baloghadamsoftware added inline comments.
================
Comment at: lib/StaticAnalyzer/Checkers/IteratorChecker.cpp:605
+ if (Pos && !Pos->isValid()) {
+ // If I do not put a tag here, some invalidation tests will fail
+ static CheckerProgramPointTag Tag("InvalidatedIteratorChecker",
----------------
NoQ wrote:
> baloghadamsoftware wrote:
> > NoQ wrote:
> > > baloghadamsoftware wrote:
> > > > NoQ wrote:
> > > > > This needs investigation, because it may be nasty.
> > > > >
> > > > > `generateNonFatalErrorNode()` returns null when the exact same
> > > > > non-fatal error node, also produced by the iterator checker with the
> > > > > exact same program state and exact same program point and exact same
> > > > > tag on the program point already exists. As far as i understand, the
> > > > > only difference your tag makes is that the tag is now different, so
> > > > > it is not merged with the existing node. However, it is worth it to
> > > > > try to find out why the node gets merged at all.
> > > > >
> > > > > This may be caused by an accidental state split. For example, if you
> > > > > are calling `generateNonFatalErrorNode()` twice in the same checker
> > > > > callback without chaining them together (passing node returned by one
> > > > > as an argument to another), this in fact splits states. I'm not
> > > > > immediately seeing such places in the code - you seem to be aware of
> > > > > this problem and avoiding it well. But still, looking at the topology
> > > > > of the exploded graph in the failing test should help finding out
> > > > > what is going on.
> > > > I made some more investigation this time. Unfortunately the case is not
> > > > what you suggest. Only one non-fatal error node is produced. I tested
> > > > it with a common tag (a global static so the tag is exactly the same at
> > > > every `generateNonFatalErrorNode()`, but the tests still pass. I
> > > > printed out the exploded graph and I found that there are indeed two
> > > > nodes with the same state ID. The tag is the default tag automatically
> > > > generated from the name of the checker. The first state is created in
> > > > function `checkPreStatement()` for `CXXOperatorCallExpr` where I copy
> > > > the state of the iterator from the formal to the actual `this`
> > > > parameter. All the test fails happen at the dereference operator call
> > > > (`*`) of another operator call (`++` or `--`). After this copy, when I
> > > > call `generateNonFatalErrorNode()` I get `nullptr` because at some
> > > > point under the hood (I debugged it when I created it originally) the
> > > > error node is considered as "not new". If I use a custom tag here, the
> > > > state ID remains, not the node ID changes.
> > > I think i see the problem. The checker subscribes to both `PreCall` and
> > > `PreStmt<CallExpr>` (to be exact, `CXXOperatorCallExpr`) and adds
> > > transitions in both cases. It results with a predecessor node in
> > > `CheckerContext` that's already tagged by the checker. Apparently this
> > > never worked, but nobody tried that.
> > >
> > > Ideally, we should make sure those callbacks use different program
> > > points, eg. introduce `PreCall`/`PostCall` program point kinds and use
> > > them.
> > >
> > > Also i wonder why are you using pre- rather than post-statement callback.
> > > You model all other operators in `PostCall`, why did those end up here?
> > > Maybe merge them? It is generally better to model pre-conditions and look
> > > for bugs in `PreStmt`/`PreCall` (before we don't care what happens within
> > > the call), and model effects in `PostStmt`/`PostCall` (because effects
> > > don't take effect until the call happens).
> > That is what I am trying to to: `Post*` for modelling and `Pre*` for
> > checking. However, this `PreStmt<CXXOperatorCallExpr>()` is special since I
> > have to move the arguments to the context of the called operator //before//
> > the call.
> Ah, it's that thing, `PreCall` then?
Yes! It seems to be working. Thank you for your help!
https://reviews.llvm.org/D32747
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