ITEC 460 - Chapter 8 Notes

basic architecture

• What can a computer do?
• arith ops
• relops
• store/retrieve from memory


• straight line ex
• branch
• access i/o devices
• What storage does it have
• asm language vs machine language

intro

• AAT is roughly independent of architecture

Stack, Call Frame, Memory

• Must look at memory for locals and params (and registers)
• Stack grows from small to large addresses
• SP points to next open location
• AR = stack frame = call frame
• FP points to start of current call frame
• call frame: look at foo bar example to see how to access
• locals and params
• step through how this works from one call to the next
• call frame: locals, saved regs, params for called
• results come back in a register, not onstack
• Use offset from fp to get to call frame
• params accessed by both: put in caller and use neg offset from (new) to access in called
• Caller pushes params, makes call, then can pop params
• Notice that fp is constant during execution of a proc
• - but sp moves and fp may change but will be restored
• Call stmt moves fp

Abstract Assembly

• Statement trees: asm instructions - don't represent values
• Expression trees: asm instr operands - represent values
• Five kinds of expression trees:
1. constant (ie integers)
2. register - string that specifies a register
3. operator - two expr trees and an operator
4. call expression - string for function name and list of expressions for operands (stack access is part of codegen)
5. Memory address - absolute rare; offset from fp common


• Eight kinds of statement trees
1. Move
2. label
3. Jump
4. Conditional Jump
5. sequential
6. call statement
7. empty
8. return

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