[clang] [clang] Redeclare function templates instances per primary template (PR #110387)

[Younan Zhang via cfe-commits]

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@@ -2146,9 +2147,15 @@ Decl *TemplateDeclInstantiator::VisitFunctionDecl(
     FunctionDecl *SpecFunc
       = FunctionTemplate->findSpecialization(Innermost, InsertPos);
 
-    // If we already have a function template specialization, return it.
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zyn0217 wrote:

nit: probably preserve the comment

https://github.com/llvm/llvm-project/pull/110387