[Bug c++/49418] New: openmp default(none) in template function

[Bug c++/49418] New: openmp default(none) in template function

[gcc-bug at safetymail dot info]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

           Summary: openmp default(none) in template function
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: gcc-bug@safetymail.info


Compilation fails, if within a template function a const argument is used
within an openmp parallel region with default(none).

If shared(x) is specified also a "predetermined 'shared'" error is produced.


Error:
$ g++ -fopenmp pf.cc
pf.cc: In function 'void g(T)':
pf.cc:11:45: error: 'x' is predetermined 'shared' for 'shared'
pf.cc: In function 'void f(T) [with T = int]':
pf.cc:5:8: error: 'x' not specified in enclosing parallel
pf.cc:5:8: error: enclosing parallel
pf.cc: In function 'void g(T) [with T = int]':
pf.cc:12:8: error: 'x' not specified in enclosing parallel
pf.cc:12:8: error: enclosing parallel

Version:
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/home/me/gcc/libexec/gcc/i686-pc-cygwin/4.6.0/lto-wrapper.exe
Target: i686-pc-cygwin
Configured with: ./configure --enable-languages=c,c++ --prefix=/home/me/gcc
--enable-libgomp
Thread model: single
gcc version 4.6.0 (GCC)

[Bug c++/49418] openmp default(none) in template function

[gcc-bug at safetymail dot info]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

--- Comment #1 from gcc-bug at safetymail dot info 2011-06-15 11:07:12 UTC ---
Created attachment 24534
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24534
test case

[Bug c++/49418] openmp default(none) in template function

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-06-21 13:32:06 UTC ---
The problem seems to be that x has T const type before instantiation, but
int (without const) after instantiation.
The spot where the const is lost is:
            type = type_decays_to (type);
            TREE_TYPE (r) = type;  
            cp_apply_type_quals_to_decl (cp_type_quals (type), r);
Does C++ really mandate stripping the toplevel qualifiers from the PARM_DECLs
here?  It isn't stripped from VAR_DECLs.
OpenMP 2.5/OpenMP 3.0 says that const qualified parameters and variables are
predetermined shared.  While it hopefully changes in some way in OpenMP 3.1
(though, the current 3.1 draft wording is likely to change, as it is backwards
incompatible with default(none)), for older standards the presence/lack of
const
makes a big difference.

[Bug c++/49418] openmp default(none) in template function

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-06-21 13:34:35 UTC ---
Perhaps the top-level quals from the older type could be used, if the standard
doesn't disallow it?  Like, if T const arg is instantiated with T int or const
int, it would be int const arg, while if it is T arg instantiated with int or
const int, it would be int arg.

[Bug c++/49418] openmp default(none) in template function

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-06-21 13:41:19 UTC ---
template <typename T>
void f (int const x)
{
#pragma omp parallel default(none)
  int y = x;
}

template <typename T>
void g (int const x)
{
#pragma omp parallel default(none) shared(x)
  int y = x;
}

void h ()
{
  f<int> (0);
  g<int> (0);
}

fails the same way, while after removing template <typename T> and <int>
the toplevel qualifier stays and it works as expected.
If the current C++ FE behavior is mandated by the standard, i.e. toplevel
qualifiers must be always dropped from function arguments when in templates and
not otherwise, OpenMP C++ support could just ignore TREE_READONLY on PARM_DECLs
in templates or something, but it looks very weird to me.

[Bug c++/49418] openmp default(none) in template function

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011.06.21 14:35:35
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-21 14:35:35 UTC ---
This is a bug, an unintended consequence of the change to type_decays_to.

[Bug c++/49418] [4.6/4.7 regression] G++ discards cv-quals from template parameter types

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.6.2
            Summary|openmp default(none) in     |[4.6/4.7 regression] G++
                   |template function           |discards cv-quals from
                   |                            |template parameter types

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-21 18:58:53 UTC ---
Changing the summary to reflect the underlying issue.

[Bug c++/49418] [4.6/4.7 regression] G++ discards cv-quals from template parameter types

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-21 19:05:28 UTC ---
Author: jason
Date: Tue Jun 21 19:05:25 2011
New Revision: 175271

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=175271
Log:
    PR c++/49418
    * call.c (cxx_type_promotes_to): Don't strip cv-quals.
    * semantics.c (lambda_return_type): Strip them here.

Added:
    trunk/gcc/testsuite/g++.dg/template/param3.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/cp/semantics.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/49418] [4.6 regression] G++ discards cv-quals from template parameter types

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.6/4.7 regression] G++    |[4.6 regression] G++
                   |discards cv-quals from      |discards cv-quals from
                   |template parameter types    |template parameter types

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-21 19:07:21 UTC ---
Fixed on trunk.

[Bug c++/49418] [4.6 regression] G++ discards cv-quals from template parameter types

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-24 02:18:46 UTC ---
Author: jason
Date: Fri Jun 24 02:18:42 2011
New Revision: 175368

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=175368
Log:
    PR c++/49418
    * typeck2.c (build_functional_cast): Strip cv-quals for value init.
    * init.c (build_zero_init_1): Not here.

Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/init.c
    trunk/gcc/cp/typeck2.c

[Bug c++/49418] [4.6 regression] G++ discards cv-quals from template parameter types

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-27 20:15:56 UTC ---
Author: jason
Date: Mon Jun 27 20:15:49 2011
New Revision: 175557

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=175557
Log:
    PR c++/49418
    * call.c (cxx_type_promotes_to): Don't strip cv-quals.
    * semantics.c (lambda_return_type): Strip them here.

Added:
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/template/param3.C
Modified:
    branches/gcc-4_6-branch/gcc/cp/ChangeLog
    branches/gcc-4_6-branch/gcc/cp/call.c
    branches/gcc-4_6-branch/gcc/cp/semantics.c
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog

[Bug c++/49418] [4.6 regression] G++ discards cv-quals from template parameter types

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49418

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

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

--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-27 20:18:04 UTC ---
Fixed for 4.6.2.