[Bug c++/107697] New: -Wredundant-move misses std::move applied to const objects (instead of const references)

[Bug c++/107697] New: -Wredundant-move misses std::move applied to const objects (instead of const references)

[dangelog at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107697

            Bug ID: 107697
           Summary: -Wredundant-move misses std::move applied to const
                    objects (instead of const references)
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dangelog at gmail dot com
  Target Milestone: ---

Hi,

Consider this testcase:



#include <vector>

using T = std::vector<int>;

void f(T); 

void use1(const T t)  { f(std::move(t)); }
void use2(const T &t) { f(std::move(t)); }
void use3() {
    const T t;
    f(std::move(t));
}




Currently -Wredundant-move warns only for case 2. But in all three cases
std::move is actually not doing anything good (copy constructor is always
selected). It would be nice if they all were diagnosed.

If I change `f` to `void f(const T &)` then there's no warning at all. I'm
thinking that probably this case should be diagnosed as well.

Clang-tidy's performance-move-const-arg diagnoses them all.

[Bug c++/107697] -Wredundant-move misses std::move applied to const objects (instead of const references)

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107697

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
           Keywords|                            |diagnostic
     Ever confirmed|0                           |1
                 CC|                            |mpolacek at gcc dot gnu.org
   Last reconfirmed|                            |2022-11-15

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed.  Currently the code does only:

  /* Also try to warn about redundant std::move in code such as
      T f (const T& t)
      {
        return std::move(t);
      }

[Bug c++/107697] -Wredundant-move misses std::move applied to const objects (instead of const references)

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107697

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I guess this is GCC 14 material at this point.