GATE CSE 2016 Set 1 | Question: 19

Question

Consider the following code segment.

x = u - t;
y = x * v; 
x = y + w;
y = t - z; 
y = x * y;

The minimum number of total variables required to convert the above code segment to static single assignment form is __________.

Comments

Can anyone give minimum variable for three address code

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this video can help in understanding SSA https://youtu.be/uqTT3gI7KU8

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Detailed Video Solution: GATE CSE 2016 - Static Single Assignment Form SSA Question

Static Single Assignment Form SSA Complete Lecture: https://www.youtube.com/watch?v=CQV8hSeMrx8  

Answer 1

x1 = u - t;
y1 = x1 * v;
x2 = y1 + w;
y2 = t - z;
y3 = x2 * y2;

Total 10 variables.

Answer 2

t1=u-t

t2=t1+v

t3=t2+w

t4=t-z

t5=t3*t4

So total number of variables required =10

{t1,t2,t3,t4,t5,u,t,v,w,z}

Answer 3

In SSA, each variable used must be assigned exactly once and declared before use.

 

$u = \text{some_val;}$
$t = \text{some_val;}$
$x = u -t;$

$v = \text{some_val;}$
$y = x * v;$

$w = \text{some_val;}$
$x_2 = y + w;$

$z = \text{some_val;}$
$y_2 = t – z;$

$y_3 = x_2 * y_2;$

 

$\text{Total Variables required in SSA} = 10$

Answer 4

Answer should be 3