1.
Introduction
2.
Structure-Preserving Transformations
2.1.
Elimination of Common Sub-Expression
2.2.
2.3.
Renaming the Temporary Variables
2.4.
3.
Algebraic Transformations
4.
Loop Optimization
5.
5.1.
What is a flow graph?
5.2.
What is loop unrolling?
5.3.
5.4.
Who is responsible for code optimization?
5.5.
What is meant by the reduction in strength?
6.
Conclusion
Last Updated: Apr 30, 2024

# Block Optimization

Prachi Singh
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Speaker
Prerita Agarwal
Data Specialist @
23 Jul, 2024 @ 01:30 PM

## Introduction

The concept of optimization revolves around the basic block. Block Optimization does not involve changes in computational results from the set of operations.

The two different scenarios of Block Optimization are as given below

1. Structure-Preserving Transformations
2. Algebraic Transformations

Also See, Top Down Parsing

## Structure-Preserving Transformations

The Structure-Preserving Transformations in basic Block Optimization include

1. Elimination of common sub-expression
3. Renaming the temporary variables
4. Interchanging two adjacent independent statements

### Elimination of Common Sub-Expression

In this elimination technique, there is no need to repeatedly compute the same sequence expression. When the same expression is repeated, the previous computation evaluates the result.

A sequence of expressions is taken as follows:

``````w: x+y
x: w-z
y: x+y
z: w-z``````

In the above series of expressions, the second and fourth expressions compute the same results. Hence they can be written as:

``````w: x+y
x: w-z
y: x+y
z: x``````

1. The situation arises when the source program contains many dead codes.
2. The code does not work for future consequences once declared and defined.
3. Let us consider the expression a:= b + c, where b is a dead symbol and does not serve future consequences. Then b can be eliminated safely.

### Renaming the Temporary Variables

Let us consider the expression a:= b+c can be renamed as d:= b+c where

a = temporary variable

d = new temporary variable

Every expression of a can be replaced by d without changing basic block optimization.

### Interchanging Two Adjacent Independent Statements

Let us consider two adjacent statements

``````a:= b+c
d:= e+f``````

The values a and d are interchangeable as the two expressions are not dependent on each other.

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## Algebraic Transformations

This transformation involves changing an expression into an equivalent algebraic set.

``````Example:
x:= x-0
x:= x*1``````

The two sets are equivalent algebraic.

During compile-time, constants are replaced by their equivalent numerical values.

Let us consider the sequence of expressions as

``````a: = b+c
d: = e+f
x: =  e+f-z``````

The above expressions can be evaluated as:

``````a: = b+c
d: = e+f
x: =   d-z``````

## Loop Optimization

Loop optimization refers to techniques used to improve the performance and efficiency of loops in computer programs. These techniques aim to minimize execution time, reduce memory usage, and enhance cache locality by optimizing loop structures and the operations within them.

Loop optimization techniques include:

• Loop Unrolling: Replicating loop bodies to reduce loop overhead and exploit instruction-level parallelism.
• Loop Fusion: Combining multiple nested loops into a single loop to reduce loop overhead and improve cache efficiency.
• Loop Tiling: Dividing loops into smaller tiles or blocks to improve cache locality and reduce memory access latency.
• Loop Interchange: Reordering nested loops to improve data locality and exploit parallelism.
• Loop Vectorization: Transforming loops to operate on multiple data elements simultaneously using vector instructions, enhancing parallelism and performance on SIMD architectures.
• Loop Blocking: Breaking down large loops into smaller blocks to improve data locality and facilitate parallel execution.
• Loop-Invariant Code Motion: Moving invariant computations outside the loop to reduce redundant computations and improve performance.

### What is a flow graph?

A flow graph is a graph that depicts basic blocks and relationships with successors.

### What is loop unrolling?

A code optimization technique that checks iteration at every step in the loop.

### What is dead code elimination?

Dead code elimination involves the removal of variables that are never used.

### Who is responsible for code optimization?

System Programmer

### What is meant by the reduction in strength?

Replacement of costly operation.

## Conclusion

Congratulations on finishing the blog!! After reading this blog, you will grasp the concept of Block Optimization.