Re: [GSoC][Static Analyzer] Ideas for proposal

[Shengyu Huang <kumom.huang@gmail.com>]

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Hi Dave,

> On 22 Feb 2023, at 15:11, Shengyu Huang <kumom.huang@gmail.com> wrote:
> 
>> But a better place to look would probably be in our bugzilla; see the
>> links on the wiki page:
>>  https://gcc.gnu.org/wiki/StaticAnalyzer 
>> The "open bugs" list currently has 41 "RFE" bugs ("request for
>> enhancement" i.e. ideas for new features), some of which might make
>> suitable GSoC ideas, and/or be of interest to you (ideally both!)
>> 
>> Also, the GSoC wiki page has some project ideas:
>>  https://gcc.gnu.org/wiki/SummerOfCode#Selected_Project_Ideas
>> 
> 
> Yeah I was also searching for interesting ideas on the bugzilla, and I will communicate to you once I have any more concrete ideas.

I spent some time searching through Bugzilla this weekend while familiarizing with the analyzer internals, and I found the following things interesting, and it’d be great if you can give me some preliminary feedback:

1. I am not sure why we added the class `shift_count_negative_diagnostic` in region-model.cc <http://region-model.cc/>, because there is a similar warning issued from c/c-typeck.cc <http://c-typeck.cc/>, and when I compiled with -fanalyzer that has the code `b = b << -1`, I got two warnings that mean the same thing. Maybe interestingly, when I compiled my test case with -O2, I got the warning from -Wshift-count-negative but not from -Wanalyzer-shift-count-negative. Would it be considered as a false negative for the analyzer? 

2. Something related to 1. is PR98447 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98447)

3. PR104955 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104955) still takes a long without -Wno-analyzer-double-free. I’d be interested in further investigating the problem (probably as you said sharing one feasible_graph can fix the problem).

4. What’s the most interesting to me are PR103533 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103533), PR104940 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104940) because I focus on formal methods in my university studies, and I’m currently looking into Dafny internals for my semester project.

5. PR105891 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105891) seems fitted to get started during the project phase, or be used as a warm-up before the official project phase.

6. PR106147 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106147) says you are implementing a prototype already, so I guess I’ll leave it out, but I am also quite interested in this analysis. At a glimpse I am not quite sure why infinite recursion and infinite loop should be treated differently (maybe it’ll become clearer to me once I am more familiar with the internals). In addition, a simple function that looks like this

void re (int c)
{
  if (c > 0)
    re (c + 1);
  else
    re (1);
}

can also be concluded as infinite recursion because there is no base case in all possible paths.

7. Other PRs that interest me: PR106006 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106006) and PR107017 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107017, already mentioned in the GSoC page).

Best,
Shengyu