[Bug c/40404] New: Comparison involving unsigned int:17 bitfield seems wrong

[Bug c/40404] New: Comparison involving unsigned int:17 bitfield seems wrong

[foo at mailinator dot com]

#include <stdio.h>
struct S {
    unsigned int ui17 : 17;
} s;
int main()
{
    s.ui17 = 0x1ffff;
    printf("%x\n", (unsigned int)s.ui17);
    if (s.ui17 >= 0xfffffffeu)
        puts("FAIL");
    return 0;
}

Maybe I don't understand GCC's rules for the promotion of bitfields, but it
seems to me that s.ui17 should evaluate to ((unsigned int)0x1ffff), which is
less than 0xfffffffeu, so "FAIL" should not be printed. But "FAIL" is printed.
I can't explain why; it's almost as if GCC is truncating the rhs to 0x1fffe
before doing the comparison!

Changing s.ui17 from 17 bits to 15 bits makes the test pass (i.e., not print
"FAIL"). I believe in that case GCC promotes s.ui17 to "unsigned short"... but
that should undergo usual arithmetic conversion to "unsigned int" at which
point we ought to see the same FAIL behavior happening.

Reproduced with GCC 4.2.4 and 4.3.3.


-- 
           Summary: Comparison involving unsigned int:17 bitfield seems
                    wrong
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: foo at mailinator dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404

[Bug c/40404] Comparison involving unsigned int:17 bitfield seems wrong

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2009-06-10 18:41 -------
unsigned int:17  gets promoted to int IIRC.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404

[Bug c/40404] Comparison involving unsigned int:17 bitfield seems wrong

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2009-06-10 20:15 -------
This has been fixed in GCC 4.4, likely by removing some shorten-compare stuff
in the frontend.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org
      Known to fail|                            |4.3.3
      Known to work|                            |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404

[Bug c/40404] Comparison involving unsigned int:17 bitfield seems wrong

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2009-06-10 20:25 -------
Can someone identify the patch that fixed that on the trunk?


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404

[Bug c/40404] Comparison involving unsigned int:17 bitfield seems wrong

[mikpe at it dot uu dot se]

------- Comment #4 from mikpe at it dot uu dot se  2009-06-12 20:41 -------
(In reply to comment #3)
> Can someone identify the patch that fixed that on the trunk?

I've identified r139702, the fix for PR37005, as the revision which fixed this
test case on gcc-4.4. That change applies easily to current gcc-4.3, so I tried
it and it did fix this test case also for gcc-4.3.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404

[Bug c/40404] Comparison involving unsigned int:17 bitfield seems wrong

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2009-06-13 13:56 -------
Thanks.  I'll have a look.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-06-13 13:56:16
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404

[Bug middle-end/40404] Comparison involving unsigned int:17 bitfield seems wrong

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2009-06-17 12:28 -------
Subject: Bug 40404

Author: rguenth
Date: Wed Jun 17 12:28:43 2009
New Revision: 148605

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=148605
Log:
2009-06-17  Richard Guenther  <rguenther@suse.de>

        PR middle-end/40404
        * gcc.c-torture/execute/pr40404.c: New testcase.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/gcc.c-torture/execute/pr40404.c
Modified:
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404

[Bug middle-end/40404] Comparison involving unsigned int:17 bitfield seems wrong

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2009-06-17 12:31 -------
Subject: Bug 40404

Author: rguenth
Date: Wed Jun 17 12:30:54 2009
New Revision: 148606

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=148606
Log:
2009-06-17  Richard Guenther  <rguenther@suse.de>

        PR middle-end/40404
        * gcc.c-torture/execute/pr40404.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr40404.c
Modified:
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404

[Bug middle-end/40404] Comparison involving unsigned int:17 bitfield seems wrong

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2009-06-17 13:06 -------
Subject: Bug 40404

Author: rguenth
Date: Wed Jun 17 13:06:21 2009
New Revision: 148610

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=148610
Log:
2009-06-17  Richard Guenther  <rguenther@suse.de>

        PR middle-end/40404
        * fold-const.c (fold_binary): Verify the type precision of the
        stripped arguments of the comparison are the same before
        folding the comparison.

        * gcc.c-torture/execute/pr40404.c: New testcase.

Added:
    branches/gcc-4_3-branch/gcc/testsuite/gcc.c-torture/execute/pr40404.c
Modified:
    branches/gcc-4_3-branch/gcc/ChangeLog
    branches/gcc-4_3-branch/gcc/fold-const.c
    branches/gcc-4_3-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404

[Bug middle-end/40404] Comparison involving unsigned int:17 bitfield seems wrong

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2009-06-17 13:07 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|4.4.0                       |4.3.4 4.4.0
         Resolution|                            |FIXED
   Target Milestone|---                         |4.3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40404