Adding instruction encoding

If the instructions need to be specific for how they are encoded with respect to bit fields, this can be done by specifying the bit field in the .td file when defining an instruction.

How to do it…

To include instruction encoding while defining instructions, proceed with the following steps:

1. A register operand that will be used to register the add instruction will have some defined encoding for its instruction. The size of the instruction is 32 bits, and the encoding for it is as follows:

   bits 0 to 3 -> src2, second register operand
   bits 4 to 11 -> all zeros
   bits 12 to 15 -> dst, for destination register
   bits 16 to 19 -> src1, first register operand
   bit 20 -> zero
   bit 21 to 24 -> for opcode
   bit 25 to 27 -> all zeros
   bit 28 to 31 -> 1110

   This can be achieved by specifying the preceding bit pattern in the .td files

2. In the TOYInstrFormats.td file, define a new variable, called Inst:

   class InstTOY<dag outs, dag ins, string asmstr, list<dag&gt...