[Bug c++/30332] New: bit-field: optimization BUG?

[Bug c++/30332] New: bit-field: optimization BUG?

[s__nakayama at infoseek dot jp]

The output is different by the optimization.

testcase:
#include <stdio.h>

struct S
{
  unsigned int long long a:33;
};


int main ()
{
  struct S x = { -1 };
  typeof(+x.a) z = x.a+10;
  printf("%llx\n", z);

  return 0;
}

result:
$ g++ bug.cpp; ./a
200000009

$ g++ -O bug.cpp; ./a
9

gcc version: 4.2 20061212


-- 
           Summary: bit-field: optimization BUG?
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: s__nakayama at infoseek dot jp


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] bit-field: optimization BUG?

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-12-30 08:28 -------
So we do x.a+10 in unsigned long long and then cast it to the bit-field type. 
I am thinking we are getting the wrong type for the typeof anyways.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] bit-field: optimization BUG?

[bangerth at dealii dot org]

------- Comment #2 from bangerth at dealii dot org  2007-01-21 05:29 -------
No, that's not the case. We can print the types:
-------------
#include <stdio.h>
#include <iostream>
#include <typeinfo>

struct S
{
  unsigned int long long a:33;
};


int main ()
{
  struct S x = { -1 };
  typeof(+x.a) z = x.a+10;
  printf("%llx\n", z);

  std::cout << typeid(x.a).name() << ' ' << typeid(z).name()
            << std::endl;

  return 0;
}
--------------

g/x> ./a.out 
200000009
y y
g/x> c++ x.cc -O2
g/x> ./a.out 
9
y y

'y' apparently encodes unsigned long long.

W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bangerth at dealii dot org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-01-21 05:29:10
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] [4.1/4.2?/4.3? regression] bit-field: optimization BUG?

[bangerth at dealii dot org]

------- Comment #3 from bangerth at dealii dot org  2007-01-21 05:32 -------
In any case, I consider this a bug in gcc. The problem doesn't happen with
gcc 3.3 or 3.4 or 4.0, so it's a regression.

That said, there's a second problem: before 4.1.x, we warned:
g/x> /home/bangerth/bin/gcc-4.0.x/bin/c++ x.cc -O2
x.cc: In function 'int main()':
x.cc:13: warning: converting negative value '-0x000000001' to 'long long
unsigned int'

This doesn't happen any more, not even with -W -Wall

W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
      Known to fail|                            |4.1.0
      Known to work|                            |3.3.6 3.4.6 4.0.1
            Summary|bit-field: optimization BUG?|[4.1/4.2?/4.3? regression]
                   |                            |bit-field: optimization BUG?


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] [4.1/4.2/4.3 regression] bit-field: optimization BUG?

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.1.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] [4.1/4.2/4.3 regression] bit-field: optimization BUG?

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] [4.1/4.2/4.3 regression] bit-field: optimization BUG?

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.1.2                       |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] [4.1/4.2/4.3 regression] bit-field: optimization BUG?

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2007-02-21 15:12 -------
With 4.1.3 for C we have, even without optimizing

> ./xgcc -B. -o t t.c -Wall
t.c: In function 'main':
t.c:13: warning: format '%llx' expects type 'long long unsigned int', but
argument 2 has type 'long unsigned int:33'
> ./t
9

For C++ we for all optimizations get
> ./t
200000009


The difference after gimplification is

main ()
{
  <unnamed type> D.2220;
  int D.2221;
  struct S x;
  <unnamed type> z;

  x.a = 8589934591;
  D.2220 = x.a;
  z = D.2220 + 10;
  printf (&"%llx\n"[0], z);
  D.2221 = 0;
  return D.2221;
}

vs.

int main() ()
{
  long long unsigned int D.2823;
  int D.2824;

  {
    struct S x;
    long long unsigned int z;

    x.a = 8589934591;
    D.2823 = x.a;
    z = D.2823 + 10;
    printf (&"%llx\n"[0], z);
    D.2824 = 0;
    return D.2824;
  }
  D.2824 = 0;
  return D.2824;
}

i.e. typeof(+x.a) yields a different result for C and C++.  For C we leave
bitfield types bigger than int alone and don't promote them.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] [4.1/4.2/4.3 regression] bit-field: optimization BUG?

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2007-12-11 13:47 -------
Related to PR33887.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |33887


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] [4.1/4.2 regression] bit-field: optimization BUG?

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2008-01-25 12:14 -------
Fixed on the trunk by the fix for PR33887.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|3.3.6 3.4.6 4.0.1           |3.3.6 3.4.6 4.0.1 4.3.0
            Summary|[4.1/4.2/4.3 regression]    |[4.1/4.2 regression] bit-
                   |bit-field: optimization BUG?|field: optimization BUG?


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] [4.2 regression] bit-field: optimization BUG?

[jsm28 at gcc dot gnu dot org]

------- Comment #7 from jsm28 at gcc dot gnu dot org  2008-07-04 21:47 -------
Closing 4.1 branch.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.1/4.2 regression] bit-   |[4.2 regression] bit-field:
                   |field: optimization BUG?    |optimization BUG?
   Target Milestone|4.1.3                       |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332

[Bug c++/30332] [4.2 regression] bit-field: optimization BUG?

[jsm28 at gcc dot gnu dot org]

------- Comment #8 from jsm28 at gcc dot gnu dot org  2009-03-30 20:20 -------
Closing 4.2 branch, fixed in 4.3.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
      Known to fail|4.1.0                       |4.1.0 4.2.5
         Resolution|                            |FIXED
   Target Milestone|4.2.5                       |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30332