[PATCH] D90042: [clang-tidy] performance-unnecessary-copy-initialization: Check for const reference arguments that are replaced template parameter type.

[Felix Berger via Phabricator via cfe-commits]

flx added a comment.

In D90042#2391246 <https://reviews.llvm.org/D90042#2391246>, @aaron.ballman wrote:

> In D90042#2390203 <https://reviews.llvm.org/D90042#2390203>, @flx wrote:
>
>> Thanks for the suggestion, I had never hear of creduce!
>
> Glad to have introduced you to it -- it's a great tool!
>
>> After a bit of trial an error I seem to have found a more minimal example:
>>
>>   namespace std {                                                                                                              
>>   template <typename> class function;                                                                                          
>>   template <typename a, typename... b> class function<a(b...)> {                                                               
>>   public:                                                                                                                      
>>     void operator()(b...);                                                                                                     
>>   };                                                                                                                           
>>   } // namespace std                                                                                                           
>>   struct c {                                                                                                                   
>>     c();                                                                                                                       
>>     c(const c &);                                                                                                              
>>   };                                                                                                                           
>>   std::function<void(c &)> f;                                                                                                  
>>   void d() {                                                                                                                   
>>     c Orig;                                                                                                                    
>>     c Copy = Orig;                                                                                                             
>>     f(Copy);                                                                                                                   
>>   }  
>>
>>
>> To be frank I can't spot a meaningful difference to the std::function copy we already have.
>
> Aha, I may have spotted it. The call operators have subtly different signatures and the signature we have in our test file is wrong. Note the `&&` in our test file compared to what the standard defines: http://eel.is/c++draft/func.wrap.func#inv which is what's causing the difference here: https://godbolt.org/z/hxfM7P

Ah! That is subtle and surprising, but makes sense. I confirmed that the new test cases fail now before the fix is put in place. Thanks for your help!


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D90042/new/

https://reviews.llvm.org/D90042