[Bug fortran/83064] DO CONCURRENT inconsistent results

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83064

--- Comment #5 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> As I said in the other bug we're seeing
>
>        real(real64), dimension(nsplit) :: tmp
>
> as "shared" amongst the outer loop iterations.
>
> ...
>
> Not sure if you need to mark compute somehow to avoid this
> and the testcase is invalid fortran or if the frontend is at fault.

IMO the testcase is valid fortran and, with my naive view of arrays returned by
a function, the returned array should be private to the function.

If I do the following changes

...
    real(real64), dimension(nsplit) :: pi, pik
...
    do concurrent (i = 1:nsplit)
        pik = compute( low(i), high(i) )
        pi(i) = sum(pik)
    end do
...

the code works as expected, at least for my limited testing.

Do you understand why the code is not parallelized with
-ftree-parallelize-loops=4?