baloghadamsoftware marked an inline comment as done.
baloghadamsoftware added inline comments.
================
Comment at: clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp:112
+Optional<SVal> ExprEngine::retrieveFromConstructionContext(
+ ProgramStateRef State, const LocationContext *LCtx,
----------------
NoQ wrote:
> balazske wrote:
> > baloghadamsoftware wrote:
> > > baloghadamsoftware wrote:
> > > > baloghadamsoftware wrote:
> > > > > baloghadamsoftware wrote:
> > > > > > NoQ wrote:
> > > > > > > baloghadamsoftware wrote:
> > > > > > > > NoQ wrote:
> > > > > > > > > Please instead re-use the code that computes the object under
> > > > > > > > > construction. That'll save you ~50 lines of code and will be
> > > > > > > > > more future-proof (eg., standalone temporaries without
> > > > > > > > > destructor technically have a construction context with 0
> > > > > > > > > items so when we implement them correctly your procedure will
> > > > > > > > > stop working).
> > > > > > > > That was so my first thought. However,
> > > > > > > > `handleConstructionContext()` is private and non-static. Now I
> > > > > > > > tried to merge the two methods: if the value is already in the
> > > > > > > > construction context, we return it, if not then we add it. Is
> > > > > > > > this what you suggest? Or did I misunderstand you? At the very
> > > > > > > > beginning I tried to simply use `handleConstructionContext()`,
> > > > > > > > but it asserted because the value was already in the map.
> > > > > > > I'd like to preserve the assertion that
> > > > > > > objects-under-construction are never filled twice; it's a very
> > > > > > > useful sanity check. What you need in your checker is a function
> > > > > > > that computes object-under-construction but doesn't put it into
> > > > > > > the objects-under-construction map. So you have to separate the
> > > > > > > computation from filling in the state.
> > > > > > OK, so I (fortunately) misundertood you. Thus I should refactor
> > > > > > this function to a calculation and a storing part?
> > > > > OK, I see what you are speaking about, but I have no idea how to do
> > > > > it properly. The problem is that the control logic of filling in the
> > > > > state also depends on the kind of the construction context. For some
> > > > > kinds we do not fill at all. Every way I try it becomes more complex
> > > > > and less correct:
> > > > >
> > > > > 1) `NewAllocatedObjectKind`: we do not add this to the state, we only
> > > > > retrieve the original.
> > > > > 2) `SimpleReturnedValueKind` and `CXX17ElidedCopyReturnedValueKind`:
> > > > > depending on whether we are in top frame we handle this case
> > > > > recursively or we do not fill at all, just return the value. What is
> > > > > the construction context item here? Maybe the `ReturnStmt`?
> > > > > 3) `ElidedTemporaryObjectKind`: this is the most problematic: we
> > > > > first handle it recursively for the construction context after
> > > > > elision, then we also fill it for the elided temporary object
> > > > > construction context as well.
> > > > >
> > > > > The only thing I can (maybe) do is to retrieve the construction
> > > > > context item. But then the switch is still duplicated for filling,
> > > > > because of the different control logic for different construction
> > > > > context kinds.
> > > > > The only thing I can (maybe) do is to retrieve the construction
> > > > > context item.
> > > >
> > > > This does not help even for retrieving the value, because its control
> > > > logic also depends on the construction context kind. If I do it, it
> > > > will be code triplication instead of duplication and results in a code
> > > > that is worse to understand than the current one.
> > > >
> > > >
> > > > Please instead re-use the code that computes the object under
> > > > construction. That'll save you ~50 lines of code and will be more
> > > > future-proof (eg., standalone temporaries without destructor
> > > > technically have a construction context with 0 items so when we
> > > > implement them correctly your procedure will stop working).
> > >
> > > Any solution I can come up with rather adds 100 to 150 lines to the code
> > > instead of saving 50. For retrieving we only have to determine the
> > > construction context item (the key). For storing we also have to
> > > calculate the value. It sounds good to calculate these things in separate
> > > functions and then have a simple retriever and store function but there
> > > are lots of recursions, double strores, non-stores, retrieving in the
> > > store function that make it too complicated.
> > >
> > > Also retrieving is more complex than just determining the item and
> > > getting the value from the context: if you look at
> > > `SimpleReturnedValueKind` and `CXX17ElidedCopyReturnedValueKind` you can
> > > see that we do not use the construction context we got in the parameter
> > > (the construction context of the return value) but the construction
> > > context of the call instead. For `ElidedTemporaryObjectKind` we take the
> > > construction context before the elusion.
> > >
> > > Future proofness: I agree, this is a problem to solve. In cases where the
> > > construction context is empty maybe we can move the calculation of the
> > > values to a separate function that is called by both the "handler" and
> > > the "retriever".
> > Do I think correctly that `retrieveFromConstructionContext` (in the
> > previous version) should return the same value as second part of
> > `handleConstructionContext`? It does not look obvious at first. Or do we
> > need a function with that purpose? If yes it looks a difficult task because
> > the similar "logic" to get the value and update the state. Probably it is
> > enough to add a flag to `handleConstructionContext` to not make new state.
> > The current code looks bad because calling a "handle" type of function
> > (that was private before) only to compute a value.
> >
> > Any solution I can come up with rather adds 100 to 150 lines to the code
> > instead of saving 50.
>
> I think the following is a fairly literal implementation of my suggestion:
>
> {F12020285}
>
> It's 26 lines shorter than your `retrieveFromConstructionContext()` (ok, not
> 50, duplicating the switch was more annoying than i expected), it adds zero
> new logic (the only new piece of logic is to track constructors that were
> modeled correctly but their elision wasn't; previously we could fit it into
> control flow), it no longer tries to reverse-engineer the original behavior
> by duplicating its logic, and it's more future-proof for the reasons
> explained above.
Thank you for working on this. The point what I did not see (and I still no
not see it) is that in your solution (and your proposal) instead of retrieving
the value from the construction context we actually recalculate it, thus we do
not use the construction context at all (except for `NewAllocatedObjectKind`)
to retrieve the location of the return value. Can we guarantee that we always
recalculate exactly the same symbolic value as the symbolic values we store in
the map? For example, for `SimpleReturnedValueKind` et. al. we conjure a new
symbolic value. Is it really the same value than that the one in the map, thus
the one which is the real location where the object is constructed? If not,
then the checkers might not work correctly because they store into the GDM
using a different region as key than they use for retrieving the value.
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https://reviews.llvm.org/D80366/new/
https://reviews.llvm.org/D80366
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