[clang] Reland: [clang] Track function template instantiation from definition (PR #125266)

[Matheus Izvekov via cfe-commits]

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@@ -2298,6 +2298,13 @@ class FunctionDecl : public DeclaratorDecl,
     FunctionDeclBits.IsLateTemplateParsed = ILT;
   }
 
+  bool isInstantiatedFromMemberTemplate() const {
+    return FunctionDeclBits.IsInstantiatedFromMemberTemplate;
+  }
+  void setInstantiatedFromMemberTemplate(bool Val = true) {
+    FunctionDeclBits.IsInstantiatedFromMemberTemplate = Val;
+  }
+
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mizvekov wrote:

The new `setInstantiatedFromMemberTemplate` is being used from existing callers, which before this patch would call this member from a FunctionTemplateDecl object, which would call `RedeclarableTemplateDecl::setInstantiatedFromMemberTemplate`.

With this patch, these callers will find `FunctionTemplateDecl::setInstantiatedFromMemberTemplate` instead.

See the implementation of the latter, where it also forwards the call to the former.

https://github.com/llvm/llvm-project/pull/125266