[Bug c/53663] New: 4.7 inconsistent inline handling of bool within union

[Bug c/53663] New: 4.7 inconsistent inline handling of bool within union

[brendan.jones.it at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

             Bug #: 53663
           Summary: 4.7 inconsistent inline handling of bool within union
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: brendan.jones.it@gmail.com


Please refer to the following:

/* -*- Mode: C ; c-basic-offset: 4 -*- */
/* gcc test_jack.c -Wall -Wextra -o test -O1 && ./test ; echo $?
   should print 0, prints 10
   gcc known to be affected:

Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --disable-build-with-cxx
--disable-build-poststage1-with-cxx --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-ppl --with-cloog --with-tune=generic --with-arch_32=i686
--build=x86_64-redhat-linux
Thread model: posix
gcc version 4.7.0 20120507 (Red Hat 4.7.0-5) (GCC) 
*/
#include <stdio.h>
union u
{
    int i = 0;
    _Bool b = 0;
};

void f(union u * vp, union u v)
{
    *vp = v;
}

int main()
{
    union u v = 0;
    union u v1 = 0;
    union u v2 = 0;

    v.i = 10;
    f(&v1, v);

    v.b = 0;
    f(&v2, v);
    if (v2.b) printf("True\n");
    else printf("False\n");
    return v2.b;
}

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |tree-optimization

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-06-13 23:19:40 UTC ---
I bet this was already fixed in 4.7.1 though I have not tested it yet.

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2012-06-14
     Ever Confirmed|0                           |1

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-06-14 08:40:43 UTC ---
The testcase does not compile for me, it has errors:

> /space/rguenther/install/gcc-4.7.0/bin/gcc t.c -Wall -Wextra -o t -O1
t.c:4:11: error: expected ':', ',', ';', '}' or '__attribute__' before '='
token
t.c: In function 'main':
t.c:15:11: error: invalid initializer
t.c:16:11: error: invalid initializer
t.c:17:11: error: invalid initializer
t.c:19:6: error: 'union u' has no member named 'i'
t.c:22:6: error: 'union u' has no member named 'b'
t.c:24:11: error: 'union u' has no member named 'b'
t.c:26:14: error: 'union u' has no member named 'b'
t.c:27:1: warning: control reaches end of non-void function [-Wreturn-type]

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[brendan.jones.it at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #3 from brendan.jones.it at gmail dot com 2012-06-14 09:00:37 UTC ---
Sorry - wrong file

/* -*- Mode: C ; c-basic-offset: 4 -*- */
/* gcc test.c -Wall -Wextra -o test -O1 && ./test ; echo $?
   should print 0, prints 10
   gcc known to be affected:

Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --disable-build-with-cxx
--disable-build-poststage1-with-cxx --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-ppl --with-cloog --with-tune=generic --with-arch_32=i686
--build=x86_64-redhat-linux
Thread model: posix
gcc version 4.7.0 20120507 (Red Hat 4.7.0-5) (GCC) 
*/

union u
{
    int i;
    _Bool b;
};

void f(union u * vp, union u v)
{
    *vp = v;
}

int main()
{
    union u v;
    union u v1;
    union u v2;

    v.i = 10;
    f(&v1, v);

    v.b = 0;
    f(&v2, v);
    return v2.b;
}

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[brendan.jones.it at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #4 from brendan.jones.it at gmail dot com 2012-06-24 07:56:59 UTC ---
Hi,

have you been able to replicate this issue with the second example I have sent?

If so is there a known workaround that we can use?

many thanks

Brendan

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[fdziarmagowski at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

Frzderzk Dziarmagowski <fdziarmagowski at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fdziarmagowski at gmail dot
                   |                            |com

--- Comment #5 from Frzderzk Dziarmagowski <fdziarmagowski at gmail dot com> 2012-09-23 10:01:02 UTC ---
The bug is WAITING for 3 months already. Could it be possible to verify it? The
problem is affecting wide range of jack-audio users.

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

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> 2012-09-23 11:56:50 UTC ---
I can reproduce the wrong-code with gcc 4.7-20120922 and 4.8-20120916, at -O1,
on x86_64-linux. -O2 avoids the wrong-code, but if I replace the "*vp = v" with
the equivalent __builtin_memcpy() then -O2 also generates wrong code. gcc-4.6
seems to work correctly.

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #7 from Mikael Pettersson <mikpe at it dot uu.se> 2012-09-23 17:14:30 UTC ---
The regression started with Richard G's fix for PR38885 in r179556:
http://gcc.gnu.org/ml/gcc-cvs/2011-10/msg00150.html
http://gcc.gnu.org/ml/gcc-patches/2011-10/msg00326.html

It may be yet another SRA problem.

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #8 from Mikael Pettersson <mikpe at it dot uu.se> 2012-09-23 18:44:53 UTC ---
(In reply to comment #7)
> It may be yet another SRA problem.

Perhaps not, -fno-tree-sra makes no difference.  Looking through the tree dumps
I see the wrong code first appearing in the .fre1 dump.  Compiling with -O1
-fno-tree-fre does avoid the wrong code.

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[fdziarmagowski at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #9 from Frzderzk Dziarmagowski <fdziarmagowski at gmail dot com> 2012-09-23 19:52:29 UTC ---
Confirmed, jackd compiled with -O1 -fno-tree-fre works as expected

[Bug tree-optimization/53663] 4.7 inconsistent inline handling of bool within union

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #10 from Mikael Pettersson <mikpe at it dot uu.se> 2012-09-23 22:12:07 UTC ---
Although -fno-tree-fre works for the test case in #c3, adjusting it to use
__builtin_memcpy() for the assignment in f() results in wrong code even with
-fno-tree-fre.

The bug seems _Bool-specific. Replacing the _Bool with unsigned char b:1 gives
working code regardless of compiler options.

[Bug tree-optimization/53663] [4.7/4.8 Regression] inconsistent inline handling of bool within union

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW
                 CC|                            |jakub at gcc dot gnu.org
            Version|unknown                     |4.7.2
   Target Milestone|---                         |4.7.3
            Summary|4.7 inconsistent inline     |[4.7/4.8 Regression]
                   |handling of bool within     |inconsistent inline
                   |union                       |handling of bool within
                   |                            |union

[Bug tree-optimization/53663] [4.7/4.8 Regression] inconsistent inline handling of bool within union

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #11 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-24 09:08:17 UTC ---
Mine.

[Bug tree-optimization/53663] [4.7/4.8 Regression] inconsistent inline handling of bool within union

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-09-24 09:14:31 UTC ---
Guess for BOOLEAN_TYPE in unions we can't look just at the single bit, but also
all other bits of the boolean type, because we rely that the bool doesn't
contain other values than false/true.

[Bug tree-optimization/53663] [4.7/4.8 Regression] inconsistent inline handling of bool within union

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #13 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-24 11:44:32 UTC ---
This boils down to the question whether reading a 1-bit precision quantity
from memory has to disregard the upper bits or not (I think we had similar
issues with SRA).  Thus, whether reading a _Bool from memory is a
bitfield extract or not (expansion does not treat it as bitfield extract
because the FIELD_DECLs size is 8, not 1).

We go into

  /* 3) Assignment from a constant.  We can use folds native encode/interpret
     routines to extract the assigned bits.  */

which has the issue that it doesn't work if TYPE_PRECISION is not equal
to TYPE_SIZE.  At least not for detecting redundant stores (it does work
for folding a read of v.b though).

I have a patch.

[Bug tree-optimization/53663] [4.7/4.8 Regression] inconsistent inline handling of bool within union

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #14 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-24 13:14:00 UTC ---
We still want to possibly optimize

extern void abort (void);

union u
{
  int i;
  _Bool b;
};

void f(union u * vp, union u v)
{
  *vp = v;
}

int main()
{
  union u v;
  union u v1;
  union u v2;

  v.i = 0;
  f(&v1, v);

  v.b = 0;
  f(&v2, v);
  if (v2.b != 0)
    abort ();
  return 0;
}

though we might be able to trigger TBAA issues when removing a store
that would merely change the effective type (without changing the
underlying value).  Of course we try hard (on the tree level) to
make DWIM code work, but still ... thus,

 <float> = 1.;
 <int> = 0;
 <float> = 0.;
 ... = <float>;

if we remove the store <float> = 0. as redundant (it stores a value
already there) then further optimizations might re-order the float
and the int store.  We don't perform redundant store elimination here
because 0. and 0 are not operand_equal_p though - but it works for shorts.

extern void abort (void);

union u
{
  int i;
  short f;
} v;

short foo (short *f)
{
  *f = 1;
  v.i = 0;
  v.f = 0;
  return *f;
}

int main()
{
  if (foo (&v.f) != 0)
    abort ();
  return 0;
}

(still doesn't break though).

[Bug tree-optimization/53663] [4.7/4.8 Regression] inconsistent inline handling of bool within union

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #15 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-25 07:52:01 UTC ---
Author: rguenth
Date: Tue Sep 25 07:51:51 2012
New Revision: 191694

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191694
Log:
2012-09-25  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/53663
    * tree-ssa-sccvn.c (vn_reference_lookup_3): Conditional
    native encode/interpret translation on VN_WALKREWRITE.

    * gcc.dg/torture/pr53663-1.c: New testcase.
    * gcc.dg/torture/pr53663-2.c: Likewise.
    * gcc.dg/torture/pr53663-3.c: Likewise.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr53663-1.c
    trunk/gcc/testsuite/gcc.dg/torture/pr53663-2.c
    trunk/gcc/testsuite/gcc.dg/torture/pr53663-3.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-sccvn.c

[Bug tree-optimization/53663] [4.7 Regression] inconsistent inline handling of bool within union

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.8.0
            Summary|[4.7/4.8 Regression]        |[4.7 Regression]
                   |inconsistent inline         |inconsistent inline
                   |handling of bool within     |handling of bool within
                   |union                       |union
      Known to fail|                            |4.7.2

--- Comment #16 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-25 07:55:30 UTC ---
Fixed on trunk sofar.

[Bug tree-optimization/53663] [4.7 Regression] inconsistent inline handling of bool within union

[fdziarmagowski at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #17 from Fryderyk Dziarmagowski <fdziarmagowski at gmail dot com> 2012-09-25 08:31:25 UTC ---
With above fix 4.7.2 works as expected too.

[Bug tree-optimization/53663] [4.7 Regression] inconsistent inline handling of bool within union

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
           Priority|P3                          |P2

[Bug tree-optimization/53663] [4.7 Regression] inconsistent inline handling of bool within union

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

--- Comment #18 from Richard Biener <rguenth at gcc dot gnu.org> 2012-12-03 16:53:39 UTC ---
Author: rguenth
Date: Mon Dec  3 16:53:25 2012
New Revision: 194101

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=194101
Log:
2012-12-03  Richard Biener  <rguenther@suse.de>

    Backport from mainline
    2012-09-24  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/53663
    * tree-ssa-sccvn.c (vn_reference_lookup_3): Conditional
    native encode/interpret translation on VN_WALKREWRITE.

    * gcc.dg/torture/pr53663-1.c: New testcase.
    * gcc.dg/torture/pr53663-2.c: Likewise.
    * gcc.dg/torture/pr53663-3.c: Likewise.

Added:
    branches/gcc-4_7-branch/gcc/testsuite/gcc.dg/torture/pr53663-1.c
    branches/gcc-4_7-branch/gcc/testsuite/gcc.dg/torture/pr53663-2.c
    branches/gcc-4_7-branch/gcc/testsuite/gcc.dg/torture/pr53663-3.c
Modified:
    branches/gcc-4_7-branch/gcc/ChangeLog
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_7-branch/gcc/tree-ssa-sccvn.c

[Bug tree-optimization/53663] [4.7 Regression] inconsistent inline handling of bool within union

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53663

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #19 from Richard Biener <rguenth at gcc dot gnu.org> 2012-12-03 16:54:13 UTC ---
Fixed.