ISRO2018-29

Question

DU-chains(Definition-Use) in compiler design:

1. consist of a definition of a variable and all its uses, reachable from that definition
2. are created using a form static code analysis
3. are prerequisite for many compiler optimization including constant propagation and common sub-expression elimination
4. All of the above

Answer 1

Ans D

Comments

Ref: https://en.m.wikipedia.org/wiki/Use-define_chain

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kheer me zeher kisne milaya tha thakur sahab?:)

Answer 2

$\underline{\textbf{Answer:}\Rightarrow}$

$\underline{\textbf{Explanation:}\Rightarrow}\;\mathrm {(d)}.$

$\underline{\textbf{Definition-Use Chain (DU Chain):}}$

It consists of definition(D) of a variable, and all the uses, U reachable from that definition without getting involved in other definitions.

$\underline{\textbf{Use-Definition Chain (UD Chain):}}$

It is a counterpart of Definition-Use Chain (DU Chain).

It is a $\color{blue}{\text{data structure}}$ that consists of use, $\mathbf U$, of a variable, and all the definitions $\mathbf{(D)}$ of that variable that can reach that use without getting involved in any other definitions.

• UD Chain most of the time means $\color{blue}{\text{assigning}}$ some value to a variable.

$\textbf{Applications:}$

1. Knowing the use-def and def-use chains are helpful in compiler optimizations including constant propagation and common sub-expression elimination.
2. Helpful in dead-code elimination.
3. instruction reordering.
4. (Implementation of ) scoping/shadowing.

Both of them are created by using $\color{magenta}{\textbf{Data flow analysis}}$. It is a form of $\color{blue}{\text{static code analysis}}$.

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https://en.m.wikipedia.org/wiki/Use-define_chain