Incorrect mangling of __bf16 in template parameter with nested namespaces.

[SagarMaheshwari99]

namespace NS1 {

    namespace NS2 {
        struct NS2_struct1 {};
    }

    template<typename tpVal, typename tpVal1>
    class Class1 {};

    template<typename tpVal>
    using Name1 = Class1<tpVal, NS2::NS2_struct1>;
}

template <typename dtype>
void MyFunc(NS1::Name1<dtype>& input) {}

typedef __bf16 bfloat16;

struct bf16_struct {
    short a;
};

int main() {
    NS1::Class1<bfloat16, NS1::NS2::NS2_struct1> input;
    MyFunc<bfloat16>(input);

    NS1::Class1<bf16_struct, NS1::NS2::NS2_struct1> input1;
    MyFunc<bf16_struct>(input1);

    return 0;
}

For __bf16 case the mangling comes out to be -
_Z6MyFuncIu6__bf16EvRN3NS16Class1IT_NS0_3NS211NS2_struct1EEE

which demangled comes out to be -
void MyFunc<__bf16>(NS1::Class1<__bf16, __bf16::NS2::NS2_struct1>&)

which is incorrect, as __bf16 is treated as a namespace here.

For bf16_struct, right mangling is produced -
_Z6MyFuncI11bf16_structEvRN3NS16Class1IT_NS1_3NS211NS2_struct1EEE

and the demangling comes out to be -
void MyFunc<bf16_struct>(NS1::Class1<bf16_struct, NS1::NS2::NS2_struct1>&)

https://godbolt.org/z/dTWxYbqhM

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Sagar Maheshwari (SagarMaheshwari99)

``` namespace NS1 {

namespace NS2 {
    struct NS2_struct1 {};
}

template<typename tpVal, typename tpVal1>
class Class1 {};

template<typename tpVal>
using Name1 = Class1<tpVal, NS2::NS2_struct1>;

}

template <typename dtype>
void MyFunc(NS1::Name1<dtype>& input) {}

typedef __bf16 bfloat16;

struct bf16_struct {
short a;
};

int main() {
NS1::Class1<bfloat16, NS1::NS2::NS2_struct1> input;
MyFunc<bfloat16>(input);

NS1::Class1<bf16_struct, NS1::NS2::NS2_struct1> input1;
MyFunc<bf16_struct>(input1);

return 0;

}

For __bf16 case the mangling comes out to be -
`_Z6MyFuncIu6__bf16EvRN3NS16Class1IT_NS0_3NS211NS2_struct1EEE`

which demangled comes out to be -
`void MyFunc<__bf16>(NS1::Class1<__bf16, __bf16::NS2::NS2_struct1>&)`

which is incorrect, as __bf16 is treated as a namespace here.


For bf16_struct, right mangling is produced -
`_Z6MyFuncI11bf16_structEvRN3NS16Class1IT_NS1_3NS211NS2_struct1EEE`

and the demangling comes out to be -
`void MyFunc<bf16_struct>(NS1::Class1<bf16_struct, NS1::NS2::NS2_struct1>&)`



https://godbolt.org/z/dTWxYbqhM



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