[clang] [NFC][analyzer] Clarify that ExplodedGraph has only one root (PR #139903)

[Donát Nagy via cfe-commits]

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@@ -46,8 +46,9 @@ void AnalyzerStatsChecker::checkEndAnalysis(ExplodedGraph &G,
   llvm::SmallPtrSet<const CFGBlock*, 32> reachable;
 
   // Root node should have the location context of the top most function.
-  const ExplodedNode *GraphRoot = *G.roots_begin();
-  const LocationContext *LC = GraphRoot->getLocation().getLocationContext();
+  // FIXME: Use `Eng.getRootLocationContext()` unless `G` can be different from
+  // the `ExplodedGraph` owned by Eng.
+  const LocationContext *LC = G.getRoot()->getLocation().getLocationContext();
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NagyDonat wrote:

Yes, I verified that the graph is owned by `Eng` and replaced this complex call with `Eng.GetRootLocationContext()`. (By the way, why does this callback receive the exploded graph as a separate argument if it is already accessible via `Eng.getGraph()`?? Yet another thing to clean up...)

https://github.com/llvm/llvm-project/pull/139903