CS451/651 Exam 2
Instructions
1. The is a closed-book exam, but you are allowed to use a single page (both sides) of notes.
2. There are 6 problems in this exam and you have 75 minutes to answer them.
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3. To receive full credit, your solution must not only be correct but also show all the steps.
4. Discussing the exam contents with anyone who has not taken the exam is a violation of the academic honesty code.
Problem 1. (10 points) Consider the following j– program:
public class Mystery { private int f = 42;
public static int f(int u, long v, int w) { int x = u + w;
Mystery m = new Mystery (); long y = m.g(u, v);
long z = (long) x * y;
return x; }
public long g(int u, long v) { int w = u * u;
Mystery m = new Mystery (); int y = u * w;
long z = m.g(w, v);
long x = (long) f + (long) w; long y = x * x;
a. (5 points) Show in detail the compilation unit context for Mystery, as built by preAnalyze(). b. (5 points) Show in detail the method/local contexts for f() and g().
Problem 2. (10 points) Classify the following casts as identity, narrowing, widening, boxing, or un- boxing. What instructions (if any) must generated for each?
a. (1.25 points)
String x = (String) (new Object());
b. (1.25 points)
char x = (char) 42;
Exam 2 (Sample)
c. (1.25 points)
char x = (char) (new Character(’*’));
d. (1.25 points)
Object x = (Object) (new String(“Hello, World”));
e. (1.25 points)
Boolean x = (Boolean) false;
f. (1.25 points)
String x = (String) (new String(“Hello, World”));
g. (1.25 points)
int x = (int)
h. (1.25 points)
char x = (char)
Problem 3. (20 points) Suppose o is an object and f an instance integer field within, a is an array of integers, and y, i and z are integers. For each of the j– statements below, using the following table, list the instructions generated and show how the runtime stack evolves as those instructions are executed.
Exam 2 (Sample)
a. (10 points)
b. (10 points)
z = ++a[i];
Problem 4. (20 points) Consider the following JVM bytecode for a j– method int mystery(int x, int y):
static int mystery(int, int); 0: iconst_1
1: istore_2
2: iload_1
3: iconst_0
4: if_icmple 18 7: iload_2
8: iload_0
10: istore_2 11: iload_1 12: iconst_1 13: isub
14: istore_1
15: goto 2 18: iload_2
19: ireturn
a. (10 points) Show how the runtime stack evolves as a result of the call mystery(3, 4). b. (5 points) What value does the above call return?
c. (5 points) What does mystery(x, y) compute and return in general?
Problem 5. (20 points) The LIR instructions for the method int mystery(int x, int y) from the previous problem are listed below.
0: LDC [1] [V32|I]
5: MOVE $a1 [V33|I]
10: MOVE [V32|I] [V34|I]
15: LDC [0] [V35|I]
20: BRANCH [LE] [V33|I] [V35|I] B4
25: MUL [V34|I] $a0 [V36|I]
30: LDC [1] [V37|I]
35: SUB [V33|I] [V37|I] [V38|I] 40: MOVE [V36|I] [V34|I]
45: MOVE [V38|I] [V33|I]
50: BRANCH B2
55: MOVE [V34|I] $v0 60: RETURN $v0
a. (10 points) Compute the liveUse and liveDef sets for each basic block in the method.
Exam 2 (Sample)
b. (10 points) Compute the liveIn and liveOut sets for each basic block in the method.
Problem 6. (20 points) The liveness intervals for the registers (all except V33 and V34) in the LIR instructions from the previous problem are listed below.
v0: [55, 60]
25] [25, 50] 5]
V35: [15, 20] V36: [25, 40] V37: [30, 35] V38: [35, 45]
a. (10 points) Compute the liveness intervals for V33 and V34.
b. (5 points) List the neighbors of the 7 vertices (V32 — V38) in the interference graph G for the method,
in ascending order.
c. (5 points) Color the graph G using 3 physical registers and draw the graph using symbols , ⋆, and for vertices, where the symbols denote the three registers.