Question

John Cocke and David Patterson made significant
contributions to Reduced Instruction Set Computer (RISC) architectures.
Answer the following questions separately for each of these two
individuals. Cite the sources you used to find your answers. Your entire
answer should be one page or less.
a. In your own words, what was his contribution to RISC architectures?
Try to be specific.

Answer 1

The early IBM 7030 - STRECH has very huge number of instruction set (nearly 730) even there were separate instructions for variable length operands. It was very useful to reduce the hardware but highlevel language compliers found it difficult to compile.

Cocke decided to make it simpler.He reduced the instruction set and made a faster machine.This had a broad impact on computer architecture research, and was later called the Reduced Instruction Set Computer (RISC) approach.cocke and some other memebers defined their instructions set and implemented it in pipelined hardware. Their PL.8 compiler, which supported both Pascal and PL.8 (a variant of PL/I for systems programming), contained the first full implementation of Cocke and others' earlier optimization techniques, as well as new ones needed for RISC like a register allocator that avoided memory access delays and an instruction scheduler that hid branching delays.

Critical to the success of RISC was an optimizing compiler able to use the reduced instruction set efficiently. A pioneer in the development of the theoretical foundation for such compilers, Cocke co-developed interval analysis with Frances Allen, a program analysis technique based on a control flow graph reduction . Cocke co-invented many of the optimizing transformations underlying today's compilers, including efficient range checking for arrays, global common subexpression elimination, code motion, operator strength reduction, constant propagation, dead code elimination, and instruction scheduling. Unlike the work of others, Cocke’s compiler optimization techniques were closely linked to related designs for the computer architecture.

The RISC idea was influenced by Cocke’s prior work on computer architecture and optimizing compiler technology. The Stretch project he worked on had the ambitious goal of being 100 times faster than existing computing systems (such as the IBM 704) while providing flexibility in addressing, floating-point arithmetic, and nonnumeric operations. The challenge of improving performance by two orders of magnitude led to several hardware and software features co-designed by Cocke, including instruction pipelining, error correcting codes (ECC), instruction scheduling, and register allocation. Most of these ideas are still used in modern computer architectures more than 50 years after their first use in Stretch. The Stretch project served as a prototype for the IBM System/360, and for the IBM Engineering Verification Engine, a special purpose parallel processor used to simulate IBM computer logic circuits.

The Stretch project focused primarily on performance without regard to cost. But Cocke observed that much of the richness of the Stretch architecture could not be exploited by the compiler. He saw that it is easier to write compilers for a simpler instruction set, and that had a major impact on the approach he took for the 801 project.