[clang] [LifetimeSafety] Fix handling of reference-type DeclRefExpr (PR #176728)

[Utkarsh Saxena via cfe-commits]

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@@ -589,9 +589,10 @@ void FactsGenerator::handleUse(const DeclRefExpr *DRE) {
   OriginList *List = getOriginsList(*DRE);
   if (!List)
     return;
-  // Remove the outer layer of origin which borrows from the decl directly. This
-  // is a use of the underlying decl.
-  List = getRValueOrigins(DRE, List);
+  // Remove the outer layer of origin which borrows from the decl directly
+  // (e.g., when this is not a reference). This is a use of the underlying decl.
+  if (!DRE->getDecl()->getType()->isReferenceType())
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usx95 wrote:

`getRValueOrigins`look correct to me. The thing which was incorrect was that we always assumed that the outer origin of a DRE is not always useful and can be peeled when considering a use.

Added some more tests that references work as intended currently.

The more principled way would be to attach "use" of all origins of all layers without peeling any layer. I think I did not do this to avoid overflooding with "UseFacts" for all DRE we see. But in principle, it wouldn't be incorrect.

https://github.com/llvm/llvm-project/pull/176728