[Bug c/35235] New: struct/union rvalue qualifiers must not propagate to members

[Bug c/35235] New: struct/union rvalue qualifiers must not propagate to members

[truedfx at gentoo dot org]

Hi,

This turns out to be a strictly conforming C99 program:

#include <stdlib.h>
int main(void) {
    const struct {
        int array[1];
    } s;
    // int *from_lvalue = s.array; // #1
    int *from_rvalue = (rand() ? s : s).array; // #2
}

#1, if uncommented, should be rejected with -std=c99 -pedantic-errors, and
quite rightly is. However, in #2, the result of the conditional expression is
not an lvalue. C99 6.7.3p3 states that type qualifiers are not meaningful for
non-lvalues. Because of that, the type of (rand() ? s : s).array is int[1], not
const int[1], and it converts to int*, not const int*. This means the
initialization should be allowed, even though there is nothing you are allowed
to do with from_rvalue afterwards. It is certainly true that this code is
complete rubbish, and this handling by gcc should not cause any problems in any
real-world code, but technically, it's a bug, so I'm reporting it here.

The code is rejected in gcc 4.1 (4.1.2), 4.2 (4.2.2) and 4.3 (4.3-20080208). It
used to be accepted in older versions (3.3.6, 3.4.6, 4.0.4), but in those older
versions, no warning was given even for #1. Because of that, I'm not sure if
this qualifies as a regression.


-- 
           Summary: struct/union rvalue qualifiers must not propagate to
                    members
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: truedfx at gentoo dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35235

[Bug c/35235] struct/union rvalue qualifiers must not propagate to members

[jsm28 at gcc dot gnu dot org]

-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |16989
              nThis|                            |
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Priority|P3                          |P4
   Last reconfirmed|0000-00-00 00:00:00         |2008-02-17 23:14:23
               date|                            |
   Target Milestone|---                         |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35235

[Bug c/35235] [4.2/4.3/4.4 Regression] struct/union rvalue qualifiers must not propagate to members

[jsm28 at gcc dot gnu dot org]

------- Comment #1 from jsm28 at gcc dot gnu dot org  2008-07-04 19:30 -------
Closing 4.1 branch.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|struct/union rvalue         |[4.2/4.3/4.4 Regression]
                   |qualifiers must not         |struct/union rvalue
                   |propagate to members        |qualifiers must not
                   |                            |propagate to members
   Target Milestone|4.1.3                       |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35235

[Bug c/35235] [4.2/4.3/4.4 Regression] struct/union rvalue qualifiers must not propagate to members

[jsm28 at gcc dot gnu dot org]

------- Comment #2 from jsm28 at gcc dot gnu dot org  2009-02-04 17:14 -------
Working on a patch.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jsm28 at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2008-12-29 07:07:08         |2009-02-04 17:14:54
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35235

[Bug c/35235] [4.2/4.3/4.4 Regression] struct/union rvalue qualifiers must not propagate to members

[jsm28 at gcc dot gnu dot org]

------- Comment #3 from jsm28 at gcc dot gnu dot org  2009-02-04 21:02 -------
Subject: Bug 35235

Author: jsm28
Date: Wed Feb  4 21:02:42 2009
New Revision: 143940

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=143940
Log:
        PR c/35235
        * c-typeck.c (build_component_ref): Do not copy qualifiers from
        non-lvalue to component.

testsuite:
        * gcc.dg/c99-array-lval-8.c: New test.

Added:
    branches/c-4_5-branch/gcc/testsuite/gcc.dg/c99-array-lval-8.c
Modified:
    branches/c-4_5-branch/gcc/ChangeLog.c45
    branches/c-4_5-branch/gcc/c-typeck.c
    branches/c-4_5-branch/gcc/testsuite/ChangeLog.c45


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35235

[Bug c/35235] [4.2/4.3/4.4/4.5 Regression] struct/union rvalue qualifiers must not propagate to members

[jsm28 at gcc dot gnu dot org]

------- Comment #4 from jsm28 at gcc dot gnu dot org  2009-03-30 01:25 -------
Subject: Bug 35235

Author: jsm28
Date: Mon Mar 30 01:25:37 2009
New Revision: 145271

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=145271
Log:
        PR c/35235
        * c-typeck.c (build_component_ref): Do not copy qualifiers from
        non-lvalue to component.

testsuite:
        * gcc.dg/c99-array-lval-8.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/c99-array-lval-8.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-typeck.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35235

[Bug c/35235] [4.2/4.3/4.4/4.5 Regression] struct/union rvalue qualifiers must not propagate to members

[jsm28 at gcc dot gnu dot org]

------- Comment #5 from jsm28 at gcc dot gnu dot org  2009-03-30 01:29 -------
Fixed for 4.5.  Fix depends on changes not suitable for backporting.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|4.0.1 3.3.3                 |4.0.1 3.3.3 4.5.0
         Resolution|                            |FIXED
   Target Milestone|4.2.5                       |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35235