[PATCH] D48436: [analyzer][UninitializedObjectChecker] Fixed a false negative by no longer filtering out certain constructor calls

Umann Kristóf via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Mon Jul 30 08:51:16 PDT 2018

Szelethus added inline comments.

Comment at: lib/StaticAnalyzer/Checkers/UninitializedObjectChecker.cpp:681-689
+    Optional<nonloc::LazyCompoundVal> OtherObject =
+        getObjectVal(OtherCtor, Context);
+    if (!OtherObject)
+      continue;
+    // If the CurrentObject is a field of OtherObject, it will be analyzed
+    // during the analysis of OtherObject.
NoQ wrote:
> Szelethus wrote:
> > NoQ wrote:
> > > It seems safer to look at `CXXConstructExpr::getConstructionKind()`.
> > > 
> > > Taking a `LazyCompoundVal` and converting it back to a region is definitely a bad idea because the region within `LazyCompoundVal` is completely immaterial and carries no meaning for the value represented by this `SVal`; it's not necessarily the region you're looking for.
> > Looking at the singleton test case, I think I need to get that region somehow, and I'm not too sure what you meant under using `CXXConstructExpr::getConstructionKind()`. One thing I could do, is similar to how `getObjectVal` works:
> > ```
> >   Loc Tmp = Context.getSValBuilder().getCXXThis(OtherCtor->getParent(),
> >                                                 Context.getStackFrame());
> > 
> >   auto OtherThis = Context.getState()->getSVal(Tmp).castAs<loc::MemRegionVal>();
> > 
> >   OtherThis.getRegion(); // Hooray!
> > ```
> > 
> > I have tested it, and it works wonders. Is this a "safe-to-use" region?
> You can directly ask `CXXConstructExpr` if it's a field or a base constructor. I could describe `getConstructionKind()` as some sort of very limited `ConstructionContext` that's available in the AST: it explains to you what sort of object is being constructed. I suspect it's enough for your purposes.
I think I'm aware of how it works, but my issue is that it's very limited:
enum ConstructionKind { CK_Complete, CK_NonVirtualBase, CK_VirtualBase, CK_Delegating }
Sadly, whether the `CXXConstructExpr` was a field construction or a "top level" (non-field) construction can't be retrieved from `getConstructionKind()`, as I understand it.

If I were to return true (say that the constructed object will be analyzed later, thus ignoring it for now) if `getConstructionKind() == CK_Complete`, the singleton testcase will fail (I have tested it). I'm very confident that I need to obtain the constructed object's `MemRegion`.


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