Loop unrolling

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#Computer Arch #Programming

本文深入探讨了循环展开技术如何通过减少或消除控制循环的指令（如指针算术和每轮迭代的结束循环测试），降低分支开销，以及隐藏延迟，特别是内存读取的延迟，来增加程序速度。具体方法包括将循环重写为一系列相似且独立的语句序列，从而显著提升执行效率。

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overview: optimize a program's execution speed at the expense of code size

The goal of loop unwinding is to increase a program's speed byreducing (or eliminating) <Not necessary eliminate iterations>instructions that control the loop, such as pointer arithmetic and "end of loop" tests on each iteration;reducing branch penalties; as well as "hiding latencies, in particular, the delay in reading data from memory".To eliminate this overhead, loops can be re-written as a repeated sequence of similar independent statements.

----From Wikipedia

My understanding:

reduce branch misprediction

gcc options:

-funroll-loops: unroll loops whose number of iterations can be determined at compile time or upon entry to the loop

-funroll-all-loops