RE: gfortran openmp: lastprivate variable is private in outer context

["Liaskovitis, Vasileios" <Vasileios dot Liaskovitis at amd dot com>]

Vasileios Liaskovitis
AMD Performance CoE
Phone: (512) 602-1473
Email: vasileios.liaskovitis@amd.com

-----Original Message-----
From: Liaskovitis, Vasileios 
Sent: Thursday, October 25, 2007 11:34 AM
To: 'gcc-bugs@gcc.gnu.org'; 'gfortran@gcc.gnu.org'
Subject: gfortran openmp: lastprivate variable is private in outer
context

Hi,

I have an issue compiling the following fortran openmp code using gcc4.3
snapshot 20071910:

      SUBROUTINE foo(a, b, n)
      DOUBLE PRECISION a, b
      INTEGER*8 i1, i2, i3, n
      DIMENSION a(n,n,n), b(n,n,n)
!$OMP PARALLEL
!$OMP+DEFAULT(SHARED)
!$OMP+PRIVATE(I3)
!$OMP DO
!$OMP+LASTPRIVATE(I1,I2)
      DO i3 = 2, n-1, 1
       DO i2 = 2, n-1, 1
        DO i1 = 2, n-1, 1
         a(i1, i2, i3) = b(i1, i2, i3);
  600    CONTINUE
        ENDDO
       ENDDO
      ENDDO
!$OMP END DO NOWAIT
!$OMP END PARALLEL
      RETURN
      END

gfortran -O2 -fopenmp foo.c -c -o foo.o

fortran2.f:11: error: lastprivate variable "i2" is private in outer
context
fortran2.f:11: error: lastprivate variable "i1" is private in outer
context

I believe this code is compliant with the OPENMP 2.5 spec, since the
DEFAULT(SHARED) clause should make the scope of i1, i2 shared in the
enclosing parallel region. Pathscale 3.0, PGI 7.0.6 and Intel 10.0.026
compile the above code successfully.

Replacing:

!$OMP+DEFAULT(SHARED)
with:
!$OMP+SHARED(I1,I2)
 
makes the code compile successfully with gfortran. 
Alternatively, keeping DEFAULT(SHARED) and fusing the OMP PARALLEL
clause with the OMP DO clause (i.e. using OMP PARALLEL DO) also solves
the problem.

(this testcase is derived from a benchmark suite that doesn't allow
source code modifications. gfortran should be able to compile this with
no code changes - if this is indeed openmp-compliant code)

Could this behavior be due to the following libgomp patch not getting
all necessary information from the fortran front-end?

http://gcc.gnu.org/ml/gcc-patches/2007-01/msg01940.html

GCC4.3 snapshot 20071910 was built and bootstrapped with the following
configuration on sles10-sp1:

Target: x86_64-unknown-linux-gnu
Configured with: /home/gcc-4.3-20071019/configure
--with-gmp-lib=/usr/local/lib/ --with-gmp-include=/usr/local/include/
--with-mpfr-lib=/usr/local/lib --with-mpfr-include=/usr/local/include/
--enable-threads=posix --prefix=/opt/gcc4.3
Thread model: posix
gcc version 4.3.0 20071019 (experimental) (GCC)


thanks,

- Vasilis