[PATCH] D86736: [analyzer][NFC] Don't bind values to ObjCForCollectionStmt, replace it with a GDM trait

[Kristóf Umann via Phabricator via cfe-commits]

Szelethus added inline comments.


================
Comment at: clang/lib/StaticAnalyzer/Core/ProgramState.cpp:327
+using ObjCForLctxPair =
+    std::pair<const ObjCForCollectionStmt *, const LocationContext *>;
+
----------------
martong wrote:
> Why it is not enough to simply have ObjCForCollectionStmt* as a key?
`Environment` is the data structure we use to bind **values** to **statements** (which would ideally be expressions only). The problem is that a statement on its own isn't enough to identify where we are in the analysis:

```lang=c++
void traverse(Graph &G) {
 // SubG may need to be modeled in different stackframes, but has the same Stmt*
 for (Graph &SubG : G->successors()) {
    traverse(SubG);
  }
}
```

`LocationContext` can be thought of as a stack function calls (or anything with a distinct stack frame). Indeed, if two `(Stmt *, LocationContext *)` pairs are equal, we're rebinding the same expression (another loop iteration, goto), if only the statements are the same, we're not in the same function call (//stack frame//).

Of course `ObjCForCollectionStmt` can not have a value, that is the whole point of the patch, but we still need a `LocationContext` to correctly identify precisely which loop we're talking about.


Repository:
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  https://reviews.llvm.org/D86736/new/

https://reviews.llvm.org/D86736