Tutorial: 10 March 1998

• Starting with any high-level language, and then producing machine code, what are the 10 most common (generic) instructions found in the resulting executable file?
  Justify your choices.
• Discuss the benefits of a RISC processor having the following features:
  • 32 registers (compared to 8 or 16 in a CISC processor)
  • three-address instructions such as:

    ADD Rs1, Rs2, Rd

    where Rs is a source operand and Rd is the destination.

Examples from tutorial

• The following instructions were selected:
  • Branch
  • Load/Store
  • Move (registers)
  • ADD
  • JSR
  • RTS
  • AND
  • OR
  • COM
  • MUL
• and the justification is based on:
  • Frequency of occurrence
  • Utility/uniqueness
  • Performance

Part 2.

• Many registers will allow variables to be stored in the processor rather than in memory.
• 3-address instructions improve processing speed as they require fewer instruction fetches, they can retain the source variables (one of which would be overwritten in a 2-address format) and the destination register can be chosen to be useful in following instructions. All these factors improve efficiency and reduce the dependency on external memory.