AsmPrinter.cpp

//===-- AsmPrinter.cpp - Common AsmPrinter code ---------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the AsmPrinter class.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Constants.h"
#include "llvm/Module.h"
#include "llvm/CodeGen/DwarfWriter.h"
#include "llvm/CodeGen/GCMetadataPrinter.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineJumpTableInfo.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/Analysis/DebugInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/FormattedStream.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Target/Mangler.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallString.h"
#include <cerrno>
using namespace llvm;

static cl::opt<cl::boolOrDefault>
AsmVerbose("asm-verbose", cl::desc("Add comments to directives."),
           cl::init(cl::BOU_UNSET));

static bool getVerboseAsm(bool VDef) {
  switch (AsmVerbose) {
  default:
  case cl::BOU_UNSET: return VDef;
  case cl::BOU_TRUE:  return true;
  case cl::BOU_FALSE: return false;
  }      
}

char AsmPrinter::ID = 0;
AsmPrinter::AsmPrinter(formatted_raw_ostream &o, TargetMachine &tm,
                       const MCAsmInfo *T, bool VDef)
  : MachineFunctionPass(&ID), FunctionNumber(0), O(o),
    TM(tm), MAI(T), TRI(tm.getRegisterInfo()),

    OutContext(*new MCContext()),
    // FIXME: Pass instprinter to streamer.
    OutStreamer(*createAsmStreamer(OutContext, O, *T,
                                   TM.getTargetData()->isLittleEndian(),
                                   getVerboseAsm(VDef), 0)),

    LastMI(0), LastFn(0), Counter(~0U), PrevDLT(NULL) {
  DW = 0; MMI = 0;
  VerboseAsm = getVerboseAsm(VDef);
}

AsmPrinter::~AsmPrinter() {
  for (gcp_iterator I = GCMetadataPrinters.begin(),
                    E = GCMetadataPrinters.end(); I != E; ++I)
    delete I->second;
  
  delete &OutStreamer;
  delete &OutContext;
}

TargetLoweringObjectFile &AsmPrinter::getObjFileLowering() const {
  return TM.getTargetLowering()->getObjFileLowering();
}

/// getCurrentSection() - Return the current section we are emitting to.
const MCSection *AsmPrinter::getCurrentSection() const {
  return OutStreamer.getCurrentSection();
}


void AsmPrinter::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesAll();
  MachineFunctionPass::getAnalysisUsage(AU);
  AU.addRequired<GCModuleInfo>();
  if (VerboseAsm)
    AU.addRequired<MachineLoopInfo>();
}

bool AsmPrinter::doInitialization(Module &M) {
  // Initialize TargetLoweringObjectFile.
  const_cast<TargetLoweringObjectFile&>(getObjFileLowering())
    .Initialize(OutContext, TM);
  
  Mang = new Mangler(*MAI);
  
  // Allow the target to emit any magic that it wants at the start of the file.
  EmitStartOfAsmFile(M);

  // Very minimal debug info. It is ignored if we emit actual debug info. If we
  // don't, this at least helps the user find where a global came from.
  if (MAI->hasSingleParameterDotFile()) {
    // .file "foo.c"
    OutStreamer.EmitFileDirective(M.getModuleIdentifier());
  }

  GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
  assert(MI && "AsmPrinter didn't require GCModuleInfo?");
  for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I)
    if (GCMetadataPrinter *MP = GetOrCreateGCPrinter(*I))
      MP->beginAssembly(O, *this, *MAI);
  
  if (!M.getModuleInlineAsm().empty())
    O << MAI->getCommentString() << " Start of file scope inline assembly\n"
      << M.getModuleInlineAsm()
      << '\n' << MAI->getCommentString()
      << " End of file scope inline assembly\n";

  MMI = getAnalysisIfAvailable<MachineModuleInfo>();
  if (MMI)
    MMI->AnalyzeModule(M);
  DW = getAnalysisIfAvailable<DwarfWriter>();
  if (DW)
    DW->BeginModule(&M, MMI, O, this, MAI);

  return false;
}

/// EmitGlobalVariable - Emit the specified global variable to the .s file.
void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
  if (!GV->hasInitializer())   // External globals require no code.
    return;
  
  // Check to see if this is a special global used by LLVM, if so, emit it.
  if (EmitSpecialLLVMGlobal(GV))
    return;

  MCSymbol *GVSym = GetGlobalValueSymbol(GV);
  printVisibility(GVSym, GV->getVisibility());

  if (MAI->hasDotTypeDotSizeDirective())
    OutStreamer.EmitSymbolAttribute(GVSym, MCSA_ELF_TypeObject);
  
  SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);

  const TargetData *TD = TM.getTargetData();
  unsigned Size = TD->getTypeAllocSize(GV->getType()->getElementType());
  unsigned AlignLog = TD->getPreferredAlignmentLog(GV);
  
  // Handle common and BSS local symbols (.lcomm).
  if (GVKind.isCommon() || GVKind.isBSSLocal()) {
    if (Size == 0) Size = 1;   // .comm Foo, 0 is undefined, avoid it.
    
    if (VerboseAsm) {
      WriteAsOperand(OutStreamer.GetCommentOS(), GV,
                     /*PrintType=*/false, GV->getParent());
      OutStreamer.GetCommentOS() << '\n';
    }
    
    // Handle common symbols.
    if (GVKind.isCommon()) {
      // .comm _foo, 42, 4
      OutStreamer.EmitCommonSymbol(GVSym, Size, 1 << AlignLog);
      return;
    }
    
    // Handle local BSS symbols.
    if (MAI->hasMachoZeroFillDirective()) {
      const MCSection *TheSection =
        getObjFileLowering().SectionForGlobal(GV, GVKind, Mang, TM);
      // .zerofill __DATA, __bss, _foo, 400, 5
      OutStreamer.EmitZerofill(TheSection, GVSym, Size, 1 << AlignLog);
      return;
    }
    
    if (MAI->hasLCOMMDirective()) {
      // .lcomm _foo, 42
      OutStreamer.EmitLocalCommonSymbol(GVSym, Size);
      return;
    }
    
    // .local _foo
    OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Local);
    // .comm _foo, 42, 4
    OutStreamer.EmitCommonSymbol(GVSym, Size, 1 << AlignLog);
    return;
  }
  
  const MCSection *TheSection =
    getObjFileLowering().SectionForGlobal(GV, GVKind, Mang, TM);

  // Handle the zerofill directive on darwin, which is a special form of BSS
  // emission.
  if (GVKind.isBSSExtern() && MAI->hasMachoZeroFillDirective()) {
    // .globl _foo
    OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);
    // .zerofill __DATA, __common, _foo, 400, 5
    OutStreamer.EmitZerofill(TheSection, GVSym, Size, 1 << AlignLog);
    return;
  }

  OutStreamer.SwitchSection(TheSection);

  // TODO: Factor into an 'emit linkage' thing that is shared with function
  // bodies.
  switch (GV->getLinkage()) {
  case GlobalValue::CommonLinkage:
  case GlobalValue::LinkOnceAnyLinkage:
  case GlobalValue::LinkOnceODRLinkage:
  case GlobalValue::WeakAnyLinkage:
  case GlobalValue::WeakODRLinkage:
  case GlobalValue::LinkerPrivateLinkage:
    if (MAI->getWeakDefDirective() != 0) {
      // .globl _foo
      OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);
      // .weak_definition _foo
      OutStreamer.EmitSymbolAttribute(GVSym, MCSA_WeakDefinition);
    } else if (const char *LinkOnce = MAI->getLinkOnceDirective()) {
      // .globl _foo
      OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);
      // FIXME: linkonce should be a section attribute, handled by COFF Section
      // assignment.
      // http://sourceware.org/binutils/docs-2.20/as/Linkonce.html#Linkonce
      // .linkonce same_size
      O << LinkOnce;
    } else {
      // .weak _foo
      OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Weak);
    }
    break;
  case GlobalValue::DLLExportLinkage:
  case GlobalValue::AppendingLinkage:
    // FIXME: appending linkage variables should go into a section of
    // their name or something.  For now, just emit them as external.
  case GlobalValue::ExternalLinkage:
    // If external or appending, declare as a global symbol.
    // .globl _foo
    OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);
    break;
  case GlobalValue::PrivateLinkage:
  case GlobalValue::InternalLinkage:
     break;
  default:
    llvm_unreachable("Unknown linkage type!");
  }

  EmitAlignment(AlignLog, GV);
  if (VerboseAsm) {
    WriteAsOperand(OutStreamer.GetCommentOS(), GV,
                   /*PrintType=*/false, GV->getParent());
    OutStreamer.GetCommentOS() << '\n';
  }
  OutStreamer.EmitLabel(GVSym);

  EmitGlobalConstant(GV->getInitializer());

  if (MAI->hasDotTypeDotSizeDirective())
    // .size foo, 42
    OutStreamer.EmitELFSize(GVSym, MCConstantExpr::Create(Size, OutContext));
  
  OutStreamer.AddBlankLine();
}


bool AsmPrinter::doFinalization(Module &M) {
  // Emit global variables.
  for (Module::const_global_iterator I = M.global_begin(), E = M.global_end();
       I != E; ++I)
    EmitGlobalVariable(I);
  
  // Emit final debug information.
  if (MAI->doesSupportDebugInformation() || MAI->doesSupportExceptionHandling())
    DW->EndModule();
  
  // If the target wants to know about weak references, print them all.
  if (MAI->getWeakRefDirective()) {
    // FIXME: This is not lazy, it would be nice to only print weak references
    // to stuff that is actually used.  Note that doing so would require targets
    // to notice uses in operands (due to constant exprs etc).  This should
    // happen with the MC stuff eventually.

    // Print out module-level global variables here.
    for (Module::const_global_iterator I = M.global_begin(), E = M.global_end();
         I != E; ++I) {
      if (!I->hasExternalWeakLinkage()) continue;
      OutStreamer.EmitSymbolAttribute(GetGlobalValueSymbol(I),
                                      MCSA_WeakReference);
    }
    
    for (Module::const_iterator I = M.begin(), E = M.end(); I != E; ++I) {
      if (!I->hasExternalWeakLinkage()) continue;
      OutStreamer.EmitSymbolAttribute(GetGlobalValueSymbol(I),
                                      MCSA_WeakReference);
    }
  }

  if (MAI->getSetDirective()) {
    OutStreamer.AddBlankLine();
    for (Module::const_alias_iterator I = M.alias_begin(), E = M.alias_end();
         I != E; ++I) {
      MCSymbol *Name = GetGlobalValueSymbol(I);

      const GlobalValue *GV = cast<GlobalValue>(I->getAliasedGlobal());
      MCSymbol *Target = GetGlobalValueSymbol(GV);

      if (I->hasExternalLinkage() || !MAI->getWeakRefDirective())
        OutStreamer.EmitSymbolAttribute(Name, MCSA_Global);
      else if (I->hasWeakLinkage())
        OutStreamer.EmitSymbolAttribute(Name, MCSA_WeakReference);
      else
        assert(I->hasLocalLinkage() && "Invalid alias linkage");

      printVisibility(Name, I->getVisibility());

      O << MAI->getSetDirective() << ' ' << *Name << ", " << *Target << '\n';
    }
  }

  GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
  assert(MI && "AsmPrinter didn't require GCModuleInfo?");
  for (GCModuleInfo::iterator I = MI->end(), E = MI->begin(); I != E; )
    if (GCMetadataPrinter *MP = GetOrCreateGCPrinter(*--I))
      MP->finishAssembly(O, *this, *MAI);

  // If we don't have any trampolines, then we don't require stack memory
  // to be executable. Some targets have a directive to declare this.
  Function *InitTrampolineIntrinsic = M.getFunction("llvm.init.trampoline");
  if (!InitTrampolineIntrinsic || InitTrampolineIntrinsic->use_empty())
    if (MCSection *S = MAI->getNonexecutableStackSection(OutContext))
      OutStreamer.SwitchSection(S);
  
  // Allow the target to emit any magic that it wants at the end of the file,
  // after everything else has gone out.
  EmitEndOfAsmFile(M);
  
  delete Mang; Mang = 0;
  DW = 0; MMI = 0;
  
  OutStreamer.Finish();
  return false;
}

void AsmPrinter::SetupMachineFunction(MachineFunction &MF) {
  // Get the function symbol.
  CurrentFnSym = GetGlobalValueSymbol(MF.getFunction());
  IncrementFunctionNumber();

  if (VerboseAsm)
    LI = &getAnalysis<MachineLoopInfo>();
}

namespace {
  // SectionCPs - Keep track the alignment, constpool entries per Section.
  struct SectionCPs {
    const MCSection *S;
    unsigned Alignment;
    SmallVector<unsigned, 4> CPEs;
    SectionCPs(const MCSection *s, unsigned a) : S(s), Alignment(a) {}
  };
}

/// EmitConstantPool - Print to the current output stream assembly
/// representations of the constants in the constant pool MCP. This is
/// used to print out constants which have been "spilled to memory" by
/// the code generator.
///
void AsmPrinter::EmitConstantPool(MachineConstantPool *MCP) {
  const std::vector<MachineConstantPoolEntry> &CP = MCP->getConstants();
  if (CP.empty()) return;

  // Calculate sections for constant pool entries. We collect entries to go into
  // the same section together to reduce amount of section switch statements.
  SmallVector<SectionCPs, 4> CPSections;
  for (unsigned i = 0, e = CP.size(); i != e; ++i) {
    const MachineConstantPoolEntry &CPE = CP[i];
    unsigned Align = CPE.getAlignment();
    
    SectionKind Kind;
    switch (CPE.getRelocationInfo()) {
    default: llvm_unreachable("Unknown section kind");
    case 2: Kind = SectionKind::getReadOnlyWithRel(); break;
    case 1:
      Kind = SectionKind::getReadOnlyWithRelLocal();
      break;
    case 0:
    switch (TM.getTargetData()->getTypeAllocSize(CPE.getType())) {
    case 4:  Kind = SectionKind::getMergeableConst4(); break;
    case 8:  Kind = SectionKind::getMergeableConst8(); break;
    case 16: Kind = SectionKind::getMergeableConst16();break;
    default: Kind = SectionKind::getMergeableConst(); break;
    }
    }

    const MCSection *S = getObjFileLowering().getSectionForConstant(Kind);
    
    // The number of sections are small, just do a linear search from the
    // last section to the first.
    bool Found = false;
    unsigned SecIdx = CPSections.size();
    while (SecIdx != 0) {
      if (CPSections[--SecIdx].S == S) {
        Found = true;
        break;
      }
    }
    if (!Found) {
      SecIdx = CPSections.size();
      CPSections.push_back(SectionCPs(S, Align));
    }

    if (Align > CPSections[SecIdx].Alignment)
      CPSections[SecIdx].Alignment = Align;
    CPSections[SecIdx].CPEs.push_back(i);
  }

  // Now print stuff into the calculated sections.
  for (unsigned i = 0, e = CPSections.size(); i != e; ++i) {
    OutStreamer.SwitchSection(CPSections[i].S);
    EmitAlignment(Log2_32(CPSections[i].Alignment));

    unsigned Offset = 0;
    for (unsigned j = 0, ee = CPSections[i].CPEs.size(); j != ee; ++j) {
      unsigned CPI = CPSections[i].CPEs[j];
      MachineConstantPoolEntry CPE = CP[CPI];

      // Emit inter-object padding for alignment.
      unsigned AlignMask = CPE.getAlignment() - 1;
      unsigned NewOffset = (Offset + AlignMask) & ~AlignMask;
      OutStreamer.EmitFill(NewOffset - Offset, 0/*fillval*/, 0/*addrspace*/);

      const Type *Ty = CPE.getType();
      Offset = NewOffset + TM.getTargetData()->getTypeAllocSize(Ty);

      // Emit the label with a comment on it.
      if (VerboseAsm) {
        OutStreamer.GetCommentOS() << "constant pool ";
        WriteTypeSymbolic(OutStreamer.GetCommentOS(), CPE.getType(),
                          MF->getFunction()->getParent());
        OutStreamer.GetCommentOS() << '\n';
      }
      OutStreamer.EmitLabel(GetCPISymbol(CPI));

      if (CPE.isMachineConstantPoolEntry())
        EmitMachineConstantPoolValue(CPE.Val.MachineCPVal);
      else
        EmitGlobalConstant(CPE.Val.ConstVal);
    }
  }
}

/// EmitJumpTableInfo - Print assembly representations of the jump tables used
/// by the current function to the current output stream.  
///
void AsmPrinter::EmitJumpTableInfo(MachineJumpTableInfo *MJTI,
                                   MachineFunction &MF) {
  const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
  if (JT.empty()) return;

  bool IsPic = TM.getRelocationModel() == Reloc::PIC_;
  
  // Pick the directive to use to print the jump table entries, and switch to 
  // the appropriate section.
  TargetLowering *LoweringInfo = TM.getTargetLowering();

  const Function *F = MF.getFunction();
  bool JTInDiffSection = false;
  if (F->isWeakForLinker() ||
      (IsPic && !LoweringInfo->usesGlobalOffsetTable())) {
    // In PIC mode, we need to emit the jump table to the same section as the
    // function body itself, otherwise the label differences won't make sense.
    // We should also do if the section name is NULL or function is declared in
    // discardable section.
    OutStreamer.SwitchSection(getObjFileLowering().SectionForGlobal(F, Mang,
                                                                    TM));
  } else {
    // Otherwise, drop it in the readonly section.
    const MCSection *ReadOnlySection = 
      getObjFileLowering().getSectionForConstant(SectionKind::getReadOnly());
    OutStreamer.SwitchSection(ReadOnlySection);
    JTInDiffSection = true;
  }
  
  EmitAlignment(Log2_32(MJTI->getAlignment()));
  
  for (unsigned i = 0, e = JT.size(); i != e; ++i) {
    const std::vector<MachineBasicBlock*> &JTBBs = JT[i].MBBs;
    
    // If this jump table was deleted, ignore it. 
    if (JTBBs.empty()) continue;

    // For PIC codegen, if possible we want to use the SetDirective to reduce
    // the number of relocations the assembler will generate for the jump table.
    // Set directives are all printed before the jump table itself.
    SmallPtrSet<MachineBasicBlock*, 16> EmittedSets;
    if (MAI->getSetDirective() && IsPic)
      for (unsigned ii = 0, ee = JTBBs.size(); ii != ee; ++ii)
        if (EmittedSets.insert(JTBBs[ii]))
          printPICJumpTableSetLabel(i, JTBBs[ii]);
    
    // On some targets (e.g. Darwin) we want to emit two consequtive labels
    // before each jump table.  The first label is never referenced, but tells
    // the assembler and linker the extents of the jump table object.  The
    // second label is actually referenced by the code.
    if (JTInDiffSection && MAI->getLinkerPrivateGlobalPrefix()[0])
      OutStreamer.EmitLabel(GetJTISymbol(i, true));

    OutStreamer.EmitLabel(GetJTISymbol(i));

    if (!IsPic) {
      // In non-pic mode, the entries in the jump table are direct references
      // to the basic blocks.
      unsigned EntrySize = MJTI->getEntrySize();
      for (unsigned ii = 0, ee = JTBBs.size(); ii != ee; ++ii) {
        MCSymbol *MBBSym = GetMBBSymbol(JTBBs[ii]->getNumber());
        OutStreamer.EmitValue(MCSymbolRefExpr::Create(MBBSym, OutContext),
                              EntrySize, /*addrspace*/0);
      }      
    } else {
      for (unsigned ii = 0, ee = JTBBs.size(); ii != ee; ++ii)
        printPICJumpTableEntry(MJTI, JTBBs[ii], i);
    }
  }
}

void AsmPrinter::printPICJumpTableEntry(const MachineJumpTableInfo *MJTI,
                                        const MachineBasicBlock *MBB,
                                        unsigned uid)  const {
  // If the target supports GPRel, use it.
  if (MAI->getGPRel32Directive() != 0) {
    MCSymbol *MBBSym = GetMBBSymbol(MBB->getNumber());
    OutStreamer.EmitGPRel32Value(MCSymbolRefExpr::Create(MBBSym, OutContext));
    return;
  }
  
  // If we have emitted set directives for the jump table entries, print 
  // them rather than the entries themselves.  If we're emitting PIC, then
  // emit the table entries as differences between two text section labels.
  const MCExpr *Val;
  if (MAI->getSetDirective()) {
    // If we used .set, reference the .set's symbol.
    Val = MCSymbolRefExpr::Create(GetJTSetSymbol(uid, MBB->getNumber()),
                                  OutContext);
  } else {
    // Otherwise, use the difference as the jump table entry.
    Val = MCSymbolRefExpr::Create(GetMBBSymbol(MBB->getNumber()), OutContext);
    const MCExpr *JTI = MCSymbolRefExpr::Create(GetJTISymbol(uid), OutContext);
    Val = MCBinaryExpr::CreateSub(Val, JTI, OutContext);
  }
  
  OutStreamer.EmitValue(Val, MJTI->getEntrySize(), /*addrspace*/0);
}


/// EmitSpecialLLVMGlobal - Check to see if the specified global is a
/// special global used by LLVM.  If so, emit it and return true, otherwise
/// do nothing and return false.
bool AsmPrinter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) {
  if (GV->getName() == "llvm.used") {
    if (MAI->hasNoDeadStrip())    // No need to emit this at all.
      EmitLLVMUsedList(GV->getInitializer());
    return true;
  }

  // Ignore debug and non-emitted data.  This handles llvm.compiler.used.
  if (GV->getSection() == "llvm.metadata" ||
      GV->hasAvailableExternallyLinkage())
    return true;
  
  if (!GV->hasAppendingLinkage()) return false;

  assert(GV->hasInitializer() && "Not a special LLVM global!");
  
  const TargetData *TD = TM.getTargetData();
  unsigned Align = Log2_32(TD->getPointerPrefAlignment());
  if (GV->getName() == "llvm.global_ctors") {
    OutStreamer.SwitchSection(getObjFileLowering().getStaticCtorSection());
    EmitAlignment(Align, 0);
    EmitXXStructorList(GV->getInitializer());
    
    if (TM.getRelocationModel() == Reloc::Static &&
        MAI->hasStaticCtorDtorReferenceInStaticMode()) {
      StringRef Sym(".constructors_used");
      OutStreamer.EmitSymbolAttribute(OutContext.GetOrCreateSymbol(Sym),
                                      MCSA_Reference);
    }
    return true;
  } 
  
  if (GV->getName() == "llvm.global_dtors") {
    OutStreamer.SwitchSection(getObjFileLowering().getStaticDtorSection());
    EmitAlignment(Align, 0);
    EmitXXStructorList(GV->getInitializer());

    if (TM.getRelocationModel() == Reloc::Static &&
        MAI->hasStaticCtorDtorReferenceInStaticMode()) {
      StringRef Sym(".destructors_used");
      OutStreamer.EmitSymbolAttribute(OutContext.GetOrCreateSymbol(Sym),
                                      MCSA_Reference);
    }
    return true;
  }
  
  return false;
}

/// EmitLLVMUsedList - For targets that define a MAI::UsedDirective, mark each
/// global in the specified llvm.used list for which emitUsedDirectiveFor
/// is true, as being used with this directive.
void AsmPrinter::EmitLLVMUsedList(Constant *List) {
  // Should be an array of 'i8*'.
  ConstantArray *InitList = dyn_cast<ConstantArray>(List);
  if (InitList == 0) return;
  
  for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i) {
    const GlobalValue *GV =
      dyn_cast<GlobalValue>(InitList->getOperand(i)->stripPointerCasts());
    if (GV && getObjFileLowering().shouldEmitUsedDirectiveFor(GV, Mang))
      OutStreamer.EmitSymbolAttribute(GetGlobalValueSymbol(GV),
                                      MCSA_NoDeadStrip);
  }
}

/// EmitXXStructorList - Emit the ctor or dtor list.  This just prints out the 
/// function pointers, ignoring the init priority.
void AsmPrinter::EmitXXStructorList(Constant *List) {
  // Should be an array of '{ int, void ()* }' structs.  The first value is the
  // init priority, which we ignore.
  if (!isa<ConstantArray>(List)) return;
  ConstantArray *InitList = cast<ConstantArray>(List);
  for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
    if (ConstantStruct *CS = dyn_cast<ConstantStruct>(InitList->getOperand(i))){
      if (CS->getNumOperands() != 2) return;  // Not array of 2-element structs.

      if (CS->getOperand(1)->isNullValue())
        return;  // Found a null terminator, exit printing.
      // Emit the function pointer.
      EmitGlobalConstant(CS->getOperand(1));
    }
}

//===--------------------------------------------------------------------===//
// Emission and print routines
//

/// EmitInt8 - Emit a byte directive and value.
///
void AsmPrinter::EmitInt8(int Value) const {
  OutStreamer.EmitIntValue(Value, 1, 0/*addrspace*/);
}

/// EmitInt16 - Emit a short directive and value.
///
void AsmPrinter::EmitInt16(int Value) const {
  OutStreamer.EmitIntValue(Value, 2, 0/*addrspace*/);
}

/// EmitInt32 - Emit a long directive and value.
///
void AsmPrinter::EmitInt32(int Value) const {
  OutStreamer.EmitIntValue(Value, 4, 0/*addrspace*/);
}

/// EmitInt64 - Emit a long long directive and value.
///
void AsmPrinter::EmitInt64(uint64_t Value) const {
  OutStreamer.EmitIntValue(Value, 8, 0/*addrspace*/);
}

//===----------------------------------------------------------------------===//

// EmitAlignment - Emit an alignment directive to the specified power of
// two boundary.  For example, if you pass in 3 here, you will get an 8
// byte alignment.  If a global value is specified, and if that global has
// an explicit alignment requested, it will unconditionally override the
// alignment request.  However, if ForcedAlignBits is specified, this value
// has final say: the ultimate alignment will be the max of ForcedAlignBits
// and the alignment computed with NumBits and the global.
//
// The algorithm is:
//     Align = NumBits;
//     if (GV && GV->hasalignment) Align = GV->getalignment();
//     Align = std::max(Align, ForcedAlignBits);
//
void AsmPrinter::EmitAlignment(unsigned NumBits, const GlobalValue *GV,
                               unsigned ForcedAlignBits,
                               bool UseFillExpr) const {
  if (GV && GV->getAlignment())
    NumBits = Log2_32(GV->getAlignment());
  NumBits = std::max(NumBits, ForcedAlignBits);
  
  if (NumBits == 0) return;   // No need to emit alignment.
  
  unsigned FillValue = 0;
  if (getCurrentSection()->getKind().isText())
    FillValue = MAI->getTextAlignFillValue();
  
  OutStreamer.EmitValueToAlignment(1 << NumBits, FillValue, 1, 0);
}

/// LowerConstant - Lower the specified LLVM Constant to an MCExpr.
///
static const MCExpr *LowerConstant(const Constant *CV, AsmPrinter &AP) {
  MCContext &Ctx = AP.OutContext;
  
  if (CV->isNullValue() || isa<UndefValue>(CV))
    return MCConstantExpr::Create(0, Ctx);

  if (const ConstantInt *CI = dyn_cast<ConstantInt>(CV))
    return MCConstantExpr::Create(CI->getZExtValue(), Ctx);
  
  if (const GlobalValue *GV = dyn_cast<GlobalValue>(CV))
    return MCSymbolRefExpr::Create(AP.GetGlobalValueSymbol(GV), Ctx);
  if (const BlockAddress *BA = dyn_cast<BlockAddress>(CV))
    return MCSymbolRefExpr::Create(AP.GetBlockAddressSymbol(BA), Ctx);
  
  const ConstantExpr *CE = dyn_cast<ConstantExpr>(CV);
  if (CE == 0) {
    llvm_unreachable("Unknown constant value to lower!");
    return MCConstantExpr::Create(0, Ctx);
  }
  
  switch (CE->getOpcode()) {
  case Instruction::ZExt:
  case Instruction::SExt:
  case Instruction::FPTrunc:
  case Instruction::FPExt:
  case Instruction::UIToFP:
  case Instruction::SIToFP:
  case Instruction::FPToUI:
  case Instruction::FPToSI:
  default: llvm_unreachable("FIXME: Don't support this constant cast 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);
  }
      
  case Instruction::Add:
  case Instruction::Sub:
  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::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 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());
    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))