[patch, Fortran] Fix PR 50690

[Tobias Burnus]

Tobias Burnus wrote:
> I had also a glance at the patch - and it looks reasonable; in 
> particular, I failed to generate a failing test case.

Actually, the test case is *not* OK.

If one compiles the original test case of the PR (or your 
workshare2.f90) with "-O" and looks at "-fdump-tree-original", one finds:

     #pragma omp parallel default(shared)
       {
         {
           real(kind=4) __var_1;
           {
             #pragma omp single
               {
                 __var_1 = __builtin_cosf (b[0])
               }
...
                 #pragma omp for schedule(static) nowait
                 for (S.1 = 1; S.1 <= 5; S.1 = S.1 + 1)
                   {
                     a[S.1 + -1] = a[S.1 + -1] * D.1730 + a[S.1 + -1] * 
D.1731;

Thus, __var_1 is a thread-local variable; however, COS() is not executed 
in all threads but only in one due to the omp single: "The single 
construct specifies that the associated structured block is executed by 
only one of the threads in the team" (2.5.3 single Construct, OpenMP 3.1).

Jakub remarks that omp single is what we expand to omp workshare if it 
is not simple enough for us.

  * * *

With the test case below, the dump looks OK, but the FE optimization 
does not combine the two cos() calls - I have no idea why. The dump 
looks as:

   #pragma omp parallel default(shared)
     {
                 D.1743 = __builtin_cosf (b[0]);
                 D.1745 = __builtin_cosf (b[0]);
...
                   #pragma omp for schedule(static) nowait
                   for (S.2 = 1; S.2 <= 10; S.2 = S.2 + 1)
                       a[S.2 + D.1750] = a[S.2 + D.1748] * D.1743 + 
a[S.2 + D.1749] * D.1745;

Tobias

PS: The test case is:

program workshare
   implicit none
   real, parameter :: eps = 3e-7
   integer :: j
   real :: A(10,5), B(5)
   B(1) = 3.344
   call random_number(a)
   !$omp parallel default(shared)
   !$omp workshare
   forall (j=1:5)
     A(:,j) = A(:,j)*cos(B(1))+A(:,j)*cos(B(1))
   end forall
   !$omp end workshare
   !$omp end parallel
   print *, A
end program workshare

subroutine parallel_workshare
   implicit none
   real, parameter :: eps = 3e-7
   integer :: j
   real :: A(10,5), B(5)
   B(1) = 3.344
   call random_number(a)
   !$omp parallel workshare default(shared)
   forall (j=1:5)
     A(:,j) = A(:,j)*cos(B(1))+A(:,j)*cos(B(1))
   end forall
   !$omp end parallel workshare
   print *, A
end subroutine parallel_workshare