[PATCH] D104136: [analyzer] Add better tracking for RetainCountChecker leak warnings

[Kristóf Umann via Phabricator via cfe-commits]

Szelethus added inline comments.


================
Comment at: clang/lib/StaticAnalyzer/Checkers/RetainCountChecker/RetainCountDiagnostics.cpp:953-957
+      // Let's traverse...
+      for (const ExplodedNode *N = ExprNode;
+           // ...all the nodes corresponding to the given expression...
+           N != nullptr && N->getStmtForDiagnostics() == E;
+           N = N->getFirstPred()) {
----------------
vsavchenko wrote:
> Szelethus wrote:
> > vsavchenko wrote:
> > > NoQ wrote:
> > > > I guess this part should ultimately be written in one place, eg. `ExplodedNode::findTag()` or something like that.
> > > > 
> > > > I'd also really like to explore the possibility to further limit the variety of nodes traversed here. What nodes are typically traversed here? Is it checker-tagged nodes or is it purge dead symbol nodes or something else?
> > > Yes, `ExplodedNode::findTag()` sounds like a great idea!
> > > 
> > > I mean it is hard to tell without calculating statistics right here and running it on a bunch of projects.  However, it is always possible to write the code that will have it the other way.  My take on it is that it is probably a mix of things.
> > > 
> > > I'd also prefer to traverse less, do you have any specific ideas here?
> > > I'd also really like to explore the possibility to further limit the variety of nodes traversed here. What nodes are typically traversed here? Is it checker-tagged nodes or is it purge dead symbol nodes or something else?
> > 
> > Is there something I'm not seeing here? Trackers basically ascend //a// path from the error node to at most the root of the ExplodedGraph (not the trimmed version, as `Tracker::track()` is called before any of that process happens), so its not much slower than `trackExpressionValue`, right?
> > 
> > Or does this, and likely many other future handlers run such a loop more often then what I imagine?
> > 
> > 
> Essentially, yes.  `trackExpressionValue` (and `Tracker::track`) ascend the graph searching for a node where the give expression is evaluated.  The problem here is that whenever we ask to track some expression, not only `trackExpressionValue` will do its traversal (much longer), but also this handler will do its (shorter).  It would be better not to do this altogether, but I personally don't see any solutions how we can cut on this part.
> At the same time, I don't think that it is performance critical, considering that the part of the graph where `N->getStmtForDiagnostics() == E` is small.
Ah, so, this is your patch:

```
E: Error Node
C: Identity function call
V: Argument evaluation
A: Origin of the argument value
---->: Nodes traversed by the tracker
====>: Nodes traversed by the handler

*              *           *           *
E->O->O->O->O->C->O->O->O->V->O->O->O->A->X->X->X

--------------->          
               ============>----------->
```
This is fine, because its just a single ascend, made a little worse by the fact that we do it for each tracked variable. But later, with more handlers, it might get worse (per variable):
```
*              *           *           *
E->O->O->O->O->C->O->O->O->V->O->O->O->A->X->X->X

--------------->           
               ============>----------->
               ===============>----->
               ==============>------------------>
               =================================>
               ======================>
```
Now, I can't immediately imagine a case where someone would add THAT many handlers, or track that many variables, even in extreme circumstances, but I don't posses a crystal ball either :^)


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  https://reviews.llvm.org/D104136/new/

https://reviews.llvm.org/D104136