[clang] [clang][dataflow] Fix crash on base-to-derived cast of unmodeled pointer value. (PR #179060)

[Yitzhak Mandelbaum via cfe-commits]

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@@ -328,9 +328,9 @@ class TransferVisitor : public ConstStmtVisitor<TransferVisitor> {
       RecordStorageLocation *Loc = nullptr;
       if (S->getType()->isPointerType()) {
         auto *PV = Env.get<PointerValue>(*SubExpr);
-        assert(PV != nullptr);
         if (PV == nullptr)
-          break;
+          PV = cast<PointerValue>(Env.createValue(S->getType()));
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ymand wrote:

`createValue` can return nullptr. It's possible that for PointerValue type it always returns nonnull, but I think that's risky to depend on. So, you need to account for that case.

Moreover, this requires a comment explaining the new behavior.

https://github.com/llvm/llvm-project/pull/179060