[Bug c++/49043] New: Returns from lambda functions incorrectly detected as "exits" from OpenMP loops in surrounding code

[Bug c++/49043] New: Returns from lambda functions incorrectly detected as "exits" from OpenMP loops in surrounding code

[bisqwit at iki dot fi]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49043

           Summary: Returns from lambda functions incorrectly detected as
                    "exits" from OpenMP loops in surrounding code
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: bisqwit@iki.fi


GCC incorrectly considers return statements within lambda functions as "exits"
from an OpenMP structured block.

For the code below, this error message is generated:

tmp3.cc: In lambda function:
tmp3.cc:7:40: error: invalid exit from OpenMP structured block

#include <iostream>
int main()
{
    #pragma omp parallel for
    for(int a=0; a<10; ++a)
    {
        auto func = [=] () { return a; };
        std::cout << func();
    }
}

Compiled with: -fopenmp -std=gnu++0x
Tested versions: 4.5.3 , 4.6.1

The purpose of this error is to catch exits from an OpenMP construct (return,
break, goto). No such thing happens when a lamdba function is called, which is
not different from calling an inlined function, therefore the error message is
misplaced.

[Bug c++/49043] [OpenMP & C++0x]: Compiler error when lambda-function within OpenMP loop

[bisqwit at iki dot fi]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49043

--- Comment #2 from Joel Yliluoma <bisqwit at iki dot fi> 2011-05-19 08:10:06 UTC ---
Even if the lambda function is not called, it happens. Merely defining the
function causes it.
Interestingly though, it does not happen if a method body is defined within the
loop. The code below does not cause the error. So it is restricted to lambda
function bodies.
It also does not happen when calling lambda functions that are defined outside
the loop.

int main()
{
    #pragma omp parallel for
    for(int a=0; a<10; ++a)
    {
        struct tmp
        {
            static int test() { return 0; }
        };
    }
}

[Bug c++/49043] [OpenMP & C++0x]: Compiler error when lambda-function within OpenMP loop

[bisqwit at iki dot fi]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49043

Joel Yliluoma <bisqwit at iki dot fi> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[C++0x] Returns from lambda |[OpenMP & C++0x]: Compiler
                   |functions incorrectly       |error when lambda-function
                   |detected as "exits" from    |within OpenMP loop
                   |OpenMP loops in surrounding |
                   |code                        |

--- Comment #1 from Joel Yliluoma <bisqwit at iki dot fi> 2011-05-19 08:05:26 UTC ---
It also happens if the lambda-function does not explicitly contain the "return"
statement.

For example, this code triggers the same error.

int main()
{
    #pragma omp parallel for
    for(int a=0; a<10; ++a)
    {
        auto func = [] () -> void { };
        func();
    }
}

[Bug c++/49043] [OpenMP & C++0x]: Compiler error when lambda-function within OpenMP loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49043

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011.05.19 08:55:08
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-19 08:55:08 UTC ---
Created attachment 24287
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24287
gcc46-pr49043.patch

Untested fix.

That said, I'd advise not to use lambdas in OpenMP regions, because the OpenMP
standard doesn't say anything about the data environment of those and how it
should behave.  Even the upcoming OpenMP 3.1 doesn't cover C++0x, I hope OpenMP
4.0 will.

[Bug c++/49043] [OpenMP & C++0x]: Compiler error when lambda-function within OpenMP loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49043

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-19 13:12:02 UTC ---
Author: jakub
Date: Thu May 19 13:11:56 2011
New Revision: 173907

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173907
Log:
    PR c++/49043
    * decl.c (check_omp_return): Stop searching on sk_function_parms.

    * testsuite/libgomp.c++/pr49043.C: New test.

Added:
    trunk/libgomp/testsuite/libgomp.c++/pr49043.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl.c
    trunk/libgomp/ChangeLog

[Bug c++/49043] [OpenMP & C++0x]: Compiler error when lambda-function within OpenMP loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49043

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

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

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-19 13:39:33 UTC ---
Fixed.

[Bug c++/49043] [OpenMP & C++0x]: Compiler error when lambda-function within OpenMP loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49043

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-19 13:14:00 UTC ---
Author: jakub
Date: Thu May 19 13:13:57 2011
New Revision: 173908

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173908
Log:
    PR c++/49043
    * decl.c (check_omp_return): Stop searching on sk_function_parms.

    * testsuite/libgomp.c++/pr49043.C: New test.

Added:
    branches/gcc-4_6-branch/libgomp/testsuite/libgomp.c++/pr49043.C
Modified:
    branches/gcc-4_6-branch/gcc/cp/ChangeLog
    branches/gcc-4_6-branch/gcc/cp/decl.c
    branches/gcc-4_6-branch/libgomp/ChangeLog

[Bug c++/49043] [OpenMP & C++0x]: Compiler error when lambda-function within OpenMP loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49043

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-07-25 09:54:13 UTC ---
*** Bug 49100 has been marked as a duplicate of this bug. ***