[Soot-list] Constant propagation analysis in SOOT

[Bernhard Berger]

Hi Zhoulai,

I think that you are correct and the result of a constant expression is not propagated. I think that you have to implement your own constant propagation if you want to do the following steps a) propagate constants b) calculate the results of "constant expressions" c) propagate the results of constant expressions and d) "merge" constants with same value. Take a look at [1] for more details on intra-procedural analysis in Soot. Furthermore there is a Visitor-Pattern for statements and expressions [2], [3].

Bernhard

[1] http://www.bodden.de/2008/09/22/soot-intra/
[2] https://github.com/Sable/soot/blob/develop/src/soot/jimple/AbstractStmtSwitch.java
[3] https://github.com/Sable/soot/blob/develop/src/soot/jimple/AbstractExprSwitch.java

Am 10.09.2013 um 09:05 schrieb Zhoulai FU <zhoulai.fu at gmail.com>:

> Hi, Bernhard,
> 
> Thanks for your quick reply.  My expected results will be a mapping from 'x' to the value lattice 3 and 'unknown', respectively for  
> 
> y=3; z=3; if (?) {x=y} else {x=z};
> and 
> y=2; z=4; if (?) {x=y} else {x=z};
> 
> If I understand correctly, the current implementation in SOOT's "soot.jimple.toolkits.scalar.ConstantPropagatorAndFolder" takes only one pass  (thus its algorithm should be  linear), so I think it would be easier to rewrite the analysis than to extend it for a more precise constant propagation.  Let me know pls if I misunderstand. 
> 
>  Zhoulai
> 
> On Sep 10, 2013, at 7:37 AM, Bernhard Berger <berber at tzi.de> wrote:
> 
>> Hi Zhoulai,
>> 
>> what is the result you want to get? Just the fact that x in print(x) is constant in all cases or that x is definitely 3 (what would be your expected result in the case that y = 2 and z = 4)? Do you want this information intra procedural or inter procedural?
>> 
>> The ConstantPropagatorAndFolder works in a intra procedural way and propagates nuemric constants and calculates the result of expressions on numeric constants. I think the current implementation can be extended to a version that checks that all definitions of a use have the same constant value. If you change the code feel free to contribute the enhancements back to the soot community.
>> 
>> Regards,
>> 
>> Bernhard 
>> 
>> Am 10.09.2013 um 07:19 schrieb Zhoulai <zell08v at gmail.com>:
>> 
>>> Dear all,
>>> 
>>> I am about to use  a constant propagation/folder  analysis under Soot framework. It seems  that there exists  one such implementation in SOOT already:
>>> 
>>> soot.jimple.toolkits.scalar.ConstantPropagatorAndFolder
>>> 
>>> However,  this implementation seems to be naive.  If I understand correctly its source code, 
>>> 
>>> http://www.massapi.com/source/sootsrc-2.4.0/src/soot/jimple/toolkits/scalar/ConstantPropagatorAndFolder.java.html
>>> 
>>> the implementation associates with local variables a constant only if this  underlined variable has a single definition site.   For example, the implementation  cannot decide that 'x' is a constant  for the snippet below:
>>> 
>>> y=3; z=3; if (?) {x=y} else {x=z};
>>> print (x);
>>> 
>>> In my application, I need that 'x' be recognized as constant. Although this is not a difficult problem, I would try to avoid code duplication whenever possible. So would you please tell me whether Soot has built in a more sophisticated constant propagation analysis than its "ConstantPropagatorAndFolder" mentioned above, such as the conditional constant propagation?  Thanks in advance. 
>>> 
>>> Zhoulai (zell)
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> Soot-list mailing list
>>> Soot-list at sable.mcgill.ca
>>> http://mailman.cs.mcgill.ca/mailman/listinfo/soot-list
>> 
> 

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