MadeEasy Test Series 2018: Compiler - Code Optimization

Question

 

Given the 3-address code for a basic block:

 

The number of registers that are needed to allocate this basic block with no spills are ________.?

My doubt here is :

1. Is there any difference in question asking for minimum numbers of registers and minimum number of variables required for 3 address code?
2. Can’t we optimize the above code using code motion?
3. If the question ask only for number of variables required in three address code ! do we need to optimize before counting?
4. If the question ask for minimum number of variables required in three address code, Only then should we optimize the code before counting?

Comments

@Shaik Masthan

how 2?

At first here we are storing a,b,c,d in 4 registers

right?

---

@ srestha there is no need of storing a,b,c,d into registers ,because  load instructions are there so we loading data from memory location to register so need of storing .

---

$2$ is minimum.

$T1 = a + b$

$T2 = T1 + c$

$T1 = T2 + d$ (we don't need a + b again so we can use T1)

$a = T1$

Answer 1

t1=a+b

t1=t1+c

t1=t1+d

a=t1