utils/TableGen/FastISelEmitter.cpp

//===- FastISelEmitter.cpp - Generate an instruction selector -------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This tablegen backend emits code for use by the "fast" instruction
// selection algorithm. See the comments at the top of
// lib/CodeGen/SelectionDAG/FastISel.cpp for background.
//
// This file scans through the target's tablegen instruction-info files
// and extracts instructions with obvious-looking patterns, and it emits
// code to look up these instructions by type and operator.
//
//===----------------------------------------------------------------------===//

#include "FastISelEmitter.h"
#include "Record.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/VectorExtras.h"
using namespace llvm;

namespace {

/// InstructionMemo - This class holds additional information about an
/// instruction needed to emit code for it.
///
struct InstructionMemo {
  std::string Name;
  const CodeGenRegisterClass *RC;
  std::string SubRegNo;
  std::vector<std::string>* PhysRegs;
};
  
/// ImmPredicateSet - This uniques predicates (represented as a string) and
/// gives them unique (small) integer ID's that start at 0.
class ImmPredicateSet {
  DenseMap<TreePattern *, unsigned> ImmIDs;
  std::vector<TreePredicateFn> PredsByName;
public:
  
  unsigned getIDFor(TreePredicateFn Pred) {
    unsigned &Entry = ImmIDs[Pred.getOrigPatFragRecord()];
    if (Entry == 0) {
      PredsByName.push_back(Pred);
      Entry = PredsByName.size();
    }
    return Entry-1;
  }
  
  const TreePredicateFn &getPredicate(unsigned i) {
    assert(i < PredsByName.size());
    return PredsByName[i];
  }
  
  typedef std::vector<TreePredicateFn>::const_iterator iterator;
  iterator begin() const { return PredsByName.begin(); }
  iterator end() const { return PredsByName.end(); }
  
};

/// OperandsSignature - This class holds a description of a list of operand
/// types. It has utility methods for emitting text based on the operands.
///
struct OperandsSignature {
  class OpKind {
    enum { OK_Reg, OK_FP, OK_Imm, OK_Invalid = -1 };
    char Repr;
  public:
    
    OpKind() : Repr(OK_Invalid) {}
    
    bool operator<(OpKind RHS) const { return Repr < RHS.Repr; }
    bool operator==(OpKind RHS) const { return Repr == RHS.Repr; }

    static OpKind getReg() { OpKind K; K.Repr = OK_Reg; return K; }
    static OpKind getFP()  { OpKind K; K.Repr = OK_FP; return K; }
    static OpKind getImm(unsigned V) {
      assert((unsigned)OK_Imm+V < 128 &&
             "Too many integer predicates for the 'Repr' char");
      OpKind K; K.Repr = OK_Imm+V; return K;
    }
    
    bool isReg() const { return Repr == OK_Reg; }
    bool isFP() const  { return Repr == OK_FP; }
    bool isImm() const { return Repr >= OK_Imm; }
    
    unsigned getImmCode() const { assert(isImm()); return Repr-OK_Imm; }
    
    void printManglingSuffix(raw_ostream &OS, ImmPredicateSet &ImmPredicates,
                             bool StripImmCodes) const {
      if (isReg())
        OS << 'r';
      else if (isFP())
        OS << 'f';
      else {
        OS << 'i';
        if (!StripImmCodes)
          if (unsigned Code = getImmCode())
            OS << "_" << ImmPredicates.getPredicate(Code-1).getFnName();
      }
    }
  };
  
  
  SmallVector<OpKind, 3> Operands;

  bool operator<(const OperandsSignature &O) const {
    return Operands < O.Operands;
  }
  bool operator==(const OperandsSignature &O) const {
    return Operands == O.Operands;
  }

  bool empty() const { return Operands.empty(); }

  bool hasAnyImmediateCodes() const {
    for (unsigned i = 0, e = Operands.size(); i != e; ++i)
      if (Operands[i].isImm() && Operands[i].getImmCode() != 0)
        return true;
    return false;
  }
  
  /// getWithoutImmCodes - Return a copy of this with any immediate codes forced
  /// to zero.
  OperandsSignature getWithoutImmCodes() const {
    OperandsSignature Result;
    for (unsigned i = 0, e = Operands.size(); i != e; ++i)
      if (!Operands[i].isImm())
        Result.Operands.push_back(Operands[i]);
      else
        Result.Operands.push_back(OpKind::getImm(0));
    return Result;
  }
  
  void emitImmediatePredicate(raw_ostream &OS, ImmPredicateSet &ImmPredicates) {
    bool EmittedAnything = false;
    for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
      if (!Operands[i].isImm()) continue;
      
      unsigned Code = Operands[i].getImmCode();
      if (Code == 0) continue;
      
      if (EmittedAnything)
        OS << " &&\n        ";
      
      TreePredicateFn PredFn = ImmPredicates.getPredicate(Code-1);
      
      // Emit the type check.
      OS << "VT == "
         << getEnumName(PredFn.getOrigPatFragRecord()->getTree(0)->getType(0))
         << " && ";
      
      
      OS << PredFn.getFnName() << "(imm" << i <<')';
      EmittedAnything = true;
    }
  }
  
  /// initialize - Examine the given pattern and initialize the contents
  /// of the Operands array accordingly. Return true if all the operands
  /// are supported, false otherwise.
  ///
  bool initialize(TreePatternNode *InstPatNode, const CodeGenTarget &Target,
                  MVT::SimpleValueType VT,
                  ImmPredicateSet &ImmediatePredicates) {
    if (InstPatNode->isLeaf())
      return false;
    
    if (InstPatNode->getOperator()->getName() == "imm") {
      Operands.push_back(OpKind::getImm(0));
      return true;
    }
    
    if (InstPatNode->getOperator()->getName() == "fpimm") {
      Operands.push_back(OpKind::getFP());
      return true;
    }

    const CodeGenRegisterClass *DstRC = 0;

    for (unsigned i = 0, e = InstPatNode->getNumChildren(); i != e; ++i) {
      TreePatternNode *Op = InstPatNode->getChild(i);

      // Handle imm operands specially.
      if (!Op->isLeaf() && Op->getOperator()->getName() == "imm") {
        unsigned PredNo = 0;
        if (!Op->getPredicateFns().empty()) {
          TreePredicateFn PredFn = Op->getPredicateFns()[0];
          // If there is more than one predicate weighing in on this operand
          // then we don't handle it.  This doesn't typically happen for
          // immediates anyway.
          if (Op->getPredicateFns().size() > 1 ||
              !PredFn.isImmediatePattern())
            return false;
          // Ignore any instruction with 'FastIselShouldIgnore', these are
          // not needed and just bloat the fast instruction selector.  For
          // example, X86 doesn't need to generate code to match ADD16ri8 since
          // ADD16ri will do just fine.
          Record *Rec = PredFn.getOrigPatFragRecord()->getRecord();
          if (Rec->getValueAsBit("FastIselShouldIgnore"))
            return false;
        
          PredNo = ImmediatePredicates.getIDFor(PredFn)+1;
        }
        
        // Handle unmatched immediate sizes here.
        //if (Op->getType(0) != VT)
        //  return false;
        
        Operands.push_back(OpKind::getImm(PredNo));
        continue;
      }

      
      // For now, filter out any operand with a predicate.
      // For now, filter out any operand with multiple values.
      if (!Op->getPredicateFns().empty() || Op->getNumTypes() != 1)
        return false;

      if (!Op->isLeaf()) {
         if (Op->getOperator()->getName() == "fpimm") {
          Operands.push_back(OpKind::getFP());
          continue;
        }
        // For now, ignore other non-leaf nodes.
        return false;
      }
      
      assert(Op->hasTypeSet(0) && "Type infererence not done?");

      // For now, all the operands must have the same type (if they aren't
      // immediates).  Note that this causes us to reject variable sized shifts
      // on X86.
      if (Op->getType(0) != VT)
        return false;

      DefInit *OpDI = dynamic_cast<DefInit*>(Op->getLeafValue());
      if (!OpDI)
        return false;
      Record *OpLeafRec = OpDI->getDef();
      
      // For now, the only other thing we accept is register operands.
      const CodeGenRegisterClass *RC = 0;
      if (OpLeafRec->isSubClassOf("RegisterClass"))
        RC = &Target.getRegisterClass(OpLeafRec);
      else if (OpLeafRec->isSubClassOf("Register"))
        RC = Target.getRegisterClassForRegister(OpLeafRec);
      else
        return false;

      // For now, this needs to be a register class of some sort.
      if (!RC)
        return false;

      // For now, all the operands must have the same register class or be
      // a strict subclass of the destination.
      if (DstRC) {
        if (DstRC != RC && !DstRC->hasSubClass(RC))
          return false;
      } else
        DstRC = RC;
      Operands.push_back(OpKind::getReg());
    }
    return true;
  }

  void PrintParameters(raw_ostream &OS) const {
    for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
      if (Operands[i].isReg()) {
        OS << "unsigned Op" << i << ", bool Op" << i << "IsKill";
      } else if (Operands[i].isImm()) {
        OS << "uint64_t imm" << i;
      } else if (Operands[i].isFP()) {
        OS << "ConstantFP *f" << i;
      } else {
        assert("Unknown operand kind!");
        abort();
      }
      if (i + 1 != e)
        OS << ", ";
    }
  }

  void PrintArguments(raw_ostream &OS,
                      const std::vector<std::string> &PR) const {
    assert(PR.size() == Operands.size());
    bool PrintedArg = false;
    for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
      if (PR[i] != "")
        // Implicit physical register operand.
        continue;

      if (PrintedArg)
        OS << ", ";
      if (Operands[i].isReg()) {
        OS << "Op" << i << ", Op" << i << "IsKill";
        PrintedArg = true;
      } else if (Operands[i].isImm()) {
        OS << "imm" << i;
        PrintedArg = true;
      } else if (Operands[i].isFP()) {
        OS << "f" << i;
        PrintedArg = true;
      } else {
        assert("Unknown operand kind!");
        abort();
      }
    }
  }

  void PrintArguments(raw_ostream &OS) const {
    for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
      if (Operands[i].isReg()) {
        OS << "Op" << i << ", Op" << i << "IsKill";
      } else if (Operands[i].isImm()) {
        OS << "imm" << i;
      } else if (Operands[i].isFP()) {
        OS << "f" << i;
      } else {
        assert("Unknown operand kind!");
        abort();
      }
      if (i + 1 != e)
        OS << ", ";
    }
  }


  void PrintManglingSuffix(raw_ostream &OS, const std::vector<std::string> &PR,
                           ImmPredicateSet &ImmPredicates,
                           bool StripImmCodes = false) const {
    for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
      if (PR[i] != "")
        // Implicit physical register operand. e.g. Instruction::Mul expect to
        // select to a binary op. On x86, mul may take a single operand with
        // the other operand being implicit. We must emit something that looks
        // like a binary instruction except for the very inner FastEmitInst_*
        // call.
        continue;
      Operands[i].printManglingSuffix(OS, ImmPredicates, StripImmCodes);
    }
  }

  void PrintManglingSuffix(raw_ostream &OS, ImmPredicateSet &ImmPredicates,
                           bool StripImmCodes = false) const {
    for (unsigned i = 0, e = Operands.size(); i != e; ++i)
      Operands[i].printManglingSuffix(OS, ImmPredicates, StripImmCodes);
  }
};

class FastISelMap {
  typedef std::map<std::string, InstructionMemo> PredMap;
  typedef std::map<MVT::SimpleValueType, PredMap> RetPredMap;
  typedef std::map<MVT::SimpleValueType, RetPredMap> TypeRetPredMap;
  typedef std::map<std::string, TypeRetPredMap> OpcodeTypeRetPredMap;
  typedef std::map<OperandsSignature, OpcodeTypeRetPredMap>
            OperandsOpcodeTypeRetPredMap;

  OperandsOpcodeTypeRetPredMap SimplePatterns;

  std::map<OperandsSignature, std::vector<OperandsSignature> >
    SignaturesWithConstantForms;
  
  std::string InstNS;
  ImmPredicateSet ImmediatePredicates;
public:
  explicit FastISelMap(std::string InstNS);

  void collectPatterns(CodeGenDAGPatterns &CGP);
  void printImmediatePredicates(raw_ostream &OS);
  void printFunctionDefinitions(raw_ostream &OS);
};

}

static std::string getOpcodeName(Record *Op, CodeGenDAGPatterns &CGP) {
  return CGP.getSDNodeInfo(Op).getEnumName();
}

static std::string getLegalCName(std::string OpName) {
  std::string::size_type pos = OpName.find("::");
  if (pos != std::string::npos)
    OpName.replace(pos, 2, "_");
  return OpName;
}

FastISelMap::FastISelMap(std::string instns)
  : InstNS(instns) {
}

void FastISelMap::collectPatterns(CodeGenDAGPatterns &CGP) {
  const CodeGenTarget &Target = CGP.getTargetInfo();

  // Determine the target's namespace name.
  InstNS = Target.getInstNamespace() + "::";
  assert(InstNS.size() > 2 && "Can't determine target-specific namespace!");

  // Scan through all the patterns and record the simple ones.
  for (CodeGenDAGPatterns::ptm_iterator I = CGP.ptm_begin(),
       E = CGP.ptm_end(); I != E; ++I) {
    const PatternToMatch &Pattern = *I;

    // For now, just look at Instructions, so that we don't have to worry
    // about emitting multiple instructions for a pattern.
    TreePatternNode *Dst = Pattern.getDstPattern();
    if (Dst->isLeaf()) continue;
    Record *Op = Dst->getOperator();
    if (!Op->isSubClassOf("Instruction"))
      continue;
    CodeGenInstruction &II = CGP.getTargetInfo().getInstruction(Op);
    if (II.Operands.empty())
      continue;

    // For now, ignore multi-instruction patterns.
    bool MultiInsts = false;
    for (unsigned i = 0, e = Dst->getNumChildren(); i != e; ++i) {
      TreePatternNode *ChildOp = Dst->getChild(i);
      if (ChildOp->isLeaf())
        continue;
      if (ChildOp->getOperator()->isSubClassOf("Instruction")) {
        MultiInsts = true;
        break;
      }
    }
    if (MultiInsts)
      continue;

    // For now, ignore instructions where the first operand is not an
    // output register.
    const CodeGenRegisterClass *DstRC = 0;
    std::string SubRegNo;
    if (Op->getName() != "EXTRACT_SUBREG") {
      Record *Op0Rec = II.Operands[0].Rec;
      if (!Op0Rec->isSubClassOf("RegisterClass"))
        continue;
      DstRC = &Target.getRegisterClass(Op0Rec);
      if (!DstRC)
        continue;
    } else {
      // If this isn't a leaf, then continue since the register classes are
      // a bit too complicated for now.
      if (!Dst->getChild(1)->isLeaf()) continue;

      DefInit *SR = dynamic_cast<DefInit*>(Dst->getChild(1)->getLeafValue());
      if (SR)
        SubRegNo = getQualifiedName(SR->getDef());
      else
        SubRegNo = Dst->getChild(1)->getLeafValue()->getAsString();
    }

    // Inspect the pattern.
    TreePatternNode *InstPatNode = Pattern.getSrcPattern();
    if (!InstPatNode) continue;
    if (InstPatNode->isLeaf()) continue;

    // Ignore multiple result nodes for now.
    if (InstPatNode->getNumTypes() > 1) continue;

    Record *InstPatOp = InstPatNode->getOperator();
    std::string OpcodeName = getOpcodeName(InstPatOp, CGP);
    MVT::SimpleValueType RetVT = MVT::isVoid;
    if (InstPatNode->getNumTypes()) RetVT = InstPatNode->getType(0);
    MVT::SimpleValueType VT = RetVT;
    if (InstPatNode->getNumChildren()) {
      assert(InstPatNode->getChild(0)->getNumTypes() == 1);
      VT = InstPatNode->getChild(0)->getType(0);
    }
    
    // For now, filter out instructions which just set a register to
    // an Operand or an immediate, like MOV32ri.
    if (InstPatOp->isSubClassOf("Operand"))
      continue;

    // For now, filter out any instructions with predicates.
    if (!InstPatNode->getPredicateFns().empty())
      continue;

    // Check all the operands.
    OperandsSignature Operands;
    if (!Operands.initialize(InstPatNode, Target, VT, ImmediatePredicates))
      continue;

    std::vector<std::string>* PhysRegInputs = new std::vector<std::string>();
    if (!InstPatNode->isLeaf() &&
        (InstPatNode->getOperator()->getName() == "imm" ||
         InstPatNode->getOperator()->getName() == "fpimmm"))
      PhysRegInputs->push_back("");
    else if (!InstPatNode->isLeaf()) {
      for (unsigned i = 0, e = InstPatNode->getNumChildren(); i != e; ++i) {
        TreePatternNode *Op = InstPatNode->getChild(i);
        if (!Op->isLeaf()) {
          PhysRegInputs->push_back("");
          continue;
        }

        DefInit *OpDI = dynamic_cast<DefInit*>(Op->getLeafValue());
        Record *OpLeafRec = OpDI->getDef();
        std::string PhysReg;
        if (OpLeafRec->isSubClassOf("Register")) {
          PhysReg += static_cast<StringInit*>(OpLeafRec->getValue( \
                     "Namespace")->getValue())->getValue();
          PhysReg += "::";

          std::vector<CodeGenRegister> Regs = Target.getRegisters();
          for (unsigned i = 0; i < Regs.size(); ++i) {
            if (Regs[i].TheDef == OpLeafRec) {
              PhysReg += Regs[i].getName();
              break;
            }
          }
        }

        PhysRegInputs->push_back(PhysReg);
      }
    } else
      PhysRegInputs->push_back("");

    // Get the predicate that guards this pattern.
    std::string PredicateCheck = Pattern.getPredicateCheck();

    // Ok, we found a pattern that we can handle. Remember it.
    InstructionMemo Memo = {
      Pattern.getDstPattern()->getOperator()->getName(),
      DstRC,
      SubRegNo,
      PhysRegInputs
    };
    
    if (SimplePatterns[Operands][OpcodeName][VT][RetVT].count(PredicateCheck))
      throw TGError(Pattern.getSrcRecord()->getLoc(),
                    "Duplicate record in FastISel table!");

    SimplePatterns[Operands][OpcodeName][VT][RetVT][PredicateCheck] = Memo;
    
    // If any of the operands were immediates with predicates on them, strip
    // them down to a signature that doesn't have predicates so that we can
    // associate them with the stripped predicate version.
    if (Operands.hasAnyImmediateCodes()) {
      SignaturesWithConstantForms[Operands.getWithoutImmCodes()]
        .push_back(Operands);
    }
  }
}

void FastISelMap::printImmediatePredicates(raw_ostream &OS) {
  if (ImmediatePredicates.begin() == ImmediatePredicates.end())
    return;
  
  OS << "\n// FastEmit Immediate Predicate functions.\n";
  for (ImmPredicateSet::iterator I = ImmediatePredicates.begin(),
       E = ImmediatePredicates.end(); I != E; ++I) {
    OS << "static bool " << I->getFnName() << "(int64_t Imm) {\n";
    OS << I->getImmediatePredicateCode() << "\n}\n";
  }
  
  OS << "\n\n";
}


void FastISelMap::printFunctionDefinitions(raw_ostream &OS) {
  // Now emit code for all the patterns that we collected.
  for (OperandsOpcodeTypeRetPredMap::const_iterator OI = SimplePatterns.begin(),
       OE = SimplePatterns.end(); OI != OE; ++OI) {
    const OperandsSignature &Operands = OI->first;
    const OpcodeTypeRetPredMap &OTM = OI->second;

    for (OpcodeTypeRetPredMap::const_iterator I = OTM.begin(), E = OTM.end();
         I != E; ++I) {
      const std::string &Opcode = I->first;
      const TypeRetPredMap &TM = I->second;

      OS << "// FastEmit functions for " << Opcode << ".\n";
      OS << "\n";

      // Emit one function for each opcode,type pair.
      for (TypeRetPredMap::const_iterator TI = TM.begin(), TE = TM.end();
           TI != TE; ++TI) {
        MVT::SimpleValueType VT = TI->first;
        const RetPredMap &RM = TI->second;
        if (RM.size() != 1) {
          for (RetPredMap::const_iterator RI = RM.begin(), RE = RM.end();
               RI != RE; ++RI) {
            MVT::SimpleValueType RetVT = RI->first;
            const PredMap &PM = RI->second;
            bool HasPred = false;

            OS << "unsigned FastEmit_"
               << getLegalCName(Opcode)
               << "_" << getLegalCName(getName(VT))
               << "_" << getLegalCName(getName(RetVT)) << "_";
            Operands.PrintManglingSuffix(OS, ImmediatePredicates);
            OS << "(";
            Operands.PrintParameters(OS);
            OS << ") {\n";

            // Emit code for each possible instruction. There may be
            // multiple if there are subtarget concerns.
            for (PredMap::const_iterator PI = PM.begin(), PE = PM.end();
                 PI != PE; ++PI) {
              std::string PredicateCheck = PI->first;
              const InstructionMemo &Memo = PI->second;

              if (PredicateCheck.empty()) {
                assert(!HasPred &&
                       "Multiple instructions match, at least one has "
                       "a predicate and at least one doesn't!");
              } else {
                OS << "  if (" + PredicateCheck + ") {\n";
                OS << "  ";
                HasPred = true;
              }

              for (unsigned i = 0; i < Memo.PhysRegs->size(); ++i) {
                if ((*Memo.PhysRegs)[i] != "")
                  OS << "  BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, "
                     << "TII.get(TargetOpcode::COPY), "
                     << (*Memo.PhysRegs)[i] << ").addReg(Op" << i << ");\n";
              }

              OS << "  return FastEmitInst_";
              if (Memo.SubRegNo.empty()) {
                Operands.PrintManglingSuffix(OS, *Memo.PhysRegs,
                                             ImmediatePredicates, true);
                OS << "(" << InstNS << Memo.Name << ", ";
                OS << InstNS << Memo.RC->getName() << "RegisterClass";
                if (!Operands.empty())
                  OS << ", ";
                Operands.PrintArguments(OS, *Memo.PhysRegs);
                OS << ");\n";
              } else {
                OS << "extractsubreg(" << getName(RetVT);
                OS << ", Op0, Op0IsKill, " << Memo.SubRegNo << ");\n";
              }

              if (HasPred)
                OS << "  }\n";

            }
            // Return 0 if none of the predicates were satisfied.
            if (HasPred)
              OS << "  return 0;\n";
            OS << "}\n";
            OS << "\n";
          }

          // Emit one function for the type that demultiplexes on return type.
          OS << "unsigned FastEmit_"
             << getLegalCName(Opcode) << "_"
             << getLegalCName(getName(VT)) << "_";
          Operands.PrintManglingSuffix(OS, ImmediatePredicates);
          OS << "(MVT RetVT";
          if (!Operands.empty())
            OS << ", ";
          Operands.PrintParameters(OS);
          OS << ") {\nswitch (RetVT.SimpleTy) {\n";
          for (RetPredMap::const_iterator RI = RM.begin(), RE = RM.end();
               RI != RE; ++RI) {
            MVT::SimpleValueType RetVT = RI->first;
            OS << "  case " << getName(RetVT) << ": return FastEmit_"
               << getLegalCName(Opcode) << "_" << getLegalCName(getName(VT))
               << "_" << getLegalCName(getName(RetVT)) << "_";
            Operands.PrintManglingSuffix(OS, ImmediatePredicates);
            OS << "(";
            Operands.PrintArguments(OS);
            OS << ");\n";
          }
          OS << "  default: return 0;\n}\n}\n\n";

        } else {
          // Non-variadic return type.
          OS << "unsigned FastEmit_"
             << getLegalCName(Opcode) << "_"
             << getLegalCName(getName(VT)) << "_";
          Operands.PrintManglingSuffix(OS, ImmediatePredicates);
          OS << "(MVT RetVT";
          if (!Operands.empty())
            OS << ", ";
          Operands.PrintParameters(OS);
          OS << ") {\n";

          OS << "  if (RetVT.SimpleTy != " << getName(RM.begin()->first)
             << ")\n    return 0;\n";

          const PredMap &PM = RM.begin()->second;
          bool HasPred = false;

          // Emit code for each possible instruction. There may be
          // multiple if there are subtarget concerns.
          for (PredMap::const_iterator PI = PM.begin(), PE = PM.end(); PI != PE;
               ++PI) {
            std::string PredicateCheck = PI->first;
            const InstructionMemo &Memo = PI->second;

            if (PredicateCheck.empty()) {
              assert(!HasPred &&
                     "Multiple instructions match, at least one has "
                     "a predicate and at least one doesn't!");
            } else {
              OS << "  if (" + PredicateCheck + ") {\n";
              OS << "  ";
              HasPred = true;
            }

            for (unsigned i = 0; i < Memo.PhysRegs->size(); ++i) {
              if ((*Memo.PhysRegs)[i] != "")
                OS << "  BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, "
                   << "TII.get(TargetOpcode::COPY), "
                   << (*Memo.PhysRegs)[i] << ").addReg(Op" << i << ");\n";
            }

            OS << "  return FastEmitInst_";

            if (Memo.SubRegNo.empty()) {
              Operands.PrintManglingSuffix(OS, *Memo.PhysRegs,
                                           ImmediatePredicates, true);
              OS << "(" << InstNS << Memo.Name << ", ";
              OS << InstNS << Memo.RC->getName() << "RegisterClass";
              if (!Operands.empty())
                OS << ", ";
              Operands.PrintArguments(OS, *Memo.PhysRegs);
              OS << ");\n";
            } else {
              OS << "extractsubreg(RetVT, Op0, Op0IsKill, ";
              OS << Memo.SubRegNo;
              OS << ");\n";
            }

             if (HasPred)
               OS << "  }\n";
          }

          // Return 0 if none of the predicates were satisfied.
          if (HasPred)
            OS << "  return 0;\n";
          OS << "}\n";
          OS << "\n";
        }
      }

      // Emit one function for the opcode that demultiplexes based on the type.
      OS << "unsigned FastEmit_"
         << getLegalCName(Opcode) << "_";
      Operands.PrintManglingSuffix(OS, ImmediatePredicates);
      OS << "(MVT VT, MVT RetVT";
      if (!Operands.empty())
        OS << ", ";
      Operands.PrintParameters(OS);
      OS << ") {\n";
      OS << "  switch (VT.SimpleTy) {\n";
      for (TypeRetPredMap::const_iterator TI = TM.begin(), TE = TM.end();
           TI != TE; ++TI) {
        MVT::SimpleValueType VT = TI->first;
        std::string TypeName = getName(VT);
        OS << "  case " << TypeName << ": return FastEmit_"
           << getLegalCName(Opcode) << "_" << getLegalCName(TypeName) << "_";
        Operands.PrintManglingSuffix(OS, ImmediatePredicates);
        OS << "(RetVT";
        if (!Operands.empty())
          OS << ", ";
        Operands.PrintArguments(OS);
        OS << ");\n";
      }
      OS << "  default: return 0;\n";
      OS << "  }\n";
      OS << "}\n";
      OS << "\n";
    }

    OS << "// Top-level FastEmit function.\n";
    OS << "\n";

    // Emit one function for the operand signature that demultiplexes based
    // on opcode and type.
    OS << "unsigned FastEmit_";
    Operands.PrintManglingSuffix(OS, ImmediatePredicates);
    OS << "(MVT VT, MVT RetVT, unsigned Opcode";
    if (!Operands.empty())
      OS << ", ";
    Operands.PrintParameters(OS);
    OS << ") {\n";
    
    // If there are any forms of this signature available that operand on
    // constrained forms of the immediate (e.g. 32-bit sext immediate in a
    // 64-bit operand), check them first.
    
    std::map<OperandsSignature, std::vector<OperandsSignature> >::iterator MI
      = SignaturesWithConstantForms.find(Operands);
    if (MI != SignaturesWithConstantForms.end()) {
      // Unique any duplicates out of the list.
      std::sort(MI->second.begin(), MI->second.end());
      MI->second.erase(std::unique(MI->second.begin(), MI->second.end()),
                       MI->second.end());
      
      // Check each in order it was seen.  It would be nice to have a good
      // relative ordering between them, but we're not going for optimality
      // here.
      for (unsigned i = 0, e = MI->second.size(); i != e; ++i) {
        OS << "  if (";
        MI->second[i].emitImmediatePredicate(OS, ImmediatePredicates);
        OS << ")\n    if (unsigned Reg = FastEmit_";
        MI->second[i].PrintManglingSuffix(OS, ImmediatePredicates);
        OS << "(VT, RetVT, Opcode";
        if (!MI->second[i].empty())
          OS << ", ";
        MI->second[i].PrintArguments(OS);
        OS << "))\n      return Reg;\n\n";
      }
      
      // Done with this, remove it.
      SignaturesWithConstantForms.erase(MI);
    }
    
    OS << "  switch (Opcode) {\n";
    for (OpcodeTypeRetPredMap::const_iterator I = OTM.begin(), E = OTM.end();
         I != E; ++I) {
      const std::string &Opcode = I->first;

      OS << "  case " << Opcode << ": return FastEmit_"
         << getLegalCName(Opcode) << "_";
      Operands.PrintManglingSuffix(OS, ImmediatePredicates);
      OS << "(VT, RetVT";
      if (!Operands.empty())
        OS << ", ";
      Operands.PrintArguments(OS);
      OS << ");\n";
    }
    OS << "  default: return 0;\n";
    OS << "  }\n";
    OS << "}\n";
    OS << "\n";
  }
  
  // TODO: SignaturesWithConstantForms should be empty here.
}

void FastISelEmitter::run(raw_ostream &OS) {
  const CodeGenTarget &Target = CGP.getTargetInfo();

  // Determine the target's namespace name.
  std::string InstNS = Target.getInstNamespace() + "::";
  assert(InstNS.size() > 2 && "Can't determine target-specific namespace!");

  EmitSourceFileHeader("\"Fast\" Instruction Selector for the " +
                       Target.getName() + " target", OS);

  FastISelMap F(InstNS);
  F.collectPatterns(CGP);
  F.printImmediatePredicates(OS);
  F.printFunctionDefinitions(OS);
}

FastISelEmitter::FastISelEmitter(RecordKeeper &R)
  : Records(R), CGP(R) {
}