code optimization

Question

please explain each optimization too!

Comments

anyone???

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is it not in the course ????

reason for downvote??

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I think D is correct ???

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yes, thats correct!

can u explain!

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Code can written like this

x = 0;
y = 10;

for(int i = 0;i<5;i++)
{
    
    x++;
    y = y<<1;
}

 

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can u pls tell me what does all these optimizations mean??

means i dont know what is constant folding , loop unrolling etc?

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Gate Fever

wait for a minute I will explain..

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no problem, take ur time!

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@kumar.dilip

u havent replied yet

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1. operation y = y*2 ( this is costly operation compare to ) y = y <<1 , so we can replace that operation. 

this is called strength reduction.

2. y = 10 remove it from high-frequency( like loop) region to low frequency is called code motion.

3.we can write both the operation y = y<<1 and x++ in the single loop ( loop unrolling)

4. x = x*0, can be written like this x = 0 ( constant folding)

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okay,thanks!

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on what basis we should judge that $x$ is a costlier operator and $y$ is a cheaper operator?