[Bug c++/26965] New: Unnecessary debug info for unused consts in C++

[Bug c++/26965] New: Unnecessary debug info for unused consts in C++

[ian at airs dot com]

Compile this C++ code with -g

enum x { i = 1 };
class c {
  static const x beg = i;
};
void bar () { }

Looking at the .s output and the readelf --debug-dump output will show that
there is no debug info for x or beg.  This is as expected: they are not used by
any actual code, so there is no need to emit debug info for them.

Now compile this code, which adds an unused inline function:

enum x { i = 1 };
class c {
  static const x beg = i;
  int foo () { return (int) beg; }
};
void bar () { }

Now I see debug info for enum x and for the const beg.  However, there is no
debug info for the unused inline function foo.  There should not be any debug
info for the enum or the const either.

This matters particularly because these cases arise in ordinary C++ code, and
in particular in the libstdc++ headers.  For example, when I compile this file
with -g:

#include <iostream>
void bar () { }

I get over 27K of debug info.  That's pretty bad.

This was better in gcc 4.0.1.  For that, I get 9K of debug info for the
<iostream> example--not great, but much better.  It changed in gcc 4.0.2.  I
believe the change was due to the patch for PR 23190, by RTH on 2005-09-08.

I don't have a patch for this.  I'm recording it so that I don't forget it.


-- 
           Summary: Unnecessary debug info for unused consts in C++
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ian at airs dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] Unnecessary debug info for unused consts in C++

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-03-31 20:05 -------
This looks very related to PR 14167.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] Unnecessary debug info for unused consts in C++

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2006-04-02 08:22 -------
Confirmed.


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pinskia 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         |2006-04-02 08:22:16
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] Unnecessary debug info for unused consts in C++

[pluto at agmk dot net]

------- Comment #3 from pluto at agmk dot net  2006-04-03 08:07 -------
(In reply to comment #0)

> (...) This is as expected: they are not used by
> any actual code, so there is no need to emit debug info for them.

so, what for is the -feliminate-unused-debug-symbols?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] Unnecessary debug info for unused consts in C++

[ian at airs dot com]

------- Comment #4 from ian at airs dot com  2006-04-03 22:57 -------
-feliminate-unused-debug-symbols only applies to stabs debugging.  I'm talking
about DWARF (which I admit I didn't say explicitly, although my examples were
all for DWARF).

You might reasonably ask about -feliminate-unused-debug-types, which does apply
to DWARF, but that is on by default.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2 Regression] Unnecessary debug info for unused consts in C++

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2006-04-03 23:02 -------
And I just checked this is a regression too.


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pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
      Known to fail|                            |4.1.0
      Known to work|                            |3.4.0
            Summary|Unnecessary debug info for  |[4.0/4.1/4.2 Regression]
                   |unused consts in C++        |Unnecessary debug info for
                   |                            |unused consts in C++
   Target Milestone|---                         |4.0.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2 Regression] Unnecessary debug info for unused consts in C++

[mmitchel at gcc dot gnu dot org]

------- Comment #6 from mmitchel at gcc dot gnu dot org  2006-06-04 18:21 -------
Does this have to do with Aldy's patches to make sure that we emit debug
information for types used in casts?


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mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2 Regression] Unnecessary debug info for unused consts in C++

[drow at gcc dot gnu dot org]

------- Comment #7 from drow at gcc dot gnu dot org  2006-06-06 04:01 -------
I'm pretty sure it's older than that.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2 Regression] Unnecessary debug info for unused consts in C++

[ian at airs dot com]

------- Comment #8 from ian at airs dot com  2006-06-06 15:42 -------
As I mentioned in the original submission, I'm pretty sure it is caused by
RTH's patch for PR 23190.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2 Regression] Unnecessary debug info for unused consts in C++

[drow at gcc dot gnu dot org]

------- Comment #9 from drow at gcc dot gnu dot org  2006-07-22 19:39 -------
Ian, could you say why you think that patch is responsible?  I wonder if your
testcase would behave any differently on either side of the patch; it might be
something different taking up all the space.

I think the situation is simpler, and harder to fix.  The debug generators make
decisions based on TREE_USED.  TREE_USED is set in many cases during parsing;
but of course we parse more functions than we necessarily emit.  As long as we
commit to outputing a particular piece of debug information during parsing
we're going to have this problem.

beg gets its mark_used during finish_id_expression, called during parsing of
c::foo.

I don't see any way to solve this without replacing TREE_USED at parse time
with a set of hash tables attached to far too many objects, reporting what each
one would like to have emitted.  But this would be awful for performance and
memory use.  I'm open to better ideas if you have one.

Meanwhile, I do not find it likely that we will fix this for 4.2.


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drow at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2 Regression] Unnecessary debug info for unused consts in C++

[ian at airs dot com]

------- Comment #10 from ian at airs dot com  2006-07-23 17:35 -------
I believe that patch is responsible because this behaviour does not happen in
gcc 4.0.1, and it does happen in gcc 4.0.2, and that was the obvious change.  I
admit that I haven't actually tried reverting that specific patch to see what
happens.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2 Regression] Unnecessary debug info for unused consts in C++

[mmitchel at gcc dot gnu dot org]

------- Comment #11 from mmitchel at gcc dot gnu dot org  2006-08-27 19:02 -------
I agree with Daniel's comments in Comment #9.

The only reliable fix is to commit to unit-at-a-time, always, for all
languages, independent of optimization.  Then, after we decide what to emit
(cgraph), we can know what debugging information to emit.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2/4.3 Regression] Unnecessary debug info for unused consts in C++

[gdr at gcc dot gnu dot org]

------- Comment #12 from gdr at gcc dot gnu dot org  2007-02-03 16:27 -------
Won't fix i GCC-4.0.x.  Adjusting milestone.


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gdr at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.0.4                       |---


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2/4.3 Regression] Unnecessary debug info for unused consts in C++

[jsm28 at gcc dot gnu dot org]

-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.1.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2/4.3 Regression] Unnecessary debug info for unused consts in C++

[mmitchel at gcc dot gnu dot org]

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mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.1.2                       |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.0/4.1/4.2/4.3 Regression] Unnecessary debug info for unused consts in C++

[steven at gcc dot gnu dot org]

------- Comment #13 from steven at gcc dot gnu dot org  2007-12-16 23:18 -------
Open regression with no activity since February 14.  Ping?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.2/4.3/4.4 Regression] Unnecessary debug info for unused consts in C++

[jsm28 at gcc dot gnu dot org]

------- Comment #14 from jsm28 at gcc dot gnu dot org  2008-07-04 20:23 -------
Closing 4.1 branch.


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jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.1/4.2/4.3/4.4 Regression]|[4.2/4.3/4.4 Regression]
                   |Unnecessary debug info for  |Unnecessary debug info for
                   |unused consts in C++        |unused consts in C++
   Target Milestone|4.1.3                       |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.2/4.3/4.4 Regression] Unnecessary debug info for unused consts in C++

[rguenth at gcc dot gnu dot org]

------- Comment #15 from rguenth at gcc dot gnu dot org  2009-03-11 21:54 -------
Honza, maybe you want to have a look here ...


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rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.3/4.4/4.5 Regression] Unnecessary debug info for unused consts in C++

[jsm28 at gcc dot gnu dot org]

------- Comment #16 from jsm28 at gcc dot gnu dot org  2009-03-31 19:32 -------
Closing 4.2 branch.


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jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.2/4.3/4.4/4.5 Regression]|[4.3/4.4/4.5 Regression]
                   |Unnecessary debug info for  |Unnecessary debug info for
                   |unused consts in C++        |unused consts in C++
   Target Milestone|4.2.5                       |4.3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.3/4.4/4.5 Regression] Unnecessary debug info for unused consts in C++

[rguenth at gcc dot gnu dot org]

------- Comment #17 from rguenth at gcc dot gnu dot org  2009-08-04 12:27 -------
GCC 4.3.4 is being released, adjusting target milestone.


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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.4                       |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.3/4.4/4.5 Regression] Unnecessary debug info for unused consts in C++

[jason at gcc dot gnu dot org]

-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jason at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2006-04-02 08:22:16         |2009-11-13 15:36:29
               date|                            |
   Target Milestone|4.3.5                       |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.3/4.4/4.5 Regression] Unnecessary debug info for unused consts in C++

[jason at gcc dot gnu dot org]

------- Comment #18 from jason at gcc dot gnu dot org  2009-11-13 17:59 -------
Subject: Bug 26965

Author: jason
Date: Fri Nov 13 17:59:26 2009
New Revision: 154157

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=154157
Log:
        PR debug/26965
        * dwarf2out.c (gen_variable_die): Don't worry about DECL_COMDAT.
        Don't emit a second declaration at any scope.

Added:
    trunk/gcc/testsuite/g++.dg/debug/dwarf2/static-data-member2.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/dwarf2out.c
    trunk/gcc/testsuite/ChangeLog


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965

[Bug c++/26965] [4.3/4.4/4.5 Regression] Unnecessary debug info for unused consts in C++

[jason at gcc dot gnu dot org]

------- Comment #19 from jason at gcc dot gnu dot org  2009-11-13 18:02 -------
Fixed for 4.5.


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jason at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26965