ISRO CSE 2011 | Question: 3

Question

In compiler terminology reduction in strength means

• A. Replacing run time computation by compile time computation
• B. Removing loop invariant computation
• C. Removing common subexpressions
• D. replacing a costly operation by a relatively cheaper one

Answer 1

Answer is D

In software engineering, strength reduction is a compiler optimization where expensive operations are replaced with equivalent but less expensive operations. The classic example of strength reduction converts "strong" multiplications inside a loop into "weaker" additions – something that frequently occurs in array addressing. 

Comments

@Arjun sir verify it

Answer 2

In compiler design strength reduction is a Machine Independent loop optimization technique.

There are expressions that consume more CPU cycles, time, and memory. These expressions should be replaced with cheaper expressions without compromising the output of expression. For example, multiplication (x * 2) is expensive in terms of CPU cycles than (x << 1) and yields the same result.

so answer is D.

Comments

Answer will be (A)

Answer 3

Replacing run time computation by compile time computation

Answer 4

option A.it is constant folding we replace our variable with its constant value
so at compile time it will be execute(internally store in symbol table at the very first stage),so it saves time during runtime
option B.its our one of the loop optimization technique
option C.its part of available expression analysis calling common sub expression elimination
option D.yes in reduction in strength mean basically we replace high complexity operator into less time taking one
ie y=x*2 can be optimized as y=x+x