[Bug libstdc++/37455] New: Code bloat for ostream.widen('\n')

[Bug libstdc++/37455] New: Code bloat for ostream.widen('\n')

[M dot Froehlich at science-computing dot de]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 1284 bytes --]

Using
gcc (GCC) 4.4.0 20080909 (experimental)
with optimization level -O3 to compile the attached c++ or .ii file, I get a
huge amount of assembly code.
See the attached source, precompiled source and assembly files.

If compiled with -Os or -O2 code size is way less.

The inlined code that appears to produce that sse instruction storm appears to
originates from ctype<char>::_M_widen_init in bits/locale_facets.h around line
1169.

I am not sure if this is a compiler/optimizer/inliner problem or if libstdc++
is just unlucky implementing the iostream/locale stuff. Since g++ compiles much
better overall optimized code with 4.4 compared to oprevious versions, I hope
that this can be fixed in libstdc++. Just my 2 cent ...

Thanks!

Mathias Fröhlich


-- 
           Summary: Code bloat for ostream.widen('\n')
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: M dot Froehlich at science-computing dot de
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] Code bloat for ostream.widen('\n')

[M dot Froehlich at science-computing dot de]

------- Comment #1 from M dot Froehlich at science-computing dot de  2008-09-10 06:55 -------
Created an attachment (id=16277)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16277&action=view)
Original c++ code.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] Code bloat for ostream.widen('\n')

[M dot Froehlich at science-computing dot de]

------- Comment #2 from M dot Froehlich at science-computing dot de  2008-09-10 06:56 -------
Created an attachment (id=16278)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16278&action=view)
Preprocessed code.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] Code bloat for ostream.widen('\n')

[M dot Froehlich at science-computing dot de]

------- Comment #3 from M dot Froehlich at science-computing dot de  2008-09-10 06:56 -------
Created an attachment (id=16279)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16279&action=view)
Generated assembly file.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] Code bloat for ostream.widen('\n')

[M dot Froehlich at science-computing dot de]

------- Comment #4 from M dot Froehlich at science-computing dot de  2008-09-10 07:06 -------
Note that the code path in question is called with every

outputstream << std::endl;

Thanks


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] Code bloat for ostream.widen('\n')

[paolo dot carlini at oracle dot com]

------- Comment #5 from paolo dot carlini at oracle dot com  2008-09-10 15:23 -------
Yes, but frankly it's unlikely that in 4.4.0 timeframe, also given the ABI
constraints, we can change the libstdc++ implementation, which admittedly has
too much code inline in this area, enough to solve this problem. We are just
unlucky that 4.3.x was less aggressive at -O3, nothing changed lately (and also
less recently) on the library side...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] Code bloat for ostream.widen('\n')

[paolo dot carlini at oracle dot com]

-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |paolo dot carlini at oracle
                   |dot org                     |dot com
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-09-10 15:34:19
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] Code bloat for ostream.widen('\n')

[M dot Froehlich at science-computing dot de]

------- Comment #6 from M dot Froehlich at science-computing dot de  2008-09-10 15:38 -------
(In reply to comment #5)
> Yes, but frankly it's unlikely that in 4.4.0 timeframe, also given the ABI
> constraints, we can change the libstdc++ implementation, which admittedly has
> too much code inline in this area, enough to solve this problem. We are just
> unlucky that 4.3.x was less aggressive at -O3, nothing changed lately (and also
> less recently) on the library side...

Ok, one idea I have while reading your comment:
Gcc has that per function optimization attributes - may be an
__attribute__((optimize ('Os'))) or something similar helps for some selected
functions in this area?

Greetings

Mathias


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] Code bloat for ostream.widen('\n')

[paolo dot carlini at oracle dot com]

------- Comment #7 from paolo dot carlini at oracle dot com  2008-09-10 15:54 -------
I have a patch in testing which changes -O3 to be the same as -O2, essentially
I moved _M_narrow_init and _M_widen_init out of line. For further tweaks,
really after 4.4.0.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] Code bloat for ostream.widen('\n')

[M dot Froehlich at science-computing dot de]

------- Comment #8 from M dot Froehlich at science-computing dot de  2008-09-10 16:13 -------
Fine!
Thanks!

Mathias


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] [4.4 Regression] Code bloat for ostream.widen('\n')

[paolo dot carlini at oracle dot com]

------- Comment #9 from paolo dot carlini at oracle dot com  2008-09-10 16:20 -------
This is a regression, not horribly serious still a regression.


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paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Code bloat for              |[4.4 Regression] Code bloat
                   |ostream.widen('\n')         |for ostream.widen('\n')
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] [4.4 Regression] Code bloat for ostream.widen('\n')

[paolo at gcc dot gnu dot org]

------- Comment #10 from paolo at gcc dot gnu dot org  2008-09-10 16:49 -------
Subject: Bug 37455

Author: paolo
Date: Wed Sep 10 16:48:47 2008
New Revision: 140238

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=140238
Log:
2008-09-10  Paolo Carlini  <paolo.carlini@oracle.com>

        PR libstdc++/37455
        * include/bits/locale_facets.h (ctype<char>::_M_narrow_init,
        ctype<char>::_M_widen_init): Don't define inline.
        * config/locale/darwin/ctype_members.cc: ... define here.
        * config/locale/gnu/ctype_members.cc: ... likewise.
        * config/locale/generic/ctype_members.cc: ... likewise.
        * config/abi/pre/gnu.ver: Export.

Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/config/abi/pre/gnu.ver
    trunk/libstdc++-v3/config/locale/darwin/ctype_members.cc
    trunk/libstdc++-v3/config/locale/generic/ctype_members.cc
    trunk/libstdc++-v3/config/locale/gnu/ctype_members.cc
    trunk/libstdc++-v3/include/bits/locale_facets.h


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455

[Bug libstdc++/37455] [4.4 Regression] Code bloat for ostream.widen('\n')

[paolo dot carlini at oracle dot com]

------- Comment #11 from paolo dot carlini at oracle dot com  2008-09-10 16:51 -------
Fixed.


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paolo dot carlini at oracle dot com changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37455