如何获取基本块A可达的基本块？

Question

我想知道一个基本块能到达的所有基本块。我该怎么做呢？

#include "llvm/IR/CFG.h"
BasicBlock *BB = ...;
for (BasicBlock *Pred : predecessors(BB)) {
}

Answer 1

您可以遍历继任者的继任者（以此类推），例如：

std::unordered_set<BasicBlock *> reachable;
std::queue<BasicBlock *> worklist;
worklist.insert(BB);
while (!worklist.empty()) {
  BasicBlock *front = worklist.front();
  worklist.pop();
  for (BasicBlock *succ : successors(front)) {
    if (reachable.count(succ) == 0) {
       /// We need the check here to ensure that we don't run 
       /// infinitely if the CFG has a loop in it
       /// i.e. the BB reaches itself directly or indirectly
       worklist.push(succ);
       reachable.push(succ);
    }
  }
}

如果我没有犯任何错误，那么你将在 while 循环结束时得到所有可到达的基本块:)

如何获取基本块A可达的基本块？

How to obtain the basic blocks that are reachable from basic block A?

llvm