simd Construct

| OPENMP API Specification: "Version 5.2 -- GIT rev 95b2e3a44"

10.4 simd Construct


Name: simd	Association: loop
Category: executable	Properties: parallelism-generating, context-matching, simdizable, pure

Separating directives

scan

Clauses

aligned, collapse, if, lastprivate, linear, nontemporal, order, private, reduction, safelen, simdlen

Binding

A simd region binds to the current task region. The binding thread set of the simd region is the current team.

Semantics

The simd construct enables the execution of multiple iterations of the associated loops concurrently by using SIMD instructions. At the beginning of each logical iteration, the loop iteration variable or the variable declared by range-decl of each associated loop has the value that it would have if the set of the associated loops was executed sequentially. 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. Each set of concurrent iterations is a SIMD chunk. Lexical forward dependences in the iterations of the original loop must be preserved within each SIMD chunk, unless an order clause that speciﬁes concurrent is present.

When an if clause is present and evaluates to false, the preferred number of iterations to be executed concurrently is one, regardless of whether a simdlen clause is speciﬁed.

Restrictions

Restrictions to the simd construct are as follows:

If both simdlen and safelen clauses are speciﬁed, the value of the simdlen length must be less than or equal to the value of the safelen length.
Only simdizable constructs can be encountered during execution of a simd region.
If an order clause that speciﬁes concurrent appears on a simd directive, the safelen clause may not also appear.

∙ The simd region cannot contain calls to the longjmp or setjmp functions.

∙ No exception can be raised in the simd region. ∙ The only random access iterator types that are allowed for the associated loops are pointer types.

Cross References

aligned clause, see Section 5.11
collapse clause, see Section 4.4.3
if clause, see Section 3.4
lastprivate clause, see Section 5.4.5
linear clause, see Section 5.4.6
nontemporal clause, see Section 10.4.1
order clause, see Section 10.3
private clause, see Section 5.4.3
reduction clause, see Section 5.5.8
safelen clause, see Section 10.4.2
scan directive, see Section 5.6
simdlen clause, see Section 10.4.3

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