University of Cape Town
Department of Computer Science
CSC3003S Final Exam
2008
Marks : 30
Time : 3 hours
Instructions:
• Answer all questions from Section A and 3 questions from Section B.
• Show all calculations where applicable.
Section A [ Answer Question ONE – this is compulsory ]
Question 1 [ 10 marks ]
Multi-core CPUs can influence the design of modern optimising compilers. Firstly, the
compiler could automatically convert traditional serial code into a parallel form, where 2 or
more pieces of code run at the same time on different CPUs/cores. Secondly, the compiler itself
could perform its processing in parallel. Answer the following questions with this in mind.
1) Describe one advantage and one disadvantage of separating the compiler front-end from the
compiler back-end. [2]
ad: easier to retarget compiler to new machine [1], easier to apply optimisations to IR [1],
easier to build compiler for new language [1]
disad: more work [1] slower compilation [1]
2) Describe one advantage in having multiple distinct layers (frame generation, code generation,
instruction selection, liveness analysis, etc.) within the compiler back-end. [1]
easier to replace or change functionality in individual parts of compiler [1]
3) Static semantics should be checked before any code is generated. Discuss 2 examples of errors
that can be checked for. [2]
use before declaration [1] size mismatch [1] array index out of bounds [1] type incompatibility
[1] etc.
4) Describe 3 typical optimisations that a compiler can perform on generated IR code, assuming
the code being optimised runs on a single CPU/core. [3]
trace analysis [1] common subexpression elimination [1] constant folding [1] etc.
5) At which point/layer in the compilation process could the code being compiled be converted
into segments that may run in parallel (assuming this is done independently of source
language)? [1]
after code generation but before liveness analysis [1]
6) Briefly describe one technique to exploit multiple cores in the compilation process itself. [1]
