[cfe-dev] trivial conditions and dataflow solver

[Guoping Long]

There are two dataflow analyses to warn uninitialized values and find live
variabels. These two examples are very good tutorials for dataflow analysis.

--
Guoping

2011/10/20 Maarten Wiggers <mwiggers at us.fujitsu.com>

> Hi Ted,****
>
> ** **
>
> Yes, I am using the DataflowSolver class. Thanks for the heads-up on
> potential removal of this class. I was under the impression that this was
> the default Flow Analysis engine, but will look at the current
> implementation of the analyses to understand alternative options.****
>
> ** **
>
> Thanks,****
>
> Maarten****
>
> ** **
>
> *From:* Ted Kremenek [mailto:kremenek at apple.com]
> *Sent:* Wednesday, October 19, 2011 10:05 PM
> *To:* Maarten Wiggers
> *Cc:* 'cfe-dev at cs.uiuc.edu'
> *Subject:* Re: [cfe-dev] trivial conditions and dataflow solver****
>
> ** **
>
> Hi Maarten,****
>
> ** **
>
> Can you be a bit more specific on what you are doing?  Are you using the
> actual DataflowSolver class?  If so, currently ALL blocks are currently
> enqueued by the solver, not just the roots.  IRRC, this was to address an
> issue that previously existed with the solver and one of the analyses, but
> now no analyses use the solver anymore this behavior certainly can be
> changed.****
>
> ** **
>
> FWIW, I was considering removing this class completely, since it is no
> longer used.****
>
> ** **
>
> Ted****
>
> ** **
>
> On Oct 19, 2011, at 6:40 PM, Maarten Wiggers wrote:****
>
>
>
> ****
>
> Hi,****
>
>  ****
>
> I am experimenting with the dataflow solver and am wondering whether the
> following is expected behavior.****
>
>  ****
>
> I took a function with a trivially true if condition. When constructing the
> CFG, clang seems to take this into account and does not generate a
> successor/predecessor relationship between blocks B1 and B3 (see below).
> However, when running the dataflow solver, I get that {field3, field2} and
> {field1} are possible sets of accesses to fields, while I would expect that
> either {field3,field1} or nothing is reported instead of {field1}.
> Currently, it seems block B1 is visited and its results are propagated, but
> it does not receive input values from B3.****
>
>  ****
>
> Is this the intended behavior? I would expect that blocks without
> predecessors and that are not entry blocks would be skipped?****
>
>  ****
>
> Thanks,****
>
> Maarten****
>
>  ****
>
> Example function:****
>
>  ****
>
> void func1()****
>
> {****
>
> field3 = 5****
>
> if(1)****
>
> field2 = 2;****
>
> else****
>
> field1 = 2;****
>
> }****
>
>  ****
>
> A dump of the CFG gives:****
>
>  ****
>
> [B4 (Entry) ]****
>
> Predecessors (0):****
>
> Successors (1): B3****
>
>  ****
>
> [B1]****
>
> 1: this->field1 = 2****
>
> Predecessors (0);****
>
> Successors (1): B0****
>
>  ****
>
> [B2]****
>
> 1: this->field2 = 2****
>
> Predecessors(1):B3****
>
> Successors(1):B0****
>
>  ****
>
> [B3]****
>
> 1: this->field3 = 5****
>
> 2: 1****
>
> T: if [B3.2]****
>
> Predecessors (1): B4****
>
> Successors(2): B2 Null****
>
>  ****
>
> [B0 (Exit) ]****
>
> Predecessors(2):B1 B2****
>
> Successors(0):****
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev****
>
> ** **
>
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