Where I can find the detail definition and use of LLVM-backend related stuff?

Question

Hi I'm learning LLVM backend and met big problem.

I'm following this tutorial and found:

1. There are huge amount of code I need to add
2. There is no detail illustration for any of these code.

One of the example would be in chapters/Chapter2/Cpu0InstrInfo.tdas follow:

//===----------------------------------------------------------------------===//
// Cpu0 profiles and nodes
//===----------------------------------------------------------------------===//

def SDT_Cpu0Ret          : SDTypeProfile<0, 1, [SDTCisInt<0>]>;

// Return
def Cpu0Ret : SDNode<"Cpu0ISD::Ret", SDTNone,
                     [SDNPHasChain, SDNPOptInGlue, SDNPVariadic]>;

//===----------------------------------------------------------------------===//
// Instruction format superclass
//===----------------------------------------------------------------------===//

include "Cpu0InstrFormats.td"

//===----------------------------------------------------------------------===//
// Cpu0 Operand, Complex Patterns and Transformations Definitions.
//===----------------------------------------------------------------------===//
// Instruction operand types

// Signed Operand
def simm16      : Operand<i32> {
  let DecoderMethod= "DecodeSimm16";
}

// Address operand
def mem : Operand<iPTR> {
  let PrintMethod = "printMemOperand";
  let MIOperandInfo = (ops GPROut, simm16);
  let EncoderMethod = "getMemEncoding";
}

// Node immediate fits as 16-bit sign extended on target immediate.
// e.g. addi, andi
def immSExt16  : PatLeaf<(imm), [{ return isInt<16>(N->getSExtValue()); }]>;

// Cpu0 Address Mode! SDNode frameindex could possibily be a match
// since load and store instructions from stack used it.
def addr : 
  ComplexPattern<iPTR, 2, "SelectAddr", [frameindex], [SDNPWantParent]>;

Why should I define simm16,memand all other stuff, what is the use of them.

I search through the intenet and found nothing about them. There is no infomation of what they are and what they do.