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

[Denis Petrov via cfe-dev]

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?

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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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