[cxx-abi-dev] Literal operator functions with 'li<length, ID>'

[David Vandevoorde]

On Aug 9, 2013, at 9:46 PM, Richard Smith <richardsmith at google.com> wrote:

> On Fri, Aug 9, 2013 at 8:42 AM, Mike Herrick <mjh at edg.com> wrote:
[...]
>>  typedef __SIZE_TYPE__ size_t;
>>  void *operator "" _s(unsigned long long) {}
>>  void *operator new(size_t) {}
>>  void *f(unsigned long long) {}
>>  template<typename T> auto f1(T x)->decltype(operator "" _s(x));
>>  template<typename T> auto f2(T x)->decltype(operator new(x));
>>  template<typename T> auto f3(T x)->decltype(f(x));
>>  int main() {
>>    f1(0);  // neither g++ nor clang use <unresolved-name> for operator ""
>> _s
>>            // g++:      _Z2f1IiEDTclli2_sfp_EET_
>>            // clang:    _Z2f1IiEDTclli2_sfp_EET_
>>            // expected: _Z2f1IiEDTclonli2_sfp_EET_
>>    f2(0);  // g++ uses <unresolved-name> for operator new
>>            // g++:      _Z2f2IiEDTclonnwfp_EET_
>>            // clang:    _Z2f2IiEDTclnwfp_EET_
>>            // expected: _Z2f2IiEDTclonnwfp_EET_
>>    f3(0);  // g++ and clang use <unresolved-name> for f
>>            // g++:      _Z2f3IiEDTcl1ffp_EET_
>>            // clang:    _Z2f3IiEDTcl1ffp_EET_
>>            // expected: _Z2f3IiEDTcl1ffp_EET_
>>  }
>> 
>> [Mangled names are from g++ 4.8.1 and clang 3.3.]   We believe
>> <unresolved-name> should be used for all of these cases.
[...]
> Why is the 'on' ever necessary when the operator is the callee of a 'cl'?


Because it's an <unresolved-name>?  Also, in the case of a literal operator, bare operators in expressions only occur for unary, binary, and ternary operators, but arguably a literal operator (or a literal operator template) isn't any of those?


> It appears that Clang never emits it, and just uses the operator-name
> directly.
> 
> Also, what about this:
> 
>  struct X{}; void operator+(X);
>  template<typename ...T> auto f4(T... x) -> decltype(operator+(x...));
>  int main() {
>    f4(X{});
>  }
> 
> Should we use 'pl' or 'ps' for the operator+ here? Clang uses 'clps', EDG
> uses 'clonps', and GCC uses 'clonpl'.


Good catch.  My vote is to go with the GCC mangling (i.e., if it could be unary or binary, go with binary).

(Here too, I don't see how to read it as not requiring the <unresolved-name> production.)

> 
> Also, what about this:
> 
> struct X {}; void operator+(X);
> struct Y; void operator+(Y);
> template<typename T> void g(void(*)(T), T);
> template<typename T> auto f(T x) -> decltype(g(operator+, x));
> void h() { f(X{}); }
> 
> Here, GCC and Clang produce _Z1fI1XEDTcl1gplfp_EET_
> EDG produces the surprising _Z1fI1XEDTcl1gL_Z9operator+Efp_EET_
> 
> Both manglings are malformed -- this looks like a case where we really do
> need the 'on', and yet no-one emits it.


Agreed.

	Daveed