[Bug c/49897] New: nesting lastprivate gives incorrect result

[markflorisson88 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49897

           Summary: nesting lastprivate gives incorrect result
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: markflorisson88@gmail.com


Nesting lastprivate doesn't work in gcc 4.5: the inner loop has a lastprivate
variable that is then also declared lastprivate on the outer loop (otherwise
there would be a race), but the result after the loop is always 0. It works
fine in gcc 4.2 to 4.4.

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SSH [1] [10:13] ~  ➤ gcc-4.5 -v
Using built-in specs.
COLLECT_GCC=gcc-4.5
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-linux-gnu/4.5.1/lto-wrapper
Target: i686-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.5.1-7ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-4.5/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.5 --enable-shared --enable-multiarch
--enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.5 --libdir=/usr/lib --enable-nls
--with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-plugin --enable-gold
--with-plugin-ld=ld.gold --enable-objc-gc --enable-targets=all --disable-werror
--with-arch-32=i686 --with-tune=generic --enable-checking=release
--build=i686-linux-gnu --host=i686-linux-gnu --target=i686-linux-gnu
Thread model: posix
gcc version 4.5.1 (Ubuntu/Linaro 4.5.1-7ubuntu2) 
SSH [0] [10:13] ~  ➤ gcc-4.5 -g -Wall -fopenmp -lgomp testomp.c
SSH [0] [10:14] ~  ➤ ./a.out
x=9, y=0, sum = 450
SSH [0] [10:14] ~  ➤ cat testomp.c
#include <stdio.h>

int main(void) {
    int i = 0, j = 0, x, y, sum = 0;
    x = 0;


    #pragma omp parallel reduction(+:sum)
    {
        #pragma omp for firstprivate(x) lastprivate(x, y)
        for (i = 0; i < 10; i++) {
            x = i;

            y = 0;
            #pragma omp parallel reduction(+:sum)
            {

                #pragma omp for firstprivate(y) lastprivate(y)
                for (j = 0; j < 10; j++) {
                    y = j;
                    sum += y;
                }
            }
        }
    }
    printf("x=%d, y=%d, sum = %d\n", x, y, sum);
    return 0;
}


SSH [0] [10:15] ~  ➤ gcc-4.4 -g -Wall -fopenmp -lgomp testomp.c
SSH [0] [10:15] ~  ➤ ./a.out
x=9, y=9, sum = 450