llvm-6502/lib/CodeGen/SelectionDAG/TargetLowering.cpp

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

#include "llvm/Target/TargetLowering.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtarget.h"
#include "llvm/GlobalVariable.h"
#include "llvm/DerivedTypes.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/SelectionDAG.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
using namespace llvm;

namespace llvm {
TLSModel::Model getTLSModel(const GlobalValue *GV, Reloc::Model reloc) {
  bool isLocal = GV->hasLocalLinkage();
  bool isDeclaration = GV->isDeclaration();
  // FIXME: what should we do for protected and internal visibility?
  // For variables, is internal different from hidden?
  bool isHidden = GV->hasHiddenVisibility();

  if (reloc == Reloc::PIC_) {
    if (isLocal || isHidden)
      return TLSModel::LocalDynamic;
    else
      return TLSModel::GeneralDynamic;
  } else {
    if (!isDeclaration || isHidden)
      return TLSModel::LocalExec;
    else
      return TLSModel::InitialExec;
  }
}
}

/// InitLibcallNames - Set default libcall names.
///
static void InitLibcallNames(const char **Names) {
  Names[RTLIB::SHL_I16] = "__ashlhi3";
  Names[RTLIB::SHL_I32] = "__ashlsi3";
  Names[RTLIB::SHL_I64] = "__ashldi3";
  Names[RTLIB::SHL_I128] = "__ashlti3";
  Names[RTLIB::SRL_I16] = "__lshrhi3";
  Names[RTLIB::SRL_I32] = "__lshrsi3";
  Names[RTLIB::SRL_I64] = "__lshrdi3";
  Names[RTLIB::SRL_I128] = "__lshrti3";
  Names[RTLIB::SRA_I16] = "__ashrhi3";
  Names[RTLIB::SRA_I32] = "__ashrsi3";
  Names[RTLIB::SRA_I64] = "__ashrdi3";
  Names[RTLIB::SRA_I128] = "__ashrti3";
  Names[RTLIB::MUL_I16] = "__mulhi3";
  Names[RTLIB::MUL_I32] = "__mulsi3";
  Names[RTLIB::MUL_I64] = "__muldi3";
  Names[RTLIB::MUL_I128] = "__multi3";
  Names[RTLIB::SDIV_I16] = "__divhi3";
  Names[RTLIB::SDIV_I32] = "__divsi3";
  Names[RTLIB::SDIV_I64] = "__divdi3";
  Names[RTLIB::SDIV_I128] = "__divti3";
  Names[RTLIB::UDIV_I16] = "__udivhi3";
  Names[RTLIB::UDIV_I32] = "__udivsi3";
  Names[RTLIB::UDIV_I64] = "__udivdi3";
  Names[RTLIB::UDIV_I128] = "__udivti3";
  Names[RTLIB::SREM_I16] = "__modhi3";
  Names[RTLIB::SREM_I32] = "__modsi3";
  Names[RTLIB::SREM_I64] = "__moddi3";
  Names[RTLIB::SREM_I128] = "__modti3";
  Names[RTLIB::UREM_I16] = "__umodhi3";
  Names[RTLIB::UREM_I32] = "__umodsi3";
  Names[RTLIB::UREM_I64] = "__umoddi3";
  Names[RTLIB::UREM_I128] = "__umodti3";
  Names[RTLIB::NEG_I32] = "__negsi2";
  Names[RTLIB::NEG_I64] = "__negdi2";
  Names[RTLIB::ADD_F32] = "__addsf3";
  Names[RTLIB::ADD_F64] = "__adddf3";
  Names[RTLIB::ADD_F80] = "__addxf3";
  Names[RTLIB::ADD_PPCF128] = "__gcc_qadd";
  Names[RTLIB::SUB_F32] = "__subsf3";
  Names[RTLIB::SUB_F64] = "__subdf3";
  Names[RTLIB::SUB_F80] = "__subxf3";
  Names[RTLIB::SUB_PPCF128] = "__gcc_qsub";
  Names[RTLIB::MUL_F32] = "__mulsf3";
  Names[RTLIB::MUL_F64] = "__muldf3";
  Names[RTLIB::MUL_F80] = "__mulxf3";
  Names[RTLIB::MUL_PPCF128] = "__gcc_qmul";
  Names[RTLIB::DIV_F32] = "__divsf3";
  Names[RTLIB::DIV_F64] = "__divdf3";
  Names[RTLIB::DIV_F80] = "__divxf3";
  Names[RTLIB::DIV_PPCF128] = "__gcc_qdiv";
  Names[RTLIB::REM_F32] = "fmodf";
  Names[RTLIB::REM_F64] = "fmod";
  Names[RTLIB::REM_F80] = "fmodl";
  Names[RTLIB::REM_PPCF128] = "fmodl";
  Names[RTLIB::POWI_F32] = "__powisf2";
  Names[RTLIB::POWI_F64] = "__powidf2";
  Names[RTLIB::POWI_F80] = "__powixf2";
  Names[RTLIB::POWI_PPCF128] = "__powitf2";
  Names[RTLIB::SQRT_F32] = "sqrtf";
  Names[RTLIB::SQRT_F64] = "sqrt";
  Names[RTLIB::SQRT_F80] = "sqrtl";
  Names[RTLIB::SQRT_PPCF128] = "sqrtl";
  Names[RTLIB::LOG_F32] = "logf";
  Names[RTLIB::LOG_F64] = "log";
  Names[RTLIB::LOG_F80] = "logl";
  Names[RTLIB::LOG_PPCF128] = "logl";
  Names[RTLIB::LOG2_F32] = "log2f";
  Names[RTLIB::LOG2_F64] = "log2";
  Names[RTLIB::LOG2_F80] = "log2l";
  Names[RTLIB::LOG2_PPCF128] = "log2l";
  Names[RTLIB::LOG10_F32] = "log10f";
  Names[RTLIB::LOG10_F64] = "log10";
  Names[RTLIB::LOG10_F80] = "log10l";
  Names[RTLIB::LOG10_PPCF128] = "log10l";
  Names[RTLIB::EXP_F32] = "expf";
  Names[RTLIB::EXP_F64] = "exp";
  Names[RTLIB::EXP_F80] = "expl";
  Names[RTLIB::EXP_PPCF128] = "expl";
  Names[RTLIB::EXP2_F32] = "exp2f";
  Names[RTLIB::EXP2_F64] = "exp2";
  Names[RTLIB::EXP2_F80] = "exp2l";
  Names[RTLIB::EXP2_PPCF128] = "exp2l";
  Names[RTLIB::SIN_F32] = "sinf";
  Names[RTLIB::SIN_F64] = "sin";
  Names[RTLIB::SIN_F80] = "sinl";
  Names[RTLIB::SIN_PPCF128] = "sinl";
  Names[RTLIB::COS_F32] = "cosf";
  Names[RTLIB::COS_F64] = "cos";
  Names[RTLIB::COS_F80] = "cosl";
  Names[RTLIB::COS_PPCF128] = "cosl";
  Names[RTLIB::POW_F32] = "powf";
  Names[RTLIB::POW_F64] = "pow";
  Names[RTLIB::POW_F80] = "powl";
  Names[RTLIB::POW_PPCF128] = "powl";
  Names[RTLIB::CEIL_F32] = "ceilf";
  Names[RTLIB::CEIL_F64] = "ceil";
  Names[RTLIB::CEIL_F80] = "ceill";
  Names[RTLIB::CEIL_PPCF128] = "ceill";
  Names[RTLIB::TRUNC_F32] = "truncf";
  Names[RTLIB::TRUNC_F64] = "trunc";
  Names[RTLIB::TRUNC_F80] = "truncl";
  Names[RTLIB::TRUNC_PPCF128] = "truncl";
  Names[RTLIB::RINT_F32] = "rintf";
  Names[RTLIB::RINT_F64] = "rint";
  Names[RTLIB::RINT_F80] = "rintl";
  Names[RTLIB::RINT_PPCF128] = "rintl";
  Names[RTLIB::NEARBYINT_F32] = "nearbyintf";
  Names[RTLIB::NEARBYINT_F64] = "nearbyint";
  Names[RTLIB::NEARBYINT_F80] = "nearbyintl";
  Names[RTLIB::NEARBYINT_PPCF128] = "nearbyintl";
  Names[RTLIB::FLOOR_F32] = "floorf";
  Names[RTLIB::FLOOR_F64] = "floor";
  Names[RTLIB::FLOOR_F80] = "floorl";
  Names[RTLIB::FLOOR_PPCF128] = "floorl";
  Names[RTLIB::FPEXT_F32_F64] = "__extendsfdf2";
  Names[RTLIB::FPROUND_F64_F32] = "__truncdfsf2";
  Names[RTLIB::FPROUND_F80_F32] = "__truncxfsf2";
  Names[RTLIB::FPROUND_PPCF128_F32] = "__trunctfsf2";
  Names[RTLIB::FPROUND_F80_F64] = "__truncxfdf2";
  Names[RTLIB::FPROUND_PPCF128_F64] = "__trunctfdf2";
  Names[RTLIB::FPTOSINT_F32_I8] = "__fixsfi8";
  Names[RTLIB::FPTOSINT_F32_I16] = "__fixsfi16";
  Names[RTLIB::FPTOSINT_F32_I32] = "__fixsfsi";
  Names[RTLIB::FPTOSINT_F32_I64] = "__fixsfdi";
  Names[RTLIB::FPTOSINT_F32_I128] = "__fixsfti";
  Names[RTLIB::FPTOSINT_F64_I32] = "__fixdfsi";
  Names[RTLIB::FPTOSINT_F64_I64] = "__fixdfdi";
  Names[RTLIB::FPTOSINT_F64_I128] = "__fixdfti";
  Names[RTLIB::FPTOSINT_F80_I32] = "__fixxfsi";
  Names[RTLIB::FPTOSINT_F80_I64] = "__fixxfdi";
  Names[RTLIB::FPTOSINT_F80_I128] = "__fixxfti";
  Names[RTLIB::FPTOSINT_PPCF128_I32] = "__fixtfsi";
  Names[RTLIB::FPTOSINT_PPCF128_I64] = "__fixtfdi";
  Names[RTLIB::FPTOSINT_PPCF128_I128] = "__fixtfti";
  Names[RTLIB::FPTOUINT_F32_I8] = "__fixunssfi8";
  Names[RTLIB::FPTOUINT_F32_I16] = "__fixunssfi16";
  Names[RTLIB::FPTOUINT_F32_I32] = "__fixunssfsi";
  Names[RTLIB::FPTOUINT_F32_I64] = "__fixunssfdi";
  Names[RTLIB::FPTOUINT_F32_I128] = "__fixunssfti";
  Names[RTLIB::FPTOUINT_F64_I32] = "__fixunsdfsi";
  Names[RTLIB::FPTOUINT_F64_I64] = "__fixunsdfdi";
  Names[RTLIB::FPTOUINT_F64_I128] = "__fixunsdfti";
  Names[RTLIB::FPTOUINT_F80_I32] = "__fixunsxfsi";
  Names[RTLIB::FPTOUINT_F80_I64] = "__fixunsxfdi";
  Names[RTLIB::FPTOUINT_F80_I128] = "__fixunsxfti";
  Names[RTLIB::FPTOUINT_PPCF128_I32] = "__fixunstfsi";
  Names[RTLIB::FPTOUINT_PPCF128_I64] = "__fixunstfdi";
  Names[RTLIB::FPTOUINT_PPCF128_I128] = "__fixunstfti";
  Names[RTLIB::SINTTOFP_I32_F32] = "__floatsisf";
  Names[RTLIB::SINTTOFP_I32_F64] = "__floatsidf";
  Names[RTLIB::SINTTOFP_I32_F80] = "__floatsixf";
  Names[RTLIB::SINTTOFP_I32_PPCF128] = "__floatsitf";
  Names[RTLIB::SINTTOFP_I64_F32] = "__floatdisf";
  Names[RTLIB::SINTTOFP_I64_F64] = "__floatdidf";
  Names[RTLIB::SINTTOFP_I64_F80] = "__floatdixf";
  Names[RTLIB::SINTTOFP_I64_PPCF128] = "__floatditf";
  Names[RTLIB::SINTTOFP_I128_F32] = "__floattisf";
  Names[RTLIB::SINTTOFP_I128_F64] = "__floattidf";
  Names[RTLIB::SINTTOFP_I128_F80] = "__floattixf";
  Names[RTLIB::SINTTOFP_I128_PPCF128] = "__floattitf";
  Names[RTLIB::UINTTOFP_I32_F32] = "__floatunsisf";
  Names[RTLIB::UINTTOFP_I32_F64] = "__floatunsidf";
  Names[RTLIB::UINTTOFP_I32_F80] = "__floatunsixf";
  Names[RTLIB::UINTTOFP_I32_PPCF128] = "__floatunsitf";
  Names[RTLIB::UINTTOFP_I64_F32] = "__floatundisf";
  Names[RTLIB::UINTTOFP_I64_F64] = "__floatundidf";
  Names[RTLIB::UINTTOFP_I64_F80] = "__floatundixf";
  Names[RTLIB::UINTTOFP_I64_PPCF128] = "__floatunditf";
  Names[RTLIB::UINTTOFP_I128_F32] = "__floatuntisf";
  Names[RTLIB::UINTTOFP_I128_F64] = "__floatuntidf";
  Names[RTLIB::UINTTOFP_I128_F80] = "__floatuntixf";
  Names[RTLIB::UINTTOFP_I128_PPCF128] = "__floatuntitf";
  Names[RTLIB::OEQ_F32] = "__eqsf2";
  Names[RTLIB::OEQ_F64] = "__eqdf2";
  Names[RTLIB::UNE_F32] = "__nesf2";
  Names[RTLIB::UNE_F64] = "__nedf2";
  Names[RTLIB::OGE_F32] = "__gesf2";
  Names[RTLIB::OGE_F64] = "__gedf2";
  Names[RTLIB::OLT_F32] = "__ltsf2";
  Names[RTLIB::OLT_F64] = "__ltdf2";
  Names[RTLIB::OLE_F32] = "__lesf2";
  Names[RTLIB::OLE_F64] = "__ledf2";
  Names[RTLIB::OGT_F32] = "__gtsf2";
  Names[RTLIB::OGT_F64] = "__gtdf2";
  Names[RTLIB::UO_F32] = "__unordsf2";
  Names[RTLIB::UO_F64] = "__unorddf2";
  Names[RTLIB::O_F32] = "__unordsf2";
  Names[RTLIB::O_F64] = "__unorddf2";
  Names[RTLIB::MEMCPY] = "memcpy";
  Names[RTLIB::MEMMOVE] = "memmove";
  Names[RTLIB::MEMSET] = "memset";
  Names[RTLIB::UNWIND_RESUME] = "_Unwind_Resume";
}

/// InitLibcallCallingConvs - Set default libcall CallingConvs.
///
static void InitLibcallCallingConvs(CallingConv::ID *CCs) {
  for (int i = 0; i < RTLIB::UNKNOWN_LIBCALL; ++i) {
    CCs[i] = CallingConv::C;
  }
}

/// getFPEXT - Return the FPEXT_*_* value for the given types, or
/// UNKNOWN_LIBCALL if there is none.
RTLIB::Libcall RTLIB::getFPEXT(EVT OpVT, EVT RetVT) {
  if (OpVT == MVT::f32) {
    if (RetVT == MVT::f64)
      return FPEXT_F32_F64;
  }
  return UNKNOWN_LIBCALL;
}

/// getFPROUND - Return the FPROUND_*_* value for the given types, or
/// UNKNOWN_LIBCALL if there is none.
RTLIB::Libcall RTLIB::getFPROUND(EVT OpVT, EVT RetVT) {
  if (RetVT == MVT::f32) {
    if (OpVT == MVT::f64)
      return FPROUND_F64_F32;
    if (OpVT == MVT::f80)
      return FPROUND_F80_F32;
    if (OpVT == MVT::ppcf128)
      return FPROUND_PPCF128_F32;
  } else if (RetVT == MVT::f64) {
    if (OpVT == MVT::f80)
      return FPROUND_F80_F64;
    if (OpVT == MVT::ppcf128)
      return FPROUND_PPCF128_F64;
  }
  return UNKNOWN_LIBCALL;
}

/// getFPTOSINT - Return the FPTOSINT_*_* value for the given types, or
/// UNKNOWN_LIBCALL if there is none.
RTLIB::Libcall RTLIB::getFPTOSINT(EVT OpVT, EVT RetVT) {
  if (OpVT == MVT::f32) {
    if (RetVT == MVT::i8)
      return FPTOSINT_F32_I8;
    if (RetVT == MVT::i16)
      return FPTOSINT_F32_I16;
    if (RetVT == MVT::i32)
      return FPTOSINT_F32_I32;
    if (RetVT == MVT::i64)
      return FPTOSINT_F32_I64;
    if (RetVT == MVT::i128)
      return FPTOSINT_F32_I128;
  } else if (OpVT == MVT::f64) {
    if (RetVT == MVT::i32)
      return FPTOSINT_F64_I32;
    if (RetVT == MVT::i64)
      return FPTOSINT_F64_I64;
    if (RetVT == MVT::i128)
      return FPTOSINT_F64_I128;
  } else if (OpVT == MVT::f80) {
    if (RetVT == MVT::i32)
      return FPTOSINT_F80_I32;
    if (RetVT == MVT::i64)
      return FPTOSINT_F80_I64;
    if (RetVT == MVT::i128)
      return FPTOSINT_F80_I128;
  } else if (OpVT == MVT::ppcf128) {
    if (RetVT == MVT::i32)
      return FPTOSINT_PPCF128_I32;
    if (RetVT == MVT::i64)
      return FPTOSINT_PPCF128_I64;
    if (RetVT == MVT::i128)
      return FPTOSINT_PPCF128_I128;
  }
  return UNKNOWN_LIBCALL;
}

/// getFPTOUINT - Return the FPTOUINT_*_* value for the given types, or
/// UNKNOWN_LIBCALL if there is none.
RTLIB::Libcall RTLIB::getFPTOUINT(EVT OpVT, EVT RetVT) {
  if (OpVT == MVT::f32) {
    if (RetVT == MVT::i8)
      return FPTOUINT_F32_I8;
    if (RetVT == MVT::i16)
      return FPTOUINT_F32_I16;
    if (RetVT == MVT::i32)
      return FPTOUINT_F32_I32;
    if (RetVT == MVT::i64)
      return FPTOUINT_F32_I64;
    if (RetVT == MVT::i128)
      return FPTOUINT_F32_I128;
  } else if (OpVT == MVT::f64) {
    if (RetVT == MVT::i32)
      return FPTOUINT_F64_I32;
    if (RetVT == MVT::i64)
      return FPTOUINT_F64_I64;
    if (RetVT == MVT::i128)
      return FPTOUINT_F64_I128;
  } else if (OpVT == MVT::f80) {
    if (RetVT == MVT::i32)
      return FPTOUINT_F80_I32;
    if (RetVT == MVT::i64)
      return FPTOUINT_F80_I64;
    if (RetVT == MVT::i128)
      return FPTOUINT_F80_I128;
  } else if (OpVT == MVT::ppcf128) {
    if (RetVT == MVT::i32)
      return FPTOUINT_PPCF128_I32;
    if (RetVT == MVT::i64)
      return FPTOUINT_PPCF128_I64;
    if (RetVT == MVT::i128)
      return FPTOUINT_PPCF128_I128;
  }
  return UNKNOWN_LIBCALL;
}

/// getSINTTOFP - Return the SINTTOFP_*_* value for the given types, or
/// UNKNOWN_LIBCALL if there is none.
RTLIB::Libcall RTLIB::getSINTTOFP(EVT OpVT, EVT RetVT) {
  if (OpVT == MVT::i32) {
    if (RetVT == MVT::f32)
      return SINTTOFP_I32_F32;
    else if (RetVT == MVT::f64)
      return SINTTOFP_I32_F64;
    else if (RetVT == MVT::f80)
      return SINTTOFP_I32_F80;
    else if (RetVT == MVT::ppcf128)
      return SINTTOFP_I32_PPCF128;
  } else if (OpVT == MVT::i64) {
    if (RetVT == MVT::f32)
      return SINTTOFP_I64_F32;
    else if (RetVT == MVT::f64)
      return SINTTOFP_I64_F64;
    else if (RetVT == MVT::f80)
      return SINTTOFP_I64_F80;
    else if (RetVT == MVT::ppcf128)
      return SINTTOFP_I64_PPCF128;
  } else if (OpVT == MVT::i128) {
    if (RetVT == MVT::f32)
      return SINTTOFP_I128_F32;
    else if (RetVT == MVT::f64)
      return SINTTOFP_I128_F64;
    else if (RetVT == MVT::f80)
      return SINTTOFP_I128_F80;
    else if (RetVT == MVT::ppcf128)
      return SINTTOFP_I128_PPCF128;
  }
  return UNKNOWN_LIBCALL;
}

/// getUINTTOFP - Return the UINTTOFP_*_* value for the given types, or
/// UNKNOWN_LIBCALL if there is none.
RTLIB::Libcall RTLIB::getUINTTOFP(EVT OpVT, EVT RetVT) {
  if (OpVT == MVT::i32) {
    if (RetVT == MVT::f32)
      return UINTTOFP_I32_F32;
    else if (RetVT == MVT::f64)
      return UINTTOFP_I32_F64;
    else if (RetVT == MVT::f80)
      return UINTTOFP_I32_F80;
    else if (RetVT == MVT::ppcf128)
      return UINTTOFP_I32_PPCF128;
  } else if (OpVT == MVT::i64) {
    if (RetVT == MVT::f32)
      return UINTTOFP_I64_F32;
    else if (RetVT == MVT::f64)
      return UINTTOFP_I64_F64;
    else if (RetVT == MVT::f80)
      return UINTTOFP_I64_F80;
    else if (RetVT == MVT::ppcf128)
      return UINTTOFP_I64_PPCF128;
  } else if (OpVT == MVT::i128) {
    if (RetVT == MVT::f32)
      return UINTTOFP_I128_F32;
    else if (RetVT == MVT::f64)
      return UINTTOFP_I128_F64;
    else if (RetVT == MVT::f80)
      return UINTTOFP_I128_F80;
    else if (RetVT == MVT::ppcf128)
      return UINTTOFP_I128_PPCF128;
  }
  return UNKNOWN_LIBCALL;
}

/// InitCmpLibcallCCs - Set default comparison libcall CC.
///
static void InitCmpLibcallCCs(ISD::CondCode *CCs) {
  memset(CCs, ISD::SETCC_INVALID, sizeof(ISD::CondCode)*RTLIB::UNKNOWN_LIBCALL);
  CCs[RTLIB::OEQ_F32] = ISD::SETEQ;
  CCs[RTLIB::OEQ_F64] = ISD::SETEQ;
  CCs[RTLIB::UNE_F32] = ISD::SETNE;
  CCs[RTLIB::UNE_F64] = ISD::SETNE;
  CCs[RTLIB::OGE_F32] = ISD::SETGE;
  CCs[RTLIB::OGE_F64] = ISD::SETGE;
  CCs[RTLIB::OLT_F32] = ISD::SETLT;
  CCs[RTLIB::OLT_F64] = ISD::SETLT;
  CCs[RTLIB::OLE_F32] = ISD::SETLE;
  CCs[RTLIB::OLE_F64] = ISD::SETLE;
  CCs[RTLIB::OGT_F32] = ISD::SETGT;
  CCs[RTLIB::OGT_F64] = ISD::SETGT;
  CCs[RTLIB::UO_F32] = ISD::SETNE;
  CCs[RTLIB::UO_F64] = ISD::SETNE;
  CCs[RTLIB::O_F32] = ISD::SETEQ;
  CCs[RTLIB::O_F64] = ISD::SETEQ;
}

/// NOTE: The constructor takes ownership of TLOF.
TargetLowering::TargetLowering(TargetMachine &tm,TargetLoweringObjectFile *tlof)
  : TM(tm), TD(TM.getTargetData()), TLOF(*tlof) {
  // All operations default to being supported.
  memset(OpActions, 0, sizeof(OpActions));
  memset(LoadExtActions, 0, sizeof(LoadExtActions));
  memset(TruncStoreActions, 0, sizeof(TruncStoreActions));
  memset(IndexedModeActions, 0, sizeof(IndexedModeActions));
  memset(ConvertActions, 0, sizeof(ConvertActions));
  memset(CondCodeActions, 0, sizeof(CondCodeActions));

  // Set default actions for various operations.
  for (unsigned VT = 0; VT != (unsigned)MVT::LAST_VALUETYPE; ++VT) {
    // Default all indexed load / store to expand.
    for (unsigned IM = (unsigned)ISD::PRE_INC;
         IM != (unsigned)ISD::LAST_INDEXED_MODE; ++IM) {
      setIndexedLoadAction(IM, (MVT::SimpleValueType)VT, Expand);
      setIndexedStoreAction(IM, (MVT::SimpleValueType)VT, Expand);
    }
    
    // These operations default to expand.
    setOperationAction(ISD::FGETSIGN, (MVT::SimpleValueType)VT, Expand);
    setOperationAction(ISD::CONCAT_VECTORS, (MVT::SimpleValueType)VT, Expand);
  }

  // Most targets ignore the @llvm.prefetch intrinsic.
  setOperationAction(ISD::PREFETCH, MVT::Other, Expand);
  
  // ConstantFP nodes default to expand.  Targets can either change this to 
  // Legal, in which case all fp constants are legal, or use addLegalFPImmediate
  // to optimize expansions for certain constants.
  setOperationAction(ISD::ConstantFP, MVT::f32, Expand);
  setOperationAction(ISD::ConstantFP, MVT::f64, Expand);
  setOperationAction(ISD::ConstantFP, MVT::f80, Expand);

  // These library functions default to expand.
  setOperationAction(ISD::FLOG , MVT::f64, Expand);
  setOperationAction(ISD::FLOG2, MVT::f64, Expand);
  setOperationAction(ISD::FLOG10,MVT::f64, Expand);
  setOperationAction(ISD::FEXP , MVT::f64, Expand);
  setOperationAction(ISD::FEXP2, MVT::f64, Expand);
  setOperationAction(ISD::FLOG , MVT::f32, Expand);
  setOperationAction(ISD::FLOG2, MVT::f32, Expand);
  setOperationAction(ISD::FLOG10,MVT::f32, Expand);
  setOperationAction(ISD::FEXP , MVT::f32, Expand);
  setOperationAction(ISD::FEXP2, MVT::f32, Expand);

  // Default ISD::TRAP to expand (which turns it into abort).
  setOperationAction(ISD::TRAP, MVT::Other, Expand);
    
  IsLittleEndian = TD->isLittleEndian();
  UsesGlobalOffsetTable = false;
  ShiftAmountTy = PointerTy = MVT::getIntegerVT(8*TD->getPointerSize());
  memset(RegClassForVT, 0,MVT::LAST_VALUETYPE*sizeof(TargetRegisterClass*));
  memset(TargetDAGCombineArray, 0, array_lengthof(TargetDAGCombineArray));
  maxStoresPerMemset = maxStoresPerMemcpy = maxStoresPerMemmove = 8;
  benefitFromCodePlacementOpt = false;
  UseUnderscoreSetJmp = false;
  UseUnderscoreLongJmp = false;
  SelectIsExpensive = false;
  IntDivIsCheap = false;
  Pow2DivIsCheap = false;
  StackPointerRegisterToSaveRestore = 0;
  ExceptionPointerRegister = 0;
  ExceptionSelectorRegister = 0;
  BooleanContents = UndefinedBooleanContent;
  SchedPreferenceInfo = SchedulingForLatency;
  JumpBufSize = 0;
  JumpBufAlignment = 0;
  IfCvtBlockSizeLimit = 2;
  IfCvtDupBlockSizeLimit = 0;
  PrefLoopAlignment = 0;

  InitLibcallNames(LibcallRoutineNames);
  InitCmpLibcallCCs(CmpLibcallCCs);
  InitLibcallCallingConvs(LibcallCallingConvs);

  // Tell Legalize whether the assembler supports DEBUG_LOC.
  const MCAsmInfo *TASM = TM.getMCAsmInfo();
  if (!TASM || !TASM->hasDotLocAndDotFile())
    setOperationAction(ISD::DEBUG_LOC, MVT::Other, Expand);
}

TargetLowering::~TargetLowering() {
  delete &TLOF;
}

static unsigned getVectorTypeBreakdownMVT(MVT VT, MVT &IntermediateVT,
                                       unsigned &NumIntermediates,
                                       EVT &RegisterVT,
                                       TargetLowering* TLI) {
  // Figure out the right, legal destination reg to copy into.
  unsigned NumElts = VT.getVectorNumElements();
  MVT EltTy = VT.getVectorElementType();
  
  unsigned NumVectorRegs = 1;
  
  // FIXME: We don't support non-power-of-2-sized vectors for now.  Ideally we 
  // could break down into LHS/RHS like LegalizeDAG does.
  if (!isPowerOf2_32(NumElts)) {
    NumVectorRegs = NumElts;
    NumElts = 1;
  }
  
  // Divide the input until we get to a supported size.  This will always
  // end with a scalar if the target doesn't support vectors.
  while (NumElts > 1 && !TLI->isTypeLegal(MVT::getVectorVT(EltTy, NumElts))) {
    NumElts >>= 1;
    NumVectorRegs <<= 1;
  }

  NumIntermediates = NumVectorRegs;
  
  MVT NewVT = MVT::getVectorVT(EltTy, NumElts);
  if (!TLI->isTypeLegal(NewVT))
    NewVT = EltTy;
  IntermediateVT = NewVT;

  EVT DestVT = TLI->getRegisterType(NewVT);
  RegisterVT = DestVT;
  if (EVT(DestVT).bitsLT(NewVT)) {
    // Value is expanded, e.g. i64 -> i16.
    return NumVectorRegs*(NewVT.getSizeInBits()/DestVT.getSizeInBits());
  } else {
    // Otherwise, promotion or legal types use the same number of registers as
    // the vector decimated to the appropriate level.
    return NumVectorRegs;
  }
  
  return 1;
}

/// computeRegisterProperties - Once all of the register classes are added,
/// this allows us to compute derived properties we expose.
void TargetLowering::computeRegisterProperties() {
  assert(MVT::LAST_VALUETYPE <= MVT::MAX_ALLOWED_VALUETYPE &&
         "Too many value types for ValueTypeActions to hold!");

  // Everything defaults to needing one register.
  for (unsigned i = 0; i != MVT::LAST_VALUETYPE; ++i) {
    NumRegistersForVT[i] = 1;
    RegisterTypeForVT[i] = TransformToType[i] = (MVT::SimpleValueType)i;
  }
  // ...except isVoid, which doesn't need any registers.
  NumRegistersForVT[MVT::isVoid] = 0;

  // Find the largest integer register class.
  unsigned LargestIntReg = MVT::LAST_INTEGER_VALUETYPE;
  for (; RegClassForVT[LargestIntReg] == 0; --LargestIntReg)
    assert(LargestIntReg != MVT::i1 && "No integer registers defined!");

  // Every integer value type larger than this largest register takes twice as
  // many registers to represent as the previous ValueType.
  for (unsigned ExpandedReg = LargestIntReg + 1; ; ++ExpandedReg) {
    EVT ExpandedVT = (MVT::SimpleValueType)ExpandedReg;
    if (!ExpandedVT.isInteger())
      break;
    NumRegistersForVT[ExpandedReg] = 2*NumRegistersForVT[ExpandedReg-1];
    RegisterTypeForVT[ExpandedReg] = (MVT::SimpleValueType)LargestIntReg;
    TransformToType[ExpandedReg] = (MVT::SimpleValueType)(ExpandedReg - 1);
    ValueTypeActions.setTypeAction(ExpandedVT, Expand);
  }

  // Inspect all of the ValueType's smaller than the largest integer
  // register to see which ones need promotion.
  unsigned LegalIntReg = LargestIntReg;
  for (unsigned IntReg = LargestIntReg - 1;
       IntReg >= (unsigned)MVT::i1; --IntReg) {
    EVT IVT = (MVT::SimpleValueType)IntReg;
    if (isTypeLegal(IVT)) {
      LegalIntReg = IntReg;
    } else {
      RegisterTypeForVT[IntReg] = TransformToType[IntReg] =
        (MVT::SimpleValueType)LegalIntReg;
      ValueTypeActions.setTypeAction(IVT, Promote);
    }
  }

  // ppcf128 type is really two f64's.
  if (!isTypeLegal(MVT::ppcf128)) {
    NumRegistersForVT[MVT::ppcf128] = 2*NumRegistersForVT[MVT::f64];
    RegisterTypeForVT[MVT::ppcf128] = MVT::f64;
    TransformToType[MVT::ppcf128] = MVT::f64;
    ValueTypeActions.setTypeAction(MVT::ppcf128, Expand);
  }    

  // Decide how to handle f64. If the target does not have native f64 support,
  // expand it to i64 and we will be generating soft float library calls.
  if (!isTypeLegal(MVT::f64)) {
    NumRegistersForVT[MVT::f64] = NumRegistersForVT[MVT::i64];
    RegisterTypeForVT[MVT::f64] = RegisterTypeForVT[MVT::i64];
    TransformToType[MVT::f64] = MVT::i64;
    ValueTypeActions.setTypeAction(MVT::f64, Expand);
  }

  // Decide how to handle f32. If the target does not have native support for
  // f32, promote it to f64 if it is legal. Otherwise, expand it to i32.
  if (!isTypeLegal(MVT::f32)) {
    if (isTypeLegal(MVT::f64)) {
      NumRegistersForVT[MVT::f32] = NumRegistersForVT[MVT::f64];
      RegisterTypeForVT[MVT::f32] = RegisterTypeForVT[MVT::f64];
      TransformToType[MVT::f32] = MVT::f64;
      ValueTypeActions.setTypeAction(MVT::f32, Promote);
    } else {
      NumRegistersForVT[MVT::f32] = NumRegistersForVT[MVT::i32];
      RegisterTypeForVT[MVT::f32] = RegisterTypeForVT[MVT::i32];
      TransformToType[MVT::f32] = MVT::i32;
      ValueTypeActions.setTypeAction(MVT::f32, Expand);
    }
  }
  
  // Loop over all of the vector value types to see which need transformations.
  for (unsigned i = MVT::FIRST_VECTOR_VALUETYPE;
       i <= (unsigned)MVT::LAST_VECTOR_VALUETYPE; ++i) {
    MVT VT = (MVT::SimpleValueType)i;
    if (!isTypeLegal(VT)) {
      MVT IntermediateVT;
      EVT RegisterVT;
      unsigned NumIntermediates;
      NumRegistersForVT[i] =
        getVectorTypeBreakdownMVT(VT, IntermediateVT, NumIntermediates,
                                  RegisterVT, this);
      RegisterTypeForVT[i] = RegisterVT;
      
      // Determine if there is a legal wider type.
      bool IsLegalWiderType = false;
      EVT EltVT = VT.getVectorElementType();
      unsigned NElts = VT.getVectorNumElements();
      for (unsigned nVT = i+1; nVT <= MVT::LAST_VECTOR_VALUETYPE; ++nVT) {
        EVT SVT = (MVT::SimpleValueType)nVT;
        if (isTypeLegal(SVT) && SVT.getVectorElementType() == EltVT &&
            SVT.getVectorNumElements() > NElts) {
          TransformToType[i] = SVT;
          ValueTypeActions.setTypeAction(VT, Promote);
          IsLegalWiderType = true;
          break;
        }
      }
      if (!IsLegalWiderType) {
        EVT NVT = VT.getPow2VectorType();
        if (NVT == VT) {
          // Type is already a power of 2.  The default action is to split.
          TransformToType[i] = MVT::Other;
          ValueTypeActions.setTypeAction(VT, Expand);
        } else {
          TransformToType[i] = NVT;
          ValueTypeActions.setTypeAction(VT, Promote);
        }
      }
    }
  }
}

const char *TargetLowering::getTargetNodeName(unsigned Opcode) const {
  return NULL;
}


MVT::SimpleValueType TargetLowering::getSetCCResultType(EVT VT) const {
  return PointerTy.SimpleTy;
}

/// getVectorTypeBreakdown - Vector types are broken down into some number of
/// legal first class types.  For example, MVT::v8f32 maps to 2 MVT::v4f32
/// with Altivec or SSE1, or 8 promoted MVT::f64 values with the X86 FP stack.
/// Similarly, MVT::v2i64 turns into 4 MVT::i32 values with both PPC and X86.
///
/// This method returns the number of registers needed, and the VT for each
/// register.  It also returns the VT and quantity of the intermediate values
/// before they are promoted/expanded.
///
unsigned TargetLowering::getVectorTypeBreakdown(LLVMContext &Context, EVT VT,
                                                EVT &IntermediateVT,
                                                unsigned &NumIntermediates,
                                                EVT &RegisterVT) const {
  // Figure out the right, legal destination reg to copy into.
  unsigned NumElts = VT.getVectorNumElements();
  EVT EltTy = VT.getVectorElementType();
  
  unsigned NumVectorRegs = 1;
  
  // FIXME: We don't support non-power-of-2-sized vectors for now.  Ideally we 
  // could break down into LHS/RHS like LegalizeDAG does.
  if (!isPowerOf2_32(NumElts)) {
    NumVectorRegs = NumElts;
    NumElts = 1;
  }
  
  // Divide the input until we get to a supported size.  This will always
  // end with a scalar if the target doesn't support vectors.
  while (NumElts > 1 && !isTypeLegal(
                                   EVT::getVectorVT(Context, EltTy, NumElts))) {
    NumElts >>= 1;
    NumVectorRegs <<= 1;
  }

  NumIntermediates = NumVectorRegs;
  
  EVT NewVT = EVT::getVectorVT(Context, EltTy, NumElts);
  if (!isTypeLegal(NewVT))
    NewVT = EltTy;
  IntermediateVT = NewVT;

  EVT DestVT = getRegisterType(Context, NewVT);
  RegisterVT = DestVT;
  if (DestVT.bitsLT(NewVT)) {
    // Value is expanded, e.g. i64 -> i16.
    return NumVectorRegs*(NewVT.getSizeInBits()/DestVT.getSizeInBits());
  } else {
    // Otherwise, promotion or legal types use the same number of registers as
    // the vector decimated to the appropriate level.
    return NumVectorRegs;
  }
  
  return 1;
}

/// getWidenVectorType: given a vector type, returns the type to widen to
/// (e.g., v7i8 to v8i8). If the vector type is legal, it returns itself.
/// If there is no vector type that we want to widen to, returns MVT::Other
/// When and where to widen is target dependent based on the cost of
/// scalarizing vs using the wider vector type.
EVT TargetLowering::getWidenVectorType(EVT VT) const {
  assert(VT.isVector());
  if (isTypeLegal(VT))
    return VT;
 
  // Default is not to widen until moved to LegalizeTypes
  return MVT::Other;
}

/// getByValTypeAlignment - Return the desired alignment for ByVal aggregate
/// function arguments in the caller parameter area.  This is the actual
/// alignment, not its logarithm.
unsigned TargetLowering::getByValTypeAlignment(const Type *Ty) const {
  return TD->getCallFrameTypeAlignment(Ty);
}

SDValue TargetLowering::getPICJumpTableRelocBase(SDValue Table,
                                                 SelectionDAG &DAG) const {
  if (usesGlobalOffsetTable())
    return DAG.getGLOBAL_OFFSET_TABLE(getPointerTy());
  return Table;
}

bool
TargetLowering::isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const {
  // Assume that everything is safe in static mode.
  if (getTargetMachine().getRelocationModel() == Reloc::Static)
    return true;

  // In dynamic-no-pic mode, assume that known defined values are safe.
  if (getTargetMachine().getRelocationModel() == Reloc::DynamicNoPIC &&
      GA &&
      !GA->getGlobal()->isDeclaration() &&
      !GA->getGlobal()->isWeakForLinker())
    return true;

  // Otherwise assume nothing is safe.
  return false;
}

//===----------------------------------------------------------------------===//
//  Optimization Methods
//===----------------------------------------------------------------------===//

/// ShrinkDemandedConstant - Check to see if the specified operand of the 
/// specified instruction is a constant integer.  If so, check to see if there
/// are any bits set in the constant that are not demanded.  If so, shrink the
/// constant and return true.
bool TargetLowering::TargetLoweringOpt::ShrinkDemandedConstant(SDValue Op, 
                                                        const APInt &Demanded) {
  DebugLoc dl = Op.getDebugLoc();

  // FIXME: ISD::SELECT, ISD::SELECT_CC
  switch (Op.getOpcode()) {
  default: break;
  case ISD::XOR:
  case ISD::AND:
  case ISD::OR: {
    ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1));
    if (!C) return false;

    if (Op.getOpcode() == ISD::XOR &&
        (C->getAPIntValue() | (~Demanded)).isAllOnesValue())
      return false;

    // if we can expand it to have all bits set, do it
    if (C->getAPIntValue().intersects(~Demanded)) {
      EVT VT = Op.getValueType();
      SDValue New = DAG.getNode(Op.getOpcode(), dl, VT, Op.getOperand(0),
                                DAG.getConstant(Demanded &
                                                C->getAPIntValue(), 
                                                VT));
      return CombineTo(Op, New);
    }

    break;
  }
  }

  return false;
}

/// ShrinkDemandedOp - Convert x+y to (VT)((SmallVT)x+(SmallVT)y) if the
/// casts are free.  This uses isZExtFree and ZERO_EXTEND for the widening
/// cast, but it could be generalized for targets with other types of
/// implicit widening casts.
bool
TargetLowering::TargetLoweringOpt::ShrinkDemandedOp(SDValue Op,
                                                    unsigned BitWidth,
                                                    const APInt &Demanded,
                                                    DebugLoc dl) {
  assert(Op.getNumOperands() == 2 &&
         "ShrinkDemandedOp only supports binary operators!");
  assert(Op.getNode()->getNumValues() == 1 &&
         "ShrinkDemandedOp only supports nodes with one result!");

  // Don't do this if the node has another user, which may require the
  // full value.
  if (!Op.getNode()->hasOneUse())
    return false;

  // Search for the smallest integer type with free casts to and from
  // Op's type. For expedience, just check power-of-2 integer types.
  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
  unsigned SmallVTBits = BitWidth - Demanded.countLeadingZeros();
  if (!isPowerOf2_32(SmallVTBits))
    SmallVTBits = NextPowerOf2(SmallVTBits);
  for (; SmallVTBits < BitWidth; SmallVTBits = NextPowerOf2(SmallVTBits)) {
    EVT SmallVT = EVT::getIntegerVT(*DAG.getContext(), SmallVTBits);
    if (TLI.isTruncateFree(Op.getValueType(), SmallVT) &&
        TLI.isZExtFree(SmallVT, Op.getValueType())) {
      // We found a type with free casts.
      SDValue X = DAG.getNode(Op.getOpcode(), dl, SmallVT,
                              DAG.getNode(ISD::TRUNCATE, dl, SmallVT,
                                          Op.getNode()->getOperand(0)),
                              DAG.getNode(ISD::TRUNCATE, dl, SmallVT,
                                          Op.getNode()->getOperand(1)));
      SDValue Z = DAG.getNode(ISD::ZERO_EXTEND, dl, Op.getValueType(), X);
      return CombineTo(Op, Z);
    }
  }
  return false;
}

/// SimplifyDemandedBits - Look at Op.  At this point, we know that only the
/// DemandedMask bits of the result of Op are ever used downstream.  If we can
/// use this information to simplify Op, create a new simplified DAG node and
/// return true, returning the original and new nodes in Old and New. Otherwise,
/// analyze the expression and return a mask of KnownOne and KnownZero bits for
/// the expression (used to simplify the caller).  The KnownZero/One bits may
/// only be accurate for those bits in the DemandedMask.
bool TargetLowering::SimplifyDemandedBits(SDValue Op,
                                          const APInt &DemandedMask,
                                          APInt &KnownZero,
                                          APInt &KnownOne,
                                          TargetLoweringOpt &TLO,
                                          unsigned Depth) const {
  unsigned BitWidth = DemandedMask.getBitWidth();
  assert(Op.getValueSizeInBits() == BitWidth &&
         "Mask size mismatches value type size!");
  APInt NewMask = DemandedMask;
  DebugLoc dl = Op.getDebugLoc();

  // Don't know anything.
  KnownZero = KnownOne = APInt(BitWidth, 0);

  // Other users may use these bits.
  if (!Op.getNode()->hasOneUse()) { 
    if (Depth != 0) {
      // If not at the root, Just compute the KnownZero/KnownOne bits to 
      // simplify things downstream.
      TLO.DAG.ComputeMaskedBits(Op, DemandedMask, KnownZero, KnownOne, Depth);
      return false;
    }
    // If this is the root being simplified, allow it to have multiple uses,
    // just set the NewMask to all bits.
    NewMask = APInt::getAllOnesValue(BitWidth);
  } else if (DemandedMask == 0) {   
    // Not demanding any bits from Op.
    if (Op.getOpcode() != ISD::UNDEF)
      return TLO.CombineTo(Op, TLO.DAG.getUNDEF(Op.getValueType()));
    return false;
  } else if (Depth == 6) {        // Limit search depth.
    return false;
  }

  APInt KnownZero2, KnownOne2, KnownZeroOut, KnownOneOut;
  switch (Op.getOpcode()) {
  case ISD::Constant:
    // We know all of the bits for a constant!
    KnownOne = cast<ConstantSDNode>(Op)->getAPIntValue() & NewMask;
    KnownZero = ~KnownOne & NewMask;
    return false;   // Don't fall through, will infinitely loop.
  case ISD::AND:
    // If the RHS is a constant, check to see if the LHS would be zero without
    // using the bits from the RHS.  Below, we use knowledge about the RHS to
    // simplify the LHS, here we're using information from the LHS to simplify
    // the RHS.
    if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
      APInt LHSZero, LHSOne;
      TLO.DAG.ComputeMaskedBits(Op.getOperand(0), NewMask,
                                LHSZero, LHSOne, Depth+1);
      // If the LHS already has zeros where RHSC does, this and is dead.
      if ((LHSZero & NewMask) == (~RHSC->getAPIntValue() & NewMask))
        return TLO.CombineTo(Op, Op.getOperand(0));
      // If any of the set bits in the RHS are known zero on the LHS, shrink
      // the constant.
      if (TLO.ShrinkDemandedConstant(Op, ~LHSZero & NewMask))
        return true;
    }
    
    if (SimplifyDemandedBits(Op.getOperand(1), NewMask, KnownZero,
                             KnownOne, TLO, Depth+1))
      return true;
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    if (SimplifyDemandedBits(Op.getOperand(0), ~KnownZero & NewMask,
                             KnownZero2, KnownOne2, TLO, Depth+1))
      return true;
    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
      
    // If all of the demanded bits are known one on one side, return the other.
    // These bits cannot contribute to the result of the 'and'.
    if ((NewMask & ~KnownZero2 & KnownOne) == (~KnownZero2 & NewMask))
      return TLO.CombineTo(Op, Op.getOperand(0));
    if ((NewMask & ~KnownZero & KnownOne2) == (~KnownZero & NewMask))
      return TLO.CombineTo(Op, Op.getOperand(1));
    // If all of the demanded bits in the inputs are known zeros, return zero.
    if ((NewMask & (KnownZero|KnownZero2)) == NewMask)
      return TLO.CombineTo(Op, TLO.DAG.getConstant(0, Op.getValueType()));
    // If the RHS is a constant, see if we can simplify it.
    if (TLO.ShrinkDemandedConstant(Op, ~KnownZero2 & NewMask))
      return true;
    // If the operation can be done in a smaller type, do so.
    if (TLO.ShrinkDemandedOp(Op, BitWidth, NewMask, dl))
      return true;

    // Output known-1 bits are only known if set in both the LHS & RHS.
    KnownOne &= KnownOne2;
    // Output known-0 are known to be clear if zero in either the LHS | RHS.
    KnownZero |= KnownZero2;
    break;
  case ISD::OR:
    if (SimplifyDemandedBits(Op.getOperand(1), NewMask, KnownZero, 
                             KnownOne, TLO, Depth+1))
      return true;
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    if (SimplifyDemandedBits(Op.getOperand(0), ~KnownOne & NewMask,
                             KnownZero2, KnownOne2, TLO, Depth+1))
      return true;
    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
    
    // If all of the demanded bits are known zero on one side, return the other.
    // These bits cannot contribute to the result of the 'or'.
    if ((NewMask & ~KnownOne2 & KnownZero) == (~KnownOne2 & NewMask))
      return TLO.CombineTo(Op, Op.getOperand(0));
    if ((NewMask & ~KnownOne & KnownZero2) == (~KnownOne & NewMask))
      return TLO.CombineTo(Op, Op.getOperand(1));
    // If all of the potentially set bits on one side are known to be set on
    // the other side, just use the 'other' side.
    if ((NewMask & ~KnownZero & KnownOne2) == (~KnownZero & NewMask))
      return TLO.CombineTo(Op, Op.getOperand(0));
    if ((NewMask & ~KnownZero2 & KnownOne) == (~KnownZero2 & NewMask))
      return TLO.CombineTo(Op, Op.getOperand(1));
    // If the RHS is a constant, see if we can simplify it.
    if (TLO.ShrinkDemandedConstant(Op, NewMask))
      return true;
    // If the operation can be done in a smaller type, do so.
    if (TLO.ShrinkDemandedOp(Op, BitWidth, NewMask, dl))
      return true;

    // Output known-0 bits are only known if clear in both the LHS & RHS.
    KnownZero &= KnownZero2;
    // Output known-1 are known to be set if set in either the LHS | RHS.
    KnownOne |= KnownOne2;
    break;
  case ISD::XOR:
    if (SimplifyDemandedBits(Op.getOperand(1), NewMask, KnownZero, 
                             KnownOne, TLO, Depth+1))
      return true;
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    if (SimplifyDemandedBits(Op.getOperand(0), NewMask, KnownZero2,
                             KnownOne2, TLO, Depth+1))
      return true;
    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
    
    // If all of the demanded bits are known zero on one side, return the other.
    // These bits cannot contribute to the result of the 'xor'.
    if ((KnownZero & NewMask) == NewMask)
      return TLO.CombineTo(Op, Op.getOperand(0));
    if ((KnownZero2 & NewMask) == NewMask)
      return TLO.CombineTo(Op, Op.getOperand(1));
    // If the operation can be done in a smaller type, do so.
    if (TLO.ShrinkDemandedOp(Op, BitWidth, NewMask, dl))
      return true;

    // If all of the unknown bits are known to be zero on one side or the other
    // (but not both) turn this into an *inclusive* or.
    //    e.g. (A & C1)^(B & C2) -> (A & C1)|(B & C2) iff C1&C2 == 0
    if ((NewMask & ~KnownZero & ~KnownZero2) == 0)
      return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::OR, dl, Op.getValueType(),
                                               Op.getOperand(0),
                                               Op.getOperand(1)));
    
    // Output known-0 bits are known if clear or set in both the LHS & RHS.
    KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
    // Output known-1 are known to be set if set in only one of the LHS, RHS.
    KnownOneOut = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
    
    // If all of the demanded bits on one side are known, and all of the set
    // bits on that side are also known to be set on the other side, turn this
    // into an AND, as we know the bits will be cleared.
    //    e.g. (X | C1) ^ C2 --> (X | C1) & ~C2 iff (C1&C2) == C2
    if ((NewMask & (KnownZero|KnownOne)) == NewMask) { // all known
      if ((KnownOne & KnownOne2) == KnownOne) {
        EVT VT = Op.getValueType();
        SDValue ANDC = TLO.DAG.getConstant(~KnownOne & NewMask, VT);
        return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::AND, dl, VT, 
                                                 Op.getOperand(0), ANDC));
      }
    }
    
    // If the RHS is a constant, see if we can simplify it.
    // for XOR, we prefer to force bits to 1 if they will make a -1.
    // if we can't force bits, try to shrink constant
    if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
      APInt Expanded = C->getAPIntValue() | (~NewMask);
      // if we can expand it to have all bits set, do it
      if (Expanded.isAllOnesValue()) {
        if (Expanded != C->getAPIntValue()) {
          EVT VT = Op.getValueType();
          SDValue New = TLO.DAG.getNode(Op.getOpcode(), dl,VT, Op.getOperand(0),
                                          TLO.DAG.getConstant(Expanded, VT));
          return TLO.CombineTo(Op, New);
        }
        // if it already has all the bits set, nothing to change
        // but don't shrink either!
      } else if (TLO.ShrinkDemandedConstant(Op, NewMask)) {
        return true;
      }
    }

    KnownZero = KnownZeroOut;
    KnownOne  = KnownOneOut;
    break;
  case ISD::SELECT:
    if (SimplifyDemandedBits(Op.getOperand(2), NewMask, KnownZero, 
                             KnownOne, TLO, Depth+1))
      return true;
    if (SimplifyDemandedBits(Op.getOperand(1), NewMask, KnownZero2,
                             KnownOne2, TLO, Depth+1))
      return true;
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
    
    // If the operands are constants, see if we can simplify them.
    if (TLO.ShrinkDemandedConstant(Op, NewMask))
      return true;
    
    // Only known if known in both the LHS and RHS.
    KnownOne &= KnownOne2;
    KnownZero &= KnownZero2;
    break;
  case ISD::SELECT_CC:
    if (SimplifyDemandedBits(Op.getOperand(3), NewMask, KnownZero, 
                             KnownOne, TLO, Depth+1))
      return true;
    if (SimplifyDemandedBits(Op.getOperand(2), NewMask, KnownZero2,
                             KnownOne2, TLO, Depth+1))
      return true;
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
    
    // If the operands are constants, see if we can simplify them.
    if (TLO.ShrinkDemandedConstant(Op, NewMask))
      return true;
      
    // Only known if known in both the LHS and RHS.
    KnownOne &= KnownOne2;
    KnownZero &= KnownZero2;
    break;
  case ISD::SHL:
    if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
      unsigned ShAmt = SA->getZExtValue();
      SDValue InOp = Op.getOperand(0);

      // If the shift count is an invalid immediate, don't do anything.
      if (ShAmt >= BitWidth)
        break;

      // If this is ((X >>u C1) << ShAmt), see if we can simplify this into a
      // single shift.  We can do this if the bottom bits (which are shifted
      // out) are never demanded.
      if (InOp.getOpcode() == ISD::SRL &&
          isa<ConstantSDNode>(InOp.getOperand(1))) {
        if (ShAmt && (NewMask & APInt::getLowBitsSet(BitWidth, ShAmt)) == 0) {
          unsigned C1= cast<ConstantSDNode>(InOp.getOperand(1))->getZExtValue();
          unsigned Opc = ISD::SHL;
          int Diff = ShAmt-C1;
          if (Diff < 0) {
            Diff = -Diff;
            Opc = ISD::SRL;
          }          
          
          SDValue NewSA = 
            TLO.DAG.getConstant(Diff, Op.getOperand(1).getValueType());
          EVT VT = Op.getValueType();
          return TLO.CombineTo(Op, TLO.DAG.getNode(Opc, dl, VT,
                                                   InOp.getOperand(0), NewSA));
        }
      }      
      
      if (SimplifyDemandedBits(Op.getOperand(0), NewMask.lshr(ShAmt),
                               KnownZero, KnownOne, TLO, Depth+1))
        return true;
      KnownZero <<= SA->getZExtValue();
      KnownOne  <<= SA->getZExtValue();
      // low bits known zero.
      KnownZero |= APInt::getLowBitsSet(BitWidth, SA->getZExtValue());
    }
    break;
  case ISD::SRL:
    if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
      EVT VT = Op.getValueType();
      unsigned ShAmt = SA->getZExtValue();
      unsigned VTSize = VT.getSizeInBits();
      SDValue InOp = Op.getOperand(0);
      
      // If the shift count is an invalid immediate, don't do anything.
      if (ShAmt >= BitWidth)
        break;

      // If this is ((X << C1) >>u ShAmt), see if we can simplify this into a
      // single shift.  We can do this if the top bits (which are shifted out)
      // are never demanded.
      if (InOp.getOpcode() == ISD::SHL &&
          isa<ConstantSDNode>(InOp.getOperand(1))) {
        if (ShAmt && (NewMask & APInt::getHighBitsSet(VTSize, ShAmt)) == 0) {
          unsigned C1= cast<ConstantSDNode>(InOp.getOperand(1))->getZExtValue();
          unsigned Opc = ISD::SRL;
          int Diff = ShAmt-C1;
          if (Diff < 0) {
            Diff = -Diff;
            Opc = ISD::SHL;
          }          
          
          SDValue NewSA =
            TLO.DAG.getConstant(Diff, Op.getOperand(1).getValueType());
          return TLO.CombineTo(Op, TLO.DAG.getNode(Opc, dl, VT,
                                                   InOp.getOperand(0), NewSA));
        }
      }      
      
      // Compute the new bits that are at the top now.
      if (SimplifyDemandedBits(InOp, (NewMask << ShAmt),
                               KnownZero, KnownOne, TLO, Depth+1))
        return true;
      assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
      KnownZero = KnownZero.lshr(ShAmt);
      KnownOne  = KnownOne.lshr(ShAmt);

      APInt HighBits = APInt::getHighBitsSet(BitWidth, ShAmt);
      KnownZero |= HighBits;  // High bits known zero.
    }
    break;
  case ISD::SRA:
    // If this is an arithmetic shift right and only the low-bit is set, we can
    // always convert this into a logical shr, even if the shift amount is
    // variable.  The low bit of the shift cannot be an input sign bit unless
    // the shift amount is >= the size of the datatype, which is undefined.
    if (DemandedMask == 1)
      return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SRL, dl, Op.getValueType(),
                                               Op.getOperand(0), Op.getOperand(1)));

    if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
      EVT VT = Op.getValueType();
      unsigned ShAmt = SA->getZExtValue();
      
      // If the shift count is an invalid immediate, don't do anything.
      if (ShAmt >= BitWidth)
        break;

      APInt InDemandedMask = (NewMask << ShAmt);

      // If any of the demanded bits are produced by the sign extension, we also
      // demand the input sign bit.
      APInt HighBits = APInt::getHighBitsSet(BitWidth, ShAmt);
      if (HighBits.intersects(NewMask))
        InDemandedMask |= APInt::getSignBit(VT.getSizeInBits());
      
      if (SimplifyDemandedBits(Op.getOperand(0), InDemandedMask,
                               KnownZero, KnownOne, TLO, Depth+1))
        return true;
      assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
      KnownZero = KnownZero.lshr(ShAmt);
      KnownOne  = KnownOne.lshr(ShAmt);
      
      // Handle the sign bit, adjusted to where it is now in the mask.
      APInt SignBit = APInt::getSignBit(BitWidth).lshr(ShAmt);
      
      // If the input sign bit is known to be zero, or if none of the top bits
      // are demanded, turn this into an unsigned shift right.
      if (KnownZero.intersects(SignBit) || (HighBits & ~NewMask) == HighBits) {
        return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SRL, dl, VT, 
                                                 Op.getOperand(0),
                                                 Op.getOperand(1)));
      } else if (KnownOne.intersects(SignBit)) { // New bits are known one.
        KnownOne |= HighBits;
      }
    }
    break;
  case ISD::SIGN_EXTEND_INREG: {
    EVT EVT = cast<VTSDNode>(Op.getOperand(1))->getVT();

    // Sign extension.  Compute the demanded bits in the result that are not 
    // present in the input.
    APInt NewBits = APInt::getHighBitsSet(BitWidth,
                                          BitWidth - EVT.getSizeInBits()) &
                    NewMask;
    
    // If none of the extended bits are demanded, eliminate the sextinreg.
    if (NewBits == 0)
      return TLO.CombineTo(Op, Op.getOperand(0));

    APInt InSignBit = APInt::getSignBit(EVT.getSizeInBits());
    InSignBit.zext(BitWidth);
    APInt InputDemandedBits = APInt::getLowBitsSet(BitWidth,
                                                   EVT.getSizeInBits()) &
                              NewMask;
    
    // Since the sign extended bits are demanded, we know that the sign
    // bit is demanded.
    InputDemandedBits |= InSignBit;

    if (SimplifyDemandedBits(Op.getOperand(0), InputDemandedBits,
                             KnownZero, KnownOne, TLO, Depth+1))
      return true;
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 

    // If the sign bit of the input is known set or clear, then we know the
    // top bits of the result.
    
    // If the input sign bit is known zero, convert this into a zero extension.
    if (KnownZero.intersects(InSignBit))
      return TLO.CombineTo(Op, 
                           TLO.DAG.getZeroExtendInReg(Op.getOperand(0),dl,EVT));
    
    if (KnownOne.intersects(InSignBit)) {    // Input sign bit known set
      KnownOne |= NewBits;
      KnownZero &= ~NewBits;
    } else {                       // Input sign bit unknown
      KnownZero &= ~NewBits;
      KnownOne &= ~NewBits;
    }
    break;
  }
  case ISD::ZERO_EXTEND: {
    unsigned OperandBitWidth = Op.getOperand(0).getValueSizeInBits();
    APInt InMask = NewMask;
    InMask.trunc(OperandBitWidth);
    
    // If none of the top bits are demanded, convert this into an any_extend.
    APInt NewBits =
      APInt::getHighBitsSet(BitWidth, BitWidth - OperandBitWidth) & NewMask;
    if (!NewBits.intersects(NewMask))
      return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::ANY_EXTEND, dl,
                                               Op.getValueType(), 
                                               Op.getOperand(0)));
    
    if (SimplifyDemandedBits(Op.getOperand(0), InMask,
                             KnownZero, KnownOne, TLO, Depth+1))
      return true;
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    KnownZero.zext(BitWidth);
    KnownOne.zext(BitWidth);
    KnownZero |= NewBits;
    break;
  }
  case ISD::SIGN_EXTEND: {
    EVT InVT = Op.getOperand(0).getValueType();
    unsigned InBits = InVT.getSizeInBits();
    APInt InMask    = APInt::getLowBitsSet(BitWidth, InBits);
    APInt InSignBit = APInt::getBitsSet(BitWidth, InBits - 1, InBits);
    APInt NewBits   = ~InMask & NewMask;
    
    // If none of the top bits are demanded, convert this into an any_extend.
    if (NewBits == 0)
      return TLO.CombineTo(Op,TLO.DAG.getNode(ISD::ANY_EXTEND, dl,
                                              Op.getValueType(),
                                              Op.getOperand(0)));
    
    // Since some of the sign extended bits are demanded, we know that the sign
    // bit is demanded.
    APInt InDemandedBits = InMask & NewMask;
    InDemandedBits |= InSignBit;
    InDemandedBits.trunc(InBits);
    
    if (SimplifyDemandedBits(Op.getOperand(0), InDemandedBits, KnownZero, 
                             KnownOne, TLO, Depth+1))
      return true;
    KnownZero.zext(BitWidth);
    KnownOne.zext(BitWidth);
    
    // If the sign bit is known zero, convert this to a zero extend.
    if (KnownZero.intersects(InSignBit))
      return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::ZERO_EXTEND, dl,
                                               Op.getValueType(), 
                                               Op.getOperand(0)));
    
    // If the sign bit is known one, the top bits match.
    if (KnownOne.intersects(InSignBit)) {
      KnownOne  |= NewBits;
      KnownZero &= ~NewBits;
    } else {   // Otherwise, top bits aren't known.
      KnownOne  &= ~NewBits;
      KnownZero &= ~NewBits;
    }
    break;
  }
  case ISD::ANY_EXTEND: {
    unsigned OperandBitWidth = Op.getOperand(0).getValueSizeInBits();
    APInt InMask = NewMask;
    InMask.trunc(OperandBitWidth);
    if (SimplifyDemandedBits(Op.getOperand(0), InMask,
                             KnownZero, KnownOne, TLO, Depth+1))
      return true;
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    KnownZero.zext(BitWidth);
    KnownOne.zext(BitWidth);
    break;
  }
  case ISD::TRUNCATE: {
    // Simplify the input, using demanded bit information, and compute the known
    // zero/one bits live out.
    APInt TruncMask = NewMask;
    TruncMask.zext(Op.getOperand(0).getValueSizeInBits());
    if (SimplifyDemandedBits(Op.getOperand(0), TruncMask,
                             KnownZero, KnownOne, TLO, Depth+1))
      return true;
    KnownZero.trunc(BitWidth);
    KnownOne.trunc(BitWidth);
    
    // If the input is only used by this truncate, see if we can shrink it based
    // on the known demanded bits.
    if (Op.getOperand(0).getNode()->hasOneUse()) {
      SDValue In = Op.getOperand(0);
      unsigned InBitWidth = In.getValueSizeInBits();
      switch (In.getOpcode()) {
      default: break;
      case ISD::SRL:
        // Shrink SRL by a constant if none of the high bits shifted in are
        // demanded.
        if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(In.getOperand(1))){
          APInt HighBits = APInt::getHighBitsSet(InBitWidth,
                                                 InBitWidth - BitWidth);
          HighBits = HighBits.lshr(ShAmt->getZExtValue());
          HighBits.trunc(BitWidth);
          
          if (ShAmt->getZExtValue() < BitWidth && !(HighBits & NewMask)) {
            // None of the shifted in bits are needed.  Add a truncate of the
            // shift input, then shift it.
            SDValue NewTrunc = TLO.DAG.getNode(ISD::TRUNCATE, dl,
                                                 Op.getValueType(), 
                                                 In.getOperand(0));
            return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SRL, dl,
                                                     Op.getValueType(),
                                                     NewTrunc, 
                                                     In.getOperand(1)));
          }
        }
        break;
      }
    }
    
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    break;
  }
  case ISD::AssertZext: {
    EVT VT = cast<VTSDNode>(Op.getOperand(1))->getVT();
    APInt InMask = APInt::getLowBitsSet(BitWidth,
                                        VT.getSizeInBits());
    if (SimplifyDemandedBits(Op.getOperand(0), InMask & NewMask,
                             KnownZero, KnownOne, TLO, Depth+1))
      return true;
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    KnownZero |= ~InMask & NewMask;
    break;
  }
  case ISD::BIT_CONVERT:
#if 0
    // If this is an FP->Int bitcast and if the sign bit is the only thing that
    // is demanded, turn this into a FGETSIGN.
    if (NewMask == EVT::getIntegerVTSignBit(Op.getValueType()) &&
        MVT::isFloatingPoint(Op.getOperand(0).getValueType()) &&
        !MVT::isVector(Op.getOperand(0).getValueType())) {
      // Only do this xform if FGETSIGN is valid or if before legalize.
      if (!TLO.AfterLegalize ||
          isOperationLegal(ISD::FGETSIGN, Op.getValueType())) {
        // Make a FGETSIGN + SHL to move the sign bit into the appropriate
        // place.  We expect the SHL to be eliminated by other optimizations.
        SDValue Sign = TLO.DAG.getNode(ISD::FGETSIGN, Op.getValueType(), 
                                         Op.getOperand(0));
        unsigned ShVal = Op.getValueType().getSizeInBits()-1;
        SDValue ShAmt = TLO.DAG.getConstant(ShVal, getShiftAmountTy());
        return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SHL, Op.getValueType(),
                                                 Sign, ShAmt));
      }
    }
#endif
    break;
  case ISD::ADD:
  case ISD::MUL:
  case ISD::SUB: {
    // Add, Sub, and Mul don't demand any bits in positions beyond that
    // of the highest bit demanded of them.
    APInt LoMask = APInt::getLowBitsSet(BitWidth,
                                        BitWidth - NewMask.countLeadingZeros());
    if (SimplifyDemandedBits(Op.getOperand(0), LoMask, KnownZero2,
                             KnownOne2, TLO, Depth+1))
      return true;
    if (SimplifyDemandedBits(Op.getOperand(1), LoMask, KnownZero2,
                             KnownOne2, TLO, Depth+1))
      return true;
    // See if the operation should be performed at a smaller bit width.
    if (TLO.ShrinkDemandedOp(Op, BitWidth, NewMask, dl))
      return true;
  }
  // FALL THROUGH
  default:
    // Just use ComputeMaskedBits to compute output bits.
    TLO.DAG.ComputeMaskedBits(Op, NewMask, KnownZero, KnownOne, Depth);
    break;
  }
  
  // If we know the value of all of the demanded bits, return this as a
  // constant.
  if ((NewMask & (KnownZero|KnownOne)) == NewMask)
    return TLO.CombineTo(Op, TLO.DAG.getConstant(KnownOne, Op.getValueType()));
  
  return false;
}

/// computeMaskedBitsForTargetNode - Determine which of the bits specified 
/// in Mask are known to be either zero or one and return them in the 
/// KnownZero/KnownOne bitsets.
void TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op, 
                                                    const APInt &Mask,
                                                    APInt &KnownZero, 
                                                    APInt &KnownOne,
                                                    const SelectionDAG &DAG,
                                                    unsigned Depth) const {
  assert((Op.getOpcode() >= ISD::BUILTIN_OP_END ||
          Op.getOpcode() == ISD::INTRINSIC_WO_CHAIN ||
          Op.getOpcode() == ISD::INTRINSIC_W_CHAIN ||
          Op.getOpcode() == ISD::INTRINSIC_VOID) &&
         "Should use MaskedValueIsZero if you don't know whether Op"
         " is a target node!");
  KnownZero = KnownOne = APInt(Mask.getBitWidth(), 0);
}

/// ComputeNumSignBitsForTargetNode - This method can be implemented by
/// targets that want to expose additional information about sign bits to the
/// DAG Combiner.
unsigned TargetLowering::ComputeNumSignBitsForTargetNode(SDValue Op,
                                                         unsigned Depth) const {
  assert((Op.getOpcode() >= ISD::BUILTIN_OP_END ||
          Op.getOpcode() == ISD::INTRINSIC_WO_CHAIN ||
          Op.getOpcode() == ISD::INTRINSIC_W_CHAIN ||
          Op.getOpcode() == ISD::INTRINSIC_VOID) &&
         "Should use ComputeNumSignBits if you don't know whether Op"
         " is a target node!");
  return 1;
}

/// ValueHasExactlyOneBitSet - Test if the given value is known to have exactly
/// one bit set. This differs from ComputeMaskedBits in that it doesn't need to
/// determine which bit is set.
///
static bool ValueHasExactlyOneBitSet(SDValue Val, const SelectionDAG &DAG) {
  // A left-shift of a constant one will have exactly one bit set, because
  // shifting the bit off the end is undefined.
  if (Val.getOpcode() == ISD::SHL)
    if (ConstantSDNode *C =
         dyn_cast<ConstantSDNode>(Val.getNode()->getOperand(0)))
      if (C->getAPIntValue() == 1)
        return true;

  // Similarly, a right-shift of a constant sign-bit will have exactly
  // one bit set.
  if (Val.getOpcode() == ISD::SRL)
    if (ConstantSDNode *C =
         dyn_cast<ConstantSDNode>(Val.getNode()->getOperand(0)))
      if (C->getAPIntValue().isSignBit())
        return true;

  // More could be done here, though the above checks are enough
  // to handle some common cases.

  // Fall back to ComputeMaskedBits to catch other known cases.
  EVT OpVT = Val.getValueType();
  unsigned BitWidth = OpVT.getSizeInBits();
  APInt Mask = APInt::getAllOnesValue(BitWidth);
  APInt KnownZero, KnownOne;
  DAG.ComputeMaskedBits(Val, Mask, KnownZero, KnownOne);
  return (KnownZero.countPopulation() == BitWidth - 1) &&
         (KnownOne.countPopulation() == 1);
}

/// SimplifySetCC - Try to simplify a setcc built with the specified operands 
/// and cc. If it is unable to simplify it, return a null SDValue.
SDValue
TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
                              ISD::CondCode Cond, bool foldBooleans,
                              DAGCombinerInfo &DCI, DebugLoc dl) const {
  SelectionDAG &DAG = DCI.DAG;
  LLVMContext &Context = *DAG.getContext();

  // These setcc operations always fold.
  switch (Cond) {
  default: break;
  case ISD::SETFALSE:
  case ISD::SETFALSE2: return DAG.getConstant(0, VT);
  case ISD::SETTRUE:
  case ISD::SETTRUE2:  return DAG.getConstant(1, VT);
  }

  if (isa<ConstantSDNode>(N0.getNode())) {
    // Ensure that the constant occurs on the RHS, and fold constant
    // comparisons.
    return DAG.getSetCC(dl, VT, N1, N0, ISD::getSetCCSwappedOperands(Cond));
  }

  if (ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1.getNode())) {
    const APInt &C1 = N1C->getAPIntValue();

    // If the LHS is '(srl (ctlz x), 5)', the RHS is 0/1, and this is an
    // equality comparison, then we're just comparing whether X itself is
    // zero.
    if (N0.getOpcode() == ISD::SRL && (C1 == 0 || C1 == 1) &&
        N0.getOperand(0).getOpcode() == ISD::CTLZ &&
        N0.getOperand(1).getOpcode() == ISD::Constant) {
      unsigned ShAmt = cast<ConstantSDNode>(N0.getOperand(1))->getZExtValue();
      if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
          ShAmt == Log2_32(N0.getValueType().getSizeInBits())) {
        if ((C1 == 0) == (Cond == ISD::SETEQ)) {
          // (srl (ctlz x), 5) == 0  -> X != 0
          // (srl (ctlz x), 5) != 1  -> X != 0
          Cond = ISD::SETNE;
        } else {
          // (srl (ctlz x), 5) != 0  -> X == 0
          // (srl (ctlz x), 5) == 1  -> X == 0
          Cond = ISD::SETEQ;
        }
        SDValue Zero = DAG.getConstant(0, N0.getValueType());
        return DAG.getSetCC(dl, VT, N0.getOperand(0).getOperand(0),
                            Zero, Cond);
      }
    }

    // If the LHS is '(and load, const)', the RHS is 0,
    // the test is for equality or unsigned, and all 1 bits of the const are
    // in the same partial word, see if we can shorten the load.
    if (DCI.isBeforeLegalize() &&
        N0.getOpcode() == ISD::AND && C1 == 0 &&
        N0.getNode()->hasOneUse() &&
        isa<LoadSDNode>(N0.getOperand(0)) &&
        N0.getOperand(0).getNode()->hasOneUse() &&
        isa<ConstantSDNode>(N0.getOperand(1))) {
      LoadSDNode *Lod = cast<LoadSDNode>(N0.getOperand(0));
      uint64_t bestMask = 0;
      unsigned bestWidth = 0, bestOffset = 0;
      if (!Lod->isVolatile() && Lod->isUnindexed() &&
          // FIXME: This uses getZExtValue() below so it only works on i64 and
          // below.
          N0.getValueType().getSizeInBits() <= 64) {
        unsigned origWidth = N0.getValueType().getSizeInBits();
        // We can narrow (e.g.) 16-bit extending loads on 32-bit target to 
        // 8 bits, but have to be careful...
        if (Lod->getExtensionType() != ISD::NON_EXTLOAD)
          origWidth = Lod->getMemoryVT().getSizeInBits();
        uint64_t Mask =cast<ConstantSDNode>(N0.getOperand(1))->getZExtValue();
        for (unsigned width = origWidth / 2; width>=8; width /= 2) {
          uint64_t newMask = (1ULL << width) - 1;
          for (unsigned offset=0; offset<origWidth/width; offset++) {
            if ((newMask & Mask) == Mask) {
              if (!TD->isLittleEndian())
                bestOffset = (origWidth/width - offset - 1) * (width/8);
              else
                bestOffset = (uint64_t)offset * (width/8);
              bestMask = Mask >> (offset * (width/8) * 8);
              bestWidth = width;
              break;
            }
            newMask = newMask << width;
          }
        }
      }
      if (bestWidth) {
        EVT newVT = EVT::getIntegerVT(Context, bestWidth);
        if (newVT.isRound()) {
          EVT PtrType = Lod->getOperand(1).getValueType();
          SDValue Ptr = Lod->getBasePtr();
          if (bestOffset != 0)
            Ptr = DAG.getNode(ISD::ADD, dl, PtrType, Lod->getBasePtr(),
                              DAG.getConstant(bestOffset, PtrType));
          unsigned NewAlign = MinAlign(Lod->getAlignment(), bestOffset);
          SDValue NewLoad = DAG.getLoad(newVT, dl, Lod->getChain(), Ptr,
                                        Lod->getSrcValue(), 
                                        Lod->getSrcValueOffset() + bestOffset,
                                        false, NewAlign);
          return DAG.getSetCC(dl, VT, 
                              DAG.getNode(ISD::AND, dl, newVT, NewLoad,
                                          DAG.getConstant(bestMask, newVT)),
                              DAG.getConstant(0LL, newVT), Cond);
        }
      }
    }

    // If the LHS is a ZERO_EXTEND, perform the comparison on the input.
    if (N0.getOpcode() == ISD::ZERO_EXTEND) {
      unsigned InSize = N0.getOperand(0).getValueType().getSizeInBits();

      // If the comparison constant has bits in the upper part, the
      // zero-extended value could never match.
      if (C1.intersects(APInt::getHighBitsSet(C1.getBitWidth(),
                                              C1.getBitWidth() - InSize))) {
        switch (Cond) {
        case ISD::SETUGT:
        case ISD::SETUGE:
        case ISD::SETEQ: return DAG.getConstant(0, VT);
        case ISD::SETULT:
        case ISD::SETULE:
        case ISD::SETNE: return DAG.getConstant(1, VT);
        case ISD::SETGT:
        case ISD::SETGE:
          // True if the sign bit of C1 is set.
          return DAG.getConstant(C1.isNegative(), VT);
        case ISD::SETLT:
        case ISD::SETLE:
          // True if the sign bit of C1 isn't set.
          return DAG.getConstant(C1.isNonNegative(), VT);
        default:
          break;
        }
      }

      // Otherwise, we can perform the comparison with the low bits.
      switch (Cond) {
      case ISD::SETEQ:
      case ISD::SETNE:
      case ISD::SETUGT:
      case ISD::SETUGE:
      case ISD::SETULT:
      case ISD::SETULE: {
        EVT newVT = N0.getOperand(0).getValueType();
        if (DCI.isBeforeLegalizeOps() ||
            (isOperationLegal(ISD::SETCC, newVT) &&
              getCondCodeAction(Cond, newVT)==Legal))
          return DAG.getSetCC(dl, VT, N0.getOperand(0),
                              DAG.getConstant(APInt(C1).trunc(InSize), newVT),
                              Cond);
        break;
      }
      default:
        break;   // todo, be more careful with signed comparisons
      }
    } else if (N0.getOpcode() == ISD::SIGN_EXTEND_INREG &&
                (Cond == ISD::SETEQ || Cond == ISD::SETNE)) {
      EVT ExtSrcTy = cast<VTSDNode>(N0.getOperand(1))->getVT();
      unsigned ExtSrcTyBits = ExtSrcTy.getSizeInBits();
      EVT ExtDstTy = N0.getValueType();
      unsigned ExtDstTyBits = ExtDstTy.getSizeInBits();

      // If the extended part has any inconsistent bits, it cannot ever
      // compare equal.  In other words, they have to be all ones or all
      // zeros.
      APInt ExtBits =
        APInt::getHighBitsSet(ExtDstTyBits, ExtDstTyBits - ExtSrcTyBits);
      if ((C1 & ExtBits) != 0 && (C1 & ExtBits) != ExtBits)
        return DAG.getConstant(Cond == ISD::SETNE, VT);
      
      SDValue ZextOp;
      EVT Op0Ty = N0.getOperand(0).getValueType();
      if (Op0Ty == ExtSrcTy) {
        ZextOp = N0.getOperand(0);
      } else {
        APInt Imm = APInt::getLowBitsSet(ExtDstTyBits, ExtSrcTyBits);
        ZextOp = DAG.getNode(ISD::AND, dl, Op0Ty, N0.getOperand(0),
                              DAG.getConstant(Imm, Op0Ty));
      }
      if (!DCI.isCalledByLegalizer())
        DCI.AddToWorklist(ZextOp.getNode());
      // Otherwise, make this a use of a zext.
      return DAG.getSetCC(dl, VT, ZextOp, 
                          DAG.getConstant(C1 & APInt::getLowBitsSet(
                                                              ExtDstTyBits,
                                                              ExtSrcTyBits), 
                                          ExtDstTy),
                          Cond);
    } else if ((N1C->isNullValue() || N1C->getAPIntValue() == 1) &&
                (Cond == ISD::SETEQ || Cond == ISD::SETNE)) {
      
      // SETCC (SETCC), [0|1], [EQ|NE]  -> SETCC
      if (N0.getOpcode() == ISD::SETCC) {
        bool TrueWhenTrue = (Cond == ISD::SETEQ) ^ (N1C->getZExtValue() != 1);
        if (TrueWhenTrue)
          return N0;
        
        // Invert the condition.
        ISD::CondCode CC = cast<CondCodeSDNode>(N0.getOperand(2))->get();
        CC = ISD::getSetCCInverse(CC, 
                                  N0.getOperand(0).getValueType().isInteger());
        return DAG.getSetCC(dl, VT, N0.getOperand(0), N0.getOperand(1), CC);
      }
      
      if ((N0.getOpcode() == ISD::XOR ||
            (N0.getOpcode() == ISD::AND && 
            N0.getOperand(0).getOpcode() == ISD::XOR &&
            N0.getOperand(1) == N0.getOperand(0).getOperand(1))) &&
          isa<ConstantSDNode>(N0.getOperand(1)) &&
          cast<ConstantSDNode>(N0.getOperand(1))->getAPIntValue() == 1) {
        // If this is (X^1) == 0/1, swap the RHS and eliminate the xor.  We
        // can only do this if the top bits are known zero.
        unsigned BitWidth = N0.getValueSizeInBits();
        if (DAG.MaskedValueIsZero(N0,
                                  APInt::getHighBitsSet(BitWidth,
                                                        BitWidth-1))) {
          // Okay, get the un-inverted input value.
          SDValue Val;
          if (N0.getOpcode() == ISD::XOR)
            Val = N0.getOperand(0);
          else {
            assert(N0.getOpcode() == ISD::AND && 
                    N0.getOperand(0).getOpcode() == ISD::XOR);
            // ((X^1)&1)^1 -> X & 1
            Val = DAG.getNode(ISD::AND, dl, N0.getValueType(),
                              N0.getOperand(0).getOperand(0),
                              N0.getOperand(1));
          }
          return DAG.getSetCC(dl, VT, Val, N1,
                              Cond == ISD::SETEQ ? ISD::SETNE : ISD::SETEQ);
        }
      }
    }
    
    APInt MinVal, MaxVal;
    unsigned OperandBitSize = N1C->getValueType(0).getSizeInBits();
    if (ISD::isSignedIntSetCC(Cond)) {
      MinVal = APInt::getSignedMinValue(OperandBitSize);
      MaxVal = APInt::getSignedMaxValue(OperandBitSize);
    } else {
      MinVal = APInt::getMinValue(OperandBitSize);
      MaxVal = APInt::getMaxValue(OperandBitSize);
    }

    // Canonicalize GE/LE comparisons to use GT/LT comparisons.
    if (Cond == ISD::SETGE || Cond == ISD::SETUGE) {
      if (C1 == MinVal) return DAG.getConstant(1, VT);   // X >= MIN --> true
      // X >= C0 --> X > (C0-1)
      return DAG.getSetCC(dl, VT, N0, 
                          DAG.getConstant(C1-1, N1.getValueType()),
                          (Cond == ISD::SETGE) ? ISD::SETGT : ISD::SETUGT);
    }

    if (Cond == ISD::SETLE || Cond == ISD::SETULE) {
      if (C1 == MaxVal) return DAG.getConstant(1, VT);   // X <= MAX --> true
      // X <= C0 --> X < (C0+1)
      return DAG.getSetCC(dl, VT, N0, 
                          DAG.getConstant(C1+1, N1.getValueType()),
                          (Cond == ISD::SETLE) ? ISD::SETLT : ISD::SETULT);
    }

    if ((Cond == ISD::SETLT || Cond == ISD::SETULT) && C1 == MinVal)
      return DAG.getConstant(0, VT);      // X < MIN --> false
    if ((Cond == ISD::SETGE || Cond == ISD::SETUGE) && C1 == MinVal)
      return DAG.getConstant(1, VT);      // X >= MIN --> true
    if ((Cond == ISD::SETGT || Cond == ISD::SETUGT) && C1 == MaxVal)
      return DAG.getConstant(0, VT);      // X > MAX --> false
    if ((Cond == ISD::SETLE || Cond == ISD::SETULE) && C1 == MaxVal)
      return DAG.getConstant(1, VT);      // X <= MAX --> true

    // Canonicalize setgt X, Min --> setne X, Min
    if ((Cond == ISD::SETGT || Cond == ISD::SETUGT) && C1 == MinVal)
      return DAG.getSetCC(dl, VT, N0, N1, ISD::SETNE);
    // Canonicalize setlt X, Max --> setne X, Max
    if ((Cond == ISD::SETLT || Cond == ISD::SETULT) && C1 == MaxVal)
      return DAG.getSetCC(dl, VT, N0, N1, ISD::SETNE);

    // If we have setult X, 1, turn it into seteq X, 0
    if ((Cond == ISD::SETLT || Cond == ISD::SETULT) && C1 == MinVal+1)
      return DAG.getSetCC(dl, VT, N0, 
                          DAG.getConstant(MinVal, N0.getValueType()), 
                          ISD::SETEQ);
    // If we have setugt X, Max-1, turn it into seteq X, Max
    else if ((Cond == ISD::SETGT || Cond == ISD::SETUGT) && C1 == MaxVal-1)
      return DAG.getSetCC(dl, VT, N0, 
                          DAG.getConstant(MaxVal, N0.getValueType()),
                          ISD::SETEQ);

    // If we have "setcc X, C0", check to see if we can shrink the immediate
    // by changing cc.

    // SETUGT X, SINTMAX  -> SETLT X, 0
    if (Cond == ISD::SETUGT && 
        C1 == APInt::getSignedMaxValue(OperandBitSize))
      return DAG.getSetCC(dl, VT, N0, 
                          DAG.getConstant(0, N1.getValueType()),
                          ISD::SETLT);

    // SETULT X, SINTMIN  -> SETGT X, -1
    if (Cond == ISD::SETULT &&
        C1 == APInt::getSignedMinValue(OperandBitSize)) {
      SDValue ConstMinusOne =
          DAG.getConstant(APInt::getAllOnesValue(OperandBitSize),
                          N1.getValueType());
      return DAG.getSetCC(dl, VT, N0, ConstMinusOne, ISD::SETGT);
    }

    // Fold bit comparisons when we can.
    if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
        VT == N0.getValueType() && N0.getOpcode() == ISD::AND)
      if (ConstantSDNode *AndRHS =
                  dyn_cast<ConstantSDNode>(N0.getOperand(1))) {
        EVT ShiftTy = DCI.isBeforeLegalize() ?
          getPointerTy() : getShiftAmountTy();
        if (Cond == ISD::SETNE && C1 == 0) {// (X & 8) != 0  -->  (X & 8) >> 3
          // Perform the xform if the AND RHS is a single bit.
          if (isPowerOf2_64(AndRHS->getZExtValue())) {
            return DAG.getNode(ISD::SRL, dl, VT, N0,
                                DAG.getConstant(Log2_64(AndRHS->getZExtValue()),
                                                ShiftTy));
          }
        } else if (Cond == ISD::SETEQ && C1 == AndRHS->getZExtValue()) {
          // (X & 8) == 8  -->  (X & 8) >> 3
          // Perform the xform if C1 is a single bit.
          if (C1.isPowerOf2()) {
            return DAG.getNode(ISD::SRL, dl, VT, N0,
                                DAG.getConstant(C1.logBase2(), ShiftTy));
          }
        }
      }
  }

  if (isa<ConstantFPSDNode>(N0.getNode())) {
    // Constant fold or commute setcc.
    SDValue O = DAG.FoldSetCC(VT, N0, N1, Cond, dl);
    if (O.getNode()) return O;
  } else if (ConstantFPSDNode *CFP = dyn_cast<ConstantFPSDNode>(N1.getNode())) {
    // If the RHS of an FP comparison is a constant, simplify it away in
    // some cases.
    if (CFP->getValueAPF().isNaN()) {
      // If an operand is known to be a nan, we can fold it.
      switch (ISD::getUnorderedFlavor(Cond)) {
      default: llvm_unreachable("Unknown flavor!");
      case 0:  // Known false.
        return DAG.getConstant(0, VT);
      case 1:  // Known true.
        return DAG.getConstant(1, VT);
      case 2:  // Undefined.
        return DAG.getUNDEF(VT);
      }
    }
    
    // Otherwise, we know the RHS is not a NaN.  Simplify the node to drop the
    // constant if knowing that the operand is non-nan is enough.  We prefer to
    // have SETO(x,x) instead of SETO(x, 0.0) because this avoids having to
    // materialize 0.0.
    if (Cond == ISD::SETO || Cond == ISD::SETUO)
      return DAG.getSetCC(dl, VT, N0, N0, Cond);

    // If the condition is not legal, see if we can find an equivalent one
    // which is legal.
    if (!isCondCodeLegal(Cond, N0.getValueType())) {
      // If the comparison was an awkward floating-point == or != and one of
      // the comparison operands is infinity or negative infinity, convert the
      // condition to a less-awkward <= or >=.
      if (CFP->getValueAPF().isInfinity()) {
        if (CFP->getValueAPF().isNegative()) {
          if (Cond == ISD::SETOEQ &&
              isCondCodeLegal(ISD::SETOLE, N0.getValueType()))
            return DAG.getSetCC(dl, VT, N0, N1, ISD::SETOLE);
          if (Cond == ISD::SETUEQ &&
              isCondCodeLegal(ISD::SETOLE, N0.getValueType()))
            return DAG.getSetCC(dl, VT, N0, N1, ISD::SETULE);
          if (Cond == ISD::SETUNE &&
              isCondCodeLegal(ISD::SETUGT, N0.getValueType()))
            return DAG.getSetCC(dl, VT, N0, N1, ISD::SETUGT);
          if (Cond == ISD::SETONE &&
              isCondCodeLegal(ISD::SETUGT, N0.getValueType()))
            return DAG.getSetCC(dl, VT, N0, N1, ISD::SETOGT);
        } else {
          if (Cond == ISD::SETOEQ &&
              isCondCodeLegal(ISD::SETOGE, N0.getValueType()))
            return DAG.getSetCC(dl, VT, N0, N1, ISD::SETOGE);
          if (Cond == ISD::SETUEQ &&
              isCondCodeLegal(ISD::SETOGE, N0.getValueType()))
            return DAG.getSetCC(dl, VT, N0, N1, ISD::SETUGE);
          if (Cond == ISD::SETUNE &&
              isCondCodeLegal(ISD::SETULT, N0.getValueType()))
            return DAG.getSetCC(dl, VT, N0, N1, ISD::SETULT);
          if (Cond == ISD::SETONE &&
              isCondCodeLegal(ISD::SETULT, N0.getValueType()))
            return DAG.getSetCC(dl, VT, N0, N1, ISD::SETOLT);
        }
      }
    }
  }

  if (N0 == N1) {
    // We can always fold X == X for integer setcc's.
    if (N0.getValueType().isInteger())
      return DAG.getConstant(ISD::isTrueWhenEqual(Cond), VT);
    unsigned UOF = ISD::getUnorderedFlavor(Cond);
    if (UOF == 2)   // FP operators that are undefined on NaNs.
      return DAG.getConstant(ISD::isTrueWhenEqual(Cond), VT);
    if (UOF == unsigned(ISD::isTrueWhenEqual(Cond)))
      return DAG.getConstant(UOF, VT);
    // Otherwise, we can't fold it.  However, we can simplify it to SETUO/SETO
    // if it is not already.
    ISD::CondCode NewCond = UOF == 0 ? ISD::SETO : ISD::SETUO;
    if (NewCond != Cond)
      return DAG.getSetCC(dl, VT, N0, N1, NewCond);
  }

  if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
      N0.getValueType().isInteger()) {
    if (N0.getOpcode() == ISD::ADD || N0.getOpcode() == ISD::SUB ||
        N0.getOpcode() == ISD::XOR) {
      // Simplify (X+Y) == (X+Z) -->  Y == Z
      if (N0.getOpcode() == N1.getOpcode()) {
        if (N0.getOperand(0) == N1.getOperand(0))
          return DAG.getSetCC(dl, VT, N0.getOperand(1), N1.getOperand(1), Cond);
        if (N0.getOperand(1) == N1.getOperand(1))
          return DAG.getSetCC(dl, VT, N0.getOperand(0), N1.getOperand(0), Cond);
        if (DAG.isCommutativeBinOp(N0.getOpcode())) {
          // If X op Y == Y op X, try other combinations.
          if (N0.getOperand(0) == N1.getOperand(1))
            return DAG.getSetCC(dl, VT, N0.getOperand(1), N1.getOperand(0), 
                                Cond);
          if (N0.getOperand(1) == N1.getOperand(0))
            return DAG.getSetCC(dl, VT, N0.getOperand(0), N1.getOperand(1), 
                                Cond);
        }
      }
      
      if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(N1)) {
        if (ConstantSDNode *LHSR = dyn_cast<ConstantSDNode>(N0.getOperand(1))) {
          // Turn (X+C1) == C2 --> X == C2-C1
          if (N0.getOpcode() == ISD::ADD && N0.getNode()->hasOneUse()) {
            return DAG.getSetCC(dl, VT, N0.getOperand(0),
                                DAG.getConstant(RHSC->getAPIntValue()-
                                                LHSR->getAPIntValue(),
                                N0.getValueType()), Cond);
          }
          
          // Turn (X^C1) == C2 into X == C1^C2 iff X&~C1 = 0.
          if (N0.getOpcode() == ISD::XOR)
            // If we know that all of the inverted bits are zero, don't bother
            // performing the inversion.
            if (DAG.MaskedValueIsZero(N0.getOperand(0), ~LHSR->getAPIntValue()))
              return
                DAG.getSetCC(dl, VT, N0.getOperand(0),
                             DAG.getConstant(LHSR->getAPIntValue() ^
                                               RHSC->getAPIntValue(),
                                             N0.getValueType()),
                             Cond);
        }
        
        // Turn (C1-X) == C2 --> X == C1-C2
        if (ConstantSDNode *SUBC = dyn_cast<ConstantSDNode>(N0.getOperand(0))) {
          if (N0.getOpcode() == ISD::SUB && N0.getNode()->hasOneUse()) {
            return
              DAG.getSetCC(dl, VT, N0.getOperand(1),
                           DAG.getConstant(SUBC->getAPIntValue() -
                                             RHSC->getAPIntValue(),
                                           N0.getValueType()),
                           Cond);
          }
        }          
      }

      // Simplify (X+Z) == X -->  Z == 0
      if (N0.getOperand(0) == N1)
        return DAG.getSetCC(dl, VT, N0.getOperand(1),
                        DAG.getConstant(0, N0.getValueType()), Cond);
      if (N0.getOperand(1) == N1) {
        if (DAG.isCommutativeBinOp(N0.getOpcode()))
          return DAG.getSetCC(dl, VT, N0.getOperand(0),
                          DAG.getConstant(0, N0.getValueType()), Cond);
        else if (N0.getNode()->hasOneUse()) {
          assert(N0.getOpcode() == ISD::SUB && "Unexpected operation!");
          // (Z-X) == X  --> Z == X<<1
          SDValue SH = DAG.getNode(ISD::SHL, dl, N1.getValueType(),
                                     N1, 
                                     DAG.getConstant(1, getShiftAmountTy()));
          if (!DCI.isCalledByLegalizer())
            DCI.AddToWorklist(SH.getNode());
          return DAG.getSetCC(dl, VT, N0.getOperand(0), SH, Cond);
        }
      }
    }

    if (N1.getOpcode() == ISD::ADD || N1.getOpcode() == ISD::SUB ||
        N1.getOpcode() == ISD::XOR) {
      // Simplify  X == (X+Z) -->  Z == 0
      if (N1.getOperand(0) == N0) {
        return DAG.getSetCC(dl, VT, N1.getOperand(1),
                        DAG.getConstant(0, N1.getValueType()), Cond);
      } else if (N1.getOperand(1) == N0) {
        if (DAG.isCommutativeBinOp(N1.getOpcode())) {
          return DAG.getSetCC(dl, VT, N1.getOperand(0),
                          DAG.getConstant(0, N1.getValueType()), Cond);
        } else if (N1.getNode()->hasOneUse()) {
          assert(N1.getOpcode() == ISD::SUB && "Unexpected operation!");
          // X == (Z-X)  --> X<<1 == Z
          SDValue SH = DAG.getNode(ISD::SHL, dl, N1.getValueType(), N0, 
                                     DAG.getConstant(1, getShiftAmountTy()));
          if (!DCI.isCalledByLegalizer())
            DCI.AddToWorklist(SH.getNode());
          return DAG.getSetCC(dl, VT, SH, N1.getOperand(0), Cond);
        }
      }
    }

    // Simplify x&y == y to x&y != 0 if y has exactly one bit set.
    // Note that where y is variable and is known to have at most
    // one bit set (for example, if it is z&1) we cannot do this;
    // the expressions are not equivalent when y==0.
    if (N0.getOpcode() == ISD::AND)
      if (N0.getOperand(0) == N1 || N0.getOperand(1) == N1) {
        if (ValueHasExactlyOneBitSet(N1, DAG)) {
          Cond = ISD::getSetCCInverse(Cond, /*isInteger=*/true);
          SDValue Zero = DAG.getConstant(0, N1.getValueType());
          return DAG.getSetCC(dl, VT, N0, Zero, Cond);
        }
      }
    if (N1.getOpcode() == ISD::AND)
      if (N1.getOperand(0) == N0 || N1.getOperand(1) == N0) {
        if (ValueHasExactlyOneBitSet(N0, DAG)) {
          Cond = ISD::getSetCCInverse(Cond, /*isInteger=*/true);
          SDValue Zero = DAG.getConstant(0, N0.getValueType());
          return DAG.getSetCC(dl, VT, N1, Zero, Cond);
        }
      }
  }

  // Fold away ALL boolean setcc's.
  SDValue Temp;
  if (N0.getValueType() == MVT::i1 && foldBooleans) {
    switch (Cond) {
    default: llvm_unreachable("Unknown integer setcc!");
    case ISD::SETEQ:  // X == Y  -> ~(X^Y)
      Temp = DAG.getNode(ISD::XOR, dl, MVT::i1, N0, N1);
      N0 = DAG.getNOT(dl, Temp, MVT::i1);
      if (!DCI.isCalledByLegalizer())
        DCI.AddToWorklist(Temp.getNode());
      break;
    case ISD::SETNE:  // X != Y   -->  (X^Y)
      N0 = DAG.getNode(ISD::XOR, dl, MVT::i1, N0, N1);
      break;
    case ISD::SETGT:  // X >s Y   -->  X == 0 & Y == 1  -->  ~X & Y
    case ISD::SETULT: // X <u Y   -->  X == 0 & Y == 1  -->  ~X & Y
      Temp = DAG.getNOT(dl, N0, MVT::i1);
      N0 = DAG.getNode(ISD::AND, dl, MVT::i1, N1, Temp);
      if (!DCI.isCalledByLegalizer())
        DCI.AddToWorklist(Temp.getNode());
      break;
    case ISD::SETLT:  // X <s Y   --> X == 1 & Y == 0  -->  ~Y & X
    case ISD::SETUGT: // X >u Y   --> X == 1 & Y == 0  -->  ~Y & X
      Temp = DAG.getNOT(dl, N1, MVT::i1);
      N0 = DAG.getNode(ISD::AND, dl, MVT::i1, N0, Temp);
      if (!DCI.isCalledByLegalizer())
        DCI.AddToWorklist(Temp.getNode());
      break;
    case ISD::SETULE: // X <=u Y  --> X == 0 | Y == 1  -->  ~X | Y
    case ISD::SETGE:  // X >=s Y  --> X == 0 | Y == 1  -->  ~X | Y
      Temp = DAG.getNOT(dl, N0, MVT::i1);
      N0 = DAG.getNode(ISD::OR, dl, MVT::i1, N1, Temp);
      if (!DCI.isCalledByLegalizer())
        DCI.AddToWorklist(Temp.getNode());
      break;
    case ISD::SETUGE: // X >=u Y  --> X == 1 | Y == 0  -->  ~Y | X
    case ISD::SETLE:  // X <=s Y  --> X == 1 | Y == 0  -->  ~Y | X
      Temp = DAG.getNOT(dl, N1, MVT::i1);
      N0 = DAG.getNode(ISD::OR, dl, MVT::i1, N0, Temp);
      break;
    }
    if (VT != MVT::i1) {
      if (!DCI.isCalledByLegalizer())
        DCI.AddToWorklist(N0.getNode());
      // FIXME: If running after legalize, we probably can't do this.
      N0 = DAG.getNode(ISD::ZERO_EXTEND, dl, VT, N0);
    }
    return N0;
  }

  // Could not fold it.
  return SDValue();
}

/// isGAPlusOffset - Returns true (and the GlobalValue and the offset) if the
/// node is a GlobalAddress + offset.
bool TargetLowering::isGAPlusOffset(SDNode *N, GlobalValue* &GA,
                                    int64_t &Offset) const {
  if (isa<GlobalAddressSDNode>(N)) {
    GlobalAddressSDNode *GASD = cast<GlobalAddressSDNode>(N);
    GA = GASD->getGlobal();
    Offset += GASD->getOffset();
    return true;
  }

  if (N->getOpcode() == ISD::ADD) {
    SDValue N1 = N->getOperand(0);
    SDValue N2 = N->getOperand(1);
    if (isGAPlusOffset(N1.getNode(), GA, Offset)) {
      ConstantSDNode *V = dyn_cast<ConstantSDNode>(N2);
      if (V) {
        Offset += V->getSExtValue();
        return true;
      }
    } else if (isGAPlusOffset(N2.getNode(), GA, Offset)) {
      ConstantSDNode *V = dyn_cast<ConstantSDNode>(N1);
      if (V) {
        Offset += V->getSExtValue();
        return true;
      }
    }
  }
  return false;
}


/// isConsecutiveLoad - Return true if LD is loading 'Bytes' bytes from a 
/// location that is 'Dist' units away from the location that the 'Base' load 
/// is loading from.
bool TargetLowering::isConsecutiveLoad(LoadSDNode *LD, LoadSDNode *Base, 
                                       unsigned Bytes, int Dist, 
                                       const MachineFrameInfo *MFI) const {
  if (LD->getChain() != Base->getChain())
    return false;
  EVT VT = LD->getValueType(0);
  if (VT.getSizeInBits() / 8 != Bytes)
    return false;

  SDValue Loc = LD->getOperand(1);
  SDValue BaseLoc = Base->getOperand(1);
  if (Loc.getOpcode() == ISD::FrameIndex) {
    if (BaseLoc.getOpcode() != ISD::FrameIndex)
      return false;
    int FI  = cast<FrameIndexSDNode>(Loc)->getIndex();
    int BFI = cast<FrameIndexSDNode>(BaseLoc)->getIndex();
    int FS  = MFI->getObjectSize(FI);
    int BFS = MFI->getObjectSize(BFI);
    if (FS != BFS || FS != (int)Bytes) return false;
    return MFI->getObjectOffset(FI) == (MFI->getObjectOffset(BFI) + Dist*Bytes);
  }
  if (Loc.getOpcode() == ISD::ADD && Loc.getOperand(0) == BaseLoc) {
    ConstantSDNode *V = dyn_cast<ConstantSDNode>(Loc.getOperand(1));
    if (V && (V->getSExtValue() == Dist*Bytes))
      return true;
  }

  GlobalValue *GV1 = NULL;
  GlobalValue *GV2 = NULL;
  int64_t Offset1 = 0;
  int64_t Offset2 = 0;
  bool isGA1 = isGAPlusOffset(Loc.getNode(), GV1, Offset1);
  bool isGA2 = isGAPlusOffset(BaseLoc.getNode(), GV2, Offset2);
  if (isGA1 && isGA2 && GV1 == GV2)
    return Offset1 == (Offset2 + Dist*Bytes);
  return false;
}


SDValue TargetLowering::
PerformDAGCombine(SDNode *N, DAGCombinerInfo &DCI) const {
  // Default implementation: no optimization.
  return SDValue();
}

//===----------------------------------------------------------------------===//
//  Inline Assembler Implementation Methods
//===----------------------------------------------------------------------===//


TargetLowering::ConstraintType
TargetLowering::getConstraintType(const std::string &Constraint) const {
  // FIXME: lots more standard ones to handle.
  if (Constraint.size() == 1) {
    switch (Constraint[0]) {
    default: break;
    case 'r': return C_RegisterClass;
    case 'm':    // memory
    case 'o':    // offsetable
    case 'V':    // not offsetable
      return C_Memory;
    case 'i':    // Simple Integer or Relocatable Constant
    case 'n':    // Simple Integer
    case 's':    // Relocatable Constant
    case 'X':    // Allow ANY value.
    case 'I':    // Target registers.
    case 'J':
    case 'K':
    case 'L':
    case 'M':
    case 'N':
    case 'O':
    case 'P':
      return C_Other;
    }
  }
  
  if (Constraint.size() > 1 && Constraint[0] == '{' && 
      Constraint[Constraint.size()-1] == '}')
    return C_Register;
  return C_Unknown;
}

/// LowerXConstraint - try to replace an X constraint, which matches anything,
/// with another that has more specific requirements based on the type of the
/// corresponding operand.
const char *TargetLowering::LowerXConstraint(EVT ConstraintVT) const{
  if (ConstraintVT.isInteger())
    return "r";
  if (ConstraintVT.isFloatingPoint())
    return "f";      // works for many targets
  return 0;
}

/// LowerAsmOperandForConstraint - Lower the specified operand into the Ops
/// vector.  If it is invalid, don't add anything to Ops.
void TargetLowering::LowerAsmOperandForConstraint(SDValue Op,
                                                  char ConstraintLetter,
                                                  bool hasMemory,
                                                  std::vector<SDValue> &Ops,
                                                  SelectionDAG &DAG) const {
  switch (ConstraintLetter) {
  default: break;
  case 'X':     // Allows any operand; labels (basic block) use this.
    if (Op.getOpcode() == ISD::BasicBlock) {
      Ops.push_back(Op);
      return;
    }
    // fall through
  case 'i':    // Simple Integer or Relocatable Constant
  case 'n':    // Simple Integer
  case 's': {  // Relocatable Constant
    // These operands are interested in values of the form (GV+C), where C may
    // be folded in as an offset of GV, or it may be explicitly added.  Also, it
    // is possible and fine if either GV or C are missing.
    ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op);
    GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(Op);
    
    // If we have "(add GV, C)", pull out GV/C
    if (Op.getOpcode() == ISD::ADD) {
      C = dyn_cast<ConstantSDNode>(Op.getOperand(1));
      GA = dyn_cast<GlobalAddressSDNode>(Op.getOperand(0));
      if (C == 0 || GA == 0) {
        C = dyn_cast<ConstantSDNode>(Op.getOperand(0));
        GA = dyn_cast<GlobalAddressSDNode>(Op.getOperand(1));
      }
      if (C == 0 || GA == 0)
        C = 0, GA = 0;
    }
    
    // If we find a valid operand, map to the TargetXXX version so that the
    // value itself doesn't get selected.
    if (GA) {   // Either &GV   or   &GV+C
      if (ConstraintLetter != 'n') {
        int64_t Offs = GA->getOffset();
        if (C) Offs += C->getZExtValue();
        Ops.push_back(DAG.getTargetGlobalAddress(GA->getGlobal(),
                                                 Op.getValueType(), Offs));
        return;
      }
    }
    if (C) {   // just C, no GV.
      // Simple constants are not allowed for 's'.
      if (ConstraintLetter != 's') {
        // gcc prints these as sign extended.  Sign extend value to 64 bits
        // now; without this it would get ZExt'd later in
        // ScheduleDAGSDNodes::EmitNode, which is very generic.
        Ops.push_back(DAG.getTargetConstant(C->getAPIntValue().getSExtValue(),
                                            MVT::i64));
        return;
      }
    }
    break;
  }
  }
}

std::vector<unsigned> TargetLowering::
getRegClassForInlineAsmConstraint(const std::string &Constraint,
                                  EVT VT) const {
  return std::vector<unsigned>();
}


std::pair<unsigned, const TargetRegisterClass*> TargetLowering::
getRegForInlineAsmConstraint(const std::string &Constraint,
                             EVT VT) const {
  if (Constraint[0] != '{')
    return std::pair<unsigned, const TargetRegisterClass*>(0, 0);
  assert(*(Constraint.end()-1) == '}' && "Not a brace enclosed constraint?");

  // Remove the braces from around the name.
  std::string RegName(Constraint.begin()+1, Constraint.end()-1);

  // Figure out which register class contains this reg.
  const TargetRegisterInfo *RI = TM.getRegisterInfo();
  for (TargetRegisterInfo::regclass_iterator RCI = RI->regclass_begin(),
       E = RI->regclass_end(); RCI != E; ++RCI) {
    const TargetRegisterClass *RC = *RCI;
    
    // If none of the the value types for this register class are valid, we 
    // can't use it.  For example, 64-bit reg classes on 32-bit targets.
    bool isLegal = false;
    for (TargetRegisterClass::vt_iterator I = RC->vt_begin(), E = RC->vt_end();
         I != E; ++I) {
      if (isTypeLegal(*I)) {
        isLegal = true;
        break;
      }
    }
    
    if (!isLegal) continue;
    
    for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); 
         I != E; ++I) {
      if (StringsEqualNoCase(RegName, RI->getName(*I)))
        return std::make_pair(*I, RC);
    }
  }
  
  return std::pair<unsigned, const TargetRegisterClass*>(0, 0);
}

//===----------------------------------------------------------------------===//
// Constraint Selection.

/// isMatchingInputConstraint - Return true of this is an input operand that is
/// a matching constraint like "4".
bool TargetLowering::AsmOperandInfo::isMatchingInputConstraint() const {
  assert(!ConstraintCode.empty() && "No known constraint!");
  return isdigit(ConstraintCode[0]);
}

/// getMatchedOperand - If this is an input matching constraint, this method
/// returns the output operand it matches.
unsigned TargetLowering::AsmOperandInfo::getMatchedOperand() const {
  assert(!ConstraintCode.empty() && "No known constraint!");
  return atoi(ConstraintCode.c_str());
}


/// getConstraintGenerality - Return an integer indicating how general CT
/// is.
static unsigned getConstraintGenerality(TargetLowering::ConstraintType CT) {
  switch (CT) {
  default: llvm_unreachable("Unknown constraint type!");
  case TargetLowering::C_Other:
  case TargetLowering::C_Unknown:
    return 0;
  case TargetLowering::C_Register:
    return 1;
  case TargetLowering::C_RegisterClass:
    return 2;
  case TargetLowering::C_Memory:
    return 3;
  }
}

/// ChooseConstraint - If there are multiple different constraints that we
/// could pick for this operand (e.g. "imr") try to pick the 'best' one.
/// This is somewhat tricky: constraints fall into four classes:
///    Other         -> immediates and magic values
///    Register      -> one specific register
///    RegisterClass -> a group of regs
///    Memory        -> memory
/// Ideally, we would pick the most specific constraint possible: if we have
/// something that fits into a register, we would pick it.  The problem here
/// is that if we have something that could either be in a register or in
/// memory that use of the register could cause selection of *other*
/// operands to fail: they might only succeed if we pick memory.  Because of
/// this the heuristic we use is:
///
///  1) If there is an 'other' constraint, and if the operand is valid for
///     that constraint, use it.  This makes us take advantage of 'i'
///     constraints when available.
///  2) Otherwise, pick the most general constraint present.  This prefers
///     'm' over 'r', for example.
///
static void ChooseConstraint(TargetLowering::AsmOperandInfo &OpInfo,
                             bool hasMemory,  const TargetLowering &TLI,
                             SDValue Op, SelectionDAG *DAG) {
  assert(OpInfo.Codes.size() > 1 && "Doesn't have multiple constraint options");
  unsigned BestIdx = 0;
  TargetLowering::ConstraintType BestType = TargetLowering::C_Unknown;
  int BestGenerality = -1;
  
  // Loop over the options, keeping track of the most general one.
  for (unsigned i = 0, e = OpInfo.Codes.size(); i != e; ++i) {
    TargetLowering::ConstraintType CType =
      TLI.getConstraintType(OpInfo.Codes[i]);
    
    // If this is an 'other' constraint, see if the operand is valid for it.
    // For example, on X86 we might have an 'rI' constraint.  If the operand
    // is an integer in the range [0..31] we want to use I (saving a load
    // of a register), otherwise we must use 'r'.
    if (CType == TargetLowering::C_Other && Op.getNode()) {
      assert(OpInfo.Codes[i].size() == 1 &&
             "Unhandled multi-letter 'other' constraint");
      std::vector<SDValue> ResultOps;
      TLI.LowerAsmOperandForConstraint(Op, OpInfo.Codes[i][0], hasMemory,
                                       ResultOps, *DAG);
      if (!ResultOps.empty()) {
        BestType = CType;
        BestIdx = i;
        break;
      }
    }
    
    // This constraint letter is more general than the previous one, use it.
    int Generality = getConstraintGenerality(CType);
    if (Generality > BestGenerality) {
      BestType = CType;
      BestIdx = i;
      BestGenerality = Generality;
    }
  }
  
  OpInfo.ConstraintCode = OpInfo.Codes[BestIdx];
  OpInfo.ConstraintType = BestType;
}

/// ComputeConstraintToUse - Determines the constraint code and constraint
/// type to use for the specific AsmOperandInfo, setting
/// OpInfo.ConstraintCode and OpInfo.ConstraintType.
void TargetLowering::ComputeConstraintToUse(AsmOperandInfo &OpInfo,
                                            SDValue Op, 
                                            bool hasMemory,
                                            SelectionDAG *DAG) const {
  assert(!OpInfo.Codes.empty() && "Must have at least one constraint");
  
  // Single-letter constraints ('r') are very common.
  if (OpInfo.Codes.size() == 1) {
    OpInfo.ConstraintCode = OpInfo.Codes[0];
    OpInfo.ConstraintType = getConstraintType(OpInfo.ConstraintCode);
  } else {
    ChooseConstraint(OpInfo, hasMemory, *this, Op, DAG);
  }
  
  // 'X' matches anything.
  if (OpInfo.ConstraintCode == "X" && OpInfo.CallOperandVal) {
    // Labels and constants are handled elsewhere ('X' is the only thing
    // that matches labels).  For Functions, the type here is the type of
    // the result, which is not what we want to look at; leave them alone.
    Value *v = OpInfo.CallOperandVal;
    if (isa<BasicBlock>(v) || isa<ConstantInt>(v) || isa<Function>(v)) {
      OpInfo.CallOperandVal = v;
      return;
    }
    
    // Otherwise, try to resolve it to something we know about by looking at
    // the actual operand type.
    if (const char *Repl = LowerXConstraint(OpInfo.ConstraintVT)) {
      OpInfo.ConstraintCode = Repl;
      OpInfo.ConstraintType = getConstraintType(OpInfo.ConstraintCode);
    }
  }
}

//===----------------------------------------------------------------------===//
//  Loop Strength Reduction hooks
//===----------------------------------------------------------------------===//

/// isLegalAddressingMode - Return true if the addressing mode represented
/// by AM is legal for this target, for a load/store of the specified type.
bool TargetLowering::isLegalAddressingMode(const AddrMode &AM, 
                                           const Type *Ty) const {
  // The default implementation of this implements a conservative RISCy, r+r and
  // r+i addr mode.

  // Allows a sign-extended 16-bit immediate field.
  if (AM.BaseOffs <= -(1LL << 16) || AM.BaseOffs >= (1LL << 16)-1)
    return false;
  
  // No global is ever allowed as a base.
  if (AM.BaseGV)
    return false;
  
  // Only support r+r, 
  switch (AM.Scale) {
  case 0:  // "r+i" or just "i", depending on HasBaseReg.
    break;
  case 1:
    if (AM.HasBaseReg && AM.BaseOffs)  // "r+r+i" is not allowed.
      return false;
    // Otherwise we have r+r or r+i.
    break;
  case 2:
    if (AM.HasBaseReg || AM.BaseOffs)  // 2*r+r  or  2*r+i is not allowed.
      return false;
    // Allow 2*r as r+r.
    break;
  }
  
  return true;
}

/// BuildSDIVSequence - Given an ISD::SDIV node expressing a divide by constant,
/// return a DAG expression to select that will generate the same value by
/// multiplying by a magic number.  See:
/// <http://the.wall.riscom.net/books/proc/ppc/cwg/code2.html>
SDValue TargetLowering::BuildSDIV(SDNode *N, SelectionDAG &DAG, 
                                  std::vector<SDNode*>* Created) const {
  EVT VT = N->getValueType(0);
  DebugLoc dl= N->getDebugLoc();
  
  // Check to see if we can do this.
  // FIXME: We should be more aggressive here.
  if (!isTypeLegal(VT))
    return SDValue();
  
  APInt d = cast<ConstantSDNode>(N->getOperand(1))->getAPIntValue();
  APInt::ms magics = d.magic();
  
  // Multiply the numerator (operand 0) by the magic value
  // FIXME: We should support doing a MUL in a wider type
  SDValue Q;
  if (isOperationLegalOrCustom(ISD::MULHS, VT))
    Q = DAG.getNode(ISD::MULHS, dl, VT, N->getOperand(0),
                    DAG.getConstant(magics.m, VT));
  else if (isOperationLegalOrCustom(ISD::SMUL_LOHI, VT))
    Q = SDValue(DAG.getNode(ISD::SMUL_LOHI, dl, DAG.getVTList(VT, VT),
                              N->getOperand(0),
                              DAG.getConstant(magics.m, VT)).getNode(), 1);
  else
    return SDValue();       // No mulhs or equvialent
  // If d > 0 and m < 0, add the numerator
  if (d.isStrictlyPositive() && magics.m.isNegative()) { 
    Q = DAG.getNode(ISD::ADD, dl, VT, Q, N->getOperand(0));
    if (Created)
      Created->push_back(Q.getNode());
  }
  // If d < 0 and m > 0, subtract the numerator.
  if (d.isNegative() && magics.m.isStrictlyPositive()) {
    Q = DAG.getNode(ISD::SUB, dl, VT, Q, N->getOperand(0));
    if (Created)
      Created->push_back(Q.getNode());
  }
  // Shift right algebraic if shift value is nonzero
  if (magics.s > 0) {
    Q = DAG.getNode(ISD::SRA, dl, VT, Q, 
                    DAG.getConstant(magics.s, getShiftAmountTy()));
    if (Created)
      Created->push_back(Q.getNode());
  }
  // Extract the sign bit and add it to the quotient
  SDValue T =
    DAG.getNode(ISD::SRL, dl, VT, Q, DAG.getConstant(VT.getSizeInBits()-1,
                                                 getShiftAmountTy()));
  if (Created)
    Created->push_back(T.getNode());
  return DAG.getNode(ISD::ADD, dl, VT, Q, T);
}

/// BuildUDIVSequence - Given an ISD::UDIV node expressing a divide by constant,
/// return a DAG expression to select that will generate the same value by
/// multiplying by a magic number.  See:
/// <http://the.wall.riscom.net/books/proc/ppc/cwg/code2.html>
SDValue TargetLowering::BuildUDIV(SDNode *N, SelectionDAG &DAG,
                                  std::vector<SDNode*>* Created) const {
  EVT VT = N->getValueType(0);
  DebugLoc dl = N->getDebugLoc();

  // Check to see if we can do this.
  // FIXME: We should be more aggressive here.
  if (!isTypeLegal(VT))
    return SDValue();

  // FIXME: We should use a narrower constant when the upper
  // bits are known to be zero.
  ConstantSDNode *N1C = cast<ConstantSDNode>(N->getOperand(1));
  APInt::mu magics = N1C->getAPIntValue().magicu();

  // Multiply the numerator (operand 0) by the magic value
  // FIXME: We should support doing a MUL in a wider type
  SDValue Q;
  if (isOperationLegalOrCustom(ISD::MULHU, VT))
    Q = DAG.getNode(ISD::MULHU, dl, VT, N->getOperand(0),
                    DAG.getConstant(magics.m, VT));
  else if (isOperationLegalOrCustom(ISD::UMUL_LOHI, VT))
    Q = SDValue(DAG.getNode(ISD::UMUL_LOHI, dl, DAG.getVTList(VT, VT),
                              N->getOperand(0),
                              DAG.getConstant(magics.m, VT)).getNode(), 1);
  else
    return SDValue();       // No mulhu or equvialent
  if (Created)
    Created->push_back(Q.getNode());

  if (magics.a == 0) {
    assert(magics.s < N1C->getAPIntValue().getBitWidth() &&
           "We shouldn't generate an undefined shift!");
    return DAG.getNode(ISD::SRL, dl, VT, Q, 
                       DAG.getConstant(magics.s, getShiftAmountTy()));
  } else {
    SDValue NPQ = DAG.getNode(ISD::SUB, dl, VT, N->getOperand(0), Q);
    if (Created)
      Created->push_back(NPQ.getNode());
    NPQ = DAG.getNode(ISD::SRL, dl, VT, NPQ, 
                      DAG.getConstant(1, getShiftAmountTy()));
    if (Created)
      Created->push_back(NPQ.getNode());
    NPQ = DAG.getNode(ISD::ADD, dl, VT, NPQ, Q);
    if (Created)
      Created->push_back(NPQ.getNode());
    return DAG.getNode(ISD::SRL, dl, VT, NPQ, 
                       DAG.getConstant(magics.s-1, getShiftAmountTy()));
  }
}