[PATCH] D101041: [analyzer] Find better description for tracked symbolic values

[Valeriy Savchenko via Phabricator via cfe-commits]

vsavchenko marked 4 inline comments as done.
vsavchenko added inline comments.


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Comment at: clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp:1532
+      // Telling the user that the value of 'a' is assigned to 'c', while
+      // correct, can be confusing.
+      StoreManager::FindUniqueBinding FB(V.getAsLocSymbol());
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martong wrote:
> vsavchenko wrote:
> > martong wrote:
> > > vsavchenko wrote:
> > > > martong wrote:
> > > > > So here, we have two or three bindings attached to `c`? `foo(b)` and `a` (and `b` as well) ?
> > > > > What is the guarantee that `FindUniqueBinding` will return with the correct one `foo(b)`? Seems like we iterate through an ImmutableMap (AVL tree) with `MemRegion*` keys. And the order of the iteration depends on pointer values. What I want to express, is that I don't see how do we find the correct binding, seems like we just find one, which might be the one we look for if we are lucky.
> > > > > 
> > > > > Perhaps we could have a lit test for this example?
> > > > Good idea, I should a test for that!
> > > > `FindUniqueBinding` does not only have a region, it also carries a flag checking if there are more than one binding.  `operator bool` then checks for both, thus guaranteeing that we won't choose random binding out of more than 1 - we won't choose at all.
> > > Yeah, I missed that about `FindUniqueBinding`. 
> > > 
> > > It's just side questions then: Could we handle multiple bindings by finding the 'last' binding and tracking that back?
> > > And in this example, what are the bindings for `c`?
> > Can you please elaborate on what you mean by 'last', like 'last used'?
> > As for `c`, you can see above that I'm looking for a node where 'c' is not bound to that value.  So, we start with the node where 'a', 'b', and 'c' all bound to symbolic value... let's say 'x'. I go up the graph to the point where 'c' is not bound to 'x' and there I look for unique binding for 'x'.  In that example, we won't find it because it has two: 'a' and 'b'.
> Thanks for the explanation!
> 
> > Can you please elaborate on what you mean by 'last', like 'last used'? 
> 
> Yes, I meant the 'last used', in this case it should be `foo(b)`.
That would be perfect actually, but not `foo(b)`, just `b`.  Reporting `foo(b)` won't give more information than the code itself already provides.
However, I don't know a simple way to get region `b` from `foo(b)` expression (of course, we are talking about more general case than just getting the first argument of `foo`).


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Comment at: clang/test/Analysis/uninit-const.cpp:78
   int t;       //expected-note {{'t' declared without an initial value}}
-  int &p = t;  //expected-note {{'p' initialized here}}
-  int &s = p;  //expected-note {{'s' initialized here}}
-  int &q = s;  //expected-note {{'q' initialized here}}
+  int &p = t;  //expected-note {{'p' initialized to the value of 't'}}
+  int &s = p;  //expected-note {{'s' initialized to the value of 'p'}}
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NoQ wrote:
> I suspect that this wording can be improved a lot. The note "`'p' initialized to the value of 't'`" sounds like an accurate description for `int p = t` but not so much for `int &p = t`. Can we detect this case and say something like "`'p' refers to 't'`" instead?
That's a good point, but it feels like a can miss some cases here and we need to handle this situation separately.


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  https://reviews.llvm.org/D101041/new/

https://reviews.llvm.org/D101041