SelectionDAGNodes.h

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//===-- llvm/CodeGen/SelectionDAGNodes.h - SelectionDAG Nodes ---*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file declares the SDNode class and derived classes, which are used to
// represent the nodes and operations present in a SelectionDAG.  These nodes
// and operations are machine code level operations, with some similarities to
// the GCC RTL representation.
//
// Clients should include the SelectionDAG.h file instead of this file directly.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_SELECTIONDAGNODES_H
#define LLVM_CODEGEN_SELECTIONDAGNODES_H

#include "llvm/Constants.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/iterator.h"
#include "llvm/ADT/ilist_node.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/ValueTypes.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/RecyclingAllocator.h"
#include "llvm/Support/DataTypes.h"
#include <cassert>

namespace llvm {

class SelectionDAG;
class GlobalValue;
class MachineBasicBlock;
class MachineConstantPoolValue;
class SDNode;
class CompileUnitDesc;
template <typename T> struct DenseMapInfo;
template <typename T> struct simplify_type;
template <typename T> struct ilist_traits;

/// SDVTList - This represents a list of ValueType's that has been intern'd by
/// a SelectionDAG.  Instances of this simple value class are returned by
/// SelectionDAG::getVTList(...).
///
struct SDVTList {
  const MVT *VTs;
  unsigned short NumVTs;
};

/// ISD namespace - This namespace contains an enum which represents all of the
/// SelectionDAG node types and value types.
///
namespace ISD {

  //===--------------------------------------------------------------------===//
  /// ISD::NodeType enum - This enum defines all of the operators valid in a
  /// SelectionDAG.
  ///
  enum NodeType {
    // DELETED_NODE - This is an illegal flag value that is used to catch
    // errors.  This opcode is not a legal opcode for any node.
    DELETED_NODE,
    
    // EntryToken - This is the marker used to indicate the start of the region.
    EntryToken,

    // TokenFactor - This node takes multiple tokens as input and produces a
    // single token result.  This is used to represent the fact that the operand
    // operators are independent of each other.
    TokenFactor,
    
    // AssertSext, AssertZext - These nodes record if a register contains a 
    // value that has already been zero or sign extended from a narrower type.  
    // These nodes take two operands.  The first is the node that has already 
    // been extended, and the second is a value type node indicating the width
    // of the extension
    AssertSext, AssertZext,

    // Various leaf nodes.
    BasicBlock, VALUETYPE, ARG_FLAGS, CONDCODE, Register,
    Constant, ConstantFP,
    GlobalAddress, GlobalTLSAddress, FrameIndex,
    JumpTable, ConstantPool, ExternalSymbol,

    // The address of the GOT
    GLOBAL_OFFSET_TABLE,
    
    // FRAMEADDR, RETURNADDR - These nodes represent llvm.frameaddress and
    // llvm.returnaddress on the DAG.  These nodes take one operand, the index
    // of the frame or return address to return.  An index of zero corresponds
    // to the current function's frame or return address, an index of one to the
    // parent's frame or return address, and so on.
    FRAMEADDR, RETURNADDR,

    // FRAME_TO_ARGS_OFFSET - This node represents offset from frame pointer to
    // first (possible) on-stack argument. This is needed for correct stack
    // adjustment during unwind.
    FRAME_TO_ARGS_OFFSET,
    
    // RESULT, OUTCHAIN = EXCEPTIONADDR(INCHAIN) - This node represents the
    // address of the exception block on entry to an landing pad block.
    EXCEPTIONADDR,
    
    // RESULT, OUTCHAIN = EHSELECTION(INCHAIN, EXCEPTION) - This node represents
    // the selection index of the exception thrown.
    EHSELECTION,

    // OUTCHAIN = EH_RETURN(INCHAIN, OFFSET, HANDLER) - This node represents
    // 'eh_return' gcc dwarf builtin, which is used to return from
    // exception. The general meaning is: adjust stack by OFFSET and pass
    // execution to HANDLER. Many platform-related details also :)
    EH_RETURN,

    // TargetConstant* - Like Constant*, but the DAG does not do any folding or
    // simplification of the constant.
    TargetConstant,
    TargetConstantFP,
    
    // TargetGlobalAddress - Like GlobalAddress, but the DAG does no folding or
    // anything else with this node, and this is valid in the target-specific
    // dag, turning into a GlobalAddress operand.
    TargetGlobalAddress,
    TargetGlobalTLSAddress,
    TargetFrameIndex,
    TargetJumpTable,
    TargetConstantPool,
    TargetExternalSymbol,
    
    /// RESULT = INTRINSIC_WO_CHAIN(INTRINSICID, arg1, arg2, ...)
    /// This node represents a target intrinsic function with no side effects.
    /// The first operand is the ID number of the intrinsic from the
    /// llvm::Intrinsic namespace.  The operands to the intrinsic follow.  The
    /// node has returns the result of the intrinsic.
    INTRINSIC_WO_CHAIN,
    
    /// RESULT,OUTCHAIN = INTRINSIC_W_CHAIN(INCHAIN, INTRINSICID, arg1, ...)
    /// This node represents a target intrinsic function with side effects that
    /// returns a result.  The first operand is a chain pointer.  The second is
    /// the ID number of the intrinsic from the llvm::Intrinsic namespace.  The
    /// operands to the intrinsic follow.  The node has two results, the result
    /// of the intrinsic and an output chain.
    INTRINSIC_W_CHAIN,

    /// OUTCHAIN = INTRINSIC_VOID(INCHAIN, INTRINSICID, arg1, arg2, ...)
    /// This node represents a target intrinsic function with side effects that
    /// does not return a result.  The first operand is a chain pointer.  The
    /// second is the ID number of the intrinsic from the llvm::Intrinsic
    /// namespace.  The operands to the intrinsic follow.
    INTRINSIC_VOID,
    
    // CopyToReg - This node has three operands: a chain, a register number to
    // set to this value, and a value.  
    CopyToReg,

    // CopyFromReg - This node indicates that the input value is a virtual or
    // physical register that is defined outside of the scope of this
    // SelectionDAG.  The register is available from the RegisterSDNode object.
    CopyFromReg,

    // UNDEF - An undefined node
    UNDEF,
    
    /// FORMAL_ARGUMENTS(CHAIN, CC#, ISVARARG, FLAG0, ..., FLAGn) - This node
    /// represents the formal arguments for a function.  CC# is a Constant value
    /// indicating the calling convention of the function, and ISVARARG is a
    /// flag that indicates whether the function is varargs or not. This node
    /// has one result value for each incoming argument, plus one for the output
    /// chain. It must be custom legalized. See description of CALL node for
    /// FLAG argument contents explanation.
    /// 
    FORMAL_ARGUMENTS,
    
    /// RV1, RV2...RVn, CHAIN = CALL(CHAIN, CALLEE,
    ///                              ARG0, FLAG0, ARG1, FLAG1, ... ARGn, FLAGn)
    /// This node represents a fully general function call, before the legalizer
    /// runs.  This has one result value for each argument / flag pair, plus
    /// a chain result. It must be custom legalized. Flag argument indicates
    /// misc. argument attributes. Currently:
    /// Bit 0 - signness
    /// Bit 1 - 'inreg' attribute
    /// Bit 2 - 'sret' attribute
    /// Bit 4 - 'byval' attribute
    /// Bit 5 - 'nest' attribute
    /// Bit 6-9 - alignment of byval structures
    /// Bit 10-26 - size of byval structures
    /// Bits 31:27 - argument ABI alignment in the first argument piece and
    /// alignment '1' in other argument pieces.
    ///
    /// CALL nodes use the CallSDNode subclass of SDNode, which
    /// additionally carries information about the calling convention,
    /// whether the call is varargs, and if it's marked as a tail call.
    ///
    CALL,

    // EXTRACT_ELEMENT - This is used to get the lower or upper (determined by
    // a Constant, which is required to be operand #1) half of the integer or
    // float value specified as operand #0.  This is only for use before
    // legalization, for values that will be broken into multiple registers.
    EXTRACT_ELEMENT,

    // BUILD_PAIR - This is the opposite of EXTRACT_ELEMENT in some ways.  Given
    // two values of the same integer value type, this produces a value twice as
    // big.  Like EXTRACT_ELEMENT, this can only be used before legalization.
    BUILD_PAIR,

    // MERGE_VALUES - This node takes multiple discrete operands and returns
    // them all as its individual results.  This nodes has exactly the same
    // number of inputs and outputs, and is only valid before legalization.
    // This node is useful for some pieces of the code generator that want to
    // think about a single node with multiple results, not multiple nodes.
    MERGE_VALUES,

    // Simple integer binary arithmetic operators.
    ADD, SUB, MUL, SDIV, UDIV, SREM, UREM,

    // SMUL_LOHI/UMUL_LOHI - Multiply two integers of type iN, producing
    // a signed/unsigned value of type i[2*N], and return the full value as
    // two results, each of type iN.
    SMUL_LOHI, UMUL_LOHI,

    // SDIVREM/UDIVREM - Divide two integers and produce both a quotient and
    // remainder result.
    SDIVREM, UDIVREM,
    
    // CARRY_FALSE - This node is used when folding other nodes,
    // like ADDC/SUBC, which indicate the carry result is always false.
    CARRY_FALSE,
    
    // Carry-setting nodes for multiple precision addition and subtraction.
    // These nodes take two operands of the same value type, and produce two
    // results.  The first result is the normal add or sub result, the second
    // result is the carry flag result.
    ADDC, SUBC,
    
    // Carry-using nodes for multiple precision addition and subtraction.  These
    // nodes take three operands: The first two are the normal lhs and rhs to
    // the add or sub, and the third is the input carry flag.  These nodes
    // produce two results; the normal result of the add or sub, and the output
    // carry flag.  These nodes both read and write a carry flag to allow them
    // to them to be chained together for add and sub of arbitrarily large
    // values.
    ADDE, SUBE,

    // RESULT, BOOL = [SU]ADDO(LHS, RHS) - Overflow-aware nodes for addition.
    // These nodes take two operands: the normal LHS and RHS to the add. They
    // produce two results: the normal result of the add, and a boolean that
    // indicates if an overflow occured (*not* a flag, because it may be stored
    // to memory, etc.).  If the type of the boolean is not i1 then the high
    // bits conform to getBooleanContents.
    // These nodes are generated from the llvm.[su]add.with.overflow intrinsics.
    SADDO, UADDO,

    // Same for subtraction
    SSUBO, USUBO,

    // Same for multiplication
    SMULO, UMULO,

    // Simple binary floating point operators.
    FADD, FSUB, FMUL, FDIV, FREM,

    // FCOPYSIGN(X, Y) - Return the value of X with the sign of Y.  NOTE: This
    // DAG node does not require that X and Y have the same type, just that they
    // are both floating point.  X and the result must have the same type.
    // FCOPYSIGN(f32, f64) is allowed.
    FCOPYSIGN,

    // INT = FGETSIGN(FP) - Return the sign bit of the specified floating point
    // value as an integer 0/1 value.
    FGETSIGN,
    
    /// BUILD_VECTOR(ELT0, ELT1, ELT2, ELT3,...) - Return a vector
    /// with the specified, possibly variable, elements.  The number of elements
    /// is required to be a power of two.
    BUILD_VECTOR,
    
    /// INSERT_VECTOR_ELT(VECTOR, VAL, IDX) - Returns VECTOR with the element
    /// at IDX replaced with VAL.  If the type of VAL is larger than the vector
    /// element type then VAL is truncated before replacement.
    INSERT_VECTOR_ELT,

    /// EXTRACT_VECTOR_ELT(VECTOR, IDX) - Returns a single element from VECTOR
    /// identified by the (potentially variable) element number IDX.
    EXTRACT_VECTOR_ELT,
    
    /// CONCAT_VECTORS(VECTOR0, VECTOR1, ...) - Given a number of values of
    /// vector type with the same length and element type, this produces a
    /// concatenated vector result value, with length equal to the sum of the
    /// lengths of the input vectors.
    CONCAT_VECTORS,
    
    /// EXTRACT_SUBVECTOR(VECTOR, IDX) - Returns a subvector from VECTOR (an
    /// vector value) starting with the (potentially variable) element number
    /// IDX, which must be a multiple of the result vector length.
    EXTRACT_SUBVECTOR,

    /// VECTOR_SHUFFLE(VEC1, VEC2, SHUFFLEVEC) - Returns a vector, of the same
    /// type as VEC1/VEC2.  SHUFFLEVEC is a BUILD_VECTOR of constant int values
    /// (maybe of an illegal datatype) or undef that indicate which value each
    /// result element will get.  The elements of VEC1/VEC2 are enumerated in
    /// order.  This is quite similar to the Altivec 'vperm' instruction, except
    /// that the indices must be constants and are in terms of the element size
    /// of VEC1/VEC2, not in terms of bytes.
    VECTOR_SHUFFLE,

    /// SCALAR_TO_VECTOR(VAL) - This represents the operation of loading a
    /// scalar value into element 0 of the resultant vector type.  The top
    /// elements 1 to N-1 of the N-element vector are undefined.
    SCALAR_TO_VECTOR,
    
    // EXTRACT_SUBREG - This node is used to extract a sub-register value. 
    // This node takes a superreg and a constant sub-register index as operands.
    // Note sub-register indices must be increasing. That is, if the
    // sub-register index of a 8-bit sub-register is N, then the index for a
    // 16-bit sub-register must be at least N+1.
    EXTRACT_SUBREG,
    
    // INSERT_SUBREG - This node is used to insert a sub-register value. 
    // This node takes a superreg, a subreg value, and a constant sub-register
    // index as operands.
    INSERT_SUBREG,
    
    // MULHU/MULHS - Multiply high - Multiply two integers of type iN, producing
    // an unsigned/signed value of type i[2*N], then return the top part.
    MULHU, MULHS,

    // Bitwise operators - logical and, logical or, logical xor, shift left,
    // shift right algebraic (shift in sign bits), shift right logical (shift in
    // zeroes), rotate left, rotate right, and byteswap.
    AND, OR, XOR, SHL, SRA, SRL, ROTL, ROTR, BSWAP,

    // Counting operators
    CTTZ, CTLZ, CTPOP,

    // Select(COND, TRUEVAL, FALSEVAL).  If the type of the boolean COND is not
    // i1 then the high bits must conform to getBooleanContents.
    SELECT,

    // Select with condition operator - This selects between a true value and 
    // a false value (ops #2 and #3) based on the boolean result of comparing
    // the lhs and rhs (ops #0 and #1) of a conditional expression with the 
    // condition code in op #4, a CondCodeSDNode.
    SELECT_CC,

    // SetCC operator - This evaluates to a true value iff the condition is
    // true.  If the result value type is not i1 then the high bits conform
    // to getBooleanContents.  The operands to this are the left and right
    // operands to compare (ops #0, and #1) and the condition code to compare
    // them with (op #2) as a CondCodeSDNode.
    SETCC,

    // Vector SetCC operator - This evaluates to a vector of integer elements
    // with the high bit in each element set to true if the comparison is true
    // and false if the comparison is false.  All other bits in each element 
    // are undefined.  The operands to this are the left and right operands
    // to compare (ops #0, and #1) and the condition code to compare them with
    // (op #2) as a CondCodeSDNode.
    VSETCC,

    // SHL_PARTS/SRA_PARTS/SRL_PARTS - These operators are used for expanded
    // integer shift operations, just like ADD/SUB_PARTS.  The operation
    // ordering is:
    //       [Lo,Hi] = op [LoLHS,HiLHS], Amt
    SHL_PARTS, SRA_PARTS, SRL_PARTS,

    // Conversion operators.  These are all single input single output
    // operations.  For all of these, the result type must be strictly
    // wider or narrower (depending on the operation) than the source
    // type.

    // SIGN_EXTEND - Used for integer types, replicating the sign bit
    // into new bits.
    SIGN_EXTEND,

    // ZERO_EXTEND - Used for integer types, zeroing the new bits.
    ZERO_EXTEND,

    // ANY_EXTEND - Used for integer types.  The high bits are undefined.
    ANY_EXTEND,
    
    // TRUNCATE - Completely drop the high bits.
    TRUNCATE,

    // [SU]INT_TO_FP - These operators convert integers (whose interpreted sign
    // depends on the first letter) to floating point.
    SINT_TO_FP,
    UINT_TO_FP,

    // SIGN_EXTEND_INREG - This operator atomically performs a SHL/SRA pair to
    // sign extend a small value in a large integer register (e.g. sign
    // extending the low 8 bits of a 32-bit register to fill the top 24 bits
    // with the 7th bit).  The size of the smaller type is indicated by the 1th
    // operand, a ValueType node.
    SIGN_EXTEND_INREG,

    /// FP_TO_[US]INT - Convert a floating point value to a signed or unsigned
    /// integer.
    FP_TO_SINT,
    FP_TO_UINT,

    /// X = FP_ROUND(Y, TRUNC) - Rounding 'Y' from a larger floating point type
    /// down to the precision of the destination VT.  TRUNC is a flag, which is
    /// always an integer that is zero or one.  If TRUNC is 0, this is a
    /// normal rounding, if it is 1, this FP_ROUND is known to not change the
    /// value of Y.
    ///
    /// The TRUNC = 1 case is used in cases where we know that the value will
    /// not be modified by the node, because Y is not using any of the extra
    /// precision of source type.  This allows certain transformations like
    /// FP_EXTEND(FP_ROUND(X,1)) -> X which are not safe for 
    /// FP_EXTEND(FP_ROUND(X,0)) because the extra bits aren't removed.
    FP_ROUND,
    
    // FLT_ROUNDS_ - Returns current rounding mode:
    // -1 Undefined
    //  0 Round to 0
    //  1 Round to nearest
    //  2 Round to +inf
    //  3 Round to -inf
    FLT_ROUNDS_,

    /// X = FP_ROUND_INREG(Y, VT) - This operator takes an FP register, and
    /// rounds it to a floating point value.  It then promotes it and returns it
    /// in a register of the same size.  This operation effectively just
    /// discards excess precision.  The type to round down to is specified by
    /// the VT operand, a VTSDNode.
    FP_ROUND_INREG,

    /// X = FP_EXTEND(Y) - Extend a smaller FP type into a larger FP type.
    FP_EXTEND,

    // BIT_CONVERT - Theis operator converts between integer and FP values, as
    // if one was stored to memory as integer and the other was loaded from the
    // same address (or equivalently for vector format conversions, etc).  The 
    // source and result are required to have the same bit size (e.g. 
    // f32 <-> i32).  This can also be used for int-to-int or fp-to-fp 
    // conversions, but that is a noop, deleted by getNode().
    BIT_CONVERT,
    
    // CONVERT_RNDSAT - This operator is used to support various conversions
    // between various types (float, signed, unsigned and vectors of those
    // types) with rounding and saturation. NOTE: Avoid using this operator as
    // most target don't support it and the operator might be removed in the
    // future. It takes the following arguments:
    //   0) value
    //   1) dest type (type to convert to)
    //   2) src type (type to convert from)
    //   3) rounding imm
    //   4) saturation imm
    //   5) ISD::CvtCode indicating the type of conversion to do
    CONVERT_RNDSAT,
    
    // FNEG, FABS, FSQRT, FSIN, FCOS, FPOWI, FPOW,
    // FLOG, FLOG2, FLOG10, FEXP, FEXP2,
    // FCEIL, FTRUNC, FRINT, FNEARBYINT, FFLOOR - Perform various unary floating
    // point operations. These are inspired by libm.
    FNEG, FABS, FSQRT, FSIN, FCOS, FPOWI, FPOW,
    FLOG, FLOG2, FLOG10, FEXP, FEXP2,
    FCEIL, FTRUNC, FRINT, FNEARBYINT, FFLOOR,
    
    // LOAD and STORE have token chains as their first operand, then the same
    // operands as an LLVM load/store instruction, then an offset node that
    // is added / subtracted from the base pointer to form the address (for
    // indexed memory ops).
    LOAD, STORE,

    // DYNAMIC_STACKALLOC - Allocate some number of bytes on the stack aligned
    // to a specified boundary.  This node always has two return values: a new
    // stack pointer value and a chain. The first operand is the token chain,
    // the second is the number of bytes to allocate, and the third is the
    // alignment boundary.  The size is guaranteed to be a multiple of the stack
    // alignment, and the alignment is guaranteed to be bigger than the stack
    // alignment (if required) or 0 to get standard stack alignment.
    DYNAMIC_STACKALLOC,

    // Control flow instructions.  These all have token chains.

    // BR - Unconditional branch.  The first operand is the chain
    // operand, the second is the MBB to branch to.
    BR,

    // BRIND - Indirect branch.  The first operand is the chain, the second
    // is the value to branch to, which must be of the same type as the target's
    // pointer type.
    BRIND,

    // BR_JT - Jumptable branch. The first operand is the chain, the second
    // is the jumptable index, the last one is the jumptable entry index.
    BR_JT,

    // BRCOND - Conditional branch.  The first operand is the chain, the
    // second is the condition, the third is the block to branch to if the
    // condition is true.  If the type of the condition is not i1, then the
    // high bits must conform to getBooleanContents.
    BRCOND,

    // BR_CC - Conditional branch.  The behavior is like that of SELECT_CC, in
    // that the condition is represented as condition code, and two nodes to
    // compare, rather than as a combined SetCC node.  The operands in order are
    // chain, cc, lhs, rhs, block to branch to if condition is true.
    BR_CC,
    
    // RET - Return from function.  The first operand is the chain,
    // and any subsequent operands are pairs of return value and return value
    // attributes (see CALL for description of attributes) for the function.
    // This operation can have variable number of operands.
    RET,

    // INLINEASM - Represents an inline asm block.  This node always has two
    // return values: a chain and a flag result.  The inputs are as follows:
    //   Operand #0   : Input chain.
    //   Operand #1   : a ExternalSymbolSDNode with a pointer to the asm string.
    //   Operand #2n+2: A RegisterNode.
    //   Operand #2n+3: A TargetConstant, indicating if the reg is a use/def
    //   Operand #last: Optional, an incoming flag.
    INLINEASM,
    
    // DBG_LABEL, EH_LABEL - Represents a label in mid basic block used to track
    // locations needed for debug and exception handling tables.  These nodes
    // take a chain as input and return a chain.
    DBG_LABEL,
    EH_LABEL,

    // DECLARE - Represents a llvm.dbg.declare intrinsic. It's used to track
    // local variable declarations for debugging information. First operand is
    // a chain, while the next two operands are first two arguments (address
    // and variable) of a llvm.dbg.declare instruction.
    DECLARE,
    
    // STACKSAVE - STACKSAVE has one operand, an input chain.  It produces a
    // value, the same type as the pointer type for the system, and an output
    // chain.
    STACKSAVE,
    
    // STACKRESTORE has two operands, an input chain and a pointer to restore to
    // it returns an output chain.
    STACKRESTORE,
    
    // CALLSEQ_START/CALLSEQ_END - These operators mark the beginning and end of
    // a call sequence, and carry arbitrary information that target might want
    // to know.  The first operand is a chain, the rest are specified by the
    // target and not touched by the DAG optimizers.
    // CALLSEQ_START..CALLSEQ_END pairs may not be nested.
    CALLSEQ_START,  // Beginning of a call sequence
    CALLSEQ_END,    // End of a call sequence
    
    // VAARG - VAARG has three operands: an input chain, a pointer, and a 
    // SRCVALUE.  It returns a pair of values: the vaarg value and a new chain.
    VAARG,
    
    // VACOPY - VACOPY has five operands: an input chain, a destination pointer,
    // a source pointer, a SRCVALUE for the destination, and a SRCVALUE for the
    // source.
    VACOPY,
    
    // VAEND, VASTART - VAEND and VASTART have three operands: an input chain, a
    // pointer, and a SRCVALUE.
    VAEND, VASTART,

    // SRCVALUE - This is a node type that holds a Value* that is used to
    // make reference to a value in the LLVM IR.
    SRCVALUE,

    // MEMOPERAND - This is a node that contains a MachineMemOperand which
    // records information about a memory reference. This is used to make
    // AliasAnalysis queries from the backend.
    MEMOPERAND,

    // PCMARKER - This corresponds to the pcmarker intrinsic.
    PCMARKER,

    // READCYCLECOUNTER - This corresponds to the readcyclecounter intrinsic.
    // The only operand is a chain and a value and a chain are produced.  The
    // value is the contents of the architecture specific cycle counter like 
    // register (or other high accuracy low latency clock source)
    READCYCLECOUNTER,

    // HANDLENODE node - Used as a handle for various purposes.
    HANDLENODE,

    // DBG_STOPPOINT - This node is used to represent a source location for
    // debug info.  It takes token chain as input, and carries a line number,
    // column number, and a pointer to a CompileUnitDesc object identifying
    // the containing compilation unit.  It produces a token chain as output.
    DBG_STOPPOINT,
    
    // DEBUG_LOC - This node is used to represent source line information
    // embedded in the code.  It takes a token chain as input, then a line
    // number, then a column then a file id (provided by MachineModuleInfo.) It
    // produces a token chain as output.
    DEBUG_LOC,

    // TRAMPOLINE - This corresponds to the init_trampoline intrinsic.
    // It takes as input a token chain, the pointer to the trampoline,
    // the pointer to the nested function, the pointer to pass for the
    // 'nest' parameter, a SRCVALUE for the trampoline and another for
    // the nested function (allowing targets to access the original
    // Function*).  It produces the result of the intrinsic and a token
    // chain as output.
    TRAMPOLINE,

    // TRAP - Trapping instruction
    TRAP,

    // PREFETCH - This corresponds to a prefetch intrinsic. It takes chains are
    // their first operand. The other operands are the address to prefetch,
    // read / write specifier, and locality specifier.
    PREFETCH,

    // OUTCHAIN = MEMBARRIER(INCHAIN, load-load, load-store, store-load, 
    //                       store-store, device)
    // This corresponds to the memory.barrier intrinsic.
    // it takes an input chain, 4 operands to specify the type of barrier, an
    // operand specifying if the barrier applies to device and uncached memory
    // and produces an output chain.
    MEMBARRIER,

    // Val, OUTCHAIN = ATOMIC_CMP_SWAP(INCHAIN, ptr, cmp, swap)
    // this corresponds to the atomic.lcs intrinsic.
    // cmp is compared to *ptr, and if equal, swap is stored in *ptr.
    // the return is always the original value in *ptr
    ATOMIC_CMP_SWAP,

    // Val, OUTCHAIN = ATOMIC_SWAP(INCHAIN, ptr, amt)
    // this corresponds to the atomic.swap intrinsic.
    // amt is stored to *ptr atomically.
    // the return is always the original value in *ptr
    ATOMIC_SWAP,

    // Val, OUTCHAIN = ATOMIC_L[OpName]S(INCHAIN, ptr, amt)
    // this corresponds to the atomic.[OpName] intrinsic.
    // op(*ptr, amt) is stored to *ptr atomically.
    // the return is always the original value in *ptr
    ATOMIC_LOAD_ADD,
    ATOMIC_LOAD_SUB,
    ATOMIC_LOAD_AND,
    ATOMIC_LOAD_OR,
    ATOMIC_LOAD_XOR,
    ATOMIC_LOAD_NAND,
    ATOMIC_LOAD_MIN,
    ATOMIC_LOAD_MAX,
    ATOMIC_LOAD_UMIN,
    ATOMIC_LOAD_UMAX,
    
    // BUILTIN_OP_END - This must be the last enum value in this list.
    BUILTIN_OP_END
  };

  /// Node predicates

  /// isBuildVectorAllOnes - Return true if the specified node is a
  /// BUILD_VECTOR where all of the elements are ~0 or undef.
  bool isBuildVectorAllOnes(const SDNode *N);

  /// isBuildVectorAllZeros - Return true if the specified node is a
  /// BUILD_VECTOR where all of the elements are 0 or undef.
  bool isBuildVectorAllZeros(const SDNode *N);

  /// isScalarToVector - Return true if the specified node is a
  /// ISD::SCALAR_TO_VECTOR node or a BUILD_VECTOR node where only the low
  /// element is not an undef.
  bool isScalarToVector(const SDNode *N);

  /// isDebugLabel - Return true if the specified node represents a debug
  /// label (i.e. ISD::DBG_LABEL or TargetInstrInfo::DBG_LABEL node).
  bool isDebugLabel(const SDNode *N);
  
  //===--------------------------------------------------------------------===//
  /// MemIndexedMode enum - This enum defines the load / store indexed 
  /// addressing modes.
  ///
  /// UNINDEXED    "Normal" load / store. The effective address is already
  ///              computed and is available in the base pointer. The offset
  ///              operand is always undefined. In addition to producing a
  ///              chain, an unindexed load produces one value (result of the
  ///              load); an unindexed store does not produce a value.
  ///
  /// PRE_INC      Similar to the unindexed mode where the effective address is
  /// PRE_DEC      the value of the base pointer add / subtract the offset.
  ///              It considers the computation as being folded into the load /
  ///              store operation (i.e. the load / store does the address
  ///              computation as well as performing the memory transaction).
  ///              The base operand is always undefined. In addition to
  ///              producing a chain, pre-indexed load produces two values
  ///              (result of the load and the result of the address
  ///              computation); a pre-indexed store produces one value (result
  ///              of the address computation).
  ///
  /// POST_INC     The effective address is the value of the base pointer. The
  /// POST_DEC     value of the offset operand is then added to / subtracted
  ///              from the base after memory transaction. In addition to
  ///              producing a chain, post-indexed load produces two values
  ///              (the result of the load and the result of the base +/- offset
  ///              computation); a post-indexed store produces one value (the
  ///              the result of the base +/- offset computation).
  ///
  enum MemIndexedMode {
    UNINDEXED = 0,
    PRE_INC,
    PRE_DEC,
    POST_INC,
    POST_DEC,
    LAST_INDEXED_MODE
  };

  //===--------------------------------------------------------------------===//
  /// LoadExtType enum - This enum defines the three variants of LOADEXT
  /// (load with extension).
  ///
  /// SEXTLOAD loads the integer operand and sign extends it to a larger
  ///          integer result type.
  /// ZEXTLOAD loads the integer operand and zero extends it to a larger
  ///          integer result type.
  /// EXTLOAD  is used for three things: floating point extending loads, 
  ///          integer extending loads [the top bits are undefined], and vector
  ///          extending loads [load into low elt].
  ///
  enum LoadExtType {
    NON_EXTLOAD = 0,
    EXTLOAD,
    SEXTLOAD,
    ZEXTLOAD,
    LAST_LOADEXT_TYPE
  };

  //===--------------------------------------------------------------------===//
  /// ISD::CondCode enum - These are ordered carefully to make the bitfields
  /// below work out, when considering SETFALSE (something that never exists
  /// dynamically) as 0.  "U" -> Unsigned (for integer operands) or Unordered
  /// (for floating point), "L" -> Less than, "G" -> Greater than, "E" -> Equal
  /// to.  If the "N" column is 1, the result of the comparison is undefined if
  /// the input is a NAN.
  ///
  /// All of these (except for the 'always folded ops') should be handled for
  /// floating point.  For integer, only the SETEQ,SETNE,SETLT,SETLE,SETGT,
  /// SETGE,SETULT,SETULE,SETUGT, and SETUGE opcodes are used.
  ///
  /// Note that these are laid out in a specific order to allow bit-twiddling
  /// to transform conditions.
  enum CondCode {
    // Opcode          N U L G E       Intuitive operation
    SETFALSE,      //    0 0 0 0       Always false (always folded)
    SETOEQ,        //    0 0 0 1       True if ordered and equal
    SETOGT,        //    0 0 1 0       True if ordered and greater than
    SETOGE,        //    0 0 1 1       True if ordered and greater than or equal
    SETOLT,        //    0 1 0 0       True if ordered and less than
    SETOLE,        //    0 1 0 1       True if ordered and less than or equal
    SETONE,        //    0 1 1 0       True if ordered and operands are unequal
    SETO,          //    0 1 1 1       True if ordered (no nans)
    SETUO,         //    1 0 0 0       True if unordered: isnan(X) | isnan(Y)
    SETUEQ,        //    1 0 0 1       True if unordered or equal
    SETUGT,        //    1 0 1 0       True if unordered or greater than
    SETUGE,        //    1 0 1 1       True if unordered, greater than, or equal
    SETULT,        //    1 1 0 0       True if unordered or less than
    SETULE,        //    1 1 0 1       True if unordered, less than, or equal
    SETUNE,        //    1 1 1 0       True if unordered or not equal
    SETTRUE,       //    1 1 1 1       Always true (always folded)
    // Don't care operations: undefined if the input is a nan.
    SETFALSE2,     //  1 X 0 0 0       Always false (always folded)
    SETEQ,         //  1 X 0 0 1       True if equal
    SETGT,         //  1 X 0 1 0       True if greater than
    SETGE,         //  1 X 0 1 1       True if greater than or equal
    SETLT,         //  1 X 1 0 0       True if less than
    SETLE,         //  1 X 1 0 1       True if less than or equal
    SETNE,         //  1 X 1 1 0       True if not equal
    SETTRUE2,      //  1 X 1 1 1       Always true (always folded)

    SETCC_INVALID       // Marker value.
  };

  /// isSignedIntSetCC - Return true if this is a setcc instruction that
  /// performs a signed comparison when used with integer operands.
  inline bool isSignedIntSetCC(CondCode Code) {
    return Code == SETGT || Code == SETGE || Code == SETLT || Code == SETLE;
  }

  /// isUnsignedIntSetCC - Return true if this is a setcc instruction that
  /// performs an unsigned comparison when used with integer operands.
  inline bool isUnsignedIntSetCC(CondCode Code) {
    return Code == SETUGT || Code == SETUGE || Code == SETULT || Code == SETULE;
  }

  /// isTrueWhenEqual - Return true if the specified condition returns true if
  /// the two operands to the condition are equal.  Note that if one of the two
  /// operands is a NaN, this value is meaningless.
  inline bool isTrueWhenEqual(CondCode Cond) {
    return ((int)Cond & 1) != 0;
  }

  /// getUnorderedFlavor - This function returns 0 if the condition is always
  /// false if an operand is a NaN, 1 if the condition is always true if the
  /// operand is a NaN, and 2 if the condition is undefined if the operand is a
  /// NaN.
  inline unsigned getUnorderedFlavor(CondCode Cond) {
    return ((int)Cond >> 3) & 3;
  }

  /// getSetCCInverse - Return the operation corresponding to !(X op Y), where
  /// 'op' is a valid SetCC operation.
  CondCode getSetCCInverse(CondCode Operation, bool isInteger);

  /// getSetCCSwappedOperands - Return the operation corresponding to (Y op X)
  /// when given the operation for (X op Y).
  CondCode getSetCCSwappedOperands(CondCode Operation);

  /// getSetCCOrOperation - Return the result of a logical OR between different
  /// comparisons of identical values: ((X op1 Y) | (X op2 Y)).  This
  /// function returns SETCC_INVALID if it is not possible to represent the
  /// resultant comparison.
  CondCode getSetCCOrOperation(CondCode Op1, CondCode Op2, bool isInteger);

  /// getSetCCAndOperation - Return the result of a logical AND between
  /// different comparisons of identical values: ((X op1 Y) & (X op2 Y)).  This
  /// function returns SETCC_INVALID if it is not possible to represent the
  /// resultant comparison.
  CondCode getSetCCAndOperation(CondCode Op1, CondCode Op2, bool isInteger);

  //===--------------------------------------------------------------------===//
  /// CvtCode enum - This enum defines the various converts CONVERT_RNDSAT 
  /// supports.
  enum CvtCode {
    CVT_FF,     // Float from Float