[Bug bootstrap/38591] New: erratic comparison failures on very fast machines

[Bug bootstrap/38591] New: erratic comparison failures on very fast machines

[ebotcazou at gcc dot gnu dot org]

Since we started building the 4.3.x compiler on very fast Linux machines (bi-
quad cores) we have observed erratic but consistent comparison failures, say
a handful of times a month.  The problematic file is always the same:

Comparing stages 2 and 3
Bootstrap comparison failure!
./sparseset.o differs
make[2]: *** [compare] Error 1

The stage 3 object file is not compiled as it should be; in fact, it can be
obtained manually by changing

#define ENABLE_ASSERT_CHECKING 1

to

/* #undef ENABLE_ASSERT_CHECKING */

in gcc/auto-host.h.

so there might be a race condition somewhere in the top-level bootstrap (note
that we have never built 4.2.x on the same machines).


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           Summary: erratic comparison failures on very fast machines
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: bootstrap
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ebotcazou at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[hjl dot tools at gmail dot com]

------- Comment #1 from hjl dot tools at gmail dot com  2008-12-21 15:20 -------
What are the differences? While working on a patch, I had an
uninitialized stack variable, which caused random comparison
failures.


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hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl dot tools at gmail dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[ebotcazou at gcc dot gnu dot org]

------- Comment #2 from ebotcazou at gcc dot gnu dot org  2008-12-21 16:07 -------
> What are the differences?

This is explained in the message.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[hjl dot tools at gmail dot com]

------- Comment #3 from hjl dot tools at gmail dot com  2008-12-21 16:18 -------
auto-host.h must exist when those files were compiled. I guess
it was generated more than once.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[ebotcazou at gcc dot gnu dot org]

------- Comment #4 from ebotcazou at gcc dot gnu dot org  2008-12-21 17:12 -------
> auto-host.h must exist when those files were compiled. I guess
> it was generated more than once.

My understanding is that it is re-generated at each stage:

auto-host.h: cstamp-h ; @true
cstamp-h: config.in config.status
        CONFIG_HEADERS=auto-host.h:config.in \
        CONFIG_FILES= \
        LANGUAGES="$(CONFIG_LANGUAGES)" $(SHELL) config.status


In case this can make a difference, the compiler is configured as follows:
--enable-languages=c,ada,c++ --disable-libada --enable-checking=release


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[hjl dot tools at gmail dot com]

------- Comment #5 from hjl dot tools at gmail dot com  2008-12-21 17:21 -------
Each stage has its own directory and auto-host.h should be
regenerated in each directory. I think it was regenerated
more than once in the same directory.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2008-12-29 22:25 -------
We also see this from time to time.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[ebotcazou at gcc dot gnu dot org]

------- Comment #7 from ebotcazou at gcc dot gnu dot org  2009-09-06 21:18 -------
In comment #6.


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ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-09-06 21:18:42
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[rwild at gcc dot gnu dot org]

------- Comment #8 from rwild at gcc dot gnu dot org  2009-09-17 16:27 -------
Does this also happen on trunk, or with branch-4_3 only?  AFAICS 4.3.3 had
  sparseset.o: sparseset.c $(SYSTEM_H) sparseset.h

in gcc/Makefile.in, which means it was lacking $(CONFIG_H) thus lacking
dependency on auto-host.h.  This was fixed in
<http://gcc.gnu.org/ml/gcc-patches/2008-07/msg01022.html>
and glancing at that patch, there may be quite a few other dependency issues
in branch-4_3.

No idea why the borked build does not fail but pick up auto-host.h from
elsewhere or so.  Or do you know for sure that auto-host.h was picked up
from the current directory?


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rwild at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rwild at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[ebotcazou at gcc dot gnu dot org]

------- Comment #9 from ebotcazou at gcc dot gnu dot org  2009-09-17 16:58 -------
> in gcc/Makefile.in, which means it was lacking $(CONFIG_H) thus lacking
> dependency on auto-host.h.  This was fixed in
> <http://gcc.gnu.org/ml/gcc-patches/2008-07/msg01022.html>
> and glancing at that patch, there may be quite a few other dependency issues
> in branch-4_3.

Thanks, will try to add the missing dependency.

> No idea why the borked build does not fail but pick up auto-host.h from
> elsewhere or so.  Or do you know for sure that auto-host.h was picked up
> from the current directory?

Couldn't a truncated auto-host.h have been picked up?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] erratic comparison failures on very fast machines

[Ralf dot Wildenhues at gmx dot de]

------- Comment #10 from Ralf dot Wildenhues at gmx dot de  2009-09-17 17:40 -------
Subject: Re:  erratic comparison failures on very fast
 machines

* ebotcazou at gcc dot gnu dot org wrote on Thu, Sep 17, 2009 at 06:58:37PM
CEST:
> > No idea why the borked build does not fail but pick up auto-host.h from
> > elsewhere or so.  Or do you know for sure that auto-host.h was picked up
> > from the current directory?
> 
> Couldn't a truncated auto-host.h have been picked up?

config.status uses mv from a temporary subdirectory to the final
location of the file, thus create it created atomically.  Autoconf 2.59
did this too.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] [4.3 regression] erratic comparison failures on very fast machines

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] [4.3 regression] erratic comparison failures on very fast machines

[rguenth at gcc dot gnu dot org]

------- Comment #11 from rguenth at gcc dot gnu dot org  2010-05-14 12:51 -------
Fixed (hopefully).


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rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591

[Bug bootstrap/38591] [4.3 regression] erratic comparison failures on very fast machines

[rguenth at gcc dot gnu dot org]

------- Comment #12 from rguenth at gcc dot gnu dot org  2010-05-14 12:51 -------
Subject: Bug 38591

Author: rguenth
Date: Fri May 14 12:51:31 2010
New Revision: 159392

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=159392
Log:
2010-05-15  Richard Guenther  <rguenther@suse.de>

        PR bootstrap/38591
        * Makefile.in (graph.o): Add missing $(CONFIG_H) dependency.
        (sparseset.o): Likewise.

Modified:
    branches/gcc-4_3-branch/gcc/ChangeLog
    branches/gcc-4_3-branch/gcc/Makefile.in


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38591