Inquiry Regarding the Usage and Implementation of Constant Propagation in CPAchecker

[Lin]

Dear CPAchecker Development Team,

I hope this message finds you well. I am currently engaged in a project where I am utilizing CPAchecker, and I have been particularly interested in the application of the constant propagation feature within your tool.

While exploring the codebase, I came across the constantPropagation setting in the FlowDependenceConfig class within the DependenceGraphBuilder module. However, I have some inquiries regarding its usage and implementation:

1. 1.Activation of Constant Propagation: Could you please provide guidance on how to properly set and activate the constantPropagation feature within CPAchecker? Is there a specific configuration file or command-line option that needs to be set? The only related config setting I have found is :  

   utils.edgeinfo.buildDepGraph = true 

   dependencegraph.flowdeps.use = true dependencegraph.flowdep.constantPropagation = true

   2.Implementation Details: I am also keen to understand the implementation details of the constant propagation feature. Could you please point me to the specific parts of the source code or documentation where I can find more information about how this feature is implemented and operates within CPAchecker? 

   Understanding these aspects will greatly aid in the effective utilization of CPAchecker in my current project. I appreciate the time and effort your team has invested in developing this powerful tool, and I look forward to your valuable insights on the above queries.

Thank you for your assistance and support.

Best regards,

Tengjie Lin

[Philipp Wendler]

Dear Tengjie Lin,

Am 17.11.23 um 19:25 schrieb Lin:

> I hope this message finds you well. I am currently engaged in a project
> where I am utilizing CPAchecker, and I have been particularly interested in
> the application of the constant propagation feature within your tool.
>
> While exploring the codebase, I came across the constantPropagation setting
> in the FlowDependenceConfig class within the DependenceGraphBuilder module.

Can you please tell me where you are looking at specifically?
We neither have a FlowDependenceConfig class nor a
DependenceGraphBuilder in the current CPAchecker main branch.

Furthermore, all the dependence-graph related stuff is only a special
component that is used only in one particular case that is not enabled
by default in CPAchecker. It is not part of the main core of CPAchecker.
Thus anything inside the dependencegraph module will have no effect
outside of this particular niche.

In CPAchecker we do not have a constant propagation that you can turn on
and off and that would affect its main mode of operation. We have some
simple inlining of "const" declarations behind the "cfa.simplifyCfa"
configuration option, but this is not constant propagation.

We have an analysis though, our value analysis, that is able to do
constant propagation and much more. It is described for example in this
paper:
https://www.sosy-lab.org/research/pub/2013-FASE.Explicit-State_Software_Model_Checking_Based_on_CEGAR_and_Interpolation.pdf
If you use the -valueAnalysis-NoCegar-join config, this will behave much
like a standard constant propagation. But it would be just CPAchecker
running constant propagation as an analysis, and not a constant
propagation feature that can be turned on in addition to an analysis.

Greetings
Philipp
--
Philipp Wendler
Software and Computational Systems Lab
LMU Munich, Germany
Oettingenstr. 67 Raum F008 - Tel.: 089/2180-9181

[Lin]

Dear Philipp Wendler and the CPAchecker Development Team,

I hope this message finds you all in good health and spirits. Thank you for your previous response, which provided valuable insights into CPAchecker's capabilities and limitations regarding constant propagation. I am writing to seek further guidance on a specific application of CPAchecker in my project.

My aim is to analyze the impact of inserting a particular function (an interrupt function, in my case) on the control flow of a main function. Specifically, I wish to use constant propagation to observe changes in the values of variables in branch condition statements before and after the insertion of this function. This approach would help identify points where inserting the function could significantly alter the main function's control flow.

Based on your previous response, I understand that CPAchecker does not have a toggleable constant propagation feature for its main mode of operation. However, the value analysis you mentioned, particularly the -valueAnalysis-NoCegar-join config that resembles standard constant propagation, seems promising for my needs. But as I understand, the valueAnalysis is implemented during the transfer from CFG (Control Flow Graph) to ART (Abstract Reachability Tree). My requirement seems more aligned with applying valueAnalysis solely at the CFG stage.

Additionally, I would like to inquire if it is possible to implement inter-procedural constant propagation at the CFG (Control Flow Graph) level within CPAchecker to achieve my goal. Could such an approach be feasible given the current features of CPAchecker, or are there alternative methods or tools within CPAchecker that could achieve my goal?

Understanding the best way to utilize CPAchecker for this purpose is crucial for my project. I appreciate your expertise and am eager to hear your recommendations.

Thank you once again for your support and guidance.

Best regards,

Tengjie Lin

[Philipp Wendler]

Dear Tengjie Lin,

Am 25.11.23 um 07:29 schrieb Lin:

> My aim is to analyze the impact of inserting a particular function (an
> interrupt function, in my case) on the control flow of a main function.
> Specifically, I wish to use constant propagation to observe changes in the
> values of variables in branch condition statements before and after the
> insertion of this function. This approach would help identify points where
> inserting the function could significantly alter the main function's
> control flow.

I don't really know the context, but it seems to me that constant
propagation is likely relatively imprecise for this purpose?
But this is up to you, of course.

> Based on your previous response, I understand that CPAchecker does not have
> a toggleable constant propagation feature for its main mode of operation.
> However, the value analysis you mentioned, particularly the
> -valueAnalysis-NoCegar-join config that resembles standard constant
> propagation, seems promising for my needs. But as I understand, the
> valueAnalysis is implemented during the transfer from CFG (Control Flow
> Graph) to ART (Abstract Reachability Tree). My requirement seems more
> aligned with applying valueAnalysis solely at the CFG stage.

Hm, why would you think that?
You could run CPAchecker on each version of your program and then
compare the resulting ARGs (they are graphs, not trees, if you use
constant propagation).

> Additionally, I would like to inquire if it is possible to implement
> inter-procedural constant propagation at the CFG (Control Flow Graph) level
> within CPAchecker to achieve my goal. Could such an approach be feasible
> given the current features of CPAchecker, or are there alternative methods
> or tools within CPAchecker that could achieve my goal?

Well, in principle this is implementable. But manipulating the CFA is
certainly not as convenient as just running an analysis on it.
And for your use case I do not see why you would need a CFA as output,
so I totally recommend to use the approach discussed above.