Lecture 09

Question 1

What is a control hazard?

Answer 1

When a conditional jump changes which instructions need to be executed.
Instructions already in the pipeline may need to be cancelled.

Question 2

What does MIPS 32’s ‘branch delay slot’ mean?

Answer 2

The instruction immediately after a branch or a jump will always be executed, regardless of whether the jump happens or not.

Question 3

Why, in MIPS assembler, is it common to see the ‘nop’ operator directly after a jump?

Answer 3

To avoid the ‘branch delay slot’ from running any other code.

Question 4

What is branch prediction and why is it useful?

Answer 4

Trying to decide if a branch in a program will be taken or not.
Predicting this can improve the efficiency of the pipeline as the expected instructions can begin loading before the jump.

Question 5

Assuming a branch is not taken is best practice for:
A - if,then,else statements
B - Loops

Answer 5

If-then-else statements.

Question 6

Assuming a branch is always taken is best practice for:
A - if,then,else statements
B - Loops

Answer 6

Loops

Question 7

In MIPS, branch destinations are:
A - Absolute
B - Relative

Answer 7

B - Relative

A jump location is the program counter plus some offset.