[Bug c++/49525] New: [4.4] wrong code and wrong warning for bitfield related operations

[Bug c++/49525] New: [4.4] wrong code and wrong warning for bitfield related operations

[marcin.slusarz at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

           Summary: [4.4] wrong code and wrong warning for bitfield
                    related operations
           Product: gcc
           Version: 4.4.5
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: marcin.slusarz@gmail.com


Created attachment 24595
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24595
testcase

Compilation of attached file generates wrong warning:
$ g++-4.4.5 -c -O2 -Wall all.c
all.c: In function ‘void test(const st_src_reg*, ureg_dst)’:
all.c:118: warning: ‘reg’ is used uninitialized in this function
all.c:118: note: ‘reg’ was declared here

And produces wrong code - at random after "test" function, src[i].Negate (one
bit unsigned bit-field) becomes 1 when src_reg[i]->negate == 0 - something
which should not happen.

The bug does not manifest when compiled with gcc instead of g++ or with g++
4.3.5 or 4.5.2.

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[marcin.slusarz at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

--- Comment #1 from Marcin Ślusarz <marcin.slusarz at gmail dot com> 2011-06-24 22:20:24 UTC ---
Created attachment 24596
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24596
g++ -v -save-temps -O2 -Wall -c all.c

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[marcin.slusarz at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

--- Comment #2 from Marcin Ślusarz <marcin.slusarz at gmail dot com> 2011-06-24 22:23:56 UTC ---
Created attachment 24597
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24597
standalone app testing this bug

I'm attaching sources of standalone app which tests this bug.

It should print:
0
0
0
0

Sometimes it prints:
1
1
1
1
a.out: main.c:14: void check_output(ureg_src*): Assertion `sum == 0' failed.

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[marcin.slusarz at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

--- Comment #3 from Marcin Ślusarz <marcin.slusarz at gmail dot com> 2011-06-24 22:37:44 UTC ---
Created attachment 24598
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24598
all.ii

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[marcin.slusarz at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

--- Comment #4 from Marcin Ślusarz <marcin.slusarz at gmail dot com> 2011-06-24 22:38:06 UTC ---
Created attachment 24599
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24599
all.s

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

--- Comment #5 from Mikael Pettersson <mikpe at it dot uu.se> 2011-06-25 12:23:48 UTC ---
I can't reproduce the runtime failure with gcc-4.6-20110621 on x86_64-linux.

I see you're using Gentoo's modified gcc-4.4.5.  Can you please try again with
a g++ built from vanilla unmodified gcc-4.4.5 (or later 4.4.x) sources?

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

Mikael Pettersson <mikpe at it dot uu.se> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mikpe at it dot uu.se

--- Comment #6 from Mikael Pettersson <mikpe at it dot uu.se> 2011-06-25 12:54:28 UTC ---
(In reply to comment #5)
> I can't reproduce the runtime failure with gcc-4.6-20110621 on x86_64-linux.

Of course I meant to write gcc-4.4-20110621 not 4.6...

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[bryancain3+gcc at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

Bryan Cain <bryancain3+gcc at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bryancain3+gcc at gmail dot
                   |                            |com

--- Comment #7 from Bryan Cain <bryancain3+gcc at gmail dot com> 2011-06-25 15:46:32 UTC ---
I have this problem using the gcc 4.4.5 build in Ubuntu 10.10, which reports
itself as "gcc (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5".  So it's not
Gentoo-specific.

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

--- Comment #8 from Mikael Pettersson <mikpe at it dot uu.se> 2011-06-25 16:40:42 UTC ---
(In reply to comment #7)
> I have this problem using the gcc 4.4.5 build in Ubuntu 10.10, which reports
> itself as "gcc (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5".  So it's not
> Gentoo-specific.

That's also a heavily modified vendor compiler.

Please try with an unmodified 4.4.5 or 4.4.6.

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[marcin.slusarz at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

--- Comment #9 from Marcin Ślusarz <marcin.slusarz at gmail dot com> 2011-06-25 18:46:53 UTC ---
Gentoo does not patch gcc severely.

See:
http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/sys-devel/gcc/gcc-4.4.5.ebuild?revision=1.10&view=markup

which adds only 2 patches:
http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/sys-devel/gcc/files/gcc-spec-env.patch?revision=1.6&view=markup
http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/sys-devel/gcc/files/4.4.0/gcc-4.4.0-softfloat.patch?revision=1.1&view=markup
(arm specific)

If that does not convince you, I can compile gcc without these patches. Just
say so.

Please note that runtime failure occurs in ~30-40% runs.

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

Mikael Pettersson <mikpe at it dot uu.se> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|mikpe at it dot uu.se       |

--- Comment #10 from Mikael Pettersson <mikpe at it dot uu.se> 2011-06-25 20:23:26 UTC ---
I don't think that .ebuild file describes everything in detail, specifically I
strongly suspect they also apply 27 patches from gcc-4.4.5-patches-1.2.tar.bz2.

I just recompiled the test case with a freshly built gcc-4.4.5 on x86_64-linux,
and ran it 100 times.  It failed zero times.

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[marcin.slusarz at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

--- Comment #11 from Marcin Ślusarz <marcin.slusarz at gmail dot com> 2011-06-26 12:48:05 UTC ---
Ok, you are right. I didn't know about these patches.

Now I compiled gcc-4.4.5 with "vanilla" USE flag - which disables all these
patches - and it still fails at runtime.

[Bug c++/49525] [4.4] wrong code and wrong warning for bitfield related operations

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49525

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
      Known to work|                            |4.6.0, 4.6.1, 4.7.0
         Resolution|                            |WORKSFORME

--- Comment #12 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-10-09 15:00:06 UTC ---
Can't reproduce with current 4_4-branch, 4_5-branch, 4_6-branch, and mainline.