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

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dgg5503 wrote:

> I agree that it's important to augment the bug reports with information about the source of the symbols. Especially for conjured and derived symbols that are produced widely because of invalidations. Loop widening is just one source of invalidation, and we could generalize it slightly.
> 
> Read this post of mine: https://discourse.llvm.org/t/memory-region-invalidation-tracking-improvements/62432 Unfortunately, I never got to implement it, but I'd be very happy as a reviewer to guide you through.

Hi @steakhal ,

I'm happy to hear others share a similar concern!

I agree that it would make more sense to generalize this beyond loop widening. However, I'm having a hard time understanding how your proposal would fit in to the augmentation of the assignment message like I do in this PR.

The part I'm most confused about is how would `SymbolInvalidationArtifact` be set/retrieved after invalidation occurs? Would this somehow be tied to symbols created as part of invalidation (like created conjured symbols in `InvalidateRegionsWorker::VisitCluster`) which could then be retrieved via `SI.Value.getAsSymbol()` and casting (speaking from the PoV of `showBRDiagnostics`)? I think I would better understand if you could please provide a small example in the context of diagnostic output. I'm fairly certain I'm lacking understanding of some static analysis design concept that's not making this click in my head...

Regardless, once I have a better understanding of how your proposal fits in, I'd be happy to give your approach a try with your guidance :).

Thank you

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