[Bug c/102558] New: missing warning comparing T[static N] to null

[Bug c/102558] New: missing warning comparing T[static N] to null

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102558

            Bug ID: 102558
           Summary: missing warning comparing T[static N] to null
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

This is the diagnostic part of pr102556:

The C99 [static N] array notation in a function parameter indicates that the
caller must provide as an argument an array with at least N element. 
Therefore, in the body of the function, the parameter may be assumed to be
nonnull, the same way as if it had been declared with attribute nonnull.

The test case below shows that GCC fails to issue a warning for the pointless
equality expression in g(), equivalent to the one in f() (although -Waddress
might be more suitable than than -Wnonnull-compare).

$ cat z.c && gcc -O2 -S -Wall z.c
__attribute__ ((nonnull)) int f (int *a)
{
  return a == 0;   // warning (good, folded to false)
}

int g (int a[static 1])
{
  return a == 0;   // missing warning (not folded)
}
z.c: In function ‘f’:
z.c:3:12: warning: ‘nonnull’ argument ‘a’ compared to NULL [-Wnonnull-compare]
    3 |   return a == 0;   // warning (good, folded to false)
      |          ~~^~~~

[Bug c/102558] missing warning comparing T[static N] to null

[muecker at gwdg dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102558

Martin Uecker <muecker at gwdg dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |muecker at gwdg dot de

--- Comment #1 from Martin Uecker <muecker at gwdg dot de> ---
Possibly fix by synthesizing a nonnull attribute:

https://gcc.gnu.org/pipermail/gcc-patches/2023-July/625559.html

[Bug c/102558] missing warning comparing T[static N] to null

[uecker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102558

uecker at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0
                 CC|                            |uecker at gcc dot gnu.org

--- Comment #2 from uecker at gcc dot gnu.org ---
Fixed on trunk.

[Bug c/102558] missing warning comparing T[static N] to null

[uecker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102558

uecker at gcc dot gnu.org changed:

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

--- Comment #3 from uecker at gcc dot gnu.org ---
.