Compiler Construction
You have been given a new programming language with a C-like syntax, with integer
variables and functions and with static binding of free variables. Your manager can
parameterise certain aspects of the language, including the following three options:
• For “int x = e;” whether the variable x has the same l-value of e or whether
a new l-value is created and initialised to the r-value of e. If e is only an
r-value then a new l-value is created in both circumstances.
• For “int f(int x) { … }” whether the variable x is passed by l-value (“by
reference”) or by r-value (“by value”). If the switch is set to “l-value” and the
value passed is only an r-value then a new l-value is created, initialised and
passed.
• For “int f(int x) { … y … }” (where the variable y is free to f)
whether the value of y is calculated at the times of its uses (association by
l-value) or at the time of the definition of f (association by r-value).
As a test of your programming skills your manager asks you to write a program
which tells how the language has been parameterised. Do so by printing a 3-digit
decimal number where the “hundreds” digit is one or two according to whether the
first option is by l-value or r-value respectively, similarly with the “tens” digit for
the second and with the “units” digit for the third option.
[10 marks]
Explain the structure of an object module which an assembler or compiler might
produce to be processed by a linker. Your answer should include discussion of the
various object module features needed to represent the compiled form of the C
program:
int a[10] = { 2,3,5,7,11,13,17,19,23,29 };
extern int b[10];
extern int g(int);
int f(int y)
{ return g(y) + b[5] + a[6];
}
[10 marks]