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

[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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cor3ntin wrote:

> These are for different things. getInstantiatedFromDecl is used to tell which function this "was instantiated from, if this is a function declaration declared locally inside of a function template".

UGH, completely missed that - all of this could use some more comments

> Because FunctionDecl has free bits, so this change has basically no space cost :)

Yeah, but 1/it's a bit confusing 2/ bits there are fairly precious

You could add a bit to FunctionTemplateSpecializationInfo::Function

I don't insist on it. However can you add some comments? It took me a while to understand and I suspect i won;t be the only one.

Thanks, I'll approve when i wake up (and sorry it took me a while to understand everything)

Oh, another solution would be to have a DenseMap of FunctionTemplateDecl -> FunctionTemplateDecl in Sema, storing specialization of friend functions template (only!) in it - hopefully these things are fairly rare - and it might simplify the change to InstantiateFunctionDefinition



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