lib/Target/PowerPC/PPCAsmPrinter.cpp

//===-- PPCAsmPrinter.cpp - Print machine instrs to PowerPC assembly --------=//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains a printer that converts from our internal representation
// of machine-dependent LLVM code to PowerPC assembly language. This printer is
// the output mechanism used by `llc'.
//
// Documentation at http://developer.apple.com/documentation/DeveloperTools/
// Reference/Assembler/ASMIntroduction/chapter_1_section_1.html
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "asmprinter"
#include "PPC.h"
#include "PPCTargetMachine.h"
#include "PPCSubtarget.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Module.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/DwarfWriter.h"
#include "llvm/CodeGen/MachineDebugInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/Support/Mangler.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Target/TargetAsmInfo.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include <iostream>
#include <set>
using namespace llvm;

namespace {
  Statistic<> EmittedInsts("asm-printer", "Number of machine instrs printed");

  struct VISIBILITY_HIDDEN PPCAsmPrinter : public AsmPrinter {
    std::set<std::string> FnStubs, GVStubs;
    const PPCSubtarget &Subtarget;
    
    PPCAsmPrinter(std::ostream &O, TargetMachine &TM, const TargetAsmInfo *T)
      : AsmPrinter(O, TM, T), Subtarget(TM.getSubtarget<PPCSubtarget>()) {
    }

    virtual const char *getPassName() const {
      return "PowerPC Assembly Printer";
    }

    PPCTargetMachine &getTM() {
      return static_cast<PPCTargetMachine&>(TM);
    }

    unsigned enumRegToMachineReg(unsigned enumReg) {
      switch (enumReg) {
      default: assert(0 && "Unhandled register!"); break;
      case PPC::CR0:  return  0;
      case PPC::CR1:  return  1;
      case PPC::CR2:  return  2;
      case PPC::CR3:  return  3;
      case PPC::CR4:  return  4;
      case PPC::CR5:  return  5;
      case PPC::CR6:  return  6;
      case PPC::CR7:  return  7;
      }
      abort();
    }

    /// printInstruction - This method is automatically generated by tablegen
    /// from the instruction set description.  This method returns true if the
    /// machine instruction was sufficiently described to print it, otherwise it
    /// returns false.
    bool printInstruction(const MachineInstr *MI);

    void printMachineInstruction(const MachineInstr *MI);
    void printOp(const MachineOperand &MO);

    void printOperand(const MachineInstr *MI, unsigned OpNo) {
      const MachineOperand &MO = MI->getOperand(OpNo);
      if (MO.isRegister()) {
        assert(MRegisterInfo::isPhysicalRegister(MO.getReg())&&"Not physreg??");
        O << TM.getRegisterInfo()->get(MO.getReg()).Name;
      } else if (MO.isImmediate()) {
        O << MO.getImmedValue();
      } else {
        printOp(MO);
      }
    }
    
    bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                         unsigned AsmVariant, const char *ExtraCode);
    bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                               unsigned AsmVariant, const char *ExtraCode);
    
    
    void printS5ImmOperand(const MachineInstr *MI, unsigned OpNo) {
      char value = MI->getOperand(OpNo).getImmedValue();
      value = (value << (32-5)) >> (32-5);
      O << (int)value;
    }
    void printU5ImmOperand(const MachineInstr *MI, unsigned OpNo) {
      unsigned char value = MI->getOperand(OpNo).getImmedValue();
      assert(value <= 31 && "Invalid u5imm argument!");
      O << (unsigned int)value;
    }
    void printU6ImmOperand(const MachineInstr *MI, unsigned OpNo) {
      unsigned char value = MI->getOperand(OpNo).getImmedValue();
      assert(value <= 63 && "Invalid u6imm argument!");
      O << (unsigned int)value;
    }
    void printS16ImmOperand(const MachineInstr *MI, unsigned OpNo) {
      O << (short)MI->getOperand(OpNo).getImmedValue();
    }
    void printU16ImmOperand(const MachineInstr *MI, unsigned OpNo) {
      O << (unsigned short)MI->getOperand(OpNo).getImmedValue();
    }
    void printS16X4ImmOperand(const MachineInstr *MI, unsigned OpNo) {
      O << (short)(MI->getOperand(OpNo).getImmedValue()*4);
    }
    void printBranchOperand(const MachineInstr *MI, unsigned OpNo) {
      // Branches can take an immediate operand.  This is used by the branch
      // selection pass to print $+8, an eight byte displacement from the PC.
      if (MI->getOperand(OpNo).isImmediate()) {
        O << "$+" << MI->getOperand(OpNo).getImmedValue()*4;
      } else {
        printOp(MI->getOperand(OpNo));
      }
    }
    void printCallOperand(const MachineInstr *MI, unsigned OpNo) {
      const MachineOperand &MO = MI->getOperand(OpNo);
      if (TM.getRelocationModel() != Reloc::Static) {
        if (MO.getType() == MachineOperand::MO_GlobalAddress) {
          GlobalValue *GV = MO.getGlobal();
          if (((GV->isExternal() || GV->hasWeakLinkage() ||
                GV->hasLinkOnceLinkage()))) {
            // Dynamically-resolved functions need a stub for the function.
            std::string Name = Mang->getValueName(GV);
            FnStubs.insert(Name);
            O << "L" << Name << "$stub";
            return;
          }
        }
        if (MO.getType() == MachineOperand::MO_ExternalSymbol) {
          std::string Name(TAI->getGlobalPrefix()); Name += MO.getSymbolName();
          FnStubs.insert(Name);
          O << "L" << Name << "$stub";
          return;
        }
      }
      
      printOp(MI->getOperand(OpNo));
    }
    void printAbsAddrOperand(const MachineInstr *MI, unsigned OpNo) {
     O << (int)MI->getOperand(OpNo).getImmedValue()*4;
    }
    void printPICLabel(const MachineInstr *MI, unsigned OpNo) {
      O << "\"L" << getFunctionNumber() << "$pb\"\n";
      O << "\"L" << getFunctionNumber() << "$pb\":";
    }
    void printSymbolHi(const MachineInstr *MI, unsigned OpNo) {
      if (MI->getOperand(OpNo).isImmediate()) {
        printS16ImmOperand(MI, OpNo);
      } else {
        O << "ha16(";
        printOp(MI->getOperand(OpNo));
        if (TM.getRelocationModel() == Reloc::PIC_)
          O << "-\"L" << getFunctionNumber() << "$pb\")";
        else
          O << ')';
      }
    }
    void printSymbolLo(const MachineInstr *MI, unsigned OpNo) {
      if (MI->getOperand(OpNo).isImmediate()) {
        printS16ImmOperand(MI, OpNo);
      } else {
        O << "lo16(";
        printOp(MI->getOperand(OpNo));
        if (TM.getRelocationModel() == Reloc::PIC_)
          O << "-\"L" << getFunctionNumber() << "$pb\")";
        else
          O << ')';
      }
    }
    void printcrbitm(const MachineInstr *MI, unsigned OpNo) {
      unsigned CCReg = MI->getOperand(OpNo).getReg();
      unsigned RegNo = enumRegToMachineReg(CCReg);
      O << (0x80 >> RegNo);
    }
    // The new addressing mode printers.
    void printMemRegImm(const MachineInstr *MI, unsigned OpNo) {
      printSymbolLo(MI, OpNo);
      O << '(';
      if (MI->getOperand(OpNo+1).isRegister() && 
          MI->getOperand(OpNo+1).getReg() == PPC::R0)
        O << "0";
      else
        printOperand(MI, OpNo+1);
      O << ')';
    }
    void printMemRegImmShifted(const MachineInstr *MI, unsigned OpNo) {
      if (MI->getOperand(OpNo).isImmediate())
        printS16X4ImmOperand(MI, OpNo);
      else 
        printSymbolLo(MI, OpNo);
      O << '(';
      if (MI->getOperand(OpNo+1).isRegister() && 
          MI->getOperand(OpNo+1).getReg() == PPC::R0)
        O << "0";
      else
        printOperand(MI, OpNo+1);
      O << ')';
    }
    
    void printMemRegReg(const MachineInstr *MI, unsigned OpNo) {
      // When used as the base register, r0 reads constant zero rather than
      // the value contained in the register.  For this reason, the darwin
      // assembler requires that we print r0 as 0 (no r) when used as the base.
      const MachineOperand &MO = MI->getOperand(OpNo);
      if (MO.getReg() == PPC::R0)
        O << '0';
      else
        O << TM.getRegisterInfo()->get(MO.getReg()).Name;
      O << ", ";
      printOperand(MI, OpNo+1);
    }
    
    virtual bool runOnMachineFunction(MachineFunction &F) = 0;
    virtual bool doFinalization(Module &M) = 0;
  };

  /// DarwinAsmPrinter - PowerPC assembly printer, customized for Darwin/Mac OS
  /// X
  struct VISIBILITY_HIDDEN DarwinAsmPrinter : public PPCAsmPrinter {
  
    DwarfWriter DW;

    DarwinAsmPrinter(std::ostream &O, PPCTargetMachine &TM,
                     const TargetAsmInfo *T)
      : PPCAsmPrinter(O, TM, T), DW(O, this, T) {
      bool isPPC64 = Subtarget.isPPC64();
    }

    virtual const char *getPassName() const {
      return "Darwin PPC Assembly Printer";
    }
    
    bool runOnMachineFunction(MachineFunction &F);
    bool doInitialization(Module &M);
    bool doFinalization(Module &M);
    
    void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.setPreservesAll();
      AU.addRequired<MachineDebugInfo>();
      PPCAsmPrinter::getAnalysisUsage(AU);
    }

    /// getSectionForFunction - Return the section that we should emit the
    /// specified function body into.
    virtual std::string getSectionForFunction(const Function &F) const;
  };
} // end of anonymous namespace

// Include the auto-generated portion of the assembly writer
#include "PPCGenAsmWriter.inc"

void PPCAsmPrinter::printOp(const MachineOperand &MO) {
  switch (MO.getType()) {
  case MachineOperand::MO_Immediate:
    std::cerr << "printOp() does not handle immediate values\n";
    abort();
    return;

  case MachineOperand::MO_MachineBasicBlock:
    printBasicBlockLabel(MO.getMachineBasicBlock());
    return;
  case MachineOperand::MO_JumpTableIndex:
    O << TAI->getPrivateGlobalPrefix() << "JTI" << getFunctionNumber()
      << '_' << MO.getJumpTableIndex();
    // FIXME: PIC relocation model
    return;
  case MachineOperand::MO_ConstantPoolIndex:
    O << TAI->getPrivateGlobalPrefix() << "CPI" << getFunctionNumber()
      << '_' << MO.getConstantPoolIndex();
    return;
  case MachineOperand::MO_ExternalSymbol:
    // Computing the address of an external symbol, not calling it.
    if (TM.getRelocationModel() != Reloc::Static) {
      std::string Name(TAI->getGlobalPrefix()); Name += MO.getSymbolName();
      GVStubs.insert(Name);
      O << "L" << Name << "$non_lazy_ptr";
      return;
    }
    O << TAI->getGlobalPrefix() << MO.getSymbolName();
    return;
  case MachineOperand::MO_GlobalAddress: {
    // Computing the address of a global symbol, not calling it.
    GlobalValue *GV = MO.getGlobal();
    std::string Name = Mang->getValueName(GV);
    int offset = MO.getOffset();

    // External or weakly linked global variables need non-lazily-resolved stubs
    if (TM.getRelocationModel() != Reloc::Static) {
      if (((GV->isExternal() || GV->hasWeakLinkage() ||
            GV->hasLinkOnceLinkage()))) {
        GVStubs.insert(Name);
        O << "L" << Name << "$non_lazy_ptr";
        return;
      }
    }

    O << Name;
    return;
  }

  default:
    O << "<unknown operand type: " << MO.getType() << ">";
    return;
  }
}

/// PrintAsmOperand - Print out an operand for an inline asm expression.
///
bool PPCAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                    unsigned AsmVariant, 
                                    const char *ExtraCode) {
  // Does this asm operand have a single letter operand modifier?
  if (ExtraCode && ExtraCode[0]) {
    if (ExtraCode[1] != 0) return true; // Unknown modifier.
    
    switch (ExtraCode[0]) {
    default: return true;  // Unknown modifier.
    case 'L': // Write second word of DImode reference.  
      // Verify that this operand has two consecutive registers.
      if (!MI->getOperand(OpNo).isRegister() ||
          OpNo+1 == MI->getNumOperands() ||
          !MI->getOperand(OpNo+1).isRegister())
        return true;
      ++OpNo;   // Return the high-part.
      break;
    }
  }
  
  printOperand(MI, OpNo);
  return false;
}

bool PPCAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                                          unsigned AsmVariant, 
                                          const char *ExtraCode) {
  if (ExtraCode && ExtraCode[0])
    return true; // Unknown modifier.
  printMemRegReg(MI, OpNo);
  return false;
}

/// printMachineInstruction -- Print out a single PowerPC MI in Darwin syntax to
/// the current output stream.
///
void PPCAsmPrinter::printMachineInstruction(const MachineInstr *MI) {
  ++EmittedInsts;

  // Check for slwi/srwi mnemonics.
  if (MI->getOpcode() == PPC::RLWINM) {
    bool FoundMnemonic = false;
    unsigned char SH = MI->getOperand(2).getImmedValue();
    unsigned char MB = MI->getOperand(3).getImmedValue();
    unsigned char ME = MI->getOperand(4).getImmedValue();
    if (SH <= 31 && MB == 0 && ME == (31-SH)) {
      O << "slwi "; FoundMnemonic = true;
    }
    if (SH <= 31 && MB == (32-SH) && ME == 31) {
      O << "srwi "; FoundMnemonic = true;
      SH = 32-SH;
    }
    if (FoundMnemonic) {
      printOperand(MI, 0);
      O << ", ";
      printOperand(MI, 1);
      O << ", " << (unsigned int)SH << "\n";
      return;
    }
  } else if (MI->getOpcode() == PPC::OR || MI->getOpcode() == PPC::OR8) {
    if (MI->getOperand(1).getReg() == MI->getOperand(2).getReg()) {
      O << "mr ";
      printOperand(MI, 0);
      O << ", ";
      printOperand(MI, 1);
      O << "\n";
      return;
    }
  }

  if (printInstruction(MI))
    return; // Printer was automatically generated

  assert(0 && "Unhandled instruction in asm writer!");
  abort();
  return;
}



std::string DarwinAsmPrinter::getSectionForFunction(const Function &F) const {
  switch (F.getLinkage()) {
  default: assert(0 && "Unknown linkage type!");
  case Function::ExternalLinkage:
  case Function::InternalLinkage: return TAI->getTextSection();
  case Function::WeakLinkage:
  case Function::LinkOnceLinkage:
    return ".section __TEXT,__textcoal_nt,coalesced,pure_instructions";
  }
}

/// runOnMachineFunction - This uses the printMachineInstruction()
/// method to print assembly for each instruction.
///
bool DarwinAsmPrinter::runOnMachineFunction(MachineFunction &MF) {
  DW.SetDebugInfo(&getAnalysis<MachineDebugInfo>());

  SetupMachineFunction(MF);
  O << "\n\n";
  
  // Print out constants referenced by the function
  EmitConstantPool(MF.getConstantPool());

  // Print out labels for the function.
  const Function *F = MF.getFunction();
  SwitchToTextSection(getSectionForFunction(*F).c_str(), F);
  
  switch (F->getLinkage()) {
  default: assert(0 && "Unknown linkage type!");
  case Function::InternalLinkage:  // Symbols default to internal.
    break;
  case Function::ExternalLinkage:
    O << "\t.globl\t" << CurrentFnName << "\n";
    break;
  case Function::WeakLinkage:
  case Function::LinkOnceLinkage:
    O << "\t.globl\t" << CurrentFnName << "\n";
    O << "\t.weak_definition\t" << CurrentFnName << "\n";
    break;
  }
  EmitAlignment(4, F);
  O << CurrentFnName << ":\n";

  // Emit pre-function debug information.
  DW.BeginFunction(&MF);

  // Print out code for the function.
  for (MachineFunction::const_iterator I = MF.begin(), E = MF.end();
       I != E; ++I) {
    // Print a label for the basic block.
    if (I != MF.begin()) {
      printBasicBlockLabel(I, true);
      O << '\n';
    }
    for (MachineBasicBlock::const_iterator II = I->begin(), E = I->end();
         II != E; ++II) {
      // Print the assembly for the instruction.
      O << "\t";
      printMachineInstruction(II);
    }
  }

  // Print out jump tables referenced by the function.
  EmitJumpTableInfo(MF.getJumpTableInfo(), MF);
  
  // Emit post-function debug information.
  DW.EndFunction();
  
  // We didn't modify anything.
  return false;
}


bool DarwinAsmPrinter::doInitialization(Module &M) {
  if (Subtarget.isGigaProcessor())
    O << "\t.machine ppc970\n";
  AsmPrinter::doInitialization(M);
  
  // Darwin wants symbols to be quoted if they have complex names.
  Mang->setUseQuotes(true);
  
  // Emit initial debug information.
  DW.BeginModule(&M);
  return false;
}

bool DarwinAsmPrinter::doFinalization(Module &M) {
  const TargetData *TD = TM.getTargetData();

  // 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->hasInitializer()) continue;   // External global require no code
    
    // Check to see if this is a special global used by LLVM, if so, emit it.
    if (EmitSpecialLLVMGlobal(I))
      continue;
    
    std::string name = Mang->getValueName(I);
    Constant *C = I->getInitializer();
    unsigned Size = TD->getTypeSize(C->getType());
    unsigned Align = TD->getPreferredAlignmentLog(I);

    if (C->isNullValue() && /* FIXME: Verify correct */
        (I->hasInternalLinkage() || I->hasWeakLinkage() ||
         I->hasLinkOnceLinkage() ||
         (I->hasExternalLinkage() && !I->hasSection()))) {
      if (Size == 0) Size = 1;   // .comm Foo, 0 is undefined, avoid it.
      if (I->hasExternalLinkage()) {
        O << "\t.globl " << name << '\n';
        O << "\t.zerofill __DATA, __common, " << name << ", "
          << Size << ", " << Align;
      } else if (I->hasInternalLinkage()) {
        SwitchToDataSection("\t.data", I);
        O << TAI->getLCOMMDirective() << name << "," << Size << "," << Align;
      } else {
        SwitchToDataSection("\t.data", I);
        O << ".comm " << name << "," << Size;
      }
      O << "\t\t; '" << I->getName() << "'\n";
    } else {
      switch (I->getLinkage()) {
      case GlobalValue::LinkOnceLinkage:
      case GlobalValue::WeakLinkage:
        O << "\t.globl " << name << '\n'
          << "\t.weak_definition " << name << '\n';
        SwitchToDataSection(".section __DATA,__datacoal_nt,coalesced", I);
        break;
      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
        O << "\t.globl " << name << "\n";
        // FALL THROUGH
      case GlobalValue::InternalLinkage:
        SwitchToDataSection("\t.data", I);
        break;
      default:
        std::cerr << "Unknown linkage type!";
        abort();
      }

      EmitAlignment(Align, I);
      O << name << ":\t\t\t\t; '" << I->getName() << "'\n";
      EmitGlobalConstant(C);
      O << '\n';
    }
  }

  bool isPPC64 = TD->getPointerSizeInBits() == 64;

  // Output stubs for dynamically-linked functions
  if (TM.getRelocationModel() == Reloc::PIC_) {
    for (std::set<std::string>::iterator i = FnStubs.begin(), e = FnStubs.end();
         i != e; ++i) {
      SwitchToTextSection(".section __TEXT,__picsymbolstub1,symbol_stubs,"
                          "pure_instructions,32", 0);
      EmitAlignment(4);
      O << "L" << *i << "$stub:\n";
      O << "\t.indirect_symbol " << *i << "\n";
      O << "\tmflr r0\n";
      O << "\tbcl 20,31,L0$" << *i << "\n";
      O << "L0$" << *i << ":\n";
      O << "\tmflr r11\n";
      O << "\taddis r11,r11,ha16(L" << *i << "$lazy_ptr-L0$" << *i << ")\n";
      O << "\tmtlr r0\n";
      if (isPPC64)
        O << "\tldu r12,lo16(L" << *i << "$lazy_ptr-L0$" << *i << ")(r11)\n";
      else
        O << "\tlwzu r12,lo16(L" << *i << "$lazy_ptr-L0$" << *i << ")(r11)\n";
      O << "\tmtctr r12\n";
      O << "\tbctr\n";
      SwitchToDataSection(".lazy_symbol_pointer", 0);
      O << "L" << *i << "$lazy_ptr:\n";
      O << "\t.indirect_symbol " << *i << "\n";
      if (isPPC64)
        O << "\t.quad dyld_stub_binding_helper\n";
      else
        O << "\t.long dyld_stub_binding_helper\n";
    }
  } else {
    for (std::set<std::string>::iterator i = FnStubs.begin(), e = FnStubs.end();
         i != e; ++i) {
      SwitchToTextSection(".section __TEXT,__symbol_stub1,symbol_stubs,"
                          "pure_instructions,16", 0);
      EmitAlignment(4);
      O << "L" << *i << "$stub:\n";
      O << "\t.indirect_symbol " << *i << "\n";
      O << "\tlis r11,ha16(L" << *i << "$lazy_ptr)\n";
      if (isPPC64)
        O << "\tldu r12,lo16(L" << *i << "$lazy_ptr)(r11)\n";
      else
        O << "\tlwzu r12,lo16(L" << *i << "$lazy_ptr)(r11)\n";
      O << "\tmtctr r12\n";
      O << "\tbctr\n";
      SwitchToDataSection(".lazy_symbol_pointer", 0);
      O << "L" << *i << "$lazy_ptr:\n";
      O << "\t.indirect_symbol " << *i << "\n";
      if (isPPC64)
        O << "\t.quad dyld_stub_binding_helper\n";
      else
        O << "\t.long dyld_stub_binding_helper\n";
    }
  }

  O << "\n";

  // Output stubs for external and common global variables.
  if (GVStubs.begin() != GVStubs.end()) {
    SwitchToDataSection(".non_lazy_symbol_pointer", 0);
    for (std::set<std::string>::iterator I = GVStubs.begin(),
         E = GVStubs.end(); I != E; ++I) {
      O << "L" << *I << "$non_lazy_ptr:\n";
      O << "\t.indirect_symbol " << *I << "\n";
      if (isPPC64)
        O << "\t.quad\t0\n";
      else
        O << "\t.long\t0\n";
        
    }
  }

  // Emit initial debug information.
  DW.EndModule();

  // Funny Darwin hack: This flag tells the linker that no global symbols
  // contain code that falls through to other global symbols (e.g. the obvious
  // implementation of multiple entry points).  If this doesn't occur, the
  // linker can safely perform dead code stripping.  Since LLVM never generates
  // code that does this, it is always safe to set.
  O << "\t.subsections_via_symbols\n";

  AsmPrinter::doFinalization(M);
  return false; // success
}



/// createDarwinCodePrinterPass - Returns a pass that prints the PPC assembly
/// code for a MachineFunction to the given output stream, in a format that the
/// Darwin assembler can deal with.
///
FunctionPass *llvm::createPPCAsmPrinterPass(std::ostream &o,
                                            PPCTargetMachine &tm) {
  return new DarwinAsmPrinter(o, tm, tm.getTargetAsmInfo());
}