[cfe-dev] [analyzer] How to analyzer the code after an indefinite loop?

[Gábor Horváth via cfe-dev]

Well, technically you can do this by changing some config values but we
have not turned these on by default yet. Mainly, because we have yet to see
strong evidence that the additional false positives worth the gain in
coverage.

On Fri, Jul 31, 2020, 6:26 PM Denis Petrov <dpetrov at accesssoftek.com> wrote:

> Gabor, thank you.
>
> Well, as I see there's no way to do this without changes/improvements in
> the core for now.
>
>
> ------------------------------
> *Denys Petrov*
> Senior С++ Developer | Kharkiv, Ukraine
>
> ------------------------------
> *От:* Gábor Horváth <xazax.hun at gmail.com>
> *Отправлено:* 30 июля 2020 г. 15:48
> *Кому:* Denis Petrov
> *Копия:* Artem Dergachev; cfe-dev
> *Тема:* Re: [cfe-dev] [analyzer] How to analyzer the code after an
> indefinite loop?
>
> Hi!
>
> There are two tools in the analyzer to help these problems but both are
> off by default as they would need some additional improvements and testing.
>
> One is loop unrolling which (when turned on) will detect specific loop
> patterns and unroll them completely (instead of stopping after 4
> iterations).
> The other is loop widening which involves restarting the analysis after
> the loop. While this increases the coverage of the analysis it can also
> trigger additional false positives as a large portion of the state needs to
> be invalidated to restart the analysis. Making this invalidation less
> severe is one way to improve the situation.
>
> Cheers,
> Gabor
>
> On Thu, 30 Jul 2020 at 14:32, Denis Petrov via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> In addition to my previous letter. I'm very concerned that we may have no
>> chance to analyze a big chunk of code in this case:
>>
>> void clang_analyzer_warnIfReached();
>> int f()
>> {
>>   int i = 0;
>>   for(int i = 0; i < 100; i++){
>>     if(i > 10){
>>       clang_analyzer_warnIfReached();
>>       // a lot of code will never be analyzed
>>     }
>>   }
>> }
>>
>> Why don't we analyze loop bodies as functions, just substitute a var `i`
>> with symbols(or constraint ranges) after reaching the limits, not
>> generating a sinks instead?
>>
>> Or there are somewhere already disscussed plans for improvement?
>>
>>
>> ------------------------------
>> *Denys Petrov*
>> Senior С++ Developer | Kharkiv, Ukraine
>>
>> ------------------------------
>> *От:* Artem Dergachev <noqnoqneo at gmail.com>
>> *Отправлено:* 28 июля 2020 г. 22:34
>> *Кому:* Denis Petrov; cfe-dev
>> *Тема:* Re: [cfe-dev] [analyzer] How to analyzer the code after an
>> indefinite loop?
>>
>> CAUTION: This email originated from outside of the organization. Do not
>> click links or open attachments unless you recognize the sender and know
>> the content is safe.  If you suspect potential phishing or spam email,
>> report it to ReportSpam at accesssoftek.com
>> Here's how you can find this out with the help of ExprInspection:
>>
>>
>> $ cat test.c
>>
>> int f(int x, int flag)
>> {
>>   int i = 0;
>>   while(i < x)
>>     i++;
>>
>>   clang_analyzer_warnIfReached();
>> }
>>
>>
>> $ clang --analyze -Xclang -analyzer-checker=debug.ExprInspection test.c
>>
>> test.c:7:3: warning: REACHABLE [debug.ExprInspection]
>>   clang_analyzer_warnIfReached();
>>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> 1 warning generated.
>>
>>
>> Here's a slightly more interesting experiment:
>>
>>
>> $ cat test.c
>>
>> int f(int x, int flag)
>> {
>>   int i = 0;
>>   while(i < x)
>>     i++;
>>
>>   if (flag) {
>>     clang_analyzer_warnIfReached();
>>     clang_analyzer_numTimesReached();
>>     return i;
>>   } else {
>>     clang_analyzer_warnIfReached();
>>     clang_analyzer_numTimesReached();
>>     return 0;
>>   }
>> }
>>
>>
>> $ clang --analyze -Xclang -analyzer-checker=debug.ExprInspection test.c
>>
>> test.c:8:5: warning: REACHABLE [debug.ExprInspection]
>>     clang_analyzer_warnIfReached();
>>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> test.c:9:5: warning: 4 [debug.ExprInspection]
>>     clang_analyzer_numTimesReached();
>>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> test.c:12:5: warning: REACHABLE [debug.ExprInspection]
>>     clang_analyzer_warnIfReached();
>>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> test.c:13:5: warning: 1 [debug.ExprInspection]
>>     clang_analyzer_numTimesReached();
>>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> 4 warnings generated.
>>
>>
>> Will you be able to figure out why is one branch reached 4 times while
>> the other branch is reached only once? You can find all your answers on the
>> exploded graph dump.
>>
>>
>> On 7/28/20 5:59 AM, Denis Petrov via cfe-dev wrote:
>>
>> Hi, community!
>>
>>
>> A quick question.
>>
>>
>> Is CSA Core able to analyze the code after some indefinite loop?
>>
>> E.g.
>> void f(int x)
>> {
>>   int i = 0;
>>   while(i < x)
>>     i++;
>>   // Interested in some code here!!
>> }
>>
>>
>> I found that Exploded graph grows going through the loop 4 times and
>> then stops to analyze the code further.
>>
>> P.S. I know about -analyzer-max-loop(4)​.
>> ------------------------------
>> *Denys Petrov*
>> Senior С++ Developer | Kharkiv, Ukraine
>>
>>
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>>
>>
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>
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