⑶ Loop Optimization

Loop Optimization（迴圈優化）是一種在程式設計中用於優化迴圈的技術。迴圈是一種重要的程式結構，用於執行重複的操作。迴圈的效率對於程序的性能至關重要，因此進行迴圈優化是提高程序性能的關鍵

Frequency Reduction (Code Motion): In frequency reduction, the amount of code in loop is decreased. A statement or expression, which can be moved outside the loop body without affecting the semantics of the program, is moved outside the loop. Example: Initial code: while(i<100) { a = Sin(x)/Cos(x) + i; i++; } Optimized code: t = Sin(x)/Cos(x); while(i<100) { a = t + i; i++; } Loop Unrolling: Loop unrolling is a loop transformation technique that helps to optimize the execution time of a program. We basically remove or reduce iterations. Loop unrolling increases the program’s speed by eliminating loop control instruction and loop test instructions. Example: Initial code: for (int i=0; i<5; i++) printf(\"Pankaj\\n\"); Optimized code: printf(\"Pankaj\\n\"); printf(\"Pankaj\\n\"); printf(\"Pankaj\\n\"); printf(\"Pankaj\\n\"); printf(\"Pankaj\\n\"); Loop Jamming: Loop jamming is the combining the two or more loops in a single loop. It reduces the time taken to compile the many number of loops. Example: Initial Code: for(int i=0; i<5; i++) a = i + 5; for(int i=0; i<5; i++) b = i + 10; Optimized code: for(int i=0; i<5; i++) { a = i + 5; b = i + 10; }