[Bug c/60838] New: bugos warning: initializer element is not a constant expression: int test = (0 ? (1,0) : 0) + 1;

[Bug c/60838] New: bugos warning: initializer element is not a constant expression: int test = (0 ? (1,0) : 0) + 1;

[potrepalov@asc-ural.ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60838

            Bug ID: 60838
           Summary: bugos warning: initializer element is not a constant
                    expression: int test = (0 ? (1,0) : 0) + 1;
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: potrepalov@asc-ural.ru

main.c:
-------------
int test = (0 ? (3, 0) : 0) + 1;
int main( void ) { return 0; }
-------------

>gcc main.c
main.c:1:12: warning: initializer element is not a constant expression


This is work, but generate warning:

#define CT_ASSERT_EXPR(ex)  (0 ? ((struct { int a:((ex) ? 1 : -1); } *)0,0) :
0)
#define CT_ASSERT(ex)       extern char ct_assert_[ CT_ASSERT_EXPR(ex)+1 ]

warning: variably modified 'ct_assert_' at file scope


According C standart:

6.6 Constant expressions

Constant expressions shall not contain assignment, increment, decrement,
function-call, or comma operators, except when they are contained within a
subexpression that is not evaluated.


6.5.15 Conditional operator

The first operand is evaluated; there is a sequence point after its evaluation.
The second operand is evaluated only if the first compares unequal to 0; the
third operand is evaluated only if the first compares equal to 0; the result is
the value of the second or third operand (whichever is evaluated), converted to
the type described below.

[Bug c/60838] bugos warning: initializer element is not a constant expression: int test = (0 ? (1,0) : 0) + 1;

[potrepalov@asc-ural.ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60838

--- Comment #1 from ilya <potrepalov@asc-ural.ru> ---
Another testcase:

main.c
-----------------
int test1 = (0 ? 0 : 0) + 1;
int test2 = (0 ? (3, 0) : 0) + 1;
int test3[(0 ? 0 : 0) + 1];
int test4[(0 ? (3, 0) : 0) + 1];

int main( void ) { return 0; }
-----------------

>gcc main.c
main.c:2:13: warning: initializer element is not a constant expression
main.c:4:5: error: variably modified ‘test4’ at file scope


Checked for:
gcc version 4.5.3 (GCC) 
gcc version 4.7.3
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Subject: [Bug c++/60836] [4.7/4.8/4.9/4.10 Regression] invalid PHI argument and ICE in verify_gimple
Date: Mon, 14 Apr 2014 07:32:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`836

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-04-14
                 CC|                            |jakub at gcc dot gnu.org
   Target Milestone|---                         |4.7.4
            Summary|[4.9 Regression] invalid    |[4.7/4.8/4.9/4.10
                   |PHI argument and ICE in     |Regression] invalid PHI
                   |verify_gimple               |argument and ICE in
                   |                            |verify_gimple
     Ever confirmed|0                           |1

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r173856.

[Bug c/60838] bugos warning: initializer element is not a constant expression: int test = (0 ? (1,0) : 0) + 1;

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60838

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I actually don't think this is a bug.  While C99/C11 say what you wrote about
Constant expressions, C89 says something else:
"Constant expressions shall not contain assignment, increment, decrement,
function-call, or comma operators, except when they are contained within the
operand of a sizeof operator."
And really:
int u = sizeof ((0 ? (3, 0) : 0) + 1);
issues no warnings even with -std=c89.  The default is still -std=gnu89, so you
may want to use e.g. -std=gnu99.

[Bug c/60838] bugos warning: initializer element is not a constant expression: int test = (0 ? (1,0) : 0) + 1;

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60838

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |jakub at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Yeah, with e.g. -std=c89 -pedantic-errors you get the desired diagnostics on
#c1 test, while with -std=c99 -pedantic-errors it is accepted.