[clang] [analyzer] Widen loops: Augment assignment note when values invalidated at the start of a loop (PR #122398)

[via cfe-commits]

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@@ -1353,6 +1353,49 @@ static void showBRDefaultDiagnostics(llvm::raw_svector_ostream &OS,
     OS << " to ";
     SI.Dest->printPretty(OS);
   }
+
+  // If the value was part of a loop widening node and its value was
+  // invalidated (i.e. replaced with a conjured symbol) then let the user know
+  // that it was due to loop widening.
+  if (SI.StoreSite && SI.Dest &&
+      SI.StoreSite->getLocation().getTag() ==
+          ExprEngine::loopWideningNodeTag()) {
+
+    // TODO: Is it always the case that there's only one predecessor?
+    assert(SI.StoreSite->hasSinglePred() &&
+           "more than one predecessor found, this needs to be handled...");
+    if (const ExplodedNode *previous = SI.StoreSite->getFirstPred()) {
+      // Was the associated memory region for this variable changed from
+      // non-Symbolic to Symbolic because of invalidation?
+      // TODO: Better yet, if there was simply a way to know if a given
+      // SVal / MemRegion was invalidated as part of the current state,
+      // then that should be more robust than what's going on here.
+      // Could we somehow make use of "RegionChanges" /
+      // "runCheckersForRegionChanges" and the ExplicitRegions parameter.
+      // Still need to somehow know when a particular Global
+      // Variable is invalidated. I have not found this to be possible with
+      // "RegionChanges" unless I'm missing something...
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dgg5503 wrote:

I tried to implement this in https://github.com/llvm/llvm-project/compare/main...dgg5503:llvm-project:dgg5503/main/invalidation-diagnostic-b but all `MemRegion`s from the `ProgramState` and before are tracked. I'm wondering if there's a way to clear `InvalidatedMemoryRegionSet` at the start of each `ProgramState`, or, if there's a different approach I should be taking...

https://github.com/llvm/llvm-project/pull/122398