[Bug c/45852] New: volatile structs are broken!

[Bug c/45852] New: volatile structs are broken!

[regehr at cs dot utah.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

           Summary: volatile structs are broken!
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: regehr@cs.utah.edu
                CC: chenyang@cs.utah.edu


gcc should not be optimizing away the read from or write to this struct.

regehr@john-home:~$ current-gcc -v
Using built-in specs.
COLLECT_GCC=current-gcc
COLLECT_LTO_WRAPPER=/home/regehr/z/compiler-install/gcc-r164818-install/libexec/gcc/i686-pc-linux-gnu/4.6.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ../configure --with-libelf=/usr/local --enable-lto
--prefix=/home/regehr/z/compiler-install/gcc-r164818-install
--program-prefix=r164818- --enable-languages=c,c++
Thread model: posix
gcc version 4.6.0 20100930 (experimental) (GCC) 

regehr@john-home:~$ current-gcc -S -o - -O1 small.c 

        .file   "small.c"
        .text
        .globl  func_1
        .type   func_1, @function
func_1:
.LFB0:
        .cfi_startproc
        rep
        ret
        .cfi_endproc
.LFE0:
        .size   func_1, .-func_1
        .globl  g_18
        .data
        .align 4
        .type   g_18, @object
        .size   g_18, 4
g_18:
        .long   -6
        .ident  "GCC: (GNU) 4.6.0 20100930 (experimental)"
        .section        .note.GNU-stack,"",@progbits

regehr@john-home:~$ cat small.c

struct S1
{
  int f0;
};

volatile struct S1 g_18 = { -6 };

void
func_1 (void)
{
  g_18 = g_18;
}

[Bug c/45852] volatile structs are broken!

[regehr at cs dot utah.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

--- Comment #1 from John Regehr <regehr at cs dot utah.edu> 2010-10-01 03:40:43 UTC ---
This problem has been there for some time: none of 3.0.0, 3.1.0, 3.2.0, 3.3.0,
3.4.0, 4.0.0, 4.1.0, 4.2.0, 4.3.0, 4.4.0, or 4.5.0 for x86 generates the right
code.

[Bug rtl-optimization/45852] volatile structs are broken!

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2010.10.01 10:27:24
          Component|c                           |rtl-optimization
     Ever Confirmed|0                           |1

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-10-01 10:27:24 UTC ---
The expander throws away the assignment.

[Bug middle-end/45852] volatile structs are broken!

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

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

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

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2010-12-14 13:43:42 UTC ---
Created attachment 22753
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22753
gcc46-pr45852.patch

Untested fix.  Alternatively if alt_rtl (or target?) has side-effects, we could
ignore it in store_expr.

[Bug middle-end/45852] volatile structs are broken!

[amonakov at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

Alexander Monakov <amonakov at gcc dot gnu.org> changed:

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

--- Comment #4 from Alexander Monakov <amonakov at gcc dot gnu.org> 2010-12-14 14:54:38 UTC ---
There's a couple of related bugs:

Optimizes away access to volatile field (unconfirmed):
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46762

Does not use volatile MEMs for assignments of structs with volatile fields:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45472

[Bug middle-end/45852] volatile structs are broken!

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2010-12-21 08:35:19 UTC ---
Author: jakub
Date: Tue Dec 21 08:35:16 2010
New Revision: 168105

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=168105
Log:
    PR middle-end/45852
    * expr.c (store_expr): Ignore alt_rtl if equal to target,
    but has side-effects.

    * gcc.target/i386/pr45852.c: New test.

Added:
    trunk/gcc/testsuite/gcc.target/i386/pr45852.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/expr.c
    trunk/gcc/testsuite/ChangeLog

[Bug middle-end/45852] volatile structs are broken!

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-01-16 20:23:04 UTC ---
Author: jakub
Date: Sun Jan 16 20:23:01 2011
New Revision: 168867

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=168867
Log:
    Backport from mainline
    2010-12-21  Jakub Jelinek  <jakub@redhat.com>

    PR middle-end/45852
    * expr.c (store_expr): Ignore alt_rtl if equal to target,
    but has side-effects.

    * gcc.target/i386/pr45852.c: New test.

Added:
    branches/gcc-4_5-branch/gcc/testsuite/gcc.target/i386/pr45852.c
Modified:
    branches/gcc-4_5-branch/gcc/ChangeLog
    branches/gcc-4_5-branch/gcc/expr.c
    branches/gcc-4_5-branch/gcc/testsuite/ChangeLog

[Bug middle-end/45852] volatile structs are broken!

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-01-16 22:56:13 UTC ---
Author: jakub
Date: Sun Jan 16 22:56:10 2011
New Revision: 168879

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=168879
Log:
    Backport from mainline
    2010-12-21  Jakub Jelinek  <jakub@redhat.com>

    PR middle-end/45852
    * expr.c (store_expr): Ignore alt_rtl if equal to target,
    but has side-effects.

    * gcc.target/i386/pr45852.c: New test.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/gcc.target/i386/pr45852.c
Modified:
    branches/gcc-4_4-branch/gcc/ChangeLog
    branches/gcc-4_4-branch/gcc/expr.c
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog

[Bug middle-end/45852] volatile structs are broken!

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

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

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

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-01-17 08:01:41 UTC ---
Fixed for 4.4+.