';
  
  PrintChildLoopComment(OS, Loop, AP.getFunctionNumber());
}


/// EmitBasicBlockStart - This method prints the label for the specified
/// MachineBasicBlock, an alignment (if present) and a comment describing
/// it if appropriate.
void AsmPrinter::EmitBasicBlockStart(const MachineBasicBlock *MBB) const {
  // Emit an alignment directive for this block, if needed.
  if (unsigned Align = MBB->getAlignment())
    EmitAlignment(Log2_32(Align));

  // If the block has its address taken, emit any labels that were used to
  // reference the block.  It is possible that there is more than one label
  // here, because multiple LLVM BB's may have been RAUW'd to this block after
  // the references were generated.
  if (MBB->hasAddressTaken()) {
    const BasicBlock *BB = MBB->getBasicBlock();
    if (VerboseAsm)
      OutStreamer.AddComment("Block address taken");
    
    std::vector<MCSymbol*> Syms = MMI->getAddrLabelSymbolToEmit(BB);

    for (unsigned i = 0, e = Syms.size(); i != e; ++i)
      OutStreamer.EmitLabel(Syms[i]);
  }

  // Print the main label for the block.
  if (MBB->pred_empty() || isBlockOnlyReachableByFallthrough(MBB)) {
    if (VerboseAsm && OutStreamer.hasRawTextSupport()) {
      if (const BasicBlock *BB = MBB->getBasicBlock())
        if (BB->hasName())
          OutStreamer.AddComment("%" + BB->getName());
      
      EmitBasicBlockLoopComments(*MBB, LI, *this);
      
      // NOTE: Want this comment at start of line, don't emit with AddComment.
      OutStreamer.EmitRawText(Twine(MAI->getCommentString()) + " BB#" +
                              Twine(MBB->getNumber()) + ":");
    }
  } else {
    if (VerboseAsm) {
      if (const BasicBlock *BB = MBB->getBasicBlock())
        if (BB->hasName())
          OutStreamer.AddComment("%" + BB->getName());
      EmitBasicBlockLoopComments(*MBB, LI, *this);
    }

    OutStreamer.EmitLabel(MBB->getSymbol());
  }
}

void AsmPrinter::EmitVisibility(MCSymbol *Sym, unsigned Visibility) const {
  MCSymbolAttr Attr = MCSA_Invalid;
  
  switch (Visibility) {
  default: break;
  case GlobalValue::HiddenVisibility:
    Attr = MAI->getHiddenVisibilityAttr();
    break;
  case GlobalValue::ProtectedVisibility:
    Attr = MAI->getProtectedVisibilityAttr();
    break;
  }

  if (Attr != MCSA_Invalid)
    OutStreamer.EmitSymbolAttribute(Sym, Attr);
}

/// isBlockOnlyReachableByFallthough - Return true if the basic block has
/// exactly one predecessor and the control transfer mechanism between
/// the predecessor and this block is a fall-through.
bool AsmPrinter::
isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB) const {
  // If this is a landing pad, it isn't a fall through.  If it has no preds,
  // then nothing falls through to it.
  if (MBB->isLandingPad() || MBB->pred_empty())
    return false;
  
  // If there isn't exactly one predecessor, it can't be a fall through.
  MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(), PI2 = PI;
  ++PI2;
  if (PI2 != MBB->pred_end())
    return false;
  
  // The predecessor has to be immediately before this block.
  const MachineBasicBlock *Pred = *PI;
  
  if (!Pred->isLayoutSuccessor(MBB))
    return false;
  
  // If the block is completely empty, then it definitely does fall through.
  if (Pred->empty())
    return true;
  
  // Otherwise, check the last instruction.
  const MachineInstr &LastInst = Pred->back();
  return !LastInst.getDesc().isBarrier();
}



GCMetadataPrinter *AsmPrinter::GetOrCreateGCPrinter(GCStrategy *S) {
  if (!S->usesMetadata())
    return 0;

  gcp_map_type &GCMap = getGCMap(GCMetadataPrinters);
  gcp_map_type::iterator GCPI = GCMap.find(S);
  if (GCPI != GCMap.end())
    return GCPI->second;
  
  const char *Name = S->getName().c_str();
  
  for (GCMetadataPrinterRegistry::iterator
         I = GCMetadataPrinterRegistry::begin(),
         E = GCMetadataPrinterRegistry::end(); I != E; ++I)
    if (strcmp(Name, I->getName()) == 0) {
      GCMetadataPrinter *GMP = I->instantiate();
      GMP->S = S;
      GCMap.insert(std::make_pair(S, GMP));
      return GMP;
    }
  
  llvm_report_error("no GCMetadataPrinter registered for GC: " + Twine(Name));
  return 0;
}