[Bug c++/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[jason at gcc dot gnu dot org]

--- Comment #18 from jason at gcc dot gnu dot org  2010-05-20 14:00 ---
Unassigning myself.


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jason at gcc dot gnu dot org changed:

   What|Removed |Added

 AssignedTo|jason at gcc dot gnu dot org|unassigned at gcc dot gnu
   ||dot org
 Status|ASSIGNED|NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164

[Bug c++/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[rguenth at gcc dot gnu dot org]

--- Comment #17 from rguenth at gcc dot gnu dot org  2010-05-20 13:24 
---
It is actually the scheduler that breaks the testcase.  Easier to look at
is -O2 -fwhole-program.  -fno-schedule-insns2 fixes it (as well as
-fno-tree-pre
or -fno-tree-dominator-opts, both of which are necessary to produce the
input to the scheduler).


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164

[Bug c++/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[rguenther at suse dot de]

--- Comment #16 from rguenther at suse dot de  2010-05-20 11:48 ---
Subject: Re:  [4.5 Regression] Aliasing bug triggered by
 Boost.Bind/Boost.Function

On Thu, 20 May 2010, jason at gcc dot gnu dot org wrote:

> --- Comment #15 from jason at gcc dot gnu dot org  2010-05-20 05:35 
> ---
> Giving all unions alias set 0 doesn't fix the testcase.  This surprises me,
> since I thought that the problem was with the union assignment
> 
>   this->functor = f.functor;
> 
> in assign_to_own.  Giving alias set 0 to all classes with a member or base of
> alias set 0 also doesn't fix the testcase.  Giving alias set 0 to all classes
> does fix the testcase.

Ok, I'll try to pin-point the exact problem.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164

[Bug c++/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[jason at gcc dot gnu dot org]

--- Comment #15 from jason at gcc dot gnu dot org  2010-05-20 05:35 ---
Giving all unions alias set 0 doesn't fix the testcase.  This surprises me,
since I thought that the problem was with the union assignment

  this->functor = f.functor;

in assign_to_own.  Giving alias set 0 to all classes with a member or base of
alias set 0 also doesn't fix the testcase.  Giving alias set 0 to all classes
does fix the testcase.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164

[Bug c++/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[jason at gcc dot gnu dot org]

--- Comment #14 from jason at gcc dot gnu dot org  2010-05-19 22:53 ---
In C++, an assignment of a union is defined to be equivalent to a byte copy:

12.8/32 "The implicitly-defined copy assignment operator for a union X copies
the object representation (3.9) of X."

3.9/4 "The object representation of an object of type T is the sequence of N
unsigned char objects taken up by the object of type T, where N equals
sizeof(T)."


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164

[Bug c++/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[jason at gcc dot gnu dot org]

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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|2010-05-17 15:50:41 |2010-05-19 22:15:45
   date||


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164

[Bug c++/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[rguenth at gcc dot gnu dot org]

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rguenth at gcc dot gnu dot org changed:

   What|Removed |Added

   Priority|P3  |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164

[Bug c++/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[pluto at agmk dot net]

--- Comment #13 from pluto at agmk dot net  2010-05-18 20:57 ---
btw. the boost::optional uses char-based storage and cast &storage
-> void* -> some_type* via address() and get_object() methods.
it looks like aliasing violation too.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164

[Bug c++/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[rguenth at gcc dot gnu dot org]

--- Comment #12 from rguenth at gcc dot gnu dot org  2010-05-18 15:02 
---
Making this a C++ frontend bug.  The only way to avoid expanding the copy
to a loop is by using memcpy which will then run into PR42834.


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rguenth at gcc dot gnu dot org changed:

   What|Removed |Added

 CC||jason at gcc dot gnu dot org
  Component|middle-end  |c++


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164