1. Topics to be covered Instruction Execution Characteristics
The Use of Large Register File
Compiler-Based Register Optimization
RISC Architecture
RISC Pipelining.
RISC versus CISC.

2. Major Advances in Computers(1)
The family concept
IBM System/
DEC PDP-8
Separates architecture from implementation
Microporgrammed control unit
Idea by Wilkes 1951
Produced by IBM S/
Cache memory
IBM S/360 model

3. Major Advances in Computers(2)
Multiple processors
Intel
Pipelining
Introduces parallelism into fetch execute cycle
Reduce instruction set computer (RISC)

4. The Next Step - RISC Reduced Instruction Set Computer Key features
Large number of general purpose registers
or use of compiler technology to optimize register use
Limited and simple instruction set
Emphasis on optimising the instruction pipeline

5. Characteristics of Some CISCs, RISCs, and Superscalar Processors

6. Driving force for CISC Software costs far exceed hardware costs
Increasingly complex high level languages
Semantic gap
Leads to:
Large instruction sets
More addressing modes
Hardware implementations of HLL statements
e.g. CASE (switch) on VAX

7. Intention of CISC Ease compiler writing Improve execution efficiency
Complex operations in microcode
Support more complex HLLs

8. Instruction Execution Characteristics
Complex Instruction Sets Are Intended To • Ease The Task Of The Compiler Writer. • Improve Execution Efficiency, Because Complex Sequences Of Operations Can Be Implemented In Microcode. • Provide Support For Even More Complex And Sophisticated Hlls.

9. The aspects of computation of interest are as follows: • Operations performed: These determine the functions to be performed by the processor and its interaction with memory. • Operands used: The types of operands and the frequency of their use determine the memory organization for storing them and the addressing modes for accessing them. • Execution sequencing: This determines the control and pipeline organization.

10. Instruction Execution Characteristics
Operations
Operands
Procedure calls
Implications

11. Operations Assignments Conditional statements
Movement of data
Conditional statements
(IF, LOOP, Call, Goto, Other)
Sequence control
Procedure call-return is very time consuming
Some HLL instruction lead to many machine code operations

12. Operands Mainly local scalar variables
Optimisation should concentrate on accessing local variables
Pascal C Average
Integer constant
Scalar variable
Array/structure

13. Procedure Calls Very time consuming
Depends on number of parameters passed
Depends on level of nesting
Most programs do not do a lot of calls followed by lots of returns
Most variables are local

14. Implications
Best support is given by optimising most used and most time consuming features
Large number of registers
Operand referencing
Careful design of pipelines
Branch prediction etc.
Simplified (reduced) instruction set