[Bug c/98539] New: incorrect warning with -Wvla-parameter for unspecified bound in multi-dim array

[Bug c/98539] New: incorrect warning with -Wvla-parameter for unspecified bound in multi-dim array

[muecker at gwdg dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98539

            Bug ID: 98539
           Summary: incorrect warning with -Wvla-parameter for unspecified
                    bound in multi-dim array
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: muecker at gwdg dot de
  Target Milestone: ---

For the following example:

void foo(int n, double x[3][*]);
void foo(int n, double x[3][n]) { }


I get the warning:

x.c:5:24: warning: argument 2 of type ‘double[3][n]’ declared as a variable
length array [-Wvla-parameter]
    5 | void foo(int n, double x[3][n])
      |                 ~~~~~~~^~~~~~~
x.c:3:24: note: previously declared as an ordinary array ‘double[3][0]’
    3 | void foo(int n, double x[3][*]);
      |                 ~~~~~~~^~~~~~~


This is incorrect, as the unspecified bound implies a variable length array and
not an ordinary array (6.7.6.2p4).

There is no warning for:

void foo(int n, double x[3][*]);
void foo(int n, double x[3][4]);

[Bug c/98539] incorrect warning with -Wvla-parameter for unspecified bound in multi-dim array

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98539

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
   Last reconfirmed|                            |2021-01-05
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
                 CC|                            |msebor at gcc dot gnu.org

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
The internal representation of [*] is the same as [0] so except in the most
significant bounds the warning can't distinguish between one and the other (see
pr98091).  It has to pick one and it chooses to consider it a VLA.  Let me
confirm this bug here and resolve pr98091 as a duplicate.

[Bug c/98539] incorrect warning with -Wvla-parameter for unspecified bound in multi-dim array

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98539

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
*** Bug 98091 has been marked as a duplicate of this bug. ***