[Bug c++/116385] New: Unevaluated usage of function parameters with typeid incorrectly considered odr-use

[Bug c++/116385] New: Unevaluated usage of function parameters with typeid incorrectly considered odr-use

[mital at mitalashok dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116385

            Bug ID: 116385
           Summary: Unevaluated usage of function parameters with typeid
                    incorrectly considered odr-use
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mital at mitalashok dot co.uk
  Target Milestone: ---

This is the example taken from https://eel.is/c++draft/basic.def.odr#example-2
but modified to use `typeid` instead of `=` to make it a non-odr-use (as the
typeid of a glvalue of a non-polymorphic type)

https://godbolt.org/z/dh6P8q4fh

```
namespace std { struct type_info; }
void f(int n) {
  [] { typeid(n); };
  struct A {
    void f() { typeid(n); }
  };
  void g(const std::type_info& = typeid(n));
  [](const std::type_info& = typeid(n)) {};
}
```

All 4 usages have an error.

<source>: In lambda function:
<source>:3:15: error: 'n' is not captured
    3 |   [] { typeid(n); };
      |               ^
<source>:3:4: note: the lambda has no capture-default
    3 |   [] { typeid(n); };
      |    ^
<source>:2:12: note: 'int n' declared here
    2 | void f(int n) {
      |        ~~~~^
<source>: In member function 'void f(int)::A::f()':
<source>:5:23: error: use of parameter from containing function
    5 |     void f() { typeid(n); }
      |                       ^
<source>:2:12: note: 'int n' declared here
    2 | void f(int n) {
      |        ~~~~^
<source>: In function 'void f(int)':
<source>:7:41: error: parameter 'n' may not appear in this context
    7 |   void g(const std::type_info& = typeid(n));
      |                                         ^
<source>:8:37: error: parameter 'n' may not appear in this context
    8 |   [](const std::type_info& = typeid(n)) {};
      |                                     ^


Unevaluated usages with `sizeof` (<https://godbolt.org/z/W81ajKsbn>) do not
error

[Bug c++/116385] Unevaluated usage of function parameters with typeid incorrectly considered odr-use

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116385

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
MSVC rejects the default argument usage:

<source>(8): error C2587: 'n': illegal use of local variable as default
parameter
<source>(3): note: see declaration of 'n'
<source>(9): error C2587: 'n': illegal use of local variable as default
parameter
<source>(3): note: see declaration of 'n'

[Bug c++/116385] Unevaluated usage of function parameters with typeid incorrectly considered odr-use

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116385

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> MSVC rejects the default argument usage:
> 
> <source>(8): error C2587: 'n': illegal use of local variable as default
> parameter
> <source>(3): note: see declaration of 'n'
> <source>(9): error C2587: 'n': illegal use of local variable as default
> parameter
> <source>(3): note: see declaration of 'n'

And lambda usage:
<source>(4): error C3493: 'n' cannot be implicitly captured because no default
capture mode has been specified

But accepts the usage in local class.

[Bug c++/116385] Unevaluated usage of function parameters with typeid incorrectly considered odr-use

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116385

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
It appears that (part of) the problem is that cp_unevaluated_operand is not
properly set when we reach process_outer_var_ref.

[Bug c++/116385] Unevaluated usage of function parameters with typeid incorrectly considered odr-use

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116385

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
In fact I see no RID_TYPEID cp_unevaluated so that's probably the problem. 
Even C++11 said "The expression is an unevaluated operand."

Probably a dup of bug 68604.