================
@@ -3158,6 +3161,33 @@ checkBuiltinTemplateIdType(Sema &SemaRef,
BuiltinTemplateDecl *BTD,
int64_t N = Index.getExtValue();
return Ts.getPackAsArray()[N].getAsType();
}
+ case BTK__type_pack_dedup: {
+ assert(Converted.size() == 2 && "__builtin_type_pack_dedup should be given
"
+ "a template and a parameter pack");
+ TemplateArgument Template = Converted[0];
+ TemplateArgument Ts = Converted[1];
+ if (Template.isDependent() || Ts.isDependent())
----------------
ilya-biryukov wrote:
We could remove the dependency on the template, but I don't think we can ignore
the dependency inside the types themselves.
Consider
```cpp
template <class T, class U, template <class...> class TL = TypeList>
struct Foo {
// 1. the substitution has to be postponed until T and U are known.
using result = __dedup<TypeList, T, U>;
// 2. this is already computed right away.
using result2 = __dedup<TypeList, int, int>;
// 3. this **could** be computed right away, but it is not now.
using result3 = __dedup<TL, int, int>
};
static_assert(__is_same(TypeList<int>, Foo<int, int>::result));
static_assert(__is_same(TypeList<int, doubel>, Foo<int, double>::result));
```
- Is there something I'm missing that would allow (1) to be substituted earlier?
- Do you feel strongly that we need to do (3) ?
> Be aware that holding this specialization will make this builtin appear in
> mangling, so I'd avoid doing that unless necessary.
I do not think we can avoid this completely (see above) and it's not
unprecedented: other builtin templates can already appear in mangling too when
the arguments are dependent. So I do think it's necessary and I'm not sure
which problems it carries.
https://github.com/llvm/llvm-project/pull/106730
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