[Soot-list] Java-Jimple mapping using SourceLnPosTag

[Marcus Mews]

Hello everybody,

    I am Marcus Mews (TU-Berlin) and about to use Soot in an academic 
prototype to perform semantic preserving refactorings. Therfor, I need 
to know certain details about Soot's mapping between Java Expressions 
and Jimple Units. For various reasons, Soot splits up Java Expressions 
like from

void JavaFoo() {
x++;
}

to

void JimpleFoo() {
     temp$1 = this.<some.Clazz: int x>;  //sline=134, eline=134, spos=1, 
epos=1
     temp$2 = temp$1 + 1;                //sline=134, eline=134, spos=1, 
epos=1
     this.<some.Clazz: int x> = temp$2;  //sline=134, eline=134, spos=1, 
epos=1
}

Another - slightly different - case is the following example: From

void JavaBar() {
x=x+1;
}

to

void JimpleBar() {
     temp$3 = this.<some.Clazz: int x>;    //sline=135, eline=135, 
spos=3, epos=3
     temp$4 = temp$3 + 1;                  //sline=135, eline=135, 
spos=3, epos=3
     this.<some.Clazz: int x> = temp$4;    //sline=135, eline=135, 
spos=1, epos=1
}


    In the first example above, the expression "x++" is substituted by 
three other expressions in the Jimple code, since there is no equivalent 
in the Jimple language, I assume. In the second example, the expression 
"x=x+1" is just split up into more trivial expressions.
    I'd like to know where each Jimple unit comes from.

    I considered using the SourceLnPosTag, but I'm not sure, whether 
this is the right thing to do; in the examples above, I also stated the 
SourceLnPosTags: In the "x++"-example, all the SourceLnPosTags point to 
the same Java code text snippet, which is as I expected (although I it 
seems odd that epos=1 instead of epos=3). But in the second example I 
don't understand the position numbers, since some Jimple units have 
equal SourceLnPosTags. Maybe the tags are incorrect or maybe I'm off the 
track here and there is a better way to retrieve each unit's Java origin?

    Anyway, I appreciate any advice or links to manuals, etc.
Thanks and regards,
    Marcus