SIMD Directive (OpenMP* API)

clause

Is one of the following:

• ALIGNED (list [:n])

• COLLAPSE (n)

• LASTPRIVATE (list)

• LINEAR (var-list[: linear-step])

• PRIVATE (list)

• REDUCTION (operator : list)

• SAFELEN(m)

  Limits the number of iterations in a SIMD chunk (set of concurrent iterations).

  The m must be a constant positive integer expression; it indicates the number of iterations allowed in a SIMD chunk.

  When this clause is used, no two iterations executed concurrently with SIMD instructions can have a greater distance in the logical iteration space than m.

  The number of iterations that are executed concurrently at any given time is defined by the implementation. Each concurrent iteration is executed by a different SIMD vector lane.

  At most one SAFELEN clause can appear in a SIMD directive.

• SIMDLEN(n)

  Specifies the preferred number of iterations to be executed concurrently. n must be a positive scalar integer constant. The number of iterations that are executed concurrently at any given time is implementation defined. Each concurrent iteration will be executed by a different SIMD lane.

  If both SIMDLEN (n) and SAFELEN (m) are specified, the value of the n must be less than or equal to the value of m.

  At most one SIMDLEN clause can appear in a SIMD directive.

do-loop

Is one or more DO iterations (DO loops). The DO iteration cannot be a DO WHILE or a DO loop without loop control. The DO loop iteration variable must be of type integer.

All loops associated with the construct must be structured and perfectly nested; that is, there must be no intervening code and no other OpenMP* Fortran directives between any two loops.

The iterations of the DO loop are distributed across the existing team of threads. The values of the loop control parameters of the DO loop associated with a DO directive must be the same for all the threads in the team.

You cannot branch out of a DO loop associated with a SIMD directive.