Analyzing Guided Auto-parallelization Reports

Analyze the output generated by GAP analysis and determine whether or not the specific suggestions are appropriate for the specified source code. For this sample tutorial, GAP generates output for the loop in scalar_dep.f90:

do i = 1, n
   if (a(i) >= 0) then
       t = i
   end if
   if (a(i) > 0) then
       a(i) = t * (1 / (a(i) * a(i)))
   end if
end do

In this example, the GAP Report generates a recommendation (remark #30761) to add the -parallel option to improve auto-parallelization. Remark #30515 indicates if variable t can be unconditionally assigned, the compiler will be able to vectorize the loop.

GAP REPORT LOG OPENED
remark #30761: Add -parallel option if you want the compiler to generate
recommendations for improving auto-parallelization.
scalar_dep.f90(44): remark #30515: (VECT) Loop at line 44 cannot be
vectorized due to conditional assignment(s) into the following variable(s): t.
This loop will be vectorized if the variable(s) become unconditionally
initialized at the top of every iteration. [VERIFY] Make sure that the value(s)
of the variable(s) read in any iteration of the loop must have been written
earlier in the same iteration.
Number of advice-messages emitted for this compilation session: 1.
END OF GAP REPORT LOG