[Bug c/32511] New: GCC inlines weak function

[Bug c/32511] New: GCC inlines weak function

[sabre at nondot dot org]

GCC generally doesn't inline weak functions, because their body may be
redefined by the linker: if the compiler inlined the call, the linker changing
the behavior of the function wouldn't change the inlined copy.  For example,
GCC does not inline this:

void bar () __attribute__((weak));
void bar () {}
void foo() { bar(); } 

However, GCC apparently overrides this if the inline keyword is added (and
potentially if the weak function is defined in a c++ class where it would be
implicit inline?).  As such, it cause the following to be inlined:

inline void bar () __attribute__((weak));
void bar () {}
void foo() { bar(); } 

However, again, this breaks the semantics of weak linkage.  If bar is redefined
at link-time, the inlined copy is not updated.  Because 'inline' is an
optimization request, not a requirement, it seems best for the compiler to
ignore the inline request in this case.

-Chris


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           Summary: GCC inlines weak function
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sabre at nondot dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-06-26 20:32 -------
Considering inline candidate bar.
 Inlining bar into foo.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[hubicka at gcc dot gnu dot org]

------- Comment #2 from hubicka at gcc dot gnu dot org  2008-02-17 19:37 -------
I think this is feature.  If users explicitely declares as inline, then we do
that, otherwise we doesn't:
  /* Don't auto-inline anything that might not be bound within
     this unit of translation.  */
  else if (!DECL_DECLARED_INLINE_P (fn)
           && DECL_REPLACEABLE_P (fn))
    inlinable = false;
otherwise we won't inline much e.g. with -fpic.

Honza


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[sabre at nondot dot org]

------- Comment #3 from sabre at nondot dot org  2008-02-17 19:48 -------
I understand the desire to optimize with -fpic, but miscompiling the code seems
unreasonable...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2008-02-17 21:05 -------
Well, I think we should error for the inline + weak combination, as it doesn't
make sense.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |accepts-invalid, wrong-code
   Last reconfirmed|0000-00-00 00:00:00         |2008-02-17 21:05:49
               date|                            |
            Version|unknown                     |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[sabre at nondot dot org]

------- Comment #5 from sabre at nondot dot org  2008-02-18 07:35 -------
That works for me.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2008-02-17 21:05:49         |2008-02-18 10:44:02
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2008-03-27 16:35 -------
Fixed.


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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2008-03-27 16:35 -------
Subject: Bug 32511

Author: rguenth
Date: Thu Mar 27 16:34:55 2008
New Revision: 133646

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=133646
Log:
2008-03-27  Richard Guenther  <rguenther@suse.de>

        PR c/32511
        * c-common.c (handle_weak_attribute): Reject combination of
        weak and inline.

        * gcc.dg/attr-weak-1.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/attr-weak-1.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-common.c
    trunk/gcc/testsuite/ChangeLog


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] GCC inlines weak function

[jason at gcc dot gnu dot org]

------- Comment #8 from jason at gcc dot gnu dot org  2010-07-01 19:28 -------
I think this change is wrong; weak definitions are also used to allow
definitions in multiple translation units without linker errors.  C++ inlines
are emitted as weak symbols, and it seems rather odd to prohibit in C something
that the C++ front end does routinely.


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jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu dot org
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511

[Bug c/32511] [4.4/4.5/4.6 regression] GCC rejects inline+weak function

[jason at gcc dot gnu dot org]

------- Comment #9 from jason at gcc dot gnu dot org  2010-07-12 13:46 -------
Marking as regression.  Weak symbols have multiple uses: allowing replacement
is one, but they are also used to allow equivalent definitions in multiple
translation units without linker errors.


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jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|accepts-invalid, wrong-code |rejects-valid
            Summary|GCC inlines weak function   |[4.4/4.5/4.6 regression] GCC
                   |                            |rejects inline+weak function


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32511