[cfe-dev] Question on LiveVariables analysis

[Anna Zaks]

> On Feb 17, 2015, at 2:59 AM, Georg Altmann <george at george-net.de> wrote:
> 
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> On 11.10.2011 05:56, Anna Zaks wrote:
>> Most likely there is some issue with the way you build the analysis
>> in your code; you should probably look at other uses of 
>> UninitializedVariables to see what you are missing. Also, try to
>> find out at which step the first symptoms of the problem occur -
>> for example, do you get a CFG different from what you see when
>> dumping the CFG with a debug checker? (See the command from Ted's
>> reply below.)
>> 
>> I noticed that you do not pass CFGBuildOptions when constructing 
>> the AnalysisContext. Here is some code from
>> AnalysisBasedWarnings.cpp, which implies that you might need to
>> request linearized CFG. // Unreachable code analysis requires a
>> linearized CFG. AC.getCFGBuildOptions().setAllAlwaysAdd();
> 
> Thank you! That just made my day!
> 
> Can anybody elaborate or give a pointer on what is meant by
> a linearized CFG in this case?

It does not refer to an existing term. Linearized CFG is the mode where each AST subexpression is represented as an element in the basic block (instead of elements being expressions, which is how CFG was originally implemented). 

(We should consider having this on by default!)

> I found this paper [1] which contains some info on CFG linearization.
> 
> Which algorithm is implemented for LiveVariables and CFG linearization
> in clang static analyzer? Any pointers?
> 
> Regards,
> Georg
> 
> 
> [1]
> paper: http://compilers.cs.uni-saarland.de/papers/karrenberg_opencl.pdf
> DOI paper: http://dx.doi.org/10.1007/978-3-642-28652-0_1
> slides: http://llvm.org/devmtg/2012-04-12/Slides/Ralf_Karrenberg.pdf
> 
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