Benefits of Common Subexpression Elimination

How Common Subexpression Elimination Works?

CSE operates on the principle of recognizing recurring subexpressions in code. A subexpression is a portion of code that computes a value and can be a part of multiple larger expressions. Instead of recomputing the same subexpression every time it appears in the code, CSE calculates it once and stores the result in a temporary variable. This variable is then used wherever the subexpression occurs in the code, effectively replacing the repetitive calculations with a single reference....

Benefits of Common Subexpression Elimination

Improved Performance: The primary advantage of CSE is enhanced performance. By reducing redundant computations, CSE significantly decreases the execution time of a program. This optimization is particularly beneficial in computationally intensive applications. Simplified Code: CSE simplifies code by removing unnecessary redundancy. Cleaner code is easier to read, maintain, and debug, leading to fewer programming errors and improved software quality. Reduced Resource Usage: Reducing redundant calculations conserves computational resources such as CPU time and memory. This can be especially advantageous in resource-constrained environments....

Example 1

C++ // before CSE int main() {     a = b + c * 2; //(c*2) is a common subexpression     x = y + c * 2;     ans = a + x; }    // after CSE int main() {     int temp = c * 2; //(c*2) is assigned to a variable temp     a = b + temp; // thus saving the time of computing (c*2)                   // again     x = y + temp;     ans = a + x; }...

Example 2

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Conclusion

C++ // before CSE int main() {     a = b * c;     b = x + y + 2; //(x+y) is a common subexpression     c = x + y + 3; }    // after CSE int main() {     int temp = x + y; //(x+y) is assigned to a variable temp     a = b * c;     b = temp         + 2; // thus saving the time of computing x+y again     c = temp + 3; }...

Frequently Asked Questions

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