[Bug c/36989] New: Wrong type for (... ? ... : ...)

[Bug c/36989] New: Wrong type for (... ? ... : ...)

[terra at gnome dot org]

With the code below, gcc complains over line 8, but not lines 14 and 17
because it deduces the wrong type for the ?: operator.  The type of that
operator's result is dependent on whether something is a null pointer
constant and not.  gcc fails to track that properly: it knows that
(const void *)0 is a null pointer constant, but it also thinks that
(void *)(void *)0 and (1 ? (void *)0 : (void *)0) are.

The chapter and verse is C99 6.15.15 #6: "if one operand is a null
pointer constant, the result has the type of the other operand;"

Null pointer constants are defined in C99 6.3.2.3 #3 to be an integer
constant expression with value zero or such an expression case to
type void *.

For the record, Sun's cc gets the invalid cases right, but also
rejects the valid case.

int
main (int argc, char **argv)
{
  int *p;
  int n;

  /* Invalid: dereferences a void * */
  *(n ? p : (const void *)0);

  /* Valid since it dereferences an int* */
  *(n ? p : (void *)0);

  /* Invalid: dereferences a void * */
  *(n ? p : (void *)(void *)0);

  /* Invalid: dereferences a void * */
  *(n ? p : (1 ? (void *)0 : (void *)0));

  return 0;
}


-- 
           Summary: Wrong type for (... ? ... : ...)
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: terra at gnome dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36989

[Bug c/36989] Wrong type for (... ? ... : ...)

[jsm28 at gcc dot gnu dot org]

------- Comment #1 from jsm28 at gcc dot gnu dot org  2008-07-31 15:44 -------
Bug 456 covers c9[09]-const-expr-[12].c, bug 5675 covers
c9[0-9]-const-expr-3.c.


*** This bug has been marked as a duplicate of 456 ***


-- 

jsm28 at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36989