You have a CISC architecture that employs bit field instructions to perform some very clever graphical operations on image data. These bit field instructions account for 5% of the code executed. However, the bit field instructions increase the cost of the silicon die by 20% and prevent the use of advanced pipelining and microarchitectural techniques. If the bit field instructions are dropped, the chip can operate at twice the rate. Typically, a bit field instruction can be replaced by seven conventional machine?level instructions. Would you advise keeping or getting rid of bit field instructions?

Question

What will be an ideal response?

Answer 1

Suppose code on the existing machine is run and it takes 5s for bit field instructions and 95s for other
instructions. If the same machine did not have bit field instructions and each bit field instruction was replaced
by 7 other instructions, the execution time would become 5s × 7 + 95s = 130s. However, the new system would
execute code twice as fast and the execution time would be 130s/2 = 65s. This would represent a speedup of
100/65 = 1.54, a definite improvement.