2020牛客多校第七场J-Pointer Analysis

指针是C语言的精髓

Statement

有四种操作

求每个指针可能指向位置

Solution

• 首先，这是道暴力模拟题
• 小写字母一定是指针指成的有向图中出度为零的点（结尾）
• 我们考虑从后往前考虑
• 一层一层遍历…
• 是不是很像$bfs?$
• 再想，更像$SPFA$的思想
• 每次从队列中取出点，合并
• 如果合并后答案变了，就放进队列里

Pseudo Code

Let worklist be a set//set or queue
For every allocation statement A = x: 
	insert x into pt(A)
	If pt(A) has been changed, add A into worklist
While worklist is not empty:
	While worklist is not empty:
		select one element X from worklist
		delete X from worklist
		For every assignment statement like Y = X:
			merge pt(X) into pt(Y)
			If pt(Y) has been changed, add Y into worklist
	For every store statement Y.f = X:
		For every object o in pt(Y):
			merge pt(X) into pt(o.f)
	For every load statement Y = X.f:
		For every object o in pt(X):
			merge pt(o.f) into pt(Y)
			 If pt(Y) has been changed, add Y into worklist