[Bug c++/48822] New: G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[Bug c++/48822] New: G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[qball at sarine dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

           Summary: G++ gets stucks and never finishes compilation when
                    enabling -O2/3 optimization options.
           Product: gcc
           Version: 4.5.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: qball@sarine.nl


Trying to compile the example below with g++ -O3 or -O2 it gets stuck in an
endless loop.

Error seems to occur in optimizing the (a == CFraction(0,0));
It only occurs when it is CFraction(0,0).  It seems to break in the '=='
implementation  on the lowestTerm() (line 69) on the CFraction(0,0);


running on a 64bit machine. (ubuntu natty)

gcc -v:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.5.2-8ubuntu4' --with-bugurl=file:///usr/share/doc/gcc-4.5/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.5 --enable-shared --enable-multiarch
--with-multiarch-defaults=x86_64-linux-gnu --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib/x86_64-linux-gnu
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.5 --libdir=/usr/lib/x86_64-linux-gnu
--enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-plugin --enable-gold --enable-ld=default
--with-plugin-ld=ld.gold --enable-objc-gc --disable-werror --with-arch-32=i686
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4) 

(4.4.5 works fine)

[Bug c++/48822] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[qball at sarine dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

--- Comment #1 from qball at sarine dot nl 2011-04-29 13:44:26 UTC ---
Created attachment 24146
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24146
Test case triggering the bug.

[Bug c++/48822] [4.5 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.04.29 13:58:16
      Known to work|                            |4.4.5, 4.6.0
   Target Milestone|---                         |4.5.4
            Summary|G++ gets stucks and never   |[4.5 Regression] G++ gets
                   |finishes compilation when   |stucks and never finishes
                   |enabling -O2/3 optimization |compilation when enabling
                   |options.                    |-O2/3 optimization options.
     Ever Confirmed|0                           |1
      Known to fail|                            |4.5.3

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-04-29 13:58:16 UTC ---
Confirmed.  It's stuck in SCCVN/FRE visiting

g_37 = PHI <g_36(12), g_38(13)>
g_38 = PHI <g_35(12), g_39(13)>
g_39 = g_37 % g_38;

Value numbering g_37 stmt = g_37 = PHI <g_36(12), g_38(13)>
Setting value number of g_37 to g_37 (changed)
Value numbering g_38 stmt = g_38 = PHI <g_35(12), g_39(13)>
Setting value number of g_38 to 0 (changed)
Value numbering g_39 stmt = g_39 = g_37 % g_38;
Setting value number of g_39 to g_39 (changed)
Value numbering g_37 stmt = g_37 = PHI <g_36(12), g_38(13)>
Setting value number of g_37 to 0 (changed)
Value numbering g_38 stmt = g_38 = PHI <g_35(12), g_39(13)>
Setting value number of g_38 to g_38 (changed)
Value numbering g_39 stmt = g_39 = g_37 % g_38;
RHS g_37 % g_38 simplified to 0 has constants 1
Setting value number of g_39 to 0 (changed)

thus it oscillates.

Maybe latent everywhere else.

Workaround: -fno-tree-fre -fno-tree-pre

[Bug c++/48822] [4.5 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[qball at sarine dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

--- Comment #3 from qball at sarine dot nl 2011-04-29 14:04:48 UTC ---
Doing -O1  -finline-small-functions breaks it aswell.

Indeed adding -fno-tree-fre fixes compilation.

Thanks.

[Bug tree-optimization/48822] [4.5/4.6/4.7 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
          Component|c++                         |tree-optimization
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |
            Summary|[4.5 Regression] G++ gets   |[4.5/4.6/4.7 Regression]
                   |stucks and never finishes   |G++ gets stucks and never
                   |compilation when enabling   |finishes compilation when
                   |-O2/3 optimization options. |enabling -O2/3 optimization
                   |                            |options.

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-04-29 14:06:24 UTC ---
  D.23284.num = 0;
  D.23284.den = 0;
...
<bb 11>:
  D.23599_34 = D.23284.den;
  if (D.23599_34 == 0)
    goto <bb 21> (<L10>);
  else
    goto <bb 12>;

<bb 12>:
  g_35 = D.23284.den;
  g_36 = D.23284.num;
  goto <bb 14>;

<bb 13>:
  g_39 = g_37 % g_38;

<bb 14>:
  # g_37 = PHI <g_36(12), g_38(13)>
  # g_38 = PHI <g_35(12), g_39(13)>
  if (g_38 != 0)
    goto <bb 13>;

and D.23599_34, g_35 and g_36 are correctly value-numbered to zero.  We then
start

Value numbering g_37 stmt = g_37 = PHI <g_36(12), g_38(13)>
Setting value number of g_37 to 0 (changed)
Value numbering g_38 stmt = g_38 = PHI <g_35(12), g_39(13)>
Setting value number of g_38 to 0 (changed)
Value numbering g_39 stmt = g_39 = g_37 % g_38;
Setting value number of g_39 to g_39 (changed)

g_39 has undefined result, thus

Value numbering g_37 stmt = g_37 = PHI <g_36(12), g_38(13)>
Setting value number of g_37 to 0
Value numbering g_38 stmt = g_38 = PHI <g_35(12), g_39(13)>
Setting value number of g_38 to g_38 (changed)
Value numbering g_39 stmt = g_39 = g_37 % g_38;
RHS g_37 % g_38 simplified to 0 has constants 1

where here is the bug that we go from VARYING to CONSTANT for g_39.

ISTR changing VN to never do that but that had lots of weird fallout.

I'm sure the issue is latent.

[Bug tree-optimization/48822] [4.5/4.6/4.7 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|4.6.0                       |
      Known to fail|                            |4.6.0, 4.7.0

--- Comment #5 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-02 11:39:58 UTC ---
Testcase that breaks since 4.5:

void foo (int *, int *);
int bar ()
{
  int a = 0;
  int b = 0;
  if (b != 0)
    {
      int ax = a;
      int bx = b;
      while (bx != 0)
        {
          int tem = ax % bx;
          ax = bx;
          bx = tem;
        }
    }
  foo (&a, &b);
}

4.4 has different PHI ordering and does

Value numbering bx_2 stmt = bx_2 = PHI <bx_5(3), tem_6(4)>
Setting value number of bx_2 to 0 (changed)
Value numbering ax_1 stmt = ax_1 = PHI <ax_4(3), bx_2(4)>
Setting value number of ax_1 to 0 (changed)
Value numbering tem_6 stmt = tem_6 = ax_1 % bx_2;
Setting value number of tem_6 to tem_6 (changed)
Value numbering bx_2 stmt = bx_2 = PHI <bx_5(3), tem_6(4)>
Setting value number of bx_2 to bx_2 (changed)
Value numbering ax_1 stmt = ax_1 = PHI <ax_4(3), bx_2(4)>
Setting value number of ax_1 to ax_1 (changed)

to avoid the issue.

[Bug tree-optimization/48822] [4.5/4.6 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.7.0
            Summary|[4.5/4.6/4.7 Regression]    |[4.5/4.6 Regression] G++
                   |G++ gets stucks and never   |gets stucks and never
                   |finishes compilation when   |finishes compilation when
                   |enabling -O2/3 optimization |enabling -O2/3 optimization
                   |options.                    |options.
      Known to fail|4.7.0                       |

--- Comment #7 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-02 13:11:53 UTC ---
Fixed on trunk sofar.

[Bug tree-optimization/48822] [4.5/4.6/4.7 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

--- Comment #6 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-02 13:11:30 UTC ---
Author: rguenth
Date: Mon May  2 13:11:27 2011
New Revision: 173250

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173250
Log:
2011-05-02  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/48822
    * tree-ssa-sccvn.c (set_ssa_val_to): Never go up the lattice.
    (process_scc): Indicate which iteration we start.

    * gcc.dg/torture/pr48822.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr48822.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-sccvn.c

[Bug tree-optimization/48822] [4.5 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.6.1
            Summary|[4.5/4.6 Regression] G++    |[4.5 Regression] G++ gets
                   |gets stucks and never       |stucks and never finishes
                   |finishes compilation when   |compilation when enabling
                   |enabling -O2/3 optimization |-O2/3 optimization options.
                   |options.                    |

--- Comment #9 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-12 14:08:22 UTC ---
.

[Bug tree-optimization/48822] [4.5/4.6 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

--- Comment #8 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-12 14:08:05 UTC ---
Author: rguenth
Date: Thu May 12 14:08:00 2011
New Revision: 173705

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173705
Log:
2011-05-12  Richard Guenther  <rguenther@suse.de>

        Backport from mainline
        2011-05-02  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/48822
    * tree-ssa-sccvn.c (set_ssa_val_to): Never go up the lattice.
    (process_scc): Indicate which iteration we start.

    * gcc.dg/torture/pr48822.c: New testcase.

Added:
    branches/gcc-4_6-branch/gcc/testsuite/gcc.dg/torture/pr48822.c
Modified:
    branches/gcc-4_6-branch/gcc/ChangeLog
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_6-branch/gcc/tree-ssa-sccvn.c

[Bug tree-optimization/48822] [4.5 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |arthur.j.odwyer at gmail
                   |                            |dot com

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-19 12:51:25 UTC ---
*** Bug 48921 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/48822] [4.5 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

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

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

--- Comment #12 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-07-04 14:24:31 UTC ---
Fixed.

[Bug tree-optimization/48822] [4.5 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

--- Comment #11 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-07-04 14:24:13 UTC ---
Author: rguenth
Date: Mon Jul  4 14:24:10 2011
New Revision: 175813

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=175813
Log:
2011-07-04  Richard Guenther  <rguenther@suse.de>

        Backport from mainline
        2011-05-02  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/48822
    * tree-ssa-sccvn.c (set_ssa_val_to): Never go up the lattice.

    * gcc.dg/torture/pr48822.c: New testcase.

Added:
    branches/gcc-4_5-branch/gcc/testsuite/gcc.dg/torture/pr48822.c
Modified:
    branches/gcc-4_5-branch/gcc/ChangeLog
    branches/gcc-4_5-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_5-branch/gcc/tree-ssa-sccvn.c