The instruction set of an architecture varies according to various features present in the architecture. This recipe demonstrates how instruction sets are defined for the target architecture.
Three things are defined in the instruction target description file: operands, an assembly string, and an instruction pattern. The specification contains a list of definitions or outputs and a list of uses or inputs. There can be different operand classes such as the register class, and immediate or more complex register + imm
operands.
Here, a simple add instruction definition is demonstrated. It takes two registers for the input and one register for the output.