[Bug c++/99795] New: -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[Bug c++/99795] New: -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[nok.raven at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

            Bug ID: 99795
           Summary: -Wnarrowing/-Woverflow false-negative in constant
                    expression in undeduced context
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nok.raven at gmail dot com
                CC: jason at redhat dot com, mpolacek at gcc dot gnu.org
  Target Milestone: ---

template <char N> struct X {};
template <class T> X<sizeof(T)> foo();
int x = sizeof(foo<char[512]>());

template <typename T>
struct bar { typedef X<sizeof(T)> t; };
bar<char[512]> y;


GCC 4.6-6 had an -Woverflow warning here; since GCC 7 -Wconversion warning was
emitted instead, but since bug 99331 is fixed there is no warning at all.

[Bug c++/99795] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-03-26
           Keywords|                            |accepts-invalid
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed, thanks for opening.

[Bug c++/99795] [8/9/10/11 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |8.5
            Summary|-Wnarrowing/-Woverflow      |[8/9/10/11 Regression]
                   |false-negative in constant  |-Wnarrowing/-Woverflow
                   |expression in undeduced     |false-negative in constant
                   |context                     |expression in undeduced
                   |                            |context

[Bug c++/99795] [8/9/10/11 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |jason at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org

[Bug c++/99795] [8/9/10/11 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Created attachment 50524
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50524&action=edit
WIP Fix

This patch uses IMPLICIT_CONV_EXPR to get the narrowing error, but more and
more changes are being necessary to prevent regressions; this isn't going to be
safe for GCC 11 at this point, so I'm going to put it aside for now.

[Bug c++/99795] [8/9/10/11 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|jason at gcc dot gnu.org           |unassigned at gcc dot gnu.org
             Status|ASSIGNED                    |NEW

[Bug c++/99795] [8/9/10/11 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/99795] [9/10/11/12 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

[Bug c++/99795] [9/10/11/12 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug c++/99795] [10/11/12/13 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.5                         |10.4

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed

[Bug c++/99795] [10/11/12/13 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.5

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.

[Bug c++/99795] [11/12/13/14 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.5                        |11.5

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.

[Bug c++/99795] [11/12 Regression] -Wnarrowing/-Woverflow false-negative in constant expression in undeduced context

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99795

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11/12/13/14 Regression]    |[11/12 Regression]
                   |-Wnarrowing/-Woverflow      |-Wnarrowing/-Woverflow
                   |false-negative in constant  |false-negative in constant
                   |expression in undeduced     |expression in undeduced
                   |context                     |context
                 CC|                            |law at gcc dot gnu.org

--- Comment #8 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Works with gcc-13 and the trunk. Adjusting regression markers.