[Soot-list] What is the purpose of UseBox and DefBox?

[周书林]

I am newbie in Soot. I am quite confused with UseBox and DefBox. In Soot
Survivors Guide, it says "Through a Unit we can retrieve values used
(getUseBoxes()), values defined (getDefBoxes()) or even both
(getUseAndDefBoxes()).  ".

And in "Analyzing Java Programs with Soot", it present an example
for getUseBoxes() and getDefBoxes() as follows:

For an unit : x =y op z;
getUseBoxes() returns {y, z, y op z}
getDefBoxes() returns {x}

But I could also get this information by getting the LeftOp and RightOp of
this AssignStmt.

So, what is the meaning of  UseBox and DefBox?

Hope for your help.

Sincerely,
Sep
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