34、静态单赋值形式与函数式中间表示

静态单赋值形式与函数式中间表示

1. 从SSA形式转换回来

在将静态单赋值（SSA）形式的程序转换回普通形式时，需要进行活跃性分析并构建干涉图。以下是相关算法：

LivenessAnalysis() =
for each variable v
    M ←{}
    for each site-of-use s of v
        if s is a φ-function with
            v as its ith argument
            let p be the ith predecessor of
                the block containing s
            LiveOutAtBlock(p, v)
        else LiveInAtStatement(s, v)

LiveOutAtBlock(n, v) =
    v is live-out at n
    if n ∉ M
        M ← M ∪ {n}
        let s be the last statement in n
        LiveOutAtStatement(s, v)

LiveInAtStatement(s, v) =
    v is live-in at s
    if s is the first statement of some block n
        v is live-in at n
        for each predecessor p of n
            LiveOutAtBlock(p,