循环不变代码外提

循环不变代码外提（英語：，缩写）在计算机编程中是指将循环不变的语句或表达式移到循环体之外，而不改变程序的语义。循环不变代码外提在英文中又被称为或，是编译器中常见的优化方法。

示例

假设有如下代码：

for (int i = 0; i < n; i++) {
    x = y + z;
    a[i] = 6 * i + x * x;
}

其中x = y + z与x * x这两步运算是循环不变的，会在优化中被移出循环体之外。经LICM优化后的代码为：

x = y + z;
t1 = x * x;
for (int i = 0; i < n; i++) {
    a[i] = 6 * i + t1;
}

Aho, Alfred V.; Sethi, Ravi; & Ullman, Jeffrey D. (1986). Compilers: Principles, Techniques, and Tools. Addison Wesley. ISBN 0-201-10088-6.
Compiler Optimizations — Hoisting

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