[llvm] [Verifier] Reject cyclic DIScope parent chains (PR #217997)

[Manuel Carrasco via llvm-commits]

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@@ -164,6 +164,9 @@ class Verifier : public InstVisitor<Verifier>, VerifierSupport {
   /// Keep track which DISubprogram is attached to which function.
   DenseMap<const DISubprogram *, const Function *> DISubprogramAttachments;
 
+  /// Cache of whether following a DIScope's scope chain repeats a node.
+  DenseMap<const Metadata *, bool> DIScopeCycleCache;
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mgcarrasco wrote:

We report all failures, and we don't stop at the first (in general, not just these ones). The cycle detection is also used at sites that are not reporting either, so caching all cases makes sense to me.

I renamed the variable to `DIScopeChainReachesCycle` in case it reads better in that way.

https://github.com/llvm/llvm-project/pull/217997