[Bug fortran/56490] New: [4.6/4.7 Regression] -Wall triggering infinite loop

[Bug fortran/56490] New: [4.6/4.7 Regression] -Wall triggering infinite loop

[o.flebbe@science-computing.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

             Bug #: 56490
           Summary: [4.6/4.7 Regression] -Wall triggering infinite loop
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: o.flebbe@science-computing.de


Created attachment 29559
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29559
Testcase: Loops forever with -O2 -Wall

Compiling testcase, gfortran seems to loop forever.

gfortran -c -O -Wall testcase.f 

leaving out -Wall seems to compile o.k.


Have to problem on several independent gcc distros: This one for instance:

COLLECT_GCC=/usr/local/gcc-4.6.3/bin/gcc
COLLECT_LTO_WRAPPER=/usr/local/gcc-4.6.3/libexec/gcc/x86_64-unknown-linux-gnu/4.6.3/lto-wrapper
Ziel: x86_64-unknown-linux-gnu
Konfiguriert mit: /soft/os/gcc/gcc-4.6.3/gcc-4.6.3/configure
--srcdir=/soft/os/gcc/gcc-4.6.3/gcc-4.6.3 --prefix=/usr/local/gcc-4.6.3
--with-included-gettext --enable-__cxa_atexit --enable-threads --enable-shared
--enable-languages=c,c++,fortran --enable-libgcj --enable-ssp --disable-libssp
--with-gmp-include=/usr/local/devel/gmp/5.0.1-static/include
--with-gmp-lib=/usr/local/devel/gmp/5.0.1-static/lib64
--with-mpfr-include=/usr/local/devel/mpfr/2.4.2-static/include
--with-mpfr-lib=/usr/local/devel/mpfr/2.4.2-static/lib64
--with-mpc-include=/usr/local/devel/mpc/0.8.1-static/include
--with-mpc-lib=/usr/local/devel/mpc/0.8.1-static/lib64
Thread-Modell: posix
gcc-Version 4.6.3 (GCC)

[Bug middle-end/56490] [4.6/4.7/4.8 Regression] -Wall triggering infinite loop

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |compile-time-hog,
                   |                            |diagnostic
   Last reconfirmed|                            |2013-03-01
          Component|fortran                     |middle-end
                 CC|                            |davidxl at google dot com
     Ever Confirmed|0                           |1
            Summary|[4.6/4.7 Regression] -Wall  |[4.6/4.7/4.8 Regression]
                   |triggering infinite loop    |-Wall triggering infinite
                   |                            |loop
   Target Milestone|---                         |4.6.4

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-01 12:09:40 UTC ---
Confirmed.

#0  0x0000000000d43262 in find_pdom (block=0x7ffff6b43340)
    at /space/rguenther/src/svn/trunk/gcc/tree-ssa-uninit.c:170
#1  0x0000000000d4358a in compute_control_dep_chain (bb=0x7ffff6d32ea0, 
    dep_bb=0x7ffff6b4b820, cd_chains=0x1d67f20, num_chains=0x7fffffffd870, 
    cur_cd_chain=0x7fffffffd860)
    at /space/rguenther/src/svn/trunk/gcc/tree-ssa-uninit.c:300
#2  0x0000000000d43574 in compute_control_dep_chain (bb=0x7ffff6b439c0, 
    dep_bb=0x7ffff6b4b820, cd_chains=0x1d67f20, num_chains=0x7fffffffd870, 
    cur_cd_chain=0x7fffffffd860)
    at /space/rguenther/src/svn/trunk/gcc/tree-ssa-uninit.c:293
#3  0x0000000000d43574 in compute_control_dep_chain (bb=0x7ffff6d32c98, 
    dep_bb=0x7ffff6b4b820, cd_chains=0x1d67f20, num_chains=0x7fffffffd870, 
    cur_cd_chain=0x7fffffffd860)
    at /space/rguenther/src/svn/trunk/gcc/tree-ssa-uninit.c:293
#4  0x0000000000d43574 in compute_control_dep_chain (bb=0x7ffff6d32a28, 
    dep_bb=0x7ffff6b4b820, cd_chains=0x1d67f20, num_chains=0x7fffffffd870, 
    cur_cd_chain=0x7fffffffd860)
    at /space/rguenther/src/svn/trunk/gcc/tree-ssa-uninit.c:293
#5  0x0000000000d43574 in compute_control_dep_chain (bb=0x7ffff6d329c0, 
    dep_bb=0x7ffff6b4b820, cd_chains=0x1d67f20, num_chains=0x7fffffffd870, 
    cur_cd_chain=0x7fffffffd860)
    at /space/rguenther/src/svn/trunk/gcc/tree-ssa-uninit.c:293

Uninit diagnostic not being properly limited and appearantly not being
linear in complexity.

[Bug middle-end/56490] [4.6/4.7/4.8 Regression] -Wall triggering infinite loop

[xinliangli at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

davidxl <xinliangli at gmail dot com> changed:

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

--- Comment #2 from davidxl <xinliangli at gmail dot com> 2013-03-01 22:45:48 UTC ---
The function has a control flow that post-dom chain is as long as 103. Limiting
the max post-dom walk length solve the problem.

[Bug tree-optimization/56490] [4.6/4.7 Regression] -Wall triggering infinite loop

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
          Component|middle-end                  |tree-optimization
      Known to work|                            |4.8.0
             Blocks|                            |47344
            Summary|[4.6/4.7/4.8 Regression]    |[4.6/4.7 Regression] -Wall
                   |-Wall triggering infinite   |triggering infinite loop
                   |loop                        |

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-08 15:51:44 UTC ---
"Fixed" on trunk by

2013-03-01  Xinliang David Li  <davidxl@google.com>

        * tree-ssa-uninit.c (compute_control_dep_chain): Limit post-dom
        walk length.

after the patch:

 uninit var analysis     :   1.05 (84%) usr

so it's still very expensive.

[Bug tree-optimization/56490] [4.6/4.7/4.8 Regression] -Wall triggering infinite loop

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|4.8.0                       |
            Summary|[4.6/4.7 Regression] -Wall  |[4.6/4.7/4.8 Regression]
                   |triggering infinite loop    |-Wall triggering infinite
                   |                            |loop
      Known to fail|                            |4.8.0

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-08 16:03:30 UTC ---
Clearly the limiting is bougs ... the issue is with large fanout BBs
we recurse in compute_control_dep_chain which leads to exponential
complexity.  Limiting that to 8^5 isn't really a fix ... (yes, you
can call that O(1)).

compute_control_dep_chain is called 65 million times(!) for the testcase
after the patch.

There has to be a better algorithmic way of implementing this.

IMHO still not fixed in 4.8.

[Bug tree-optimization/56490] [4.6/4.7/4.8 Regression] -Wall triggering infinite loop

[xinliangli at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

--- Comment #5 from davidxl <xinliangli at gmail dot com> 2013-03-08 16:21:13 UTC ---
(In reply to comment #4)
> Clearly the limiting is bougs ... the issue is with large fanout BBs
> we recurse in compute_control_dep_chain which leads to exponential
> complexity.  Limiting that to 8^5 isn't really a fix ... (yes, you
> can call that O(1)).
> 
> compute_control_dep_chain is called 65 million times(!) for the testcase
> after the patch.
> 
> There has to be a better algorithmic way of implementing this.
> 
> IMHO still not fixed in 4.8.

Right. 

However for on demand computation like this,  limiting is still needed. For
this particular case, limiting the depth to 3 (or may be smaller) won't cause
any regressions.

[Bug tree-optimization/56490] [4.7/4.8/4.9 Regression] -Wall triggering infinite loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.6.4                       |4.7.4

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-04-12 15:15:57 UTC ---
GCC 4.6.4 has been released and the branch has been closed.

[Bug tree-optimization/56490] [4.7/4.8/4.9 Regression] -Wall triggering infinite loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

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

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

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
>From what I can see, the main problem is that on this testcase (and apparently
also on gcc/ada/par.adb) in a single toplevel compute_control_dep_chain call
(i.e. one with cur_chain_len == 0) we can end up with millions of nested
compute_control_dep_chain, and at least on the testcase from this PR all
unsuccessful (num_chains == 0 after the call).

The quick fix can be just to have a counter and return immediate once we reach
the counter (say 1000) during the nested invocations.

For something better, perhaps in addition to such limiting we could watch for
basic blocks on which we've already called compute_control_dep_chain, and if
that call has been unsuccesful previously, record the cur_chain_len at which it
has been called.  If we call it on such a bb again at the same or higher
cur_chain_len level, we could assume it is likely going to fail again.
The reason why I'm saying likely is that there is the:

  for (i = 0; i < cur_chain_len; i++)
    {
      edge e = (*cur_cd_chain)[i];
      /* Cycle detected. */
      if (e->src == bb)
        return false;
    }
loop and with different start of the cur_cd_chain perhaps it could succeed even
when it failed before.

[Bug tree-optimization/56490] [4.7/4.8/4.9 Regression] -Wall triggering infinite loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 32184
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32184&action=edit
gcc49-pr56490.patch

Untested fix (cleanups plus the limiting param).

[Bug tree-optimization/56490] [4.7/4.8/4.9 Regression] -Wall triggering infinite loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Fri Feb 21 09:53:56 2014
New Revision: 207988

URL: http://gcc.gnu.org/viewcvs?rev=207988&root=gcc&view=rev
Log:
    PR tree-optimization/56490
    * params.def (PARAM_UNINIT_CONTROL_DEP_ATTEMPTS): New param.
    * tree-ssa-uninit.c: Include params.h.
    (compute_control_dep_chain): Add num_calls argument, return false
    if it exceed PARAM_UNINIT_CONTROL_DEP_ATTEMPTS param, pass
    num_calls to recursive call.
    (find_predicates): Change dep_chain into normal array,
    cur_chain into auto_vec<edge, MAX_CHAIN_LEN + 1>, add num_calls
    variable and adjust compute_control_dep_chain caller.
    (find_def_preds): Likewise.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/params.def
    trunk/gcc/tree-ssa-uninit.c

[Bug tree-optimization/56490] [4.7/4.8 Regression] -Wall triggering infinite loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.9.0
            Summary|[4.7/4.8/4.9 Regression]    |[4.7/4.8 Regression] -Wall
                   |-Wall triggering infinite   |triggering infinite loop
                   |loop                        |

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Hopefully fixed/worked around on the trunk.

[Bug tree-optimization/56490] [4.7/4.8 Regression] -Wall triggering infinite loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Thu Mar  6 08:12:02 2014
New Revision: 208372

URL: http://gcc.gnu.org/viewcvs?rev=208372&root=gcc&view=rev
Log:
    * Makefile.in (tree-ssa-uninit.o): Depend on $(PARAMS_H).

    Backport from mainline
    2014-02-21  Jakub Jelinek  <jakub@redhat.com>

    PR tree-optimization/56490
    * params.def (PARAM_UNINIT_CONTROL_DEP_ATTEMPTS): New param.
    * tree-ssa-uninit.c: Include params.h.
    (compute_control_dep_chain): Add num_calls argument, return false
    if it exceed PARAM_UNINIT_CONTROL_DEP_ATTEMPTS param, pass
    num_calls to recursive call.
    (find_predicates): Change dep_chain into normal array, add num_calls
    variable and adjust compute_control_dep_chain caller.
    (find_def_preds): Likewise.

Modified:
    branches/gcc-4_8-branch/gcc/ChangeLog
    branches/gcc-4_8-branch/gcc/Makefile.in
    branches/gcc-4_8-branch/gcc/params.def
    branches/gcc-4_8-branch/gcc/tree-ssa-uninit.c

[Bug tree-optimization/56490] [4.7 Regression] -Wall triggering infinite loop

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56490

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|4.7.4                       |4.8.3
      Known to fail|                            |4.7.4

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed in 4.8.3.