[Bug c++/56095] New: Crash casting function pointer as non-type template argument

[Bug c++/56095] New: Crash casting function pointer as non-type template argument

[spoo at zarbosoft dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

             Bug #: 56095
           Summary: Crash casting function pointer as non-type template
                    argument
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: spoo@zarbosoft.com


g++ crashes when trying to cast a function pointer to another function pointer
as a non-type template argument.  I get a strange error in 4.6.3, and 4.7.2
segfaults.

Platform: Ubuntu 12.04.1 LTS
uname -a: Linux cerberus 3.2.0-35-generic #55-Ubuntu SMP Wed Dec 5 17:42:16 UTC
2012 x86_64 x86_64 x86_64 GNU/Linux

Code (c.cxx):
int *a(void) { return 0; }
typedef void (*IntermediarySignature)(void);
template <IntermediarySignature b> void z(void) {}

int main(int argc, char **argv)
{
    z<(IntermediarySignature)a>();
    z<reinterpret_cast<IntermediarySignature>(a)>();
    return 0;
}

4.7 output:
> g++-4.7 -std=c++11 c.cxx 
c.cxx: In function ‘int main(int, char**)’:
c.cxx:7:30: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-4.7/README.Bugs> for instructions.
Preprocessed source stored into /tmp/cc8vdZAa.out file, please attach this to
your bugreport.

If line 7 is commented out (the c-style cast), there's a segfault on line 8.

4.6 output:
> g++ -std=c++0x c.cxx 
c.cxx: In function ‘int main(int, char**)’:
c.cxx:7:30: error: ‘(IntermediarySignature)a’ is not a valid template argument
for type ‘void (*)()’ because function ‘#‘nop_expr’ not supported by
dump_decl#<declaration error>’ has not external linkage
c.cxx:7:30: error: no matching function for call to ‘z()’
c.cxx:7:30: note: candidate is:
c.cxx:3:41: note: template<void (* b)()> void z()
c.cxx:8:48: error: ‘(IntermediarySignature)a’ is not a valid template argument
for type ‘void (*)()’ because function ‘#‘nop_expr’ not supported by
dump_decl#<declaration error>’ has not external linkage
c.cxx:8:48: error: no matching function for call to ‘z()’
c.cxx:8:48: note: candidate is:
c.cxx:3:41: note: template<void (* b)()> void z()

[Bug c++/56095] Crash casting function pointer as non-type template argument

[spoo at zarbosoft dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

--- Comment #1 from Rendaw <spoo at zarbosoft dot com> 2013-01-24 06:39:12 UTC ---
I tried one more case, casting before using the template:

Code (c.cxx):
int *a(void) { return 0; }
typedef void (*IntermediarySignature)(void);
template <IntermediarySignature b> void z(void) {}

int main(int argc, char **argv)
{
    constexpr IntermediarySignature c = (IntermediarySignature)a;
    z<c>();
    return 0;
}

4.7 output:
> g++-4.7 -std=c++11 c.cxx 
c.cxx: In function ‘int main(int, char**)’:
c.cxx:8:7: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-4.7/README.Bugs> for instructions.
Preprocessed source stored into /tmp/ccw2QOq9.out file, please attach this to
your bugreport.

4.6 output:
> g++ -std=c++0x c.cxx 
c.cxx: In function ‘int main(int, char**)’:
c.cxx:8:7: error: ‘(IntermediarySignature)a’ is not a valid template argument
for type ‘void (*)()’ because function ‘#‘nop_expr’ not supported by
dump_decl#<declaration error>’ has not external linkage
c.cxx:8:7: error: no matching function for call to ‘z()’
c.cxx:8:7: note: candidate is:
c.cxx:3:41: note: template<void (* b)()> void z()

[Bug c++/56095] Crash casting function pointer as non-type template argument

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

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

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

--- Comment #2 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-01-24 11:56:31 UTC ---
While I agree that the ICE needs to be fixed, let me add in here that any
conversion that requires the equivalent of a reinterpret_cast is not valid in a
constant expression in C++11. Furthermore, there are even more fundamental
restrictions on the form of the non-type template arguments as described in
[temp.arg.nontype] p1, which exclude *any* form of a cast expression at that
place. These rules also exclude the case that you tried in your second example
where you are attempting to use a constexpr variable.

The essential wording here is:

"a constant expression (5.19) that designates the address of [..] a function
with external or internal linkage, including function templates and function
template-ids [..], expressed (ignoring parentheses) as &id-expression, except
that the & may be omitted if the name refers to a function [..]"

Basically this means you can only directly name a function here such as

z<a>();

which of course won't work in your case because of the incompatible signature.

[Bug c++/56095] Crash casting function pointer as non-type template argument

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-invalid-code

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-24 12:01:32 UTC ---
I cant reproduce the crash with any version

[Bug c++/56095] Crash casting function pointer as non-type template argument

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

--- Comment #4 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-01-24 12:07:25 UTC ---
(In reply to comment #3)
> I cant reproduce the crash with any version

Here is what I get with my mingw-64 gcc 4.8.0 20130120 (experimental):

"main.cpp||In function 'int main(int, char**)':|
main.cpp|7|internal compiler error: tree check: expected tree that contains
'decl minimal' structure, have 'nop_expr' in decl_linkage, at cp/tree.c:3527"

When I use 

http://liveworkspace.org/code/47sr7W$0

I also get "source.cpp:7:33: internal compiler error: Segmentation fault"

[Bug c++/56095] [4.6/4.7/4.8 Regression] Crash casting function pointer as non-type template argument

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org
            Summary|Crash casting function      |[4.6/4.7/4.8 Regression]
                   |pointer as non-type         |Crash casting function
                   |template argument           |pointer as non-type
                   |                            |template argument

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-24 12:11:13 UTC ---
I can, with everything starting from
http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=166167
You need --enable-checking=yes compiler though.

[Bug c++/56095] [4.6/4.7/4.8 Regression] Crash casting function pointer as non-type template argument

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
   Target Milestone|---                         |4.6.4

[Bug c++/56095] [4.6/4.7/4.8 Regression] Crash casting function pointer as non-type template argument

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-01-24
     Ever Confirmed|0                           |1

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-24 12:13:56 UTC ---
Doh, sorry, copy'n'paste failure. I copied the test wrong.

[Bug c++/56095] [4.6/4.7/4.8 Regression] Crash casting function pointer as non-type template argument

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> 2013-01-25 20:01:35 UTC ---
Author: jason
Date: Fri Jan 25 20:01:29 2013
New Revision: 195474

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195474
Log:
    PR c++/56095
    * pt.c (convert_nontype_argument_function): Handle invalid input.
    (convert_nontype_argument): Likewise.

Added:
    trunk/gcc/testsuite/g++.dg/template/fn-ptr2.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c

[Bug c++/56095] [4.6/4.7 Regression] Crash casting function pointer as non-type template argument

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.6/4.7/4.8 Regression]    |[4.6/4.7 Regression] Crash
                   |Crash casting function      |casting function pointer as
                   |pointer as non-type         |non-type template argument
                   |template argument           |

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-25 20:04:59 UTC ---
Fixed on the trunk so far.

[Bug c++/56095] [4.6/4.7 Regression] Crash casting function pointer as non-type template argument

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|4.6.4                       |4.8.0

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> 2013-01-25 20:20:22 UTC ---
And we usually don't backport fixes for invalid code.

[Bug c++/56095] [4.6/4.7 Regression] Crash casting function pointer as non-type template argument

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56095

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> 2013-03-17 02:33:46 UTC ---
Author: jason
Date: Sun Mar 17 02:33:38 2013
New Revision: 196722

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196722
Log:
    PR c++/56095
    * class.c (resolve_address_of_overloaded_function): Accept a
    reference to function for target_type.
    (instantiate_type): Likewise.
    * pt.c (convert_nontype_argument): Pass it to
    convert_nontype_argument_function.

Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/class.c
    trunk/gcc/cp/pt.c