[Bug c/37064] New: missing warning on pure function with side-effects

[Bug c/37064] New: missing warning on pure function with side-effects

[sebor at roguewave dot com]

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gcc assumes that functions defined with the pure attribute have no side
effects and do not modify program state, including through pointers passed
to such functions as arguments. The function below does modify the object
pointed to by its argument. It would be useful if gcc issued a diagnostic
for this and other similar violations of the "pure" assumption, analogously
to how it diagnoses noreturn functions that do return.

$ cat -n t.C && g++ -c -O2 -Wall -W t.C
     1  int f0 () __attribute ((noreturn));
     2  int f0 () { return 0; }
     3
     4  int f1 (int*) __attribute ((pure));
     5  int f1 (int *i)
     6  {
     7      *i = 0;
     8      return 0;
     9  }
    10
t.C: In function ‘int f0()’:
t.C:2: warning: function declared ‘noreturn’ has a ‘return’ statement
t.C:2: warning: ‘noreturn’ function does return


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           Summary: missing warning on pure function with side-effects
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sebor at roguewave dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37064

[Bug c/37064] missing warning on pure function with side-effects

[sebor at roguewave dot com]

------- Comment #1 from sebor at roguewave dot com  2008-08-08 19:47 -------
Similarly, functions declared with the const attribute such as f1() in the
test case below that violate the compiler's assumptions should be diagnosed:

$ cat -n t.C && g++ -c -O2 -Wall -W t.C
     1  extern int i;
     2  int f1 () __attribute ((const));
     3  int f1 ()
     4  {
     5      return i;
     6  }
     7


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37064

[Bug c/37064] missing warning on pure function with side-effects

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2008-08-08 20:53 -------
Confirmed.


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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2008-08-08 20:53:56
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37064

[Bug c/37064] missing warning on pure function with side-effects

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2008-08-08 21:01 -------


*** This bug has been marked as a duplicate of 18487 ***


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pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37064