[Bug c++/56889] New: =delete(ing) default copy and move operations for a polymorphic type gives compilation error messages

[Bug c++/56889] New: =delete(ing) default copy and move operations for a polymorphic type gives compilation error messages

[amalisperid at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

             Bug #: 56889
           Summary: =delete(ing) default copy and move operations for a
                    polymorphic type gives compilation error messages
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: amalisperid@yahoo.com


Created attachment 29834
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29834
smalltestfile

when I add 
 Stack(const Stack&)=delete;
   Stack& operator=(const Stack&)=delete;
   //no move operations
   Stack(Stack&&)=delete;
   Stack& operator=(Stack&&)=delete;
to the stack polymorphic type in the attached file, the compiler gives error
messages. But if I don't add these methods, as Bjarne Stroutstrup's programming
language fourth edition-third chapter draft copy- says,
'In case you forgot to delete a copy or move operation, no harm is done. A move
operation is not implicitly generated for a class where the user has explicitly
declared a destructor. Furthermore, the generation of copy operations are
deprecated in this case
(§42.2.3). This can be a good reason to explicitly define a destructor even
where the compiler would have implicitly provided one (§17.2.3).
The C++ Programming Language, 4th edition ©2012 by Pearson Education, Inc.
Reproduced in draft form with the permission of the publisher.', my program
gives nomore compiler error messages, and it works as I expect it to.
However, I think the compiler should allow me to specify the copy and move
methods as =delete in the Stack polymorphic type.


-------------- Build: Debug in TestforError ---------------

x86_64-w64-mingw32-g++.exe -Wall -fexceptions  -g  -std=c++0x -Wextra -Wall -v
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Albert\Desktop\Amali\TestforError\main.cpp" -o obj\Debug\main.o
Using built-in specs.
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-I/temp/mingw-prereq/x86_64-w64-mingw32-static/include' CPPFLAGS=
LDFLAGS='-pipe -L/temp/x64-480-win32-seh-r1/libs/lib
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-L/temp/x64-480-win32-seh-r1/mingw64/opt/lib'
Thread model: win32
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'-shared-libgcc' '-mtune=core2' '-march=nocona'

c:/amali/x64-4.8.0-release-win32-seh-rev1/mingw64/bin/../libexec/gcc/x86_64-w64-mingw32/4.8.0/cc1plus.exe
-E -quiet -v -iprefix
c:\amali\x64-4.8.0-release-win32-seh-rev1\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.8.0/
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ignoring duplicate directory
"c:/amali/x64-4.8.0-release-win32-seh-rev1/mingw64/lib/gcc/../../lib/gcc/x86_64-w64-mingw32/4.8.0/include/c++/x86_64-w64-mingw32"
ignoring duplicate directory
"c:/amali/x64-4.8.0-release-win32-seh-rev1/mingw64/lib/gcc/../../lib/gcc/x86_64-w64-mingw32/4.8.0/include/c++/backward"
ignoring duplicate directory
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ignoring nonexistent directory
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ignoring duplicate directory
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ignoring nonexistent directory
"C:/gccbuild/msys/temp/x64-480-win32-seh-r1/mingw64/mingw/include"
#include "..." search starts here:
#include <...> search starts here:

c:\amali\x64-4.8.0-release-win32-seh-rev1\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.8.0/include/c++

c:\amali\x64-4.8.0-release-win32-seh-rev1\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.8.0/include/c++/x86_64-w64-mingw32

c:\amali\x64-4.8.0-release-win32-seh-rev1\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.8.0/include/c++/backward

c:\amali\x64-4.8.0-release-win32-seh-rev1\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.8.0/include

c:\amali\x64-4.8.0-release-win32-seh-rev1\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.8.0/include-fixed

c:\amali\x64-4.8.0-release-win32-seh-rev1\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.8.0/../../../../x86_64-w64-mingw32/include
End of search list.
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c:/amali/x64-4.8.0-release-win32-seh-rev1/mingw64/bin/../libexec/gcc/x86_64-w64-mingw32/4.8.0/cc1plus.exe
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-fexceptions -fno-strict-aliasing -fwrapv -o main.s
GNU C++ (rev1, Built by MinGW-builds project) version 4.8.0
(x86_64-w64-mingw32)
    compiled by GNU C version 4.7.2, GMP version 5.1.1, MPFR version 3.1.2, MPC
version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++ (rev1, Built by MinGW-builds project) version 4.8.0
(x86_64-w64-mingw32)
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version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 198a59f18ac22b34b3ce85756ec21810
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp: In function
'void StackAbst::constanduse()':
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:92:46: error:
use of deleted function
'StackAbst::vector_stack<int>::vector_stack(std::initializer_list<int>)'
    vector_stack<int> vst{1,2,3,4,5,6,7,8,9,10};
                                              ^
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:39:19: note:
'StackAbst::vector_stack<int>::vector_stack(std::initializer_list<int>)' is
implicitly deleted because the default definition would be ill-formed:
       using Base::Base;
                   ^
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:39:19: error:
no matching function for call to 'StackAbst::Stack<int>::Stack()'
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:39:19: note:
candidates are:
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:19:4: note:
StackAbst::Stack<T>::Stack(StackAbst::Stack<T>&&) [with T = int] <deleted>
    Stack(Stack&&)=delete;
    ^
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:19:4: note:  
candidate expects 1 argument, 0 provided
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:16:4: note:
StackAbst::Stack<T>::Stack(const StackAbst::Stack<T>&) [with T = int] <deleted>
    Stack(const Stack&)=delete;
    ^
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:16:4: note:  
candidate expects 1 argument, 0 provided
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp: In
instantiation of 'StackAbst::vector_stack<T>*
StackAbst::vector_stack<T>::clone() const [with T = int]':
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:102:1:  
required from here
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:43:39: error:
use of deleted function 'StackAbst::vector_stack<int>::vector_stack(const
StackAbst::vector_stack<int>&)'
          return new vector_stack(*this); // using copy constructor
                                       ^
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:32:7: note:
'StackAbst::vector_stack<int>::vector_stack(const
StackAbst::vector_stack<int>&)' is implicitly deleted because the default
definition would be ill-formed:
 class vector_stack : public Stack<T>, private std::vector<T>{
       ^
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:32:7: error:
use of deleted function 'StackAbst::Stack<T>::Stack(const StackAbst::Stack<T>&)
[with T = int]'
C:\Users\Pugazhendhi Albert\Desktop\Amali\TestforError\main.cpp:16:4: error:
declared here
    Stack(const Stack&)=delete;
    ^
Process terminated with status 1 (0 minutes, 0 seconds)
13 errors, 0 warnings
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Subject: [Bug rtl-optimization/56885] ICE: in assign_by_spills, at lra-assigns.c:1268 with -O -fschedule-insns -fselective-scheduling
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56885

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-04-09
                 CC|                            |mpolacek at gcc dot
                   |                            |gnu.org, vmakarov at gcc
                   |                            |dot gnu.org
   Target Milestone|---                         |4.8.1
     Ever Confirmed|0                           |1

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> 2013-04-09 06:15:49 UTC ---
Confirmed with trunk/4.8, but with 4.6/4.7 I see:

x.c:20:1: error: unable to find a register to spill in class ‘DIREG’
x.c:20:1: error: this is the insn:
(insn 33 36 35 5 (parallel [
            (set (reg:DI 2 cx [80])
                (const_int 0 [0]))
            (set (reg/f:DI 0 ax [78])
                (plus:DI (reg/f:DI 1 dx [77])
                    (reg:DI 2 cx [80])))
            (set (mem:BLK (reg/f:DI 1 dx [77]) [0 S15 A8])
                (const_int 0 [0]))
            (use (reg:QI 6 bp [81]))
            (use (reg:DI 2 cx [80]))
        ]) x.c:16 884 {*rep_stosqi}
     (expr_list:REG_DEAD (reg/f:DI 1 dx [77])
        (expr_list:REG_UNUSED (reg:DI 2 cx [80])
            (expr_list:REG_UNUSED (reg/f:DI 0 ax [78])
                (nil)))))
x.c:20: confused by earlier errors, bailing out
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idV885

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> 2013-04-09 06:29:13 UTC ---
Anyway, started with
http://gcc.gnu.org/viewcvs/gcc?view=revision&revision\x192719

[Bug c++/56889] =delete(ing) default copy and move operations for a polymorphic type gives compilation error messages

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler at
                   |                            |googlemail dot com

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-04-09 09:10:52 UTC ---
There are several problems in your example:

1) You have not declared a default constructor in template Stack, but you have
provided user-declared constructors (The deleted ones). This has the effect
that the Stack template has a no implicitly declared default constructor, which
again has the effect that the initializer-list constructor generated by the
compiler in vector_stack is deleted, because it would implicitly call the
missing default constructor of Stack. Solution: Add a (defaulted) default
constructor to the Stack template.

2) The clone function in vector_stack would call the copy constructor of that
type. But this one is deleted, because the Stack template has an explicitly
deleted copy constructor. This is a design error.
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Subject: [Bug middle-end/56883] error openmp parallel for order
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idV883

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
          Component|c++                         |middle-end
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |

[Bug c++/56889] =delete(ing) default copy and move operations for a polymorphic type gives compilation error messages

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

--- Comment #2 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-04-09 09:36:29 UTC ---
(In reply to comment #1)
In addition I would like to remark that the precise declaration state of the
inherited initializer-list constructor in vector_stack is unclear, because of

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1573

But the existing wording implies that any usage of this constructor would be
ill-formed because of the unavailable default constructor of its base class.
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Subject: [Bug other/56881] Miscompilation (optimisation failure?) causing NULL dereference and segfault at runtime
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idV881

Chung-Ju Wu <jasonwucj at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jasonwucj at gmail dot com

--- Comment #1 from Chung-Ju Wu <jasonwucj at gmail dot com> 2013-04-09 09:52:35 UTC ---
(In reply to comment #0)
>
>   hs1 = (Hideset)domalloc(len*sizeof(Hideset));
>   memmove(hs1, nhs, len*sizeof(Hideset));
>   hidesets[nhidesets] = hs1;
>

IMHO, if domalloc() does return NULL for some cases,
having NULL-checking statement before/inside memmove is required.

[Bug c++/56889] =delete(ing) default copy and move operations for a polymorphic type gives compilation error messages

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-04-09 12:26:18 UTC ---
As Daniel says, you're missing a default constructor.

And if you define the type as non-copyable then obviously you can't copy it.

This is not a GCC bug.

[Bug c++/56889] =delete(ing) default copy and move operations for a polymorphic type gives compilation error messages

[amalisperid at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

--- Comment #4 from Amali Praveena <amalisperid at yahoo dot com> 2013-04-09 19:02:32 UTC ---
Hi Jonathan,
     The Stack in the example is an abstract type, so I'm explicitly saying
that this abstract type cannot be copied or moved; but the derived class
vector_stack, which provides implementation for this abstract type is copyable
through clone function. Since the compiler won't know to which more derived
class the Stack points to at run time and so it cannot copy it, I've provided
the clone function (clone pattern).

This is what bjarne stroustrup says in his draft version of PL Fourth Edition,
as I quoted before.
Here is that section from the book.
3.3.4 Prev enting Copy and Move [tour2.copy.hier]
Using the default copy or move for a class in a hierarchy is typically a
disaster: Given only
a pointer to a base, we simply don’t know what members the derived class has
(§3.3.3), so
we can’t know how to copy them. So, the best thing to do is usually to delete
the default
copy and move operations; that is, to eliminate to default definitions of those
two operations:
class Shape {
public:
Sha pe(const Sha pe&) =delete; // no copy operations
Sha pe& opera tor=(const Sha pe&) =delete;
Sha pe(Sha pe&&) =delete; // no move operations
Sha pe& opera tor=(Shape&&) =delete;
˜Sha pe();
// ...
};
Now an attempt to copy a Sha pe will be caught by the compiler. If you need to
copy an
object in a class hierarchy, write some kind of clone function (§22.2.4).
In case you forgot to delete a copy or move operation, no harm is done. A move
operation
is not implicitly generated for a class where the user has explicitly declared
a destructor.
Furthermore, the generation of copy operations are deprecated in this case
(§42.2.3). This can be a good reason to explicitly define a destructor even
where the compiler
would have implicitly provided one (§17.2.3).
The C++ Programming Language, 4th edition ©2012 by Pearson Education, Inc.
Reproduced in draft form with the permission of the publisher. D R A F T

Thanks,
Amali.


________________________________
 From: redi at gcc dot gnu.org <gcc-bugzilla@gcc.gnu.org>
To: amalisperid@yahoo.com 
Sent: Tuesday, 9 April 2013 10:26 PM
Subject: [Bug c++/56889] =delete(ing) default copy and move operations for a
polymorphic type gives compilation error messages


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

Jonathan Wakely <redi at gcc dot gnu.org> changed:

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----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-04-09
12:26:18 UTC ---
As Daniel says, you're missing a default constructor.

And if you define the type as non-copyable then obviously you can't copy it.

This is not a GCC bug.
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Subject: [Bug c++/56896] New: Missing DIR_SEPARATOR if --with-gxx-include-dir configured as subdir of sysroot
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idV896

             Bug #: 56896
           Summary: Missing DIR_SEPARATOR if --with-gxx-include-dir
                    configured as subdir of sysroot
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: rmansfield@qnx.com


If gcc is configured with --with-sysroot=<path> and
--with-gxx-include-dir=<path>/<subpath> then gcc_gxx_include_dir will end up as
a relative path, and then incpath.c will trip the trailing sysroot
DIR_SEPARATOR and construct an invalid path.

e.g.

~/gnu/gcc/trunk/tmp/gcc$ ./xgcc -v
Using built-in specs.
COLLECT_GCC=./xgcc
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --enable-languages=c++ --disable-bootstrap
--with-gxx-include-dir=/home/ryan/foo/bar/usr/include/4.9.0
--with-sysroot=/home/ryan/foo/bar/
Thread model: posix
gcc version 4.9.0 20130409 (experimental) [trunk revision 197644] (GCC)
## --------- ##
## Platform. ##
~/gnu/gcc/trunk/tmp$ grep -nr gcc_gxx_include_dir *
gcc/Makefile:623:gcc_gxx_include_dir = usr/include/4.9.0
gcc/Makefile:624:gcc_gxx_include_dir_add_sysroot = 1
gcc/Makefile:1108:    "gxx_include_dir=$(gcc_gxx_include_dir)" \
gcc/Makefile:4055:  -DGPLUSPLUS_INCLUDE_DIR=\"$(gcc_gxx_include_dir)\" \
gcc/Makefile:4056:
-DGPLUSPLUS_INCLUDE_DIR_ADD_SYSROOT=$(gcc_gxx_include_dir_add_sysroot) \
gcc/Makefile:4057:
-DGPLUSPLUS_TOOL_INCLUDE_DIR=\"$(gcc_gxx_include_dir)/$(target_noncanonical)\"
\
gcc/Makefile:4058:
-DGPLUSPLUS_BACKWARD_INCLUDE_DIR=\"$(gcc_gxx_include_dir)/backward\" \
gcc/config.log:6339:gcc_gxx_include_dir='usr/include/4.9.0'
gcc/config.log:6340:gcc_gxx_include_dir_add_sysroot='1'
gcc/config.status:682:S["gcc_gxx_include_dir_add_sysroot"]="1"
gcc/config.status:683:S["gcc_gxx_include_dir"]="usr/include/4.9.0"


~/gnu/gcc/trunk/tmp/gcc$ ./xgcc -B. ~/hw.cc -v
Reading specs from ./specs
COLLECT_GCC=./xgcc
COLLECT_LTO_WRAPPER=./lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --enable-languages=c++ --disable-bootstrap
--with-gxx-include-dir=/home/ryan/foo/bar/usr/include/4.9.0
--with-sysroot=/home/ryan/foo/bar/
Thread model: posix
gcc version 4.9.0 20130409 (experimental) [trunk revision 197644] (GCC)
COLLECT_GCC_OPTIONS='-B' '.' '-v' '-mtune=generic' '-march=x86-64'
 ./cc1plus -quiet -v -iprefix
/home/ryan/gnu/gcc/trunk/tmp/gcc/../lib/gcc/x86_64-unknown-linux-gnu/4.9.0/
-isystem ./include -isystem ./include-fixed -D_GNU_SOURCE /home/ryan/hw.cc
-quiet -dumpbase hw.cc -mtune=generic -march=x86-64 -auxbase hw -version -o
/tmp/cclOMQFL.s
GNU C++ (GCC) version 4.9.0 20130409 (experimental) [trunk revision 197644]
(x86_64-unknown-linux-gnu)
    compiled by GNU C version 4.7.2, GMP version 5.0.2, MPFR version 3.1.0-p3,
MPC version 0.9
GGC heuristics: --param ggc-min-expand0 --param ggc-min-heapsize@96
ignoring nonexistent directory
"/home/ryan/gnu/gcc/trunk/tmp/gcc/../lib/gcc/x86_64-unknown-linux-gnu/4.9.0/include"
ignoring nonexistent directory
"/home/ryan/gnu/gcc/trunk/tmp/gcc/../lib/gcc/x86_64-unknown-linux-gnu/4.9.0/include-fixed"
ignoring nonexistent directory
"/home/ryan/gnu/gcc/trunk/tmp/gcc/../lib/gcc/x86_64-unknown-linux-gnu/4.9.0/../../../../x86_64-unknown-linux-gnu/include"
ignoring nonexistent directory "/home/ryan/foo/barusr/include/4.9.0"
ignoring nonexistent directory
"/home/ryan/foo/barusr/include/4.9.0/x86_64-unknown-linux-gnu"
ignoring nonexistent directory "/home/ryan/foo/barusr/include/4.9.0/backward"
<snip>

Or:

~/gnu/gcc/trunk/tmp/gcc$ ./xgcc -B. ~/hw.cc --sysroot=/foo/bar
<snip>
ignoring nonexistent directory "/foo/barusr/include/4.9.0"
ignoring nonexistent directory
"/foo/barusr/include/4.9.0/x86_64-unknown-linux-gnu"
ignoring nonexistent directory "/foo/barusr/include/4.9.0/backward"

I'm not sure if the following is sufficient, or if the gcc_gxx_include_dir
should never end up without a leading DIR_SEPARATOR.

Index: gcc/incpath.c
==================================================================--- gcc/incpath.c    (revision 197644)
+++ gcc/incpath.c    (working copy)
@@ -179,7 +179,8 @@
           char *sysroot_no_trailing_dir_separator = xstrdup (sysroot);
           size_t sysroot_len = strlen (sysroot);

-          if (sysroot_len > 0 && sysroot[sysroot_len - 1] == DIR_SEPARATOR)
+          if (sysroot_len > 0 && sysroot[sysroot_len - 1] == DIR_SEPARATOR
+          && p->fname[0] == DIR_SEPARATOR)
         sysroot_no_trailing_dir_separator[sysroot_len - 1] = '\0';
           str = concat (sysroot_no_trailing_dir_separator, p->fname, NULL);
           free (sysroot_no_trailing_dir_separator);

[Bug c++/56889] =delete(ing) default copy and move operations for a polymorphic type gives compilation error messages

[daniel.kruegler at googlemail dot com]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

--- Comment #5 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-04-09 19:13:55 UTC ---
This issue is not the right place for discussing programming idioms, but as a
last comment to the code: Your reference to PL alone does not solve your
programing error: You need to define a copy constructor in vector_stack,
because the compiler-defined one is also deleted (because of the deleted one in
the base class), or define the clone function without a copy constructor.
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Subject: [Bug c++/56889] Þlete(ing) default copy and move operations for a polymorphic type gives compilation error messages
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

--- Comment #6 from Amali Praveena <amalisperid at yahoo dot com> 2013-04-09 19:23:38 UTC ---
Hi Daniel,
The Stack template is an abstract type, so I don't have to add default
constructor to it, do I? Since the abstract type can't be copied/moved, i'm
explicitly specifying those functions as delete; but the derived classes
(vector_stack) are copyable through clone function(clone pattern).
 I tried to do the following (adding default constructor), which still gave me
an error(both options):
template<class T>
class Stack{
   public:
   // pure virtual member functions
   virtual Stack* clone() const=0; // polymorphic
   virtual ~Stack() {} // explicitly define a destructor
   // no copy operations Bug No:- 56889
   Stack() // option 1
   {
   }
   Stack()=default; // option 2
   Stack(const Stack&)=delete;
   Stack& operator=(const Stack&)=delete;
   //no move operations
   Stack(Stack&&)=delete;
   Stack& operator=(Stack&&)=delete;
   virtual bool empty() const=0; // const member function
   virtual std::size_t size() const=0; // const member function
   virtual T& top()=0;
   virtual const T& top() const=0; // const member function
   virtual void push(const T& x)=0;
   virtual void pop()=0;
};
Here is a section from Bjarne stroustrup's PL fourth edition draft version :
Preventing Copy and Move [tour2.copy.hier]
Using the default copy or move for a class in a hierarchy is typically a
disaster: Given only
a pointer to a base, we simply don’t know what members the derived class has
(§3.3.3), so
we can’t know how to copy them. So, the best thing to do is usually to delete
the default
copy and move operations; that is, to eliminate to default definitions of those
two operations:
class Shape {
public:
Sha pe(const Sha pe&) =delete; // no copy operations
Sha pe& opera tor=(const Sha pe&) =delete;
Sha pe(Sha pe&&) =delete; // no move operations
Sha pe& opera tor=(Shape&&) =delete;
ËœSha pe();
// ...
};
Now an attempt to copy a Sha pe will be caught by the compiler. If you need to
copy an
object in a class hierarchy, write some kind of clone function (§22.2.4).
In case you forgot to delete a copy or move operation, no harm is done. A move
operation
is not implicitly generated for a class where the user has explicitly declared
a destructor.
Furthermore, the generation of copy operations are deprecated in this case
(§42.2.3). This can be a good reason to explicitly define a destructor even
where the compiler
would have implicitly provided one (§17.2.3).
A base class in a class hierarchy is just one example of an object we wouldn’t
want to
copy.
The C++ Programming Language, 4th edition ©2012 by Pearson Education, Inc.
Reproduced in draft form with the permission of the publisher. D R A F T
thanks,
Amali.


________________________________
 From: daniel.kruegler at googlemail dot com <gcc-bugzilla@gcc.gnu.org>
To: amalisperid@yahoo.com 
Sent: Tuesday, 9 April 2013 7:10 PM
Subject: [Bug c++/56889] =delete(ing) default copy and move operations for a
polymorphic type gives compilation error messages


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler at
                   |                            |googlemail dot com

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com>
2013-04-09 09:10:52 UTC ---
There are several problems in your example:

1) You have not declared a default constructor in template Stack, but you have
provided user-declared constructors (The deleted ones). This has the effect
that the Stack template has a no implicitly declared default constructor, which
again has the effect that the initializer-list constructor generated by the
compiler in vector_stack is deleted, because it would implicitly call the
missing default constructor of Stack. Solution: Add a (defaulted) default
constructor to the Stack template.

2) The clone function in vector_stack would call the copy constructor of that
type. But this one is deleted, because the Stack template has an explicitly
deleted copy constructor. This is a design error.
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Subject: [Bug c++/51424] [C++11] G++ should diagnose self-delegating constructors
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idQ424

--- Comment #1 from Andrew Schepler <aschepler at gmail dot com> 2013-04-09 19:38:15 UTC ---
The diagnostic is easy in the direct case of delegating to the same
constructor, but difficult in the indirect case of multiple delegating
constructors. (The condition might still be detectable if enough constructors
can be inlined.)  This difficulty is presumably why the Standard specifies "no
diagnostic required".

But yes, it seems like a good idea to support a warning for the easy case.

[Bug c++/56889] =delete(ing) default copy and move operations for a polymorphic type gives compilation error messages

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-04-11 12:42:52 UTC ---
You keep quoting Stroustrup but your code is still broken.

Your clone() function copies the object. The object is not copyable.  What is
so difficult to understand?

Add a copy constructor to vector_stack or change the clone function.

This is not a GCC bug!

[Bug c++/56889] =delete(ing) default copy and move operations for a polymorphic type gives compilation error messages

[amalisperid at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

--- Comment #8 from Amali Praveena <amalisperid at yahoo dot com> 2013-04-12 03:39:35 UTC ---
Hi reddit,
Yes, it's not a GCC bug.  I had a problem with copy constructors in version
4.7.0 but got Internal Compilation Error. I'm now working with GCC 4.8.0 in
which this is fixed. I think I got confused with this.
I thought of adding these delete functions to the abstract class and test it.
Since vector_stack doesn't have any pointer members/ members of its own, I can
rely on compiler to generate a default copy constructor for this more derived
class of Stack.
Option 1:
As you say, because I have made copy/move operations in the abstract
type(Stack) =delete, I think I should define a default copy
constructor/assignment and move constructor/assignment in all more derived
classes of Stack. 
Option 2:
Change the clone function. However, Clone pattern is often implemented using
copy constructor. Until now, I haven't seen it done in some other ways. 

Thanks,
Amali.


________________________________
 From: redi at gcc dot gnu.org <gcc-bugzilla@gcc.gnu.org>
To: amalisperid@yahoo.com 
Sent: Thursday, 11 April 2013 10:42 PM
Subject: [Bug c++/56889] =delete(ing) default copy and move operations for a
polymorphic type gives compilation error messages



http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56889

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-04-11
12:42:52 UTC ---
You keep quoting Stroustrup but your code is still broken.

Your clone() function copies the object. The object is not copyable.  What is
so difficult to understand?

Add a copy constructor to vector_stack or change the clone function.

This is not a GCC bug!
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From: "vapier at gentoo dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/56928] New: false positive when using -Wstrict-overflow
Date: Fri, 12 Apr 2013 03:45:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56928

             Bug #: 56928
           Summary: false positive when using -Wstrict-overflow
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vapier@gentoo.org
            Target: x86_64-linux-gnu


i've got some code that is triggering a warning when using gcc-4.8.0 and -O2
with -Wstrict-overflow.  pretty sure the warning is wrong -- when i tweak the
code slightly (in unrelated ways), it goes away.

playing with older versions shows that 4.[234].x work, but 4.[5678].x fail

the reduced test case:
$ cat test.i
struct stat {
    int st_mode;
};
const char *foo(char c, int x, struct stat s)
{   
    int i;
    char dynamic = 0;
    if (c == 1)
        for (i = 0; i < x; i++)
            dynamic = 1;
    if (!dynamic || !(s.st_mode & 1))
        return dynamic ? "d" : "!d";
}

$ gcc -O2 -c test.i -Wstrict-overflow 
test.i: In function ‘foo’:
test.i:12:24: warning: assuming signed overflow does not occur when simplifying
conditional to constant [-Wstrict-overflow]
   return dynamic ? "d" : "!d";
                        ^
>From gcc-bugs-return-419886-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Apr 12 05:06:30 2013
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Subject: [Bug tree-optimization/56928] [4.6/4.7/4.8/4.9 Regression] false positive when using -Wstrict-overflow
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idV928

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-04-12
          Component|c                           |tree-optimization
   Target Milestone|---                         |4.6.4
            Summary|false positive when using   |[4.6/4.7/4.8/4.9
                   |-Wstrict-overflow           |Regression] false positive
                   |                            |when using
                   |                            |-Wstrict-overflow
     Ever Confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-04-12 05:06:26 UTC ---
Visiting PHI node: dynamic_3 = PHI <0(2), dynamic_2(11)>

    Argument #0 (2 -> 5 executable)
    0
    Value: [0, 0]

    Argument #1 (11 -> 5 executable)
    dynamic_2
    Value: [0, 1]
Meeting
  [0, 0]
and
  [0, 1]
to
  [0, 1]
Found new range for dynamic_3: [0, +INF(OVF)]


I don't see any overflow there or even a way to cause the overflow.

Looks like there is a bad type issue, dynamic is char but it is being treated
as a boolean type internally.