[Bug c++/67217] New: [concepts] Constraints are ignored when specializing union templates

[Bug c++/67217] New: [concepts] Constraints are ignored when specializing union templates

[Casey at Carter dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67217

            Bug ID: 67217
           Summary: [concepts] Constraints are ignored when specializing
                    union templates
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Casey at Carter dot net
  Target Milestone: ---

r226833 incorrectly compiles this program without diagnostics:

template <class T>
  requires __is_same_as(T, double)
union A {};

int main() { A<int>{}; }

despite that int does not satisfy the constraints of A. Changing the expression
__is_same_as(T, double) to true, false, 42, or (new T) has no effect - the
program compiles without diagnostics.

Compiling *this* program, however:

template <class>
union B {};

template <class T>
  requires false
union B<T> {};

int main() {
  B<int>{};
}

incorrectly produces diagnostics:

~/gcc6-r226833/bin/g++ -std=gnu++1z foo.cpp -c
foo.cpp: In function ‘int main()’:
foo.cpp:9:10: error: ambiguous template instantiation for ‘union B<int>’
   B<int>{};
          ^
foo.cpp:6:7: note: candidates are: template<class T> union B<T> [with T = int]
 union B<T> {};
       ^
foo.cpp:6:12: note:                 template<class T> union B<T> [with T = int]
 union B<T> {};
            ^
foo.cpp:6:13: note:                 template<class T> union B<T> [with T = int]
 union B<T> {};
             ^
foo.cpp:9:10: error: invalid use of incomplete type ‘union B<int>’
   B<int>{};
          ^
foo.cpp:2:7: note: declaration of ‘union B<int>’
 union B {};
       ^

It would appear that constraints are not being checked on union templates.
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Subject: [Bug middle-end/67133] [6 Regression] ICE at -Os and above on x86_64-linux-gnu in gimple_op, at gimple.h:2274
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67133

--- Comment #23 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #21)
> OTOH users like infer_nonnull_range_by_attribute cannot rely on
> gimple_call_fntype being "compatible" with the actual call (like in
> terms of number of arguments).  So
> 
> lacks a check that idx < gimple_call_num_args.

And what would happen if the nonnull attribute refers to a different argument
that still satisfies the check? For example, fntype may have more arguments
than the call and the one marked as nonnull may still satisfy the check, yet
not be the actual argument that was marked as nonnull.

There must be a way to "fix" the attributes or mark them as not "compatible".
Asking "users" of the attributes to "guess" if the attributes are compatible
seems fragile.
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Subject: [Bug middle-end/67133] [6 Regression] ICE at -Os and above on x86_64-linux-gnu in gimple_op, at gimple.h:2274
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67133

--- Comment #24 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #23)

> And what would happen if the nonnull attribute refers to a different
> argument that still satisfies the check? For example, fntype may have more
> arguments than the call and the one marked as nonnull may still satisfy the
> check, yet not be the actual argument that was marked as nonnull.

Then operand_equal_p would return false.
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Subject: [Bug libfortran/48664] Use autoconf test instead of target blacklist to determine weak undefined reference support
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idH664

Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2015-08-14
                 CC|                            |fxcoudert at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |fxcoudert at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> ---
Patch available: https://gcc.gnu.org/ml/gcc-patches/2015-08/msg00796.html

[Bug c++/67217] [concepts] Constraints are ignored when specializing union templates

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67217

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |klaus.doldinger64@googlemai
                   |                            |l.com

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
*** Bug 83000 has been marked as a duplicate of this bug. ***