The loop count directive indicates the loop count is likely to be an integer constant. The syntax for this directive is shown below:
Syntax |
|---|
|
!DEC$ LOOP COUNT (n) |
where n is an integer value.
The value of loop count affects heuristics used in software pipelining and data prefetch.
Example: Using loop count |
|---|
|
subroutine loop_count(a, b, N) integer :: i, N, b(N), c(N) !DEC$ LOOP COUNT (1000) ! This should enable software pipeling ! for this loop. do i = 1, 1000 b(i) = a(i) + 1 enddo end subroutine loop_count |
For more details on this directive, see "Directive Enhanced Compilation", section "General Directives", in the Intel®Fortran Language Reference.
The distribute point directive indicates a preference for performing loop distribution. The syntax for this directive is shown below:
Syntax |
|---|
|
!DEC$ DISTRIBUTE POINT |
Loop distribution may cause large loops be distributed into smaller ones. This strategy might enable more loops to get software-pipelined.
If the directive is placed inside a loop, the distribution is performed after the directive and any loop-carried dependency is ignored.
If the directive is placed before a loop, the compiler will determine where to distribute and data dependency is observed. Multiple distribute directive are supported if they are placed inside the loop.
When the directives are placed inside the loop, they cannot be put inside an IF statement.
Example: Using distribute point |
|---|
|
subroutine dist1(a, b, c, d, N) integer :: i, N, a(N), b(N), c(N), d(N) !DEC$ DISTRIBUTE POINT do i = 1, N b(i) = a(i) + 1 c(i) = a(i) + b(i) ! Compiler will decide where to distribute. ! Data dependency is observed. d(i) = c(i) + 1 enddo end subroutine dist1
subroutine dist2(a, b, c, d, N) integer :: i, N, a(N), b(N), c(N), d(N) do i = 1, N b(i) = a(i) + 1 !DEC$ DISTRIBUTE POINT ! Distribution will start here, ignoring all ! loop-carried dependency. c(i) = a(i) + b(i) d(i) = c(i) + 1 enddo end subroutine dist2 |