SLIDE 3 3
- Execution model (2)
- MEM-MEM
– A single instruction takes the operands from memory, computes the result and puts it back in memory – No internal (general-purpose) registers are required
– At most one operand can be taken directly from memory – At least 1 general-purpose register is required
– Both operands and results are internal registers
- Execution models comparison
Example
Where A, B and C are memory elements (i.e., variables)
MEM-MEM MEM-REG MEM-REG-1 REG-REG STACK ADD A,B,C LOAD R1,B LOAD B LOAD R1,B PUSH B ADD R3,R1,C ADD C LOAD R2,C PUSH C STORE A,R3 STORE A ADD R3,R1,R2 ADD STORE A,R3 POP A A <-- B+C R1 <-- B R1 <-- B R1 <-- B R3 <-- R1+C R1 <-- R1+C R2 <-- C A <-- R3 A <-- R1 R3 <-- B+C A <-- R3 PUSH B PUSH C ADD POP A C B B B+C
