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GO Classes DPP | COMPILER|CODE OPTIMIZATION

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1 1 vote

Consider the following three-address code sequence used for a loop:

i = 0
L1: t1 = i * 4
t2 = base + t1
val = load t2
i = i + 1
if i < 100 goto L1

Which optimization technique would most effectively transform this code to reduce the number of multiplications inside the loop, and what would be the resulting change to line $2$?

  1. Constant Folding; $\verb|t1 = 0|$
     
  2. Dead Code Elimination; Line $2$ is removed entirely.
     
  3. Strength Reduction; $\verb|t1 = t1 + 4|$ (with initialization $\verb|t1 = 0|$ before the loop). 
     
  4. Loop Unrolling; The loop body is copied $100$ times to remove the branch.

1 Answer

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Strength Reduction replaces a "heavy" operation like multiplication inside a loop with a "lighter" one like addition. By initializing $\verb|t1|$ to $0$ and adding $4$ in each iteration, the compiler eliminates the costly $\verb|i*4|$ calculation.
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