[cfe-dev] [analyzer] Thoughts on Temporary Destructors

[Anna Zaks]

Is it possible to have the same (similar) positive results just by teaching the analyzer about the custom assertions? If yes, I’d suggest you to use that as a patch on your private branch. Or you might consider teaching the TOT analyzer to accept a list of such assertions. This could be used in cases the source code cannot be annotated with ‘noreturn'.

As Jordan and Ted had mentioned, just reverting the patch results in unexpected behavior in both ObjC and C++.
See cfe/trunk/test/Analysis/live-variables.cpp for the C++ example. There, even though the dereference of 'p’ is guarded by ‘p != 0’, we reported a null pointer dereference.

Anna.

On Feb 10, 2014, at 2:38 AM, Daniel Connelly <dconnelly at google.com> wrote:

> (cc: klimek at google.com, djasper at google.com)
> 
> As a bit of a follow-up, we are still very interested in getting this worked out, as it's a significant barrier to the Analyzer's usefulness. All of our C++ projects make extensive use of custom assertions. For example,
> 
> CHECK(condition) << "something happened with the hydrospanners";
> 
> which logs a message and kills the program if the condition isn't met. None of these custom assertions are pruning code paths due to the missing conditional expression support. For example, when building Chromium, the difference between running without and with the reverted patch is 1982 reported errors vs. 3210 reported errors. This number is a bit conservative, since we also have this problem in dependent libraries that don't (but could) use analyzer_noreturn on their assertions; the real cost is that about 50% of all errors reported by the analyzer are false positives of this form.
> 
> 
> On Fri, Jan 31, 2014 at 11:32 AM, Daniel Connelly <dconnelly at google.com> wrote:
> After digging into this for a couple of weeks across the 2013/2014 boundary, I now doubt that my 20% time will be enough to properly implement this support. Anybody who's interested should feel free to work on this instead, as I'll not be moving forward with it. Jordan, thanks for the pointers and the summary of the problem!
> 
> 
> On Wed, Dec 18, 2013 at 1:55 AM, Jordan Rose <jordan_rose at apple.com> wrote:
> 
> On Dec 16, 2013, at 6:57 , Daniel Connelly <dconnelly at google.com> wrote:
> 
>> On Fri, Dec 13, 2013 at 7:13 PM, Jordan Rose <jordan_rose at apple.com> wrote:
>> 
>> In discussing the first problem, Ted and Anna realized that the liveness information for nested && and || expressions was still incorrect: the outermost expression may potentially depend on all of the inner expressions, but that means that those sub-expressions are always considered live (since expressions are marked dead, in a reverse analysis, at the point of evaluation, and there are paths that don't evaluate a particular sub-expression in a complex logical expression). This wasn't an issue before because && and || didn't actually use those expressions to compute their value, but it's still incorrect.
>> 
>> Is this http://llvm.org/bugs/show_bug.cgi?id=18159 ?
> 
> Yes.
> 
>> Thanks for the overview. This is all pretty new to me, so I'm going to dig into the problem for a couple of days and hopefully come up with some intelligent questions.
> 
> 
> Sorry for the blast of information. If you want an easier place to start playing with the analyzer, you could try hacking on productizing SimpleStreamChecker. (And if you haven't watched our talk from last year's LLVM dev meeting, I definitely suggest taking the time to do so. It's aimed at checker writers, but still describes the general structure of the analyzer. It's linked near the top of http://clang-analyzer.llvm.org/checker_dev_manual.html)
> 
> Jordan
> 
> 
> 
> -- 
> Daniel Connelly | Software Engineer – Chrome | dconnelly at google.com | 
> 
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> 
> 
> 
> -- 
> Daniel Connelly | Software Engineer – Chrome | dconnelly at google.com | 
> 
> Google Germany GmbH
> Dienerstr. 12
> 80331 München
> 
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
> Geschäftsführer: Graham Law, Christine Elizabeth Flores
> 

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