Code360 powered by Coding Ninjas X Code360 powered by Coding Ninjas X
Table of contents
Structure-Preserving Transformations
Elimination of Common Sub-Expression
Elimination of Dead Code
Renaming the Temporary Variables
Interchanging Two Adjacent Independent Statements
Algebraic Transformations
Loop Optimization
Frequently Asked Questions
What is a flow graph?
What is loop unrolling?
What is dead code elimination?
Who is responsible for code optimization?
What is meant by the reduction in strength?
Last Updated: Apr 30, 2024

Block Optimization

Author Prachi Singh
0 upvote
Leveraging ChatGPT - GenAI as a Microsoft Data Expert
Prerita Agarwal
Data Specialist @
23 Jul, 2024 @ 01:30 PM


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

Compiler Design

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
  2. Elimination of Dead Code
  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

Elimination of Dead Code

  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.

Get the tech career you deserve, faster!
Connect with our expert counsellors to understand how to hack your way to success
User rating 4.7/5
1:1 doubt support
95% placement record
Akash Pal
Senior Software Engineer
326% Hike After Job Bootcamp
Himanshu Gusain
Programmer Analyst
32 LPA After Job Bootcamp
After Job

Algebraic Transformations

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

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.

Frequently Asked Questions

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.


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

Recommend Reading:

Do check out The Interview guide for Product Based Companies as well as some of the Popular Interview Problems from Top companies like Amazon, Adobe, Google, Uber, Microsoft, etc. on Coding Ninjas Studio.

Also check out some of the Guided Paths on topics such as Data Structure and Algorithms, Competitive Programming, Operating Systems, Computer Networks, DBMS, System Design, etc. as well as some Contests, Test Series, Interview Bundles, and some Interview Experiences curated by top Industry Experts only on Coding Ninjas Studio.


Live masterclass