[clang] [ItaniumMangle] Use mangleType instead of mangleNameOrStandardSubstitution in mangleCXXCtorVTable function (PR #109970)

[Matheus Izvekov via cfe-commits]

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@@ -7326,11 +7326,13 @@ void ItaniumMangleContextImpl::mangleCXXCtorVTable(const CXXRecordDecl *RD,
                                                    raw_ostream &Out) {
   // <special-name> ::= TC <type> <offset number> _ <base type>
   CXXNameMangler Mangler(*this, Out);
+  QualType RDType = getASTContext().getRecordType(RD);
+  QualType TypeType = getASTContext().getRecordType(Type);
   Mangler.getStream() << "_ZTC";
-  Mangler.mangleNameOrStandardSubstitution(RD);
+  Mangler.mangleType(RDType);
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mizvekov wrote:

The only difference here is whether we perform / add a substitution for RD.

We only ever see a problem for `mangleCXXCtorVTable` because it's the only user of `mangleNameOrStandardSubstitution` which mangles anything at all after a call to that function.

I can't find this production in the ItaniumABI docs, but if the comment is right, I think performing this substitution is correct.

I'd prefer we fix `mangleNameOrStandardSubstitution` itself.
We could rename it to `mangleCXXRecordDecl`, have it take a CXXRecordDecl*, and handle the substitutions there.
This would avoid the same trap in a potential future user.

CC @rjmccall @zygoloid 

https://github.com/llvm/llvm-project/pull/109970