Class 32: An Abstract Assembly Language

Held Wednesday, April 18, 2001

Summary

Today we consider the design of an abstract assembly language representation.

Notes

• Does anyone have any other thoughts on our candidates?
• Presentation teams follow. Please pick a topic and preferred time by Friday. (Earlier requests get priority for picking slots.)
  • Team Foo: Kensler, Galacia, Staicut
  • Team Bar: Baszler, Magar, Vickery
  • Team Baz: Fuller, Gerking, Kern
  • Team Xyzzy: Corvino, Gu, Krivin
  • Team Q: Broadwell, Carey, Simonson
• Code and outline for today are vague. Sorry. Expect sample code in lab tomorrow.

Overview

• Why an abstract assembly language
• Representing locations and values
• Representing individual instructions
• Combining instructions

The Design of an Abstract Assembly Language

• Why: Lets us leave some topics until later.
  • Register allocation
  • Valid operands for certain operations
  • ...
• Concerns:
  • Like assembly, but more abstract
  • Easy to translate to most CISC architectures.
  • Easy and fast to build
• So:
  • Rely on common operations
  • Think about translation
• One key idea: Use a tree of instructions rather than a sequence.
• Two basic types: instruction and operand.

Common Operands

• Specified value.
• Standard register, such as stack pointer.
• Known register (rare).
• Place on stack.
• Temporary (to be converted to a register or value on stack).
• Indirection
• Offset
• Array reference?

Common Operations

• What operations or operation-like things do you expect to see in an assembly language?
• Add a label.
• Jump to a label.
• Conditional jump.
• Arithmetic operations.
• Move values.
• Push and pop stack values?
• Procedure call.
• Procedure return.
• ...