[HW8] What do In and Out represent?

[ssamt]

이름 Your Name

김병권

질문 Question

In(a, b) : The value defined in b enters to a
Out(a, b) : The value defined in b goes out from a

These parts don't seem to be on our lecture slides, and I can't understand it based on this explanation alone. What does it mean for a value to "go out"? Could you please provide some example, or a more detailed explanation?

번역본 Translated Version

No response

[FatsyBear09]

I'm also confused about this. Is it possible to just give the inference rule for this one?

[goodtaeeun]

The current README description appears to be misleading.

To correctly implement the analysis, you should refer to the lecture slides to define the rules for Path, Edge, and Alarm. These are the key facts that the slides describe and that your analysis must implement.

The facts In and Out are auxiliary and not shown in the slides. However, they are essential for tracking the data flow and representing the data reachability.

To illustrate, consider this simple example:

1: x = 3;
2: x = 4;
3: z = 5;
4: y = x;

The control flow here is straightforward: it goes from line 1 → 2 → 3 -> 4.

Data flow, however, is more subtle. For instance, the value of x defined at line 1 flows out of line 1 and into line 2. But it doesn't reach line 3 because it is killed by the new definition of x at line 2. However, the value of x defined at line 2 flows out of line 2, reaches line 3, flows out of line 3 and eventually reaches line 4. Thus, the x used at line 4 is the x defined at line 2.

The In and Out facts help describe such reachability — i.e., whether a definition of a variable reaches a particular program point.

Since we have a grasp of what they are, here are the more descriptive definitions of the rules.

• In(a,b): The data defined by command a flows into the command b. In the example, it would be In(1,2) or In(2,3)
• Out(a,b): The data defined by command a flows out of command b. The most trivial case would be the defining commands, where there is always an Out for the data defined by themselves, such as Out(1,1)

Note: We will not provide the detailed inference rules for these relations — part of your task in this homework is to design and implement them yourself.

[moonx010]

@goodtaeeun I do not understand why only Out(2, 3) is made for non trivial Outs. Cloud you please tell the definition of In and Out in Korean? Its really confusing

[goodtaeeun]

재정의된 변수의 값은 재정의될 때 덮어씌어지기 때문에 기존 변수의 값이 더 이상 실행흐름을 따라 전달되지 않는다고 생각하시면 되겠습니다.

[moonx010]

그러면 위 예시에서 Out(3, 4), Out(2, 4) 도 derive 되는게 맞는걸까요?

[goodtaeeun]

아 그렇겠네요. 다만 그 뒤에 실행될 코드가 없어서 무의미하기에 따로 표기하지는 않았습니다.

[moonx010]

아하 넵넵 감사합니다!