[Bug c++/103746] New: GCC 12 rejects code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and clang accepts it

[Bug c++/103746] New: GCC 12 rejects code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and clang accepts it

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

            Bug ID: 103746
           Summary: GCC 12 rejects code on "call to non-‘constexpr’
                    function ‘glsl::vec3&
                    glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and
                    clang accepts it
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
  Target Milestone: ---

Created attachment 52012
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52012&action=edit
testcase

Building Firefox with trunk fails on many errors of type:

src/glsl.h: In constructor ‘constexpr glsl::mat3::mat3(glsl::Float,
glsl::Float, glsl::Float, glsl::Float, glsl::Float, glsl::Float, glsl::Float,
glsl::Float, glsl::Float)’:
src/glsl.h:2427:30: error: call to non-‘constexpr’ function ‘glsl::vec3&
glsl::vec3::operator=(glsl::vec3&&)’
 2427 |     data[0] = vec3(d1, d2, d3);
      |                              ^


I am not qite sure if this is valid error, however it is not diagnosed by GCC
11 and clang.  The catch is that it also come from rust code and things that
are imported to tree, so in order to build the firefox for testing, I would
welcome a way to avoid this error even if it is valid (perhaps with
-fpermissive?)

testcase fails with:
g++ -O2 /tmp/test.ii -std=c++17 -Wno-attributes

[Bug c++/103746] GCC 12 rejects code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and clang accepts it

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-12-16
             Status|UNCONFIRMED                 |WAITING
     Ever confirmed|0                           |1
                 CC|                            |marxin at gcc dot gnu.org

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
You likely attached a wrong test-case, it's something with
LZ4_decompress_safe_usingDict.

[Bug c++/103746] GCC 12 rejects code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and clang accepts it

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

--- Comment #2 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Created attachment 52013
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52013&action=edit
Correct testcase

Oops, uploaded inrrect testcase.  This should be current one.

[Bug c++/103746] GCC 12 rejects code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and clang accepts it

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|1                           |0
             Status|WAITING                     |UNCONFIRMED

[Bug c++/103746] [12 Regression] GCC 12 rejects code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and clang accepts it

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|GCC 12 rejects code on      |[12 Regression] GCC 12
                   |"call to non-‘constexpr’    |rejects code on "call to
                   |function ‘glsl::vec3&       |non-‘constexpr’ function
                   |glsl::vec3::operator=(glsl: |‘glsl::vec3&
                   |:vec3&&)’" while gcc 11 and |glsl::vec3::operator=(glsl:
                   |clang accepts it            |:vec3&&)’" while gcc 11 and
                   |                            |clang accepts it
           Keywords|                            |rejects-valid
   Target Milestone|---                         |12.0

[Bug c++/103746] [12 Regression] GCC 12 rejects code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and clang accepts it

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r12-5256-g37326651b439bac5.

[Bug c++/103746] [12 Regression] Rejected code "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" since r12-5256-g37326651b439bac5

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
                 CC|                            |jason at gcc dot gnu.org
            Summary|[12 Regression] GCC 12      |[12 Regression] Rejected
                   |rejects code on "call to    |code "call to
                   |non-‘constexpr’ function    |non-‘constexpr’ function
                   |‘glsl::vec3&                |‘glsl::vec3&
                   |glsl::vec3::operator=(glsl: |glsl::vec3::operator=(glsl:
                   |:vec3&&)’" while gcc 11 and |:vec3&&)’" since
                   |clang accepts it            |r12-5256-g37326651b439bac5

[Bug c++/103746] [12 Regression] Rejected code "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" since r12-5256-g37326651b439bac5

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

--- Comment #4 from Martin Liška <marxin at gcc dot gnu.org> ---
Reduced test-case:

struct VectorType {
  void operator=(VectorType);
};
template <typename> using V4 = VectorType;
using Float = V4<float>;
struct vec3 {
  Float x;
};
struct mat3 {
  vec3 data[3];
  constexpr mat3() { data[2] = vec3(); }
};

$ g++ ff.ii -c
ff.ii: In constructor ‘constexpr mat3::mat3()’:
ff.ii:11:37: error: call to non-‘constexpr’ function ‘vec3&
vec3::operator=(vec3&&)’
   11 |   constexpr mat3() { data[2] = vec3(); }
      |                                     ^
ff.ii:6:8: note: ‘vec3& vec3::operator=(vec3&&)’ is not usable as a ‘constexpr’
function because:
    6 | struct vec3 {
      |        ^~~~
ff.ii:2:8: note: defaulted constructor calls non-‘constexpr’ ‘void
VectorType::operator=(VectorType)’
    2 |   void operator=(VectorType);
      |        ^~~~~~~~
ff.ii:2:8: note: ‘void VectorType::operator=(VectorType)’ declared here

[Bug c++/103746] [12 Regression] GCC 12 rejects code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and clang accepts it

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|1                           |0
            Summary|[12 Regression] Rejected    |[12 Regression] GCC 12
                   |code "call to               |rejects code on "call to
                   |non-‘constexpr’ function    |non-‘constexpr’ function
                   |‘glsl::vec3&                |‘glsl::vec3&
                   |glsl::vec3::operator=(glsl: |glsl::vec3::operator=(glsl:
                   |:vec3&&)’" since            |:vec3&&)’" while gcc 11 and
                   |r12-5256-g37326651b439bac5  |clang accepts it
             Status|NEW                         |UNCONFIRMED

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This code is definitely not valid but -fimplicit-constexpr will allow it to
compile already.

[Bug c++/103746] [12 Regression] GCC 12 rejects code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" while gcc 11 and clang accepts it

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> ---
Note Clang and ICC accept the code, while GCC and MSVC reject it.

[Bug c++/103746] [12 Regression] Rejected code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" since r12-5256-g37326651b439bac5

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
That patch is changing extactly this code. In fact MSVC rejects this code for
the same reason as GCC.

Jason added -fimplicit-constexpr and then found that there was some invalid
code accepted and he fixed that.

[Bug c++/103746] [12 Regression] Rejected code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" since r12-5256-g37326651b439bac5

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
MSVC error:

<source>(12): error C3615: constexpr function 'mat3::mat3' cannot result in a
constant expression
<source>(12): note: failure was caused by call of undefined function or one not
declared 'constexpr'
<source>(12): note: see usage of 'vec3::operator ='

As mentioned -fimplicit-constexpr will workaround the issue really.

[Bug c++/103746] [12 Regression] Rejected code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" since r12-5256-g37326651b439bac5

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Oh it is IFNDR (Ill-formed, no diagnostic required) code too :). So accepting
the code is fine so is rejecting it but it is still ill-formed.

[Bug c++/103746] [12 Regression] Rejected code on "call to non-‘constexpr’ function ‘glsl::vec3& glsl::vec3::operator=(glsl::vec3&&)’" since r12-5256-g37326651b439bac5

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103746

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|INVALID                     |FIXED

--- Comment #10 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
I wonder if -fimplicit-constexpr should not be parf of -fpermissive?
That was my attempt to workaround it.