GATE-CS-2017 (Set 2) - Chapter 36

Introduction

The GATE-CS-2017 (Set 2) examination included a question from Chapter 36 of the syllabus, which focused on the topic of compiler design. This topic is of great importance to all programmers, as it deals with the creation and optimization of software that translates high-level programming languages into machine code that the computer can understand and execute.

Overview

The question in the GATE-CS-2017 (Set 2) examination asked about the optimization of code using loop unrolling and the transformation of a basic block with a single conditional jump into a two-way conditional jump. These concepts are fundamental to compiler design, as they are used to improve the performance and efficiency of code.

Loop Unrolling

Loop unrolling is a technique used by compilers to optimize loops. The basic idea is to reduce the number of times the loop control variable is updated, and to perform multiple iterations of the loop in each pass. This reduces the overhead associated with loop control and improves performance.

The code for a loop might look like this:

for(i = 0; i < n; i++) {
    // code to be executed
}

To unroll this loop, we might modify the code to look like this:

for(i = 0; i < n-2; i += 2) {
    // code to be executed
    // code to be executed
}
for(; i < n; i++) {
    // code to be executed
}

Here, we have unrolled the loop by a factor of 2, meaning that we perform two iterations of the loop in each pass. This reduces the overhead associated with the loop control variable and improves performance.

Two-Way Conditional Jump

A two-way conditional jump is a type of jump instruction used in compilers to optimize code. The basic idea is to transform a basic block with a single conditional jump into a two-way conditional jump, which can improve the efficiency of the code.

Consider the following code:

if(condition) {
    // code to be executed if condition is true
} else {
    // code to be executed if condition is false
}

To transform this code into a two-way conditional jump, we might modify it to look like this:

if(!condition) {
    // code to be executed if condition is false
    goto end_of_block;
}
// code to be executed if condition is true
end_of_block:

Here, we have transformed the single conditional jump into a two-way conditional jump, which can improve the efficiency of the code by eliminating the need for a branch instruction.

Conclusion

The concepts of loop unrolling and two-way conditional jump are fundamental to compiler design, and are essential for all programmers who want to create efficient and optimized code. Understanding these concepts can help programmers improve the performance of their code, and can lead to more efficient and effective software development.