Compiler Design
Final Exam , Spring 1995.

e

Answer All Questions:

NAME:

LOGIN NAME:

This is an open book, open notes examination. There are eight questions. All questions carry 15 points. Some questions have a and b parts in which case they are weighed equally. If you get 100 points, then you have max-ed the paper. It is possible that you get more than 100 points, which will be counted as extra points towards your grade. Goodluck and have a happy summer.

Problem Points Scored Points Possible

1 15

2 15

3 15

4 15

5 15

6 15

7 15

8 15

a)Construct minimum state DFA for the following regular expression: b) Write a Lex program to reverse the letters in each word for a given text. (e.g. if the input is : begin I am Smart end the output is: ngieb I ma tramS dne ) A word is a bunch of letters and digits separated by spaces or newlines or tabs.

a) Consider the grammar

S -> ( S ) S | ) S ( S | epsilon

The terminal symbols are ( and ). Is the above grammar ambiguous and explain with examples.

b) Construct a SLR parsing table for the following grammar.

E -> E + T | T
T -> T F | F
F -> F * | a | b

Give a syntax directed translation scheme ( a pseudo yacc program will suffice) to differentiate expressions formed by applying the arithmetic operators + and * to the variable x and constants. Assume no simplification takes place. As an example if the input is x * (x + 1995) , the output will be 1 * (x + 1995) + x * ( 1 + 0) . The rules for differentiation: diff(E1+E2) = diff(E1)+ diff(E2); diff(E1*E2) = E2* diff(E1) + E1*diff(E2);

a) Find the most general unifier for the following type expressions:



b) What is the type of the following function (please derive the steps in the style of 6.12

fun member(a,x) = 
if null(x) then error
else if a = hd(x) then x
else member(a, tl(x));

Assume the type of error is void.

a)Suppose the procedure swap2 is declared as follows:

procedure swap2(x,y: integer);
	procedure f() : integer;
		var x:integer;
	begin (* f *)
		z := x; x: = y; return z
	end f;
begin (* swap2 *)
	y := f()
end swap2;

Describe the effect of the procedure call swap2(i,A[i]) under each of the following parameter-passing methods:

• call-by-value
• call-by-reference
• call-by-value-result
• call-by-name

b) Do problem 7.8 page 457 just the b) part only.

a) Do problem 8.14 page 510. b) Convert the following into three address statements.

main()
{ int i, a[5],b[5];
 for (i=0;i<5;i++)
 a[b[i]] = b[a[i]];
}

a) What information should be maintained in an abstract syntax tree, so that assembler code can be generated by walking down the tree. b) For this C program segment, construct the tree and generate the assembler code you are allowed to use pseudo assembler code.

for (i=0;i<10;i++)
	a[i] = random() % 2;

a) Find the optimal code on a single register machine. You are allowed to rearrange the statements but preserve the same functionality.

a:=b+c; d:=e; f:= a* c;

b) For Fig 10.74 (page 713) Compute the live variables at the end of each block.

 
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